Gamma-hadron spectra in $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

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Under the assumption that a quark-gluon plasma droplet is produced in $p$ + A collisions, $\gamma$-triggered hadron spectra [1,2] are studied within a next-to-leading-order perturbative QCD parton model with the medium-modified parton fragmentation functions in $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The initial conditions and space-time evolution of the small system of hot and dense medium is simulated by superSONIC hydrodynamic model [3] and parton energy loss in such a medium is described by the high-twist (HT) approach [4]. The scaled jet transport coefficient $\hat{q}/T^3$ in this HT approach is extracted from single hadron in central A + A collisions because its values from single and dihadron suppressions are similar [5]. Numerical results show that $\gamma$-hadron spectra for $p_T^\gamma=12-40$ GeV/$c$ in this scenario are suppressed by 10% $\sim$ 20% in the most central 0 - 10% $p$ + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The suppression becomes weaker with higher transverse momentum of the triggered-$\gamma$. As a comparison, $\gamma$-hadron suppression in Pb + Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ and 5.02 TeV is also predicted.

References [1] X. N. Wang, Z. Huang and I. Sarcevic, Phys. Rev. Lett. 77, 231 (1996) [2] H. Zhang, J. F. Owens, E. Wang and X. N. Wang, Phys. Rev. Lett. 103, 032302 (2009) [3] R. D. Weller and P. Romatschke, Phys. Lett. B 774, 351 (2017) [4] W. t. Deng and X. N. Wang, Phys. Rev. C 81, 024902 (2010) [5] M. Xie, S. Y. Wei, G. Y. Qin and H. Z. Zhang, Eur. Phys. J. C 79, no. 7, 589 (2019).

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