nucl-th digest · Sep 3, 2021

[Submitted on 1 Sept 2021]

Probing triaxial deformation of atomic nuclei in high-energy heavy ion collisions

Most atomic nuclei are deformed with a quadrupole shape described by its overall strength $β_{2}$ and triaxiality $γ$ . The deformation can be accessed in high-energy heavy-ion collisions by measuring the collective flow response of the produced quark-gluon plasma to the eccentricity $ε_{2}$ and the density gradient $d_{⊥}$ in the initial state. Using analytical estimate and a Glauber model, I show that the variances, $⟨ ε_{2}^{2} ⟩$ or $⟨(δ d_{⊥} / d_{⊥})^{2} ⟩$ , and skewnesses, $⟨ ε_{2}^{2} δ d_{⊥} / d_{⊥} ⟩$ or $⟨(δ d_{⊥} / d_{⊥})^{3} ⟩$ , have a simple analytical form of $a^{'} + b^{'} β_{2}^{2}$ and $a^{'} + (b^{'} + c^{'} cos (3 γ)) β_{2}^{3}$ , respectively. From these, I constructed several normalized skewnesses to isolate the $γ$ dependence from that of $β_{2}$ , and show that the correlations between any normalized skewness and any variance can constrain simultaneously the $β_{2}$ and $γ$ . Assuming a linear relation with elliptic flow $v_{2}$ and mean-transverse momentum $[p_{T}]$ of final state particles, similar conclusions are also expected for the variances and skewnesses of $v_{2}$ and $[p_{T}]$ . Our findings motivate a dedicated system scan of high-energy heavy ion collisions to measure triaxiality of atomic nuclei. This is better done by collisions of prolate, $cos (3 γ) = 1$ , and oblate nuclei, $cos (3 γ) = - 1$ , with well known $β_{2}$ values to calibrate the coefficients $b^{'}$ and $c^{'}$ , followed by collisions of species of interest especially those with known $β_{2}$ but unknown $γ$ . The results demonstrate the unique opportunities offered by high-energy collisions as a tool to perform interdisciplinary nuclear physics studies.

Comments:: 20 pages, 14 figures, plus 3 appendix, published version
Subjects:: Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:: 2109.00604 [pdf]

PRC(2022)·108 citations

Semiempirical formula for electroweak response functions in the two-nucleon emission channel in neutrino-nucleus scattering

A semi-empirical formula for the electroweak response functions in the two-nucleon emission channel is proposed. The method consists in expanding each one of the vector-vector, axial-axial and vector-axial responses as sums of six sub-responses. These corresponds to separating the meson-exchange currents as the sum of three currents of similar structure, and expanding the hadronic tensor, as the sum of the separate contributions from each current plus the interferences between them. For each sub-response we factorize the coupling constants, the electroweak form factors, the phase space and the delta propagator, for the delta forward current. The remaining spin-isospin contributions are encoded in coefficients for each value of the momentum transfer,

q

. The coefficients are fitted to the exact results in the relativistic mean field model of nuclear matter, for each value of

q

. The dependence on the energy transfer,

ω

is well described by the semi-empirical formula. The

q

-dependency of the coefficients of the sub-responses can be parameterized or can be interpolated from the provided tables. The description of the five theoretical responses is quite good. The parameters of the formula, the Fermi momentum, number of particles relativistic effective mass, vector energy the electroweak form factors and the coupling constants, can be modified easily. This semi-empirical formula can be applied to the cross-section of neutrinos, antineutrinos and electrons.

Comments:: Revised version with 32 pages, 11 figures
Subjects:: Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:: 2109.00854 [pdf]

PRD(2021)·21 citations

Friday·September 3, 2021

Probing triaxial deformation of atomic nuclei in high-energy heavy ion collisions

Semiempirical formula for electroweak response functions in the two-nucleon emission channel in neutrino-nucleus scattering

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