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Global fit of electron and neutrino elastic scattering data to determine the strange quark contribution to the vector and axial form factors of the nucleon

S. F. Pate, V. Papavassiliou, J. P. Schaub, D. P. Trujillo, M. V. Ivanov, M. B. Barbaro, and C. Giusti
Phys. Rev. D 109, 093001 – Published 10 May 2024
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  • MOTIVATION: STRANGE QUARK CONTRIBUTION…
  • ELASTIC ELECTROWEAK SCATTERING AS A…
  • MODELS FOR THE STRANGENESS FORM FACTORS
  • NUCLEAR MODELS FOR CARBON USED IN…
  • RESULTS OF OUR FITS
  • CONCLUSIONS AND NEXT STEPS
  • ACKNOWLEDGMENTS
  • APPENDICES
    • References

    Abstract

    We present a global fit of neutral-current elastic (NCE) neutrino-scattering data and parity-violating electron-scattering (PVES) data with the goal of determining the strange quark contribution to the vector and axial form factors of the proton. Previous fits of this form included data from a variety of PVES experiments (PVA4, HAPPEx, G0, SAMPLE) and the NCE neutrino and anti-neutrino data from BNL E734. These fits did not constrain the strangeness contribution to the axial form factor GAs(Q2) at low Q2 very well because there was no NCE data for Q2<0.45  GeV2. Our new fit includes for the first time MiniBooNE NCE data from both neutrino and antineutrino scattering; this experiment used a hydrocarbon target and so a model of the neutrino interaction with the carbon nucleus was required. Three different nuclear models have been employed: a relativistic Fermi gas model, the superscaling approximation model, and a spectral function model. We find a tremendous improvement in the constraint of GAs(Q2) at low Q2 compared to previous work, although more data is needed from NCE measurements that focus on exclusive single-proton final states, for example from MicroBooNE.

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    • Received 19 February 2024
    • Accepted 1 April 2024

    DOI:https://doi.org/10.1103/PhysRevD.109.093001

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Electroweak interactions in nuclear physicsNucleus-neutrino interactions
    1. Physical Systems
    Nucleons
    1. Properties
    Form factorsMagnetic momentNucleon spin structure
    Nuclear PhysicsParticles & Fields

    Authors & Affiliations

    S. F. Pate1,*, V. Papavassiliou1, J. P. Schaub1,†, D. P. Trujillo1,‡, M. V. Ivanov2, M. B. Barbaro3,4, and C. Giusti5

    • 1Physics Department, New Mexico State University, Las Cruces, New Mexico, 88003, USA
    • 2Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784, Bulgaria
    • 3Dipartimento di Fisica, Università di Torino, Via P. Giuria 1, 10125 Torino, Italy
    • 4INFN, Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy
    • 5INFN, Sezione di Pavia, Via A. Bassi 6, I-27100 Pavia, Italy

    • *spate@nmsu.edu
    • †Present address: South Puget Sound Community College, 2011 Mottman Road SW, Olympia, Washington, 98512, USA.
    • ‡Present address: Mercurial AI, 222 Merchandise Mart Plaza, Chicago, Illinois, 60654, USA.

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    Issue

    Vol. 109, Iss. 9 — 1 May 2024

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    Images

    • Figure 1
      Figure 1

      Independent determinations of the strangeness form factors of the nucleon using subsets of existing experimental data: Liu et al. (green squares) [29]; Androić et al. (blue triangles) [15]; Baunack et al. (red squares) [23]; Pate et al. (open circles use HAPPEx and E734 data, and closed circles use G0-Forward and E734 data) [26]. This selection of results is representative and not intended to be exhaustive.

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    • Figure 2
      Figure 2

      The RFG, SuSA, and SF scaling functions compared with the world averaged longitudinal inclusive electron scattering data [69].

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    • Figure 3
      Figure 3

      An illustration of the effect of the introduction of the MiniBooNE neutral current data into our global fit. The data points are the same as in Fig. 1. The black solid line is the central value for the modified-dipole fit not using the MiniBooNE data. The red solid line includes the MiniBooNE data using the spectral function nuclear model. The dashed lines represent the 70% confidence limit for each fit. As mentioned in the text, the vector form factors fit is only slightly affected by the introduction of the MiniBooNE data, while the constraints on the axial form factor are greatly improved.

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    • Figure 4
      Figure 4

      Comparison between our fits and the PVES asymmetry data from the G0-Forward [14] experiment. The red line shows the results from a fit using the z-expansion model for GAs and the RFG nuclear model. The other five fits give nearly identical results for these data and so only one fit is shown here.

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    • Figure 5
      Figure 5

      Comparison between our fits and the NC neutrino-proton and antineutrino-proton data from the BNL E734 [9] experiment. The red line shows the results of the fit using the z-expansion model for GAs and the RFG nuclear model, while the blue line shows the result using the modified-dipole model for GAs and the SF nuclear model. The other four fits show similar results for these data.

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    • Figure 6
      Figure 6

      Comparison between our fits and the NC scattering data from MiniBooNE [11, 12]. The upper panel shows the yield from the inclusive measurement of final state protons, the middle panel shows the p/(p+n) yield ratio from the exclusive measurement, and the lower panel shows the cross sections from both the neutrino and antineutrino measurements. All three fits shown use the z-expansion model for GAs. The red line shows the results of the fit using the RFG nuclear model, the blue line shows the result using the SuSA nuclear model, and the black line is with the SF nuclear model. In all three cases the results for RFG (red) and SF (black) are very similar to each other and the lines almost overlap. Fit results using instead the modified-dipole model for GAs produce very similar results to those shown here.

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    • Figure 7
      Figure 7

      Illustration of the vector and axial strangeness form factors from our global fits. The fits in the left panel use the modified-dipole model for the strangeness axial form factor GAs, while in the right panel the z-expansion model is used. The black solid line shows the fit with the SuSA nuclear model, and the red line is with the SF model. The dashed lines represent the 70% confidence limit for each fit. The results from the RFG and SF models are extremely similar, and so we have only shown the SF results in this figure.

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