SUS-11-011 : Search for new physics in events with opposite-sign dileptons and missing transverse energy

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Abstract

A search is presented for physics beyond the standard model (SM) in final states with opposite-sign isolated lepton pairs accompanied by hadronic jets and missing transverse energy. Two complementary search strategies are performed using LHC data recorded at a center-of-mass energy s√=7 TeV with the CMS detector, corresponding to an integrated luminosity of 0.98 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.

Approved Plots from SUS-11-011

Figure Abbreviated Caption
Figure 1: Distributions of (top left) missing tranverse energy Emiss, (top right) scalar sum of jet transverse energies (HT), (bottom left) dilepton invariant mass m(ll), and (bottom right) dilepton transverse momentum pT(ll) for SM MC and data after preselection. The last bin contains the overflow. The MC has been normalized to match the data by applying a scale factor of 1.13. Here VV indicates the sum of WW, WZ, and ZZ. The MC distributions for the LM6 benchmark point are also shown.
Figure 2 (a): Results of the maximum likelihood fit to the dilepton mass distribution for events containing ee and μμ lepton pairs in the control region defined as 100 < HT < 300 GeV, Emiss > 100 GeV. In the extended fit the number of signal nS, Z nZ and tt nB events is extracted as well.
Figure 2 (b): Results of the maximum likelihood fit to the dilepton mass distribution for events containing eμ lepton pairs in the control region defined as 100 < HT < 300 GeV, Emiss > 100 GeV. In the extended fit the number of signal nS, Z nZ and tt nB events is extracted as well.
Figure 2 (c): 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 > 100 GeV. In the extended fit the number of signal nS, Z nZ and tt nB events is extracted as well.
Figure 2 (d): Results of the maximum likelihood fit to the dilepton mass distribution for events containing eμ lepton pairs in the signal region HT > 300 GeV, Emiss > 100 GeV. In the extended fit the number of signal nS, Z nZ and tt nB events is extracted as well.
Figure 3: Distributions of Emiss vs. HT for data. The high Emiss (high HT) signal region is indicated with the blue dotted (red striped) region.
Figure 4 (a): Distributions of y vs. HT in data. The signal region Emiss > 275 GeV, HT > 300 GeV is indicated with thick black lines. The f(y) and g(HT) functions are measured using events in the green and red shaded areas, respectively.
Figure 4 (b): Distributions of y vs. HT in data. The signal region Emiss > 200 GeV, HT > 600 GeV is indicated with thick black lines. The f(y) and g(HT) functions are measured using events in the green and red shaded areas, respectively.
Figure 5 (a): Distributions of pT(ll) scaled by the Emiss acceptance correction factor K (predicted) and Emiss (observed) for SM MC and data. The high Emiss signal region is indicated by the vertical line in the plot.
Figure 5 (b): Distributions of pT(ll) scaled by the Emiss acceptance correction factor K (predicted) and Emiss (observed) for SM MC and data. The high HT signal region is indicated by the vertical line in the plot.
Figure 6: CLS 95% confidence level upper limit on cross-section times acceptance as a function of the endpoint in the invariant mass spectrum assuming a triangular shaped signal.
Figure 7: The observed 95% CL exclusion contour at NLO (solid red line) and the expected exclusion contour (dashed blue line) with ±1σ variation (shaded blue region) in the CMSSM (m0,m1/2) plane for tanβ = 10, A0 = 0 and μ > 0. The area below the curve is excluded by this measurement. Exclusion limits obtained from previous experiments are presented as filled areas in the plot. Thin grey lines correspond to constant squark and gluino masses. This exclusion is based on the results of the high HT signal region, for which the observed yield is 4 events and the expected background yield is 5.1 1.7 events. The exclusion contour based on 34 pb−1 2010 data is also displayed. The 2011 observed and expected exclusion contours in TGraph format can be found here.
AN 2011/269 Fig. 20: The distributions f(y) and g(HT ) extracted from tt MC.
AN 2011/269 Fig. 21 (left): Distributions of y vs. HT for tt MC. The signal regions E_T^{miss} > 275 GeV, H_T > 300 GeV (left) are indicated with thick black lines. The f(y) and g(HT ) functions are measured using events in the green and red shaded areas, respectively.

Re-interpretation in terms of simplified models

The language of simplified models has been introduced recently (see e.g. here and here) to establish an efficient communication channel between the LHC experiments and the theory communities who have proposed a general set of simplified models with which LHC data can be interpreted. A similar approach has been taken before in the hadronic channel with 2010 data -- see here.

The above results have been re-interpreted in terms of the simplified models given in the following table. The signal efficiencies as a function of the mass parameters of the simplified model are also given below, together with upper limit plots on the production cross section. The data for these plots are also available as a ROOT file: T1lh_OS.root. The regions with 
small 
ΔΜ(gluino,LSP)
 and
 low gluino 
mass
 are 
excluded since they are
 dominated by 
statistical 
errors 
and
 signal 
modeling uncertainty. Signal contamination in control regions has not been taken into account when computing the upper limits on the production cross sections.

Figure Abbreviated Caption
Simplified model topology "T1Lh". mchi20=0.5*(mGL+mLSP)
Signal efficiencies for T1Lh, for the "high HT" selection.
Signal efficiencies for T1Lh, for the "high MET" selection.
Upper limit on production cross section, for T1Lh, assuming a branching ratio of 1. For each point, the result of the "best" selection (i.e. the minimal value for the upper limit) is taken. Superimposed are 95% CL exclusion contours, assuming a "reference SUSY cross section", for decoupled squarks: m(~q)>>m(~g).

Approved Tables from SUS-11-011

Table1: Data yields and MCprediction safter preselection, using the quoted NLO production cross sections σ. The tt → l+l− corrresponds to dilepton tt, including t → W → τ → l, tt → fake includes all other tt decay modes. The samples of MC tt, W± + jets, and single-top events were generated with MADGRAPH. The Drell–Yan sample (which includes events with invariant masses as low as 10 GeV/c2) was generated using a mixture of MADGRAPH and PYTHIA and includes decays to the τ+τ− final state. All other samples were generated with PYTHIA. The LM1, LM3 and LM6 benchmark scenarios are defined in the text; the quoted σ values refer to the total production cross section for SUSY particles in these scenarios. Uncertainties are statistical only.
Table 2: Summary of the observed and predicted yields in the 2 signal regions. The uncertainty in the MC prediction is statistical only. The systematic uncertainties on the ABCD’ and pT(ll) method predictions are discussed in the text. The background yield Nbkg is the error-weighted average of the 2 data-driven predictions. The non-SM yield UL is a CLS 95% confidence level upper limit. The LM1, LM3 and LM6 yields include uncertainties from MC statistics, trigger efficiency, lepton selection efficiency, hadronic energy scale and integrated luminosity.
Table 3: Summary of the opposite-flavor subtraction results. The quantity Delta is defined in Eq. 4. The CLS 95% CL upper limit on this quantity, as well as the predicted values in the LM1, LM3 and LM6 scenarios, are also summarized. The LM1, LM3 and LM6 uncertainties are from MC statistics, trigger efficiency, lepton selection efficiency, hadronic energy scale and integrated luminosity.

Table 4: Summary of model-dependent limits. The efficiency and acceptance are defined in the text; the efficiency uncertainty is dominated by the uncertainty in the hadronic energy scale. The CLS 95% CL UL on the quantity σ X A is indicated, as well as the value of this quantity for the LM1, LM3 and LM6 scenarios.

-- AlexTapper - 27-Jul-2011

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng Figure_001.png r1 manage 174.6 K 2011-07-27 - 10:45 AlexTapper  
PNGpng Figure_002-a.png r1 manage 214.0 K 2011-07-27 - 10:58 AlexTapper  
PNGpng Figure_002-b.png r1 manage 158.8 K 2011-07-27 - 10:58 AlexTapper  
PNGpng Figure_002-c.png r1 manage 197.2 K 2011-07-27 - 10:59 AlexTapper  
PNGpng Figure_002-d.png r1 manage 159.2 K 2011-07-27 - 10:59 AlexTapper  
PNGpng Figure_003.png r1 manage 169.6 K 2011-07-27 - 10:59 AlexTapper  
PNGpng Figure_004-a.png r1 manage 198.7 K 2011-07-27 - 10:59 AlexTapper  
PNGpng Figure_004-b.png r1 manage 186.6 K 2011-07-27 - 11:00 AlexTapper  
PNGpng Figure_005-a.png r1 manage 120.5 K 2011-07-27 - 11:00 AlexTapper  
PNGpng Figure_005-b.png r1 manage 105.6 K 2011-07-27 - 11:00 AlexTapper  
PNGpng Figure_006.png r1 manage 169.0 K 2011-07-27 - 11:00 AlexTapper  
PNGpng Figure_007.png r1 manage 235.3 K 2011-07-27 - 11:00 AlexTapper  
GIFgif OS_msugra.gif r1 manage 11.5 K 2011-08-25 - 19:55 BenHooberman Figure produced by the macro contours.C which contains the exclusion contours in TGraph form
Unknown file formatroot T1lh_OS.root r1 manage 20.3 K 2011-09-12 - 17:49 MariarosariaDalfonso electronic version of the plots below
PDFpdf comparisonOS_xSec.pdf r1 manage 19.2 K 2011-09-30 - 12:30 Walten  
PNGpng comparisonOS_xSec.png r1 manage 43.2 K 2011-09-30 - 12:31 Walten  
C source code fileC contours.C r2 r1 manage 7.2 K 2011-08-25 - 19:52 BenHooberman ROOT macro to produce exclusion contours
PDFpdf fig20.pdf r1 manage 16.7 K 2011-08-22 - 16:27 BenHooberman AN 2011/269 Fig. 20 (pdf)
PNGpng fig20.png r1 manage 16.2 K 2011-08-22 - 16:27 BenHooberman AN 2011/269 Fig. 20 (png)
PNGpng fig21.png r2 r1 manage 26.6 K 2011-08-22 - 16:29 BenHooberman AN 2011/269 Fig. 21 (left)
PDFpdf h_eff_T1lh_OS_2010_HT.pdf r1 manage 13.9 K 2011-09-30 - 12:30 Walten  
PNGpng h_eff_T1lh_OS_2010_HT.png r1 manage 10.8 K 2011-09-30 - 12:30 Walten  
PDFpdf h_eff_T1lh_OS_2010_met.pdf r1 manage 14.3 K 2011-09-30 - 12:30 Walten  
PNGpng h_eff_T1lh_OS_2010_met.png r1 manage 10.9 K 2011-09-30 - 12:30 Walten  
PNGpng table1.png r1 manage 77.7 K 2011-08-16 - 18:52 BenHooberman Table 1
PNGpng table2.png r2 r1 manage 50.7 K 2011-08-16 - 18:59 BenHooberman Table 2
PNGpng table3.png r1 manage 28.4 K 2011-08-16 - 18:53 BenHooberman Table 3
PNGpng table4.png r1 manage 43.2 K 2011-08-16 - 18:53 BenHooberman Table 4
Topic revision: r15 - 2011-09-30 - Walten
 
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