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Nuclear Theory·nucl-th

Thursday·October 19, 2017

5 papers—3 primary·2 cross-listed

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  1. 04

    [Submitted on 17 Oct 2017] (cross-list from hep-ph)

    Nucleon form factors in dispersively improved Chiral Effective Field Theory II: Electromagnetic form factors

    J. M. Alarcón🇺🇸 · C. Weiss🇺🇸

    We study the nucleon electromagnetic form factors (EM FFs) using a recently developed method combining Chiral Effective Field Theory (EFT) and dispersion analysis. The spectral functions on the two-pion cut at are constructed using the elastic unitarity relation and an representation. EFT is used to calculate the real functions (ratios of the complex partial-wave amplitudes and the timelike pion FF), which are free of rescattering. Rescattering effects are included through the empirical timelike pion FF . The method allows us to compute the isovector EM spectral functions up to GeV with controlled accuracy (LO, NLO, and partial N2LO). With the spectral functions we calculate the isovector nucleon EM FFs and their derivatives at (EM radii, moments) using subtracted dispersion relations. We predict the values of higher FF derivatives with minimal uncertainties and explain their collective behavior. We estimate the individual proton and neutron FFs by adding an empirical parametrization of the isoscalar sector. Excellent agreement with the present low- FF data is achieved up to 0.5 GeV for , and up to 0.2 GeV for . Our results can be used to guide the analysis of low- elastic scattering data and the extraction of the proton charge radius.

    Comments:
    14 pages, 10 figures, 6 tables
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1710.06430 [pdf]
    PRC(2018)·37 citations
  2. 05

    [Submitted on 17 Oct 2017] (cross-list from hep-lat)

    Nucleon axial coupling from Lattice QCD

    Chia Cheng Chang🇺🇸 · Amy Nicholson🇺🇸 · Enrico Rinaldi🇺🇸 · Evan Berkowitz🇩🇪 · Nicolas Garron🇬🇧 · David Brantley🇺🇸 · Henry Monge-Camacho🇺🇸 · Chris Monahan🇺🇸 · Chris Bouchard🇺🇸 · M.A. Clark🇺🇸 · Balint Joo🇺🇸 · Thorsten Kurth🇺🇸 and 3 other authors

    We present state-of-the-art results from a lattice QCD calculation of the nucleon axial coupling, , using Möbius Domain-Wall fermions solved on the dynamical HISQ ensembles after they are smeared using the gradient-flow algorithm. Relevant three-point correlation functions are calculated using a method inspired by the Feynman-Hellmann theorem, and demonstrate significant improvement in signal for fixed stochastic samples. The calculation is performed at five pion masses of ~MeV, three lattice spacings of ~fm, and we do a dedicated volume study with . Control over all relevant sources of systematic uncertainty are demonstrated and quantified. We achieve a preliminary value of , with a relative uncertainty of 1.33\%.

    Comments:
    18 pages, 8 figures, Lattice 2017 Proceedings
    Subjects:
    High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1710.06523 [pdf]
    EPJ Web Conf.(2018)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE