Search for Three-Jet Resonances in pp Collisions at √s = 7 TeV


Results are reported from a search for the production of three-jet resonances in pp collisions at a center-of-mass energy √s = 7 TeV. The study uses the data sample collected by the CMS experiment at the LHC in 2011, corresponding to an integrated luminosity of 5.0 fb-1. Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed for the presence of resonances in the three-jet invariant mass spectrum. The number of events observed is found to be in agreement with the expectation from standard model processes. Limits are set on the cross section for gluino pair production in an R-parity-violating supersymmetry model, for gluino masses greater than 280 GeV. Assuming a branching fraction for gluino decay into three jets of 100%, gluino masses below 460 GeV are excluded at 95% confidence level. These results significantly extend the range of previous limits.

This analysis has been submitted to PLB and is documented in CMS paper EXO-11-060

Approved Plots from EXO-11-060 (Click on blue names in the right column to download files)

Figure Abbreviated Caption
M400_Opt.png M400_Opt.pdf: Optimization schematic with signal Gaussian and expected background within a 2 sigma window about the mean of the Gaussian. The correct triplets are modeled by a Gaussian parameterization (blue line), and the background shape by a four-parameter modified power law function (red line). The optimization procedure uses the number of triplets in the signal divided by the number of signal plus background triplets (S/S+B).
M400Fit.png M400Fit.pdf: Simultaneous fitting of Gaussian (blue line) plus four-parameter modified power law fit of background (black line) for a 400 GeV gluino. From the optimization procedure, we apply a 6th jet pT cut of 70 GeV and that each triplet satisfy Mjjj TRIPLET < pTTRIPLET - 160 GeV.
M400_Accept.png M400_Accept.pdf: Example of the acceptance determination showing the sample 400 GeV gluino triplets passing all pre-selection and optimized requirements, namely a 6th jet pT cut of 70 GeV and Mjjj TRIPLET < pTTRIPLET - 160 GeV. The fitting of the sample is done simultaneously for the Gaussian signal (blue line) and four-parameter modified power law background fit (black line). The red line shows the Gaussian only component of the signal sample without the background contribution added, and the gold shaded region represents a basic truth-matched signal component.
GluinoAccept.png GluinoAccept.pdf: Acceptance of the gluino signal as a function of its mass. Ten mass points are sampled, ranging from 250 GeV to 1.5 TeV, and the gluino acceptance is parameterized by a 2nd-degree polynomial (black line) for the entire mass range. A 3rd-degree polynomial fit (red dashed line) is used to cross-check the main parameterization, with the difference taken as part of the systematic uncertainty.
M400_2D.png M400_2D.pdf: Simulated triplet jet mass Mjjj versus the triplet scalar pT of all 20 triplets for a gluino mass of 400 GeV, shown as a contoured distribution, with that of the triplets whose jets all originate from the same gluino parent overlaid. The expectation for the QCD background is shown in the inset. All triplets falling to the right of the dashed line pass the requirement of Mjjj TRIPLET < pTTRIPLET - 160 GeV.
ThreeJetMass.png ThreeJetMass.pdf:Mass distribution for selected jet triplets. The four-parameter background fit is shown by the solid line. The NLO expectation for a 300 GeV gluino signal is shown by the dotted line, and that of a 450 GeV gluino signal by the dash-dotted line. Each of the two is normalized to the integrated luminosity of the 5.0 fb-1 data sample.
DataResiduals.png DataResiduals.pdf: Difference between the measured triplet mass distribution and the fitted background parametrization, divided by the fitted value, shown for both data and the NLO expectation of two gluino models, one with a gluino mass of 300 GeV and the other with a gluino mass of 450 GeV.
DataPulls.png DataPulls.pdf: Difference between the measured triplet mass distribution and the fitted background parametrization, divided by the statistical uncertainty δ, shown for both data and the NLO expectation of two gluino models, one with a gluino mass of 300 GeV and the other with a gluino mass of 450 GeV.
GluinoLimits.png GluinoLimits.pdf: Observed and expected 95% CL upper limits on the cross section times branching fraction for gluino pair production followed by RPV decay of each gluino to three light -flavored quark jets. Also shown are the ±1σ and ±2σ bands on the expected limit, as well as the theoretical LO and NLO cross sections for gluino production, assuming a branching fraction of a gluino decay into three jets of 100%.
Topic attachments
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PDFpdf DataPulls.pdf r2 r1 manage 26.6 K 2012-08-15 - 13:11 DanDuggan  
PNGpng DataPulls.png r2 r1 manage 123.7 K 2012-08-15 - 13:12 DanDuggan  
PDFpdf DataResiduals.pdf r2 r1 manage 23.3 K 2012-08-15 - 13:12 DanDuggan  
PNGpng DataResiduals.png r2 r1 manage 120.8 K 2012-08-15 - 13:13 DanDuggan  
PDFpdf GluinoAccept.pdf r3 r2 r1 manage 15.5 K 2012-08-15 - 13:13 DanDuggan  
PNGpng GluinoAccept.png r3 r2 r1 manage 94.1 K 2012-08-15 - 13:13 DanDuggan  
PDFpdf GluinoLimits.pdf r2 r1 manage 25.7 K 2012-08-15 - 13:14 DanDuggan  
PNGpng GluinoLimits.png r2 r1 manage 138.4 K 2012-08-15 - 13:14 DanDuggan  
PDFpdf M400Fit.pdf r2 r1 manage 22.2 K 2012-08-15 - 13:15 DanDuggan  
PNGpng M400Fit.png r2 r1 manage 99.0 K 2012-08-15 - 13:15 DanDuggan  
PDFpdf M400_2D.pdf r2 r1 manage 223.1 K 2012-08-15 - 13:15 DanDuggan  
PNGpng M400_2D.png r2 r1 manage 323.8 K 2012-08-15 - 13:16 DanDuggan  
PDFpdf M400_Accept.pdf r2 r1 manage 17.5 K 2012-08-15 - 13:16 DanDuggan  
PNGpng M400_Accept.png r2 r1 manage 101.2 K 2012-08-15 - 13:17 DanDuggan  
PDFpdf M400_Opt.pdf r2 r1 manage 15.9 K 2012-08-15 - 13:17 DanDuggan  
PNGpng M400_Opt.png r2 r1 manage 95.1 K 2012-08-15 - 13:17 DanDuggan  
PDFpdf ThreeJetMass.pdf r2 r1 manage 25.4 K 2012-08-15 - 13:18 DanDuggan  
PNGpng ThreeJetMass.png r2 r1 manage 86.4 K 2012-08-15 - 13:18 DanDuggan  
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