1. Forward Detectors and Measurement of Proton-Antiproton Collision Rates by Zachary Einzig, Mentor Michele Gallinaro INTRODUCTION THE DETECTORS EXPERIMENTAL SETUP ACKNOWLEDGEMENTS The Tevatron collider at Fermilab accelerates protons (p) and antiprotons (  p) in opposite directions. The proton beam and the antiproton beams are squeezed together at two points: CDF and D0. It is at these interaction points that collisions occur. When a head-on collision takes place, the energies of the proton and antiproton are available to make a variety of particles with high transversal momentum and which are tracked by several detectors surrounding the interaction point. The CDF detector at Fermilab. The scintillator is a plastic doped with a material that is easily excited by a charged particle. When the charged particle traverses the scintillator, it excites an electron, which then drops back to a normal state and releases a photon. Many photons are produced by one charged particle. The scintillator is attached to a light guide which transports the photons produced in the scintillator to the PMT. Light (photons) that enters one end is internally reflected to the other end with high efficiency. Photons arriving from the light guide are focused onto the PMT photocathode. Upon arrival, a photon knocks out an electron. The electrons are multiplied through a series of dynodes in the PMT. A voltage is applied to the PMT and distributed to the dynodes to create a gradient. The electrons travel down the gradient releasing more electrons every time they hit a dynode. Top Counter Bottom Counter Test Counter Computer INTERACTION POINT coincidence We test our counters by seeing how they respond to charged particles. For this purpose cosmic rays are used. The top and bottom counter serve as triggers, selecting muons from cosmic rays. When a muon goes through the counter, the signal is carried to the discriminator. When there is a coincidence between top and bottom counters (because of a muon) the discriminator opens the gate. Whenever the gate is open, the computer records the signal from the test counter through an analog-to-digital converter (ADC). The ADC measures the charge of the signal (the conversion is 0.25 pc/ADC count). ADC Dr. Michele Gallinaro Professor Professor Konstantin Goulianos Outreach Program D RESULTS ADC spectrum for one of the counters tested. The response of the detector is recorded by the ADC and the spectrum analyzed with the program ROOT. The position (MPV) and the width (sigma) of the peak corresponding to a minimum ionizing particle (MIP) traversing the detectors is studied. The position of the MIP peak is proportional of the gain of the PMT.The events at low ADC counts represent the background (pedestal). CONCLUSIONS MIP peak position at different PMT voltages. Each detector may have different gain at the same voltage; however, it is important to have uniformity among the BSC detectors. This graph shows how the position of the MIP peak changes with voltage (HV). Therefore, by adjusting the HV it is possible to equalize the counters response and thus have a uniform response. I have studied different characteristics of the BSC detectors, assembled them, and evaluated their performances. I made several graphs of MIP peak position, MIP peak vs. voltage and compared them. Though the points differ, the slopes are consistent within the uncertainty. This means that although the specific gains of the PMTs are different, the way they react to increasing voltages is the same. From the ADC spectra, it is possible to conclude that the BSC detectors are able to give a clear separation between signal and background when a muon is passing through it. The signal is well above the background noise and the trigger level can be set above the pedestal to only select particles traversing the detectors. A study of the performance of the BSC detectors installed at CDF to measure the beam loss and proton-antiproton collision rates was conducted. The beam loss provides a quality control of the data-taking at the Tevatron and at CDF. The beam loss is measured by timing the signals appropriately, before the collisions occurs. A linear response of the coincidence rate with the instantaneous luminosity indicates the detectors are performing well and can provide an independent measurement of the collision rates. Top: Cross section of the beamline near the interaction point. Left: BSC detectors surrounding the beam pipe The detectors studied, the beam shower counters (BSC), are scintillator detectors and are used at the CDF detector at Fermilab. These are able to detect charged particles. They are made of three parts: a scintillator, a light guide, and a photomultiplier tube (PMT). open gate trigger gate test signal However, most of the collisions are soft, resulting in particles produced in the forward direction. The detectors studied are in the forward regions of the interaction point and are used to determine rates of beam losses in order to monitor the quality of the beam, and to measure the collision rates. The coincidence of the signals of the BSC counters placed on opposite sides of the interaction point is a result of a p collision. The different colors correspond to different run numbers. The coincidence rate (N) is related to the instantaneous luminosity (L) through the relation N=  L  where   is the cross section accepted by the counters. The coincidence of the signals of the BSC counters placed on opposite sides of the interaction point is a result of a p  p collision. The different colors correspond to different run numbers. The coincidence rate (N) is related to the instantaneous luminosity (L) through the relation N=  L  where   is the cross section accepted by the counters. BSC coincidence rate at different instantaneous luminosity from colliding beam data at CDF. Proton and antiproton beam loss rates measured with the BSC counters at CDF. Beam loss rates are measured at CDF to monitor the quality of the beam. p loss rate  p loss rate