Wed·Aug 26, 2020Wednesday·August 26, 2020

1. 01*

   Backward-angle Exclusive pi0 Production above the Resonance Region

   W.B. Li🇺🇸 · G.M. Huber🇨🇦 · J.R. Stevens🇺🇸 · K. Semenov-Tian-Shansky🇷🇺 · L. Szymanowski🇵🇱 · B. Pire🇫🇷 · M. Amaryan🇺🇸 · D. Androic🇭🇷 · K. Aniol🇺🇸 · D. Armstrong · T. Averett🇺🇸 · C. Ayerbe Gayoso🇺🇸 and 50 other authors

   The proposed measurement is a dedicated study of the exclusive electroproduction process,1H(e,e'p)pi0, in the backward-angle regime (u-channel process) above the resonance region. The produced pi0 is emitted 180 degrees opposite to the virtual-photon momentum. This study also aims to apply the well-known Rosenbluth separation technique that provides the model-independent differential cross-sections at the never explored u-channel kinematics region. Currently, the "soft-hard transition" in u-channel meson production remains an interesting and unexplored subject. The available theoretical frameworks offer competing interpretations for the observed backward-angle cross section peaks. In a "soft" hadronic Regge exchange description, the backward meson production comes from the interference between nucleon exchange and the meson produced via re-scattering within the nucleon. Whereas in the "hard" GPD-like backward collinear factorization regime, the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes (TDAs), otherwise known as super skewed parton distributions (SuperSPDs). Both TDAs and SPDs are universal non-perturbative objects of nucleon structure accessible only through backward-angle kinematics. The separated cross sections:sigma_T,sigma_L and T/L ratio at Q2=2-6 GeV2, provide a direct test of two predictions from the TDA model. The magnitude and u-dependence of the separated cross sections also provide a direct connection to the re-scattering Regge picture. The extracted interaction radius (from u-dependence) at different Q2 can be used to study the soft-hard transition in the u-channel kinematics. The acquisition of these data will be an important step forward in validating the existence of a backward factorization scheme of the nucleon structure function and establishing its applicable kinematic range.

   nucl-ex11 citations
2. 02*

   Measurement of the high-energy contribution to the Gerasimov-Drell-Hearn sum rule

   M. M. Dalton🇺🇸 · A. Deur🇺🇸 · C. D. Keith🇺🇸 · S. Širca🇸🇮 · J. Stevens🇺🇸

   We propose to measure the high-energy behavior of the integrand of the Gerasimov-Drell-Hearn (GDH) sum rule on the proton and the neutron up to 12 GeV. The convergence of the GDH integral will be investigated for the first time and to high precision. The validity of the GDH sum rule on the neutron will be accurately tested for the first time, while for the proton the uncertainty will be improved by $25\%$ relative. The data will allow precision testing of Regge phenomenology in the polarized domain. The $a_1$ and $f_1$ Regge trajectory intercepts will be obtained to an order of magnitude higher precision than the current best estimates. The data will also contribute to the determination of the real and imaginary parts of the spin-dependent Compton amplitude, the polarizability correction to hyperfine splitting in hydrogen, and to studying the transition between polarized DIS and diffractive regimes. The experiment will require a circularly polarized photon beam (produced from a longitudinally polarized electron beam) with a flux approximately 1/3 of the GlueX-II experiment E12-13-003. The experiment will run in two configurations which require two different CEBAF beam energies. A new longitudinal polarized proton and deuteron target will be needed in Hall D. The experiment will require 21 PAC days at the nominal CEBAF energy and another 12 PAC days at an energy 1/3 to 1/2 of the nominal.

   nucl-exhep-ex11 citations
3. 03*

   Nuclear suppression from coherent $J/\psi$ photoproduction at the Large Hadron Collider

   V. Guzey🇷🇺 · E. Kryshen (St. Petersburg, INP)🇷🇺 · M. Strikman (Penn State U.)🇺🇸 · M. Zhalov (St. Petersburg, INP)🇷🇺

   Using the data on coherent $J/\psi$ photoproduction in Pb-Pb ultraperipheral collisions (UPCs) obtained in Runs 1 and 2 at the Large Hadron Collider (LHC), we determined with a good accuracy the nuclear suppression factor of $S_{Pb}(x)$ in a wide range of the momentum fraction $x$, $10^{-5}\le x\le 0.04$. In the small-$x$ region $x<10^{-3}$, our ${\chi }^2$ fit favors a flat form of $S_{Pb}(x)\approx 0.6$ with approximately a 5% accuracy for $x=6\times 10^{-4}-10^{-3}$ and a 25% error at $x=10^{-4}$. At the same time, uncertainties of the fit do not exclude a slow decrease of $S_{Pb}(x)$ in the small-$x$ limit. At large $x$, $S_{Pb}(x)$ is constrained to better than 10% precision up to $x=0.04$ and is also consistent with the value of $S_{Pb}(x)$ at $⟨x⟩=0.042$, which we extract from the Fermilab data on the $A$ dependence of the cross section of coherent $J/\psi$ photoproduction on fixed nuclear targets. The resulting uncertainties on $S_{Pb}(x)$ are small, which indicates the potential of the LHC data on coherent charmonium photoproduction in Pb-Pb UPCs to provide additional constraints on small-$x$ nPDFs. We explicitly demonstrate this using as an example the EPPS16 and nCTEQ16 nuclear parton distribution functions, whose uncertainties decrease severalfold after the Bayesian reweighting of the discussed UPC data.

   ↳ hep-phnucl-exnucl-thPLB(2021)·47 citations
4. 04*

   Study of three-neutron bound and continuum states

   Souichi Ishikawa🇯🇵

   The three-neutron ($3n$) system is studied by numerical calculations with the Faddeev three-body formalism for a realistic nucleon-nucleon (NN) potential. A response function for the transition from ${}^3\mathrm{H}$ to $3n$ continuum states by an isospin excitation operator is calculated, from which no evidence of $3n$ resonance state is found. Different methods to extrapolate the $3n$ energy from bound state energies with an extra attractive effect to the NN potential are examined. While extrapolations with attractive effects by enhanced NN potentials or three-body potentials result the non-existence of $3n$ resonance states, one by external trapping potentials leads to a positive $3n$ energy, which may be considered as a resonance state. It is found that this contradiction is due to a general defect of the trapping method.

   ↳ nucl-thnucl-exPRC(2020)·13 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.