Thu·May 3, 2018Thursday·May 3, 2018

1. 01*

   Enhanced low-energy $\gamma$-decay strength of ${}^{70}$Ni and its robustness within the shell model

   A. C. Larsen🇳🇴 · J. E. Midtbø🇳🇴 · M. Guttormsen🇳🇴 · T. Renstrøm🇳🇴 · S. N. Liddick🇺🇸 · A. Spyrou · S. Karampagia · B. A. Brown🇺🇸 · O. Achakovskiy · S. Kamerdzhiev · D. L. Bleuel🇺🇸 · A. Couture🇺🇸 and 10 other authors

   Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their $\gamma$-emission probability at very low $\gamma$ energies. In this work, we present measurements of the $\gamma$-decay strength of ${}^{70}$Ni over the wide range $1.3\le E_{\gamma }\le 8$ MeV. A significant enhancement is found in the $\gamma$-decay strength for transitions with $E_{\gamma }<3$ MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed $E1$-strength calculations within the quasiparticle time-blocking approximation, which describe our data above $E_{\gamma }\simeq 5$ MeV very well. Moreover, large-scale shell-model calculations indicate an $M1$ nature of the low-energy $\gamma$ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich ${}^{72,74,76}\mathrm{Ni}$.

   nucl-exnucl-thPRC(2018)·48 citations
2. 02*

   J/$\psi$ production as a function of event multiplicity in pp collisions at $\sqrt{s}$ = 13 TeV using EMCal-triggered events with ALICE at the LHC

   Cristiane Jahnke (for the ALICE Collaboration)🇧🇷

   The study of the J/$\psi$ production in pp collisions provides important information on perturbative and non-perturbative quantum chromodynamics. Using high multiplicity pp events, we can study how charmonium production depends on the event activity. These measurements are used to investigate the possible influence of multiple partonic interactions to the J/$\psi$ production and the interplay between soft and hard processes.In this work we report on studies of J/$\psi$ production as a function of event multiplicity in pp collisions at $\sqrt{s}$ = 13 TeV at mid-rapidity with ALICE. The J/$\psi$ are reconstructed via their dielectron decay channel in events where at least one of the decay electrons was triggered on by the Electromagnetic Calorimeter (EMCal). The availability of a high-$p_{\mathrm{T}}$ electron trigger enhances the sampled luminosity significantly relative to the available minimum-bias triggered data set and extends the $p_{\mathrm{T}}$ reach for the J/$\psi$ measurement. Using these data, the J/$\psi$ measurement is performed in the transverse momentum interval $8<p_{\mathrm{T}}<30\text{GeV}/c$.

   ↳ hep-exnucl-ex3 citations
3. 03*

   Nucleon axial form factor from a Bayesian neural-network analysis of neutrino-scattering data

   Luis Alvarez-Ruso🇪🇸 · Krzysztof M. Graczyk🇵🇱 · Eduardo Saul-Sala🇪🇸

   The Bayesian approach for feed-forward neural networks has been applied to the extraction of the nucleon axial form factor from the neutrino-deuteron scattering data measured by the Argonne National Laboratory (ANL) bubble chamber experiment. This framework allows to perform a model-independent determination of the axial form factor from data.. When the low $0.05<Q^2<0.10$ GeV${}^2$ data is included in the analysis, the resulting axial radius disagrees with available determinations. Furthermore, a large sensitivity to the corrections from the deuteron structure is obtained. In turn, when the low-$Q^2$ region is not taken into account, with or without deuteron corrections, no significant deviations from the dipole ansatz have been observed. A more accurate determination of the nucleon axial form factor requires new precise measurements of neutrino-induced quasielastic scattering on hydrogen and deuterium.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2019)·35 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.