Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session S3: Electron Beams for Parity ExperiementsInvited Session
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Sponsoring Units: DNP DPB Chair: Gordon Cates, University of Virginia Room: Ballroom B |
Monday, April 18, 2016 1:30PM - 2:06PM |
S3.00001: Polarized electrons for parity violation experiments at Jefferson Lab. Invited Speaker: Matthew Poelker Since 1998, noteworthy electron scattering experiments at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab have employed parity violation as a tool to probe hadronic structure. These experiments, together with experiments performed at other labs, have quantified the strange quark-antiquark pair contribution to the elastic electroweak form factors of the nucleon. More recently, the focus of parity-violation electron scattering experiments at CEBAF has shifted to making precise measurements of the weak mixing angle, $\theta_{\mathrm{w}}$, and the search for physics beyond the Standard Model. Following the successful completion of the CEBAF energy upgrade, a new era of physics experimentation begins. Experiments at traditional ``parity violation'' Halls A and C can expect to receive polarized beam at 11 GeV. This contribution discusses the characteristics of polarized beams at higher energy, focusing on the helicity-correlated beam properties. The talk also describes planned accelerator improvements that should make it possible to successfully complete proposed parity violation experiments that are more challenging than those completed to date. [Preview Abstract] |
Monday, April 18, 2016 2:06PM - 2:42PM |
S3.00002: The control and measurement of helicity correlated beam asymmetries for parity-violation experiments Invited Speaker: Kent Paschke The availability of high current, high polarization electron beams from laser-driven GaAs photocathodes has enabled a broad program studying parity violation in electron scattering. Measurements of the parity-violating beam-helicity asymmetry are used to study the structure of nuclei or to test the Standard Model of electroweak interactions. With experiments requiring a precision around 1 part-per-billion, asymmetric beam properties between the two beam helicity states threaten to become a leading source of experimental uncertainty. Changes in various beam properties must be considered, including intensity, energy, trajectory, shape, and halo. The measurement and control of helicity-correlated changes in these properties will be discussed from the perspective of the electron-scattering experimentalist. [Preview Abstract] |
Monday, April 18, 2016 2:42PM - 3:18PM |
S3.00003: Technology and techniques for parity experiments at Mainz: Past, Present and Future Invited Speaker: Juergen Diefenbach For almost 20 years the Mainz accelerator facility MAMI delivered polarized electron beam to the parity violation experiment A4 that measured the contributions of strange sea quarks to the proton electromagnetic factors. Parity violation asymmetries were of the order of A$\approx$5 ppm. Currently the A1 collaboration carries out single spin asymmetry measurements at MAMI (A$\approx$20 ppm) to prepare for a measurement of neutron skin depth on lead (A$\approx$1 ppm). For such high precision experiments active stabilization and precise determination of beam parameters like current, energy, position, and angle are essential requirements in addition to precision electron beam polarimetry. For the future P2 experiment at the planned superconducting accelerator MESA in Mainz the requirements for beam quality will be even higher. P2 will measure the weak mixing angle with 0.15 percent total uncertainty and, in addition, the neutron skin depth of lead as well as parity violation in electron scattering off $^{12}$C. A tiny asymmetry of only -0.03 ppm creates the needs to combine digital feedback with feedforward stabilizations along with new polarimetry developments like a hydro-Moller and a double-Mott polarimeter to meet the goals for systematic uncertainty. This talk gives an overview of our experience with polarimetry, analog feedbacks and compensation techniques for apparative asymmetries at the A4 experiment. It finally leads to the requirements and new techniques for the pioneering P2 experiment at MESA. First results from beam tests currently carried out at the existing MAMI accelerator, employing high speed analog/digital conversion and FPGAs for control of beam parameters, will be presented. [Preview Abstract] |
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