Measurement of the B→m+m− branching fraction and search for B0→m+m− with the CMS experiment

Q: What decays are investigated in this study?

The analysis searches for the rare decays B→μ+μ− and B0→μ+μ− using CMS data from pp collisions at √s = 7 and 8 TeV.

Q: What limits or evidence are reported for B0→μ+μ−?

For B0→μ+μ−, the study sets an upper limit B(B0→μ+μ−) < 1.1×10−9 at the 95% confidence level, while B→μ+μ− shows an excess with 4.3σ significance.

Aug 27, 2026

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Results are presented from a search for rare decays B→μ+μ− and B0→μ+μ− in pp collisions at √s = 7 and 8 TeV, using CMS data samples with integrated luminosities of 5 and 20 fb−1. An unbinned maximum-likelihood fit to the dimuon invariant-mass distribution yields a branching fraction B(B→μ+μ−)=(3.010..09)×10−9, with uncertainties including statistical and systematic contributions. An excess of B→μ+μ− events over background is observed with a 4.3 standard-deviation significance. For B0→μ+μ−, an upper limit B(B0→μ+μ−)<1.1×10−9 at 95% confidence level is set. Both results are consistent with Standard Model expectations.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages31

Reading Time1 h 18 min

AccessFree to download

Abstract

Introduction and Standard Model context

Data samples and analysis strategy

Signal region and background modeling

Monte Carlo simulation and normalization/control samples

Detector description and event reconstruction

Coordinate system and subdetectors

Trigger and event selection

arXiv : 1307 .5025v3 [hep-ex] 4 Oct 2013 EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-PH-EP/2013-129 2013/10/08 CMS-BPH-13-004 Measurement of the B ! m + m 􀀀 branching fraction and search for B0 ! m + m 􀀀 with the CMS experiment The CMS Collaboration 􀀃 Abstract Results are presented from a search for the rare decays B ! m+ m 􀀀 and B0 ! m+ m 􀀀 in pp collisions at ps = 7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20 fb 􀀀1, respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood ﬁt to the dimuon invariant mass distribution gives a branching fraction B (B ! m+ m 􀀀 ) = (3.010..09) 􀀂 10 􀀀9, where the uncertainty includes both statistical and systematic contributions. An excess of B ! m+ m 􀀀 events with respect to background is observed with a signiﬁcance of 4.3 standard deviations. For the decay B0 ! m+ m 􀀀 an upper limit of B (B0 ! m+ m 􀀀 ) < 1.1 􀀂 10 􀀀9 at the 95% conﬁdence level is determined. Both results are in agreement with the expectations from the standard model. Published in Physical Review Letters as doi:10 . 1103/PhysRevLett .111 .101804 . 􀀍c 2013 CERN for the beneﬁt of the CMS Collaboration. CC-BY-3.0 license 􀀃 See Appendix B for the list of collaboration members In the standard model (SM) of particle physics, tree-level diagrams do not contribute to ﬂavorchanging neutral-current (FCNC) decays. However, FCNC decays may proceed through higherorder loop diagrams, and this opens up the possibility for contributions from non-SM particles. In the SM, the rare FCNC decays B (B0 ) ! m+ m 􀀀 have small branching fractions of B (B ! m+ m 􀀀 ) = (3.57 􀀆 0.30) 􀀂 10 􀀀9, corresponding to the decay-time integrated branching fraction, and B (B0 ! m+ m 􀀀 ) = (1.07 􀀆 0.10) 􀀂 10 􀀀10 [1, 2] . Charge conjugation is implied throughout this Letter. Several extensions of the SM, such as supersymmetric models with nonuniversal Higgs boson masses [3], speciﬁc models containing leptoquarks [4], and the minimal supersymmetric standard model with large tan b [5, 6], predict enhancements to the branching fractions for these rare decays. The decay rates can also be suppressed for speciﬁc choices of model parameters [7] . Over the past 30 years, signiﬁcant progress in sensitivity has been made, with exclusion limits on the branching fractions improving by ﬁve orders of magnitude. The ARGUS [8], UA1 [9], CLEO [10], Belle [11], BaBar [12], CDF [13], D0 [14], ATLAS [15], CMS [16], and LHCb [17] experiments have all published limits on these decays. The LHCb experiment has subsequently shown evidence, with 3.5 standard deviation signiﬁcance, for the decay B ! m+ m 􀀀 with B (B ! m+ m 􀀀 ) = (3.211..52) 􀀂 10 􀀀9 [18] . This Letter reports a measurement of B (B ! m+ m 􀀀 ) based on a simultaneous search for B ! m+ m 􀀀 and B0 ! m+ m 􀀀 decays using a data sample of pp collisions corresponding to integrated luminosities of 5 fb 􀀀1 at p s = 7 TeV and 20 fb 􀀀1 at 8 TeV collected by the Compact Muon Solenoid (CMS) experiment atthe Large Hadron Collider (LHC). For these data, the peak luminosity varied from 3.5 􀀂 1030 to 7.7 􀀂 1033cm 􀀀2s 􀀀1 . The average number of interactions per bunch crossing (pileup) was 9 (21) at p s = 7 (8)TeV. The search for the B ! m+ m 􀀀 signal, where B denotes B or B0, is performed in the dimuon invariant mass regions around the B and B0 masses. To avoid possible biases, the signal region 5.20 < mmm < 5.45 GeV was kept blind until all selection criteria were established. For the 7 TeV data, this Letter reports a re-analysis of the data used in the previous result [16], where the data were re-blinded. The combinatorial dimuon background, mainly from semileptonic decays of separate B mesons, is evaluated by extrapolating the data in nearby mass sidebands into the signal region. Monte Carlo (MC) simulations are used to account for backgrounds from B and Lb decays. These background samples consist of B ! hmn, B ! hmm, and Lb ! pmn decays, as w

FAQs

What decays are investigated in this study?

The analysis searches for the rare decays B→μ+μ− and B0→μ+μ− using CMS data from pp collisions at √s = 7 and 8 TeV.

How is the branching fraction for B→μ+μ− extracted?

An unbinned maximum-likelihood fit to the dimuon invariant-mass distribution is used to determine B(B→μ+μ−), including statistical and systematic uncertainties.

What limits or evidence are reported for B0→μ+μ−?

For B0→μ+μ−, the study sets an upper limit B(B0→μ+μ−) < 1.1×10−9 at the 95% confidence level, while B→μ+μ− shows an excess with 4.3σ significance.

Aug 27, 2026

Upload by Oliver