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-11-014

Abstract

This note reports a search for the Higgs boson decaying to W⁺W^- in pp collisions at sqrt{s} = 7 TeV. The analysis is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 1.55 fb^-1. W⁺W^- candidates are selected in events with two leptons, electrons or muons. No significant excess above the Standard Model background expectation is observed, and upper limits on Higgs boson production are derived, excluding the presence of a Higgs boson with a mass in the range [147 - 194] GeV/c² at 95% C.L. using the CLs approach.

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 analysis is performed, optimized for each mass point, where the Higgs signal normalization is extracted by subtracting the background expected yields from the data counts for each H 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. No evidence of Higgs boson is found and the results are interpreted as an exclusion of a wide H mass range. The expected exclusion range at 95% CL is between 135 and 200 GeV for a Standard Model Higgs, while the observed one is [147 - 194] GeV/c² at 95% C.L. using the CLs approach. Below we report the table with detailed exclusion limits for a range of masses 115-300 GeV/c².

* Cut based analysis results: Higgs Cross section / SM Higgs Cross section limits evaluated with CLs method.

Mass [GeV/c2]	Observed	Median Expected	68% probability band	95% probability band
115	6.32649	4.22347	[3.02735,6.11041]	[2.31588,8.67718]
120	4.48928	2.6272	[1.86641,3.77479]	[1.50822,5.14783]
130	2.28451	1.29467	[0.950825,1.82184]	[0.72437,2.54299]
140	1.20125	0.776354	[0.551954,1.09008]	[0.420855,1.51755]
150	0.922221	0.547016	[0.382896,0.777648]	[0.273836,1.07516]
160	0.498218	0.284275	[0.16644,0.428573]	[0.10427,0.60257]
170	0.467593	0.306607	[0.177748,0.463758]	[0.0944892,0.64674]
190	0.785681	0.665427	[0.459851,0.97443]	[0.325339,1.36967]
200	1.26236	0.967304	[0.672679,1.39747]	[0.510445,1.94207]
250	1.97736	1.87344	[1.31175,2.69628]	[1.0084,3.80185]
300	2.97786	2.15053	[1.5054,3.07299]	[1.19551,4.34792]
350	2.85515	2.01793	[1.39494,2.92167]	[1.06908,4.07263]
400	2.75774	2.25272	[1.61292,3.29429]	[1.22701,4.59224]
450	2.43132	2.89446	[2.05477,4.20222]	[1.50695,5.95797]
500	3.5578	3.9329	[2.74443,5.76567]	[2.06293,8.10109]
550	3.79315	5.35366	[3.9136,7.73434]	[3.11088,10.9697]
600	4.8772	7.66369	[5.43584,10.9373]	[4.37011,15.5232]

Figures from CMS-HIG-11-014

Figure	Label	Description
	Figure 1a png, pdf	leptons deltaphi for 0 jet bin
	Figure 1b png, pdf	leptons deltaphi for 1 jet bin
	Figure 1c png, pdf	leptons invariant mass for 0 jet bin
	Figure 1d png, pdf	leptons invariant mass for 1 jet bin
	Figure 2b png, pdf	Cut flow evolutions in the 0-jet bin for mH=130 GeV/c2 SM Higgs selection. The first step corresponds to the dilepton selection; the second step corresponds to the projected MET requirements; the third step corresponds to the Z veto; the fourth step corresponds to the jet veto; the fifth step corresponds to the top veto. All cuts up to this point correspond to the WW common preselection. The last set of requirements depends on the Higgs mass selection. The sixth and seventh steps correspond to the pTmax and pTmin requirements, respectively; the eighth step corresponds to the mll requirement, while the ninth step corresponds to the mT two-side requirement. Finally, the last step corresponds to the Δφ ll requirement. All the appropriate background normalizations and scale factors from data are at every step included in the signal and background expectations.
	Figure 2a png, pdf	Cut flow evolutions in the 0-jet bin for mH=140 GeV/c2 SM Higgs selection. The first step corresponds to the dilepton selection; the second step corresponds to the projected MET requirements; the third step corresponds to the Z veto; the fourth step corresponds to the jet veto; the fifth step corresponds to the top veto. All cuts up to this point correspond to the WW common preselection. The last set of requirements depends on the Higgs mass selection. The sixth and seventh steps correspond to the pTmax and pTmin requirements, respectively; the eighth step corresponds to the mll requirement, while the ninth step corresponds to the mT two-side requirement. Finally, the last step corresponds to the Δφ ll requirement. All the appropriate background normalizations and scale factors from data are at every step included in the signal and background expectations.
	Figure 2b png, pdf	Cut flow evolutions in the 0-jet bin for mH=160 GeV/c2 SM Higgs selection. The first step corresponds to the dilepton selection; the second step corresponds to the projected MET requirements; the third step corresponds to the Z veto; the fourth step corresponds to the jet veto; the fifth step corresponds to the top veto. All cuts up to this point correspond to the WW common preselection. The last set of requirements depends on the Higgs mass selection. The sixth and seventh steps correspond to the pTmax and pTmin requirements, respectively; the eighth step corresponds to the mll requirement, while the ninth step corresponds to the mT two-side requirement. Finally, the last step corresponds to the Δφ ll requirement. All the appropriate background normalizations and scale factors from data are at every step included in the signal and background expectations.
	Figure 3 png, pdf	95% C.L. expected and observed upper limits on the cross section times branching ratio σ(H) x BR(H → WW → 2l2ν), relative to the SM value using a cut-based event selection, obtained using the CLs approach.

Tables from the PAS

Data counts and expected background at WW selection.

Expected number of signal and background events from the data-driven methods for an integrated luminosity of 1.54 fb^-1 after applying the WW selection requirements. Statistical and systematic uncertainties on the processes are reported. The DY process corresponds to the dimuon and dielectron final states. The WW contribution corresponds to the estimated value from the simulation.

jet bin	data	all bkg.	qq → WW	gg → WW	ttbar+tW	W+ γ
0-jet	811	771.2 ± 70.0	494.8 ± 44.6	23.8 ± 2.2	72.6 ± 18.8	12.3 ± 2.3
1-jet	435	427.6 ± 32.1	152.1 ± 13.8	8.2 ± 0.8	156.3 ± 19.8	3.4 ± 1.0
2-jet	252	235.4 ± 22.3	33.2 ± 3.1	1.5 ± 0.1	131.7 ± 16.8	1.6 ± 0.7

jet bin	WZ,ZZ not in DY	DY+WZ+ZZ	Z → ττ	W+jets
0-jet	12.0 ± 1.3	15.2 ± 5.1	1.9 ± 0.6	138.5 ± 50.2
1-jet	10.1 ± 1.1	16.3 ± 4.3	14.9 ± 2.2	56.3 ± 20.6
2-jet	2.2 ± 0.3	28.3 ± 11.5	4.3 ± 0.9	22.6 ± 8.6

Data counts and expected background at H selection (mH = 140 GeV/c²)

process	Higgs	qq → WW	gg → WW	VV	top	DY	W+jets	Σ bkg	data
0-jet bin, same-flavor	18.8 ± 4.2	31.5 ± 5.5	1.5 ± 0.8	0.8 ± 0.1	3.1 ± 1.1	0.1 ± 0.0	5.6 ± 2.3	44.0 ± 6.2	46
0-jet bin, opposite-flavor	15.9 ± 3.6	29.1 ± 5.1	1.3 ± 0.7	0.5 ± 0.1	1.4 ± 0.5	3.1 ± 4.2	5.3 ± 2.2	40.6 ± 7.0	41
1-jet bin, same-flavor	6.6 ± 2.2	8.3 ± 3.1	0.5 ± 0.3	0.5 ± 0.1	5.6 ± 1.2	0.2 ± 0.1	2.4 ± 1.1	17.8 ± 3.5	23
1-jet bin, opposite-flavor	4.6 ± 1.5	5.8 ± 2.2	0.3 ± 0.2	0.3 ± 0.1	3.2 ± 0.8	1.2 ± 2.7	1.5 ± 0.9	12.6 ± 3.7	23
2-jet bin	0.5 ± 0.1	0.6 ± 0.2	0.1 ± 0.1	0.0 ± 0.0	2.6 ± 1.5	0.8 ± 0.6	1.0 ± 0.6	5.3 ± 1.7	7

Data counts and expected background at H selection for three mass points (0-jet bin, same-flavor)

mass	Higgs	qq → WW	gg → WW	VV	top	DY	W+jets	Σ bkg	data
120	7.6 ± 1.7	33.7 ± 5.9	1.3 ± 0.7	0.8 ± 0.1	3.0 ± 1.1	0.1 ± 0.0	19.4 ± 7.3	62.3 ± 9.5	67
140	18.8 ± 4.2	31.5 ± 5.5	1.5 ± 0.8	0.8 ± 0.1	3.1 ± 1.1	0.1 ± 0.0	5.6 ± 2.3	44.0 ± 6.2	46
160	26.6 ± 6.1	13.5 ± 2.4	1.3 ± 0.7	0.3 ± 0.1	1.9 ± 0.9	0.0 ± 0.0	2.0 ± 1.1	19.0 ± 2.9	18

Summary of systematic uncertainties

Summary of all systematic uncertainties (relative). This is just an indicative table, since the precise values depend on the final state and jet-bin.

|

• Same-sign estimation
  

Pre/Post-EPS data

• Top estimation: scale factors between data and simulation
  
• W+jets estimation: number of events per fb-1
  

Additional plots for public talks

	Δφ ll 2 jet bin png, pdf	leptons Δφ for 2 jet bin
	mll 2 jet bin png, pdf	leptons invariant mass for 2 jet bin
	projected MET 0 jet bin png, pdf	projected MET 0 jet bin
	projected MET 1 jet bin png, pdf	projected MET 1 jet bin
	projected MET 2 jet bin png, pdf	projected MET 2 jet bin
	Higgs transverse mass 0 jet bin png, pdf	Higgs transverse mass 0 jet bin
	Higgs transverse mass 1 jet bin png, pdf	Higgs transverse mass 1 jet bin
	Higgs transverse mass 2 jet bin png, pdf	Higgs transverse mass 2 jet bin
	leading lepton pT 0 jet bin png, pdf	leading lepton pT 0 jet bin
	leading lepton pT 1 jet bin png, pdf	leading lepton pT 1 jet bin
	leading lepton pT 2 jet bin png, pdf	leading lepton pT 2 jet bin
	trailing lepton pT 0 jet bin png, pdf	trailing lepton pT 0 jet bin
	trailing lepton pT 1 jet bin png, pdf	trailing lepton pT 1 jet bin
	trailing lepton pT 2 jet bin png, pdf	trailing lepton pT 2 jet bin