Abstract
An angular analysis of the B0 → K*0e+e− decay is performed using a data sample corresponding to an integrated luminosity of 9 fb−1 of pp collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared (q2) interval between 0.0008 and 0.257 GeV2, where the rate is dominated by the B0 → K*0γ transition with a virtual photon. The fraction of longitudinal polarisation of the K*0 meson, FL, is measured to be FL = (4.4 ± 2.6 ± 1.4)%, where the first uncertainty is statistical and the second systematic. The {A}_{mathrm{T}}^{mathrm{Re}} observable, which is related to the lepton forward-backward asymmetry, is measured to be {A}_{mathrm{T}}^{mathrm{Re}} = −0.06 ± 0.08 ± 0.02. The {A}_{mathrm{T}}^{(2)} and {A}_{mathrm{T}}^{mathrm{Im}} transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be {A}_{mathrm{T}}^{(2)} = 0.11 ± 0.10 ± 0.02 and {A}_{mathrm{T}}^{mathrm{Im}} = 0.02 ± 0.10 ± 0.01. The results are consistent with Standard Model predictions and provide the world’s best constraint on the b → sγ photon polarisation.
Highlights
Background studiesSeveral sources of specific background are considered, with studies performed using samples of simulated events unless stated otherwise
This paper presents an angular analysis of the B0 → K∗0e+e− decay1 in the region of q2 between 0.0008 and 0.257 GeV2
The uncertainties on the transverse asymmetries are much smaller than the experimental sensitivity of the results presented in this paper
Summary
The study reported here is based on pp collision data, corresponding to an integrated luminosity of 9 fb−1, collected at the Large Hadron Collider (LHC) with the LHCb detector [47]. Charged particles are identified using information from two ring-imaging Cherenkov detectors (RICH), electromagnetic (ECAL) and hadronic (HCAL) calorimeters and muon chambers. The online event selection is performed by a trigger, which consists of a hardware stage, based on information from the calorimeters and muon system, followed by a software stage, which fully reconstructs the event. Candidates are selected if the hardware trigger requirements were passed by objects in the rest of the event that are independent of the decay products of the signal B0 candidate. The simulated samples are corrected for known differences between data and simulation in kinematics, particle identification, detector occupancy, hardware trigger efficiency and reconstruction effects, based on a general approach developed by the LHCb collaboration for tests of lepton universality [33]
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