First Measurement of the Z→μ+μ- Angular Coefficients in the Forward Region of pp Collisions at s=13  TeV

The first study of the angular distribution of μ+μ- pairs produced in the forward rapidity region via the Drell-Yan reaction pp→γ*/Z+X→ℓ+ℓ-+X is presented, using data collected with the LHCb detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.1  fb-1. The coefficients of the five leading terms in the angular distribution are determined as a function of the dimuon transverse momentum and rapidity. The results are compared to various theoretical predictions of the Z-boson production mechanism and can also be used to probe transverse-momentum-dependent parton distributions within the proton.