Search for supersymmetry in events with a lepton and missing energy at the LHC

Abstract

Preliminary results are reported from a search for physics beyond the standard model (SM) in proton-proton collisions at a center-of-mass energy of 7 TeV, focusing on the signature with a single, isolated, high-transverse momentum lepton (electron or muon), energetic jets, and large missing transverse momentum. The data sample comprises an integrated luminosity of 1.1 fb⁻¹, recorded by the CMS experiment at the LHC. The search is motivated by models of new physics, including supersymmetry. SM backgrounds are determined from control samples in the data using two complementary methods. The observed yields of events in the signal region are consistent with the background predictions. The results are interpreted in terms of limits on the parameter space for the constrained minimal supersymmetric extension of the standard model.

Link to approved PAS pending.

Approved Plots from SUS-11-015 ( click on [PDF] to get .pdf )

Figure	Abbreviated Caption
	HT distribution after preselection requirement of 1 muon, HT>300,MET>60,3 Jets PDF
	MET distribution after preselection requirement of 1 muon, HT>300,MET>60,3 Jets PDF
	Muon pT distribution after preselection requirement of 1 muon, HT>300,MET>60,3 Jets PDF

	HT distribution after preselection requirement of 1 Electron, HT>300,MET>60,3 Jets PDF
	MET distribution after preselection requirement of 1 Electron, HT>300,MET>60,3 Jets PDF
	Electron pT distribution after preselection requirement of 1 Electron, HT>300,MET>60,3 Jets PDF

	Muon pT vs MET in the muon channel for TTBar and W+Jets events PDF
	Muon pT vs MET in the muon channel for SUSY LM1 events PDF

	MET distribution in data (solid points) combining muon and electron channel, SM prediction (red histogram) and dilepton contribution in (blue histogram), log scale. PDF
	MET distribution in data (solid points) combining muon and electron channel, SM prediction (red histogram) and dilepton contribution in (blue histogram), linear scale. PDF

	Dilepton prediction in MC for events with HT > 500. PDF
	Single tau prediction in MC for events with HT > 500. PDF

	Dilepton prediction in Data for events with HT > 500. PDF
	Single tau prediction in Data for events with HT > 500. PDF

CMSSM limit from the lepton spectrum method with HT > 500 and MET>250. PDF The 95% C.L. upper limits on the signal yield are Observed limit: 32.9 Median expected: 27.8 + 1 sigma expected: 40.1 - 1 sigma expected: 22.4

CMSSM limit from the lepton spectrum method with HT > 500 and MET>350. PDF The 95% C.L. upper limits on the signal yield are Observed limit: 8.8 Median expected: 11.8 + 1 sigma expected: 16.9 - 1 sigma expected: 8.4

	MT distribution in electron events passing preselection with ST(lep) between 150 and 250 GeV. PDF
	ST(lepton) distribution in electron events passing preselection with ST(lep) between 150 and 250 GeV. PDF
	Electron pT distribution in electron events passing preselection with ST(lep) between 150 and 250 GeV. PDF

	MT distribution in muon events passing preselection with ST(lep) between 150 and 250 GeV. PDF
	ST(lepton) distribution in muon events passing preselection with ST(lep) between 150 and 250 GeV. PDF
	Muon pT distribution in Muctron events passing preselection with ST(lep) between 150 and 250 GeV. PDF

	LP distribution in muon events for ST(lep) between 250 to 350 GeV. PDF
	LP distribution in muon events for ST(lep) between 350 to 450 GeV. PDF
	LP distribution in muon events for ST(lep) greater than 450 GeV. PDF

	LP distribution in electron events for ST(lep) between 250 to 350 GeV. PDF
	LP distribution in electron events for ST(lep) between 350 to 450 GeV. PDF
	LP distribution in electron events for ST(lep) greater than 450 GeV. PDF

Fit results on DATA in the electron channel for the ST(lep) between 150 to 250 GeV. PDF

Fit results on DATA in the electron channel for the ST(lep) between 250 to 350 GeV. PDF

Comparison of the number of events observed in the data and the expectations from the background estimation method in the different ST bins for the muon channel. The red error-bars indicate the statistical uncertainty of the data only. PDF

Comparison of the number of events observed in the data and the expectations from the background estimation method in the different ST bins for the electron channel. The red error-bars indicate the statistical uncertainty of the data only. PDF

CMSSM limit from the lepton projection method.PDF

CMSSM limits from both the lepton spectrum and lepton projection methods.PDF

CMSSM limits from both the lepton spectrum and lepton projection methods, including 1 sigma bands.PDF

Event display of high MET event in the muon channel. png

Event display of high MET event in the electron channel. png

Tables from SUS-11-015

Table

Caption

Comparison of SM background yields predicted from control samples in data with expectation based on simulated event samples normalized to the integrated luminosity of the data sample. The yields are given for the defined signal regions (loose selection: MET > 250 GeV and HT > 500 GeV, tight selection: MET > 350 GeV and HT > 500 GeV). The quoted uncertainties are statistical and systematic. For the single-top and Z+jets, only simulated event (MC) samples are used. The QCD prediction from simulated event samples yields zero events for both the loose and the tight selections, but these are denoted as not available (n.a.) because the size of the samples is not sufficiently large to assess this background with a useful precision.

Predicted and observed yields in the signal regions for the loose selection (HT > 500 GeV, MET > 250 GeV) and the tight selection (HT > 500, MET > 350 GeV). The quoted uncertain- ties are statistical and systematic. All background contributions are determined from control samples in the data, except for the single-top and Z-plus-jets contributions, which are obtained from simulated event (MC) samples.

Summary of systematic uncertainties for the subtraction of the backgound from single- lepton contributions using the lepton-spectrum method.

Expected event yields in the signal region, LP < 0.15, with 1.14 fb−1 in the muon and electron channels. The MC values are only listed for illustration purposes, since the estimate of the number of SM events in the signal region uses the method described in the text. The contribution from QCD multijet production is expected to be negligible and is thus not included in the table.

Event yields in the muon control sample with < 3 jets and HT > 200 GeV in the signal region, LP < 0.15. The row “SM estimate” is the number of events expected in the signal region, as estimated from the number of events seen in the control region multiplied by the Monte Carlo translation factor RCS. The first uncertainty on the prediction shown is the statistical uncertainty from the control region, the second stems from statistical (limited MC) uncertainty on RCS. The row “data” is the number of events seen in data in the signal region.

Sources of systematic uncertainty and their effect on the translation factor, RCS, in the muon channel. The relative uncertainty in the estimated number of events in the signal region, stemming from the limited statistics of the control region, is also listed for comparison.

Sources of systematic uncertainty and their effect on the translation factor, RCS, in the electron channel. The relative uncertainty in the estimated number of events in the signal region, stemming from the limited statistics of the control region, is also listed for comparison.

Event yields in data and MC for the muon search sample with ≥ 3 jets and HT > 500 GeV. The MC yields (in columns “Total MC”) are listed for reference only. The background estimate which is used in comparing to the yields in the data is the result of the procedure described earlier and is listed in the column labelled “SM estimate”.

Event yields in data and predictions of the numbers of EWK and QCD events for the electron search sample with ≥ 3 jets and HT > 500 GeV. The sum of predicted EWK events and predicted QCD events in the control region is constraint to be equal to the total number of data events. The background estimate which is used in comparing to the yields in the data is the result of the procedure described earlier and is listed in the row labeled “SM estimate”. The uncertainty shown for the SM estimate are the full systematic uncertainties. The uncertain- ties shown for the EWK and QCD contributions are only the statistical uncertainties from the predictions.