# Study of nuclear deformation effects in Au+Au and U+U collisions from STAR experiment

- Institution: CERN
- Department: Conferences
- Speaker: Jiangyong Jia
- Year: 2021
- Language: English
- Subjects: Physics
- Source: [CERN](https://videos.cern.ch/record/3018469)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Tweens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

Nuclear deformation is a ubiqutous phenomenon for most atomic nuclei, reflecting collective motion induced by interaction between valance nucleons and shell structure. In most cases, the deformation has a quadrupole shape $\beta$ that is axially and refection symmetric, either prolate $\beta>0$ or oblate $\beta<0$. Collisions of deformed nucleus lead to large shape and size fluctuations in the initial state geometry, which after collective expansion, lead to enhance fluctuation of harmonic flow $v_n$ and event-by-event mean transverse momentum $\[p_T\]$. Therefore detailed study of the $v_n$, and $\[p_T\]$ and correlations between them could probe the deformation parameter. In this talk, we present results of $\[p_T\]$ fluctuations and $v_n^2-\[p_T\]$ correlation for $n=2,3,4$ in near-spherical $^{197}$Au+$^{197}$Au collisions at $\sqrt{s_{NN}}=200$ GeV and highly-deformed $^{238}$U+$^{238}$U collisions at $\sqrt{s_{NN}}=193$ GeV. Significant differences for mean, variance $c_2$ and skewness $c_3$ of $\[p_T\]$ fluctuations are observed between the two systems as a function of centrality. The recently proposed intensive skewness of $c_3\langle\[p_T\]\rangle/c_2^2$, sensitive to the initial size fluctuation, is found to differ significantly between the two systems, particular in the ultra-central collisions. The $v_2^2-\[p_T\]$ results remain positive over the full centrality in Au+Au collisions, while they change sign in 0-5\% central U+U collisions. In contrast, the $v_3^2-\[p_T\]$ and $v_4^2-\[p_T\]$ results are nearly identical between these two systems. The sign-change of $v_2^2-\[p_T\]$ is used to provide novel ways to constrain $\beta$ for Uranium nuclei in heavy ion collisions. Comparison with state-of-art model calculations is discussed..

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## Lectures

1. [Study of nuclear deformation effects in Au+Au and U+U collisions from STAR experiment](https://invisiblenetwork.ai/learn/cern/3018469/11b495be97c5), 22 min (CERN's player)