Search for Physics Beyond the Standard Model in Opposite-Sign Dilepton Events at sqrt(s) = 7 TeV

TL;DR

This CMS study investigates physics beyond the Standard Model in final states with opposite-sign dileptons, jets, and missing transverse energy using 34 pb$^{-1}$ of 7 TeV data. A signal region defined by $H_{ ext{T}}$ and $y= E_{ ext{T}}^{\text{miss}}/\sqrt{H_{ ext{T}}}$ is pursued, with two independent data-driven background methods (ABCD and $p_{ ext{T}}( ext{ll})$) plus a complementary hadronic-trigger analysis. The observed yield is consistent with SM expectations, leading to Bayesian 95% CL upper limits on non-SM contributions and exclusion of CMSSM benchmarks LM0 and LM1, with competitive sensitivity relative to Tevatron/LEP. The paper also provides practical guidance and acceptance/efficiency information to test other BSM models against these limits, facilitating broader applicability of the results.

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. The search is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 34 inverse picobarns. No evidence for an event yield beyond SM expectations is found. An upper limit on the non-SM contribution to the signal region is deduced from the results. This limit is interpreted in the context of the constrained minimal supersymmetric model. Additional information is provided to allow testing the exclusion of specific models of physics beyond the SM.

Figures (4)

• Figure 1: Distributions of (top left) scalar sum of jet transverse energies ($H_{\mathrm{T}}$), (top right) $y\equiv E_{\mathrm{T}}^{\text{miss}}\xspace/\sqrt{H_{\mathrm{T}}\xspace}$, (bottom left) dilepton invariant mass $M(\ell\ell)$, and (bottom right) dilepton transverse momentum $p_{\mathrm{T}}\xspace(\ell\ell)$ for SM MC and data after preselection. The last bin contains the overflow. Here ${t}\overline{{t}}\rightarrow \ell^{+}\ell^{-}$ corresponds to dilepton ${t}\overline{{t}}$, including ${t} \to \mathrm{W} \to \tau \to \ell$; ${t}\overline{{t}}\rightarrow \mathrm{other}$ includes all other ${t}\overline{{t}}$ decay modes, and VV indicates the sum of $\mathrm{W}\mathrm{W}$, $\mathrm{W}{Z}$, and ${Z}{Z}$. The MC distributions for the LM1 benchmark points are also shown.
• Figure 2: Distributions of $y$ vs. $H_{\mathrm{T}}$ for SM MC (2-dimensional histogram) and data (scatter plot). Here our choice of the ABCD regions is also shown.
• Figure 3: Distributions of $y$ (observed) and ${p_{\mathrm{T}}\xspace(\ell\ell)}/\sqrt{H_{\mathrm{T}}\xspace}$ scaled by the correction factor $K_{50}$ (predicted) for (left) the signal region and (right) the control region A, for both MC and data. The vertical dashed line indicates the search region defined by $y>8.5\,\text{Ge\spaceV}\xspace^{1/2}$. The deficit at low $y$ is due to the $E_{\mathrm{T}}^{\text{miss}}\xspace > 50\,\text{Ge\spaceV}\xspace$ preselection requirement.
• Figure 4: The observed 95% CL exclusion contour at NLO (solid red line) and LO (dashed blue line) in the CMSSM $(m_0,m_{1/2})$ plane for $\tan\beta=3$, $A_0 = 0$ and $\mu > 0$. 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.