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Title: Testing the Standard Model by precision measurement of the weak charges of quarks

Abstract

In a global analysis of the latest parity-violating electron scattering measurements on nuclear targets, we demonstrate a significant improvement in the experimental knowledge of the weak neutral-current lepton-quark interactions at low-energy. The precision of this new result, combined with earlier atomic parity-violation measurements, limits the magnitude of possible contributions from physics beyond the Standard Model - setting a model-independent, lower-bound on the scale of new physics at ~1 TeV.

Authors:
; ; ;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
902781
Report Number(s):
JLAB-THY-07-636; DOE/OR/23177-0039
TRN: US0702992
DOE Contract Number:
AC05-06OR23177
Resource Type:
Journal Article
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCURACY; ELECTRONS; GLOBAL ANALYSIS; PHYSICS; QUARKS; SCATTERING; STANDARD MODEL; TARGETS; TESTING; WEAK NEUTRAL CURRENTS

Citation Formats

Ross Young, Roger Carlini, Anthony Thomas, and Julie Roche. Testing the Standard Model by precision measurement of the weak charges of quarks. United States: N. p., 2007. Web.
Ross Young, Roger Carlini, Anthony Thomas, & Julie Roche. Testing the Standard Model by precision measurement of the weak charges of quarks. United States.
Ross Young, Roger Carlini, Anthony Thomas, and Julie Roche. Tue . "Testing the Standard Model by precision measurement of the weak charges of quarks". United States. doi:. https://www.osti.gov/servlets/purl/902781.
@article{osti_902781,
title = {Testing the Standard Model by precision measurement of the weak charges of quarks},
author = {Ross Young and Roger Carlini and Anthony Thomas and Julie Roche},
abstractNote = {In a global analysis of the latest parity-violating electron scattering measurements on nuclear targets, we demonstrate a significant improvement in the experimental knowledge of the weak neutral-current lepton-quark interactions at low-energy. The precision of this new result, combined with earlier atomic parity-violation measurements, limits the magnitude of possible contributions from physics beyond the Standard Model - setting a model-independent, lower-bound on the scale of new physics at ~1 TeV.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • In a global analysis of the latest parity-violating electron scattering measurements on nuclear targets, we demonstrate a significant improvement in the experimental knowledge of the weak neutral-current lepton-quark interactions at low energy. The precision of this new result, combined with earlier atomic parity-violation measurements, places tight constraints on the size of possible contributions from physics beyond the standard model. Consequently, this result improves the lower-bound on the scale of relevant new physics to {approx}1 TeV.
  • The Qweak collaboration is currently preparing a measurement of the proton's weak charge Q{sub w}{sup p} = (1-4 sin{sup 2} {theta}{sub w}) at the Thomas Jefferson National Accelerator Facility (TJNAF). The experiment has been designed to produce a 4.1% measurement of the weak charge, via a 2.5% measurement of the parity violating asymmetry in the number of elastically scattered 1 GeV electrons from protons, at forward angles. At the proposed precision, the experiment would produce a 0.3% measurement of the weak mixing angle at a momentum transfer of {approx_equal}0.16 GeV, making it the most precise stand alone measurement of themore » weak mixing angle at low momentum transfer. In combination with other parity measurements, Qweak will also provide a high precision determination of the weak charges of the up and down quarks. Our proposed measurement of Q{sub w}{sup 2} will be performed with significantly smaller statistical and systematic errors than existing low Q{sup 2} data. Any significant deviation from the Standard Model prediction at low momentum transfer (Q{sup 2}) would be a signal of new physics, whereas agreement would place new and significant constraints on possible Standard Model extensions. The experiment is currently being prepared for installation, beginning in late 2009, and data taking beginning in mid 2010.« less
  • It is shown that if Goldstone particles are absent in a model of the strong and electroweak interactions based on the symmetry group G/sub L/xG/sub R/ (where G/sub L/,R = (SU(3)xSU(2)xU(1))/sub L/,R) with a renormalized Higgs potential, the necessary electric charges of the quarks (Q/sub u/ = 2/3, Q/sub d/ = -1/3, Q/sub ..nu../ = 0, Q/sub e/ = -1) are unambiguously fixed. The phenomenological aspects of such a model are considered. A mechanism is proposed for the creation of small Dirac neutrino masses, related to the hierarchy of ''left'' and ''right'' mass scales in broken G/sub L/xG/sub R/ symmetry,more » which (in contrast to standard approaches) does not require the introduction of additional superheavy neutrinos (the result that we obtain is me-italicapprox.(m/sup 2/(W/sup + -//sub L/)/ m/sup 2/(W/sup + -//sub R/))m/sub e/, where W/sup + -//sub L/ and W/sup + -//sub R/ are the charged weak bosons and m(W/sup + -//sub R/)>>m(W/sup + -//sub L/)).« less
  • The Qweak collaboration is currently preparing a measurement of the proton's weak charge Q{sub W}{sup p} = (1-4 sin{sup 2{theta}}{sub W}) at the Thomas Jefferson National Accelerator Facility (TJNAF). The experiment has been designed to produce a 4.1% measurement of the weak charge, via a 2.5% measurement of the parity violating asymmetry in the number of elastically scattered 1 GeV electrons from protons, at forward angles. At the proposed precision, the experiment would produce a 0.3% measurement of the weak mixing angle at a momentum transfer of {approx_equal} 16 GeV, making it the most precise stand alone measurement of themore » weak mixing angle at low momentum transfer. In combination with other parity measurements, Qweak will also provide a high precision determination of the weak charges of the up and down quarks. Our proposed measurement of Q{sub W}{sup p} will be performed with significantly smaller statistical and systematic errors than existing low Q{sup 2} data. Any significant deviation from the Standard Model prediction at low momentum transfer (Q{sup 2}) would be a signal of new physics, whereas agreement would place new and significant constraints on possible Standard Model extensions. The experiment is currently being installed. Commissioning of the experiment will begin in May 2010 and the first production data will be taken in the Fall of 2010.« less
  • The energy distribution of the {nu}{sub {ital e}} from the decay of unpolarized {mu}{sup +} has been calculated on the basis of the most general four-fermion interaction. It depends on a parameter called {omega} which equals zero in the standard-model. It is shown that the recent measurement of the reaction {sup 12}C({nu}{sub {ital e}},{ital e}{sup {minus}}){sup 12}Ng.s. with {nu}{sub {ital e}} from {mu}{sup +} decay at rest not only yields the absorption cross section, but also independently determines {omega} with a precision of {Delta}{omega}=0.026 for 100 measured events. This corresponds to {vert bar}{ital g}{sub {ital L}{ital L}}{sup {ital S}}{vert bar}{le}0.37,more » where {ital g}{sub {ital L}{ital L}}{sup {ital S}} describes a scalar interaction with left-handed {mu} and {ital e} and right-handed neutrinos.« less