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  • richardmitnick 12:50 pm on January 4, 2019 Permalink | Reply
    Tags: , Nuclear phase diagram, , , , , Star detector, Upgrade of the Time Projection Chamber (TPC)   

    From Brookhaven National Lab: “Startup Time for Ion Collisions Exploring the Phases of Nuclear Matter” 

    From Brookhaven National Lab

    January 4, 2019
    Karen McNulty Walsh
    kmcnulty@bnl.gov
    (631) 344-8350 or

    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    1
    The Relativistic Heavy Ion Collider (RHIC) is actually two accelerators in one. Beams of ions travel around its 2.4-mile-circumference rings in opposite directions at nearly the speed of light, coming into collision at points where the rings cross.

    BNL RHIC Campus

    January 2 marked the startup of the 19th year of physics operations at the Relativistic Heavy Ion Collider (RHIC), a U.S. Department of Energy Office of Science user facility for nuclear physics research at Brookhaven National Laboratory. Physicists will conduct a series of experiments to explore innovative beam-cooling technologies and further map out the conditions created by collisions at various energies. The ultimate goal of nuclear physics is to fully understand the behavior of nuclear matter—the protons and neutrons that make up atomic nuclei and those particles’ constituent building blocks, known as quarks and gluons.

    BNL RHIC Star detector

    2
    The STAR collaboration’s exploration of the “nuclear phase diagram” so far shows signs of a sharp border—a first-order phase transition—between the hadrons that make up ordinary atomic nuclei and the quark-gluon plasma (QGP) of the early universe when the QGP is produced at relatively low energies/temperatures. The data may also suggest a possible critical point, where the type of transition changes from the abrupt, first-order kind to a continuous crossover at higher energies. New data collected during this year’s run will add details to this map of nuclear matter’s phases.

    Many earlier experiments colliding gold ions at different energies at RHIC have provided evidence that energetic collisions create extreme temperatures (trillions of degrees Celsius). These collisions liberate quarks and gluons from their confinement with individual protons and neutrons, creating a hot soup of quarks and gluons that mimics what the early universe looked like before protons, neutrons, or atoms ever formed.

    “The main goal of this run is to turn the collision energy down to explore the low-energy part of the nuclear phase diagram to help pin down the conditions needed to create this quark-gluon plasma,” said Daniel Cebra, a collaborator on the STAR experiment at RHIC. Cebra is taking a sabbatical leave from his position as a professor at the University of California, Davis, to be at Brookhaven to help coordinate the experiments this year.

    STAR is essentially a house-sized digital camera with many different detector systems for tracking the particles created in collisions. Nuclear physicists analyze the mix of particles and characteristics such as their energies and trajectories to learn about the conditions created when ions collide.

    By colliding gold ions at various low energies, including collisions where one beam of gold ions smashes into a fixed target instead of a counter-circulating beam, RHIC physicists will be looking for signs of a so-called “critical point.” This point marks a spot on the nuclear phase diagram—a map of the phases of quarks and gluons under different conditions—where the transition from ordinary matter to free quarks and gluons switches from a smooth one to a sudden phase shift, where both states of matter can coexist.

    STAR gets a wider view

    STAR will have new components in place that will increase its ability to capture the action in these collisions. These include new inner sectors of the Time Projection Chamber (TPC)—the gas-filled chamber particles traverse from their point of origin in the quark-gluon plasma to the sensitive electronics that line the inner and outer walls of a large cylindrical magnet. There will also be a “time of flight” (ToF) wall placed on one of the STAR endcaps, behind the new sectors.

    “The main purpose of these is to enhance STAR’s sensitivity to signatures of the critical point by increasing the acceptance of STAR—essentially the field of view captured in the pictures of the collisions—by about 50 percent,” said James Dunlop, Associate Chair for Nuclear Physics in Brookhaven Lab’s Physics Department.

    “Both of these components have large international contributions,” Dunlop noted. “A large part of the construction of the iTPC sectors was done by STAR’s collaborating institutions in China. The endcap ToF is a prototype of a detector being built for an experiment called Compressed Baryonic Matter (CBM) at the Facility for Antiproton and Ion Research (FAIR) in Germany. The early tests at RHIC will allow CBM to see how well the detector components behave in realistic conditions before it is installed at FAIR while providing both collaborations with necessary equipment for a mutual-benefit physics program,” he said.

    Tests of electron cooling

    3
    A schematic of low-energy electron cooling at RHIC, from right: 1) a section of the existing accelerator that houses the beam pipe carrying heavy ion beams in opposite directions; 2) the direct current (DC) electron gun and other components that will produce and accelerate the bright beams of electrons; 3) the line that will transport and inject cool electrons into the ion beams; and 4) the cooling sections where ions will mix and scatter with electrons, giving up some of their heat, thus leaving the ion beam cooler and more tightly packed.

    Before the collision experiments begin in mid-February, RHIC physicists will be testing a new component of the accelerator designed to maximize collision rates at low energies.

    “RHIC operation at low energies faces multiple challenges, as we know from past experience,” said Chuyu Liu, the RHIC Run Coordinator for Run 19. “The most difficult one is that the tightly bunched ions tend to heat up and spread out as they circulate in the accelerator rings.”

    That makes it less likely that an ion in one beam will strike an ion in the other.

    To counteract this heating/spreading, accelerator physicists at RHIC have added a beamline that brings accelerated “cool” electrons into a section of each RHIC ring to extract heat from the circulating ions. This is very similar to the way the liquid running through your home refrigerator extracts heat to keep your food cool. But instead of chilled ice cream or cold cuts, the result is more tightly packed ion bunches that should result in more collisions when the counter-circulating beams cross.

    Last year, a team led by Alexei Fedotov demonstrated that the electron beam has the basic properties needed for cooling. After a number of upgrades to increase the beam quality and stability further, this year’s goal is to demonstrate that the electron beam can actually cool the gold-ion beam. The aim is to finish fine-tuning the technique so it can be used for the physics program next year.

    Berndt Mueller, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics, noted, “This 19th year of operations demonstrates once again how the RHIC team — both accelerator physicists and experimentalists — is continuing to explore innovative technologies and ways to stretch the physics capabilities of the most versatile particle accelerator in the world.”

    See the full article here .


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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 2:18 pm on July 3, 2017 Permalink | Reply
    Tags: A new Fast Interaction Trigger (FIT) system, , ALICE detector upgrades enter production phase, ALICE will be able to further investigate the properties of Quark-Gluon Plasma in pp p-Pb and Pb-Pb collisions, ALPIDE pixel chips will guarantee higher granularity and reduced material budget, , Introduction of a Muon Forward Tracker (MFT), Replacement of the Inner Traking System (ITS), Run 3 of LHC after the two-year long shut down (LS2) that will start at the end of 2018, Upgrade of the Time Projection Chamber (TPC)   

    From ALICE at the LHC at CERN: “ALICE detector upgrades enter production phase” 

    CERN
    CERN New Masthead

    16 June 2017
    Virginia Greco

    The activities for the upgrade of the ALICE detector and instrumentation proceed on schedule. Validated the prototypes, now the components have to be produced, assembled and tested in order to be ready for installation during the next 2-year long shut down of LHC (2019-2020).

    1
    Scheme of the upgrade of the ALICE detector. [From Zhongbao Yin’s talk at the LHCP2017 Conference]

    While the extended end-of-year shutdown has concluded and the LHC has been switched on again, the activities for the upgrade of the ALICE detector have entered a new phase. The prototypes of the various new components have been tested and validated, so that now production can start.

    This major upgrade will increase the performance of the detector in order to fully exploit the higher interaction rate of about 50 kHz that is expected in Run 3 of LHC, after the two-year long shut down (LS2) that will start at the end of 2018.

    The upgraded ALICE detector will be able to cope with the increased readout rate and will provide better vertex resolution and tracking efficiency at low pT. At the same time, it will preserve its excellent particle identification properties.

    The upgrade programme foresees the replacement of the Inner Traking System (ITS) associated to a new beam pipe with a smaller diameter, the introduction of a Muon Forward Tracker (MFT), the upgrade of the Time Projection Chamber (TPC), and the substitution of the V0 and T0 detectors with a new Fast Interaction Trigger (FIT) system. The readout electronics has also been partially redesigned, together with the Central Trigger Processor (CTP) and the DAQ and Offline Data systems.

    The new ITS will be a 7-layer barrel structure made of carbon fiber and equipped with dedicated silicon pixel sensors (ALPIDE), replacing the previous 6-layer detector that used strip, drift and pixel sensors. Being smaller (approximately 30 um x 30 um), thinner (50 um on the inner barrel and 100 um on the outer) and monolithic (sensor and readout chip are integrated in the same silicon structure), the ALPIDE pixel chips will guarantee higher granularity and reduced material budget. As a result, the track position resolution at the primary vertex will be improved by a factor of 3 with respect to the present detector.

    The ALPIDE chip is employed as well in the Muon Forward Tracker (MFT), which is a new vertex detector for muons; combined with the existing Muon Spectrometer, it will allow precise identification of secondary vertices and better mass resolution. Composed of 5 disks of silicon pixel detectors, it will be placed between the central barrel detector and the hadron absorber of the Muon Spectrometer.

    The upgrade of the TPC involves replacing the multi-wire chambers, which limit the event readout rate to 3.5 kHz, with quadruple-GEM chambers designed to minimize ion back-flow and to allow continuous, untriggered readout. New front-end electronics will be also needed. The new TPC will be able to operate at 50 kHz preserving its current performance in terms of tracking, momentum resolution and particle identification.

    The FIT will be dedicated to forward trigger and to the measurement of a number of parameters, including luminosity, collision time, as well as multiplicity and centrality of heavy ion collisions. This new detector, which will replace the existing V0 and T0, will consist of two arrays of Cherenkov radiators, equipped with micro-channel plate detectors and photomultipliers, and of a single, large-size scintillator ring. The FIT will provide larger acceptance and finer segmentation than the present two, without compromising the time resolution.

    As a consequence of the increased luminosity and interaction rate of LHC, a significantly larger amount of data will have to be processed and selected. Thus, a new Central Trigger Processor and a powerful data processing system integrating some online and offline functionalities have been designed as well.

    With this upgraded detector and instrumentation, ALICE will be able to further investigate the properties of Quark-Gluon Plasma in pp, p-Pb and Pb-Pb collisions. In particular, the goal for next runs is to perform high-precision measurements that will shed light on thermodynamics, evolution and flow of the QGP, as well as on parton interactions with the medium.

    See the full article here .

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