Fri·Sep 8, 2023Friday·September 8, 2023

1. 01*

   A novel approach to the global analysis of proton form factors in elastic electron-proton scattering

   Craig McRae🇨🇦 · P. G. Blunden🇨🇦

   We present a novel method for the global analysis of elastic electron-proton scattering when combining data sets from experiments with different overall normalization uncertainties. The method is a modification of one employed by the NNPDF collaboration in the fitting of parton distribution data. This method is an alternative to the 'penalty trick' method traditionally employed in global fits to proton electric and magnetic form factors, while avoiding the biases inherent in that approach. We discuss issues that arise when extending the method to nonlinear models. For data with $Q^2>1$ GeV${}^2$ we find relatively minor differences to traditional model fits when the normalization uncertainties from different experiments are correctly accounted for. We discuss implications of this method for the well-known discrepancy between the form factor ratio $G_E/G_M$ extracted from the Rosenbluth and polarization transfer techniques.

   ↳ hep-phnucl-exnucl-thPRC(2024)·4 citations
2. 02*

   Universality of $nn$ distributions of $s$-wave $2n$ halos and the unitary limit

   Matthias Göbel🇩🇪 · Hans-Werner Hammer🇩🇪 · Daniel R. Phillips🇺🇸

   We calculate neutron-neutron relative-energy distributions of $s$-wave two-neutron ($2n$) halo nuclei using Halo Effective Field Theory (Halo EFT) at leading order. At this order these systems are described by the $2n$ separation energy, the neutron-core ($nc$) virtual-state energy and the neutron-neutron ($nn$) scattering length. We focus on knockout reactions where the removal of the core is sudden, such that the final-state interactions are dominated by the $nn$ interaction. We consider the neutron relative-energy distribution for the nuclei ${}^{11}$Li, ${}^{14}$Be, ${}^{17}$B, ${}^{19}$B, and ${}^{22}$C. We show that the ground-state neutron momentum distributions of all these nuclei stem from a single curve, which can be obtained by taking both the neutron-core and neutron-neutron interaction to the unitary limit. This universal description can be extended to the final distribution measured in experiment by including $nn$ final-state interactions via the approximate technique of enhancement factors. For all the nuclei considered we find good agreement between the full leading-order Halo EFT calculation and the universal prediction obtained in this way. The universality of the ground-state momentum distribution in two-neutron Borromean halos can thus be tested by dividing the experimental results from sudden core knockout by the enhancement factor and comparing to the unitary-limit prediction.

   ↳ nucl-thnucl-exPRC(2024)·2 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.