Search for supersymmetery in final states with missing transverse energy and 0, 1, 2, or ≥ 3 b jets in 8 TeV pp collisions

Abstract

A search for supersymmetry in the jets and missing transverse energy final state is performed in pp collisions at a centre of mass energy of 8 TeV. The data sample corresponds to an integrated luminosity of 3.9/fb collected by the CMS experiment at the LHC. In this search, a kinematic variable, AlphaT, is used as the main discriminator between events with genuine and mis-reconstructed missing transverse energy. The search is performed in a signal region that is binned in the scalar sum of the transverse energy of jets and the number of jets identified to originate from a bottom quark. No excess of events over the standard model expectation is found. Exclusion limits are set in a simplified model of gluino pair production and decay to a final state of two top-antitop quark pairs and two neutralinos.

Closure Test Plot

Link to figure Abbreviated Caption
syst.png HT-dependent systematic uncertainties are assigned to the translation factors obtained from simulation, which account for theoretical uncertainties and limitations in the simulation modelling of kinematics and instrumental effects. The magnitudes of these systematic uncertainties are determined from data with a representative set of closure tests, in which yields from one of the three control samples, along with the corresponding translation factors obtained from simulation, are used to predict the yields in another control sample. The samples are selected to ensure that potential signal contamination in a wide variety of SUSY models, including those considered in this analysis, are negligible. Therefore, the closure tests carried out both between and within control samples probe the properties of the relevant SM backgrounds. In particular, the closure tests address the modelling in simulation of the relative contributions of the main SM backgrounds (W+jets, top and Z+jets), the kinematics of important observables such as AlphaT, and the reconstruction of b jets.

To account for evolving conditions throughout the data-taking period a differing trigger for muon+jets and di-muon+jets control samples is used in the first two HT bins, while the trigger for the gamma+jets sample is only efficient for the last six HT bins.

The first three closure tests are carried out within the muon+jets sample. The first probes the modelling of the AlphaT distribution in genuine MET events (circles), whilst the second (squares) and third (triangles) examine the relative composition between W+jets and top events, as well as the modelling of the reconstruction of b jets. These are particularly important for the estimation of the W+jets and top component of the SM background. The fourth (crosses) and fifth (stars) closure tests are performed between different control samples, and are important for establishing a consistent estimation of the irreducible component of Z decaying to two neutrinos. The fourth test connects the muon+jets and di-muon+jets control samples testing the relative contributions of Z+jets to W+jets and top events. The fifth test establishes the consistency between the di-muon+jets and gamma+jets samples. The closure tests are overlaid on top of grey bands that represent the HT-dependent systematic uncertainties assigned to the translation factors used in the likelihood function.

SM Expectation Plots

Link to figure Abbreviated Caption
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the hadronic data sample when requiring exactly zero reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line, barely visible due to the small S/B).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the hadronic data sample when requiring exactly one reconstructed b jet per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the hadronic data sample when requiring exactly two reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the hadronic data sample when requiring at least three reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the muon + jets data sample when requiring exactly zero reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line, barely visible due to the small S/B).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the muon + jets data sample when requiring exactly one reconstructed b jet per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line, barely visible due to the small S/B).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the muon + jets data sample when requiring exactly two reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the muon + jets data sample when requiring at least three reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown. For illustrative purposes only, the expected yields from pair produced 800 GeV gluinos, each decaying to a top-antitop quark pair and a 100 GeV neutralino, are superimposed on top of the SM expectation (magenta solid line).
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the di-muon + jets data sample when requiring exactly zero reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown.
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the di-muon + jets data sample when requiring exactly one reconstructed b jet per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown.
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the di-muon + jets data sample when requiring exactly two reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown.
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the photon + jets data sample when requiring exactly zero reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown.
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the photon + jets data sample when requiring exactly one reconstructed b jet per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown.
Comparison of the observed yields and SM expectations given by the simultaneous fit in bins of HT for the photon + jets data sample when requiring exactly two reconstructed b jets per event. The observed event yields in data (black dots) and the expectations and their uncertainties, as determined by the simultaneous fit, for all SM processes (light blue solid line with dark blue bands) are shown.

SMS interpretation (T1tttt)

Link to figure Abbreviated Caption
T1tttt-limit.png Exclusion cross-section versus model spectrum for pair-produced gluinos, each decaying to a top quark-antiquark pair and a neutralino LSP. The colour scale indicates the observed cross section upper limit (95% C.L.) for each model point, as a function of the mass of the produced particle and the LSP mass. The solid black line indicates the observed exclusion region assuming nominal NLO SUSY production cross section. The dashed black line indicates the median expected exclusion region, with the dotted (-1sigma) and dotted-dashed (+1sigma) black lines indicating the expected exclusion regions with experimental uncertainties.
Topic attachments
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PNGpng T1tttt-limit.png r1 manage 117.0 K 2012-07-05 - 00:57 RobBainbridge  
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PNGpng T1tttt.png r1 manage 6.6 K 2012-07-04 - 13:57 RobBainbridge  
PDFpdf hadronic_signal_fit_logy55_0b.pdf r2 r1 manage 14.8 K 2012-07-05 - 02:36 EdwardLaird  
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