skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Single spin asymmetries in electron-nucleon scattering at low and intermediate energies
Abstract The target normal single-spin asymmetry in electron nucleon scattering is studied in the framework of the 1/Nc expansion of QCD, which allows for a rigorous description in the energy range that includes the Δ resonance and below the second baryon resonance region. The asymmetry is driven by the absorptive part of the two-photon exchange component of the scattering amplitude, being therefore the most unambiguous two-photon exchange effect. Such amplitude is shown to be described up to the next to leading order in the 1/Nc expansion only in terms of the charge and magnetic form factors of the nucleons, a consequence of the approximate SU(4) spin flavor symmetry valid in the large Nc limit for baryons. A discussion is provided of the 1/Nc expansion framework along with the results for the asymmetries in elastic (e−N↑→e−N), inelastic (e−N↑→e−Δ), and inclusive scattering.  more » « less
Award ID(s):
1913562
PAR ID:
10555486
Author(s) / Creator(s):
;
Publisher / Repository:
Sissa Medialab
Date Published:
Page Range / eLocation ID:
182-192
Format(s):
Medium: X
Location:
Durham, NC, USA
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Physical review letters)
    A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to the imaginary part of the two-photon exchange process. We report a 2% precision measurement of the beam-normal single-spin asymmetry in elastic electron-proton scattering with a mean scattering angle of θlab=7.9° and a mean energy of 1.149 GeV. The asymmetry result is Bn=−5.194±0.067(stat)±0.082 (syst) ppm. This is the most precise measurement of this quantity available to date and therefore provides a stringent test of two-photon exchange models at far-forward scattering angles (θlab→0) where they should be most reliable. 
    more » « less
  2. ; ; ; ; (, Journal of High Energy Physics)
    null (Ed.)
    A bstract We present a method to determine the leading-order (LO) contact term contributing to the nn → ppe − e − amplitude through the exchange of light Majorana neutrinos. Our approach is based on the representation of the amplitude as the momentum integral of a known kernel (proportional to the neutrino propagator) times the generalized forward Compton scattering amplitude n ( p 1 ) n ( p 2 ) W + ( k ) → $$ p\left({p}_1^{\prime}\right)p\left({p}_2^{\prime}\right){W}^{-}(k) $$ p p 1 ′ p p 2 ′ W − k , in analogy to the Cottingham formula for the electromagnetic contribution to hadron masses. We construct model-independent representations of the integrand in the low- and high-momentum regions, through chiral EFT and the operator product expansion, respectively. We then construct a model for the full amplitude by interpolating between these two regions, using appropriate nucleon factors for the weak currents and information on nucleon-nucleon ( NN ) scattering in the 1 S 0 channel away from threshold. By matching the amplitude obtained in this way to the LO chiral EFT amplitude we obtain the relevant LO contact term and discuss various sources of uncertainty. We validate the approach by computing the analog I = 2 NN contact term and by reproducing, within uncertainties, the charge-independence-breaking contribution to the 1 S 0 NN scattering lengths. While our analysis is performed in the $$ \overline{\mathrm{MS}} $$ MS ¯ scheme, we express our final result in terms of the scheme-independent renormalized amplitude $$ {\mathcal{A}}_{\nu}\left(\left|\mathbf{p}\right|,\left|\mathbf{p}^{\prime}\right|\right) $$ A ν p p ′ at a set of kinematic points near threshold. We illustrate for two cutoff schemes how, using our synthetic data for $$ {\mathcal{A}}_{\nu } $$ A ν , one can determine the contact-term contribution in any regularization scheme, in particular the ones employed in nuclear-structure calculations for isotopes of experimental interest. 
    more » « less
  3. ; ; ; (, Proceedings of Science)
    Calculations of the elastic I=3/2 nucleon-pion scattering phase shifts on two lattice QCD ensembles with mπ=200MeV and 280MeV are presented. The ensembles both employ Nf=2+1 Wilson clover fermions. We determine the Δ(1232) resonance parameters from a finite volume scattering analysis. In one study the single partial wave simplification is employed to compute the p-wave amplitude while in the other we treat the partial wave mixing between s- and p-wave contributions. Fitting our data to a Breit-Wigner resonance model we find mΔ/mπ=7.13(9) and 4.75(5) on the two ensembles respectively, showing that for a lighter quark mass the resonance mass moves from near the Nπ threshold to near the Nππ threshold, in agreement with experiment. 
    more » « less
  4. ; ; ; (, Physics Letters B)
    N → transitions offer new possibilities for exploring the isovector component of the QCD quark angular momentum (AM) operator causing the J u−d flavor asymmetry in the nucleon. We extend the concept of QCD AM to transitions between baryon states, using light-front densities of the energy-momentum tensor in transversely localized states. We calculate the N → transition AM in the 1/Nc expansion, connect it with the J u−d flavor asymmetry in the nucleon, and estimate the values using lattice QCD results. In the same setup, we connect the transition AM to the transition GPDs sampled in hard exclusive electroproduction processes with N → transitions, enabling experimental study of the transition AM. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Nuovo cimento B, to appear)
    Recent results studying the masses and widths of low-lying baryon resonances in lattice QCD are presented. The S-wave Nπ scattering lengths for both total isospins I=1/2 and I=3/2 are inferred from the finite-volume spectrum below the inelastic threshold together with the I=3/2 P-wave containing the Δ(1232) resonance. A lattice QCD computation employing a combined basis of three-quark and meson-baryon interpolating operators with definite momentum to determine the coupled channel Σπ-NKbar scattering amplitude in the Λ(1405) region is also presented. Our results support the picture of a two-pole structure suggested by theoretical approaches based on SU(3) chiral symmetry and unitarity. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email