"Search for the standard model Higgs boson decaying to bottom quarks in pp collisions at √s=7 TeV"

This is a condensed description with plots for the analysis CMS-HIG-11-031 (Accepted by PLB)

Abstract

A search for the standard model Higgs boson (H) decaying to bb when produced in association with weak vector bosons (V) is reported for the following modes: W(μν)H, W(eν)H, Z(μμ)H, Z(ee)H and Z(νν)H. The search is performed in a data sample corresponding to an integrated luminosity of 4.7 /fb, recorded by the CMS detector in proton-proton collisions at the LHC with a center-of-mass energy of 7 TeV. No significant excess of events above the expectation from background is observed. Upper limits on the VH production cross section times the H to bb branching ratio, with respect to the expectations for a standard model Higgs boson, are derived for a Higgs boson in the mass range 110 to 135 GeV. In this range, the observed 95% confidence level upper limits vary from 3.4 to 7.5 times the standard model prediction; the corresponding expected limits vary from 2.7 to 6.7 times the standard model prediction.

Main Results

95% CL Limits for BDT and Mjj Analyses

Expected and observed 95% CL upper limits on the product of the VH production cross section times the H to bb branching ratio, with respect to the expectations for a standard model Higgs boson. The primary results are those from the BDT analysis, the m(jj) analysis is presented as a cross check.

Mass (GeV) BDT (Exp) BDT (Obs) Mjj (Exp) Mjj (Obs)
110 2.7 3.1 3.1 3.4
115 3.1 5.2 3.2 5.6
120 3.6 4.4 4.1 6.1
125 4.3 5.7 4.7 6.3
130 5.3 9.0 6.4 10.5
135 6.7 7.5 7.7 8.9

Further details

At the LHC the main SM Higgs boson production mechanism is gluon fusion, with a cross section of 17 pb for mH = 120 GeV. However, in this production mode, the detection of the H to bb decay is considered nearly impossible due to overwhelming dijet pro- duction expected from quantum-chromodynamic (QCD) interactions. The same holds true for the next most copious production mode, through vector-boson fusion, with a cross section of 1.3 pb. Processes in which a low-mass Higgs boson is produced in association with a vector boson have cross sections of 0.66 pb and 0.36 pb for WH and ZH, respectively.

The limits are based on the observed event count and background estimate in signal-enriched regions defined by the output discriminant of a boosted-decision-tree algorithm (BDT analysis). As a cross-check, limits are also derived from the observed event count in the invariant mass distribution of H to bb candidates (m(jj) analysis).

The background processes to VH production are vector-boson+jets, tt, single-top, dibosons (VV) and QCD multijet production. The event selection for the BDT analysis is based first on the kinematic reconstruction of the vector bosons and the Higgs boson decay into two b-tagged jets. Backgrounds are then substantially reduced by requiring a significant boost in the pT of the vector boson and the Higgs boson. The boost requirements in the Z(ll)H and WH analyses are pT > 100 and pT > 150 GeV, respectively. The corresponding efficiencies for signal events are approximately 25% and 10%. For the Z(νν)H analysis the boost requirement is pT > 160 GeV.

Appropriate control regions that are orthogonal to the signal region are identified in data and used to adjust the Monte Carlo simulation normalization for the most important background processes: W + jets and Z + jets (with light- and heavy-flavor jets), and top production.

No significant excess of events is observed in any channel, and the results of all channels are combined to obtain 95% CL upper limits on the Higgs boson production cross section in the VH modes with H to bb, relative to the standard model prediction.

Figures from the paper

All public plots and tables from this analysis are collected here. Click on a figure to enlarge it, then double click to go to normal size again.

FIGURE FILES Description

VHbb_BDT_Log.png png, gif, pdf Distribution of the BDT output, for mH=115 GeV, for each mode after all selection criteria are applied. The solid histograms for the backgrounds and the signal are summed cumulatively. The line histogram for signal is also shown superimposed. The data is represented by points with error bars.

VHbb_Mjj_Combined.png png, gif, pdf Dijet invariant mass distribution, combined for all channels, for events that pass the m(jj) analysis selection. The solid histograms for the backgrounds and the signal are summed cumulatively. The line histogram for signal and for VV backgrounds are also shown superimposed. The data is represented by points with error bars.

BDTLimits.png png, gif, pdf Expected and observed 95% CL upper limits on the product of the VH production cross section times the H to bb branching ratio, with respect to the expectations for a standard model Higgs boson, for the BDT analysis. Shown are the median expected limit (dashed), one- (green) and two-sigma (yellow) bands, and the observed limits (solid with points).

Additional material from PAS CMS-HIG-11-031

BDT-Limits.PNG png, gif, pdf 95% CL limits on the VH(bb) production cross section divided by the standard model predicted cross section computed with the results of the BDT analysis using the LHC CLs method. Shown are the median expected limit (dashed), one- (green) and two-sigma (yellow) bands, and the observed limits (solid with points).

Mjj-Limits.PNG png, gif, pdf 95% CL limits on the VH(bb) production cross section divided by the standard model predicted cross section computed with the results of the M(jj) analysis using the LHC CLs method. Shown are the median expected limit (dashed), one- (green) and two-sigma (yellow) bands, and the observed limits (solid with points).

Additional BDT Plots from PAS CMS-HIG-11-031

WmnHBDTLog.PNG png, gif, pdf Distribution of the BDT output for W(μν)H(bb) events after all selection criteria are applied except for the final cut on the BDT itself. The signal plot (black histogram) is for MH = 115 GeV.

WenHBDTLog.PNG png, gif, pdf Distribution of the BDT output for W(eν)H(bb) events after all selection criteria are applied except for the final cut on the BDT itself. The signal plot (black histogram) is for MH = 115 GeV.

ZmmHBDTLog.PNG png, gif, pdf Distribution of the BDT output for Z(μμ)H(bb) events after all selection criteria are applied except for the final cut on the BDT itself. The signal plot (black histogram) is for MH = 115 GeV.

ZeeHBDTLog.PNG png, gif, pdf Distribution of the BDT output for Z(ee)H(bb) events after all selection criteria are applied except for the final cut on the BDT itself. The signal plot (red histogram) is for MH = 115 GeV.

ZnnHBDTLog.PNG png, gif, pdf Distribution of the BDT output for Z(νν)H(bb) events after all selection criteria are applied except for the final cut on the BDT itself. The signal plot (black histogram) is for MH = 115 GeV.

Additional Signal Region M(jj) Plots from PAS CMS-HIG-11-031

WmnHMjjLog.PNG png, gif, pdf Distribution of the Mjj output for W(μν)H(bb) events after all selection criteria are applied except for the final cut on the Mjj itself. The signal plot (black histogram) is for MH = 115 GeV.

WenHMjjLog.PNG png, gif, pdf Distribution of the Mjj output for W(eν)H(bb) events after all selection criteria are applied except for the final cut on the Mjj itself. The signal plot (black histogram) is for MH = 115 GeV.

ZmmHMjjLog.PNG png, gif, pdf Distribution of the Mjj output for Z(μμ)H(bb) events after all selection criteria are applied except for the final cut on the Mjj itself. The signal plot (red histogram) is for MH = 115 GeV.

ZeeHMjjLog.PNG png, gif, pdf Distribution of the Mjj output for Z(ee)H(bb) events after all selection criteria are applied except for the final cut on the Mjj itself. The signal plot (red histogram) is for MH = 115 GeV.

ZnnHMjjLog.PNG png, gif, pdf Distribution of the Mjj output for Z(νν)H(bb) events after all selection criteria are applied except for the final cut on the Mjj itself. The signal plot (black histogram) is for MH = 115 GeV.

VH_Combind.png png, gif, pdf Distribution of the Mjj output for all VH modes combined after all selection criteria are applied. The signal plot (red histogram) is for MH = 125 GeV.

Background Control Regions from PAS CMS-HIG-11-031

.png png, gif, pdf Distribution of dijet pT in the W + bb control region for W(μν)H(bb).

.png png, gif, pdf Distribution of dijet invariant mass in the W + bb control region for W(eν)H(bb).

.png png, gif, pdf Distribution of missing energy in the Z(μμ) control region for Z(νν)H(bb).

.png png, gif, pdf Distribution of dijet pt in the W + udcsg control region for Z(νν)H(bb).

.png png, gif, pdf Distribution of dijet invariant mass in the ttbar control region for Z(μμ)H(bb).

.png png, gif, pdf Distribution of b-tag discriminator output for the Higgs daughter with the lowest value in the Z + bb control region for Z(ee)H(bb).
Topic attachments
I Attachment History Action Size Date Who Comment
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PNGpng BDT-Limits.PNG r1 manage 249.7 K 2011-12-12 - 21:42 JimOlsen Combined limits from BDT analyses (png)
PDFpdf BDT-Limits.pdf r1 manage 14.3 K 2011-12-12 - 21:42 JimOlsen Combined limits from BDT analyses
GIFgif BDTLimits.gif r1 manage 43.7 K 2012-03-05 - 11:13 NiklasMohr  
PDFpdf BDTLimits.pdf r1 manage 14.1 K 2012-03-05 - 11:13 NiklasMohr  
PNGpng BDTLimits.png r1 manage 91.3 K 2012-03-05 - 11:12 NiklasMohr  
GIFgif Mjj-Limits.GIF r1 manage 110.4 K 2011-12-12 - 21:44 JimOlsen Combined limits from Mjj analyses (gif)
PNGpng Mjj-Limits.PNG r1 manage 121.7 K 2011-12-12 - 21:44 JimOlsen Combined limits from Mjj analyses (png)
PDFpdf Mjj-Limits.pdf r1 manage 14.3 K 2011-12-12 - 21:58 JimOlsen  
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GIFgif VHbb_BDT_Log.gif r1 manage 92.8 K 2012-03-05 - 11:13 NiklasMohr  
PDFpdf VHbb_BDT_Log.pdf r1 manage 203.9 K 2012-03-05 - 11:14 NiklasMohr  
PNGpng VHbb_BDT_Log.png r1 manage 174.2 K 2012-03-05 - 11:13 NiklasMohr  
PDFpdf VHbb_Combined.pdf r1 manage 28.3 K 2011-12-13 - 02:49 JimOlsen  
GIFgif VHbb_Mjj_Combined.gif r1 manage 79.7 K 2012-03-05 - 11:14 NiklasMohr  
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GIFgif WmnHMjjLog.GIF r1 manage 171.1 K 2011-12-12 - 23:17 JimOlsen  
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PDFpdf ZeeHMjjLog.pdf r1 manage 17.0 K 2011-12-12 - 23:17 JimOlsen  
GIFgif ZeeH_Zbb_csv2.gif r1 manage 209.8 K 2011-12-13 - 04:47 JimOlsen  
PDFpdf ZeeH_Zbb_csv2.pdf r1 manage 18.7 K 2011-12-13 - 04:46 JimOlsen  
PNGpng ZeeH_Zbb_csv2.png r1 manage 459.3 K 2011-12-13 - 04:46 JimOlsen  
GIFgif ZmmH-ttbar-bbmass.gif r1 manage 233.9 K 2011-12-13 - 04:16 JimOlsen  
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GIFgif ZmmHBDTLog.GIF r1 manage 162.0 K 2011-12-12 - 23:03 JimOlsen  
PNGpng ZmmHBDTLog.PNG r1 manage 360.0 K 2011-12-12 - 23:02 JimOlsen  
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GIFgif ZmmHMjjLog.GIF r1 manage 161.6 K 2011-12-12 - 23:45 JimOlsen  
PNGpng ZmmHMjjLog.PNG r1 manage 178.7 K 2011-12-12 - 23:45 JimOlsen  
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GIFgif ZnnHMjjLog.GIF r2 r1 manage 177.4 K 2011-12-13 - 02:38 JimOlsen  
PNGpng ZnnHMjjLog.PNG r2 r1 manage 192.7 K 2011-12-13 - 02:36 JimOlsen  
PDFpdf ZnnHMjjLog.pdf r1 manage 19.6 K 2011-12-12 - 23:45 JimOlsen  
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