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Nuclear Theory·nucl-th

Wednesday·December 16, 2020

7 papers—2 primary·5 cross-listed

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  1. 01

    Fluid velocity from transverse momentum spectra

    Anthony Guillen🇫🇷 · Jean-Yves Ollitrault🇫🇷

    We parametrize the transverse momentum distribution of outgoing hadrons in ultrarelativistic nucleus-nucleus collisions as a superposition of boosted thermal distributions. In this approach, which generalizes the conventional blast wave, the momentum distribution is determined by the distribution of the fluid velocity. We analyze the difference between this generalized blast-wave parametrization and a full hydrodynamic calculation. We then apply the generalized blast-wave fit to experimental data on Pb+Pb collisions at . The fit is reasonable up to , much beyond the range where hydrodynamics is usually applied, but not perfect. Based on the differences between the fit and the data, we argue that an ideal hydrodynamic calculation cannot fit simultaneously all identified particle spectra, irrespective of the specific implementation. In particular, data display a significant excess of pions at low , whose physical interpretation is discussed. Data also show that the distribution of the fluid velocity becomes broader as the collision becomes less central. This broadening is explained by event-by-event hydrodynamic calculations, where it results from the centrality dependence of initial-state fluctuations.

    nucl-thhep-phPRC(2021)·13 citations
  2. 02

    Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis

    Alex Gnech

    Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of Li and Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to Li abundance and recently the +d Li + and the p+LiBe+ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

    nucl-thnucl-ex0 citations

Affiliations

first authorsco-authorsvia INSPIRE