-- SupriyaJain, IaIashvili - 30-Mar-2012

TOP-11-010
Search for Zí resonances decaying to top-antitop pairs in dilepton+jets final state in pp collisions at √s = 7 TeV

Abstract

We present a search for narrow-width resonances decaying to top-antitop pairs using 5.0 /fb of data recorded by the CMS detector in pp collisions at √s = 7 TeV. No significant deviation from Standard Model prediction is observed. We set 95% confidence-level (CL) upper limits on the production cross section of the narrow-width resonance times its branching fraction to top-antitop for different resonance masses. We also exclude the existence of a leptophobic topcolor particle Z' of width Γ(Z') = 0.012M(Z') with mass M(Z') < 1.1 TeV at 95% CL.

Event Yields

Tables/Figures Caption
Expected yields for SM backgrounds and observed data in the ee, μμ, and eμ channels.
Distribution of the transverse momentum of the highest-pT electron in the ee channel. The hatched region shows the total uncertainty on the SM background.
Distribution of the pseudorapidity of the highest-pT jet in the μμ channel. The hatched region shows the total uncertainty on the SM background.
Distribution of ∆φ between the missing transverse energy and highest-pT lepton in the eμ channel. The hatched region shows the total uncertainty on the SM background.

Systematic Uncertainties

Table Caption
Rate and shape uncertainties from different components affecting the total expected number of signal and background events. The QCD normalization uncertainty is indicated by the minimum and maximum values across the three channels.

Invariant Mass Distributions

Figures Caption
Distribution of the invariant mass of the two leading leptons, two leading jets and missing transverse energy in the ee channel. The pz of the two neutrinos is assummed to be zero. The hatched region shows the total uncertainty on the SM background.
Distribution of the invariant mass of the two leading leptons, two leading jets and missing transverse energy in the μμ channel. The pz of the two neutrinos is assummed to be zero. The hatched region shows the total uncertainty on the SM background.
Distribution of the invariant mass of the two leading leptons, two leading jets and missing transverse energy in the eμ channel. The pz of the two neutrinos is assummed to be zero. The hatched region shows the total uncertainty on the SM background.

Bayesian Neural Network (MVA) Analysis

Figures Caption
Distribution of BNN output discriminant normalized to unity in the ee channel.
Distribution of BNN output discriminant normalized to unity in the μμ channel.
Distribution of BNN output discriminant normalized to unity in the eμ channel.
Distributions of BNN output discriminant normalized to the observed data in the ee channel. The hatched region shows the total uncertainty on the SM background.
Distributions of BNN output discriminant normalized to the observed data in the μμ channel. The hatched region shows the total uncertainty on the SM background.
Distributions of BNN output discriminant normalized to the observed data in the eμ channel. The hatched region shows the total uncertainty on the SM background.

Results: Limits

Table/Figure Caption
Upper limits on σ(Z')∗ B(Z' → tt ̄) using the BNN output distributions between [0, 1] from the ee, μμ, and eμ channels. All systematic uncertainties are included with correlations.
Upper limits on σ(Z') ∗ B(Z' → tt ̄) versus M(Z') . Also shown is the theoretical prediction for a leptophobic Z' (arXiv:hep-ph/9911288,arXiv:1112.4928,arXiv:1004.0876). [Note: the asymmetric nature of uncertainties on the expected limits are a feature of the particular choice of test-statistic used in the CLs method.]

Summary

Using a data sample corresponding to 5.0 /fb of √s = 7 TeV pp collisions, a search for heavy bosons decaying to top-antitop pairs, with subsequent leptonic decay modes, revealed no significant excess beyond expectations from the standard model. This allowed the derivation of 95% CL limits on the product of the production cross section and branching ratio in this decay mode for various masses of narrow width resonances, which is in turn utilized to exclude the existence a leptophobic topcolor particle Z' with width Γ(Z') = 0.0012M(Z') for masses M(Z') < 1.1 TeV.

- SupriyaJain, IaIashvili - 30-Mar-2012

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng BNN_limits_50bins_1.png r1 manage 19.2 K 2012-04-01 - 00:42 SupriyaJain  
PNGpng PAS_limits.png r1 manage 33.5 K 2012-03-30 - 00:22 SupriyaJain  
PNGpng PAS_signalyields.png r1 manage 47.5 K 2012-03-30 - 00:17 SupriyaJain  
PNGpng PAS_systematics.png r1 manage 47.2 K 2012-03-30 - 00:22 SupriyaJain  
PNGpng electron_BNNnorm.png r1 manage 17.8 K 2012-03-30 - 00:26 SupriyaJain  
PNGpng electron_BNNoutput.png r2 r1 manage 29.8 K 2012-04-01 - 00:42 SupriyaJain  
PNGpng electron_InvMass_2j2l2nu.png r2 r1 manage 26.5 K 2012-04-01 - 00:43 SupriyaJain  
PNGpng electron_LeadingLeptonPt.png r2 r1 manage 32.1 K 2012-04-01 - 00:43 SupriyaJain  
PNGpng emu_BNNnorm.png r1 manage 17.8 K 2012-03-30 - 00:27 SupriyaJain  
PNGpng emu_BNNoutput.png r2 r1 manage 30.8 K 2012-04-01 - 00:43 SupriyaJain  
PNGpng emu_InvMass_2j2l2nu.png r2 r1 manage 27.1 K 2012-04-01 - 00:44 SupriyaJain  
PNGpng emu_MissingEtDeltaPhi.png r2 r1 manage 28.9 K 2012-04-01 - 00:44 SupriyaJain  
PNGpng muon_BNNnorm.png r1 manage 17.6 K 2012-03-30 - 00:26 SupriyaJain  
PNGpng muon_BNNoutput.png r2 r1 manage 30.8 K 2012-04-01 - 00:44 SupriyaJain  
PNGpng muon_InvMass_2j2l2nu.png r2 r1 manage 27.4 K 2012-04-01 - 00:45 SupriyaJain  
PNGpng muon_LeadingJetEta.png r2 r1 manage 31.5 K 2012-04-01 - 00:45 SupriyaJain  
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Topic revision: r6 - 2012-04-02 - RobertoChierici
 
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