High Energy Nuclear Physics
It was my prividledge to work for Dr. Jamie Nagle at the University of Colorado at Boulder. Under his supervision, I engaged in hardware development for the PHENIX collaboration and developed analysis algorithm's for data analysis.
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The Hadronic Calorimeter
PHENIX, an experiment at the Relativistic Heavy Ion Collider (RHIC) seeks to explore the properties of the quark gluon plasma by accelerating and colliding heavy nuclei. sPHENIX is a new detector being built to replace PHENIX and further investigate this fluid's properties. The sPHENIX detector at RHIC will contain an electromagnetic (EMCal) and a hadronic (HCal) calorimeter for the detection of particles ejected in heavy ion collisions. The hadronic calorimeter will be composed of layers of steel plates that alternate with plastic scintillators. Within the scintillator panels, wavelength shifting fiber optic cables are embedded and coupled to silicon photo multipliers (SiPMs) which record the total energy deposited in the detector for each event.
I attended Fermi National Accelerator Laboratory i(FNAL) n April 21 - 24, 2016 to test the prototype hadronic calorimeter that I was involved in developing and constructing as part of my Honors Thesis Project at CU-Boulder. At FNAL I I learned how to operate the DAQ (i.e. I ran the accelerator) and became familiar with the general details of how an accelerator works. The results of these tests are published in IEEE.
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In addition to designing and testing components of the HCal, I developed an automated testing stand that was used to test the performance of each individual scintillating tile destined for the sPHENIX HCal. The test stand that I I developed measured the signal uniformity of each panel by flashing an array of 405nm LED's and recording SiPM counts at that position. One such sensitivity scan can be seen below.
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Event Pile-Up Algorithm
While a member of the Nagle laboratory, I developed an algorithm to flag events with multiple interactions by examining the time dependence of data from the two Beam-Beam Counters (BBCs)– detectors surrounding the beam pipe on opposite ends of the interaction region, providing coverage for 3.1 < |η| < 3.9. Each BBC is an array of 64 PMTs arranged radially surrounding the beam pipe at each end of PHENIX that detects the time each tube is hit by a particle and integrates the charge deposited. The algorithm I developed weights the PMT time distribution of one bunch crossing by the charge detected and looks for two independent signals. The algorithms are tested with data, in which events with double interactions are artificially produced using data from a low collision frequency run.
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Event pile up is a problem that all collider experiments must account for, if they are to take meaningful data. Many experiments rely on a silicon vertex tracker directly surrounding the interaction region to identify multiple primary vertices within one bunch crossing (illustrated in ). This method, however, is vulnerable to several negative effects. High energy collisions produce a large number of high energy particles that expand out from the interaction region to the outer edges of the detector. Over an experiment’s full lifetime, billions of such events can degrade the silicon by punching holes in the detector. Eventually, given enough radiation damage, a silicon tracker can even be made obsolete. Secondly, solid state tracking detectors are not ideal for identifying double events because they are costly and difficult to make. The high cost results in silicon vertex tracking detectors having a comparatively small coverage (z = 0±10 cm in PHENIX) compared to the overall length of the experiment. One can easily imagine a double event where both events lie at opposite ends of the interaction region but their averaged position appears to be at the center of the experiment.
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The double event algorithm I developed does not rely on delicate silicon vertex detectors with restricted coverage and will work as long as the experiment is equipped with spectator ion counters at opposite ends of the interaction region. This algorithm was pushed to the PHENIX collaboration library where its efficacy was proven in the analysis of nearly 30 different experiments, ultimately in a series of experiments reported in a Nature Physics paper.
