Tue·May 16, 2023Tuesday·May 16, 2023

1. 01*

   Measurement of the helicity asymmetry $\mathbb{E}$ for the $\vec{\gamma }\vec{p}\to p{\pi }^0$ reaction in the resonance region

   K. Chan · N. Zachariou · M. Bashkanov · W. J. Briscoe · S. Fegan · V. L. Kashevarov · K. Nikonov · A. Sarantsev · A. Schmidt · I. I. Strakovsky · D. P. Watts · R. L. Workman

   The double-spin-polarization observable $\mathbb{E}$ for $\vec{\gamma }\vec{p}\to p{\pi }^0$ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies $E_{\gamma }$ from 0.367 to $2.173\mathrm{GeV}$ (corresponding to center-of-mass energies from 1.240 to $2.200\mathrm{GeV}$) for pion center-of-mass angles, $\cos {\theta }_{{\pi }^0}^{c.m.}$, between -0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties.

   nucl-exEPJA(2023)·4 citations
2. 02*

   Global polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=19.6$ and $27$ GeV

   The STAR Collaboration

   In relativistic heavy-ion collisions, a global spin polarization, $P_{\mathrm{H}}$, of $\Lambda$ and $\bar{\Lambda }$ hyperons along the direction of the system angular momentum was discovered and measured across a broad range of collision energies and demonstrated a trend of increasing $P_{\mathrm{H}}$ with decreasing $\sqrt{s_{\mathrm{NN}}}$. A splitting between $\Lambda$ and $\bar{\Lambda }$ polarization may be possible due to their different magnetic moments in a late-stage magnetic field sustained by the quark-gluon plasma which is formed in the collision. The results presented in this study find no significant splitting at the collision energies of $\sqrt{s_{\mathrm{NN}}}=19.6$ and $27$ GeV in the RHIC Beam Energy Scan Phase II using the STAR detector, with an upper limit of $P_{\bar{\Lambda }}-P_{\Lambda }<0.24$% and $P_{\bar{\Lambda }}-P_{\Lambda }<0.35$%, respectively, at a 95% confidence level. We derive an upper limit on the naïve extraction of the late-stage magnetic field of $B<9.4\cdot 10^{12}$ T and $B<1.4\cdot 10^{13}$ T at $\sqrt{s_{\mathrm{NN}}}=19.6$ and $27$ GeV, respectively, although more thorough derivations are needed. Differential measurements of $P_{\mathrm{H}}$ were performed with respect to collision centrality, transverse momentum, and rapidity. With our current acceptance of $|y|<1$ and uncertainties, we observe no dependence on transverse momentum and rapidity in this analysis. These results challenge multiple existing model calculations following a variety of different assumptions which have each predicted a strong dependence on rapidity in this collision-energy range.

   nucl-exPRC(2023)·66 citations
3. 03*

   Neural Network predictions of inclusive electron-nucleus cross sections

   O. Al Hammal🇫🇷 · M. Martini🇫🇷 · J. Frontera-Pons🇫🇷 · T. H. Nguyen🇻🇳 · R. Perez-Ramos🇫🇷

   We investigate whether a neural network approach can reproduce and predict the electron-nucleus cross sections in the kinematical domain of present and future accelerator-based neutrino oscillation experiments. For this purpose, we consider the large amount of data available to the community via the web-page ``Quasielastic Electron Nucleus scattering archive'', and use a residual, fully connected feedforward neural network. We illustrate the training performances of the neural network by comparing its results with experimental data for the electron double-differential cross section on carbon. The agreement between predictions and data is remarkable from quasielastic to deep-inelastic scattering. To test the predicting power of the neural network we consider the numerous kinematical conditions for which experimental cross sections on calcium are available. Furthermore, we show the predictions of the electron scattering cross sections on oxygen, argon, and titanium: nuclei of particular interest in the context of present and future accelerator-based neutrino oscillation program. The agreement between these predictions and the data is comparable to the one of other theoretical models commonly used to calculate electron and neutrino cross sections, such as SuSAv2 and GiBUU. Results obtained with GENIE, a Monte Carlo event generator, are also discussed for comparison. The good performances obtained with our neural network suggest that neural networks could be exploited for theoretical and experimental investigations of electron- and neutrino-nucleus scattering.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2023)·8 citations
4. 04*

   NN scattering with NDelta coupling: Dibaryon resonances without "dibaryons"?

   J. A. Niskanen (Helsinki Institute for Physics, University of Helsinki)🇫🇮

   It is known that at their threshold intermediate two-baryon NDelta states can produce resonance-like structures in some isospin one states, often interpreted as more exotic manifest six-quark states. This paper applies the coupled-channel method to study details of the NDelta effect in isospin one NN scattering with interactions constrained to exclude the influence of such extraneous hypothetical particles in two respects. Firstly, the calculated phase parameters are fitted below pion inelasticity, i.e. far below the region of "dibaryons". Secondly, the strength of the NN --> NDelta transition is constrained to agree with the pion production reaction NN --> dpi, fairly independent of the details of the pure "diagonal" NN potential and its effect practically as strong as the NN itself. The results may be considered as a necessary background for searches of additional dibaryon effects. Optimal conditions for resonant NDelta appearances involve a decrease of the orbital angular momentum in the transition NN --> NDelta, as is the case in the 1D2 and 3F3 waves. Also the effective NDelta threshold as well as its width are state dependent. Detailed complex phase shift results are presented for isospin one partial waves up to J=6, where NDelta excitation is still found to be comparable to or even larger than one pion exchange.

   ↳ nucl-thnucl-exEPJA(2024)·3 citations
5. 05*

   Baryon inhomogeneities driven charge dependent directed flow in heavy ion collisions

   Tribhuban Parida🇮🇳 · Sandeep Chatterjee🇮🇳

   Electromagnetic field in heavy ion collisions are expected to cause charge dependent directed flow splitting ($\Delta v_1$). Such charge dependent $\Delta v_1$ has been observed by the STAR collaboration. We demonstrate that relativistic dissipative fluid dynamic simulations with baryon diffusion that include realistic model of baryon stopping in the initial condition and no contribution from electromagnetic field describe the measured $\Delta v_1$ for observables involving baryons and anti-baryons. This suggests strong background contribution from baryon current as a response to initial state baryon inhomogeneities to such charge dependent $\Delta v_1$ involving baryons and anti-baryons. Our current model calculations that only account for the evolution of the baryon charge and not electric charge and strangeness miss the observed $\Delta v_1$ of mesons leaving their interpretation open.

   ↳ nucl-thhep-phnucl-ex13 citations
6. 06*

   Isospin compositions of correlated sources in the Fermi energy domain

   R. Ogul🇹🇷 · A. S. Botvina🇩🇪 · M. Bleicher🇩🇪 · N. Buyukcizmeci🇹🇷 · A. Ergun🇹🇷 · H. Imal🇹🇷 · Y. Leifels🇩🇪 · W. Trautmann🇩🇪

   Isotopic yield distributions of nuclei produced in peripheral collisions of ${}^{80}$Kr+${}^{40,48}$Ca at 35 MeV/nucleon are studied. Experimental results obtained by the FAZIA Collaboration at the LNS facility in Catania are compared with calculations performed with the statistical multifragmentation model (SMM). The fragments with atomic number $Z=19-24$ observed at forward angles are successfully described with the ensemble method previously established for reactions at higher energy. Using the SMM results, the isotopic compositions of the projectile residues are reconstructed. The results indicate a significant isospin exchange between the projectile and target nuclei, not far from isospin equilibrium, during the initial phase of the reaction. The two groups of light fragments with $Z=1-4$, experimentally distinguished by their velocities relative to coincident heavy projectile fragments, are found to originate from different sources. The isotopic composition of the slower group is consistent with emission from a low-density neck, enriched in neutrons, and satisfactorily reproduced with SMM calculations for a corresponding neck source of small mass.

   ↳ nucl-thnucl-exPRC(2023)·5 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.