Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session JJ: Instrumentation - Beamline |
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Chair: Wouter Deconinck, College of William and Mary Room: Blue Point I |
Friday, October 25, 2013 10:30AM - 10:42AM |
JJ.00001: Proton Polarimetry at RHIC Oleg Eyser The Relativistic Heavy Ion Collider (RHIC) has provided polarized proton-proton collisions to experiments for the past decade with beam polarizations of $P$=55\% at beam energies of up to 255 GeV. The polarization of the proton beams is measured through spin dependent elastic scattering off a polarized hydrogen jet target and similarly monitored with Carbon fiber targets several times throughout the typical 8 hours of a stored RHIC fill. With recent advancements in beam luminosities, the largely increased data sets have enabled unprecedented possibilities to study systematic effects in the polarimeters. We will discuss details of the background contributions, properties of the polarized beams, and their implications on systematic uncertainties. The beam polarization as well as its uncertainty are vital input to the RHIC experiments since they directly affect the scale uncertainty of any polarized observable. [Preview Abstract] |
Friday, October 25, 2013 10:42AM - 10:54AM |
JJ.00002: Precision Electron Beam Polarimetry in Hall C at Jefferson Lab David Gaskell The electron beam polarization in experimental Hall C at Jefferson Lab is measured using two devices. The Hall-C/Basel M\o ller polarimeter measures the beam polarization via electron-electron scattering and utilizes a novel target system in which a pure iron foil is driven to magnetic saturation (out of plane) using a superconducting solenoid. A Compton polarimeter measures the polarization via electron-photon scattering, where the photons are provided by a high-power, CW laser coupled to a low gain Fabry-Perot cavity. In this case, both the Compton-scattered electrons and backscattered photons provide measurements of the beam polarization. Results from both polarimeters, acquired during the Q-Weak experiment in Hall C, will be presented. In particular, the results of a test in which the M\o ller and Compton polarimeters made interleaving measurements at identical beam currents will be shown. In addition, plans for operation of both devices after completion of the Jefferson Lab 12 GeV Upgrade will also be discussed. [Preview Abstract] |
Friday, October 25, 2013 10:54AM - 11:06AM |
JJ.00003: Mott Polarimeter Upgrade at Jefferson Lab M. McHugh, A.K. Opper, J. Grames, M. Poelker, R. Suleiman, C. Horowitz, S. Rhodes, X. Roca Maza, C. Sinclair A Mott polarimeter with a design optimized for 5.5 MeV/c has been in routine use at the CEBAF accelerator for well over a decade, providing polarization measurements approaching 1\% accuracy. Measurements with different target elements (Au, Ag, Cu) over decades of target thicknesses (100 -- 10,000 angstroms), and beam energies between 2 and 8 MeV allow us to determine the effective analyzing power with a high degree of certainty. Recent and planned improvements in our polarimeter configuration, detectors and data acquisition system, coupled with a low 31 MHz repetition rate beam allow us to distinguish and suppress electrons that do not originate from the target foil. This work coupled with a significant effort to produce a detailed GEANT4 model of the polarimeter is part of an effort to determine systematic uncertainties at the level of the theoretically calculated analyzing power. We describe our activities and a series of planned measurements that will allow us to demonstrate and possibly improve the precision and accuracy of polarization measurements at JLab, as required for future parity violation experiments. [Preview Abstract] |
Friday, October 25, 2013 11:06AM - 11:18AM |
JJ.00004: Simulation of the SBS Polarimeter for GEp(5) Experiment Yang Wang Before running experiment GEp(5), we need to predict the characteristic performance of the Focal Plane Polarimeter (FPP) required for the experiment with a simulation of the processes involved. In the simulation, the probability that a proton incident on the polarimeter will generate a single and charged particle which can be detected by the tracking detectors is evaluated. In this talk, the results of the simulation will be displayed, such as the scattering angle distribution, the interaction position and the cone-test result of the detected charged particles; prediction for the probability to detect a single charged track versus incident proton momentum will be shown. Simulation of the conditions of experiment GEp($2\gamma$) was made to check the reliability of the simulation. The difference between the simulation and the experiment data will be discussed. [Preview Abstract] |
Friday, October 25, 2013 11:18AM - 11:30AM |
JJ.00005: Development of a Hydrogen M{\o}ller Polarimeter for Precision Parity-Violating Electron Scattering Valerie M. Gray Parity-violating electron scattering experiments allow for testing the Standard Model at low energy accelerators. Future parity-violating electron scattering experiments, like the P2 experiment at the Johannes Gutenberg University, Mainz, Germany, and the MOLLER and SoLID experiments at Jefferson Lab will measure observables predicted by the Standard Model to high precision. In order to make these measurements, we will need to determine the polarization of the electron beam to sub-percent precision. The present way of measuring the polarization, with M{\o}ller scattering in iron foils or using Compton laser backscattering, will not easily be able to reach this precision. The novel Hydrogen M{\o}ller Polarimeter presents a non-invasive way to measure the electron polarization by scattering the electron beam off of atomic hydrogen gas polarized in a 7\,Tesla solenoidal magnetic trap. This apparatus is expected to be operational by 2016 in Mainz. Currently, simulations of the polarimeter are used to develop the detection system at College of William \& Mary, while the hydrogen trap and superconducting solenoid magnet are being developed at the Johannes Gutenberg University, Mainz. I will discuss the progress of the design and development of this novel polarimeter system. [Preview Abstract] |
Friday, October 25, 2013 11:30AM - 11:42AM |
JJ.00006: Tagger Microscope Development and Construction for the GlueX Experiment Alex Barnes, James McIntyre, Richard Jones The GlueX experiment will use a 9 GeV linearly polarized photon beam to search for mesons with gluonic excitations, and measure their spectrum and couplings. To create a polarized photon beam, the 12 GeV electron beam from CEBAF will pass through a 20$\mu$m thick diamond wafer and undergo coherent bremsstrahlung. In order to know the energy of the photon the post-bremsstrahlung electron energy is analyzed in a dipole spectrometer. A highly segmented tagging detector called the microscope will intercept the electrons within the region 3.0-3.6 GeV, to permit tagging of photons in the region of the coherent peak 8.4-9.0 GeV at rates up to $10^{8}$ $\gamma$/s. These electrons are incident on scintillating fibers which provide 4 MeV energy resolution and propagate the signal to Silicon Photomultiplier (SiPM) sensors that are mounted on custom high speed circuit boards. The scintillating fibers and electronics are under construction at the University of Connecticut. The development and construction of the Tagger Microscope and the electronics will be presented. [Preview Abstract] |
Friday, October 25, 2013 11:42AM - 11:54AM |
JJ.00007: The JLAB Hall D Photon Beamline Alexander Somov The CEBAF energy upgrade to 12 GeV provides an opportunity to produce high-energy photon beams which will be used for a new generation of photoproduction experiments. The GlueX, one of the flagship experiments of the 12 GeV program, will make use of a linearly polarized photon beam to search for mesons with gluonic excitations. The photon beam will be produced in the coherent bremsstrahlung process by 12 GeV electrons incident on a thin radiator. The fraction of linearly polarized photons can be increased by passing the photon beam through a two-stage collimation system. The energy of each photon in the energy range of interest can be determined by measuring the momentum of the recoil (``tagged'') electron in the tagger broad-band hodoscope or the microscope detectors. The photon flux and the polarization fraction can be measured using the pair spectrometer (and the triplet production polarimeter). The main Hall D photon beamline components will be presented. [Preview Abstract] |
Friday, October 25, 2013 11:54AM - 12:06PM |
JJ.00008: The GlueX Start Counter Eric Pooser The GlueX experiment will be one of the largest photo-production facilities in the world and is currently under construction. This experiment will use the coherent bremsstrahlung technique to produce a 9 GeV linearly polarized photon beam incident on a liquid H$_{2}$ target. A Start Counter detector has been designed to identify the accelerator electron beam buckets, approximately 2 ns apart, and to provide accurate timing information. It is now under construction at Florida International University (FIU). This detector is designed to operate at photon intensities of up to 10$^{8}\gamma$/s in the coherent peak. It consists of an array of 30 individual scintillators with ``pointed'' ends that bend toward the beam at the downstream end. SiPM detectors, which comprise the readout system, are placed as close as possible at the end of each scintillator. The EJ-200 scintillator is best suited for the timing studies with a fast decay time of 2.0 ns. The physical properties of the scintillators, configured to the desired geometry, have been studied extensively at FIU. Geant4 simulations are currently underway to replicate and to understand our experimental results. The results of these timing studies and simulations are discussed. [Preview Abstract] |
Friday, October 25, 2013 12:06PM - 12:18PM |
JJ.00009: Next-Generation Polarized $^3$He Targets for Electron Scattering Experiments Yunxiao Wang, Maduka Kaluarachchi, Daniel Matyas, Gordon Cates A next-generation spin-exchange polarized $^3$He target will be described that is being developed for high-luminosity experiments that will follow the JLab $\rm12\,GeV$ upgrade, including a measurement of neutron elastic form-factor ratio $G_E^n/G_M^n$, up to 10$\,GeV^2$. Spin-exchange polarized $^3$He target cells have historically had two chambers: a pumping chamber, in which the $^3$He is polarized, and a target chamber, through which the electron beam passes. In the past, the mixing of gas between the two chambers has been due to diffusion through a single {\it transfer tube}, something that limits polarization at high electron-beam currents. In the next-generation targets, two transfer tubes will be used, one of which is heated, in order to produce well-controlled and rapid convective flow. Further innovations include the use of two pumping chambers, so that gas can be polarized more quickly, and metal end windows. Space limitations make it challenging to limit the magnetic-field inhomogeneities experienced by these new larger targets, so particular effort is going into understanding and controlling polarization losses during polarimetry measurements. Results will be presented on prototype targets developed for a measurement of the spin asymmetry $A_1^n$ in JLab's Hall A. [Preview Abstract] |
Friday, October 25, 2013 12:18PM - 12:30PM |
JJ.00010: Development of the Low Granularity Pair Spectrometer counters in Hall D at Jlab Nathan Dzbenski, Tamara McNeel, Kyle Bowman The pair spectrometer in the photon beam line of Hall D at Jlab is designed to calibrate and monitor the linear beam polarization and the relative tagging efficiency of the photon tagger via a well known electron-positron pair production measurement. This system includes a thin foil converter, a dipole magnet, and two identical left and right arm detector packages. Each detector package covers the electron or position energy from 3 GeV to 6.25 GeV, which consists of a front detector array for fine position resolution and a back scintillating hodoscopes for fast timing. This presentation will focus on the development and construction of the Low Granularity Pair Spectrometer counters. [Preview Abstract] |
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