First determination of the weak charge of the proton
Author(s)
Guo, Fang, Ph. D. Massachusetts Institute of Technology
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Massachusetts Institute of Technology. Department of Physics.
Advisor
Stanley Kowalski.
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The Qweak experiment measures the parity violating asymmetry in elastic e[upper script right arrow]p scattering at Q² = 0.02455 (GeV/c)² with a 180 [mu]A and 88.7% longitudinally polarized electron beam of 1.165 GeV and a 34.4 cm liquid hydrogen target in experimental Hall C at Jefferson Lab. As the Q² at the Qweak experiment is much lower than all previous experiments, the Qweak measurement can be considered as the first direct determination of the weak charge of the proton, Qp/w, which is related to the weak mixing angle, sin2 [theta]w, an important Standard Model parameter. The preliminary and blinded asymmetry of the Run 2 data set, which constitutes approximately 60% of all the data collected in the experiment, is Aep/PV = -232.7 +/- 8.7 (stat) +/- 6.4 (syst) ppb. The value of Qp/w obtained by fitting this blinded asymmetry and earlier parity violating electron scattering (PVES) data at higher Q² is Qp/w (PVES) = 0.0705 +/- 0.0051. When combining this result with the ¹³³Cs atomic parity violation (APV) measurement, further constraints can be placed on the neutral weak quark coupling constants C₁u and C₁d. The combined PVES and APV analysis yields the blinded neutron's weak charge to be Qn/w (PVES+APV) = -0.9798 +/- 0.0065. The Qweak experiment also measures the parity violating asymmetry in nonresonance inelastic e[upper script right arrow]p scattering at Q² ~/= 0.09 (GeV/c)² with 3.35 GeV electron beams to provide inputs for the [gamma]Z box calculation. The preliminary measured inelastic asymmetry is Aep/inelastic-PV = 2.91 +/- 0.35 ppm.
Description
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. Cataloged from PDF version of thesis. Includes bibliographical references (pages 177-188).
Date issued
2016Department
Massachusetts Institute of Technology. Department of PhysicsPublisher
Massachusetts Institute of Technology
Keywords
Physics.