4–10 Apr 2022
Auditorium Maximum UJ
Europe/Warsaw timezone
Proceedings submission deadline extended to September 11, 2022

Constraints on neutron skin thickness and nuclear deformations using relativistic heavy-ion collisions from STAR

6 Apr 2022, 09:00
20m
medium aula A (Auditorium Maximum UJ)

medium aula A

Auditorium Maximum UJ

Oral presentation Initial state physics and approach to thermal equilibrium Parallel Session T01: Initial state physics and approach to thermal equilibrium

Speaker

Haojie Xu (Huzhou University)

Description

RHIC's capability to perform relativistic collisions of various ion species provides a unique opportunity to explore and constrain neutron skin thickness and deformation parameters of nuclei.

The study of neutron skin thickness $\Delta r_{np}$ of nuclei can help us directly infer nuclear symmetry energy. Such information is of critical importance to the equation of state of dense nuclear matter in neutron stars and the medium formed in heavy-ion collisions. The $\Delta r_{np}$ has traditionally been measured in low-energy hadronic and nuclear scattering experiments over decades. An alternate recent measurement using parity-violating electroweak interactions by the PREX-II experiment has yielded a large neutron skin thickness of Pb nucleus [1] that is in tension with the world-wide data established in hadronic collisions. In isobar collisions at relativistic energies, the effect of neutron skin was predicted [2] to yield different multiplicities and elliptic flows. They, in turn, provide an unconventional but more precise method to probe the neutron skin [3]. The idea is to compare the produced hadron multiplicities ($N_{\rm ch}$) [3], the mean transverse momenta ($\langle p_\mathrm{T}\rangle$) [4], and the net charge multiplicities ($\Delta Q$) [5] to trace back to the neutron skin differences between the isobar nuclei.

Nuclear deformation, a ubiquitous phenomenon for most atomic nuclei, reflects collective motion induced by the interaction between valence nucleons and shell structure. In most cases, the deformation has a quadrupole shape that is characterized by overall strength $\beta_2$ and triaxiality $\gamma$, and/or an octuple shape $\beta_3$. In relativistic collisions of two nuclei such deformations enhance the fluctuations of bulk observables that are sensitive to initial state geometry [6]. The deformation parameters can be constrained from the precision measurements of the ratios of harmonic anisotropy coefficients $v_2$, $v_3$, mean transverse momentum $[p_\mathrm{T}]$ fluctuations (mean, variance and skewness), and their Pearson correlation coefficient $\rho(v_n^2,[p_\mathrm{T}])$ between two isobar systems [7]. In Au+Au and U+U collisions the same can be done by performing measurement of $v_2$, cumulants of $[p_\mathrm{T}]$ distributions, and $\rho(v_n^2,[p_\mathrm{T}])$ [8].

In this talk we will discuss the aforementioned measurements in Au+Au, U+U and isobar $^{96}$Ru+$^{96}$Ru and $^{96}$Zr+$^{96}$Zr collisions at $\sqrt{s_{NN}}=200$ GeV using the STAR detector. We will discuss how we extract the neutron skin thickness and the symmetry energy slope parameter from these data. We will contrast our results in the context of the global data on symmetry energy and tension with the PREX-II data. We will discuss how the significant deviations of the ratios of $v_2$ and $v_3$ from unity in isobar collisions are indicative of large quadrupole and octuple deformations in Ru and Zr nuclei, respectively [9]. We will also discuss how the relative enhancement of $[p_\mathrm{T}]$-skewness, sign-change of $[p_\mathrm{T}]$-kurtosis and the suppression of $\rho(v_n^2,[p_\mathrm{T}])$ in U+U relative to Au+Au collisions are consistent with a large prolate deformation of the uranium nuclei.

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[1]~D. Adhikari et al. (PREX Collaboration), Phys. Rev. Lett. 126, 172502 (2021), arXiv:2102.10767 [nucl-th].

[2]~H. j. Xu, X. Wang, H. Li et al., Phys. Rev. Lett. 121, 022301 (2018), arXiv:1710.03086 [nucl-th].

[3]~H. Li, H. j. Xu, Y. Zhou et al., Phys. Rev. Lett. 125, 222301 (2020) arXiv:1910.06170 [nucl-th].

[4]~H. j. Xu, W. Zhao, H. Li et al., arXiv:2111.14812 [nucl-th].

[5]~H. j. Xu, H. Li, Y. Zhou et al., Phys. Rev. C 105, L011901 (2022), arXiv:2105.04052 [nucl-th].

[6]~C. Zhang and J. Jia, Phys. Rev. Lett. 128, 022301 (2022), arXiv:2109.01631 [nucl-th].

[7]~J. Jia and C. J. Zhang, arXiv:2111.15559 [nucl-th].

[8]~J. Jia, S. Huang and C. Zhang, Phys. Rev. C 105, 014906 (2022), arXiv:2105.05713 [nucl-th].

[9]~M. Abdallah et al. (STAR Collaboration), Phys. Rev. C 105, 014901 (2022), arXiv:2109.00131 [nucl-ex].

Primary author

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