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  • richardmitnick 10:48 am on March 31, 2020 Permalink | Reply
    Tags: "High-Precision Digitizer for High Luminosity LHC", Accelerator Science, , , , , ,   

    From CERN Accelerating News: “High-Precision Digitizer for High Luminosity LHC” 

    From CERN Accelerating News

    1
    CERN developed a digitizer to ensure the high-precision measurement of the current delivered to the superconducting magnets of the HL-LHC.

    One of the key elements of the LHC high-luminosity upgrade project is the replacement of the magnets that focus the beams near the interaction points of ATLAS and CMS, where particle collision occurs. The new higher field magnets also call for higher precision powering, which is strongly dependent on the performance of the electric current measurement chain. The CERN Electrical Power Converters Group developed a new metrology-grade digitizer, part of that high-precision measurement system. The new digitizer will be employed in the power converters of the Inner Triplet quadrupoles and separation/recombination dipole magnets of the HL-LHC. This Analog-to-Digital Converter (ADC), named HPM7177, was designed at the High-Precision Measurements section and first tested in 2019.

    The main goal of the High-Luminosity LHC (HL–LHC) project [1] is to increase the luminosity of the LHC beam, both instantaneous and integrated. For that purpose, the project foresees the replacement of several magnets in the LHC. Among the most important are the Inner Triplet (IT) quadrupoles on each side of the interaction points of the ATLAS and CMS experiments. The IT quads contribute to increasing luminosity by reducing the beam size at the interaction point. This improvement requires a fine tuning of the beam parameters, which translates into unprecedented performance requirements for the magnetic field stability and accuracy and, consequently, for the electric current that generates it [2].

    To power magnets in particle accelerators, electrical power converters are used. They are commonly employed as controlled current sources. At CERN, power converters use high-precision current feedback loops, implemented digitally, to deliver the current to the magnets. As a consequence, both the reference current and the measured current need to be provided in the digital domain. The reference current is sent digitally by the control room. However, the current in the magnets is sensed in analog by means of a Direct-Current Current Transformer (DCCT) and therefore needs to be converted into a digital code. A high-precision ADC is used for that purpose.

    The requirements for the power converters are unprecedented in terms of current stability, noise, and repeatability [2]. Since power converter performance depends greatly on the quality of the measurement used for the feedback, the DCCT and the ADC are crucial for delivering the required precision. Short-term stability (1mHz < f < 100mHz) of 0.05ppm (parts per million) rms, 12h stability of 0.2ppm p-p (in isothermal conditions) and linearity of 1ppm, are just a few of the challenging requirements imposed on the ADCs [3].

    1
    Typical measurements at the nominal digitizer full scale of 10 V using a portable voltage standard. The main plot shows a 12-hour record, while the inset is a zoom-in to a 20-minute section of it. HL-LHC requirements are indicated by double arrows (power converter) and dashed lines (ADC). (Image: CERN)

    The HPM7177 digitizer, an entire stand-alone measurement system, was developed to answer these constraints. Its core element is a commercial high-resolution ADC integrated circuit, selected after an extensive market survey [4] and test campaign. The digitizer employs precision circuits for the scaling of the analog signals. Digital logic functionality is implemented in a field-programmable gate array (FPGA), which takes care of the ADC chip initialization and readout, the communication and synchronization protocol, as well as the built-in calibration and self-test features of the system.

    Different aspects of the HPM7177 design address the challenges generated by the need for stable measurements on the timescale of a typical LHC cycle. Electronic components exhibit various kinds of noise, including the omnipresent 1/f or “flicker” type with spectral density rising at low frequencies. To minimize low-frequency electronic noise, the voltage scaling circuits employ bulk metal foil resistors and auto-zero operational amplifiers. Ultimately, the performance on longer timescales is limited by the voltage reference, which is the best one presently available on the market. External influences such as temperature variations and electromagnetic interference (EMI) also affect the measurements.The digitizer has very low temperature-dependent drift on the order of tens of ppb (parts per billion) per degree Celsius, achieved by active temperature stabilization of the sub-module that contains all precision circuits. On the system level, multiple measures are taken to ensure EMI immunity, since the ADCs often have to operate in a potentially noisy environment near power converters.

    A characterization campaign, carried out using reference equipment from the standards laboratory at CERN, proved that HPM7177 meets the most challenging requirements for the HL-LHC project. To gain more confidence on and knowledge of the device, the team of developers have planned to collaborate with the German national institute of metrology (PTB – Braunschweig) to characterize the digitizer using their 10V Programmable Josephson Voltage Synthesizer [5]. This system generates test voltages with ultimate stability using the Josephson effect – a quantum phenomenon in superconductors that links frequency to voltage and is currently used for the practical realization of the Volt in the International System of Units (SI).

    The full design documentation of the HPM7177 is available under the CERN Open Hardware License [6].

    References:

    [1] G. Apollinari, I. Béjar Alonso, O. Brüning, P. Fessia, M. Lamont, L. Rossi, and L. Tavian, “HL-LHC Technical Design Report,” Tech. Rep. EDMS n. 1723851 v.0.71, CERN, Geneva, 2016. https://edms.cern.ch/document/1723851/0.71

    [2] Update of beam dynamics requirements for HL-LHC electrical circuits. CERN-ACC-2019-0030. Gamba, Davide (CERN) ; Arduini, Gianluigi (CERN) ; Cerqueira Bastos, Miguel (CERN) ; Coello De Portugal – Martinez Vazquez, Jaime Maria (Universitat Politecnica Catalunya (ES)) ; De Maria, Riccardo (CERN) ; Giovannozzi, Massimo (CERN) ; Martino, Michele (CERN) ; Tomas Garcia, Rogelio (CERN) https://cds.cern.ch/record/2656907?ln=en

    [3] HL-LHC Power Converter, ADC and DCCT Requirements; Miguel Cerqueira Bastos, CERN EDMS 2048827 https://edms.cern.ch/document/2048827/2

    [4] N. Beev. Analog-to-digital conversion beyond 20 bits. Proceedings of I2MTC-2018, Houston, TX (2018) https://cds.cern.ch/record/2646282/

    [5] Josephson Technology at PTB-Braunschweig https://www.ptb.de/cms/en/ptb/fachabteilungen/abt2/fb-24/ag-243/forschung-243.html

    [6] HPM7177 Open Hardware Repository wiki page https://ohwr.org/project/opt-adc-10k-32b-1cha/wikis/

    See the full article here .


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    Accelerating News is a quarterly online publication for the accelerator community.
    ISSN: 2296-6536

    The publication showcases news and results from the biggest accelerator research and development projects such as ARIES, HL-LHC, TIARA, FCC study, EuroCirCol, EUPRAXIA, EASITrain as well as interesting stories on other accelerator applications. The newsletter also collects upcoming accelerator research conferences and events.

    Accelerating News is published 4 times a year, in mid March, mid June, mid September and mid December.

    You can read Accelerating News via the homepage http://www.acceleratingnews.eu (link is external) or by email.

    To subscribe to Accelerating News, enter your email in the “Subscribe to our newsletter” box in the footer.

    History

    Accelerating News evolved from the EuCARD quarterly project newsletter (see past issues), which was first published in June 2009 to a subscription list of approximately 200. Initiated by EuCARD and in collaboration with additional FP7 co-funded projects, the first edition of Accelerating News was published in April 2012 to an initial distribution list of about 800 subscribers. Currently more than 1750 members receive the quarterly issues.

     
  • richardmitnick 9:45 am on March 31, 2020 Permalink | Reply
    Tags: "10 years of LHC physics, Accelerator Science, , , in numbers", , ,   

    From Symmetry: “10 years of LHC physics, in numbers” 

    Symmetry Mag
    From Symmetry<

    03/30/20
    Sarah Charley

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova

    How do you measure a decade of LHC research?

    LHC

    CERN map

    CERN LHC Tunnel

    CERN LHC particles

    In 2010, the Large Hadron Collider research program jumped into full swing as scientists started collecting physics data from particle collisions in the LHC for the first time.

    How has this gigantic, global scientific effort affected the world? Symmetry pulled together a few numbers to find out.

    278
    petabytes of data

    In the last decade, LHC experiments collected almost 280 petabytes of data, which scientists recorded on tape. You would need to stream Netflix 24/7 for more than 15,000 years to eventually use that much data! But from another perspective, platforms like Facebook (which has 2.5 billion users) collect that much data in 70 days!

    ~8 million
    Higgs bosons

    CERN CMS Higgs Event May 27, 2012

    CERN ATLAS Higgs Event

    While it’s impossible to know the actual number of Higgs bosons the LHC has produced (see Accounting for the Higgs), scientists can use the Standard Model’s equations to predict how many Higgs bosons the LHC should have produced. Scientists consider all the different ways Higgs bosons can be made, the likelihood of each process, and the energy and total number of collisions. Studying those Higgs bosons, scientists have precisely defined the mass, charge, spin and half-life of the Higgs. They continue to examine the many different ways the Higgs interacts with other particles and use it as a tool to search for new physics beyond the Standard Model.

    Standard Model of Particle Physics, Quantum Diaries

    2,725
    scientific papers

    Every week the number of scientific papers that LHC scientists have published steadily increases as they comb through the data to study rare phenomena and search for new physics. This includes work by thousands of graduate students on their way to earning their PhDs.

    7.5 billion
    Worldwide LHC Computing Grid requests

    Physicists need a huge amount of computing power to do their research—much more than a standard laptop can support. Every day several thousand physicists submit a total of about 2 million “jobs” to the WLCG. Each “job” is an important brick in the growing body of scientific work.

    39.5 quadrillion
    collisions

    The number of collisions recorded by the four main experiments at the LHC is close to 40 quadrillion, or, as physicists say it, 395 “inverse femtobarns.” (Each inverse femtobarn corresponds to about 100 trillion collisions.) For reference, the LHC’s predecessor—the Tevatron particle collider at the US Department of Energy’s Fermi National Accelerator Laboratory—delivered a then-unprecedented more than 20 fb^-1 to its two experiments over the course of 25 years of proton-antiproton collisions.

    FNAL/Tevatron map


    FNAL/Tevatron

    Now the number of LHC collisions recorded by just the ATLAS or CMS experiment (~190 fb^-1) is equivalent to the total number of ants on Earth.

    15
    new partners

    CERN is governed by 23 member states, but scientists from more than 600 institutions around the world work on the experiments and projects it hosts. Since 2010, CERN has formally added 15 new countries—Albania, Bangladesh, Costa Rica, Kazakhstan, Latvia, Lebanon, Mongolia, Nepal, Palestine, Paraguay, the Philippines, Qatar, Sri Lanka, Thailand and Tunisia—to its research community through official bilateral cooperation agreements. Today, the total number of collaborating countries is around 80. US institutions are supported by the Department of Energy’s Office of Science.

    1
    microgram of protons

    When running, the LHC has more than 300 trillion protons circling through its two beampipes. But they’re so tiny that even if you combined all the protons accelerated in the machine since 2010, they would only amount to a pile about the size of a speck of pollen.

    >1 million
    visitors

    CERN has hosted more than 45,000 guided tours in 32 languages through its public visit program, allowing more than 1 million visitors to discover the work of the world’s biggest physics laboratory. And for two special Open Day weekends—one in 2013 and another in 2019—CERN welcomed an average of 36,000 visitors a day! That’s roughly the same daily average as Disneyland Paris. Open Day visitors had access to numerous sites such as the LHC tunnel that are normally only accessible to authorized personnel.

    250
    artists

    Each year the Arts at CERN program invites artists to work alongside particle physicists and engineers at CERN. The resulting installations, choreography and multimedia projects travel the world and inspire countless art and science enthusiasts. In 2019, for example, more than 80,000 visitors took in the traveling exhibit Quantum/Broken Symmetries, which featured pieces by 10 artists who did work at CERN.

    130
    public events

    The Globe of Science and Innovation at CERN isn’t just an iconic landmark; it’s also a venue for conferences, shows, panels, film screenings and artistic performances. Since 2010, about 40,000 visitors have attended an event hosted by CERN inside the Globe. CERN also organizes events in the local community, including talks at schools, science fairs and panel discussions at movie theaters.

    >50
    computing collaborations

    Since 2010, CERN openlab has set up over 50 collaborative projects through which CERN computer scientists work with leading tech companies on joint R&D. The companies get to test their latest products in CERN’s cutting-edge research environment, and CERN gets the chance to try out emerging technologies. For example, current projects with companies Intel and Micron are exploring how machine learning can be used to further improve the processing of data from particle collisions. At the same time, projects with Oracle and Siemens are using such technologies to help improve control systems for the LHC.

    >300
    knowledge transfer projects

    CERN’s Knowledge Transfer department collaborates with academic and industrial organizations to find new uses outside of particle physics research for technology developed at CERN. Since 2010, CERN has signed more than 300 knowledge transfer contracts with universities and companies working in fields such as safety, medtech and aerospace engineering. A notable collaboration is a father-and-son medical team who used CERN Medipix read-out chips to develop the world’s first 3D color X-ray in 2018.

    10,329
    educators

    CERN’s national and international teacher programs welcome groups of educators to the lab for anywhere between three days and two weeks. During their stays, teachers visit experiments, talk with physicists, and discuss ways to bring modern physics into their classrooms. More than 10,000 educators have participated.

    2,947
    summer students

    Since 2010 almost 3,000 undergraduates have participated in the CERN summer student programs, including more than 150 students from the United States. These students receive training, tutoring and mentorship as they dip their toes into real scientific research and learn what particle physics is all about.

    ~10 million
    cups of coffee

    The restaurants at CERN go through about 30 kilograms of coffee a day. Considering every kilogram of coffee generally makes between 120 and 140 cups, that’s roughly 4,000 cups a day!

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:41 am on March 25, 2020 Permalink | Reply
    Tags: "Plasma polarised by spin-orbit effect", Accelerator Science, , , , , , , ,   

    From CERN Courier: “Plasma polarised by spin-orbit effect” 


    From CERN Courier

    23 March 2020

    A report from the ALICE experiment

    1
    Fig. 1. The spin alignment of (spin-1) K*0 mesons (red circles) can be characterised by deviations from ρ00 = 1/3, which is estimated here versus their transverse momenta, pT. The same variable was estimated for (spin-0) K0S mesons (magenta stars), and K*0 mesons produced in proton–proton collisions with negligible angular momentum (hollow orange circles), as systematic tests. Credit: CERN

    Spin-orbit coupling causes fine structure in atomic physics and shell structure in nuclear physics, and is a key ingredient in the field of spintronics in materials sciences. It is also expected to affect the development of the quickly rotating quark–gluon plasma (QGP) created in non-central collisions of lead nuclei at LHC energies. As such plasmas are created by the collisions of lead nuclei that almost miss each other, they have very high angular momenta of the order of 107ħ – equivalent to the order of 1021 revolutions per second. While the extreme magnetic fields generated by spectating nucleons (of the order of 1014 T, CERN Courier Jan/Feb 2020 p17) quickly decay as the spectator nucleons pass by, the plasma’s angular momentum is sustained throughout the evolution of the system as it is a conserved quantity. These extreme angular momenta are expected to lead to spin-orbit interactions that polarise the quarks in the plasma along the direction of the angular momentum of the plasma’s rotation. This should in turn cause the spins of vector (spin-1) mesons to align if hadronisation proceeds via the recombination of partons or by fragmentation. To study this effect, the ALICE collaboration recently measured the spin alignment of the decay products of neutral K* and φ vector mesons produced in non-central Pb–Pb collisions.

    Spin alignment can be studied by measuring the angular distribution of the decay products of the vector mesons. It is quantified by the probability ρ00 of finding a vector meson in a spin state 0 with respect to the direction of the angular momentum of the rotating QGP, which is approximately perpendicular to the plane of the beam direction and the impact parameter of the two colliding nuclei. In the absence of spin-alignment effects, the probability of finding a vector meson in any of the three spin states (–1, 0, 1) should be equal, with ρ00 = 1/3.

    The ALICE collaboration measured the angular distributions of neutral K* and φ vector mesons via their hadronic decays to Kπ and KK pairs, respectively. ρ00 was found to deviate from 1/3 for low-pT and mid-central collisions at a level of 3σ (figure 1). The corresponding results for φ mesons show a deviation of ρ00 values from 1/3 at a level of 2σ. The observed pT dependence of ρ00 is expected if quark polarisation via spin-orbit coupling is subsequently transferred to the vector mesons by hadronisation, via the recombination of a quark and an anti-quark from the quark–gluon plasma. The data are also consistent with the initial angular momentum of the hot and dense matter being highest for mid-central collisions and decreasing towards zero for central and peripheral collisions.

    The results are surprising, however, as corresponding quark-polarisation values obtained from studies with Λ hyperons are compatible with zero. A number of systematic tests have been carried out to verify these surprising results. K0S mesons do indeed yield ρ00 = 1/3, indicating no spin alignment, as must be true for a spin-zero particle. For proton–proton collisions, the absence of initial angular momentum also leads to ρ00 = 1/3, consistent with the observed neutral K* spin alignment being the result of spin-orbit coupling.

    The present measurements are a step towards experimentally establishing possible spin-orbit interactions in the relativistic-QCD matter of the quark–gluon plasma. In the future, higher statistics measurements in Run 3 will significantly improve the precision, and studies with the charged K*, which has a magnetic moment seven times larger than neutral K*, may even allow a direct observation of the effect of the strong magnetic fields initially experienced by the quark–gluon plasma.
    Further reading

    ALICE Collaboration 2019 arXiv:1910.14408.

    ALICE Collaboration 2019 arXiv:1909.01281.

    See the full article here .


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    Please help promote STEM in your local schools.


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN/ATLAS detector

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    SixTRack CERN LHC particles

     
  • richardmitnick 2:11 pm on March 24, 2020 Permalink | Reply
    Tags: "Scientists search for origin of proton mass", Accelerator Science, , Chirality is related to a quantum mechanical property called spin., , Higgs is responsible for the mass of the quarks. The rest of it has a different origin., Ninety-nine percent of mass might originate from this process of chirality flipping in the vacuum., Only 1% of the mass of the proton comes from the Higgs field. ALICE scientists examine a process that could help explain the rest., , , , Protons are made up of fundamental particles called quarks and gluons. Quarks are very light and as far as scientists know gluons have no mass at all., Quarks like people can be left- or right-handed- a concept called chirality., , The constant flipping of quarks from one handedness to the other is how theorists explain the majority of the proton’s mass.   

    From Symmetry: “Scientists search for origin of proton mass” 

    Symmetry Mag
    From Symmetry<

    03/24/20
    Sarah Charley

    1
    Courtesy of CERN

    Only 1% of the mass of the proton comes from the Higgs field. ALICE scientists examine a process that could help explain the rest.

    When protons and nuclei inside the Large Hadron Collider smash directly into each other, their energy can transform into new types of matter such as the famed Higgs boson, known for its association with a field that gives fundamental particles mass. But when nuclei merely graze each other, a different amazing thing happens: They generate some of the strongest magnetic fields in the universe.

    These ultra-intense magnetic fields are enabling scientists to peer inside atoms to answer a fundamental question: How do protons get most of their mass?

    Protons are made up of fundamental particles called quarks and gluons. Quarks are very light, and, as far as scientists know, gluons have no mass at all. Yet protons are much heavier than the combined masses of the three quarks they each contain.

    “There is a lot of publicity about the origin of mass because of the Higgs boson,” says Dmitri Kharzeev, a theorist with a joint appointment at Stony Brook University and the Department of Energy’s Brookhaven National Laboratory. “But the Higgs is responsible for the mass of the quarks. The rest of it has a different origin.”

    The origin of mass

    Quarks are very light, accounting for only about 1% of the proton’s overall mass. The plausible—yet still unproven—theoretical explanation for this discrepancy is related to how quarks move through the vacuum.

    This vacuum is not empty, says Sergei Voloshin, a professor at Wayne State University and a member of the ALICE experiment at CERN. The vacuum is actually filled with undulating fields that constantly burp particle-antiparticle pairs into and out of existence.

    The three quarks that give protons their identity are forever jostling with these ethereal particle-antiparticle pairs. When one of these quarks gets too close to a vacuum-produced antiquark, it is annihilated and disappears in a burst of energy.

    But the proton doesn’t wither and die when its quark is zapped out of existence; rather, the partner quark from the vacuum-produced particle-antiparticle pair steps in and takes the annihilated quark’s place (a plot twist straight out of The Talented Mr. Ripley).

    Scientists think that this incessant interchange of quarks is responsible for making a proton appear more massive than the sum of its quarks.

    A matter of handedness

    From the outside, not much appears to change in this swap. The annihilated quark is immediately replaced by a seemingly identical twin, making this process difficult to observe. Luckily for LHC scientists, they are not exactly identical: Quarks, like people, can be left- or right-handed, a concept called chirality.

    Chirality is related to a quantum mechanical property called spin and roughly translates to whether the quark spins clockwise or counterclockwise as it moves along a particular direction through space. (Visualize beads spinning as they slide along a wire.)

    Because of the properties of the vacuum, the replacement quark will always have the opposite handedness from the original. That constant flipping of quarks from one handedness to the other is how theorists explain the majority of the proton’s mass.

    “Ninety-nine percent of mass might originate from this process of chirality flipping in the vacuum,” Kharzeev says. “When we step on a scale, the number we see might be the result of these chirality-flipping transitions.”

    Physics inside a magnetic field

    In 2004, when Kharzeev was the head of the Nuclear Theory Group at Brookhaven Lab, he had an idea for how they could experimentally search for evidence of quark chirality flipping, which had never been observed.

    Because quarks are charged, they should interact with a magnetic field. “Normally, we never think about this interaction, because the magnetic fields we can create in the laboratory are extremely weak compared to the strength of quarks’ interactions with each other,” Kharzeev says. “However, we realized that when charged ions are colliding, they are accompanied by an electromagnetic field, and this field can be used to probe the chirality of quarks.”

    When they did the math, they found that positively charged ions grazing each other inside a particle collider like the LHC will generate a magnetic field two orders of magnitude stronger than the one at the surface of the strongest magnetic field known to exist. This would be enough to override the quarks’ strong attraction to each other.

    “Measuring the magnetic field’s strength and its lifetime was the primary goal of a recent ALICE data analysis,” says Voloshin. “The study yielded somewhat unexpected results, but they were still consistent with the existence of the strong magnetic field required for sorting of quarks according to their handedness.”

    Within a strong magnetic field, a quark’s motion is no longer random. The magnetic field automatically sorts quarks according to their chirality, with their handedness steering them toward either the field’s north or south pole.

    A hearty, hot soup of quarks

    It’s nearly impossible to catch a quark flipping its chirality inside a proton, Kharzeev says.

    “Inside a proton, left-handed quarks transition into right-handed quarks, and right-handed quarks transition back into left-handed quarks,” he says. “We will always see a mixture of left- and right-handed quarks.”

    To study whether quark chirality flipping happens, physicists need to catch several large and unexpected imbalances between the number of right- and left-handed quarks.

    Luckily, heavy nuclei collisions produce the perfect conditions for quarks to change their handedness. When two nuclei hit each other at high speeds, their protons and neutrons melt into a quark-gluon plasma, which is one of the hottest and densest materials known to exist in the universe. The liberated quarks swimming through this plasma can shift their identities with ease.

    “It’s like pretzels before they’re baked,” Kharzeev says. “You can easily mold the dough and change the twist.”

    The vacuum of space is not homogeneous—there are knots of gluon field that preferentially twist these doughy quarks one way or the other. If chirality flipping is happening, then scientists should catch an imbalance in the number of left- and right-handed quarks that shoot out from the plasma.

    “The average handedness over all the collisions should be the same,” Kharzeev says, “but the fluctuations from collision to collision should be very large; we should see some quark-gluon plasmas that are preferentially righted-handed and others that are preferentially left-handed.” Due to the presence of magnetic field, the handedness of the plasma translates into observable charge asymmetry of produced particles—this is the “chiral magnetic effect” proposed by Kharzeev.

    Shortly after Kharzeev proposed the idea of sorting quarks according to their handedness in the strong magnetic field of colliding nuclei, Voloshin designed a way to test this theory using the ALICE experiment, whose US participation is funded by the Department of Energy. The initial results show evidence for quarks sorting themselves according to chirality. But more research needs to be done before scientists can be sure.

    See the full article here .


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    Please help promote STEM in your local schools.


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:30 pm on March 10, 2020 Permalink | Reply
    Tags: "New LHCb analysis still sees previous intriguing results", Accelerator Science, , , , , ,   

    From CERN LHCb: “New LHCb analysis still sees previous intriguing results” 

    Cern New Bloc

    Cern New Particle Event


    From CERN LHCb

    10 March, 2020
    Ana Lopes

    The new analysis continues to find tension with the Standard Model, but more data are needed to identify its cause.

    Standard Model of Particle Physics, Quantum Diaries

    2
    The LHCb experiment at CERN. (Image: CERN.)

    At a seminar today at CERN, the LHCb collaboration presented a new analysis of data from a specific transformation, or “decay”, that a particle called B0 meson can undergo. The analysis is based on twice as many B0 decays as previous LHCb analyses, which had disclosed some tension with the Standard Model of particle physics. The tension is still present in the new analysis, but more data are needed to identify its nature.

    The decay in question is the decay of a B0 meson, which is made up of a bottom quark and a down quark, into a K* meson (containing a strange quark and down quark) and a pair of muons. It is a rare process: The Standard Model predicts only one such decay for every million B0 decays. In many theories that extend the Standard Model, new unknown particles can also contribute to the decay, resulting in a change of the rate at which the decay should occur. In addition, the distribution of the angles of the B0 decay products with respect to the parent B0 – that is, of the muons and the kaon and pion from the K* decay – can also be affected by the presence of new particles.

    In previous studies of this decay, the LHCb team analysed data from the first run of the Large Hadron Collider and found a deviation from Standard Model predictions in one parameter calculated from the angular distributions, technically known as P5′. In the new study, the LHCb team has added LHC data from the machine’s second run to their analysis and still sees a deviation from Standard Model calculations in P5′ as well as other parameters. However, the old and new results have a statistical significance of about 3 standard deviations, whereas 5 standard deviations are the gold standard in particle physics. It is therefore too soon to tell whether the deviation is statistically significant and, if so, whether it is caused by a new particle or an unknown experimental or theoretical effect.

    “This is a very exciting time to be doing what we call flavour physics,” said Mat Charles, LHCb’s Physics Coordinator. “Here and in other related analyses, we keep seeing moderate tensions with the Standard Model. We still don’t know how this mystery will turn out – nothing has yet reached the level of solid proof – but we’re very much looking forward to the next round of results using the full LHCb data, which will roughly double the number of events again.”

    Read more on the LHCb page.

    See the full article here .

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    Please help promote STEM in your local schools.

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    LHCb
    CERN LHCb New II

    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

     
  • richardmitnick 3:14 pm on March 10, 2020 Permalink | Reply
    Tags: "Accounting for the Higgs", Accelerator Science, , , , , , , ,   

    From Symmetry: “Accounting for the Higgs” 

    Symmetry Mag
    From Symmetry<

    03/10/20
    Sarah Charley

    Only a fraction of collision events that look like they produce a Higgs boson actually produce a Higgs boson. Luckily, it doesn’t matter.

    CERN CMS Higgs Event May 27, 2012

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    I’ll let you in on a little secret: Even though physicists have produced millions of Higgs bosons at the Large Hadron Collider, they’ve never actually seen one. Higgs bosons are fragile things that dissolve immediately after they’re born. But as they die, they produce other particles, which, if they’re created at the LHC, can travel through a particle detector and leave recognizable signatures.

    Here’s another secret: Higgs signatures are identical to the signatures of numerous other processes. In fact, every time the Higgs signs its name in a detector, there are many more background processes leaving the exact same marks.

    For instance, one of the Higgs boson’s cleanest signatures is two photons with a combined mass of around 125 billion electronvolts. But for every 10 diphotons that look like a Higgs signature, only about one event actually belongs to a Higgs.

    So how can scientists study something that they cannot see and cannot isolate? They employ the same technique FBI agents use to uncover illegal money laundering schemes: accounting.

    In money laundering, “dirty” money (from illegal activities) is mixed with “clean” money from a legitimate business like a car wash. It all looks the same, so determining which Benjamins came from drugs versus which came from detailing is impossible. But agents don’t need to look at the individual dollars; they just need to look for suspiciously large spikes in profit that cannot be explained by regular business activities.

    In physics, the accounting comes from a much-loved set of equations called the Standard Model.

    Standard Model of Particle Physics, Quantum Diaries

    Physicists have spent decades building and perfecting the Standard Model, which tells them what percentage of the time different subatomic processes should happen. Scientists know which signatures are associated with which processes, so if they see a signature more often than expected, it means there is something happening outside the purview of the Standard Model: a new process.

    Clever accounting is how scientists originally discovered the Higgs boson in 2012. Theorists predicted what the Higgs signatures should look like, and when physicists went searching, they consistently saw some of these signatures more frequently than they could explain without the Higgs boson. When scientists added the mathematics for the Higgs boson into the equations, the predictions matched the data.

    Today, physicists use this accounting method to search for new particles. Many of these new particles are predicted to be rarer than Higgs bosons (for reference, Higgs bosons are produced in about one in a billion collisions). Many processes are also less clear-cut, and just the act of standardizing the accounting is a challenge. (To return to the money laundering analogy, it would be like FBI agents investigating an upscale bar, where a sudden excess could be explained by a generous tip.)

    To find these complex and subtle signs of mischief, scientists need a huge amount of data and a finely tuned model. Future runs of the LHC will be dedicated to building up these enormous datasets so that scientists can dig through the books for numbers that the Standard Model cannot explain.

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 5:09 pm on March 4, 2020 Permalink | Reply
    Tags: "25 years on: A single top quark partners with the Z boson", Accelerator Science, , , , , ,   

    From CERN ATLAS via phys.org: “25 years on: A single top quark partners with the Z boson” 

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    CERN ATLAS another view Image Claudia Marcelloni ATLAS CERN


    From CERN ATLAS

    via


    phys.org

    1
    Figure 1: The neural network output (ONN) distribution for one of the signal regions. Data is shown in black. The simulated signal is shown in magenta. Backgrounds are shown in other colours. The high part of the ONN spectrum is dominated by signal events. Credit: ATLAS Collaboration/CERN

    A quarter-century after its discovery, physicists at the ATLAS Experiment at CERN are gaining new insight into the heaviest-known particle, the top quark. The huge amount of data collected during Run 2 of the LHC (2015-2018) has allowed physicists to study rare production processes of the top quark in great detail, including its production in association with other heavy elementary particles.

    In a new paper [https://arxiv.org/abs/2002.07546], the ATLAS Collaboration reports the observation of a single top quark produced in association with a Z boson (tZq) using the full Run-2 dataset, thereby confirming earlier results by ATLAS and CMS using smaller datasets. To achieve this new result, physicists studied over 20 billion collision events recorded by the ATLAS detector, looking for events with three isolated leptons (electrons or muons), a momentum imbalance in the plane perpendicular (transverse) to the proton beam, and two or three jets of hadrons originating from the fragmentation of quarks (with one jet originating from a b-quark). Only about 600 candidate events with such a signature were identified (i.e. the signal region) and, despite strict selection criteria, only about 120 of those are expected to come from the tZq production process.

    To best separate their signal from background processes, ATLAS physicists trained an artificial neural network to identify tZq events using precisely simulated data. The neural network provided each event with a score (Onn) that represented how much it looked like the signal process. To check that the simulation fed to the neural network gave a good description of the real data, physicists looked at events with similar signatures (control regions) that are dominated by background processes. Various kinematic distributions of the 600 selected signal-region events were also checked.

    2
    Figure 2: Distribution of the reconstructed Z boson transverse momentum for events with a neural network output (ONN) > 0.4. Data is shown in black. The simulated signal is shown in magenta. Backgrounds are shown in other colours. Credit: ATLAS Collaboration/CERN

    Researchers evaluated the neural network score in both signal (Figure 1) and control regions so that the background levels could be constrained using real data. The tZq signal was extracted and the rate of such events being produced in the given data sample (i.e. the cross-section) was computed. The uncertainty on the extracted cross-section is 14%. This is over a factor of two more precise than the previous ATLAS result, which was based on almost four times less data (from 2015 and 2016). The cross-section was found to be in agreement with the prediction from Standard Model, confirming that even the heaviest particles in the Standard Model still behave as point-like elementary particles.

    Further, by selecting for events identified by the neural network as very likely to be tZq events (ONN > 0.4), ATLAS physicists could examine whether the kinematic distributions are well described by the Standard Model calculations. Figure 2 shows that this is indeed the case.

    With the observation of the tZq production process now confirmed, ATLAS researchers can anticipate its study in even greater detail. Measurements of the cross-section as a function of kinematic variables will allow physicists to carefully probe the top quark’s interactions with other particles. Will more data unveil some unexpected features? Look forward to seeing what Nature is hiding in the top world.

    See the full article here .


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    About Science X in 100 words

    Science X™ is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004 (Physorg.com), Science X’s readership has grown steadily to include 5 million scientists, researchers, and engineers every month. Science X publishes approximately 200 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Science X community members enjoy access to many personalized features such as social networking, a personal home page set-up, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.
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    CERN Courier

    Quantum Diaries
    QuantumDiaries

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    CERN LHC Grand Tunnel
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  • richardmitnick 1:49 pm on March 3, 2020 Permalink | Reply
    Tags: "The Hyper-Kamiokande project is officially approved.", Accelerator Science, , Hyper-Kamiokande is designed to elucidate the origin of matter and the Grand Unified Theory of elementary particles., International contributions will also include data acquisition system; water system upgrade; detector calibration systems; and downstream offline computing system., International contributions will include the near/intermediate detector complex., International contributions will include the rest of photosensors for the inner detector; sensor covers and light collectors; photosensors for the outer detector; and readout electronics., J-PARC accelerator upgrade, , ,   

    From University of Tokyo: “The Hyper-Kamiokande project is officially approved.” 

    From University of Tokyo

    12/February/2020

    Hyper-Kamiokande, a neutrino physics laboratory to be 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.

    Hyper-Kamiokande (HK or Hyper-K) project is the world-leading international scientific research project hosted by Japan aiming to elucidate the origin of matter and the Grand Unified Theory of elementary particles. The project consists of the Hyper-K detector, which has an 8.4 times larger fiducial mass than its predecessor, Super-Kamiokande, equipped with newly developed high-sensitivity photosensors and a high-intensity neutrino beam produced by an upgraded J-PARC accelerator facility.

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

    The supplementary budget for FY2019 which includes the first-year construction budget of 3.5 billion yen for the Hyper-Kamiokande project was approved by the Japanese Diet. The Hyper-K project has officially started. The operations will begin in 2027.

    The overall Japanese contribution will include the cavern excavation, construction of the tank (water container) and its structure, half of the photosensors for the inner detector, main part of the water system, Tier 0 offline computing, together with J-PARC accelerator upgrade and construction of a new experimental facility for the near detector complex. International contributions will include the rest of photosensors for the inner detector, sensor covers and light collectors, photosensors for the outer detector, readout electronics, data acquisition system, water system upgrade, detector calibration systems, downstream offline computing system, and the near/intermediate detector complex.

    We would like to work together with domestic and international colleagues in Hyper-K for the development of neutrino physics and astrophysics.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Tokyo aims to be a world-class platform for research and education, contributing to human knowledge in partnership with other leading global universities. The University of Tokyo aims to nurture global leaders with a strong sense of public responsibility and a pioneering spirit, possessing both deep specialism and broad knowledge. The University of Tokyo aims to expand the boundaries of human knowledge in partnership with society. Details about how the University is carrying out this mission can be found in the University of Tokyo Charter and the Action Plans.

     
  • richardmitnick 1:40 pm on February 27, 2020 Permalink | Reply
    Tags: "‘Flash photography’ at the LHC", Accelerator Science, , , , , , ,   

    From Symmetry: “‘Flash photography’ at the LHC” 

    Symmetry Mag
    From Symmetry<

    02/27/20
    Sarah Charley

    1
    Photo by Tom Bullock

    An extremely fast new detector inside the CMS detector will allow physicists to get a sharper image of particle collisions.

    Some of the best commercially available high-speed cameras can capture thousands of frames every second. They produce startling videos of water balloons popping and hummingbirds flying in ultra-slow motion.

    But what if you want to capture an image of a process so fast that it looks blurry if the shutter is open for even a billionth of a second? This is the type of challenge scientists on experiments like CMS and ATLAS face as they study particle collisions at CERN’s Large Hadron Collider.

    When the LHC is operating to its full potential, bunches of about 100 billion protons cross each other’s paths every 25 nanoseconds. During each crossing, which lasts about 2 nanoseconds, about 50 protons collide and produce new particles. Figuring out which particle came from which collision can be a daunting task.

    “Usually in ATLAS and CMS, we measure the charge, energy and momentum of a particle, and also try to infer where it was produced,” says Karri DiPetrillo, a postdoctoral fellow working on the CMS experiment at the US Department of Energy’s Fermilab. “We’ve had timing measurements before—on the order of nanoseconds, which is sufficient to assign particles to the correct bunch crossing, but not enough to resolve the individual collisions within the same bunch.”

    Thanks to a new type of detector DiPetrillo and her collaborators are building for the CMS experiment, this is about to change.

    CERN/CMS Detector

    Physicists on the CMS experiment are devising a new detector capable of creating a more accurate timestamp for passing particles. The detector will separate the 2-nanosecond bursts of particles into several consecutive snapshots—a feat a bit like taking 30 billion pictures a second.

    This will help physicists with a mounting challenge at the LHC: collision pileup.

    Picking apart which particle tracks came from which collision is a challenge. A planned upgrade to the intensity of the LHC will increase the number of collisions per bunch crossing by a factor of four—that is from 50 to 200 proton collisions—making that challenge even greater.

    Currently, physicists look at where the collisions occurred along the beamline as a way to identify which particular tracks came from which collision. The new timing detector will add another dimension to that.

    “These time stamps will enable us to determine when in time different collisions occurred, effectively separating individual bunch crossings into multiple ‘frames,’” says DiPetrillo.

    DiPetrillo and fellow US scientists working on the project are supported by DOE’s Office of Science, which is also contributing support for the detector development.

    According to DiPetrillo, being able to separate the collisions based on when they occur will have huge downstream impacts on every aspect of the research. “Disentangling different collisions cleans up our understanding of an event so well that we’ll effectively gain three more years of data at the High-Luminosity LHC. This increase in statistics will give us more precise measurements, and more chances to find new particles we’ve never seen before,” she says.

    The precise time stamps will also help physicists search for heavy, slow moving particles they might have missed in the past.

    “Most particles produced at the LHC travel at close to the speed of light,” DiPetrillo says. “But a very heavy particle would travel slower. If we see a particle arriving much later than expected, our timing detector could flag that for us.”

    The new timing detector inside CMS will consist of a 5-meter-long cylindrical barrel made from 160,000 individual scintillating crystals, each approximately the width and length of a matchstick. This crystal barrel will be capped on its open ends with disks containing delicately layered radiation-hard silicon sensors. The barrel, about 2 meters in diameter, will surround the inner detectors that compose CMS’s tracking system closest to the collision point. DiPetrillo and her colleagues are currently working out how the various sensors and electronics at each end of the barrel will coordinate to give a time stamp within 30 to 50 picoseconds.

    “Normally when a particle passes through a detector, the energy it deposits is converted into an electrical pulse that rises steeply and the falls slowly over the course of a few nanoseconds,” says Joel Butler, the Fermilab scientist coordinating this project. “To register one of these passing particles in under 50 picoseconds, we need a signal that reaches its peaks even faster.”

    Scientists can use the steep rising slopes of these signals to separate the collisions not only in space, but also in time. In the barrel of the detector, a particle passing through the crystals will release a burst of light that will be recorded by specialized electronics. Based on when the intense flash of light arrives at each sensor, physicists will be able to calculate the particle’s exact location and when it passed. Particles will also produce a quick pulse in the endcaps, which are made from a new type of silicon sensor that amplifies the signal. Each silicon sensor is about the size of a domino and can determine the location of a passing particle to within 1.3 millimeters.

    The physicists working on the timing detector plan to have all the components ready and installed inside CMS for the start-up of the High Luminosity LHC in 2027

    “High-precision timing is a new concept in high-energy physics,” says DiPetrillo. “I think it will be the direction we pursue for future detectors and colliders because of its huge physics potential. For me, it’s an incredibly exciting and novel project to be on right now.”

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:23 pm on February 24, 2020 Permalink | Reply
    Tags: "ATLAS experiment searches for natural supersymmetry using novel techniques", Accelerator Science, , , , , ,   

    From CERN ATLAS via phys.org: “ATLAS experiment searches for natural supersymmetry using novel techniques” 

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    CERN ATLAS another view Image Claudia Marcelloni ATLAS CERN


    From CERN ATLAS

    via


    phys.org

    February 24, 2020

    1
    Visualisation of the highest jet multiplicity event selected in a control region used to make predictions of the background from multijet production. This event was recorded by ATLAS on 18 July 2018, and contains 19 jets, illustrated by cones. Yellow blocks represent the calorimeter energy measured in in noise-suppressed clusters. Of the reconstructed jets, 16 (10) have transverse momenta above 50 GeV (80 GeV). Credit: ATLAS Collaboration/CERN

    In new results presented at CERN, the ATLAS Experiment’s search for supersymmetry (SUSY) reached new levels of sensitivity. The results examine a popular SUSY extension studied at the Large Hadron Collider (LHC): the “Minimal Supersymmetric Standard Model” (MSSM), which includes the minimum required number of new particles and interactions to make predictions at the LHC energies. However, even this minimal model introduces a large amount of new parameters (masses and other properties of the new particles), whose values are not predicted by the theory (free parameters).

    To frame their search, ATLAS physicists look for “natural” SUSY, which assumes the various corrections to the Higgs mass comparable in magnitude and their sum close to the electroweak scale (v ~ 246 GeV). Under this paradigm, the supersymmetric partners of the third-generation quarks (“top and bottom squarks”) and gluons (“gluinos”) could have masses close to the TeV scale, and would be produced through the strong interaction at rates large enough to be observed at the LHC.

    In a recent CERN LHC seminar, the ATLAS Collaboration presented new results in the search for natural SUSY, including searches for top squarks and gluinos using the full LHC Run-2 dataset collected between 2015 and 2018. The new results explore previously uncovered, challenging regions of the free parameter space. This is achieved thanks to new analysis techniques improving the identification of low-energy (“soft”) and high-energy (“boosted”) particles in the final state.

    ATLAS’ search for top squarks was performed by selecting proton–proton collisions containing up to one electron or muon. For top-squark masses less than the top-quark mass of 173 GeV (see Figure 1), the resulting decay products tend to be soft and therefore difficult to identify. Physicists developed new techniques based on charged-particle tracking to better identify these decay products, thus significantly improving the experimental sensitivity. For larger top-squark masses, the decay products are boosted, resulting in high-energy, close-by decay products. Physicists improved the search in this regime by using, among other techniques, more precise estimates of the statistical significance of the missing transverse momentum in a collision event.

    3
    Figure 1: Schematic representation of the various topologies of top-squark decays in the scenarios presented at today’s seminar (see link in footer). The region where the top-squark is lighter than the neutralino is not allowed in the models considered. Credit: ATLAS Collaboration/CERN

    The new search for gluinos looks at events containing eight or more “jets”—collimated sprays of hadrons—and missing transverse momentum generated by the production of stable neutralinos in the gluino decays, which, similar to neutrinos, are not directly detected by ATLAS. Physicists employed new reconstruction techniques to improve the energy resolution of the jets and the missing transverse momentum, allowing them to better separate the putative signal from background processes. These take advantage of “particle-flow” jet algorithms [https://arxiv.org/abs/1703.10485] that combine information from both the tracking detector and the calorimeter system.

    4
    Figure 2: Updated exclusion limits on (left) gluino and (right) top-squark production including the new results presented by ATLAS at the CERN LHC seminar today. Credit: ATLAS Collaboration/CERN

    ATLAS physicists also optimised their event-selection criteria to enhance the contribution of possible SUSY signals compared to the Standard Model background processes. No excess was observed in the data. The results were used to derive exclusion limits on MSSM-inspired simplified models in terms of gluino, top-squark and neutralino masses (see Figure 2).

    The new analyses significantly extend the sensitivity of the searches and further constrain the available parameter space for natural SUSY. The exclusion of heavy top squarks is extended from 1 to 1.25 TeV. The search continues.

    More information: CERN LHC Seminar: Constraining natural supersymmetry with the ATLAS detector by Jeanette Miriam Lorenz indico.cern.ch/event/868249/

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    CERN Courier

    Quantum Diaries
    QuantumDiaries

    CERN map


    CERN LHC Grand Tunnel
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