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1. Preliminary searches for spin-dependent interactions using sidebands of nuclear spin-precession signals

   https://doi.org/10.1063/5.0174672  

   Shortino, J; Knappe-Grueneberg, S; Voigt, J; Chu, P-H; Reid, A; Snow, W M; Kilian, W (January 2024, Review of Scientific Instruments)

   Various theories beyond the Standard Model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter. A new P-odd and T-odd interaction between polarized and unpolarized nucleons proportional to s⃗⋅r̂ is one such possibility, where r⃗=rr̂ is the spatial vector connecting the nucleons, and s⃗ is the spin of the polarized nucleon. Such an interaction involving a scalar coupling gsN at one vertex and a pseudoscalar coupling gpn at the polarized nucleon vertex can be induced by the exchange of spin-0 pseudoscalar bosons. We describe a new technique to search for interactions of this form and present the first measurements of this type. We show that future improvements to this technique can improve the laboratory upper bound on the product gsNgpn by two orders of magnitude for interaction ranges at the 100 micron scale. 

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2. Determining the helicity structure of the nucleon at the Electron Ion Collider in China

   https://doi.org/10.1007/JHEP08(2021)034  

   Anderle, Daniele Paolo; Hou, Tie-Jiun; Xing, Hongxi; Yan, Mengshi; Yuan, C.-P.; Zhao, Yuxiang (August 2021, Journal of High Energy Physics)

   A bstract Understanding how sea quarks behave inside a nucleon is one of the most important physics goals of the proposed Electron-Ion Collider in China (EicC), which is designed to have a 3.5 GeV polarized electron beam (80% polarization) colliding with a 20 GeV polarized proton beam (70% polarization) at instantaneous luminosity of 2 × 10 33 cm − 2 s − 1 . A specific topic at EicC is to understand the polarization of individual quarks inside a longitudinally polarized nucleon. The potential of various future EicC data, including the inclusive and semi-inclusive deep inelastic scattering data from both doubly polarized electron-proton and electron- 3 He collisions, to reduce the uncertainties of parton helicity distributions is explored at the next-to-leading order in QCD, using the Error PDF Updating Method Package ( e P ump ) which is based on the Hessian profiling method. We show that the semi-inclusive data are well able to provide good separation between flavour distributions, and to constrain their uncertainties in the x > 0 . 005 region, especially when electron- 3 He collisions, acting as effective electron-neutron collisions, are taken into account. To enable this study, we have generated a Hessian representation of the DSSV14 set of PDF replicas, named DSSV14H PDFs. 

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3. Excited state analysis in the quasi-PDF matrix elements

   https://doi.org/10.22323/1.334.0097  

   Li, Ruizi; Yang, Yi-Bo; Lin, Huey-Wen (May 2019, The 36th Annual International Symposium on Lattice Field Theory (LATTICE2018))

   We study and demonstrate the ground-state extrapolation of the unpolarized and polarized nucleon quark quasi-PDF matrix elements in a highly boosted hadron frame on the lattice. The calculation is done using the Wilson clover quark on a MILC’s dynamical Nf = 2+1+1 highly improved staggered quarks (HISQ) ensemble with one step hypercubic smearing, and with the lattice spacing a∼0.09 fm and pion mass 310 MeV. Applying the Gaussian momentum-smeared quark sources and comparing various fits in 1-, 2-, and 3-state fitting models, we show that excited state contributions can be under control in the lattice calculation of the nucleon quark quasi-PDF matrix elements. 

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4. First Measurement of Deeply Virtual Compton Scattering on the Neutron with Detection of the Active Neutron

   https://doi.org/10.1103/PhysRevLett.133.211903  

   Hobart, A; Niccolai, S; Čuić, M; Kumerički, K; Achenbach, P; Alvarado, J S; Armstrong, W R; Atac, H; Avakian, H; Baashen, L; et al (November 2024, Physical Review Letters)

   Measuring deeply virtual Compton scattering (DVCS) on the neutron is one of the necessary steps to understand the structure of the nucleon in terms of generalized parton distributions (GPDs). Neutron targets play a complementary role to transversely polarized proton targets in the determination of the GPD $E$. This poorly known and poorly constrained GPD is essential to obtain the contribution of the quarks’ angular momentum to the spin of the nucleon. DVCS on the neutron was measured for the first time selecting the exclusive final state by detecting the neutron, using the Jefferson Lab longitudinally polarized electron beam, with energies up to 10.6 GeV, and the CLAS12 detector. The extracted beam-spin asymmetries, combined with DVCS observables measured on the proton, allow a clean quark-flavor separation of the imaginary parts of the Compton form factors $\mathcal{H}$and $\mathcal{E}$. Published by the American Physical Society2024 

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5. New results in the CTEQ-TEA global analysis of parton distributions in the nucleon

   https://doi.org/10.1140/epjp/s13360-024-05865-x  

   Ablat, A.; Courtoy, A.; Dulat, S.; Guzzi, M.; Hobbs, T_J; Hou, T-J; Huston, J.; Mohan, K.; Lin, H-W; Nadolsky, P.; et al (December 2024, The European Physical Journal Plus)

   Abstract This report summarizes the latest developments in the CTEQ-TEA global analysis of parton distribution functions (PDFs) in the nucleon. The focus is on recent NNLO fits to high-precision LHC data at 8 and 13 TeV, including Drell–Yan, jet, and top-quark pair production, pursued on the way toward the release of the new generation of CTEQ-TEA general-purpose PDFs. The report also discusses advancements in statistical and numerical methods for PDF determination and uncertainty quantification, highlighting the importance of robust and replicable uncertainties for high-stakes observables. Additionally, it covers phenomenological studies related to PDF determination, such as the interplay of experimental constraints, exploration of correlations between high-xnucleon sea and low-energy parity-violating measurements, fitted charm in the nucleon, the photon PDF in the neutron, and simultaneous SMEFT-PDF analyses. 

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