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Title: Precision measurement of the weak charge of the proton

Abstract

Large experimental programmes in the fields of nuclear and particle physics search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson completed the set of particles predicted by the standard model, which currently provides the best description of fundamental particles and forces. Yet, this theory’s limitations include a failure to predict fundamental parameters, such as the mass of the Higgs boson, and the inability to account for dark matter and energy, gravity, and the matter–antimatter asymmetry in the Universe, among other phenomena. These limitations have inspired searches for physics beyond the standard model in the post-Higgs era through the direct production of additional particles at high-energy accelerators, which have so far been unsuccessful. Examples include searches for supersymmetric particles, which connect bosons (integer-spin particles) with fermions (half-integer-spin particles), and for leptoquarks, which mix the fundamental quarks with leptons. Alternatively, indirect searches using precise measurements of well predicted standard-model observables allow highly targeted alternative tests for physics beyond the standard model because they can reach mass and energy scales beyond those directly accessible by today’s high-energy accelerators. Such an indirect search aims to determine the weak charge of the proton, which defines the strengthmore » of the proton’s interaction with other particles via the well known neutral electroweak force. Because parity symmetry (invariance under the spatial inversion (x, y, z)→(-x, -y, -z)) is violated only in the weak interaction, it provides a tool with which to isolate the weak interaction and thus to measure the proton’s weak charge. Here we discuss the value 0.0719±0.0045, where the uncertainty is one standard deviation, derived from our measured parity-violating asymmetry in the scattering of polarized electrons on protons, which is -226.5±9.3 parts per billion (the uncertainty is one standard deviation). Our value for the proton’s weak charge is in excellent agreement with the standard model and sets multi-teraelectronvolt-scale constraints on any semi-leptonic parity-violating physics not described within the standard model. Our results show that precision parity-violating measurements enable searches for physics beyond the standard model that can compete with direct searches at high-energy accelerators and, together with astronomical observations, can provide fertile approaches to probing higher mass scales.« less

Authors:
;
Publication Date:
Research Org.:
Mississippi State Univ., Mississippi State, MS (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Org.:
The Jefferson Lab Qweak Collaboration
OSTI Identifier:
1599332
Alternate Identifier(s):
OSTI ID: 1438370
Report Number(s):
JLAB-PHY-17-2571; DOE/OR/23177-4233
Journal ID: ISSN 0028-0836; 6623253105; TRN: US1900426
Grant/Contract Number:  
FG02-07ER41528; AC05-06OR23177
Resource Type:
Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Name: Nature (London); Journal Volume: 557; Journal Issue: 7704; Journal ID: ISSN 0028-0836
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Androić, D., and Armstrong, D. Precision measurement of the weak charge of the proton. United States: N. p., 2018. Web. doi:10.1038/s41586-018-0096-0.
Androić, D., & Armstrong, D. Precision measurement of the weak charge of the proton. United States. doi:10.1038/s41586-018-0096-0.
Androić, D., and Armstrong, D. Wed . "Precision measurement of the weak charge of the proton". United States. doi:10.1038/s41586-018-0096-0. https://www.osti.gov/servlets/purl/1599332.
@article{osti_1599332,
title = {Precision measurement of the weak charge of the proton},
author = {Androić, D. and Armstrong, D.},
abstractNote = {Large experimental programmes in the fields of nuclear and particle physics search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson completed the set of particles predicted by the standard model, which currently provides the best description of fundamental particles and forces. Yet, this theory’s limitations include a failure to predict fundamental parameters, such as the mass of the Higgs boson, and the inability to account for dark matter and energy, gravity, and the matter–antimatter asymmetry in the Universe, among other phenomena. These limitations have inspired searches for physics beyond the standard model in the post-Higgs era through the direct production of additional particles at high-energy accelerators, which have so far been unsuccessful. Examples include searches for supersymmetric particles, which connect bosons (integer-spin particles) with fermions (half-integer-spin particles), and for leptoquarks, which mix the fundamental quarks with leptons. Alternatively, indirect searches using precise measurements of well predicted standard-model observables allow highly targeted alternative tests for physics beyond the standard model because they can reach mass and energy scales beyond those directly accessible by today’s high-energy accelerators. Such an indirect search aims to determine the weak charge of the proton, which defines the strength of the proton’s interaction with other particles via the well known neutral electroweak force. Because parity symmetry (invariance under the spatial inversion (x, y, z)→(-x, -y, -z)) is violated only in the weak interaction, it provides a tool with which to isolate the weak interaction and thus to measure the proton’s weak charge. Here we discuss the value 0.0719±0.0045, where the uncertainty is one standard deviation, derived from our measured parity-violating asymmetry in the scattering of polarized electrons on protons, which is -226.5±9.3 parts per billion (the uncertainty is one standard deviation). Our value for the proton’s weak charge is in excellent agreement with the standard model and sets multi-teraelectronvolt-scale constraints on any semi-leptonic parity-violating physics not described within the standard model. Our results show that precision parity-violating measurements enable searches for physics beyond the standard model that can compete with direct searches at high-energy accelerators and, together with astronomical observations, can provide fertile approaches to probing higher mass scales.},
doi = {10.1038/s41586-018-0096-0},
journal = {Nature (London)},
number = 7704,
volume = 557,
place = {United States},
year = {2018},
month = {5}
}

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Cited by: 26 works
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Figures / Tables:

Figure 1 Figure 1: | Schematic showing the basic features of parity-violating electron scattering from the proton, with its three constituent quarks. The incoming electron with helicity +1 scatters away from the plane of the “PV mirror”. The image in the PV mirror shows the incoming electron with the opposite helicity −1,more » and instead of scattering into the plane of the PV mirror (as it would in a real mirror), it scatters out of the plane of the PV mirror. The dominant EM interaction, mediated by the photon (blue wave), conserves parity. The weak interaction, mediated by the neutral Z0 boson (dashed red line), violates parity. The weak interaction is studied experimentally by exploiting PV through reversals of the incident beam helicity, which mimic the PV mirror “reflection”.« less

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    Works referencing / citing this record:

    Nuclear-spin dependent parity violation in optically trapped polyatomic molecules
    journal, July 2019


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