More Like this

1. Single spin asymmetries in electron-nucleon scattering at low and intermediate energies

   https://doi.org/10.22323/1.456.0182  

   Goity, Jose Luis; Weiss, Christian (July 2024, Sissa Medialab)

   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
2. Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons

   https://doi.org/10.1007/JHEP12(2020)010  

   Airapetian, A.; Akopov, N.; Akopov, Z.; Aschenauer, E. C.; Augustyniak, W.; Avakian, R.; Bacchetta, A.; Belostotski, S.; Bryzgalov, V.; Capitani, G. P.; et al (December 2020, Journal of High Energy Physics)

   null (Ed.)

   A bstract A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos ( ϕ−ϕ S ) modulations provide evidence for a sizable worm-gear (II) distribution, $$ {g}_{1\mathrm{T}}^q\left(x,{\mathrm{p}}_T^2\right) $$ g 1 T q x p T 2 . Most of the other modulations are found to be consistent with zero with the notable exception of large sin ( ϕ S ) modulations for charged pions and K + . 

   more » « less
3. Proton form factor ratio \mu_p G_E^p/G_M^p from double spin asymmetry

   Liyanage, A.; Armstrong, W.; Kang, H.; Maxwell, J.; Mulholland, J.; Ndukum, L.; Ahmidouch, A.; Albayrak, I.; Asaturyan, A.; Ates, O.; et al (March 2020, Physical review)

   The ratio of the electric to magnetic form factors of the proton, μpGEp/GMp, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared Q2=5.66(GeV/c)2 using double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of μpGEp/GMp agrees with the Q2 dependence of previous recoil polarization data and reconfirms the discrepancy at high Q2 between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at Q2=2.06(GeV/c)2 has been measured as μpGEp/GMp=0.720±0.176stat±0.039sys, which is in agreement with an earlier measurement using the polarized target technique at similar kinematics. The form factor ratio at Q2=5.66(GeV/c)2 has been determined as μpGEp/GMp=0.244±0.353stat±0.013sys, which represents the highest Q2 measurement reached using double spin asymmetries with polarized target to date. 

   more » « less
4. MUSE: The MUon Scattering Experiment

   https://doi.org/10.21468/SciPostPhysProc.5.023  

   Cline, Ethan; Bernauer, Jan; Downie, Evangeline J.; Gilman, Ronald (January 2021, SciPost Physics Proceedings)

   MUSE is a high-precision muon scattering experiment aiming todetermine the proton radius. Muon, electron, and pion scattering will bemeasured at the same time. Two-photon exchange corrections will bedetermined with data using both beam polarities. 

   more » « less
5. Firm spin and parity assignments for high-lying, low-spin levels in stable Si isotopes

   J. Sinclair, M. Scheck (April 2020, The European physical journal)

   A natural silicon target was investigated in a natSi( , γ ′) photon-scattering experiment with fully linearlypolarised, quasi-monochromatic  rays in the entrance channel. The mean photon energies used were Eγ =9.33, 9.77, 10.17, 10.55, 10.93, and 11.37 MeV, and the relative energy spread (full width at half maximum) of the incident beam was ΔEγ /Eγ ≈ 3.5–4 %. The observed angular distributions for the ground-state decay allow firm spin and parity assignments for several levels of the stable even-even silicon isotopes. 

   more » « less