"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.
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.
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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. |
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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. |
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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). |
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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). |
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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). |
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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. |
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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. |
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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. |
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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. |
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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
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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Distribution of dijet pT in the W + bb control region for W(μν)H(bb). |
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Distribution of dijet invariant mass in the W + bb control region for W(eν)H(bb). |
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Distribution of missing energy in the Z(μμ) control region for Z(νν)H(bb). |
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Distribution of dijet pt in the W + udcsg control region for Z(νν)H(bb). |
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Distribution of dijet invariant mass in the ttbar control region for Z(μμ)H(bb). |
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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). |