Identification of Upsilon Particles Using the Preshower Detector in STAR

1. Identification of Upsilon Particles Using the Preshower Detector in STAR Jay Dunkelberger, University of Florida 2007 Texas A&M Cyclotron Institute REU Advisor: Dr. Saskia Mioduszewski Importance of Heavy Quarkonia Quark-Gluon Plasma Barrel Electromagnetic Calorimeter • In the QGP it is expected that the formation of heavy quarkonia will be suppressed • This has already been observed at lower energies for J/ψ particles, however the measurement of J/ψ suppression is complicated, at RHIC energies, by the competing recombination of J/ψ particles • The upsilon particle has a much larger mass than J/ψ, greatly reducing the chance of recombination. The relative suppressions of these particles could be an important sign of the QGP • Quarks are the constituents of all hadronic matter • They interact with each other by the strong force which is mediated by gluons • Quarks are confined to exist in either pairs (mesons) or triplets (baryons) • At temperatures above 10¹² K • the boundaries of various • hadrons overlap • Quarks enter a deconfined • state and become a new phase of matter called the Quark-Gluon Plasma (QGP) • Consists of 4800 towers covering the entire azimuthal • range • Each tower is made up of 21 layers of Pb and scintillator • Particles interact with the Pb layers and • produce showers which are converted • to light in the scintillator • 84% of electrons shower in the first two • layers of the BEMC as opposed to only • 6% of hadrons • The first two layers of each tower have • their values read out separately and • form the Preshower detector Detecting Upsilon Particles An Illustration of Quark-Gluon Plasma We looked for Υ particles that decayed to a positron and an electron. We used a combinatorial method to generate opposite-sign pairs and created an invariant mass plot. We then used the same method making like-sign pairs to create a background. We incorporated the BPRS into our analysis to reduce the number of hadrons in our calculation. Finally, we subtracted out the background and looked for an Υ mass peak at ~9.5 GeV/c². This analysis requires a great deal of statistics and is ongoing. BEMC Tower The STAR Experiment Barrel Preshower Detector (BPRS) • Located at Brookhaven National Laboratory as part of the Relativistic Heavy Ion Collider (RHIC) • Au nuclei are accelerated to .99995c and • collide head-on inside the detector, possibly • resulting in the creation of QGP • STAR has several subsystems (e.g., Time • Projection Chamber, EM Calorimeter) to track the • products of these collisions and look for signs of • the QGP The BPRS allows for the reduction of hadronic background by taking advantage of the fact that electrons generally shower earlier than hadrons. The BPRS has not yet been used as a part of STAR’s analysis. We began work on a quality assurance analysis to include the BPRS in STAR’s run status table database. Reduction of Hadronic Background Layout of RHIC Diagram of the STAR Detector A rough analysis of the Preshower detector’s effectiveness. The graphs show energy loss with distance (dE/dx) as measured in STAR’s Time Projection Chamber. The right is with a cut on a signal in the Preshower while the left is without. The red peak results from hadrons while the blue is from electrons. Integrating these Gaussians showed that the relative yield of electrons increased by about a factor of two when the Preshower is included. A comparison of the raw ADC output of the BEMC and BPRS detectors, which are used in STAR’s status table package. Status tables are needed to catalogue towers that are giving erroneous data.