Search for physics beyond the standard model in events with two leptons, jets, and missing transverse energy in pp collisions at sqrt(s)=8 TeV

Physics Analysis Summary

Link to PAS-SUS-12-019.

Abstract

This note presents a search for physics beyond the standard model in final states with two opposite-sign same-flavor leptons, jets, and missing transverse energy, in a sample of 8 TeV pp collisions collected with the CMS detector at the CERN LHC. The experimental analysis focuses on searches for a kinematic edge in the invariant mass distribution of the opposite-sign same-flavor lepton pair. The size of the data sample corresponds to an integrated luminosity of 19.4 fb-1. We do not observe evidence for a statistically significant signal.

Acronyms

• SF = same-flavor, used to abbreviate the sample of two opposite-sign leptons of same flavor, i.e, ee + μμ
• OF = opposite-flavor, used to abbreviate the sample of two opposite-sign leptons that are of opposite (different) flavor, i.e., eμ
• FS = flavor-symmetric, used to denote any process that produces the same rate of SF and OF lepton pairs, e.g., top pair production, W⁺W^-
• DY = Drell-Yan

Preselection

• N_lep ≥ 2 with p_T > 20 GeV and |η| < 2.4
• N_jets ≥ 2 with p_T > 40 GeV and |η| < 3.0

Signal regions

• (N_jets ≥ 2 .AND. MET > 150 GeV ) .OR. (N_jets ≥ 3 .AND. MET > 100 GeV)
• central region (both leptons within |η| < 1.4)
  • kinematic fit in 20 < m(ll) < 300 GeV
  • counting experiment in 20 < m(ll) < 70 GeV
• forward region (at least one lepton with |η| > 1.4)
  • kinematic fit in 20 < m(ll) < 300 GeV
  • counting experiment in 20 < m(ll) < 70 GeV

Plots (click on plot to get PDF version)

Figure	Caption
	Figure 1a : MET distributions for SF sample for m(ll) > 20 GeV and Njets ≥ 2. The error bars show the statistical uncertainties of data and MC samples, while the shaded band depicts the MC statistical and systematic uncertainty added in quadrature
	Figure 1b : MET distributions for OF sample for m(ll) > 20 GeV and Njets ≥ 2. The error bars show the statistical uncertainties of data and MC samples, while the shaded band depicts the MC statistical and systematic uncertainty added in quadrature
	Figure 2a : Fit results for the signal-plus-background hypothesis in comparison to the measured dilepton mass distributions, in the central region, projected on the SF event sample. The combined fit shape is shown as a blue, solid line. The individual fit components are indicated by dashed lines. The flavor-symmetric background is denoted as FS and is displayed with a black dashed line. The Drell–Yan contribution is denoted as DY and is displayed with a red dashed line. The extracted signal component is denoted as Signal and is displayed with a green dashed line.
	Figure 2b : Fit results for the signal-plus-background hypothesis in comparison to the measured dilepton mass distributions, in the central region, projected on the OF event sample. The combined fit shape is shown as a blue, solid line.
	Figure 2c : Fit results for the signal-plus-background hypothesis in comparison to the measured dilepton mass distributions, in the forward region, projected on the SF event sample. The combined fit shape is shown as a blue, solid line. The individual fit components are indicated by dashed lines. The flavor-symmetric background is denoted as FS and is displayed with a black dashed line. The Drell–Yan contribution is denoted as DY and is displayed with a red dashed line. The extracted signal component is denoted as Signal and is displayed with a green dashed line.
	Figure 2d : Fit results for the signal-plus-background hypothesis in comparison to the measured dilepton mass distributions, in the forward region, projected on the OF event sample. The combined fit shape is shown as a blue, solid line.
	Figure 3a : Comparison between the observed and estimated SM background dilepton mass distributions in the central region, where the SM backgrounds are evaluated from control samples (see CMS-PAS-SUS-12-019 for details) rather than from the fit.
	Figure 3b : Comparison between the observed and estimated SM background dilepton mass distributions in the forward region, where the SM backgrounds are evaluated from control samples (see CMS-PAS-SUS-12-019 for details) rather than from the fit.
	Figure 4a : Data compared with SM simulation for the SF event sample in the central rapidity region. Example signal scenarios based on the pair production of bottom-squarks is shown (see CMS-PAS-SUS-12-019 for details).
	Figure 4b : Data compared with SM simulation for the OF event sample in the central rapidity region. Example signal scenarios based on the pair production of bottom-squarks is shown (see CMS-PAS-SUS-12-019 for details).

Tables

Table	Caption
	Table 1: Results for RSF/OF in the signal regions. The values of rμe and RT listed for the control region method are not used directly in the analysis and are listed for purposes of comparison only.
	Table 2: Result of the unbinned maximum likelihood fit. Event yields measured and estimated in the signal regions. Statistical and systematic uncertainties are added in quadrature.
	Table 3: Results of the counting experiment. Event yields measured and estimated in the signal regions. Statistical and systematic uncertainties are added in quadrature.
	Table 4: Event yields for the mbottom-squark = 225 GeV, mneutralino-two = 150 GeV signal model for different selection requirements. The signal is normalized to the integrated luminosity of 19.4 fb-1 using a cross section of 9.9 pb. The uncertainties are statistical.
	Table 5: Event yields for the mbottom-squark = 350 GeV, mneutralino-two = 275 GeV signal model for different selection requirements. The signal is normalized to the integrated luminosity of 19.4 fb-1 using a cross section of 807 fb. The uncertainties are statistical.
	Table 6: Event yields for the mbottom-squark = 400 GeV, mneutralino-two = 150 GeV signal model for different selection requirements. The signal is normalized to the integrated luminosity of 19.4 fb-1 using a cross section of 357 fb. The uncertainties are statistical.

Auxiliary material

Figure	Caption
	Background hypothesis fit to the dilepton mass distributions, in the central rapidity region projected on the SF event sample. The combined fit shape is shown as a blue, solid line. The individual fit components are indicated by dashed lines.
	Background hypothesis fit to the dilepton mass distributions, in the central rapidity region projected on the OF event sample. The combined fit shape is shown as a blue, solid line.
	Background hypothesis fit to the dilepton mass distributions, in the forward rapidity region projected on the SF event sample. The combined fit shape is shown as a blue, solid line. The individual fit components are indicated by dashed lines.
	Background hypothesis fit to the dilepton mass distributions, in the forward rapidity region projected on the OF event sample. The combined fit shape is shown as a blue, solid line.

Figure	Caption
	Signal plus background hypothesis fit to the same-flavor (SF) dilepton mass distributions, in simulation with signal injection. The combined fit shape is shown as a blue, solid line. The individual fit components are indicated by dashed lines.
	Signal plus background hypothesis fit to the opposite-flavor (OF) dilepton mass distributions, in MC simulation with signal injection. The combined fit shape is shown as a blue, solid line.
	Background hypothesis fit to the same-flavor (SF) dilepton mass distributions, in simulation with signal injection. The combined fit shape is shown as a blue, solid line. The individual fit components are indicated by dashed lines.
	Background hypothesis fit to the same-flavor (OF) dilepton mass distributions, in simulation with signal injection. The combined fit shape is shown as a blue, solid line.

SLHA files for models containing an edge

The SLHA files for the scan producing an edge at 70 GeV can be found here: link to SLHA files

The SLHA files for the scan including sleptons and producing an edge in different positions depending on the mass hierarchy can be found here: link to SLHA files

Further information

This analysis is documented in CMS-PAS-SUS-12-019.
The Table and Figure numbers in this twiki correspond to the table and figure numbers in the document.

-- KostasTheofilatos - 21 Jul 2014