Speaker
Description
In high energy heavy-ion collisions, the strong electromagnetic (EM) fields of the nuclei can produce energetic, high-density photon fluxes, leading to photon-induced interactions. Recently, significant enhancements of $e^{+}e^{-}$ pair and J/$\psi$ production at very low transverse momentum ($p_{T}$) were observed by the STAR [1, 2] and ALICE [3] collaborations in peripheral hadronic A+A collisions. The excess yields exhibit a much weaker centrality dependence compared to the expectation for hadronic production, and are consistent with coherent photon-photon and photon-nucleus interactions. The measured $p_{T}$ broadening for $e^{+}e^{-}$ pairs may indicate the existence of a strong magnetic field in the medium. Measurements with $\mu^{+}\mu^{-}$ pairs provide a complementary channel to investigate these phenomena.
In 2014 and 2016, the STAR experiment at RHIC recorded large samples of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV with di-muon triggers utilizing the Muon Telescope Detector. In this poster, we will present invariant mass and yield distributions as a function of centrality for inclusive $\mu^{+}\mu^{-}$ pair production at $p_{T} < 0.15$ GeV/$c$ in the mass range large than 2.6 GeV/$c^{2}$. The $p_{T}^{2}$ distribution of the excess yields for these very low $p_{T}$ $\mu^{+}\mu^{-}$ pairs will also be shown. Physics implications will be discussed together with model comparisons.
[1] J. Adam et al. (STAR Collaboration), Phys. Rev. Lett. 121 (2018) 132301.
[2] J. Adam et al. (STAR Collaboration), arXiv: 1904.11658v1.
[3] J. Adam et al. (ALICE Collaboration), Phys. Rev. Lett. 116 (2016) 222301.
