"Search for new physics in events with opposite-sign leptons, jets and missing transverse energy"

This is a condensed description with plots for the analysis CMS-SUS-11-011

Abstract

A search is presented for physics beyond the standard model (SM) in final states with an opposite-sign isolated lepton pair accompanied by jets and missing transverse energy. Two complementary search strategies are performed using LHC data recorded at a center-of-mass energy of sqrt(s) = 7 TeV corresponding to an integrated luminosity of 4.7 fb-1. The first search probes models with a specific dilepton production mechanism, which leads to a characteristic kinematic edge in the dilepton mass distribution. The second search probes models with heavy, colored objects which decay to final states including invisible particles, leading to very large hadronic activity and missing transverse energy. No evidence for an event yield beyond SM expectations is found. Upper limits on the non-SM contributions to the signal regions are deduced from the results, which are used to exclude a region of the parameter space of the constrained minimal supersymmetric extension of the standard model. Additional information related to detector efficiencies and response is provided to allow testing whether specific models of new physics are excluded by these results.

Link to the 1 fb-1 analysis PAS CMS-PAS-SUS-11-011

Figures

Click on a figure to enlarge it, then double click to go to normal size again.

FIGURE FILES Description
stacks_47fb_Jan31_dyCor_fakeCor_paper.png png, pdf Figure 1: Distributions of (top left) missing tranverse energy ETmiss, (top right) scalar sum of jet transverse energies (HT), (bottom left) dilepton transverse momentum pT(ll), and (bottom right) jet multiplicity for SM MC and data after preselection. The last bin contains the overflow.

edgeSignalMet150-GT.png png, pdf Figure 2 (a):Results of the maximum likelihood fit to the dilepton mass distribution for events containing ee and μμ lepton pairs in the signal region HT > 300 GeV, Emiss > 150 GeV for an example value of the kinematic edge position mmax = 280 GeV.

edgeOFOSSignalMet150-GT.png png, pdf Figure 2 (b): Results of the maximum likelihood fit to the dilepton mass distribution for events containing eμ lepton pairs (background) in the signal region HT > 300 GeV, ETmiss > 150 GeV.

scatter_47fb.png png, pdf Figure 3 (a): Distributions of ETmiss vs. HT for data in the light lepton channels. The signal regions are indicated as shaded regions.

ht_vs_met_yields_MergedData.png png, pdf Figure 3 (b): Distributions of ETmiss vs. HT for data in the hadronic tau channels. The signal regions are indicated as shaded regions.

ptll_R4.png png, pdf Figure 4 (a): The observed ETmiss distribution (red points) and ETmiss distribution predicted by the pT(ll) method (blue points with shaded errors) in data for the region 125 < HT < 300 GeV. The error bars on the predicted ETmiss distribution are statistical, and also include systematic uncertainties for points in the signal regions indicated by the vertical dashed lines.

ptll_HighMet_47fb.png png, pdf Figure 4 (b): The observed ETmiss distribution (red points) and ETmiss distribution predicted by the pT(ll) method (blue points with shaded errors) in data for the region HT > 300 GeV. The error bars on the predicted ETmiss distribution are statistical, and also include systematic uncertainties for points in the signal regions indicated by the vertical dashed lines.

ptll_SR2_47fb.png png, pdf Figure 4 (c): The observed ETmiss distribution (red points) and ETmiss distribution predicted by the pT(ll) method (blue points with shaded errors) in data for the region HT > 600 GeV. The error bars on the predicted ETmiss distribution are statistical, and also include systematic uncertainties for points in the signal regions indicated by the vertical dashed lines.

yields_summary_taus.png png, pdf Figure 5: Summary of the background predictions and observed yields in the four signal regions including taus.

limitSignalMet150-GT.png png, pdf Figure 6: CLS 95% confidence level upper limit on the signal yield as a function of the endpoint in the invariant mass spectrum, mcut, assuming a triangular shaped signal (black dots and line). The hatched band shows the variation of the expected limit assuming two alternate signal shapes. A benchmark SUSY scenario with the dilepton mass shape and 20% of the expected LM1 yield is shown for the position of the kinematic edge in this model mmax = 78 GeV.

RA6_nominal.png png, pdf Figure 7: The observed 95% CL exclusion contour at (solid red line), the expected exclusion contour (solid blue line), the variation in the observed and expected exclusions from the variation of PDF, renormalization and factorization scale, and αS theoretical uncertainties (dashed red and dashed blue lines), the ±1σ uncertainty in the median expected exclusion (dotted blue lines), and the observed exclusion contour based on 34 pb-1 2010 data in the opposite-sign dilepton channel (purple shaded region), in the CMSSM (m0, m1/2) plane for tanBeta = 10, A0 = 0 and mu > 0. The area below the curve is excluded by this measurement. Exclusion limits obtained from previous experiments are presented as shaded areas in the plot. Thin grey lines correspond to constant squark and gluino masses. This exclusion is based on the results of the search for opposite sign light lepton pairs accompanied by large ETmiss and HT.

RA6_band.png png, pdf The observed 95% CL exclusion contour at (solid red line), the expected exclusion contour (solid blue line), the variation in the observed and expected exclusions from the variation of PDF, renormalization and factorization scale, and αS theoretical uncertainties (dashed red and dashed blue lines), the ±1σ uncertainty in the median expected exclusion (dotted blue lines), and the observed exclusion contour based on 34 pb-1 2010 data in the opposite-sign dilepton channel (purple shaded region), in the CMSSM (m0, m1/2) plane for tanBeta = 10, A0 = 0 and mu > 0. The area below the curve is excluded by this measurement. Exclusion limits obtained from previous experiments are presented as shaded areas in the plot. Thin grey lines correspond to constant squark and gluino masses. This exclusion is based on the results of the search for opposite sign light lepton pairs accompanied by large ETmiss and HT. This plot is the same as above, but with an alternate style

makeLeptonPlots.png png, pdf Figure 8 (a):The efficiency to pass the light lepton selection as function of the generator-level pT.

LM6_tauefficiency.png png, pdf Figure 8 (b): The efficiency to pass the hadronic tau selection as function of the generator-level visible tau pT.

met_turnon_LM6.png png, pdf Figure 9 (a): The efficiency to pass the signal region ETmiss requirements as a function of the generator-level quantities. The vertical lines represent the requirements applied to the reconstruction level quantities. These efficiencies are calculated using the LM6 Monte Carlo, but they are not expected to depend strongly on the underlying physics.

ht_turnon_LM6.png png, pdf Figure 9 (b): The efficiency to pass the signal region HT requirements as a function of the generator-level quantities. The vertical lines represent the requirements applied to the reconstruction level quantities. These efficiencies are calculated using the LM6 Monte Carlo, but they are not expected to depend strongly on the underlying physics.

Tables from the Paper

TABLE FILES Description

png, pdf Table1: Data yields and MC predictions in the light lepton channels after preselection, using the quoted NLO production cross sections σ. The tt ̄ → l+l− corrresponds to dilepton tt ̄ with no W → τ decays, tt ̄ → lτ∓/τ+τ−refers to dilepton tt ̄ with at least 1 W → τ decay, and tt ̄ → fake includes all other tt ̄ decay modes. The LM points are benchmark SUSY scenarios which are defined in the text. All uncertainties include the statistical component and the 4.5% uncertainty in the integrated integrated luminosity. The data yield is in agreement with the MC prediction, but the MC is not used quantitatively in the search.

png, pdf Table2: Data yields and MC predictions in the hadronic tau channels after preselection, using the quoted NLO production cross sections σ. The channel with two hadronic tau decays is not presented because the trigger is not efficient in the preselection region. The samples of MC tt ̄, W + jets, and single-top events were generated with MADGRAPH. All other samples were generated with PYTHIA. The error indicated represents statistic and systematic errors.

png, pdf Table 3: Summary of the observed same-flavor (SF), opposite-flavor(OF) and total yields and predicted yields in the 3 signal regions. The uncertainty in the MC prediction and yields for the benchmark SUSY LM scenarios are statistical only. The first uncertainty on the pT(ll) method prediction is statistical and the second is systematic; the systematic uncertainty is discussed in the text. The non-SM yield UL is a CLS 95% confidence level upper limit.

png, pdf Table4: Summaryoftheobservedandpredictedyieldsinthefoursignalregionsforchannels including taus. The first indicated error is statistical and the second is systematic; the systematic uncertainties on the TL ratio and p_T(ll) method predictions are discussed in the text.

png, pdf Table 5: Values of the fitted parameters (according to $ f(p_T) = \epsilon_{\rm \infty} \{{\rm erf} [(p_{T} - C)/\sigma] \} + \epsilon_C \{ 1 - {\rm erf}[(p_T - C)/\sigma]\}$) for the lepton selection efficiencies of Fig. 8.

png, pdf Table 6: Values of the fitted parameters (according to $ f(x) = 0.5 \times \epsilon_{\infty} \times ( {\rm erf}((x-C)/\sigma) + 1 ) $) for the ETmiss and HT selection efficiencies of Fig. 9.

Additional Material

FIGURE FILES Description

OS_ZtoEE.png png Invariant mass of opposite sign di-electron pairs after the dilepton selection. The last bin contains the overflow.

OS_ZtoEE.png png Invariant mass of opposite sign di-muon pairs after the dilepton selection. The last bin contains the overflow.

edgeSignalMet150LM1x0.2-GT.png png, pdf Simulation, no data!
Results of the maximum likelihood fit for ee and mm lepton pairs on simulation. This plot can be used to illustrate the components of the fit. The simulated signal has the shape of LM1, but only 20% of its yield.

png, pdf Transverse mass defined by the electron momentum and MET. Filled histograms show e-tau_h events from SM. Staged on top is the TL prediction for e-tau_fake events. The hatched band denotes the statistical plus systematic error for the prediction. Data and prediction are found to be consistent.
Topic attachments
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PDFpdf LM6_tauefficiency.pdf r1 manage 15.7 K 2012-03-01 - 15:53 NiklasMohr  
PNGpng LM6_tauefficiency.png r1 manage 119.9 K 2012-03-01 - 15:53 NiklasMohr  
PNGpng OS_ZtoEE.png r1 manage 79.5 K 2012-03-01 - 19:43 MatthiasEdelhoff  
PNGpng OS_ZtoMuMu.png r1 manage 74.1 K 2012-03-01 - 19:43 MatthiasEdelhoff  
PDFpdf RA6_band.pdf r1 manage 41.4 K 2012-03-01 - 18:38 BenHooberman CMSSM plot (alternate style)
PNGpng RA6_band.png r1 manage 264.1 K 2012-03-02 - 09:39 BenHooberman  
PDFpdf RA6_nominal.pdf r2 r1 manage 24.0 K 2012-06-20 - 15:31 DanielSprenger Update to final version
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PDFpdf ht_turnon_LM6.pdf r1 manage 19.5 K 2012-03-01 - 15:51 NiklasMohr  
PNGpng ht_turnon_LM6.png r1 manage 173.4 K 2012-03-01 - 15:51 NiklasMohr  
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PDFpdf makeLeptonPlots.pdf r1 manage 19.6 K 2012-03-01 - 15:53 NiklasMohr  
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PDFpdf table1.pdf r2 r1 manage 130.7 K 2012-03-09 - 15:25 MatthiasEdelhoff  
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