Measurement of exclusive Υ photoproduction from protons in p Pb collisions at s NN = 5.02 TeV

Abstract

The exclusive photoproduction of ${\rm Y}\left(\mathrm{nS}\right)$ meson states from protons, $\gamma p\to {\rm Y}\left(\mathrm{nS}\right)p$ (with $n=1,2,3$ ), is studied in ultraperipheral $p$ Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02\text{TeV}$ . The measurement is performed using the ${\rm Y}\left(\mathrm{nS}\right)\to {\mu }^{+}{\mu }^{-}$ decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6 ${\text{nb}}^{-1}$ . Differential cross sections as functions of the ${\rm Y}\left(\mathrm{nS}\right)$ transverse momentum squared $p_T^2$ , and rapidity y, are presented. The ${\rm Y}\left(1S\right)$ photoproduction cross section is extracted in the rapidity range $\left|y\right|<2.2$ , which corresponds to photon-proton centre-of-mass energies in the range $91<W_{\gamma p}<826\text{GeV}$ . The data are compared to theoretical predictions based on perturbative quantum chromodynamics and to previous measurements.

Keywords: CMS; UPC; Y; pPb; photoproduction.