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Title: Extracting nucleon strange and anapole form factors from data

Abstract

Using the complete world set of parity violating electron scattering data up to Q{sup 2} {approx} 0.3 GeV{sup 2}, we extract the current best determination of the strange electric and magnetic form factors of the proton, as well as the weak axial form factors of the proton and neutron at Q{sup 2} = 0.1 GeV{sup 2}. The results are consistent with state of the art calculations of all four form factors, with the latter including the anapole contribution.

Authors:
; ; ;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
881105
Report Number(s):
JLAB-THY-06-479; DOE/ER/40150-3839
TRN: US0602896
DOE Contract Number:
AC05-84ER40150
Resource Type:
Journal Article
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ELECTRONS; FORM FACTORS; NEUTRONS; NUCLEONS; PARITY; PROTONS; SCATTERING

Citation Formats

R.D. Young, J. Roche, R.D. Carlini, and A.W. Thomas. Extracting nucleon strange and anapole form factors from data. United States: N. p., 2006. Web.
R.D. Young, J. Roche, R.D. Carlini, & A.W. Thomas. Extracting nucleon strange and anapole form factors from data. United States.
R.D. Young, J. Roche, R.D. Carlini, and A.W. Thomas. 2006. "Extracting nucleon strange and anapole form factors from data". United States. doi:. https://www.osti.gov/servlets/purl/881105.
@article{osti_881105,
title = {Extracting nucleon strange and anapole form factors from data},
author = {R.D. Young and J. Roche and R.D. Carlini and A.W. Thomas},
abstractNote = {Using the complete world set of parity violating electron scattering data up to Q{sup 2} {approx} 0.3 GeV{sup 2}, we extract the current best determination of the strange electric and magnetic form factors of the proton, as well as the weak axial form factors of the proton and neutron at Q{sup 2} = 0.1 GeV{sup 2}. The results are consistent with state of the art calculations of all four form factors, with the latter including the anapole contribution.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2006,
month = 4
}
  • The complete world set of parity-violating electron scattering data up to Q{sup 2}{approx}0.3 GeV{sup 2} is analyzed. We extract the current experimental determination of the strange electric and magnetic form factors of the proton, as well as the weak axial form factors of the proton and neutron, at Q{sup 2}=0.1 GeV{sup 2}. Within experimental uncertainties, we find that the strange form factors are consistent with zero, as are the anapole contributions to the axial form factors. Nevertheless, the correlation between the strange and anapole contributions suggest that there is only a small probability that these form factors all vanish simultaneously.
  • The strange quark contribution to the vector and axial form factors of the nucleon has been determined for momentum transfers in the range 0.45<Q{sup 2}<1.0 GeV{sup 2}. The results are obtained via a combined analysis of forward-scattering, parity-violating elastic e-vectorp asymmetry data from the G0 and HAPPEx experiments at Jefferson Lab and elastic {nu}p- and {nu}p-scattering data from Experiment 734 at Brookhaven National Laboratory. The parity-violating asymmetries measured in elastic e-vectorp scattering at forward angles establish a relationship between the strange vector form factors G{sub E}{sup s} and G{sub M}{sup s}, with little sensitivity to the strange axial form factormore » G{sub A}{sup s}. However, elastic neutrino scattering at low Q{sup 2} is dominated by the axial form factor, with some significant sensitivity to the vector form factors as well. Combination of the two data sets allows the simultaneous extraction of G{sub E}{sup s},G{sub M}{sup s}, and G{sub A}{sup s} over a significant range of Q{sup 2} for the very first time. The Q{sup 2} dependence of the strange axial form factor suggests that the strange quark contribution to the proton spin, {delta}s, is negative.« less
  • Cited by 6
  • Here, we report a calculation of the nucleon axial form factorsmore » $$G_A^q(Q^2)$$ and $$G_P^q(Q^2)$$ for all three light quark flavors $$q\in\{u,d,s\}$$ in the range $$0\leq Q^2\lesssim 1.2\text{ GeV}^2$$ using lattice QCD. Our work was done using a single ensemble with pion mass 317 MeV and made use of the hierarchical probing technique to efficiently evaluate the required disconnected loops. We perform nonperturbative renormalization of the axial current, including a nonperturbative treatment of the mixing between light and strange currents due to the singlet-nonsinglet difference caused by the axial anomaly. The form factor shapes are fit using the model-independent $z$ expansion. From $$G_A^q(Q^2)$$, we determine the quark contributions to the nucleon spin and axial radii. By extrapolating the isovector $$G_P^{u-d}(Q^2)$$, we obtain the induced pseudoscalar coupling relevant for ordinary muon capture and the pion-nucleon coupling constant. We also found that the disconnected contributions to $$G_P$$ form factors are large, and give an interpretation based on the dominant influence of the pseudoscalar poles in these form factors.« less
    Cited by 6
  • We analyze the nucleon matrix element of the strange quark vector current in a nucleon-model-independent dispersive approach with input from the current world data set for the isoscalar electromagnetic form factors. The update of Jaffe{close_quote}s minimal three-pole {ital Ansatz} for the spectral functions yields a 40{percent} larger (Sachs) strangeness radius (r{sub s}{sup 2}){sub Sachs}=0.20 fm{sup 2} and a by 20{percent} reduced magnitude of the strangeness magnetic moment {mu}{sub s}={minus}0.26. In the pole approximation these values are shown to be upper bounds. After extending the {ital Ansatz} in order to implement the asymptotic QCD momentum dependence (which the three-pole form factorsmore » cannot reproduce), we find the magnitude of the three-pole results reduced by up to a factor of 2.5. The signs of the leading moments originate primarily from the large {phi}-meson couplings and are generic in the pole approximation. {copyright} {ital 1997} {ital The American Physical Society}« less