1. Moller Polarimeter Q-weak: First direct measurement of the weak charge of the proton Nuruzzaman (https://userweb.jlab.org/~nur/)https://userweb.jlab.org/~nur/ Advisors: Liguang Tang & Dave Mack The Standard Model The Standard Model (SM) is the most successful elementary particle theory developed so far that explains EM, weak, and strong interactions. The weak charge of the proton, Q p W, is suppressed in the SM and can be expressed as a function of the weak mixing angle θ W. References [1] http://www.jlab.org/qweak/http://www.jlab.org/qweak/ [2] Mark Dalton, DNP Meeting, Fall 2012 at Newport Beach, CA. Acknowledgements I would like to acknowledge my advisors Liguang Tang, Dave Mack, and other fellow Q-weak Collaborators. Four Forces Forces in nature are divided into four fundamental categories namely strong, weak, electromagnetic and gravitational. Weak Force The weak force operates only extremely short distance scales. The strength of the weak force between interacting quarks and other weakly interacting particles can be characterized by their weak charge (distinct from their electric charge). Basics and Motivation Q-weak The objective of the Q-weak experiment is to measure the weak charge of proton with an uncertainty of 4% via the parity violating asymmetry in electron-proton scattering [1]. At small scattering angles, the asymmetry can be written as: A PV has a size of ~230 ppb (like finding a hair on top of the Eiffel tower). B(Q 2 ) is a function of the structure of the nucleon and constrained by other experiments. Results A PV Q2GFQ2GF 4√2πα [Q p W + Q 2 B(Q 2 )] = − = σ + - σ - σ + + σ - Preliminary Result Using our commissioning data set, the reduced asymmetry is shown in the figure. Hadronic part has been extracted using available electron scattering data. Impact of Q-weak The SM predicts the running of sin 2 θ W (Q) based on the measurement done at the Z-pole. Q-weak will measure sin 2 θ W (Q) to 0.3% with full statistics. Any discrepancy from the SM prediction would be indicative of TeV-scale new PV physics. The proton, consisting of three quarks, is the simplest particle that experiences all the fundamental forces. The weak force stands distinct because it violates a fundamental symmetry of nature called parity. This distinctness is often exploited to measure properties related to the weak force. Ongoing Extract the weak charge of proton with complete data set. This work is supported by DOE and NSF. Q 2 [GeV 2 ] The Q p weak experiment will provide the most precise low energy measurement of this SM parameter to date. Estimated statistical and systematic uncertainties are shown below [2]. A0A0 Q2GFQ2GF 4√2πα A 0 = − A p LR = A PV, Extracted Q p W = 0.0945 ± 0.0156(stat) ± 0.0132(sys) ± 0.001(th) [2]. The result is ~1.1 σ higher than the Q p W (SM) = 0.0712 ± 0.0008. Kinematics E beam : 1.16 GeV I beam : ~ 180 μA Polarization ~87% Luminosity: 2 x 10 39 s -1 cm -2 Target = 35cm Cryopower =2.5 kW The Q-weak Experiment Jefferson Lab The Q-weak experiment was performed at Hall-C of Thomas Jefferson National Accelerator Facility (Jlab) during November 2010 to May 2012 although preparation started in 2001. Hall-C and Q-weak Apparatus A polarized electron beam was incident on a 35 cm long liquid Hydrogen target with beam current 180 μA. A toroidal magnet was used to bend the scattered collimated electrons from the target to the Cherenkov detectors that measured yields. Achievements World’s highest power Hydrogen target to date. Designed with computational fluid dynamics (CFD) to reduce density fluctuations. New Compton polarimeter with existing Moller polarimeter. Radiation-hard eight fused silica (quartz) Cherenkov detectors. New robust beam modulation system to measure detector sensitivities for different beam parameters. Luminosity monitors for background measurements. Target Main Detector Beam Modulation Magnets Lumi Monitors Compton Polarimeter (θ = 8° ± 2°) Eight Fused Silica (quartz) Cherenkov Detectors e-e- p θ s(+) e-e- p θ s(-) Parity is a reversal of spatial directions (like looking in a mirror) ~100 collaborators, 22 Students, many postdocs and young faculty ~300 m Hair ~ 0.06 mm Q p W = 1 - 4sin 2 θ W ≈ 0.07 (SM) The Q-weak experiment is a search for or constraint on new physics beyond the SM by measuring Q p W.