Search for the Higgs Boson Decaying to W+W in the Fully Leptonic Final State

This is a condensed description with plots for the analysis CMS-HIG-11-024

Abstract

We report a search for the Higgs boson decaying to W+W in pp collisions at sqrt(s) = 7 TeV. The data were collected at the LHC with the CMS detector, and correspond to an integrated luminosity of 4.6 fb−1. W+W candidates are selected in events with two leptons (electrons or muons). No significant excess above Standard Model back- ground expectations is observed, and upper limits on the Higgs boson production are derived. The presence of a Standard Model Higgs boson is excluded for a mass in the range [129 - 270] GeV/c2 at 95% C.L.

Main Results

A search has been made for a Higgs boson decaying in a pair of W bosons in the CMS detector. Events are classified according the exclusive jet multiplicity: 0, 1 and 2. The analysis of events with 0, 1 jets is optimized for gg → H → WW, while the one for events with 2 jets is optimized for Vector Boson Fusion (VBF) qq → H → WW. A cut and count and Multivariate (Boosted Decision Tree - BDT) analysis is performed, optimized for each mass point. The main backgrounds (W+W-, top, Drell Yan, W+jets) are estimated with data-driven techniques. The uncertainty on the background normalization represent the largest source of systematics of the analysis, together with the theoretical uncertainties on the Higgs cross section. No evidence of Higgs boson is found and the results are interpreted as an exclusion of a wide H mass range. With a multivariate shape analysis, the expected exclusion range at 95% CL is between 127 and 270 GeV for a Standard Model Higgs, while the observed one is [129 - 270] GeV/c2 at 95% C.L. using the CLs approach. With the cut based analysis, the expected exclusion range at 95% CL is between 129 and 236 GeV for a Standard Model Higgs, while the observed one is [132 - 238] GeV/c2 at 95% C.L. using the CLs approach. The excess of events observed for hypothesised Higgs boson masses at the low end of the explored range makes the observed limits weaker than the expected ones. To ascertain the origin of this excess, more data are required. Below we report the table with detailed exclusion limits for a range of masses 110-300 GeV/c2.

  • results with the BDT analysis:
Higgs Mass Observed Median exp. 68% band 95% band
110 8.81 5.59 [4.21, 8.02] [3.47, 11.0]
115 5.05 2.70 [1.97, 3.86] [1.62, 5.35]
120 2.69 1.58 [1.14, 2.28] [0.91, 3.15]
125 1.52 1.12 [0.80, 1.55] [0.60, 2.08]
130 0.97 0.75 [0.53, 1.07] [0.41, 1.46]
140 0.66 0.43 [0.31, 0.61] [0.25, 0.84]
150 0.46 0.29 [0.21, 0.42] [0.16, 0.57]
160 0.25 0.15 [0.11, 0.22] [0.10, 0.31]
170 0.27 0.17 [0.13, 0.24] [0.10, 0.34]
180 0.29 0.25 [0.18, 0.35] [0.14, 0.48]
190 0.37 0.37 [0.27, 0.54] [0.21, 0.74]
200 0.53 0.52 [0.37, 0.73] [0.29, 1.02]
250 0.85 0.96 [0.69, 1.41] [0.56, 1.93]
300 1.25 1.09 [0.77, 1.57] [0.62, 2.16]
350 1.02 0.98 [0.70, 1.40] [0.58, 1.95]
400 1.38 1.04 [0.77, 1.47] [0.63, 2.09]
450 1.08 1.44 [1.02, 2.08] [0.80, 3.01]
500 1.14 1.91 [1.27, 2.91] [0.96, 4.31]
550 2.05 2.76 [1.88, 4.26] [1.39, 6.14]
600 1.92 3.85 [2.44, 6.22] [1.73, 10.3]

png, pdf Exclusion limit with shape analysis

  • results with the cut-based analysis:
Higgs Mass Observed Median exp. 68% band 95% band
110 8.7 6.6 [4.8, 9.3] [3.7, 13.0]
115 4.0 3.2 [2.3, 4.4] [1.9, 6.3]
120 2.4 1.9 [1.4, 2.6] [1.1, 3.7]
130 1.2 0.8 [0.6, 1.2] [0.5, 1.7]
140 0.6 0.5 [0.4, 0.7] [0.3, 1.0]
150 0.5 0.4 [0.3, 0.6] [0.2, 0.7]
160 0.3 0.2 [0.2, 0.3] [0.1, 0.4]
170 0.3 0.2 [0.2, 0.3] [0.1, 0.4]
180 0.2 0.3 [0.2, 0.4] [0.2, 0.6]
190 0.2 0.4 [0.2, 0.6] [0.2, 0.8]
200 0.6 0.6 [0.4, 0.9] [0.4, 1.2]
250 1.1 1.3 [0.7, 1.8] [0.7, 2.5]
300 1.7 1.5 [1.1, 2.1] [0.8, 3.0]
350 1.5 1.4 [1.1, 2.0] [0.8, 2.9]
400 1.7 1.6 [1.1, 2.2] [0.8, 3.1]
450 1.8 1.8 [1.3, 2.8] [1.0, 4.0]
500 2.3 2.6 [1.8, 3.9] [1.4, 5.9]
550 3.9 3.6 [2.5, 5.4] [1.9, 8.5]
600 5.9 5.0 [3.5, 7.9] [2.8, 12.8]

png, pdf Exclusion limit with cut-based analysis

Paper figures

png, pdf Δφ ll in the 0-jet bin at WW selection level
png, pdf Δφ ll in the 1-jet bin at WW selection level
png, pdf dilepton invariant mass in the 0-jet bin at Higgs selection level
png, pdf dilepton invariant mass in the 1-jet bin at Higgs selection level
png, pdf BDT output in the 0-jet bin for opposite flavor final state
png, pdf BDT output in the 0-jet bin for same flavor final state
png, pdf BDT output in the 1-jet bin for opposite flavor final state
png, pdf BDT output in the 1-jet bin for same flavor final state

Paper tables

Yields at the WW selection level

Backgrounds are rescaled to the data-driven expectations

njets data all bkg. qq→WW gg→WW ttbar+tW W+jets
0-jet 1359 1364.8 9.3 980.6 5.2 58.8 0.7 147.3 2.5 99.3 5.0
1-jet 909 951.4 9.8 416.8 3.6 23.8 0.5 334.8 3.0 74.3 4.6
2-jet 703 714.8 13.5 154.7 2.2 5.1 0.2 413.5 2.7 37.9 3.6

njets WZ/ZZ DY→ll DY→ττ
0-jet 33.0 0.5 16.6 4.0 26.8 3.5 2.4 0.5
1-jet 28.7 0.5 39.4 6.4 13.0 2.6 20.6 0.4
2-jet 15.1 0.3 56.1 11.7 10.8 3.6 21.6 2.1

Yields at the Higgs selection level

  • cut based approach in the 0-jet category:
mH DY→ll ttbar+tW W+jets WZ+ZZ+Wγ WW all bkg. H→WW data
120 8.8 9.2 6.7 1.0 14.7 4.7 6.1 1.5 100.3 7.2 136.7 12.7 15.7 0.8 136
130 13.7 7.8 10.6 1.6 17.6 5.5 7.4 1.6 142.2 10.0 191.5 14.0 45.2 2.1 193
160 3.4 3.4 10.5 1.4 3.0 1.5 2.2 0.4 82.6 5.4 101.7 6.8 122.9 5.6 111
200 2.7 3.7 23.3 3.1 3.4 1.5 3.2 0.3 108.2 4.5 140.8 6.8 48.8 2.2 159
250 0.3 0.6 36.2 4.8 6.7 2.1 5.7 0.7 101.8 4.5 150.8 6.9 23.5 1.1 152
300 0.7 1.9 41.6 5.4 6.5 2.1 7.0 0.7 87.5 3.9 143.3 7.2 20.2 0.9 147
400 0.2 0.2 35.9 4.7 5.5 1.8 9.3 1.1 59.8 2.7 110.8 5.8 17.5 0.8 109

  • breakdown by channel for one mass (uncertainty on signal reporting also theory systematics) (mH=120 GeV)
channel all bkg. mh=120 GeV data
sf 50.6 9.8 4.7 1.1 49
of 86.1 8.2 11.0 2.5 87
total 136.7 12.7 15.7 2.7 136

  • cut based approach in the 1-jet category:
mH DY→ll ttbar+tW W+jets WZ+ZZ+Wγ WW all bkg. H→WW data
120 6.6 2.3 17.2 1.0 5.4 2.4 3.2 0.6 27.0 4.7 59.5 5.9 6.5 0.3 72
130 5.3 2.5 25.6 1.4 6.5 2.5 4.0 0.6 38.5 6.6 79.9 7.7 17.6 0.8 105
160 4.2 1.4 27.9 1.4 3.2 1.4 1.9 0.3 33.7 5.5 70.8 6.0 60.2 2.6 86
200 14.6 5.3 59.4 2.8 5.2 1.8 2.2 0.1 49.3 2.2 130.8 6.7 25.8 1.1 111
250 12.9 6.8 83.8 3.9 5.9 2.1 3.3 0.2 60.3 2.8 166.2 8.6 14.8 0.6 158
300 12.8 4.8 83.6 3.9 6.2 2.2 3.8 0.4 57.5 2.7 163.9 7.1 13.7 0.6 168
400 8.3 3.2 60.6 2.9 6.2 2.1 3.9 0.5 44.6 2.2 123.6 5.3 12.2 0.5 128

  • breakdown by channel for one mass (uncertainty on signal reporting also theory systematics) (mH=120 GeV)
channel all bkg. mh=120 GeV data
sf 20.4 2.6 1.7 0.5 26
of 39.1 5.3 4.8 1.7 46
total 59.5 5.9 6.5 1.7 72

  • cut based approach in the 2-jet category:
mH DY→ll ttbar+tW W+jets WZ+ZZ+Wγ WW all bkg. H→WW data
120 1.9 1.4 5.5 2.8 0.7 0.6 1.8 1.5 1.3 0.2 11.3 3.6 1.1 0.1 8
130 2.7 1.9 6.5 3.2 0.7 0.6 1.8 1.5 1.6 0.2 13.3 4.0 2.7 0.2 10
160 2.7 1.9 8.4 3.9 1.2 0.8 1.8 1.5 1.9 0.2 15.9 4.6 12.2 0.7 12
200 3.2 2.1 9.4 4.2 1.2 0.8 1.8 1.5 2.2 0.2 17.8 5.0 8.4 0.5 13
250 3.3 2.1 12.2 5.2 1.2 0.8 1.9 1.5 3.3 0.3 21.8 5.9 5.6 0.3 19
300 3.3 2.1 14.1 5.8 1.1 0.8 1.9 1.5 3.4 0.3 23.7 6.4 4.2 0.2 20
400 3.3 2.1 14.1 5.8 1.1 0.8 1.9 1.5 3.5 0.3 23.8 6.4 2.5 0.1 20

Other figures

Kinematic variables at the WW selection level

Δφ ll the 0-jet / 1-jet / 2-jet bin at the Higgs selection level
png, pdf png, pdf png, pdf other formats
dilepton invariant mass the 0-jet / 1-jet / 2-jet bin at the WW selection level
png, pdf png, pdf png, pdf other formats
leading lepton pT the 0-jet / 1-jet / 2-jet bin at the WW selection level
png, pdf png, pdf png, pdf other formats
trailing lepton pT the 0-jet / 1-jet / 2-jet bin at the WW selection level
png, pdf png, pdf png, pdf other formats
dilepton pT the 0-jet / 1-jet / 2-jet bin at the WW selection level
png, pdf png, pdf png, pdf other formats
transverse mass the 0-jet / 1-jet / 2-jet bin at the WW selection level
png, pdf png, pdf png, pdf other formats

Kinematic variables at the Higgs selection level

Δφ ll in the 0-jet / 1-jet at the Higgs selection level
png, pdf png, pdf other formats
dilepton invariant mass in the 0-jet / 1-jet at the Higgs selection level
png, pdf png, pdf other formats
leading lepton pT in the 0-jet / 1-jet at the Higgs selection level
png, pdf png, pdf other formats
trailing lepton pT in the 0-jet / 1-jet at the Higgs selection level
png, pdf png, pdf other formats
transverse mass in the 0-jet / 1-jet at the Higgs selection level
png, pdf png, pdf other formats

Cuts evolution

cuts evolution in 0-jet for mH = 130 / 140 GeV.
png, pdf png, pdf other formats

Cut based exclusion limits

0-jet opposite flavor / same flavor.
png, pdf png, pdf other formats
1-jet opposite flavor / same flavor.
png, pdf png, pdf other formats
2-jet.
png, pdf other formats
0+1+2 jets combined limit, zoom at low mass.
png, pdf png, pdf other formats

Shape based exclusion limits

  • Boosted Decision Tree results
0-jet opposite flavor / same flavor. Bayesian method.
png, pdf, txt png, pdf, txt other formats
1-jet opposite flavor / same flavor. Bayesian method
png, pdf, txt png, pdf, txt other formats
0+1+2 jet combined. Zoom at low mass. CLs method. Equivalent with Bayesian method.
png, pdf other formats

  • Dilepton invariant mass resuts:
The following describe the distribution of the dilepton invariant mass used to extract the limits:
Delta Phi ll in the 0-jet OF / 0-jet SF / 1-jet OF / 1-jet SF at the Higgs selection level except mll selection
png, pdf png, pdf png, pdf png, pdf other formats

The following figures show the results obtained with the mll:

0+1+2 jet combined. Zoom at low mass.
png, pdf other formats

Signal Injection test

The figure shows the test where, on top of the expected background, we injected a signal of Higgs boson with mH=124 GeV. Results are obtained with asymptotic CLs approximation with BDT shape analysis.

mH=124 GeV signal injected for cut-based / BDT-based. Zoom at low mass.
png, pdf png, pdf other formats

Fermiophobic Higgs limits

Fermiophobic Higgs limit in low / full mass.
png, pdf png, pdf other formats

Higgs Mass Observed Median exp. 68% band 95% band
110 2.0 2.3 [1.6, 3.7] [1.1, 6.0]
115 1.6 2.0 [1.3, 3.1] [1.0, 5.1]
120 1.4 1.7 [1.1, 2.5] [0.8, 4.0]
130 1.3 1.5 [1.0, 2.4] [0.7, 3.8]
140 1.1 1.4 [1.0, 2.2] [0.7, 3.6]
150 1.0 1.3 [0.9, 2.1] [0.6, 3.4]
160 0.8 1.0 [0.7, 1.6] [0.5, 2.7]
170 0.7 1.0 [0.6, 1.5] [0.4, 2.4]
180 0.8 1.1 [0.7, 1.8] [0.5, 3.0]
190 1.0 1.4 [0.9, 2.2] [0.7, 3.8]
200 1.3 1.7 [1.1, 2.7] [0.8, 4.5]
250 2.3 3.0 [2.0, 5.0] [1.4, 9.0]
300 3.3 4.0 [2.7, 6.5] [1.9, 10.5]
350 4.4 5.5 [3.7, 8.3] [2.6, 12.8]
400 6.3 7.8 [5.2, 12.0] [3.7, 17.8]
450 8.9 10.9 [7.3, 16.9] [5.2, 26.1]
500 11.6 14.2 [9.4, 21.7] [6.6, 34.3]
550 14.9 18.7 [12.6, 28.6] [8.8, 45.1]
600 18.9 24.8 [16.4, 38.3] [11.7, 59.7]

EPS 2011 vs post EPS 2011

We have reanalyzed the dataset presented at EPS 2011 conference with the new analysis (1.1 fb-1). We find the same excess shown before, while the excess is no more there in the full dataset minus the EPS dataset. We conclude that it was a statistical fluctuation.

Current analysis performed on EPS2011 / post-EPS2011 dataset.
png, pdf png, pdf other formats

Selections definition

WW selection

The following cuts constitute what in the paper is called WW selection (which in independent on the Higgs mass)

Selection [units] ee,μμ
pTmax [GeV/c] 20 20
pTmin [GeV/c] 15 10
third lepton veto applied applied
opposite-sign requirement applied applied
mll [GeV/c2] 20 12
projected MET [GeV] 40 20
Z mass veto applied ---
Δφ(ll-jetmax) [dg.] 165 ---
top veto applied applied
pTll [GeV/c] 45 45

Higgs selection

The following cuts constitute what in the paper is called Higgs selection (which is dependent on the Higgs mass)

mH pTmax pTmin mll Δφll mT
[GeV/c2] [GeV/c] [GeV/c] [GeV/c2] dg. [GeV/c2]
115 20 10(15) 40 115 [80,110]
120 20 10(15) 40 115 [80,120]
130 25 10(15) 45 90 [80,125]
140 25 15 45 90 [80,130]
150 27 25 50 90 [80,150]
160 30 25 50 60 [90,160]
170 34 25 50 60 [110,170]
180 36 25 60 70 [120,180]
190 38 25 80 90 [120,190]
200 40 25 90 100 [120,200]
250 55 25 150 140 [120,250]
300 70 25 200 175 [120,300]
350 80 25 250 175 [120,350]
400 90 25 300 175 [120,400]
450 110 25 350 175 [120,450]
500 120 25 400 175 [120,500]
550 130 25 450 175 [120,550]
600 140 25 500 175 [120,600]
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