A search for the decays of a new heavy particle in multijet events with the razor variables at CMS in pp collisions at √s = 7 TeV

Link to documentation in CDS

CMS-PAS-SUS-12-009

Abstract

A search is performed for the pair production of a new heavy resonance that decays into high jet-multiplicity final states with missing transverse energy using 4.98 0.11 fb-1 of data collected by the CMS experiment in 2011 at the CERN Large Hadron Collider. The razor variables are used to study events with at least six jets, where at least one jet is identified as coming from the decay of a b-quark. These events are characterised by large MR and small R2 and are in a different kinematic region than previously studied. This analysis is sensitive to SUSY and SUSY-like signatures with the production of a high number of jets, such as top squark or t′ pair production.

The Razor Variables

The analysis uses the Razor kinematic variables to discriminate between signal and background. One of the variable, MR, is a measurement of the typical energy scale of the process and it is related to the masses of the SUSY particles for signal events. The other variable, R = MRT/MR, quantifies the unbalance the event, as a result of the presence of two missing particles. The numerator of R, MRT, is smaller than the value MΔ at which MR peaks. This results in a value of R smaller than one. While signal events have R ~ 0.3, events from background with no real missing transverse energy have R ~ 0.




The likelihood fit




Figure 1: Background extrapolation





p-value of the observed yield in bins of MR and R2 with respect to the prediction from the background model. The background model is obtained from a ML fit in the green region, then extrapolated to the signal region.



Figure 2:




Projection of the 2D fit result on MR (left) and R2 (right) for the BJet box using the full 2011 CMS MultiJet dataset. The blue histogram is the total SM prediction as obtained from a single large pseudo-experiment based on the 2D fit, while the histogram uncertainties show the 68% range from the covariance matrix. The breakdown of the different background components is also shown. The fit is performed in the R2-MR sideband and projected into the full region to allow comparison between the prediction from the fit and the data. The ratio shown is the full SM prediction divided by the data distribution. No significant trend is seen.

Table 2:




Limit on t' -> t + invisible particle

We interpret the absence of an excess in the MR vs R2 tail in terms of an cross-section limit on the pair production of a heavy top partner t', which then decays to a top quark and a missing particle. The cross-section limit is translates into a mass limit under the assumption that the t' is a scalar (e.g. a stop) or a fermion (e.g. a KK partner of the top in UED)

Figure 3




Expected and observed 95% CL limits in the (mt′, mLSP) SMS T2tt plane from the razor multijet analysis as derived from the BJet box. The black (red) lines show the observed (expected)limit for the scalar (left) and the spin-1/2 fermion (right) t'.The theoretical uncertainties arising from 0 1/2 scale and parton distribution function uncertainties are also shown by the narrow lines. The colour scale shows the model independent cross-section excluded in this SMS. The solid grey region indicates model points where the analysis was found to have dependence on initial state radiation modelling in the simulation of signal events above a pre-defined tolerance; no interpretation is presented for these model points.

Figure 5


Expected and observed limits for pair-produced top partners with the mass of the invisible particle fixed to 50 GeV. In each case, the relevant theoretical cross-sections and uncertainties are shown.



Figure 6


Signal MC efficiencies,relative to the total number of events per SMS point, for the LeptonBVeto (left), BVeto (center), and BJet (right) boxes as a function of the SMS T2tt model parameters. It can be seen that the signal efficiency in the two data control regions is very low.



Figure 7


Average values of MR (left) and R2 (right) for the BJet box as a function of the SMS T2tt parameters.



Limit on g -> t t + LSP

We interpret the absence of an excess in the MR vs R2 tail in terms of an cross-section limit on the pair production of two gluinos, each decaying to a pair of top quarks and a LSP.

Figure 4




Figure 5


Expected and observed limits for pair-produced gluinos with the mass of the invisible particle fixed to 50 GeV. In each case, the relevant theoretical cross-sections and uncertainties are shown. No model points where the analysis was seen to have dependence on initial state radiation modelling in the simulation of signal events above a pre-defined tolerance were found.



Figure 8


Signal MC efficiencies,relative to the total number of events per SMS point, for the LeptonBVeto (top left), BVeto (top right), and BJet (bottom) boxes as a function of the SMS T1tttt model parameters. It can be seen that the signal efficiency in the two data control regions is very low.



Figure 9


Average values of MR (left) and R2 (right) for the BJet box as a function of the SMS T1tttt parameters.



Additional Plots

Expected limits on the SMS planes

Expected limit for the pair-production of gluinos (left) and the top-partners t' (right). The black lines correspond to the expected limit in the case of a SUSY-like QCD cross section, as well as for a factor-3 enhanced and a factor-3 reduced cross section. The red lines in the right plot show the corresponding expected limits for a sermonic partner of the top.

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Fig6a.pdf r2 r1 manage 18.0 K 2012-07-01 - 11:27 MaurizioPierini  
PNGpng Fig6a.png r3 r2 r1 manage 100.6 K 2012-07-01 - 11:59 MaurizioPierini  
PDFpdf Fig6b.pdf r2 r1 manage 17.9 K 2012-07-01 - 11:27 MaurizioPierini  
PNGpng Fig6b.png r3 r2 r1 manage 101.1 K 2012-07-01 - 11:59 MaurizioPierini  
PDFpdf Fig6c.pdf r2 r1 manage 17.8 K 2012-07-01 - 11:27 MaurizioPierini  
PNGpng Fig6c.png r3 r2 r1 manage 100.4 K 2012-07-01 - 11:59 MaurizioPierini  
PDFpdf Fig7a.pdf r3 r2 r1 manage 17.3 K 2012-07-01 - 15:23 MaurizioPierini  
PNGpng Fig7a.png r3 r2 r1 manage 98.6 K 2012-07-01 - 15:22 MaurizioPierini  
PDFpdf Fig7b.pdf r3 r2 r1 manage 17.7 K 2012-07-01 - 15:23 MaurizioPierini  
PNGpng Fig7b.png r3 r2 r1 manage 94.8 K 2012-07-01 - 15:23 MaurizioPierini  
PDFpdf Fig8a.pdf r1 manage 16.3 K 2012-07-01 - 12:11 MaurizioPierini  
PNGpng Fig8a.png r1 manage 89.1 K 2012-07-01 - 12:11 MaurizioPierini  
PDFpdf Fig8b.pdf r1 manage 16.3 K 2012-07-01 - 12:11 MaurizioPierini  
PNGpng Fig8b.png r1 manage 93.1 K 2012-07-01 - 12:11 MaurizioPierini  
PDFpdf Fig8c.pdf r1 manage 16.1 K 2012-07-01 - 12:11 MaurizioPierini  
PNGpng Fig8c.png r1 manage 90.7 K 2012-07-01 - 12:11 MaurizioPierini  
PDFpdf Fig9a.pdf r2 r1 manage 15.9 K 2012-07-01 - 15:23 MaurizioPierini  
PNGpng Fig9a.png r2 r1 manage 89.2 K 2012-07-01 - 15:23 MaurizioPierini  
PDFpdf Fig9b.pdf r2 r1 manage 16.1 K 2012-07-01 - 15:23 MaurizioPierini  
PNGpng Fig9b.png r2 r1 manage 92.1 K 2012-07-01 - 15:23 MaurizioPierini  
PDFpdf Figure1.pdf r2 r1 manage 69.6 K 2012-07-04 - 16:20 MaurizioPierini  
PNGpng Figure1.png r1 manage 73.7 K 2012-06-28 - 16:29 MaurizioPierini  
PDFpdf Figure2.pdf r4 r3 r2 r1 manage 110.0 K 2012-07-04 - 17:50 MaurizioPierini  
PNGpng Figure2.png r3 r2 r1 manage 83.9 K 2012-06-29 - 17:48 MaurizioPierini  
PDFpdf Figure2a.pdf r3 r2 r1 manage 22.4 K 2012-07-01 - 17:53 MaurizioPierini  
PNGpng Figure2a.png r2 r1 manage 130.3 K 2012-07-01 - 17:53 MaurizioPierini  
PDFpdf Figure2b.pdf r2 r1 manage 19.5 K 2012-07-01 - 17:52 MaurizioPierini  
PNGpng Figure2b.png r2 r1 manage 116.2 K 2012-07-01 - 17:52 MaurizioPierini  
PDFpdf Figure5a.pdf r4 r3 r2 r1 manage 26.9 K 2012-07-01 - 11:00 MaurizioPierini  
PNGpng Figure5a.png r4 r3 r2 r1 manage 163.5 K 2012-07-01 - 11:00 MaurizioPierini  
PDFpdf Figure5b.pdf r4 r3 r2 r1 manage 22.3 K 2012-07-01 - 15:33 MaurizioPierini  
PNGpng Figure5b.png r4 r3 r2 r1 manage 144.1 K 2012-07-01 - 15:33 MaurizioPierini  
PNGpng MR_MRT_example.png r2 r1 manage 44.2 K 2012-07-01 - 18:30 MaurizioPierini  
Unknown file formatroot T1tttt.root r1 manage 20.5 K 2012-06-28 - 19:44 MaurizioPierini  
PDFpdf T1tttt_limit_expected.pdf r1 manage 144.9 K 2012-06-29 - 17:33 MaurizioPierini  
PNGpng T1tttt_limit_expected.png r1 manage 120.2 K 2012-06-29 - 17:33 MaurizioPierini  
PDFpdf T1tttt_observed_withExpected_isr.pdf r1 manage 20.8 K 2012-07-01 - 13:03 WillReece  
PNGpng T1tttt_observed_withExpected_isr.png r1 manage 140.5 K 2012-07-01 - 13:03 WillReece  
Unknown file formatroot T2tt.root r1 manage 25.7 K 2012-06-28 - 19:45 MaurizioPierini  
PDFpdf T2tt_limit_expected.pdf r1 manage 160.4 K 2012-06-29 - 17:33 MaurizioPierini  
PNGpng T2tt_limit_expected.png r1 manage 120.2 K 2012-06-29 - 17:33 MaurizioPierini  
PDFpdf T2tt_spin0_observed_withExpected_isr.pdf r1 manage 21.3 K 2012-07-01 - 13:05 WillReece  
PNGpng T2tt_spin0_observed_withExpected_isr.png r1 manage 104.9 K 2012-07-01 - 13:05 WillReece  
PDFpdf T2tt_spin12_observed_withExpected_isr.pdf r1 manage 21.7 K 2012-07-01 - 13:05 WillReece  
PNGpng T2tt_spin12_observed_withExpected_isr.png r1 manage 121.1 K 2012-07-01 - 13:05 WillReece  
PDFpdf Table1.pdf r3 r2 r1 manage 109.9 K 2012-07-04 - 16:19 MaurizioPierini  
PNGpng Table1.png r1 manage 60.0 K 2012-06-28 - 16:31 MaurizioPierini  
PNGpng Untitled.png r1 manage 55.5 K 2012-06-29 - 22:11 WillReece  
PDFpdf p-valueMap.pdf r2 r1 manage 14.9 K 2012-07-02 - 17:18 MaurizioPierini  
PNGpng p-valueMap.png r2 r1 manage 71.9 K 2012-07-02 - 17:18 MaurizioPierini  
Edit | Attach | Watch | Print version | History: r18 < r17 < r16 < r15 < r14 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r18 - 2012-07-05 - EvaHalkiadakis
 
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    CMSPublic All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2019 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding TWiki? Send feedback