Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV

TL;DR

The CMS 7 TeV analysis targets new physics in events with at least three jets and large missing transverse momentum, using 36 pb^-1 of data. Backgrounds from Z(νν)+jets, W+jets/ttbar, and QCD multijet processes are estimated entirely from data through gamma+jets control samples, muon+jets lost-lepton/tau_h methods, and data-driven QCD techniques (rebalance-and-smear and factorization). No excess is observed; the results are interpreted within the CMSSM and in Simplified Model Spectra, setting 95% CL limits on SUSY particle masses and production cross sections. The study demonstrates robust, largely data-driven background estimation for MET-based multijet searches and provides early LHC constraints on gluino/squark scenarios even at low integrated luminosity.

Abstract

A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 inverse picobarns collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets.

Figures (8)

• Figure 1: The (left) $\slash\mkern-12mu{H}_{\text{T}}$ and (right) $H_{\mathrm{T}}$ distributions for the data and MC simulation samples with all baseline selection cuts applied except the $\slash\mkern-12mu{H}_{\text{T}}$ and $H_{\mathrm{T}}$ requirements, respectively. The distributions for the individual backgrounds are shown separately, along with the predicted distributions for the LM1 SUSY point. However, these simulated distributions are not used to estimate the backgrounds in this analysis. Instead, the backgrounds are determined directly from the data.
• Figure 2: The (left) $\slash\mkern-12mu{H}_{\text{T}}$ and (right) $H_{\mathrm{T}}$ distributions from the R&S method applied to simulation events, compared to the actual MC distribution (MC truth), for events passing $\geq3$ jets, $H_{\mathrm{T}}\xspace\geq300\,\text{Ge\spaceV}\xspace$, and $\Delta\phi(\hbox{$\slash\mkern-12mu{H}_{\text{T}}$}\xspace,\mathrm{jet\,1\hbox{-}3})$ selections, and additionally $\hbox{$\slash\mkern-12mu{H}_{\text{T}}$}\xspace{} > 150 \,\text{Ge\spaceV}\xspace$ for the right plot.
• Figure 3: Ratio of the reconstructed jet transverse momentum to the generated transverse momentum for jets with $p_{\mathrm{T}}\xspace^{\rm gen}\geq300\,\text{Ge\spaceV}\xspace$. Distributions are shown for (left) different values of $f^{\mathrm{ECAL}}_{\mathrm{masked}}\xspace$ and (right) gluons and different quark flavours.
• Figure 4: Total signal efficiency for the $\slash\mkern-12mu{H}_{\text{T}}$ (left) and $H_{\mathrm{T}}$ (right) selections, as a function of $m_0$ and $m_{1/2}$. The other CMSSM parameters are $\tan\beta=10$, $\mu>0$, and $A_0=0$.
• Figure 5: The expected and observed $95\%$ CL upper limits in the CMSSM $m_0$--$m_{1/2}$ (left) and gluino--squark (right) mass planes for LO and NLO cross sections. The $\pm1$ standard deviation ($\sigma$) band corresponds to the expected limit. The contours are the combination of the $H_{\mathrm{T}}$ and the $\slash\mkern-12mu{H}_{\text{T}}$ selections such that the contours are the envelope with respect to the best sensitivity. The CMSSM parameters are $\tan\beta=10$, $\mu>0$, and $A_0=0$. The limit from the earlier CMS analysis is shown as a blue line and limits from other experiments as the shaded regions. For the area labeled "$\tilde{\tau}$ LSP" the stau becomes the LSP. The LM1 SUSY benchmark scenario is shown as a point.