Scalar Top Quark Search with Jets and Missing Transverse Momentum in pp Collisions at sqrt(s)= 7 TeV


Physics Analysis Summary on CDS

A search for scalar top quarks is presented in final states with jets and missing transverse momentum. The data sample of proton-proton collisions used corresponds to an integrated luminosity of 4.98 / fb collected at sqrt(s) = 7 TeV with the CMS detector at the LHC. The data is found to be in agreement with the predicted backgrounds. Exclusion limits are set in simplified models with the top squark decaying to an undetected particle and jets, either through an on-shell top quark, or through a chargino. For a massless undetected particle, we respectively exclude at 95 percent C.L. top squark masses between 295 and 375 GeV and between 280 and 375 GeV, the latter for a chargino at 75 percent of the top squark mass.



selection.png Search region selections

table1.png Number of expected simulated and observed data events for an integrated luminosity of 4.98 fb-1.

table5.png Total prediction for the lost e, mu and tau backgrounds along with the considered uncertainties.

table3.png Summary of the prediction of the Z(nunu)+jets background in all the search regions.Yields from simulation are normalized to leading-order cross section.

table4.png Summary of the corrections and the corresponding systematic uncertainties on the Z(nunu)+jets background prediction in all search region

table5.png Prediction for the QCD multijet background, along with the statistical and systematic uncertainties

results.png Number of predicted, expected from simulation, and observed events for an integrated luminosity of 4.98 fb-1.

Figure Figure Abbreviated Caption
T2tt.png T2bw.png Figure 1: Diagrams of the simplified models of direct stop pair production considered, either with a decay to an on-shell top quark (left) or via chargino (right).

Figure Abbreviated Caption
spectrum_met_log.png Figure 2: Missing transverse momentum distribution for events passing the baseline selection. Data yields are compared to the analysis background predictions. Two signal models are shown overlaid to the background.

Figure Figure Abbreviated Caption
qcd_dphi_closure_no_min_bDPhi.png qcd_dphi_closure_geq1_min_bDPhi.png Figure 3: Distributions of minimum Δφ between the leading three jets and MET, for events passing selection criteria as stated in the titles. The out-of-the-box simulation versus the reweighted QCD prediction is compared to the data yield in these plots. All QCD distributions are stacked on top of the non-QCD contribution.

Figure Abbreviated Caption
barchart.png Figure 4: Number of events predicted, observed, and expected from simulation, for various search regions, and split per background component. The hatched band represents the total uncertainty on the prediction. Two signal models are shown overlaid to the background.

Figure Figure Abbreviated Caption
1d_T2tt.png 1d_T2bw.png Figure 5: Expected and observed 95% CL upper limits (baseline selection) on the direct stop pair production cross section, for the decay in Stop → top+LSP (left) and Stop → b + chargino, chargino → W LSP for x=0.25,0.5,0.75 where x = x * m(stop) + (1-x) * m(LSP). The limits are shown as a function of the stop mass for LSP mass of 0 GeV, considering a theory uncertainty of 15% for each point.

Figure Figure Abbreviated Caption
2d_T2tt.png 2d_T2bw.png Figure 6: Expected and observed 95% CL upper limits (baseline selection) on the direct stop pair production cross section, for the decay in Stop → top+LSP (left) and Stop → b + chargino, chargino → W LSP for x=0.75 (right) where x = x * m(stop) + (1-x) * m(LSP). The limits are shown as a function of the stop and the LSP mass, considering a theory uncertainty of 15% for each point.

Figure Figure Abbreviated Caption
2d_T2tt.png 2d_T2bw.png Extra 1: Selection efficiency (baseline selection) on the direct stop pair production cross section, for the decay in Stop → top+LSP (left) and Stop → b + chargino, chargino → W LSP for x=0.75 (right) where x = x * m(stop) + (1-x) * m(LSP).
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Topic revision: r2 - 2012-11-20 - StevenLowette
 
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