First Observation of Forward Z → b anti-b Production in pp Collisions at √s = 8 TeV

The decay Z → b anti-b is reconstructed in pp collision data, corresponding to 2 fb^−1 of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of √s = 8 TeV. The product of the Z production cross-section and the Z → b anti-b branching fraction is measured for candidates in the fiducial region defined by two particle-level b-quark jets with pseudorapidities in the range 2.2 < η < 4.2, with transverse momenta p_T > 20 GeV and dijet invariant mass in the range 45 < m_jj < 165 GeV. From a signal yield of 5462 ± 763 Z → b anti-b events, where the uncertainty is statistical, a production cross-section times branching fraction of 332 ± 46 ± 59 pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the Z → b anti-b production in the forward region of pp collisions.