Angular analysis of B0 d → K∗μ+μ− decays in pp collisions at $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

Abstract

Angular analysis of B 0 d → K * µ + µ − decays in p p collisions at √ s = 8 TeV with the ATLAS detector The ATLAS Collaboration An angular analysis of the decay B 0 d → K * µ + µ − is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb −1 of integrated luminosity collected during 2012 at centre-of-mass energy of √ s = 8 TeV. Measurements of the K * longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.Flavour-changing neutral currents (FCNC) have played a significant role in the construction of the Standard Model of particle physics (SM). These processes are forbidden at tree level and can proceed only via loops, hence are rare. An important set of FCNC processes involve the transition of a b-quark to an sµ + µ − final state mediated by electroweak box and penguin diagrams. If heavy new particles exist, they may contribute to FCNC decay amplitudes, affecting the measurement of observables related to the decay under study. Hence FCNC processes allow searches for contributions from sources of physics beyond the SM (hereafter referred to as new physics). This analysis focuses on the decay B 0 d → K * 0 (892)µ + µ − , where K * 0 (892) → K + π − . Hereafter, the K * 0 (892) is referred to as K * and charge conjugation is implied throughout, unless stated otherwise. In addition to angular observables such as the forward-backward asymmetry A FB 1, there is considerable interest in measurements of the charge asymmetry, differential branching fraction, isospin asymmetry, and ratio of rates of decay into dimuon and dielectron final states, all as a function of the invariant mass squared of the dilepton system q 2 . All of these observable sets can be sensitive to different types of new physics that allow for FCNCs at tree or loop level. The BaBar, Belle, CDF, CMS, and LHCb collaborations have published the results of studies of the angular distributions forThe LHCb Collaboration has reported a potential hint, at the level of 3.4 standard deviations, of a deviation from SM calculations [3,4] in this decay mode when using a parameterization of the angular distribution designed to minimise uncertainties from hadronic form factors. Measurements using this approach were also reported by the Belle and CMS Collaborations [6,8] and they are consistent with the LHCb experiment's results and with the SM calculations. This paper presents results following the methodology outlined in Ref. [3] and the convention adopted by the LHCb Collaboration for the definition of angular observables described in Ref. [9]. The results obtained here are compared with theoretical predictions that use the form factors computed in Ref. [10].This article presents the results of an angular analysis of the decay B 0 d → K * µ + µ − with the ATLAS detector, using 20.3 fb −1 of pp collision data at a centre-of-mass energy √ s = 8 TeV delivered by the Large Hadron Collider (LHC...

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