First determination of the weak charge of the proton
Name
958294725-MIT.pdf
Description
Full printable version
Size
27.37 MB
Format
Adobe PDF
Checksum (MD5)
754f48f001ab4d7c377f8388288c6d3f
Author(s)
Guo, Fang, Ph. D. Massachusetts Institute of Technology
Advisor(s)
Stanley Kowalski.
Date Issued
2016
Publisher
Massachusetts Institute of Technology
Abstract
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).
Subjects
Physics.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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