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  • richardmitnick 7:38 pm on October 14, 2014 Permalink | Reply
    Tags: , , CERN LHCb, , , , ,   

    From New Scientist vis FNAL: “Two new strange and charming particles appear at LHC” 

    NewScientist

    New Scientist

    08 October 2014
    Nicola Jenner

    Two new particles have been discovered by the LHCb experiment at CERN’s Large Hadron Collider near Geneva, Switzerland. One of them has a combination of properties that has never been observed before.

    CERN LHCb New
    LHCb

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    The particles, named DS3*(2860)– and DS1*(2860)–, are about three times as massive as protons.

    Physicists analyzed LHCb observations of an energy peak that had been spotted in 2006 by the BaBar experiment at Stanford University in California, but whose cause was still unknown.

    “Our result shows that the BaBar peak is caused by two new particles,” says Tim Gershon of Warwick University, UK, lead author of the discovery.
    The force is strong

    Mesons are particles that contain two quarks – subatomic particles that make up matter and are thought to be indivisible. These quarks are bound together by the strong force, one of the four fundamental forces that also keeps the constituents of nuclei together within atoms. This force is one of the less well-understood parts of the standard model of particle physics, the incomplete theory that describes how particles interact.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Quarks come in six different flavours known as up, down, strange, charm, bottom and top, in order from lightest to heaviest. The new particles each contain one charm antiquark and one strange quark.

    Significantly, DS3*(2860)– also has a spin value of 3, making this discovery the first ever observation of a spin-3 particle containing a charm quark.

    In other mesons, the quarks can be configured in one of several different ways to give the particle an overall spin value less than three, and this makes the quarks’ exact properties ambiguous. However, for a spin value of three there is no such ambiguity, making DS3*(2860)–’s precise configuration clear.

    Combined with the particle’s charm quark, this may make DS3*(2860)– a key player for exploring the strong force, because the calculations involved are more straightforward for heavy quarks than for lighter ones.

    The LHCb team used a technique known as Dalitz plot analysis to untangle the data peak into its two components, a complex technique that had never before been used on LHC data.

    The technique helps separate and visualise the different paths a particle can take as it decays. Now that it has been used successfully on the LHCb dataset, says Gershon, it can hopefully be applied to more LHC data to help discover further particles and understand how they are bound together.

    “This is a lovely piece of experimental physics,” says Robert Jaffe of the Massachusetts Institute of Technology in Cambridge. “Although it doesn’t probe the limits of the standard model, it may shine light on the dynamics of quarks and gluons. The fact that LHCb was able to use Dalitz plot methods is a testimony to the quantity and high quality of the data they’ve accumulated. We can look forward to other similar discoveries in the future using this method.”

    See the full article here.

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  • richardmitnick 1:29 pm on October 9, 2014 Permalink | Reply
    Tags: , , CERN LHCb, , , , University of Warwick   

    From Warwick: “Discovery of new subatomic particle sheds light on fundamental force of nature “ 

    University of Warwick

    University of Warwick

    9 October 2014
    No Writer Credit

    The discovery of a new particle will “transform our understanding” of the fundamental force of nature that binds the nuclei of atoms, researchers argue.

    Led by scientists from the University of Warwick, the discovery of the new particle will help provide greater understanding of the strong interaction, the fundamental force of nature found within the protons of an atom’s nucleus.

    what
    Credit: Science and Technology Facilities Council

    Named Ds3*(2860)ˉ, the particle, a new type of meson,[1] was discovered by analysing data collected with the LHCb detector at CERN’s Large Hadron Collider (LHC)[2]. The LHCb experiment, which is run by a large international collaboration, is designed to study the properties of particles containing beauty and charm quarks and has unique capability for this kind of discovery.

    CERN LHCb New
    LHCb

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    CERN LHC

    The new particle is bound together in a similar way to protons. Due to this similarity, the Warwick researchers argue that scientists will now be able to study the particle to further understand strong interactions.

    Along with gravity, the electromagnetic interaction and weak nuclear force, strong-interactions are one of four fundamental forces. Lead scientist Professor Tim Gershon, from The University of Warwick’s Department of Physics, explains:

    “Gravity describes the universe on a large scale from galaxies to [Isaac] Newton’s falling apple, whilst the electromagnetic interaction is responsible for binding molecules together and also for holding electrons in orbit around an atom’s nucleus.

    “The strong interaction is the force that binds quarks, the subatomic particles that form protons within atoms, together. It is so strong that the binding energy of the proton gives a much larger contribution to the mass, through [Albert] Einstein’s equation E = mc2, than the quarks themselves.[3]”

    Due in part to the forces’ relative simplicity, scientists have previously been able to solve the equations behind gravity and electromagnetic interactions, but the strength of the strong interaction makes it impossible to solve the equations in the same way.

    “Calculations of strong interactions are done with a computationally intensive technique called Lattice QCD,” says Professor Gershon. “In order to validate these calculations it is essential to be able to compare predictions to experiments. The new particle is ideal for this purpose because it is the first known that both contains a charm quark and has spin 3.”

    There are six quarks known to physicists; Up, Down, Strange, Charm, Beauty and Top. Protons and neutrons are composed of up and down quarks, but particles produced in accelerators such as the LHC can contain the unstable heavier quarks. In addition, some of these particles have higher spin values than the naturally occurring stable particles.

    “Because the Ds3*(2860)ˉ particle contains a heavy charm quark it is easier for theorists to calculate its properties. And because it has spin 3, there can be no ambiguity about what the particle is,” adds Professor Gershon. “Therefore it provides a benchmark for future theoretical calculations. Improvements in these calculations will transform our understanding of how nuclei are bound together.”

    Spin is one of the labels used by physicists to distinguish between particles. It is a concept that arises in quantum mechanics that can be thought of as being similar to angular momentum: in this sense higher spin corresponds to the quarks orbiting each other faster than those with a lower spin.

    Warwick Ph.D. student Daniel Craik, who worked on the study, adds “Perhaps the most exciting part of this new result is that it could be the first of many similar discoveries with LHC data. Whether we can use the same technique, as employed with our research into Ds3*(2860)ˉ, to also improve our understanding of the weak interaction is a key question raised by this discovery. If so, this could help to answer one of the biggest mysteries in physics: why there is more matter than antimatter in the Universe.”

    The results are detailed in two papers that will be published in the next editions of the journals Physical Review Letters and Physical Review D. Both papers have been given the accolade of being selected as Editors’ Suggestions.

    [1] The Ds3*(2860)ˉ particle is a meson that contains a charm anti-quark and a strange quark. The subscript 3 denotes that it has spin 3, while the number 2860 in parentheses is the mass of the particle in the units of MeV/c2 that are favoured by particle physicists. The value of 2860 MeV/c2 corresponds to approximately 3 times the mass of the proton.

    [2] The particle was discovered in the decay chain Bs0→D0K–π+ , where the Bs0, D0, K– and π+ mesons contain respectively a bottom anti-quark and a strange quark, a charm anti-quark and an up quark, an up anti-quark and a strange quark, and a down anti-quark and an up quark. The Ds3*(2860)ˉ particle is observed as a peak in the mass of combinations of the D0 and K– mesons. The distributions of the angles between the D0, K– and π+ particles allow the spin of the Ds3*(2860)ˉ meson to be unambiguously determined.

    [3] Quarks are bound by the strong interaction into one of two types of particles: baryons, such as the proton, are composed of three quarks; mesons are composed of one quark and one anti-quark, where an anti-quark is the antimatter version of a quark.

    See the full article here.

    Warwick Campus

    The establishment of the University of Warwick was given approval by the government in 1961 and received its Royal Charter of Incorporation in 1965.

    The idea for a university in Coventry was mooted shortly after the conclusion of the Second World War but it was a bold and imaginative partnership of the City and the County which brought the University into being on a 400-acre site jointly granted by the two authorities. Since then, the University has incorporated the former Coventry College of Education in 1978 and has extended its land holdings by the purchase of adjoining farm land.

    The University initially admitted a small intake of graduate students in 1964 and took its first 450 undergraduates in October 1965. In October 2013, the student population was over 23,000 of which 9,775 are postgraduates. Around a third of the student body comes from overseas and over 120 countries are represented on the campus.

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  • richardmitnick 7:33 pm on September 21, 2014 Permalink | Reply
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    From BBC: “‘Artificial retina’ could detect sub-atomic particles” 

    BBC

    18 September 2014
    Melissa Hogenboom

    The human eye has inspired physicists to create a processor that can analyse sub-atomic particle collisions 400 times faster than currently possible.

    In these collisions, protons – ordinary matter – are smashed together at close to light speeds.

    pro
    The quark structure of the proton. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons

    These powerful smash-ups could yield new particles and help scientists understand matter’s mirror, antimatter.

    anti
    The quark structure of the antiproton

    The experimental processor could speed up the analysis of data from the collisions.

    Published in the pre-print arXiv server, the algorithm has been proposed for possible use in Large Hadron Collider (LHC) experiments at Cern in 2020. It could also be useful in any field where fast, efficient pattern recognition capabilities are needed.

    CERN LHC Grand Tunnel
    LHC

    The processor works in a similar way to the retina’s incredible ability to recognise patterns extremely quickly.
    Snapshots in time

    That is, individual neurons in our retinas are specialised to respond to particular shapes or orientations, which they do automatically before our brain is even consciously aware of what we are processing.

    pd
    Image of particle decay LHC machines produce 40 million collisions per second

    Cern physicist Diego Tonelli, one of a team of collaborators of the work, explained that the “artificial retina” detects a snapshot of the trajectory of each collision which is then immediately analysed.

    These snapshots are then mapped into an algorithm that can run on a computer, automatically scanning and analysing the charged particle trajectories, or tracks. Exposing the detector to future collisions will then allow teams sift out the interesting events.

    Data crunching

    Speed is of the essence here. There are roughly 40 million collisions per second and each can result in hundreds of charged particles.

    The scientists then have to plough through an incredible amount of data. It’s spotting the deviations from the norm that may give hints of new physics.

    lhcb
    LHCb experiment
    The LHC will be switched on again in early 2015

    An algorithm like this could therefore provide a useful way of crunching through this vast amount of data, in real time.

    “It’s 400 times faster than anything existing or foreseen for high energy physics applications. If implemented in a real experiment it will allow us to collect more interesting data more quickly,” Dr Tonelli told the BBC.

    Flavour physics

    The LHC has been switched off since February 2013 but is due to begin its hunt for new physics in 2015 when the giant machine will once again begin smashing together protons.

    As this happens, they break down and free up a huge amounts of energy that forms many neutral and charged particles. It’s the trajectories of the charged ones that can be observed.

    col
    Particle collisions
    A collision in the Large Hadron Collider creates tracks of charged particles

    The new algorithm is not aimed at the type of physics used to find the famous Higgs boson, instead it’s intended to be used for “flavour physics” which deals with the interaction of the basic components of matter, the quarks.

    Commenting on the work, Tara Shears a Cern particle physicist from the University of Liverpool, said it could be extremely useful to automatically “give us most information about what we want to study – Higgs, dark matter, antimatter and so on. The artificial retina algorithm looks like it does this brilliantly”.

    “When our detectors take these snapshots of the collisions – to us that’s like the picture that your eye sees and when your brain is scanning that picture and making sense of it, well we try and codify those rules into an algorithm that we run on computers that do the job for us automatically,” Prof Shears told the BBC’s Inside Science programme.

    “When the LHC continues… we will start to operate with a more intense beam of protons getting a much higher data rate, and then this problem of sifting out what you really want to study becomes really really pressing,” she added.

    “This artificial retinal algorithm is one of the latest steps in our mission to [understand the Universe], and it’s really good, it does the job vast banks of computers normally do.”

    The algorithm has been developed with the 2020 upgrade of the LHC in mind, which will have even more powerful collisions.

    See the full article here.

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  • richardmitnick 2:25 pm on June 6, 2014 Permalink | Reply
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    From Symmetry: “LHCb glimpses possible sign of new physics” 

    Symmetry

    June 06, 2014
    Sarah Charley

    This week at the LHC Physics conference in New York City, the LHCb collaboration presented a result that could be a hint of new physics.

    CERN LHCb New
    LHCb at CERN

    LHCb, one of the four largest experiments at the Large Hadron Collider, is run by scientists from more than 50 institutions worldwide, including four universities in the United States. It examines the properties of certain particles to look for deviations from the Standard Model of particle physics.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The Standard Model predicts that electrons, muons and taus—all members of the lepton particle family—should behave in the same way and be produced in equal amounts in particle decays.

    “The Standard Model doesn’t distinguish between muons and electrons in these decays,” says Tom Blake, a Royal Society University Research Fellow working on this analysis. “As far as our equations are concerned, they are the same particle, so we should see them produced in near equal amounts.”

    In a result announced this week, LHCb scientists revealed that they have seen a hint that particles defy this Standard Model prediction. This could be caused by interference from undiscovered particles or forces.

    LHCb scientists saw the difference in decays of particles containing b-quarks. Typically, these particles decay to light hadrons shortly after they are produced. But in very rare instances, they create two leptons and a hadron instead.

    According to the Standard Model, this type of decay should have created an equal number of electrons and muons. Instead, they found that electrons were produced 25 percent of the time more often. If data collected in the next run of the LHC continues to support this result, it could be a sign of physics beyond the Standard Model.

    “If we continue to see this discrepancy, it could be evidence of a new particle—like a heavier cousin of the Z boson—interfering with the muon production,” says Michel De Cian, a postdoc at the University of Heidelberg, who presented the result.

    Previously, the Belle collaboration in Japan and the BaBar collaboration at SLAC also measured the ratio of muons to electrons produced during this decay. Both Belle and Babar found that the ratio was one-to-one, but the statistical uncertainty was so great that neither experiment was able to draw solid conclusions.

    The LHCb experiment does not yet have enough data to confirm or refute whether nature follows the Standard Model’s predictions either.

    “It’s interesting but inconclusive,” De Cian says. “We don’t have a large enough statistical significance to make any claims yet.”

    De Cian and Blake both hope that the next run of the LHC will provide more data and will help them shed light on the dark cracks and corners of the Standard Model.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 7:17 am on May 10, 2014 Permalink | Reply
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    From LHCb at CERN: “Polarisation confirmed” 

    CERN New Masthead

    CERN LHCb New
    LHCb

    2014-05-09
    Anaïs Schaeffer

    The polarisation of photons emitted in the decay of a bottom quark into a strange quark, as predicted by the Standard Model, has just been observed for the first time by the LHCb collaboration. More detailed research is still required to determine the value of this polarisation with precision.

    event
    In this LHCb event, K, π and γ are emitted from a B+ → K+π-π+γ decay. This was investigated by the LHCb collaboration in order to study the photon (γ) polarisation.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    In this LHCb event, K, π and γ are emitted from a B+ → K+π-π+γ decay. This was investigated by the LHCb collaboration in order to study the photon (γ) polarisation.

    If we imagine that photons are like little spinning tops which spin around an axis aligned with their direction of propagation, we can identify two types of photons. Those that are “right-handed” turn in the same direction as a corkscrew, and those that are “left-handed” turn in the opposite direction. If for a large number of decays of a given type we can observe an imbalance between the production of right-handed photons and the production of left-handed protons, we can say that there is a polarisation.

    At CERN, the LHCb collaboration has been looking at precisely this phenomenon. In particular it has been studying the polarisation of the photon (γ) emitted in the decay of a bottom quark (b) into a strange quark (s): b → sγ. According to the predictions of the Standard Model of particle physics, the photons emitted in this decay should almost always be left-handed. But until now, this polarisation had not been demonstrated in an experiment. “Thanks to the data gathered by LHCb in 2011 and 2012, we have been able to study around 14,000 b → sγ decays,” explains Olivier Schneider, a physicist at EPFL and a member of the LHCb collaboration. “By counting the number of photons emitted in different directions, we have successfully demonstrated polarisation (see box). Further research is needed to determine if this is polarisation with an excess of left-handed photons, as predicted by the Standard Model, or an excess of right-handed photons, and in what proportions.”

    If the polarisation turns out to be different from the Standard Model prediction, where almost 100% left-handed photons are expected, it could mean a U-turn for particle physics: “If our research eventually shows a right-handed polarisation, or even just a left-handed polarisation different to that predicted by the Standard Model, it would open the door to new physics,” enthuses Olivier Schneider. “In fact, various theories beyond the Standard Model predict other polarisation values for the b → sγ transition. If these predictions were confirmed, it would open up a whole new front for particle physics.” Something which would be music to the ears of many physicists.

    Want to know more?

    fig 1
    Figure 1: the light blue plane is defined by the momenta of the K+, π- and π+ particles. By comparing the number of photons detected above (up) and below (down) this plane, physicists can calculate the Aud asymmetry, which is proportional to the photon polarisation.

    To be more precise, the LHCb collaboration investigated the B+ → K+π-π+γ decay, in which the b → sγ transition takes place. The imbalance between right-handed photons and left-handed photons can be revealed by the “up-down asymmetry (Aud)”, which was measured by comparing the number of photons detected above (up) and below (down) the plane defined by the K+, π- and π+ momenta in the rest frame of these three particles (see Figure 1).

    The Aud asymmetry was calculated for four mass intervals of the Kππ system: between 1100 and 1300 MeV/c2; between 1300 and 1400 MeV/c2; between 1400 and 1600 MeV/c2; and between 1600 and 1900 MeV/c2. These four Aud measurements are globally incompatible with the zero value, with a statistical significance of 5.2 sigma (see Figure 2), which indicates that the photons are indeed polarised.

    fig 2
    Figure 2: measurements of the Aud asymmetry for four mass intervals of the Kππ system.
    Note that the Aud asymmetry does not directly provide the λ polarisation value, but is proportional to it according to the relationship: Aud = k * λ, where k is a constant that is in principle different for each mass interval of the Kππ system. A more detailed study could allow the value of k to be determined for each mass of the Kππ system. This would also allow the polarisation to be calculated.

    See the full article here.

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  • richardmitnick 7:17 pm on April 9, 2014 Permalink | Reply
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    From CERN: “LHCb confirms existence of exotic hadrons” 

    CERN New Masthead

    9 Apr 2014
    Cian O’Luanaigh

    The Large Hadron Collider beauty (LHCb) collaboration today announced results that confirm the existence of exotic hadrons – a type of matter that cannot be classified within the traditional quark model.

    Hadrons are subatomic particles that can take part in the strong interaction – the force that binds protons inside the nuclei of atoms. Physicists have theorized since the 1960s, and ample experimental evidence since has confirmed, that hadrons are made up of quarks and antiquarks that determine their properties. A subset of hadrons, called mesons, is formed from quark-antiquark pairs, while the rest – baryons – are made up of three quarks.

    But since it was first proposed physicists have found several particles that do not fit into this model of hadron structure. Now the LHCb collaboration has published an unambiguous observation of an exotic particle – the Z(4430) – that does not fit the quark model.

    lhcb
    A view of the LHCb experiment at underground Point 8 on the Large Hadron Collider (LHC). The prominent tube is the LHC beam pipe, in which protons circulate at close to the speed of light (Image: Anna Pantelia/CERN)

    The Belle Collaboration reported the first evidence for the Z(4430) in 2008. They found a tantalizing peak in the mass distribution of particles that result from the decays of B mesons. Belle later confirmed the existence of the Z(4430) with a significance of 5.2 sigma on the scale that particle physicists use to describe the certainty of a result.

    LHCb reports a more detailed measurement of the Z(4430) that confirms that it is unambiguously a particle, and a long-sought exotic hadron at that. They analysed more than 25,000 decays of B mesons selected from data from 180 trillion (180 ×1012) proton-proton collisions in the Large Hadron Collider.

    “The significance of the Z (4430) signal is overwhelming – at least 13.9 sigma* – confirming the existence of this state,” says LHCb spokesperson Pierluigi Campana. “The LHCb analysis establishes the resonant nature of the observed structure, proving that this is really a particle, and not some special feature of the data.”

    See the full article here.

    [*I did not realize that a sigma value could be this high, until I discovered this chart here.]

    chart
    Example of two sample populations with the same mean and different standard deviations. Red population has mean 100 and SD 10; blue population has mean 100 and SD 50

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  • richardmitnick 9:10 am on March 7, 2014 Permalink | Reply
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    From CERN Courier: “Charmonium produced in unusual topology sheds light on QCD” 

    CERN LHCb New

    CERN LHCb Original

    The LHCb collaboration has released updated measurements of central exclusive production of the J/ψ and ψ(2S) mesons (LHCb collaboration 2014).

    Central exclusive production is a class of reactions in which one or two particles are produced from a beam collision, but the colliding hadrons emerge intact. At the LHC this leads to an unusual and distinctive topology of low-multiplicity events contained in a small rapidity interval with large rapidity gaps on either side. J/ψ and ψ(2S) mesons are produced when a photon emitted from one proton interacts with a pomeron (a colourless combination of gluons) from the other. Measurements of the process can be used to test QCD predictions – to improve our understanding of the distribution of gluons inside the proton – and are also sensitive to saturation effects.

    graph
    Photoproduction cross-section

    LHCb’s ability to trigger on low-momentum particles and the low number of proton–proton interactions per beam crossing provide an ideal environment to study these processes with particularly low multiplicity. Using data collected in 2011, around 56,000 central exclusive J/ψ and 1500 ψ(2S) mesons have been identified by reconstructing their decays to pairs of muons. While non-resonant backgrounds are very small, the challenge in the analysis is to estimate the larger background that arises when J/ψ and ψ(2S) mesons are produced and one or both of the colliding protons dissociate. As LHCb is instrumented in the forward region mainly, this effect often cannot be detected directly. Instead the collaboration has developed methods to estimate the background rate from the portion of events that are detected.

    The measured cross-sections are compared to theoretical predictions, as well as to photoproduction measurements from the HERA electron–proton collider and from fixed-target experiments. Although these environments are quite different from collisions at the LHC, the underlying process is the same. In the former a photon is emitted from an incoming electron beam, while the latter use photon beams directly.

    The figure shows a model-dependent comparison of the LHCb results with those from the other types of experiment. It plots the photoproduction cross-section as a function of the photon–proton centre-of-mass energy (W). There is a two-fold ambiguity in converting LHCb’s proton–proton differential cross-section to a photoproduction cross-section, corresponding to the photon being either an emitter or a target. This is resolved using recent results from the H1 experiment at HERA (H1 collaboration 2013). The data in the figure show broad consistency over two orders of magnitude, but are in marginal agreement with a single power-law distribution expected from leading-order QCD. Better agreement is provided either at next-to-leading order QCD (Jones et al. 2013) or by including saturation effects (Gay Ducati et al. 2013).

    See the full article here.


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  • richardmitnick 11:27 pm on March 1, 2014 Permalink | Reply
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    From LHCb at CERN: “Welcome to the LHCb experiment” 

    CERN New Masthead

    CERN LHCb Original

    team
    LHCb is an experiment set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today

    Fourteen billion years ago, the Universe began with a bang. Crammed within an infinitely small space, energy coalesced to form equal quantities of matter and antimatter. But as the Universe cooled and expanded, its composition changed. Just one second after the Big Bang, antimatter had all but disappeared, leaving matter to form everything that we see around us — from the stars and galaxies, to the Earth and all life that it supports.

    chart
    LHCb delivered and recorded luminosity in 2012, +1.1/fb indicates recorded luminosity in 2010-2011. The number of proton-proton (pp) collisions visible at LHCb, as well as the numbers of cc and bb quark pair produced within LHCb acceptance in 2010-2012 are also shown.

    28 February 2014: First observation of photon polarisation in b→sγ transition.

    The LHCb Collaboration has submitted today for publication a paper reporting the first observation of photon polarisation in b→sγ transition. The full 3 fb-1 Run 1 data sample was used to obtain this result. The Collaboration has presented already the first evidence for the photon polarization in this process at the summer 2013 conferences using about 2/3 of the whole data sample, see the news of 19 July 2013 for an introduction.

    Photon polarization is the quantum mechanical description of the classical polarized sinusoidal plane electromagnetic wave. Individual photon can have either right or left circular polarization or a superposition of both, read more here.

    The beauty particles decay mainly into charm particles, less frequently into strange particles. About once in every 3000 decays into strange particles a photon is emitted. At the underlying quark level a beauty b quark turns into a strange quark s by emitting a photon γ. This famous b→sγ transition is considered as a very interesting process in which signs of new physics could show up. The first evidence for this process was obtained by the CLEO Collaboration in 1993 and since then it was intensively studied in many experiments. This decays occurs only rarely since it requires a quantum fluctuation where a pair of heavy particles (a top quark and a W boson) appear and then rapidly vanish. The interaction between these particles is such that the emitted photon is expected to be almost 100% (left-handed) polarized. However, since the “virtual” top and W particles are not seen in the detector, they could equally well be replaced by other even heavier particles that are predicted in various theories that go beyond the Standard Model. Such theories have been proposed to address important unresolved questions in particle physics, such as the origin of the imbalance between matter and antimatter seen in the Universe. These models generally predict different values for the photon polarisation, and therefore it is seen as one of the most important measurements that can be made with the latest generation of experiments.

    graphs
    Researchers from the LHCb experiment have now succeeded to observe a non-vanishing value of the polarisation for the first time with a significance of 5.2σ. The analysis is based on nearly 14000 B+→K+π- π+ γ decays, for which the distribution of the γ angle with respect to the normal to the plane defined by the kaon and two pion system is studied in four intervals of the K+π- π+ mass which are shown in the image. The two curves are fits to the data points, allowing photon polarisation (solid blue curve) or setting it to zero (dashed red curve).

    This investigation is conceptually similar to the historical Wu experiment that discovered parity violation by measuring the asymmetry of the direction of a particle emitted in a weak decay.

    See the full article here.

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  • richardmitnick 6:26 am on October 30, 2013 Permalink | Reply
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    From LHCb at CERN: “Welcome to the LHCb experiment” 

    CERN New Masthead

    LHCb is an experiment set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today.

    LHCb

    Fourteen billion years ago, the Universe began with a bang. Crammed within an infinitely small space, energy coalesced to form equal quantities of matter and antimatter. But as the Universe cooled and expanded, its composition changed. Just one second after the Big Bang, antimatter had all but disappeared, leaving matter to form everything that we see around us — from the stars and galaxies, to the Earth and all life that it supports.

    chart
    LHCb delivered and recorded luminosity in 2012, +1.1/fb indicates recorded luminosity in 2010-2011. The number of proton-proton (pp) collisions visible at LHCb, as well as the numbers of cc and bb quark pair produced within LHCb acceptance in 2010-2012 are also shown.

    See the full article here.

    Meet CERN in a variety of places:

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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

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  • richardmitnick 7:28 am on August 9, 2013 Permalink | Reply
    Tags: , , , CERN LHCb,   

    From CERN: “Tracking new physics—horse or zebra?” 

    CERN New Masthead

    9 Aug 2013
    Ashley Jeanne Wennersherron

    If you hear hoof beats, common sense says the cause is more than likely a horse. Yet, the possibility still exists that you’re actually hearing a zebra. Physicists at LHCb are applying that same logic to an unusual finding in a recent analysis of the B meson.

    lhcb
    A view of the LHCb detector. (Image: Maximilien Brice/CERN)

    Around one in every million B mesons decays into an excited kaon and two muons. The decay can occur in several different ways, so physicists classify them in what they call bins. The Standard Model predicts precisely the probability of the angles of these particle decays in each bin. The experiment can measure this probability, so it is an observable. Any difference between the measured observable and prediction could indicate new physics.

    Nicola Serra of LHCb, one of the analysts of the B meson decay data from 2011, and his colleagues found such a difference.

    “Most of the observables we measured in this analysis were close to Standard Model expectations, but a particular observable showed a sizable discrepancy,” he says.

    On the ‘sigma’ scale that physicists use to describe the certainty of a result, Serra’s discrepancy between the expected and the measured result scored 3.7 sigma – there could be evidence for new physics but they need more data to confirm it. When they considered the probability of seeing that particular deviation with all of the data from the entire analysis, the sigma level dropped to 2.8 sigma, translating to a half a percent chance that the discrepancy is caused by statistical fluctuation. (The gold standard for a discovery is 5 sigma.)

    A team of theorists then looked at the same decay and included more observables than the LHCb group did. They found, with this aggregation of many measurements, a consistent pattern of deviations that boosted the sigma to 4.5. That’s almost to the level of discovery, but within parameters that measure the presence of possible new physics. These parameters are more inclusive than those the LHCb team used.

    ‘The theoretical interpretation is very interesting; that can’t be denied,’ says Serra. ‘As an experimentalist, I have to focus on the data itself instead of the interpretation. If we see something that differs from the prediction, it’s crucial to understand if the pattern is real or not.’

    If there’s a deviation from the prediction, experimentalists try to understand if something is wrong with the data. Only once all of the machine systematics and statistics are checked and double-checked can they say, with certainty, that there is a true discrepancy.

    ‘The experimental paper only shows the data. The theory paper is the one that gives the interpretation. Both are pieces of a puzzle and they fit together nicely,’ says Joaquim Matias, a theorist from Autonomous University of Barcelona and one of the paper’s authors. ‘The experimentalists found deviations and the theorists showed that they can be explained within a consistent picture for the first time.’”

    See the full article here.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries


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