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  • richardmitnick 11:47 am on July 11, 2018 Permalink | Reply
    Tags: , , CERN Courier, , MICE experiment, , ,   

    From CERN Courier: “Muons cooled for action” 


    From CERN Courier

    9 July 2018
    Manuela Boscolo, INFN-LNF
    Patrick Huber, Virginia Tech
    Kenneth Long, Imperial College London and STFC.

    The recent demonstration of muon ionisation-cooling by the MICE collaboration opens a path to a neutrino factory and muon collider.

    Rutherford Appleton Lab Muon Ionization Cooling Experiment (or MICE) is a high energy physics experiment

    Fundamental insights into the constituents of matter have been gained by observing what happens when beams of high-energy particles collide. Electron–positron, proton–proton, proton–antiproton and electron–proton colliders have all contributed to the development of today’s understanding, embodied in the Standard Model of particle physics (SM). The Large Hadron Collider (LHC) brings 6.5 TeV proton beams into collision, allowing the Higgs boson and other SM particles to be studied and searches for new physics to be carried out. To reach physics beyond the LHC will require hadronic colliders at higher energies and/or lepton colliders that can deliver substantially increased precision.

    A variety of options are being explored to achieve these goals. For example, the Future Circular Collider study at CERN is investigating a 100 km-circumference proton–proton collider with beam energies of around 50 TeV the tunnel for which could also host an electron–positron collider (CERN Courier June 2018 p15).

    CERN FCC Future Circular Collider map

    Electron–positron annihilation has the advantage that all of the beam energy is available in the collision, rather than being shared between the constituent quarks and gluons as it is in hadronic collisions. But to reach very high energies requires either a state-of-the-art linear accelerator, such as the proposed Compact Linear Collider or the International Linear Collider, or a circular accelerator with an extremely large bending radius.

    Cern Compact Linear Collider


    CLIC Collider annotated

    ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

    Muons to the fore

    A colliding-beam facility based on muons has a number of advantages. First, since the muon is a lepton, all of the beam energy is available in the collision. Second, since the muon is roughly 200 times heavier than the electron and thus emits around 109 times less synchrotron radiation than an electron beam of the same energy, it is possible to produce multi-TeV collisions in an LHC-sized circular collider. The large muon mass also enhances the direct “s-channel” Higgs-production rate by a factor of around 40,000 compared to that in electron–positron colliders, making it possible to scan the centre-of-mass energy to measure the Higgs-boson line shape directly and to search for closely spaced states.

    __________________________________________________________
    2
    __________________________________________________________

    Stored muon beams could also serve the long-term needs of neutrino physicists (see box 1). In a neutrino factory, beams of electron and muon neutrinos are produced from the decay of muons circulating in a storage ring. It is straightforward to tune the neutrino-beam energy because the neutrinos carry away a substantial fraction of the muon’s energy. This, combined with the excellent knowledge of the beam composition and energy spectrum resulting from the very well-known characteristics of muon decays, makes the neutrino factory the ideal place to make precision measurements of neutrino properties and to look for oscillation phenomena that are outside the standard, three-neutrino-mixing paradigm.

    Given the many benefits of a muon collider or neutrino factory, it is reasonable to ask why one has yet to be built. The answer is that muons are unstable, decaying with a mean lifetime at rest of 2.2 microseconds. This presents two main challenges: first, a high-intensity primary beam must be used to create the muons that will form the beam; and, second, once captured, the muon beam must be accelerated rapidly to high energy so that the effective lifetime of the muon can be extended by the relativistic effect of time dilation.

    One way to produce beams for a muon collider or neutrino factory is to harness the muons produced from the decay of pions when a high-power (few-MW), multi-GeV proton beam strikes a target such as carbon or mercury. For this approach, new proton accelerators with the required performance are being developed at CERN, Fermilab, J-PARC and at the European Spallation Source.

    ESS European Spallation Source, currently under construction in Lund, Sweden.

    The principle of the mercury target was proved by the MERIT experiment that operated on the Proton Synchrotron at CERN. However, at the point of production, the tertiary muon beam emerging from such schemes occupies a large volume in phase space. To maximise the muon yield, the beam has to be “cooled” – i.e. its phase-space volume reduced – in a short period of time before it is accelerated.

    __________________________________________________________

    __________________________________________________________

    The proposed solution is called ionisation cooling, which involves passing the beam through a material in which it loses energy via ionisation and then re-accelerating it in the longitudinal direction to replace the lost energy. Proving the principle of this technique is the goal of the Muon Ionization Cooling Experiment (MICE) collaboration, which, following a long period of development, has now reported its first observation of ionisation cooling.

    An alternative path to a muon collider called the Low Emittance Muon Accelerator (LEMMA), recently proposed by accelerator physicists at INFN in Italy and the ESRF in France, provides a naturally cooled muon beam with a long lifetime in the laboratory by capturing muon–antimuon pairs created in electron–positron annihilation.

    Cool beginnings

    The benefits of a collider based on stored muon beams were first recognised by Budker and Tikhonin at the end of the 1960s. In 1974, when CERN’s Super Proton Synchrotron (SPS) was being brought into operation, Koshkarev and Globenko showed how muons confined within a racetrack-shaped storage ring could be used to provide intense neutrino beams. The following year, the SPS proton beam was identified as a potential muon source and the basic parameters of the muon beam, storage ring and neutrino beam were defined.

    The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator. (Image: Julien Ordan/CERN

    It was quickly recognised that the performance of this facility—the first neutrino factory to be proposed – could be enhanced if the muon beam was cooled. In 1978, Budker and Skrinsky identified ionisation cooling as a technique that could produce sufficient cooling in a timeframe short compared to the muon lifetime and, the following year, Neuffer proposed a muon collider that exploited ionisation cooling to increase the luminosity.

    The study of intense, low-emittance muon beams as the basis of a muon collider and/or neutrino factory was re-initiated in the 1990s, first in the US and then in Europe and Japan. Initial studies of muon production and capture, phase-space manipulation, cooling and acceleration were carried out and neutrino- and energy-frontier physics opportunities evaluated. The reduction of the tertiary muon-beam phase space was recognised as a key technological challenge and at the 2001 NuFact workshop the international MICE collaboration was created, comprising 136 physicists and engineers from 40 institutes in Asia, Europe and the US.

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    3
    __________________________________________________________

    he MICE cooling cell, in common with the cooling channels studied since the seminal work of the 1990s, is designed to operate at a beam momentum of around 200 MeV/c. This choice is a compromise between the size of the ionisation-cooling effect and its dependence on the muon energy, the loss rate of muon-beam intensity through decay, and the ease of acceleration following the cooling channel. The ideal absorber has, at the same time, a large ionisation energy loss per unit length (to maximise ionisation cooling) and a large radiation length (to minimise heating through multiple Coulomb scattering). Liquid hydrogen meets these requirements and is an excellent absorber material; a close runner-up, with the practical advantage of being solid, is lithium hydride. MICE was designed to study the properties of both. The critical challenges faced by the collaboration therefore included: the integration of high-field superconducting magnets operating in a magnetically coupled lattice; high-gradient accelerating cavities capable of operation in a strong magnetic field; and the safe implementation of liquid-hydrogen absorber modules – all solved through more than a decade of R&D.

    In 2003 the MICE collaboration submitted a proposal to mount the experiment (figure 1) on a new beamline at the ISIS proton and muon source at the Science and Technology Facilities Council’s (STFC) Rutherford Appleton Laboratory in the UK. Construction began in 2005 and first beam was delivered on 29 March 2008. The detailed design of the spectrometer solenoids was also carried out at this time and the procurement process was started. During the period from 2008 to 2012, the collaboration carried out detailed studies of the properties of the beam delivered to the experiment and, in parallel, designed and fabricated the focus-coil magnets and a first coupling coil.

    4
    No image caption or credit.

    Delays were incurred in addressing issues that arose in the manufacture of the spectrometer solenoids. This, combined with the challenges of integrating the four-cavity linac module with the coupling coil, led, in November 2014, to a reconfiguration of the MICE cooling cell. The simplified experiment required two, single-cavity modules and beam transport was provided by the focus-coil modules. An intense period of construction followed, culminating with the installation of the spectrometer solenoids and the focus-coil module in the summer of 2015. Magnet commissioning progressed well until, a couple of months later, a coil in the downstream solenoid failed during a training quench. The modular design of the apparatus meant the collaboration was able to devise new settings rapidly, but it proved not to be possible to restore the downstream spectrometer magnet to full functionality. This, combined with the additional delays incurred in the recovery of the magnet, eventually led to the cancellation of the installation of the RF cavities in favour of the extended operation of a configuration of the experiment without the cavities.

    It is interesting to reflect, as was done in a recent lessons-learnt exercise convened by the STFC, whether a robust evaluation of alternative options for the cooling-demonstration lattice at the outset of MICE might have identified the simplified lattice as a “less-risky” option and allowed some of the delays in implementing the experiment to be avoided.

    5

    The bulk of the data-taking for MICE was carried out between November 2015 and December 2017, using lithium-hydride and liquid-hydrogen absorbers. The campaign was successful: more than 5 × 108 triggers were collected over a range of initial beam momentum and emittance for a variety of configurations of the magnetic channel for each absorber material. The key parameter to measure when demonstrating ionisation cooling is the “amplitude” of each muon – the distance from the beam centre in transverse phase space, reconstructed from its position and momentum. The muon’s amplitude is measured before it enters the absorber and again as it leaves, and the distributions of amplitudes are then examined for evidence of cooling: a net migration of muons from high to low amplitudes. As can be seen (figure 2), the particle density in the core of the MICE beam is increased as a result of the beam’s passage through the absorber, leading to a lower transverse emittance and thereby providing a higher neutrino flux or a larger luminosity.

    The MICE observation of the ionisation-cooling of muon beams is an important breakthrough, achieved through the creativity and tenacity of the collaboration and the continuous support of the funding agencies and host laboratory. The results match expectations, and the next step would be to design an experiment to demonstrate cooling in all six phase-space dimensions.

    Completing the MICE programme

    Having completed its experimental programme, MICE will now focus on the detailed analysis of the factors that determine ionisation-cooling performance over a range of momentum, initial emittance and lattice configurations for both liquid-hydrogen and lithium-hydride absorbers. MICE was operated such that data were recorded one particle at a time. This single-particle technique will allow the collaboration to study the impact of transverse-emittance growth in rapidly varying magnetic fields and to devise mechanisms to mitigate such effects. Furthermore, MICE has taken data to explore a scheme in which a wedge-shaped absorber is used to decrease the beam’s longitudinal emittance while allowing a controlled growth in its transverse emittance. This is required for a proton-based muon collider to reach the highest luminosities.

    With the MICE observation of ionisation cooling, the last of the proof-of-principle demonstrations of the novel technologies that underpin a proton-based neutrino factory or muon collider has now been delivered. The drive to produce lepton–antilepton collisions at centre-of-mass energies in the multi-TeV range can now include consideration of the muon collider, for which two routes are offered: one, for which the R&D is well advanced, that exploits muons produced using a high-power proton beam and which requires ionisation cooling; and one that exploits positron annihilation with electrons at rest to create a high-energy cold muon source. The high muon flux that can be achieved using the proton-based technique has the potential to serve a neutrino-physics programme of unprecedented sensitivity, and the MICE collaboration’s timely results will inform the coming update of the European Strategy for Particle Physics.

    See the full article here .


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  • richardmitnick 10:55 am on July 11, 2018 Permalink | Reply
    Tags: CERN Courier, E821 storage-ring experiment at Brookhaven National Laboratory, , , , ,   

    From CERN Courier: “Muons accelerated in Japan” 


    From CERN Courier

    9 July 2018

    1
    Installation. No image credit.

    Muons have been accelerated by a radio-frequency accelerator for the first time, in an experiment performed at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, Japan. The work paves the way for a compact muon linac that would enable precision measurements of the muon anomalous magnetic moment and the electric dipole moment.

    Japan Proton Accelerator Research Complex J-PARC, located in Tokai village, Ibaraki prefecture, on the east coast of Japan


    Japan Proton Accelerator Research Complex J-PARC, located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    Around 15 years ago, the E821 storage-ring experiment at Brookhaven National Laboratory (BNL) reported the most precise measurement of the muon anomalous magnetic moment (g-2).

    1
    E821 storage-ring experiment at Brookhaven National Laboratory (BNL)

    Achieving an impressive precision of 0.54 parts per million (ppm), the measured value differs from the Standard Model prediction by more than three standard deviations. Following a major effort over the past few years, the BNL storage ring has been transported to and upgraded at Fermilab and recently started taking data to improve on the precision of E821.

    FNAL Muon g-2 studio

    In the BNL/Fermilab setup, a beam of protons enters a fixed target to create pions, which decay into muons with aligned spins. The muons are then transferred to the 14 m-diameter storage ring, which uses electrostatic focusing to provide vertical confinement, and their magnetic moments are measured as they precess in a magnetic field.

    The new J-PARC experiment, E34, proposes to measure muon g-2 with an eventual precision of 0.1 ppm by storing ultra-cold muons in a mere 0.66 m-diameter magnet, aiming to reach the BNL precision in a first phase. The muons are produced by laser-ionising muonium atoms (bound states of a positive muon and an electron), which, since they are created at rest, results in a muon beam with very little spread in the transverse direction – thus eliminating the need for electrostatic focusing.

    The ultracold muon beam is stored in a high-precision magnet where the spin-precession of muons is measured by detecting muon decays. This low-emittance technique, which allows a smaller magnet and lower muon energies, enables researchers to circumvent some of the dominant systematic uncertainties in the previous g-2 measurement. To avoid decay losses, the J-PARC approach requires muons to be accelerated via a conventional radio-frequency accelerator.

    In October 2017, a team comprising physicists from Japan, Korea and Russia successfully demonstrated the first acceleration of negative muonium ions, reaching an energy of 90 keV. The experiment was conducted using a radio-frequency quadrupole linac (RFQ) installed at a muon beamline at J-PARC, which is driven by a high-intensity pulsed proton beam. Negative muonium atoms were first accelerated electrostatically and then injected into the RFQ, after which they were guided to a detector through a transport beamline. The accelerated negative muonium atoms were identified from their time of flight: because a particle’s velocity at a given energy is uniquely determined from its mass, its type is identified by measuring the velocity (see figure).

    The researchers are now planning to further accelerate the beam from the RFQ. In addition to precise measurements in particle physics, the J-PARC result offers new muon-accelerator applications including the construction of a transmission muon microscope for use in materials and life-sciences research, says team member Masashi Otani of KEK laboratory. “Part of the construction of the experiment has started with partial funding, which includes the frontend muon beamline and detector. The experiment can start properly three years after full funding is provided.”

    Muon acceleration is also key to a potential muon collider and neutrino factory, for which it is proposed that the large, transverse emittance of the muon beam can be reduced using ionisation cooling (see Muons cooled for action).

    See the full article here .


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  • richardmitnick 10:01 am on July 11, 2018 Permalink | Reply
    Tags: , CERN Courier,   

    From CERN Courier- “Viewpoint: A golden age for neutrinos” 


    From CERN Courier

    9 July 2018
    Albert De Roeck

    20 years since the discovery of neutrino oscillations, a complete understanding is within our grasp.

    1
    Inside a prototype detector module for the international DUNE experiment, which was built at CERN and is about to be filled with liquid argon before undergoing its first tests with beam. Credit: CERN-201710-248-3

    Super-Kamiokande experiment in Japan announced the first evidence for atmospheric-neutrino flavour oscillations. Since neutrinos can only oscillate among different flavours if at least some of them have a non-zero mass, the result proved that neutrinos are massive, albeit with very small mass values. This is not expected in the Standard Model.

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    Neutrino physics was already an active field, but the 1998 observation sent it into overdrive. The rich scientific programme and record attendance of the Neutrino 2018 conference in Heidelberg last month (see Neutrino physics shines bright in Heidelberg) is testament to our continued fascination with neutrinos. Many open questions remain: what generates the tiny masses of the known neutrinos, and what is their mass ordering? Are there more than the three known neutrino flavours, such as additional sterile or right-handed versions? Is there CP violation in the neutrino sector and, if so, how large is it? In addition, there are solar neutrinos, atmospheric neutrinos, cosmic/supernova neutrinos, relic neutrinos, geo-neutrinos, reactor neutrinos and accelerator-produced neutrinos – allowing for a plethora of experimental and theoretical activity.

    Many of these questions are expected to be answered in the next decade thanks to vigorous experimental efforts. Concerning neutrino-flavour oscillations, new results are anticipated in the short term from the accelerator-based T2K and NOvA experiments in Japan and the US, respectively.

    T2K map, T2K Experiment, Tokai to Kamioka, Japan

    FNAL/NOvA experiment map


    FNAL NOvA detector in northern Minnesota

    These experiments probe the CP-violating phase in the neutrino-flavour mixing matrix and the ordering of the neutrino mass states; evidence for large CP violation could be established, in particular thanks to the planned ND280 near-detector upgrade of T2K.

    The next generation of accelerator-based experiments is already under way. The Deep Underground Neutrino Experiment (DUNE) in South Dakota, US, which will use a neutrino beam sent from Fermilab, is taking shape and two large prototypes of the DUNE far detector are soon to be tested at CERN.

    ProtoDune

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    In Japan, plans are shaping up for Hyper-Kamiokande, a large detector with a fiducial volume around 10 times larger than that of Super-Kamiokande, and this effort is complemented with other sensitivity improvements and a possible second detector in Korea for analysing a neutrino beam sent from J-PARC in Japan. These experiments, which are planned to come online in 2026, will allow precision neutrino-oscillation measurements and provide decisive statements on the neutrino mass hierarchy and CP-violating phase.

    Hyper-Kamiokande, a neutrino physics laboratory located underground in the Mozumi Mine of the Kamioka Mining and Smelting Co. near the Kamioka section of the city of Hida in Gifu Prefecture, Japan.

    Important insights are also expected from reactor sources. In China, the JUNO experiment should start in 2021 and could settle the mass-hierarchy question and determine complementary oscillation parameters.

    JUNO Neutrino detector, at Kaiping, Jiangmen in Southern China

    Meanwhile, very-short-baseline reactor experiments – such as PROSPECT, STEREO, SoLid, NEOS and DANSS – are soon to join the hunt for sterile neutrinos. Together with detectors at the short-baseline neutrino beam at Fermilab (SBND, MicroBooNE and ICARUS), the next few years should see conclusive results on the existence of sterile neutrinos. In particular, the recently reported update on the intriguing excess seen by the MiniBooNE experiment will be scrutinised.

    Yale PROSPECT Neutrino experiment


    Yale PROSPECT—A Precision Oscillation and Spectrum Experiment

    FNAL Short Baseline Neutrino Detector

    FNAL/MicroBooNE

    FNAL/ICARUS

    FNAL/MiniBooNE

    Together with the ever-increasing sensitivities achieved by double-beta-decay experiments, which test whether neutrinos have a Majorana mass term, the SHiP experiment is proposed to search for right-handed neutrinos, while KATRIN in Germany has just started its campaign to measure the mass of the electron antineutrino with sub-eV precision. The interplay with astronomy and cosmology, using detectors such as IceCUBE and KM3NeT, which survey atmospheric neutrinos, further underlines the vibrancy and breadth of modern neutrino physics. Also, the European Spallation Source, under construction in Sweden, is investigating the possibility of a precise neutrino-measurement programme.

    Neutrino experiments are spread around the globe, but Europe is a strong player. A discussion forum on neutrino physics for the update of the European strategy for particle physics will be hosted by CERN on 22–24 October. Clearly, neutrino science promises many exciting results in the near future.

    See the full article here .


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  • richardmitnick 9:23 am on June 4, 2018 Permalink | Reply
    Tags: , , , , CERN Courier, , , ,   

    From CERN Courier: “Higgs boson reaches the top” 


    From CERN Courier

    Jun 1, 2018
    No writer credit

    The CMS collaboration has published the first direct observation of the coupling between the Higgs boson and the top quark, offering an important probe of the consistency of the Standard Model (SM). In the SM, the Higgs boson interacts with fermions via a Yukawa coupling, the strength of which is proportional to the fermion mass. Since the top quark is the heaviest particle in the SM, its coupling to the Higgs boson is expected to be the largest and thus the dominant contribution to many loop processes, making it a sensitive probe of hypothetical new physics.

    1
    Combined likelihood analysis

    The associated production of a Higgs boson with a top quark–antiquark pair (ttH) is the best direct probe of the top-Higgs Yukawa coupling with minimal model dependence, and thus a crucial element to verify the SM nature of the Higgs boson. However, its small production rate – constituting only about 1% of the total Higgs production cross-section – makes the ttH measurement a considerable challenge.

    The CMS and ATLAS collaborations reported first evidence for the process last year, based on LHC data collected at a centre-of-mass energy of 13 TeV (CERN Courier May 2017 p49 and December 2017 p12). The first observation, constituting statistical significance above five standard deviations, is based on an analysis of the full 2016 CMS dataset recorded at an energy of 13 TeV and by combining these results with those collected at lower energies.

    The ttH process gives rise to a wide variety of final states, and the new CMS analysis combines results from a number of them. Top quarks decay almost exclusively to a bottom quark (b) and a W boson, the latter subsequently decaying either to a quark and an antiquark or to a charged lepton and its associated neutrino. The Higgs-boson decay channels include the decay to a bb quark pair, a τ+τ– lepton pair, a photon pair, and combinations of quarks and leptons from the decay of intermediate on- or off-shell W and Z bosons. These five Higgs-boson decay channels were analysed by CMS using sophisticated methods, such as multivariate techniques, to separate signal from background events. Each channel poses different experimental challenges: the bb channel has the largest rate but suffers from a large background of events containing a top-quark pair and jets, while the photon and Z-boson pair channels offer the highest signal-to-background ratio at a very small rate.

    CMS observed an excess of events with respect to the background-only hypothesis at a significance of 5.2 standard deviations. The measured values of the signal strength in the considered channels are consistent with each other, and a combined value of 1.26 +0.31/–0.26 times the SM expectation is obtained (see figure). The measured production rate is thus consistent with the SM prediction within one standard deviation. The result establishes the direct Yukawa coupling of the Higgs boson to the top quark, marking an important milestone in our understanding of the properties of the Higgs boson.

    Further reading

    https://arxiv.org/abs/1804.02610
    https://arxiv.org/abs/1803.05485
    https://journals.aps.org/prd/abstract/10.1103/PhysRevD.97.072003

    See the full article here .


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  • richardmitnick 3:16 pm on June 2, 2018 Permalink | Reply
    Tags: , , CERN Courier, , Chinese CEPC project, , , ,   

    From CERN Courier: “China’s bid for a circular electron–positron collider” 


    From CERN Courier

    Jun 1, 2018
    Jie Gao
    Institute of High Energy Physics
    University of Chinese Academy of Sciences

    1
    A future collider in China

    Physicists in China have completed a conceptual design report for a 100 km-circumference collider that, in conjunction with a possible linear collider in Japan, would open a new era for high-energy physics in Asia.

    ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

    Chinese accelerator-based research in high-energy physics is a relatively recent affair. It began in earnest in October 1984 with the construction of the 240 m-circumference Beijing Electron Positron Collider (BEPC) at the Institute of High Energy Physics. BEPC’s first collisions took place in 1988 at a centre-of-mass energy of 1.89 GeV. At the time, SLAC in the US and CERN in Europe were operating their more energetic PEP and LEP electron–positron colliders, respectively, while the lower-energy electron–positron machines ADONE (Frascati), DORIS (DESY) and VEPP-4 (BINP Novosibirsk) were also in operation.



    Beijing Electron Positron Collider (BEPC)

    SLAC SSRL


    SLAC SSRL PEP collider map

    CERN LEP Collider


    CERN LEP Collider

    ADONE INFN-LNF synchrotron radiation beamline

    DESY DORIS


    DESY DORIS III

    VEPP-4 (BINP Novosibirsk)

    Beginning in 2006, the BEPCII upgrade project saw the previous machine replaced with a double-ring scheme capable of colliding electrons and positrons at the same beam energy as that of BEPC but with a luminosity 100 times higher (1033 cm−2 s−1). BEPCII, whose collisions are recorded by the Beijing Spectrometer III (BES III) detector, switched on two years later and continues to produce results today, with a particular focus on the study of charm and light-hadron decays.

    BESS III

    China also undertakes non-accelerator-based research in high-energy physics via the Daya Bay neutrino experiment, which was approved in 2006 and announced the first observation of the neutrino mixing angle θ13 in March 2012.

    Daya Bay, approximately 52 kilometers northeast of Hong Kong and 45 kilometers east of Shenzhen, China

    The discovery of the Higgs boson at CERN’s Large Hadron Collider [see below] in July 2012 raises new opportunities for a large-scale accelerator.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    Thanks to the low mass of the Higgs, it is possible to produce it in the relatively clean environment of a circular electron–positron collider – in addition to linear electron–positron colliders such as the International Linear Collider (ILC) [see schematic above] and the Compact Linear Collider (CLIC) – with reasonable luminosity, technology, cost and power consumption.

    CLIC Collider annotated


    CERN/CLIC

    The Higgs boson is the cornerstone of the Standard Model (SM), yet is also responsible for most of its mysteries: the naturalness problem, the mass-hierarchy problem and the vacuum-stability problem, among others. Therefore, precise measurements of the Higgs boson serve as excellent probes of the fundamental physics principles underlying the SM and of exploration beyond the SM.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.


    Standard Model of Particle Physics from Symmetry Magazine

    4
    Fig. 1.

    In September 2012, Chinese scientists proposed a 50–70 km circumference 240 GeV Circular Electron Positron Collider (CEPC) in China, serving two large detectors for Higgs studies. The tunnel for such a machine could also host a Super Proton Proton Collider (SppC) to reach energies beyond the LHC (figure 1). CERN is also developing, via the Future Circular Collider (FCC) study, a proposal for a large (100 km circumference) tunnel, which could host high-energy electron–positron (FCC-ee), proton–proton (FCC-hh) or electron–proton (FCC-he) colliders (see CERN thinks bigger).

    CERN Future Circular Collider


    FCC Future Circular Collider at CERN

    Progress in both projects is proceeding fast, although many open questions remain – not least how to organise and fund these next great steps in our exploration of fundamental particles.

    China Circular Electron Positron Collider (CEPC) map

    Precision leap

    CEPC is a Higgs factory capable of producing one million clean Higgs bosons over a 10 year period. As a result, the couplings between the Higgs boson and other particles could be determined to an accuracy of 0.1–1% – roughly one order of magnitude better than that expected of the high-luminosity LHC upgrade and challenging the most advanced next-to-next-to-leading-order SM calculations (figure 2). By lowering the centre-of-mass energy to that of the Z pole at around 90 GeV, without the need to change hardware, CEPC could produce at least 10 billion Z bosons per year. As a super Z – and W – factory, CEPC would shed light on rare decays and heavy-flavour physics and mark a factor-10 leap in the precision of electroweak measurements.

    4
    Fig. 2.

    The latest CEPC baseline design is a 100 km double ring (figure 3, left) with a single-beam synchrotron-radiation power of 30 MW at the Higgs pole, and with the same superconducting radio-frequency accelerator system for both electron and positron beams. CEPC could work both at Higgs- and Z-pole energies with a luminosity of 2 × 1034 cm–2 s–1 and 16 × 1034 cm–2 s–1, respectively. The alternative design of CEPC is based on a so-called advanced partial double-ring scheme (figure 3, right) with the aim of reducing the construction cost. Preliminary designs for the two CEPC detectors are shown in figure 4.

    5
    Fig. 3.

    Concerning the SppC baseline, it has been decided to start with 12 T dipole magnets made from iron-based high-temperature superconductors to allow proton–proton collisions at a centre-of-mass energy of 75 TeV and a luminosity of 1035 cm–2 s–1. The SppC SC magnet design is different to the Nb3Sn-based magnets planned by the FCC-hh study, which are targeting a field of 16 T to allow protons to collide at a centre-of-mass energy of 100 TeV. The Chinese design also envisages an upgrade to 20 T magnets, which will take the SppC collision energy to beyond 100 TeV. Discovered just over a decade ago, iron-based superconductors have a much higher superconducting transition temperature than conventional superconductors, and therefore promise to reduce the cost of the magnets to an affordable level. To conduct the relevant R&D, a national network in China has been established and already more than 100 m of iron-based conductor cable has been fabricated.

    6
    Fig. 4.

    The CEPC is designed as a facility where both machines can coexist in the same tunnel (figure 5). It will have a total of four detector experimental halls, each with a floor area of 2000 m2 – two for CEPC and another two for SppC experiments. The tunnel is around 6 m wide and 4.8 m high, hosting the CEPC main ring (comprising two beam pipes), the CEPC booster and SppC. The SppC will be positioned outside of CEPC to accommodate other collision modes, such as an electron–proton, in the far future. The FCC study, which is aiming to complete a Conceptual Design Report (CDR) by the end of the year, adopts a similar staged approach (see CERN thinks bigger [link is above]).

    7
    Fig. 5.

    China on track

    Since the first CEPC proposal, momentum has grown. In June 2013, the 464th Fragrant Hill Meeting (a national meeting series started in 1994 for the long-term strategic development of China’s science and technology) was held in Beijing and devoted to developing China’s high-energy physics following the discovery of the Higgs boson. Two consensuses were reached: the first was to support the ILC and participate in its construction with in-kind contributions, with R&D funds to be requested from the Chinese government; the second was a recognition that a circular electron–positron Higgs factory – the next collider after BEPCII in China – and a Super proton–proton collider built afterwards in the same tunnel is an important historical opportunity for fundamental science.

    n 2014, the International Committee for Future Accelerators (ICFA) released statements supporting studies of energy-frontier circular colliders and encouraged global coordination. ICFA continues to support international studies of circular colliders, in addition to support for linear machines, reflecting the strategic vision of the international high-energy community. In April 2016, during the AsiaHEP and Asian Committee for Future Accelerators (ACFA) meeting in Kyoto, positive statements were made regarding the ILC and a China-led effort on CEPC-SppC. In September that year, at a meeting of the Chinese Physics Society, it was concluded that CEPC is the first option for a future high-energy accelerator project in China, with the strategic aim of making it a large international scientific project. Pre-conceptual design reports (pre-CDRs) for CEPC-SppC were completed at the beginning of 2015 with an international review, based on a single ring-based “pretzel” orbit scheme. A CEPC International Advisory Committee (IAC) was established and, in 2016, the Chinese Ministry of Science and Technology (MOST) allocated 36 million RMB (€4.6 million) for the CEPC study, and in 2018 another 32 million RMB (€4.1 million) has been approved by MOST.

    Ensuring that a large future circular collider maximises its luminosity is a major challenge. The CEPC project has studied the use of a crab-waist collision scheme, which is also being studied for FCC-ee. Each of the double-ring schemes for CEPC have been studied systematically with the aim of comparing the luminosity potentials. On 15 January last year, CEPC-SppC baseline and alternative designs for the CDR were decided, laying the ground for the completion of the CEPC CDR at the end of 2017. Following an international review in June, the CEPC CDR will be published in July 2018.

    While technical R&D continues – both for the CEPC machine and its two large detectors – a crucial issue is how to pay for such a major international project. In addition to the initial funding from MOST, other potential channels include the National Science Foundation of China (NSFC), the Chinese Academy of Sciences (CAS) and local governments. For example, two years ago Beijing Municipal allocated more than 500 million RMB (€65 million) to the Institute of High Energy Physics for superconducting RF development, and in 2018 CAS plans to allocate 200 million RMB (€26 million) to study high-temperature superconductors for magnets, including studies in materials science, industry and projects such as SppC. While not specifically intended for CEPC-SppC, such investments will have strong synergies with high-energy physics and, in November 2017, the CEPC-SppC Industrial Promotion Consortium was established with the aim of supporting mutual efforts between CEPC-SppC and industry.

    A five-year-long Technical Design Report (TDR) effort to optimise the CEPC-SppC design and technologies, and prepare for industrial production, started this year. Construction of CEPC could begin as early as 2022 and be completed by the end of the decade. CEPC would operate for about 10 years, while SppC is planned to start construction in around 2040 and be completed by the mid-2040s. The CEPC-SppC TDR phase after the CDR is critical, both for key-component R&D and industrialisation. R&D has already started towards high-Q, high-field 1.3 GHz and 650 MHz superconducting cavities; 650 MHz high-power high-efficiency klystrons; 12 kW cryogenic systems, 12 T iron-based high temperature superconducting dipoles, and other enabling technologies. Construction of a new 4500 m2 superconducting RF facility in Beijing called the Platform of Advanced Photon Source began in May 2017 to be completed in 2020, and could serve as a supporting facility for different projects.

    International ambition

    CEPC-SppC is a Chinese-proposed project to be built in China, but its nature is an international collaboration for the high-energy physics community worldwide. Following the creation of the CEPC-SppC IAC in 2015, more than 20 MoUs have been signed with many institutes and universities around the world, such as the Budker Institute of Nuclear Physics (BINP; Russia); National Research Nuclear University MEPhI (Moscow, Russia) and the University of Rostock (Germany).

    In August 2017, ICFA endorsed an ILC operating at a centre-of-mass energy of 250 GeV (ILC250), with energy-upgrade possibilities in the future (CERN Courier January/February 2018 p7). Although CEPC and ILC250 start with the same energy to study the Higgs boson, the ultimate goals are totally different from each other: SppC is for a 100 TeV proton–proton collider and ILC is a 1 TeV (maximum) electron–positron collider. The existence of both, however, would offer a highly complementary physics programme operating for a period of decades. The specific feature of CEPC is its small-scale superconducting RF system, (and its relatively large AC power consumption (300 MW for CEPC compared to 110 MW for ILC250). As for the cost, CEPC in its first phase includes part of the cost of SppC for its long tunnel, whereas ILC would upgrade its energy by increasing tunnel length accordingly later.

    8

    Deciding where to site the CEPC-SppC involves numerous considerations. Technical criteria are roughly quantified as follows: earthquake intensity less than seven on the Richter scale; earthquake acceleration less than 0.1 g; ground surface-vibration amplitude less than 20 nm at 1–100 Hz; granite bedrock around 50–100 m deep, and others. The site-selection process started in February 2015, and so far six sites have been considered: Qinhuangdao in Hebei Province; Huangling county in Shanxi Province; Shenshan Special District in Guangdong Province; Baoding (Xiongan) in Heibei Province; Huzhou in Zhejiang Province and Changchun in Jilin Province, where the first three sites have been prospected underground (figure 6). More sites, such as Huzhou in Zhejiang Province, will be considered in the future before a final selection decision. According to Chinese civil construction companies involved in the siting process, a 100 km tunnel will take less than five years to dig using drill-and-blast methods, and around three years if a tunnel boring machine is employed.

    2018 is a milestone year for Higgs factories in Asia. As CEPC completes its CDR, the global high-energy physics community is waiting for a potential positive declaration from the Japanese government, by the end of the year, on their intention to host ILC250 in Japan, upgradable to higher energies. It is also a key moment for high-energy physics in Europe. FCC will complete its CDR by the end of the year, while CLIC released an updated 380 GeV baseline-staging scenario (CERN Courier November 2016 p20), and the European Strategy for Particle Physics update process will get under way (CERN Courier April 2018 p7). Hopefully, both ILC250 and CEPC-SppC will be included in the update together with FCC, while with respect to the US strategy we are looking forward to the next “P5” meeting following the European update.

    During the past five years, CEPC-SppC has kept to schedule both in design and R&D, together with strong team development and international collaboration. On 28 March this year, the Chinese government announced the “Implementation method to support China-initiated large international science projects and plans”, with the goal of identifying between three and five preparatory projects, one or two of which will be put to construction, by 2020. Hopefully, CEPC will be among those selected.

    Related journal articles
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  • richardmitnick 1:22 pm on June 2, 2018 Permalink | Reply
    Tags: CERN Courier, , , HESS proves the power of TeV astronomy, MAGIC observatory in the Canary Islands, TeV photons, VERITAS in Arizona at FLWO   

    From CERN Courier: “HESS proves the power of TeV astronomy” 


    From CERN Courier

    Jun 1, 2018
    Merlin Kole
    Department of Particle Physics
    University of Geneva.

    1
    Supernova-remnant candidates

    For hundreds of years, discoveries in astronomy were all made in the visible part of the electromagnetic spectrum. This changed in the past century when new objects started being discovered at both longer wavelengths, such as radio, and shorter wavelengths, up to gamma-ray wavelengths corresponding to GeV energies. The 21st century then saw another extension of the range of astronomical observations with the birth of TeV astronomy.

    The High Energy Stereoscopic System (HESS) – an array of five telescopes located in Namibia in operation since 2002 – was the first large ground-based telescope capable of measuring TeV photons (followed shortly afterwards by the MAGIC observatory in the Canary Islands and, later, VERITAS in Arizona).

    HESS Cherenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, altitude, 1,800 m (5,900 ft) near the Gamsberg searches for cosmic rays

    MAGIC Cherenkov gamma ray telescope on the Canary island of La Palma, Spain Altitude 2,200 m (7,200 ft) Edit this at Wikidata

    CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory in AZ, USA, Altitude 2,606 m (8,550 ft)

    To celebrate its 15th anniversary, the HESS collaboration has published its largest set of scientific results to date in a special edition of Astronomy and Astrophysics. Among them is the detection of three new candidates for supernova remnants that, despite being almost the size of the full Moon on the sky, had thus far escaped detection.

    Supernova remnants are what’s left after massive stars die. They are the prime suspect for producing the bulk of cosmic rays in the Milky Way and are the means by which chemical elements produced by supernovae are spread in the interstellar medium. They are therefore of great interest for different fields in astrophysics.

    HESS observes the Milky Way in the energy range 0.03–100 TeV, but its telescopes do not directly detect TeV photons. Rather, they measure the Cherenkov radiation produced by showers of particles generated when these photons enter Earth’s atmosphere. The energy and direction of the primary TeV photons can then be determined from the shape and direction of the Cherenkov radiation.

    Using the characteristics of known TeV-emitting supernova remnants, such as their shell-like shape, the HESS search revealed three new objects at gamma-ray wavelengths, prompting the team to search for counterparts of these objects in other wavelengths. Only one, called HESS J1534-571 (figure, left), could be connected to a radio source and thus be classified as a supernova remnant. For the two other sources, HESS J1614-518 and HESS J1912+101, no clear counterparts were found. These objects thus remain candidates for supernova remnants.

    The lack of an X-ray counterpart to these sources could have implications for cosmic-ray acceleration mechanisms. The cosmic rays thought to originate from supernova remnants should be directly connected to the production of high-energy photons. If the emission of TeV photons is a result of low-energy photons being scattered by high-energy cosmic-ray electrons originating from a supernova remnant (as described by leptonic emission models), soft X-rays would also be produced while such electrons travelled through magnetic fields around the remnant. The lack of detection of such X-rays could therefore indicate that the TeV photons are not linked to such scattering but are instead associated with the decay of high-energy cosmic-ray pions produced around the remnant, as described by hadronic emission models. Searches in the X-ray band with more sensitive instruments than those available today are required to confirm this possibility and bring deeper insight into the link between supernova remnants and cosmic rays.

    The new supernova-remnant detections by HESS demonstrate the power of TeV astronomy to identify new objects. The latest findings increase the anticipation for a range of discoveries from the future Cherenkov Telescope Array (CTA). With more than 100 telescopes, CTA will be more sensitive to TeV photons than HESS, and it is expected to substantially increase the number of detected supernova remnants in the Milky Way.

    See the full article here. .


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  • richardmitnick 12:43 pm on June 2, 2018 Permalink | Reply
    Tags: , , , CERN Courier, DESY 2030, , ,   

    From CERN Courier: “DESY sets out vision for the future” 


    From CERN Courier

    Apr 19, 2018
    No writer credit found

    1

    On 20 March, the DESY laboratory in Germany presented its strategy for the coming decade, outlining the areas of science and innovation it intends to focus on. DESY is a member of the Helmholtz Association, a union of 18 scientific-technical and medical-biological research centres in Germany with a workforce of 39,000 and annual budget of €4.5 billion. The laboratory’s plans for the 2020s include building the world’s most powerful X-ray microscope (PETRA IV), expanding the European X-ray free-electron laser (XFEL), and constructing a new centre for data and computing science.

    2
    PETRA IV Roadmap


    European XFEL


    XFEL Tunnel

    Founded in 1959, DESY became a leading high-energy-physics laboratory and today remains among the world’s top accelerator centres. Since the closure of the HERA collider in 2007, the lab’s main accelerators have been used to generate synchrotron radiation for research into the structure of matter, while DESY’s particle-physics division carries out experiments at other labs such as those at CERN’s Large Hadron Collider.

    Together with other facilities on the Hamburg campus, DESY aims to strengthen its role as a leading international centre for research into the structure, dynamics and function of matter using X rays. PETRA IV is a major upgrade to the existing light source at DESY that will allow users to study materials and other samples in 100 times more detail than currently achievable, approaching the limit of what is physically possible with X rays. A technical design report will be submitted in 2021 and first experiments could be carried out in 2026.

    DESY Petra III interior


    DESY Petra III

    Together with the international partners and operating company of the European XFEL, DESY is planning to comprehensively expand this advanced X-ray facility (which starts at the DESY campus and extends 3.4 km northwest). This includes developing the technology to increase the number of X-ray pulses from 27,000 to one million per second (CERN Courier July/August 2017 p18).

    As Germany’s most important centre for particle physics, DESY will continue to be a key partner in international projects and to set up an attractive research and development programme. DESY’s Zeuthen site, located near Berlin, is being expanded to become an international centre for astroparticle physics, focusing on gamma-ray and neutrino astronomy as well as on theoretical astroparticle physics. A key contribution to this effort is a new science data-management centre for the planned Cherenkov Telescope Array (CTA), the next-generation gamma-ray observatory.

    HESS Cherenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg searches for cosmic rays

    DESY is also responsible for building CTA’s medium-sized telescopes and, as Europe’s biggest partner in the neutrino telescope IceCube located in the Antarctic, is playing an important role in upgrades to the facility.

    IceCube Gen-2 DeepCore annotated


    IceCube Gen-2 DeepCore PINGU annotated


    U Wisconsin ICECUBE neutrino detector at the South Pole

    The centre for data and computing science will be established at the Hamburg campus to meet the increasing demands of data-intensive research. It will start working as a virtual centre this year and there are plans to accommodate up to six scientific groups by 2025. The centre is being planned together with universities to integrate computer science and applied mathematics.

    Finally, the DESY 2030 report lists plans to substantially increase technology transfer to allow further start-ups in the Hamburg and Brandenburg regions. DESY will also continue to develop and test new concepts for building compact accelerators in the future, and is developing a new generation of high-resolution detector systems.

    “We are developing the campus in Hamburg together with partners at all levels to become an international port for science. This could involve investments worth billions over the next 15 years, to set up new research centres and facilities,” said Helmut Dosch, chairman of DESY’s board of directors, at the launch event. “The Zeuthen site, which we are expanding to become an international centre for astroparticle physics, is undergoing a similarly spectacular development.”

    See the full article here .


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  • richardmitnick 11:11 am on May 31, 2018 Permalink | Reply
    Tags: , , CERN Courier, , LC Newsline, , ,   

    From CERN Courier- “High-gradient X-band technology: from TeV colliders to light sources and more” 


    From CERN Courier

    Brought forward by LC Newsline May 31, 2018

    Mar 23, 2018
    Walter Wuensch

    1
    X-band technology

    Technologies developed for the Compact Linear Collider promise smaller accelerators for applications outside high-energy physics.

    The demanding and creative environment of fundamental science is a fertile breeding ground for new technologies, especially unexpected ones. Many significant technological advances, from X-rays to nuclear magnetic resonance and the Web, were not themselves a direct objective of the underlying research, and particle accelerators exemplify this dynamic transfer from the fundamental to the practical. From isotope separation, X-ray radiotherapy and, more recently, hadron therapy, there are now many categories of accelerators dedicated to diverse user communities across the sciences, academia and industry. These include synchrotron light sources, X-ray free-electron lasers (XFELs) and neutron spallation sources, and enable research that often has direct societal and economic implications.

    SLAC/LCLS


    European XFEL


    XFEL Tunnel

    ORNL Spallation Neutron Source


    ORNL Spallation Neutron Source

    During the past decade or so, high-gradient linear accelerator technology developed for fundamental exploration has matured to the point where it is being transferred to applications beyond high-energy physics. Specifically, the unique requirements for the Compact Linear Collider (CLIC) project at CERN have led to a new high-gradient “X-band” accelerator technology that is attracting the interest of light-source and medical communities, and which would have been difficult for those communities to advance themselves due to their diverse nature.

    CLIC Collider annotated


    CERN/CLIC

    Set to operate until the mid-2030s, the Large Hadron Collider (LHC) collides protons at an energy of 13 TeV. One possible path forward for particle physics in the post-LHC, “beyond the Standard Model”, era is a high-energy linear electron–positron collider. CLIC envisions an initial-energy 380 GeV centre-of-mass facility focused on precision measurements of the Higgs boson and the top quark, which are promising targets to search for deviations from the Standard Model (CERN Courier November 2016 p20). The machine could then, guided by the results from the LHC and the initial-stage linear collider, be lengthened to reach energies up to 3 TeV for detailed studies of this high energy regime. CLIC is overseen by the Linear Collider Collaboration along with the International Linear Collider (ILC), a lower energy electron–positron machine envisaged to operate initially at 250 GeV (CERN Courier January/February 2018 p7).

    ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

    The accelerator technology required by CLIC has been under development for around 30 years and the project’s current goals are to provide a robust and detailed design for the update of the European Strategy for Particle Physics, with a technical design report by 2026 if resources permit. One of the main challenges in making CLIC’s 380 GeV initial energy stage cost effective, while guaranteeing its reach to 3 TeV, is generating very high accelerating gradients. The gradient needed for the high-energy stage of CLIC is 100 MV/m, which equates to 30 km of active acceleration. For this reason, the CLIC project has made a major investment in developing high-­gradient radio-frequency (RF) technology that is feasible, reliable and cheap.

    Evading obstacles

    Maximising the accelerating gradient leads to a shorter linac and thus a less expensive facility. But there are two main limiting factors: the increasing need of peak RF power and the limitation of accelerating-structure surfaces to support increasingly strong electromagnetic fields. Circumventing these obstacles has been the focus of CLIC activities for several years.

    2
    Figure 1

    One way to mitigate the increasing demand for peak power is to use higher frequency accelerating structures (figure 1), since the power needed for fixed-beam energy goes up linearly with gradient but goes down approximately with the inverse square root of the RF frequency. The latest XFELs SACLA in Japan and SwissFEL in Switzerland operate at “C-band” frequencies of 5.7 GHz, which enables a gradient of around 30 MV/m and a peak power requirement of around 12 MW/m in the case of SwissFEL.

    SACLA Free-Electron Laser Riken Japan

    SwissFEL Paul Sherrer Institute, based in Villigen and Würenlingen

    This increase in frequency required a significant technological investment, but CLIC’s demand for 3 TeV energies and high beam current requires a peak power per metre of 200 MW/m! This challenge has been under study since the late 1980s, with CLIC first focusing on 30 GHz structures and the Next Linear Collider/Joint Linear Collider community developing 11.4 GHz “X-band” technology. The twists and turns of these projects are many, but the NLC/JLC project ceased in 2005 and CLIC shifted to X-band technology in 2007. CLIC also generates high peak power using a two-beam scheme in which RF power is locally produced by transferring energy from a low-energy, high-current beam to a high-energy, low-current beam. In contrast to the ILC, CLIC adopts normal-conducting RF technology to go beyond the approximately 50 MV/m theoretical limit of existing superconducting cavity geometries.

    The second main challenge when generating high gradients is more fundamental than the practical peak-power requirements. A number of phenomena come to life when the metal surfaces of accelerating structures are subject to very high electromagnetic fields, the most prominent being vacuum arcing or breakdown, which induces kicks to the beam that result in a loss of luminosity. A CLIC accelerating structure operating at 100 MV/m will have surface electric fields in excess of 200 MV/m, sometimes leading to the formation of a highly conductive plasma directly above the surface of the metal. Significant progress has been made in understanding how to maximise gradient despite this effect, and a key insight has been the identification of the role of local power flow. Pulsed surface heating is another troubling high-field phenomenon faced by CLIC, where ohmic losses associated with surface currents result in fatigue damage to the outer cavity wall and reduced performance. Understanding these phenomena has been essential to guide the development of an effective design and technology methodology for achieving gradients in excess of 100 MV/m.

    Test-stand physics

    Critical to CLIC’s development of high-gradient X-band technology has been an investment in four test stands, which allowed investigations of the complex, multi-physics effects that affect high-power behaviour in operational structures (figure 2). The test stands provided the RF klystron power, dedicated instrumentation and diagnostics to operate, measure and optimise prototype RF components. In addition, to investigate beam-related effects, one of the stands was fed by a beam of electrons from the former “CTF3” facility. This has since been replaced by the CLEAR test facility, at which experiments will come on line again next year (CERN Courier November 2017 p8).

    While the initial motivation for the CLIC test stands was to test prototype components, high-gradient accelerating structures and high-power waveguides, the stands are themselves prototype RF units for linacs – the basic repeatable unit that contains all the equipment necessary to accelerate the beam. A full linac, of course, needs many other subsystems such as focusing magnets and beam monitors, but the existence of four operating units that can be easily visited at CERN has made high-gradient and X-band technology serious options for a number of linac applications in the broader accelerator community. An X-band test stand at KEK has also been operational for many years and the group there has built and tested many CLIC prototype structures.

    KEK X-band Test Facilities 4 X-band Test Facilities at KEK Single Klystron (50 MW) test stand up and running NEXTEF

    3
    Figure 2

    With CLIC’s primary objective being to provide practical technology for a particle-physics facility in the multi-TeV range, it is rather astonishing that an application requiring a mere 45 MeV beam finds itself benefiting from the same technology. This small-scale project, called Smart*Light, is developing a compact X-ray source for a wide range of applications including cultural heritage, metallurgy, geology and medical, providing a practical local alternative to a beamline at a large synchrotron light source. Led by the University of Eindhoven in the Netherlands, Smart*Light produces monochromatic X-rays via inverse Compton scattering, in which X-rays are produced by “bouncing” a laser pulse off an electron beam. The project teams aims to make the equipment small and inexpensive enough to be able to integrate it in a museum or university setting, and is addressing this objective with a 50 MV/m-range linac powered by one of the two standard CLIC test-stand configurations (a 6 MW Toshiba klystron). Funding has been awarded to construct the first prototype system and, once operational, Smart*Light will pursue commercial production.

    Another Compton-source application is the TTX facility at Tsinghua University in China, which is based on a 45 MeV beam.

    TTX facility at Tsinghua University in China

    The Tsinghua group plans to increase the energy of the X-rays by upgrading the energy of their electron linac, which must be done by increasing the accelerating gradient because the facility is housed in an existing radiation-shielded building. The energy increase will occur in two steps: the first will raise the accelerating gradient by upgrading parts of the existing S-band 3 GHz RF system, and the second will be to replace sections with an X-band system to increase the gradient up to 70 MV/m. The Tsinghua X-band power source will also implement a novel “corrector cavity” system to flatten the power compressed pulse that is also now part of the 380 GeV CLIC baseline design. Tsinghua has successfully tested a standard CLIC structure to more than 100 MV/m at KEK, demonstrating that high-gradient technology can be transferred, and has taken delivery of a 50 MW X-band klystron for use in a test stand.

    Perhaps the most significant X-band application is XFELs, which produce intense and short X-ray bursts by passing a very low-emittance electron beam through an undulator magnet. The electron linac represents a substantial fraction of the total facility cost and the number of XFELs is presently quite limited. Demand for facilities also exceeds the available beam time. Operational facilities include LCWS at SLAC, FERMI at Trieste and SACLA at Riken, while the European XFEL in Germany, the Pohang Light Source in Korea and SwissFEL are being commissioned (CERN Courier July/August 2017 p18), and it is expected that further facilities will be built in the coming years.

    XFEL applications

    CLIC technology, both the high-frequency and high-gradient aspects, has the potential to significantly reduce the cost of such X-ray facilities, allowing them to be funded at the regional and possibly even university scale. In combination with other recent advances in injectors and undulators, the European Union project CompactLight has recently received a design study grant to examine the benefits of CLIC technology and to prepare a complete technical design report for a small-scale facility (CERN Courier December 2017 p8).

    A similar type of electron linac, in the 0.5–1 GeV range, is being proposed by Frascati Laboratory in Italy for XFEL development, in addition to the study of advanced plasma-acceleration techniques. To fit the accelerator in a building on the Frascati campus, the group has decided to use a high-gradient X-band for their linac and has joined forces with CLIC to develop it. The cooperation includes Frascati staff visiting CERN to help run the high-gradient test facilities and the construction of their own test stand at Frascati, which is an important advance in testing its capability to use CLIC technology.

    4
    Figure 3

    In addition to providing a high-performance technology for acceleration, high-gradient X-band technology is the basis for two important devices that manipulate the beam in low-emittance and short-bunch electron linacs, as used in XFELs and advanced development linacs. The first is the energy-spread lineariser, which uses a harmonic of the accelerating frequency to correct the energy spread along the bunch and enable shorter bunches. A few years ago a collaboration between Trieste, PSI and CERN made a joint order for the first European X-band frequency (11.994 GHz) 50 MW klystrons from SLAC, and jointly designed and built the lineariser structures, which have significantly improved the performance of the Elettra light source in Trieste and become an essential element of SwissFEL.

    Following the CLIC test stand and lineariser developments, a new commercial X-band klystron has become available, this time at the lower power of 6 MW and supplied by Canon (formerly Toshiba). This new klystron is ideally suited for lineariser systems and one has recently been constructed at the soft X-ray XFEL at SINAP in Shanghai, which has a long-standing collaboration with CLIC on high-gradient and X-band technology. Back in Europe, Daresbury Laboratory has decided to invest in a lineariser system to provide the exceptional control of the electron bunch characteristics needed for its XFEL programme, which is being developed at its CLARA test facility. Daresbury has been working with CLIC to define the system, and is now procuring an RF power system based on the 6 MW Toshiba klystron and pulse compressor. This will certainly be a major step in the ease of adoption of X-band technology.

    The second major high-gradient X-band beam manipulation application is the RF deflector, which is used at the end of an XFEL to measure the bunch characteristics as a function of position along the bunch. High-gradient X-band technology is well suited to this application and there is now widespread interest to implement such systems. Teams at FLASH2, FLASH-Forward and SINBAD at DESY, SwissFEL and CLIC are collaborating to define common hardware, including a variable polarisation deflector to allow a full 6D characterisation of the electron bunch. SINAP is also active in this domain. The facility is awaiting delivery of three 50 MW CPI klystrons to power the deflectors and will build a standard CLIC test structure for tests at CERN in addition to a prototype X-band XFEL structure in the context of CompactLight.

    The rich exchange between different projects in the high-gradient community is typified by PSI and in particular the SwissFEL. Many essential features of the SwissFEL have a linear-collider heritage, such as the micron-precision diamond machining of the accelerating structures, and SwissFEL is now returning the favour. For example, a pair of CLIC X-band test accelerating structures are being tested at CERN to examine the high-gradient potential of PSI’s fabrication technology, showing excellent results: both structures can operate at more than 115 MV/m and demonstrate potential cost savings for CLIC. In addition, the SwissFEL structures have been successfully manufactured to micron precision in a large production series – a level of tolerance that has always been an important concern for CLIC. Now that the PSI fabrication technology is established, the laboratory is building high-gradient structures for other projects such as Elettra, which wishes to increase its X-ray energy and flux but has performance limitations with its 3 GHz linac.

    Beyond light sources

    High-gradient technology is now working its way beyond electron linacs, particularly in the treatment of cancer. The most common accelerator-based cancer treatment is X-rays, but protons and heavy ions offer many potential advantages. One drawback of hadron therapy is the high cost of the accelerators, which are currently circular. A new generation of linacs offer the potential for smaller, lower cost facilities with additional flexibility.

    The TERA foundation has studied such linac-based solutions and a firm called ADAM is now commercialising a version with a view to building a compact hadron-therapy centre (CERN Courier January/February 2018 p25). To demonstrate the potential of high gradients in this domain, members of CLIC received support from the CERN knowledge transfer fund to adapt CLIC technology to accelerate protons in the relevant energy range, and the first of two structures is now under test. The predicted gradient above was 50 MV/m, but the structure has exceeded 55 MV/m and also behaves consistently when compared to the almost 20 CLIC structures. We now know that it is possible to reach high accelerating gradients even for protons, and projects based on compact linacs can now move forward with confidence.

    5
    Figure 4

    Collaboration has driven the wider adoption of CLIC’s high-gradient technology. A key event took place in 2005 when CERN management gave CLIC a clear directive that, with LHC construction limiting available resources, the study must find outside collaborators. This was achieved thanks to a strong effort by CLIC researchers, also accompanied by a great deal of activity in electron linacs in the accelerator community.

    We should not forget that the wider adoption of X-band and high-gradient technology is extremely important for CLIC itself. First, it enlarges the commercial base, driving costs down and reliability up, and making firms more likely to invest. Another benefit is the improved understanding of the technology and its operability by accelerator experts, with a broadened user base bringing new ideas. Harnessing the creative energy of a larger group has already yielded returns to the CLIC study, for instance addressing important industrialisation and cost-reduction issues.

    The role of high-gradient and X-band technology is expanding steadily, with applications at a surprisingly wide range of scales. Despite having started in large linear colliders, the use of the technology now starts to be dominated by a proliferation of small-scale applications. Few of these were envisaged when CLIC was formulated in the late 1980s – XFELs were in their infancy at the time. As the technology is applied further, its performance will rise even more, perhaps even leading to the use of smaller applications to build a higher energy collider. The interplay of different communities can make advances beyond what any could on their own, and it is an exciting time to be part of this field.

    See the full article here .


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  • richardmitnick 4:39 pm on February 20, 2018 Permalink | Reply
    Tags: "Rare hyperon-decay anomaly under the spotlight, , , CERN Courier, , , , ,   

    From CERN Courier: “Rare hyperon-decay anomaly under the spotlight” 


    CERN Courier

    Feb 16, 2018

    1
    The invariant mass distribution

    The LHCb collaboration has shed light on a long-standing anomaly in the very rare hyperon decay Σ+ → pµ+µ– first observed in 2005 by Fermilab’s HyperCP experiment. The HyperCP team found that the branching fraction for this process is consistent with Standard Model (SM) predictions, but that the three signal events observed exhibited an interesting feature: all muon pairs had invariant masses very close to each other, instead of following a scattered distribution.

    This suggested the existence of a new light particle, X0, with a mass of about 214 MeV/c2, which would be produced in the Σ+ decay along with the proton and would decay subsequently to two muons. Although this particle has been long sought in various other decays and at several experiments, no experiment other than HyperCP has so far been able to perform searches using the same Σ+ decay mode.

    The large rate of hyperon production in proton–proton collisions at the LHC has recently allowed the LHCb collaboration to search for the Σ+ → pµ+µ– decay. Given the modest transverse momentum of the final-state particles, the probability that such a decay is able to pass the LHCb trigger requirements is very small. Consequently, events where the trigger is activated by particles produced in the collisions other than those in the decay under study are also employed.

    This search was performed using the full Run 1 dataset, corresponding to an integrated luminosity of 3 fb–1 and about 1014 Σ+ hyperons. An excess of about 13 signal events is found with respect to the background-only expectation, with a significance of four standard deviations. The dimuon invariant- mass distribution of these events was examined and found to be consistent with the SM expectation, with no evidence of a cluster around 214  eV/c2. The signal yield was converted to a branching fraction of (2.1+1.6–1.2) × 10–8 using the known Σ+ → pπ0 decay as a normalisation channel, in excellent agreement with the SM prediction. When restricting the sample explicitly to the case of a decay with the putative X0 particle as an intermediate state, no excess was found. This sets an upper limit on the branching fraction at 9.5 × 10–9 at 90% CL, to be compared with the HyperCP result (3.1+2.4–1.9 ± 1.5) × 10–8.

    This result, together with the recent search for the rare decay KS → μ+μ– shows the potential of LHCb in performing challenging measurements with strange hadrons. As with a number of results in other areas reported recently, LHCb is demonstrating its power not only as a b-physics experiment but as a general-purpose one in the forward region. With current data, and in particular with the upgraded detector thanks to the software trigger from Run 3 onwards, LHCb will be the dominant experiment for the study of both hyperons and KS mesons, exploiting their rare decays to provide a new perspective in the quest for physics beyond the SM.

    See the full article here .

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  • richardmitnick 4:22 pm on February 20, 2018 Permalink | Reply
    Tags: CERN Courier, , TUCAN collaboration TRIUMF UltraCold Advanced Neutron source, UCN- ultracold neutrons   

    From TRIUMF: “TRIUMF’s (ultra)cool experiment fires up” 

    TRIUMF

    1

    While all the science at TRIUMF is very cool, only one experiment can lay claim to being the (ultra)coolest of them all: the ultracold neutron (UCN) facility.
    Scientists tell us that at the very beginning of the universe, equal amounts of matter and antimatter must have been created from the energy of the Big Bang. However, all around us, we see a beautiful universe made only of matter. So arises one of the oldest unsolved mysteries in physics: where did all the antimatter go?
    The basic idea of how the universe could have ended up composed of only matter has been known for decades, but theorists have struggled to define a theory by which this mechanism could be realized; likewise, experimentalists have yet to definitively spot where this mechanism might be occurring. Scientists are looking in a variety of places, one being in the infinitesimally fine properties of one well-known subatomic particle: the neutron.
    But, in order to use the neutrons for this purpose, the particles must first be cooled and slowed down to ultra-low speeds (5 metres per second, about the speed of a human sprinter), and then collected in special bottles. That isn’t easy, since neutrons are moving at a substantial fraction of the speed of light when they are first produced. And yet…
    On Monday, November 13th, 2017, the TUCAN Collaboration at TRIUMF achieved a major milestone by producing the first ultra-cold neutrons (UCNs) ever created in Canada.

    UCNs like those produced at TRIUMF move slow enough (~5 m/s, compared to ~500 m/s for air molecules) and with such low energy that they actually can be trapped and contained inside special bottles. This makes UCNs ideal for a variety of important fundamental physics measurements, including determining the neutron electric dipole moment (the nEDM). The nEDM is currently predicted to be vanishingly small, but if it is measured to be larger than expected, it could aid in solving the puzzle of why there is much more matter than antimatter in the universe!

    The Japanese-Canadian TUCAN (TRIUMF Ultra Cold Advanced Neutron source) collaboration formed in 2010 with the goal of creating the world’s most intense UCN source to measure the nEDM with unprecedented precision. Between 2014 and 2016, a new proton beamline at TRIUMF was constructed to supply a spallation target for neutron production. During the most recent TRIUMF’s annual cyclotron shutdown period, the UCN source prototype from Japan was installed above the target. The secret behind creating UCNs lies in superfluid helium, which is cooled down to a temperature of less than 1 degree above absolute zero (<1K).

    The TUCAN collaboration celebrated its first major milestone in November 2016 when it achieved its first beam-on-target; just a year later, the newly-installed UCN cryostat reached its design temperature of approximately 0.8K. Now, the first Canadian UCNs have been created from hot spallation neutrons produced using a 1 microamp, 480 MeV proton beam. The approximate 50000 UCNs counted per “shot” (pulse of protons on target) were well within expectation, enabling the planned experimental program to be carried out. This will include characterizing the source to aid in the development of the next-generation source, with which TUCAN hopes to achieve orders of magnitude more UCNs. The upgraded source will be deployed for the flagship nEDM experiment, which TUCAN hopes to run by 2020.

    Congratulations to the TUCAN and UCN facility teams!

    This project is led by the University of Winnipeg under principal investigator Prof. Jeff Martin and is supported by TRIUMF, CFI, BCKDF, MRF, and NSERC in Canada, and by KEK and RCNP in Japan.

    From CERN Courier:

    Feb 16, 2018
    Neutrons cooled for interrogation

    2
    A proton beamline at TRIUMF

    Researchers at TRIUMF in Canada have reported the first production of ultracold neutrons (UCN), marking an important step towards a future neutron electric dipole moment (nEDM) experiment at the Vancouver laboratory. Precision measurements of the nEDM are a sensitive probe of physics beyond the Standard Model: if a nonzero value were to be measured, it would suggest a new source of CP violation, possibly related to the baryon asymmetry of the universe.

    The TUCAN collaboration (TRIUMF UltraCold Advanced Neutron source) aims to measure nEDM a factor 30 better than the present best measurement, which has a precision of 3 × 10–26 e cm and is consistent with zero. For this to be possible, physicists need to provide the world’s highest density of ultracold neutrons. In 2010 a collaboration between Canada and Japan was established to realise such a facility and a prototype UCN source was shipped to Canada and installed at TRIUMF in early 2017.

    The setup uses a unique combination of proton-induced spallation and a superfluid helium UCN source that was pioneered in Japan. A tungsten block stops a beam of protons, producing a stream of fast neutrons that are then slowed in moderators and converted to ultracold speeds (less than around 7 ms–1) by phonon scattering in superfluid helium. The source is based on a non-thermal down-scattering process in superfluid helium below 1 K, which gives the neutrons an effective temperature of a few mK. The ultracold temperature is below the neutron optical potential for many materials, which means the neutrons are totally reflected for all angles of incidence and can be stored in bottles for periods of up to hundreds of seconds.

    Tests late last year demonstrated the highest current operation of this particular source, resulting in the most UCNs it has ever produced (> 300,000) in a single 60-second-long irradiation at a 10 µA proton beam current. This is a record for TRIUMF, but the UCN source intensity is still two orders of magnitude below what is needed for the nEDM experiment.

    Funding of C$15.7 million to upgrade the UCN facility, a large proportion of which was granted by the Canada Foundation for Innovation in October 2017, will enable the TUCAN team to increase the production of neutrons at higher beam current to levels competitive with other planned nEDM experiments worldwide. These include proposals at the Paul Scherrer Institute in Switzerland, Los Alamos National Laboratory in the US, the Institut Laue–Langevin in France and others in Germany and Russia. The neutron EDM is experiencing intense competition, with most projects differing principally in the way they propose to produce the ultracold neutrons (CERN Courier September 2016 p27).

    The nEDM experimental campaign at TRIUMF is scheduled to start in 2021. “The TRIUMF UCN source is the only one combining a spallation source of neutrons with a superfluid helium production volume, providing the project its uniqueness and competitive edge,” says team member Beatrice Franke.

    See the full TRIUMF article here.
    See the full CERN Courier article here .

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    Canada’s national laboratory for particle and nuclear physics
    Member Universities:
    University of Alberta, University of British Columbia, Carleton University, University of Guelph, University of Manitoba, Université de Montréal, Simon Fraser University,
    Queen’s University, University of Toronto, University of Victoria, York University. Not too shabby, eh?

    Associate Members:
    University of Calgary, McMaster University, University of Northern British Columbia, University of Regina, Saint Mary’s University, University of Winnipeg, How bad is that !!

     
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