Angular correlations in exclusive dijet photoproduction in ultra-peripheral PbPb collisions at $\sqrt{s_{NN}} = 5.02~\mathrm{TeV}$

Exclusive dijet photoproduction has been measured in ultra-peripheral lead-lead (PbPb) collisions at $\sqrt{s_{NN}} = 5.02~\mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of $0.38~\mathrm{nb}^{-1}$ collected by the CMS Collaboration. For each dijet, the transverse momentum vectors of the leading and subleading jets are measured and their vector sum and vector difference determined. The azimuthal angle between the vector sum and vector difference defines an angle $\phi$. The distribution of $\phi$ and, in particular, the second Fourier harmonic $\langle \cos(2\phi) \rangle$ is measured. The dependence of $\langle \cos(2\phi) \rangle$ on the sum of the jet momentum vectors provides the first azimuthal anisotropy measurement related to exclusive dijet production.