Measurement of exclusive $\Upsilon$ photoproduction from protons in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

Abstract

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