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  • richardmitnick 11:46 am on July 7, 2021 Permalink | Reply
    Tags: "ALICE is “FIT” for Run 3 after last new subdetector installation", , ALICE at CERN (CH), , , , ,   

    From ALICE at CERN (CH) : “ALICE is “FIT” for Run 3 after last new subdetector installation” 

    From ALICE at CERN (CH)

    6 July, 2021

    1
    The FIT detector (Fast Interaction Trigger) was installed in the ALICE cavern during LS2 in June 2021 (Image: CERN)

    The ALICE detector is being steadily reassembled after three years of dismantling, building, testing and reinstallation of the subdetectors. This major LHC experiment received its last new subdetector on Monday, 21 June 2021, when the Fast Interaction Trigger (FIT) was lowered into the Point 2 cavern. The 300-kg disk, together with the three other FIT arrays, will serve as an interaction trigger, online luminometer, initial indicator of the vertex position and forward multiplicity counter. It is now secured next to the central tracking detectors inside the L3 magnet.

    This polyvalent subdetector was conceptualised, reviewed and approved by the ALICE Technical Board in early 2013. It is the fruit of an intense R&D effort involving prototype tests at the Proton Synchrotron. Among the 60-plus scientists from 17 institutions who contributed to the FIT design, construction, testing and installation, the Muscovite team at the Russian Institute for Nuclear Research faced major challenges with the design of the new, fully digital, front-end electronics and readout system.

    FIT relies on three state-of-the-art detector technologies underpinning components grouped into five arrays surrounding the LHC beamline, at -1, +3, +17, and -19 metres from the interaction point. The diversity of the detection techniques and the scattered positions are needed in order to fulfil the subdetector’s many required functionalities. Among the three components that make up the FIT detector, the FT0 is the fastest: comprising 208 optically separated quartz radiators, its expected time resolution for high-multiplicity heavy-ion collisions is about 7 picoseconds, ranking FIT among the fastest detectors in high-energy physics experiments. This impressively precise timing is crucial for online vertex determination and for identifying charged lepton and hadron species using time-of-flight.

    The second component, a segmented scintillator called FV0, innovates with a novel light-collection scheme designed and manufactured at UNAM, Mexico. The largest of the three components, the FV0 makes use of its size to provide optimal acceptance, which is vital for extracting centrality and determining the event plane – key parameters characterising a heavy-ion collision.

    Finally, the Forward Diffractive Detector (FDD), consisting of two nearly identical scintillator arrays, can tag photon-induced or diffractive processes by recognising the absence of activity in the forward direction. It also serves as a background monitoring tool.

    Now that it is soundly wedged inside the ALICE detector, the FIT is expected to stay there until the end of Run 4. Its installation, which comes after that of the Time Projection Chamber, the Muon Forward Tracker and the Inner Tracking System, brings ALICE one step closer to the end of LS2 activities. The closing of the L3 magnet door and the installation of the final station of the muon spectrometer are scheduled to take place by the end of July and the end of August, respectively. Then a few months of commissioning will take ALICE to the start of Run 3, scheduled for the end of February 2022.

    See the full article here .


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  • richardmitnick 4:11 pm on June 10, 2021 Permalink | Reply
    Tags: "ALICE finds that charm hadronisation differs at the LHC", , ALICE at CERN (CH), , , , ,   

    From ALICE at CERN (CH) : “ALICE finds that charm hadronisation differs at the LHC” 

    From ALICE at CERN (CH)

    10 June, 2021
    Andrea Dainese

    New measurements by the ALICE collaboration show that the way charm quarks form hadrons in proton-proton collisions differs significantly from expectations based on electron collider measurements.

    Quarks are among the elementary particles of the Standard Model of Particle Physics.

    Besides up and down quarks, which are the basic building blocks of ordinary matter in the Universe, four other quark flavours exist and are also abundantly produced in collisions at particle accelerators like the CERN Large Hadron Collider. Quarks are not observed in isolation due to a fundamental aspect of the strong interaction, known as colour charge confinement. Confinement requires particles that carry the charge of the strong interaction, called colour, to form states that are colour-neutral. This in turn forces quarks to undergo a process of hadronisation, i.e. to form hadrons, which are composite particles mostly made of a quark and an antiquark (mesons) or of three quarks (baryons). The only exception is the heaviest quark, the top, which decays before it has time to hadronise.

    At particle accelerators, quarks with a large mass, such as the charm quark, are produced only in the initial interactions between the colliding particles. Depending on the type of beam used, these can be electron-positron, electron-proton or proton-proton collisions (as at the LHC). The subsequent hadronisation of charm quarks into mesons (D0, D+, Ds) or baryons (𝛬c, 𝛯c, …) occurs on a long space-time scale and was considered to be universal – that is, independent of the species of the colliding particles – until the recent findings by the ALICE collaboration.

    The large data samples collected during Run 2 of the LHC allowed ALICE to count the vast majority of charm quarks produced in the proton-proton collisions by reconstructing the decays of all charm meson species and of the most abundant charm baryons (𝛬c and 𝛯c). The charm quarks were found to form baryons almost 40% of the time, which is four times more often than what was expected based on measurements previously made at colliders with electron beams (e+e- and ep in the figure below).

    These measurements show that the process of colour-charge confinement and hadron formation is still a poorly understood aspect of the strong interaction. Current theoretical explanations of baryon enhancement include the combination of multiple quarks produced in proton-proton collisions and new mechanisms in the neutralisation of the colour charge. Additional measurements during the next run of the LHC will allow these theories to be scrutinised and further our knowledge of the strong interaction.

    See the full article here .


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  • richardmitnick 11:40 am on December 9, 2020 Permalink | Reply
    Tags: "ALICE opens avenue for high-precision studies of strong force", , ALICE at CERN (CH), , , One of the biggest challenges in nuclear physics today is understanding the strong interaction between hadrons with different quark content from first principles., , , , The collaboration shows how proton-proton collisions at the Large Hadron Collider can reveal the strong interaction between composite particles called hadrons.   

    From ALICE at CERN (CH): “ALICE opens avenue for high-precision studies of strong force” 

    From From ALICE at CERN (CH)

    December 10, 2020

    1
    An artist’s impression of the ALICE study of the interaction between the rarest of the hyperons, Omega (Ω) hyperon (left), which contains three strange quarks, and a proton (right).

    The collaboration shows how proton-proton collisions at the Large Hadron Collider can reveal the strong interaction between composite particles called hadrons.

    In a paper published today in Nature, the ALICE collaboration describes a technique that opens a door to high-precision studies at the Large Hadron Collider (LHC) of the dynamics of the strong force between hadrons.

    Hadrons are composite particles made of two or three quarks bound together by the strong interaction, which is mediated by gluons. This interaction also acts between hadrons, binding nucleons (protons and neutrons) together inside atomic nuclei. One of the biggest challenges in nuclear physics today is understanding the strong interaction between hadrons with different quark content from first principles, that is, starting from the strong interaction between the hadrons’ constituent quarks and gluons.

    Calculations known as lattice quantum chromodynamics (QCD) can be used to determine the interaction from first principles, but these calculations provide reliable predictions only for hadrons containing heavy quarks, such as hyperons, which have one or more strange quarks. In the past, these interactions were studied by colliding hadrons together in scattering experiments, but these experiments are difficult to perform with unstable (i.e. rapidly decaying) hadrons such as hyperons. This difficulty has so far prevented a meaningful comparison between measurements and theory for hadron-hadron interactions involving hyperons.

    Enter the new study from the collaboration behind ALICE, one of the main experiments at the LHC. The study shows how a technique based on measuring the momentum difference between hadrons produced in proton-proton collisions at the LHC can be used to reveal the dynamics of the strong interaction between hyperons and nucleons, potentially for any pair of hadrons. The technique is called femtoscopy because it allows the investigation of spatial scales close to 1 femtometre (10−15 metres) – about the size of a hadron and the spatial range of the strong-force action.

    This method has previously allowed the ALICE team to study interactions involving the Lambda (Λ) and Sigma (Σ) hyperons, which contain one strange quark plus two light quarks, as well as the Xi (Ξ) hyperon, which is composed of two strange quarks plus one light quark. In the new study, the team used the technique to uncover with high precision the interaction between a proton and the rarest of the hyperons, the Omega (Ω) hyperon, which contains three strange quarks.

    “The precise determination of the strong interaction for all types of hyperons was unexpected,” says ALICE physicist Laura Fabbietti, professor at the Technical University of Munich. “This can be explained by three factors: the fact that the LHC can produce hadrons with strange quarks in abundance, the ability of the femtoscopy technique to probe the short-range nature of the strong interaction, and the excellent capabilities of the ALICE detector to identify particles and measure their momenta.”

    “Our new measurement allows for a comparison with predictions from lattice QCD calculations and provides a solid testbed for further theoretical work,” says ALICE spokesperson Luciano Musa. “Data from the next LHC runs should give us access to any hadron pair.”

    “ALICE has opened a new avenue for nuclear physics at the LHC – one that involves all types of quarks,” concludes Musa.

    /Public Release. The material in this public release comes from the originating organization and may be of a point-in-time nature, edited for clarity, style and length. View in full here.

    See the full article here .


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    Please help promote STEM in your local schools.

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