Study of multi-muon events produced in \(p\bar{p}\) interactions at  \(\sqrt{s}=1.96\) TeV

The European Physical Journal C, Jul 2010

We report the results of a study of multi-muon events produced at the Fermilab Tevatron collider and acquired with the CDF II detector using a dedicated dimuon trigger. The production cross section and kinematics of events in which both muon candidates are produced inside the beam pipe of radius 1.5 cm are successfully modeled by known processes which include heavy flavor production. In contrast, we are presently unable to fully account for the number and properties of the remaining events, in which at least one muon candidate is produced outside of the beam pipe, in terms of the same understanding of the CDF II detector, trigger, and event reconstruction.

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Study of multi-muon events produced in \(p\bar{p}\) interactions at  \(\sqrt{s}=1.96\) TeV

The CDF Collaboration - Received: 17 August 2009 / Revised: 27 January 2010 / Published online: 12 June 2010 The Author(s) 2010. This article is published with open access at Springerlink.com Abstract We report the results of a study of multi-muon events produced at the Fermilab Tevatron collider and acquired with the CDF II detector using a dedicated dimuon trigger. The production cross section and kinematics of events in which both muon candidates are produced inside the beam pipe of radius 1.5 cm are successfully modeled by known processes which include heavy flavor production. In contrast, we are presently unable to fully account for the number and properties of the remaining events, in which at least one muon candidate is produced outside of the beam pipe, in terms of the same understanding of the CDF II detector, trigger, and event reconstruction. This Letter summarizes the findings of a study of multimuon production in pp interactions at s = 1.96 TeV [1]. The investigation was motivated by the presence of several inconsistencies that affect or affected the bb production at the Tevatron: (a) the ratio of the observed bb correlated production cross section to the next-to-leading-order QCD prediction is 1.15 0.21 when b quarks are selected via secondary vertex identification, whereas this ratio is found to be significantly larger than two when identifying b quarks through their semileptonic decays [2, 3]; (b) sequential semileptonic decays of single b quarks are supposedly the main source of dileptons with invariant mass smaller than that of a b quark, but the observed dimuon invariant mass spectrum is not well modeled by the simulation Electronic supplementary material The online version of this article (doi:10.1140/epjc/s10052-010-1336-0) contains supplementary material, which is available to authorized users. hVisitor from University of Edinburgh, Edinburgh EH9 3JZ, United iVisitor from Universidad Iberoamericana, Mexico D.F., Mexico. of this process [4]; and (c) the value of , the average time integrated mixing probability of b flavored hadrons derived from the ratio of muon pairs from b and b quarks semileptonic decays with same and opposite sign charge, is measured at hadron colliders to be larger than that measured by the LEP experiments [5, 6]. This analysis follows and complements a recent study [7] by the CDF collaboration which has used a dimuon data sample to re-measure the correlated b,b cross section. We use the same data and Monte Carlo simulated samples, and the same analysis methods. The data sample is defined by events containing two central (|| < 0.7) muons, each with transverse momentum pT 3 GeV/c, and with invariant mass larger than 5 GeV/c2. The determination of the data sample composition relies upon the high precision charged particle tracking provided by the CDF II detector [812]. Accurate track impact parameter1 and primary event vertex determinations are provided by a large central drift chamber surrounding a trio of silicon tracking devices collectively referred to in this letter as the SVX. The SVX is composed of eight layers of silicon microstrip detectors ranging in radius from 1.5 to 28 cm in the pseudorapidity region || < 1. In [7], the value of b,b is determined by fitting the impact parameter distribution of these primary muons with the expected shapes from all sources believed to be significant: semileptonic heavy flavor decays, prompt quarkonia decays, DrellYan production, and instrumental backgrounds from prompt hadrons or hadrons from heavy flavor decays which mimick a muon signal.2 In the following, the sum of these processes will be referred to as the prompt plus heavy flavor (P + HF) contribution to the dimuon sample. To ensure an accurate impact parameter measurement, analyses performed by the CDF collaboration customarily require that each muon track is reconstructed using silicon hits in at least three out of the eight SVX layers (referred to as standard SVX selection in the following). However, in order to properly model the data with the templates of the various P + HF sources, the study in [7] has used stricter selection criteria, referred to as tight SVX selection in the following, by requiring muon tracks with hits in the two innermost layers of the SVX detector, and at least in two of the 1The impact parameter is defined as the distance of closest approach of a track to the primary event vertex in the transverse plane with respect to the beamline. 2We follow the methodology pioneered by previous measurements that ignored other possible sources of muons. For example, muon tracks from pion and kaon in-flight-decays inside the tracking volume were regarded as prompt tracks because the track reconstruction algorithms were believed to remove decay muons with an appreciable kink. next four outer layers. The size of each P + HF source in the data sample is evaluated by dividing the event yield returned by the fit by the corresponding efficiency of (...truncated)


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