Measurement of the forward-central bbˉ production asymmetry

The conference note is available here

More detailed information: ANA note 2013-007

Abstract

A measurement of the forward-central bbˉ production asymmetry is reported based on data collected by {\mbox{LHCb}\xspace} in 2011 at √s=7TeV corresponding to an integrated luminosity of 1.0~fb−1. Events are selected that have two identified b jets, one of which is flavor tagged by the presence of a displaced muon with high momentum. The following results are obtained:

AbbˉFC=(0.5±0.5(stat)±0.5(syst))%,

AbbˉFC(Mbbˉ>100 GeV)=(4.3±1.7(stat)±2.4(syst) )%.

The asymmetry in the high-mass region is not corrected for the bbˉ mass resolution. Studies of simulated data estimate the dilution due to the di-jet mass resolution to be a few percent.

Figures

(Note, eps versions are available under attachments).

Caption	Figure
Di-jet b bbar mass distributions for (solid black) all events, (dashed red) flavor-tagged events and (dotted blue) doubly- flavor-tagged events.
Distributed B candidate masses for B->J/psi K+ decays used in the flavor-tagging study. Asymmetric Gaussian distributions are used for the signal PDFs; the combinatorial backgrounds are taken to be exponential
Distributed B candidate masses for B+->D0pi+ decays used in the flavor-tagging study. Asymmetric Gaussian distributions are used for the signal PDFs; the combinatorial backgrounds are taken to be exponential, while the PDF of the partially-reconstructed background in B+->D0pi+ is obtained from simulation
Observed (black solid) pseudo-lifetime distribution of flavor-tagged b jets. The signal shape (red dashed) is taken from simulation, while the background shape (blue dotted) is assumed to be uniform. The background is estimated to be O(0.2%)
Observed time dependence of the tagging purity (black points). The (solid blue) curve is the predicted distribution obtained from simulation and has no free parameters
Observed y distributions for all events. The dashed distribution (mirror data) corresponds to delta y -> - delta y
Observed y distributions for events with measured Mbb > 100 GeV. The dashed distribution (mirror data) corresponds to delta y -> - delta y