Search for new physics in proton-proton collisions at 7 TeV in events with a single lepton, jets, and missing transverse momentum

Abstract

Results are reported from a search for new physics beyond the Standard Model in proton-proton collisions at a center-of-mass energy = 7 TeV, focusing on the signature with a single isolated lepton, energetic jets, and large missing transverse momentum. The data sample comprises an integrated luminosity of 36.1 pb−1 recorded by the CMS experiment at the Large Hadron Collider. The presence of the lepton indicates an electroweak decay; the multiple jets can be produced in the complex decay chains of heavy objects; and the large missing momentum is associated with the presence of unobserved (weakly interacting) particles. The missing momentum can arise either from neutrino production, or, in models based on supersymmetry (SUSY), from production of the lightest supersymmetric particle. The observed number of events is consistent with Standard Model expectations based on data-driven background estimates using control samples. The results are interpreted in terms of constraints on SUSY parameter space.

Approved Plots from SUS-10-006 ( click on plot to get .pdf )

Figure Abbreviated Caption
RA4_Mu_pf-4j30_met_lin.gif Fig.1a: Distribution of missing transverse energy in the muon channel. The preselection requirements as well as MET>25 GeV have been applied. The yield for W+jets has been adjusted to have equal event numbers for data and simulation.
RA4_Mu_pf-4j30_ht_lin.gif Fig.1b: Distribution of HT in the muon channel. The preselection requirements as well as MET>25 GeV have been applied. The yield for W+jets has been adjusted to have equal event numbers for data and simulation.
RA4_Mu_pf-4j30_lepton_pt_lin.gif Fig.1c: Distribution of muon pT. The preselection requirements as well as MET>25 GeV have been applied. The yield for W+jets has been adjusted to have equal event numbers for data and simulation.
RA4_Ele_pf-4j30_met_lin.gif Fig.2a: Distribution of missing transverse energy in the electron channel. The preselection requirements as well as MET>25 GeV have been applied. The yield for W+jets has been adjusted to have equal event numbers for data and simulation.
RA4_Ele_pf-4j30_ht_lin.gif Fig.2b: Distribution of HT in the electron channel. The preselection requirements as well as MET>25 GeV have been applied. The yield for W+jets has been adjusted to have equal event numbers for data and simulation.
RA4_Ele_pf-4j30_lepton_pt_lin.gif Fig.2c: Distribution of electron pT. The preselection requirements as well as MET>25 GeV have been applied. The yield for W+jets has been adjusted to have equal event numbers for data and simulation.
RA4_table_regions.gif Tab.1: Definition of loose and tight regions for the ABCD method.
RA4_table_region_counts_a.png Tab.2: Predicted and observed yields in the different regions of the ABCD method. The yields from simulation are included for comparison - the actual prediction is based on data.
RA4_Mu_pf-4j30_mc_htVSkinMetSig.gif Fig.3a: Distribution of HT vs. MET/sqrt(HT) for standard model backgrounds (simulation) in the muon channel. The control regions ABC and the signal region D are shown for the tight selection.
RA4_Mu_pf-4j30_lm1_htVSkinMetSig.gif Fig.3b: Distribution of HT vs. MET/sqrt(HT) for the SUSY benchmark point LM1 (simulation) in the muon channel.
RA4_Ele_pf-4j30_data_htVSkinMetSig.gif Fig.3c: Distribution of HT vs. MET/sqrt(HT) for data in the electron channel.
RA4_Mu_pf-4j30_data_htVSkinMetSig.gif Fig.3d: Distribution of HT vs. MET/sqrt(HT) for data in the muon channel.
RA4_Mu-ht300_pf-4j30_kinMetSig.gif Fig.4a: Distribution of MET/sqrt(HT) in the muon channel for HT>300 GeV. The yield for W+jets has been adjusted like for Fig. 1 and 2.
RA4_Ele-ht300_pf-4j30_kinMetSig.gif Fig.4b: Distribution of MET/sqrt(HT) in the electron channel for HT>300 GeV. The yield for W+jets has been adjusted like for Fig. 1 and 2.
SM-ptmu-met.gif Fig.5: ttbar+Wjets MC, pt(mu) vs. MET, >=4 jets. In SM events the neutrino and lepton pt are anti-correlated in a given event. However, their overall spectra are very similar. The lepton spectrum method predicts the MET distribution using the lepton pt distribution.
LM1-ptmu-met.gif Fig.6: SUSY LM1 MC, pt(mu) vs. MET, >=4 jets. In SUSY events the correlation between MET and lepton pt is very different than the SM. This is because the MET is mainly from the Lightest Supersymmetric Particles (LSPs).

DataActualVsPredictedElectronTightSelectionMuPtSmeared_v2.gif Fig.7: Lepton Spectrum Method, electron channel: MET distribution, observed vs. predicted, HT>500 GeV.
DataActualVsPredictedMuonTightSelectionSmeared_v2.gif Fig.8: Lepton Spectrum Method, muon channel: MET distribution, observed vs. predicted, HT>500 GeV.
TightSelectionNumbers.gif Tab.3: Numbers observed and predicted for lepton spectrum method, tight selection (1 e or mu, >=4 jets, MET>250 GeV and HT>500 GeV)
RA4_ExclusionLimit_tanb3.gif Fig.9: tanbeta 3 exclusion plot. Limit is calculated using lepton spectrum method tight selection. Observed limit based on 2 observed events and predicted background of 3.6+/-2.9 events. Calculated 95% C.L. upper limit of 4.1 signal events using Feldman-Cousins method
RA4_ExclusionLimit_ATLAScomparison_tanb3.gif Fig.10: tanbeta 3 exclusion plot, comparison with ATLAS.
RA4_ExclusionLimit_tanb10.gif Fig.11: tanbeta 10 exclusion plot. Limit is calculated using lepton spectrum method tight selection. Observed limit based on 2 observed events and predicted background of 3.6+/-2.9 events. Calculated 95% C.L. upper limit of 4.1 signal events using Feldman-Cousins method
RA4_ExclusionLimit_tanb50.gif Fig.12: tanbeta 50 exclusion plot. Limit is calculated using lepton spectrum method tight selection. Observed limit based on 2 observed events and predicted background of 3.6+/-2.9 events. Calculated 95% C.L. upper limit of 4.1 signal events using Feldman-Cousins method.
RA4_Efficiency_tanb3.png Fig.11: Plot of efficiency for tight selection with tanbeta=3.
RA4_Efficiency_tanb10.png Fig.13: Plot of efficiency for tight selection with tanbeta=10.
RA4_Efficiency_tanb50.png Fig.14: Plot of efficiency for tight selection with tanbeta=50.
Topic attachments
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GIFgif RA4_Mu-ht300_pf-4j30_kinMetSig.gif r1 manage 13.0 K 2011-03-22 - 16:58 WolfgangAdam  
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GIFgif RA4_Mu_pf-4j30_ht_lin.gif r1 manage 12.9 K 2011-03-22 - 16:34 WolfgangAdam  
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GIFgif SM-ptmu-met.gif r3 r2 r1 manage 41.6 K 2011-03-21 - 20:11 UnknownUser  
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