Search for direct production of stops decaying to a charm and LSP using the monojet + MET final state

Abstract

A search for the pair production of light top squarks in 8 TeV pp collision events containing a jet and missing transverse momentum is presented. The data sample is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 19.7 fb−1. The number of observed events is found to be consistent with the standard model contributions determined from the collision data, and limits are set down to a minimum mass difference, m(stop) - m(chi-0), of 10 GeV/c2.

Approved Plots from SUS-13-009 PAS

Figure Caption
Jet1Pt.jpg Transverse momentum distribution of the leading pT jet . The figure is shown with all analysis cuts applied, apart from the cuts on the leading jet. Cuts include pT(j2)>60GeV/c, NJets ≤ 2 and Δφ(j1, j2) < 2.5. Differences between data and MC in the lower bins are due to inefficiencies in the trigger before we reach 100% efficiency (at pT(j1) = 110 GeV)
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Jet1Eta.jpg Pseudorapidity distribution of the leading pT jet . The figure is shown with all analysis cuts applied, apart from the cuts on the leading jet. Cuts include pT(j2)>60GeV/c, abs(η(j1)) < 2.4, NJets ≤ 2 and Δφ(j1, j2) < 2.5.
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NJet.jpg The jet multiplicity distribution. The figure is shown with all analysis cuts applied, except jet multiplicity. Cuts include pT(j1) > 110GeV/c, pT(j2)>60GeV/c, abs(η(j1)) < 2.4, and Δφ(j1, j2) < 2.5.
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dPhi_Jet1_Jet2.jpg The Δφ(j1, j2) distribution. The figure is shown with all analysis cuts applied except φ(j1, j2)<2.5. Cuts include pT(j1) > 110GeV/c, pT(j2)>60GeV/c, abs(η(j1)) < 2.4, and NJets ≤ 2.
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MetLep1.jpg Missing transverse momentum after all selection cuts for data and SM backgrounds. Representative signal points for stop signal, where m(stop)=250 GeV /cc and m(chi-0)=240 GeVcc are also overlaid.
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ZleplepMT_60_120.jpg The dimuon invariant mass distribution is shown for data (black full points with error bars) and simulation (histogram) for 60 < Mμμ < 120 GeV /c2. The MC prediction has been normalized to the data yields. There is no significant non-Z background.
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ZleplepPT_60_120.jpg The dimuon pT distribution is shown for data (black full points with error bars) and simulation (histogram) for 60 < Mμμ < 120 GeV/c2. The MC prediction has been normalized to the data yields. There is no significant non-Z background.
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WlepnuMT.jpg The transverse mass distribution MT in the single muon data control sample and predictions for W(μν), tt, Z(μμ), diboson and single-top production.
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WlepnuPT2_50_100.jpg The W transverse momentum distribution in the single muon data control sample and predictions for W(μν), tt, Z(μμ), diboson and single-top production.
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Accep_stopM_j1300.jpg Signal acceptances at pT(j1) > 300 GeV /c for all mass points studied. The acceptance is greatest for small mass differences and large top squark mass where the signal is most ’monojet’ like. Acceptance values shown are before reweighting due to ISR mis-modelling.
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Limit10.jpg Observed and expected limits on top squark production cross section as a function of the top squark mass for ΔM = 10 GeV /c2.
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Limit20.jpg Observed and expected limits on top squark production cross section as a function of the top squark mass for ΔM = 20 GeV /c2.
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Limit30.jpg Observed and expected limits on top squark production cross section as a function of the top squark mass for ΔM = 30 GeV /c2.
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Limit40.jpg Observed and expected limits on top squark production cross section as a function of the top squark mass for ΔM = 40 GeV /c2.
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Limit60.jpg Observed and expected limits on top squark production cross section as a function of the top squark mass for ΔM = 60 GeV /c2.
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Limit80.jpg Observed and expected limits on top squark production cross section as a function of the top squark mass for ΔM = 80 GeV /c2.
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limits_stop_DM.jpg Observed and expected ±1σ limits on top squark production cross section on both the (m(stop), m(stop) − m(chi-0) ) mass plane. The colour plot shows the observed production cross section for each signal point.
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limits_stop_LSP.jpg Observed and expected ±1σ limits on top squark production cross section on both the (m(stop), m(chi-0) ) mass plane.
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Supplementary Plots from SUS-13-009

Figure Caption

PFAK5JetNeuHadEngFrac.jpg Distribution of Neutral Hadronic Jet Energy Fractionof the leading jet, after jet cleaning cuts are applied.
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PFAK5JetNeuEmEngFrac.jpg Distribution of Neutral Electromagnetic Jet Energy Fractionof the leading jet, after jet cleaning cuts are applied.
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PFAK5JetChaHadEngFrac.jpg Distribution of Charged Hadronic Jet Energy Fractionof the leading jet, after jet cleaning cuts are applied.
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PFAK5JetChaEmEngFrac.jpg Distribution of Charged Neutral Electromagnetic Jet Energy Fraction of the leading jet, after jet cleaning cuts are applied.
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PFAK5JetNeuHadEngFrac2.jpg Distribution of Neutral Hadronic Jet Energy Fractionof the leading jet, after jet cleaning cuts are applied.
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PFAK5JetNeuEmEngFrac2.jpg Distribution of Charged Neutral Electromagnetic Jet Energy Fraction of the leading jet, after jet cleaning cuts are applied.
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Jet1Pt_110.jpg Transverse momentum distribution of the leading pT jet . The figure is shown with all analysis cuts applied. Cuts include pT(j1) > 110GeV/c, abs(η(j1)) < 2.4, pT(j2)>60GeV/c, abs(η(j1)) < 2.4, NJets ≤ 2 and Δφ(j1, j2) < 2.5.
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Jet1Eta_N.jpg Pseudorapidity distribution of the leading pT jet . The figure is shown with all analysis cuts applied. Cuts include pT(j1) > 110GeV/c, abs(η(j1)) < 2.4, pT(j2)>60GeV/c, abs(η(j1)) < 2.4, NJets ≤ 2 and Δφ(j1, j2) < 2.5.
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NJet_N.jpg The jet multiplicity distribution. The figure is shown with all analysis cuts applied. Cuts include pT(j1) > 110GeV/c, pT(j2)>60GeV/c, abs(η(j1)) < 2.4, NJets ≤ 2 and Δφ(j1, j2) < 2.5.
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dPhi_Jet1_Jet2_N.jpg The Δφ(j1, j2) distribution. The figure is shown with all analysis cuts applied. Cuts include pT(j1) > 110GeV/c, pT(j2)>30GeV/c, abs(η(j1)) < 2.4, Δφ(j1, j2) < 2.5 and NJets ≤ 2.
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optimisation_Limit_10.jpg Expected limit as a function of pT(j1) GeV /c, for ΔM = 10 GeV /c2.
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optimisation_Limit_20.jpg Expected limit as a function of pT(j1) GeV /c for ΔM = 20 GeV /c2.
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optimisation_Limit_30.jpg Expected limit as a function of pT(j1) GeV /c, for ΔM = 30 GeV /c2.
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optimisation_Limit_40.jpg Expected limit as a function of pT(j1) GeV /c for ΔM = 40 GeV /c2.
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optimisation_Limit_60.jpg Expected limit as a function of pT(j1) GeV /c, for ΔM = 60 GeV /c2.
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optimisation_Limit_80.jpg Expected limit as a function of pT(j1) GeV /c for ΔM = 80 GeV /c2.
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optimalLimits_JPG.jpg Optimal pT(j1) threshold at which limits are set across m_stop, ΔM phase space. An improvement is seen at low stop masses, where a lower threshold optimises the limit.
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charmpt.jpg Generator level charm quark pT distribution for 150GeV top squarks for different values of the neutralino mass.
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Cut Flow table for representative signal points

LHE files for reference and comparison, for the two signal points for which the cut flows are shown below, can be found at

/afs/cern.ch/user/r/rlucas/public/SUS-13-009/8TeV_T2cc_200_120.lhe   
 
/afs/cern.ch/user/r/rlucas/public/SUS-13-009/8TeV_T2cc_250_240.lhe

T2ccCutFlow.jpg Signal acceptance * efficiency, shown in %, for each step of the event selection, where the statistical errors are shown. Numbers are for two representative mass points; (mstop , mLSP) = (250,240) and(200,120).
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Topic attachments
I Attachment History Action Size Date Who Comment
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