EXO-11-101: Search in leptonic channels for heavy resonances decaying to long-lived neutral particles

Abstract

A search is performed for heavy resonances decaying to two long-lived massive neutral particles, each decaying to leptons. The experimental signature is a distinctive topology consisting of a pair of oppositely charged leptons originating at a separated secondary vertex. Events were collected by the CMS detector at the LHC during pp collisions at √s = 7 TeV, and selected from data samples corresponding to 4.1 (5.1) fb-1 of integrated luminosity in the electron (muon) channel. No significant excess is observed above standard model expectations, and an upper limit is set with 95% confidence level on the production cross section times the branching fraction to leptons, as a function of the long-lived massive neutral particle lifetime. The plots below are in the following order: Selection, Tracking Efficiency, Background, Limits. Paper submitted to JHEP, arXiv:1211.2472v1, CDS record.

Figure Abbreviated Caption
dielectron_decayLengthSignificance2D.png The transverse decay length significance of the candidates for the dielectron channel. It is required to be more than 8 standard deviations.
dimuon_decayLengthSignificance2D.png The transverse decay length significance of the candidates for the dimuon channel. It is required to be more than 5 standard deviations.
dielecloose_1_decayLengthSignificance2D.png The transverse decay length significance of the candidates for the dielectron channel with loosened cuts. Specifically, the cuts on the individual lepton d0 and the decay length significance Lxy/σ are removed.
dimuloose_1_decayLengthSignificance2D.png The transverse decay length significance of the candidates for the dimuon channels with loosened cuts. Specifically, the cuts on the individual lepton d0 and the decay length significance Lxy/σ are removed.
dielectron_massPrompt.png The invariant mass distribution of dielectron candidates after applying all selection cuts except the ones on transverse impact parameter significance and on vertex flight direction, and with the decay length significance cut inverted.

This predominantly selects prompt background such as Z bosons. The agreement of both shape and normalisation between data and Monte Carlo simulation demonstrates a good understanding of the Standard Model backgrounds.

dimuon_massPrompt.png The invariant mass distribution of dimuon candidates after applying all selection cuts except the ones on transverse impact parameter significance and on vertex flight direction, and with the decay length significance cut inverted.

This predominantly selects prompt background such as Z bosons. The agreement of both shape and normalisation between data and Monte Carlo simulation demonstrates a good understanding of the Standard Model backgrounds.

dielectron_massDisplaced.png The reconstructed dielectron mass in the dielectron channel, after all selection cuts have been applied.
dimuon_massDisplaced.png The reconstructed dimuon mass in the dimuon channel, after all selection cuts have been applied.
track_effi_electrons_DisplacedE_50GeV_stdRECO_20120105.png Track reconstruction efficiency for single, isolated electrons of pT = 50 GeV/c as a function of the transverse impact parameter. The efficiency has little dependence on pT.
track_effi_muons_DisplacedMu_50GeV_stdRECO_20120105.png Track reconstruction efficiency for single, isolated muons of pT = 50 GeV/c as a function of the transverse impact parameter. The efficiency has little dependence on pT.
styled_EffVsDxy.png Efficiency of the tracker to find a track, given a cosmic-ray muon reconstructed in the muon chambers, as a function of the transverse impact parameter of the muon. Only muons with -10 cm < z0 < 10 cm are used.
styled_EffVsDz.png Efficiency of the tracker to find a track, given a cosmic-ray muon reconstructed in the muon chambers, as a function of the longitudinal impact parameter of the muon when no cut is applied on this variable. Only muons with -4 cm < d0 < 4 cm are used.
SignalEff.png The efficiency of X → l+l decays to pass all selection criteria, both for H0 → XX events in which only one long-lived exotic decays to the chosen lepton species (ε1) and for the case where both decay to the chosen lepton species (ε2). The uncertainties on these efficiencies are not shown in the table. They are dominated by the 20% relative uncertainty related to the tracking performance.
BackgroundFit_MCAll_electron_pt41 Fit to the transverse decay length significance of the candidates in simulated background events for the dielectron channel.
BackgroundFit_MCAll_muon_pt33 Fit to the transverse decay length significance of the candidates in simulated background events for the dimuon channel.
BackgroundPDFWinter_electronDataPrompt_BWTurnOnPlusExp_Paper Distribution of the dielectron mass and the fitted shape in a data sample with lifetime-related selection requirements removed). The shape used is that of a Breit--Wigner distribution times a turn-on function, added to an exponential term.
BackgroundPDFWinter_muonDataPrompt_BWTurnOnPlusExp_Paper Distribution of the dimuon mass and the fitted shape in a data sample with lifetime-related selection requirements removed). The shape used is that of a Breit--Wigner distribution times a turn-on function, added to an exponential term.
limitsBayesianWinterEventsElectron41Exp.png The 95% confidence level upper limit on the mean number of X bosons that could pass the selection requirements in the electron channel. A yellow band indicates the 95% uncertainty on the expected limit, but is almost entirely hidden by the observed limit points.
limitsBayesianWinterEventsMuon33Exp.png The 95% confidence level upper limit on the mean number of X bosons that could pass the selection requirements in the muon channel. A yellow band indicates the 95% uncertainty on the expected limit, but is almost entirely hidden by the observed limit points.
limitsCLsLifetimeElectronsMH400.png 95% confidence level upper limits on σ×B for the electron channel for a H0 mass of 400 GeV/c2.
limitsCLsLifetimeElectronsMH1000.png 95% confidence level upper limits on σ×B for the electron channel for a H0 mass of 1000 GeV/c2.
limitsCLsLifetimeMuonsMH125.png 95% confidence level upper limits on σ×B for the muon channel for a H0 mass of 125 GeV/c2.
limitsCLsLifetimeMuonsMH200.png 95% confidence level upper limits on σ×B for the muon channel for a H0 mass of 200 GeV/c2.
limitsCLsLifetimeMuonsMH400.png 95% confidence level upper limits on σ×B for the muon channel for a H0 mass of 400 GeV/c2.
limitsCLsLifetimeMuonsMH1000.png 95% confidence level upper limits on σ×B for the muon channel for a H0 mass of 1000 GeV/c2.
EventDisplay_MCSignal_3DTower.png An example of a simulated Monte Carlo event event with a H0 mass of 400 GeV/c2 and X boson mass of 150 GeV/c2.
EventDisplay_MCSignal_RPhi.png An example of a simulated Monte Carlo event event (r-φ view) with a H0 mass of 400 GeV/c2 and X boson mass of 150 GeV/c2.

-- IanTomalin - 15-Nov-2012

Topic attachments
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PDFpdf BackgroundPDFWinter_muonDataPrompt_BWTurnOnPlusExp_Paper.pdf r1 manage 33.1 K 2012-11-16 - 16:50 NunoLeonardo  
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PNGpng EventDisplay_MCSignal_RPhi.png r2 r1 manage 558.4 K 2012-11-25 - 12:19 NunoLeonardo  
PDFpdf SignalEff.pdf r3 r2 r1 manage 119.7 K 2012-11-21 - 03:02 NunoLeonardo  
PNGpng SignalEff.png r3 r2 r1 manage 900.8 K 2012-11-21 - 03:01 NunoLeonardo  
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PNGpng dielectron_decayLengthSignificance2D.png r4 r3 r2 r1 manage 16.8 K 2012-11-27 - 12:53 NunoLeonardo  
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PNGpng dielectron_massPrompt.png r2 r1 manage 202.9 K 2012-11-16 - 18:32 NunoLeonardo  
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PDFpdf dimuon_massPrompt.pdf r3 r2 r1 manage 63.6 K 2012-11-29 - 12:55 NunoLeonardo  
PNGpng dimuon_massPrompt.png r2 r1 manage 284.4 K 2012-11-29 - 13:00 NunoLeonardo  
PDFpdf limitsBayesianWinterEventsElectron41Exp.pdf r2 r1 manage 27.7 K 2012-11-16 - 13:05 NunoLeonardo  
PNGpng limitsBayesianWinterEventsElectron41Exp.png r2 r1 manage 91.9 K 2012-11-16 - 13:05 NunoLeonardo  
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PNGpng limitsBayesianWinterEventsMuon33Exp.png r2 r1 manage 82.4 K 2012-11-16 - 13:05 NunoLeonardo  
PDFpdf limitsCLsLifetimeElectronsMH1000.pdf r2 r1 manage 33.2 K 2012-11-16 - 13:05 NunoLeonardo  
PNGpng limitsCLsLifetimeElectronsMH1000.png r2 r1 manage 143.7 K 2012-11-16 - 13:05 NunoLeonardo  
PDFpdf limitsCLsLifetimeElectronsMH400.pdf r2 r1 manage 32.0 K 2012-11-16 - 13:05 NunoLeonardo  
PNGpng limitsCLsLifetimeElectronsMH400.png r2 r1 manage 131.2 K 2012-11-16 - 13:05 NunoLeonardo  
PDFpdf limitsCLsLifetimeMuonsMH1000.pdf r2 r1 manage 35.9 K 2012-11-16 - 13:03 NunoLeonardo  
PNGpng limitsCLsLifetimeMuonsMH1000.png r2 r1 manage 139.2 K 2012-11-16 - 13:03 NunoLeonardo  
PDFpdf limitsCLsLifetimeMuonsMH125.pdf r1 manage 33.7 K 2012-11-16 - 19:05 NunoLeonardo  
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PNGpng limitsCLsLifetimeMuonsMH200.png r2 r1 manage 112.6 K 2012-11-16 - 13:03 NunoLeonardo  
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