Search for Supersymmetry in Final States with a Single Lepton, B-jets, and Missing Transverse Energy in Proton-Proton Collisions at √s = 7 TeV

Abstract

A search motivated by supersymmetric models with light top squarks is presented using proton-proton collision data recorded with the CMS detector at a center-of-mass energy of sqrt(s)=7 TeV during 2011, corresponding to an integrated luminosity of 4.98 inverse femtobarns. The analysis is based on final states with a single lepton, b-quark jets, and missing transverse energy. Standard model yields are predicted from data using two different approaches. The observed event numbers are found to be compatible with these predictions. Results are interpreted in the context of the constrained minimal supersymmetric standard model and of a simplified model with four top quarks in the final state.

Link to paper

PAS-SUS-11-028

Approved Plots from SUS-11-028 ( click on plot to get .pdf )

	H_T for data compared to the different SM processes. The muon and electron channels are combined and at least one b tag is required. The CMS data are represented by solid points and the simulated SM events by stacked histograms. The two lines represent possible signal scenarios. The simulation is normalized to the integrated luminosity of the data sample.
	Y_MET for data compared to the different SM processes. The muon and electron channels are combined and at least one b tag is required. The CMS data are represented by solid points and the simulated SM events by stacked histograms. The two lines represent possible signal scenarios. The simulation is normalized to the integrated luminosity of the data sample.
	YMET vs HT for the SM background. The muon and electron channels are combined and at least one b tag is required.
	YMET vs HT for the low mass signal point LM8. The muon and electron channels are combined and at least one b tag is required.
	The 95% CL limit using the CLs technique for the CMSSM model with tanβ=10, A0=0GeV and mu>0. The area below the solid red line is excluded.
	Acceptance times efficiency for the simplified model "T1tttt". At least three b-tags are required.
	The 95% cross-section upper limit using the CLs technique for the simplified model ”T1tttt” for the inclusive three b-tag selection. The area below the solid line is excluded.

Tables	Comment
	Table 5: Definition of the different regions used for the factorization method with H_T and Y_MET. Two sets of selections are defined depending on the number of b tags. Region D is expected to be signal dominated.
	Table 6: Correlation factor κ between HT and YMET for the main SM background processes and a for different number of b tags, for the two signal regions. For purposes of illustration, the corresponding results for a sample with 0 b tags is also shown. While the 0 b-tag sample is dominated by W+jets events, the channels that include b tags contain mainly tt events. Only statistical uncertainties are shown.
	Table 7: Overview of the uncertainties on the correlation factor κ for the different b-tag selections. The signal regions corresponding to the number of required b tags are as defined in Table 5. All systematic uncertainties are added in quadrature. The variations in JES, JER, plepton, and unclustered energy are propagated to the MET. The row labeled ’0 b tag’ addresses the difference between the values of κ in data and simulation.
	Table 8: Systematic uncertainties in the signal region for the different selections for the SM simulation, needed for the comparison with data (as in Table 10). The signal regions corresponding to the number of required b tags are as defined in Table 5. All uncertainties are summed in quadrature. The variations in JES, JER, plepton, and unclustered energy are propagated to the MET.
	Table 10: Number of reconstructed (ND) and predicted (Nˆ D) events in the signal region for the factorization method for the SM, two possible signal scenarios (LM6, LM8), and data. The first uncertainties are statistical and the second systematic. The systematic uncertainty on Nˆ D in data is equal to the uncertainty on κ. The systematic uncertainty in simulation includes the uncertainty on the absolute rate of simulated events, as discussed in the text. The exclusive 0 b-tag selection is shown for comparison as well.

Supporting Plot

Comment

B-tag efficiency as function of the jet pT in simulated TT+Jets events after the event selection w/o any b-tag requirement. Scale factors are applied to match differences between the b-tag efficiency in data and that in simulated events. The distribution is fitted with a function that consists of a linear function between 40 and 90 GeV, a constant between 90 and 185 GeV and a linear function between 185 and 670 GeV. The fit parameters are the efficiency at 40 GeV (p0), the slope of the first linear function (p1) and the slope of the second linear function (p2).