Measurements of $\phi^*$ differential cross sections for Drell--Yan events in pp collisions at $\sqrt{s}=8~\mathrm{TeV}$

Measurements of $\phi^*$ differential cross sections for inclusive Drell--Yan events in the dielectron and dimuon final states are presented. The kinematic variable $\phi^*$, constructed from the lepton angles, is correlated with the transverse momentum of the vector boson. The data were collected with the CMS experiment at a centre-of-mass energy of 8~TeV and correspond to an integrated luminosity of $19.7~\mathrm{fb}^{-1}$. The differential cross section $\mathrm{d}\sigma / \mathrm{d}\phi^*$ normalised to the total cross section within the fiducial volume is measured with a precision of about $1\%$ and is compared with theoretical predictions. The measured spectrum, for the range $\phi^*<0.1$, differs from the theoretical predictions by at most $5\%$ (ResBos), $4\%$ ($\mathrm{M{\small AD}G{\small RAPH}}$) and $9\%$ (POWHEG). For higher values of $\phi^*$ the deviations are as high as $9\%$, $5\%$ and $18\%$ in the three cases respectively.