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Search for the Higgs Boson Decaying to W+W− in the Fully Leptonic Final State in pp collisions at sqrt(s)=8 TeV


This is a condensed description with plots for the analysis CMS-HIG-12-017

Abstract

We report a search for the Higgs boson decaying to W+W− in pp collisions at sqrt(s) = 8 TeV. The data were collected at the LHC with the CMS detector, and correspond to an integrated luminosity of 5.1 fb−1. The W+W− candidates are selected in events with two opposite charged leptons and large missing transverse energy. Upper limits on the Higgs boson production relative to the standard model Higgs expectation are derived. The Standard Model Higgs boson is excluded for a mass in the range [129 - 520] GeV at 95% confidence level when these results are combined together with the analysis performed at sqrt(s)=7 TeV.

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. 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. The expected exclusion range at 95% CL when considering the results at 7 and 8 TeV, based on a MVA shape analysis and a cut based analysis respectively is between 122 and 450 GeV for a Standard Model Higgs, while the observed one is [129 - 520] GeV/c2 at 95% C.L. using the CLs approach. The observed (expected) upper limits are about 2.2 (1.2) times de SM expectation for a mass of 125 GeV A small excess of events is observed for hypothetical low Higgs boson masses which makes the observed limits weaker than the expected ones.

Below we report the table with detailed exclusion limits for a range of masses 110-600 GeV/c2, for the cut based 8 TeV analysis and for the 7 and 8 TeV analysis combined, based on a MVA shape analysis and a cut based analysis respectively.

  • results with the cut-based analysis:
8 TeV analysis 7 TeV + 8 TeV analysis
Higgs Mass Observed Median exp. 68% band 95% band Observed Median exp. 68% band 95% band
110 8.9 5.4 [ 2.9, 3.9] [ 7.6, 10.1] 6.1 3.9 [ 2.1, 2.8] [ 5.4, 7.3]
115 4.4 2.9 [ 1.6, 2.1] [ 4.1, 5.5] 3.6 2.0 [ 1.1, 1.4] [ 2.8, 3.7]
120 3.2 1.8 [ 1.0, 1.3] [ 2.5, 3.3] 2.2 1.2 [ 0.7, 0.9] [ 1.7, 2.2]
125 1.9 1.2 [ 0.6, 0.8] [ 1.6, 2.2] 1.4 0.8 [ 0.5, 0.6] [ 1.2, 1.6]
130 1.4 0.8 [ 0.5, 0.6] [ 1.1, 1.6] 0.9 0.6 [ 0.3, 0.4] [ 0.8, 1.1]
135 1.0 0.6 [ 0.3, 0.5] [ 0.9, 1.2] 0.7 0.5 [ 0.2, 0.3] [ 0.6, 0.8]
140 0.8 0.5 [ 0.3, 0.4] [ 0.7, 0.9] 0.6 0.3 [ 0.2, 0.2] [ 0.5, 0.7]
150 0.7 0.3 [ 0.2, 0.2] [ 0.5, 0.7] 0.5 0.2 [ 0.1, 0.2] [ 0.3, 0.5]
160 0.4 0.2 [ 0.1, 0.1] [ 0.3, 0.4] 0.3 0.2 [ 0.1, 0.1] [ 0.2, 0.3]
170 0.4 0.2 [ 0.1, 0.2] [ 0.3, 0.4] 0.3 0.2 [ 0.1, 0.1] [ 0.2, 0.3]
180 0.5 0.3 [ 0.2, 0.2] [ 0.4, 0.6] 0.3 0.2 [ 0.1, 0.2] [ 0.3, 0.4]
190 0.8 0.4 [ 0.2, 0.3] [ 0.6, 0.8] 0.4 0.3 [ 0.2, 0.2] [ 0.4, 0.6]
200 1.1 0.5 [ 0.3, 0.4] [ 0.7, 1.0] 0.5 0.4 [ 0.2, 0.3] [ 0.6, 0.8]
250 2.3 1.1 [ 0.6, 0.8] [ 1.5, 2.0] 0.6 0.8 [ 0.4, 0.5] [ 1.1, 1.4]
300 1.9 1.2 [ 0.6, 0.9] [ 1.6, 2.2] 0.8 0.8 [ 0.4, 0.6] [ 1.1, 1.5]
350 1.3 1.1 [ 0.6, 0.8] [ 1.5, 2.0] 0.7 0.7 [ 0.4, 0.5] [ 1.0, 1.3]
400 1.3 1.2 [ 0.7, 0.9] [ 1.7, 2.3] 0.8 0.8 [ 0.4, 0.6] [ 1.1, 1.4]
450 1.3 1.5 [ 0.8, 1.1] [ 2.1, 2.9] 0.7 1.0 [ 0.5, 0.7] [ 1.4, 1.9]
500 1.5 2.1 [ 1.1, 1.5] [ 2.9, 3.9] 0.9 1.4 [ 0.7, 1.0] [ 1.9, 2.6]
550 2.0 2.7 [ 1.5, 2.0] [ 3.8, 5.1] 1.2 1.9 [ 1.0, 1.4] [ 2.6, 3.5]
600 2.7 3.8 [ 2.0, 2.7] [ 5.3, 7.1] 1.5 2.7 [ 1.4, 1.9] [ 3.7, 5.0]

Paper figures

ww_analysis16_0_dphi_incl_0j.png Δφ ll in the 0-jet bin at WW selection level
ww_analysis16_0_dphi_incl_1j.png Δφ ll in the 1-jet bin at WW selection level

limits_nj_cut_8TeV-CLs-asymptotic_logx_logy.png Exclusion limit with cut-based analysis at 8 TeV
limits_nj_shape7TeV_cut8TeV-CLs-asymptotic_logx_logy.png Exclusion limit with shape based analysis at 7 TeV and cut-based analysis at 8 TeV

Paper tables

Yields at the WW selection level

Backgrounds are rescaled to the data-driven expectations
njets data all bkg. WW ttbar+tW W+jets
0-jet 1594 1501 ± 21 1046.1 ± 7.2 164.2 ± 5.4 158.2 ± 7.1
1-jet 1186 1162 ± 27 381.0 ± 4.0 527.3 ± 8.4 122.6 ± 6.7
2-jet 1295 1412 ± 24 177.0 ± 2.8 886.5 ± 11.1 94.9 ± 6.4

njets WZ/ZZ DY→ll Wγ
0-jet 32.6 ± 0.6 73 ± 27 27.1 ± 3.9
1-jet 30.3 ± 0.6 77 ± 24 23.7 ± 5.2
2-jet 20.8 ± 0.5 227 ± 20 5.6 ± 2.1

Yields at the Higgs selection level

  • cut based approach in the 0-jet category, emu final state *:
mH H→WW pp→WW WZ+ZZ+Z/gamma* Top W+jets W&gamma* all bkg. data
125 23.9 ± 5.2 87.6 ± 9.5 2.2 ± 0.2 9.3 ± 2.7 19.1 ± 7.2 6.0 ± 2.3 124.2 ± 12.4 158
130 35.3 ± 7.6 96.8 ± 10.5 2.5 ± 0.3 10.1 ± 2.8 20.7 ± 7.8 6.3 ± 2.4 136.3 ± 13.6 169
160 98.3 ± 21.2 53.6 ± 5.9 1.2 ± 0.1 6.3 ± 1.7 2.5 ± 1.3 0.2 ± 0.1 63.9 ± 6.3 79
400 16.6 ± 4.8 50.5 ± 5.8 1.5 ± 0.2 26.1 ± 5.7 4.5 ± 2.0 0.7 ± 0.5 83.3 ± 8.4 92

  • cut based approach in the 0-jet category, ee/mumu final state *:
mH H→WW pp→WW WZ+ZZ+Z/gamma* Top W+jets W&gamma* all bkg. data
125 14.9 ± 3.3 60.4 ± 6.7 37.7 ± 12.5 1.9 ± 0.5 10.8 ± 4.3 4.6 ± 2.5 115.5 ± 15.0 123
130 23.5 ± 5.1 67.4 ± 7.5 41.3 ± 15.9 2.3 ± 0.6 11.0 ± 4.3 4.8 ± 2.5 126.8 ± 18.3 134
160 86.0 ± 18.7 44.5 ± 4.9 11.3 ± 13.4 3.8 ± 0.9 1.3 ± 1.1 0.4 ± 0.3 61.4 ± 14.4 92
400 12.3 ± 3.6 37.1 ± 4.3 5.7 ± 1.3 20.0 ± 4.7 3.4 ± 1.9 13.6 ± 4.8 79.9 ± 8.3 55

  • cut based approach in the 1-jet category, emu final state *:
mH H→WW pp→WW WZ+ZZ+Z/gamma* Top W+jets W&gamma* all bkg. data
125 10.3 ± 3.0 19.5 ± 3.7 2.4 ± 0.3 22.3 ± 2.0 11.7 ± 4.6 5.9 ± 3.2 61.7 ± 7.0 54
130 15.7 ± 4.7 22.0 ± 4.1 2.6 ± 0.3 25.1 ± 2.2 12.8 ± 5.1 6.0 ± 3.2 68.5 ± 7.6 64
160 52.6 ± 14.9 20.1 ± 4.0 1.6 ± 0.2 21.5 ± 1.8 5.0 ± 2.3 0.9 ± 0.5 49.2 ± 5.0 62
400 11.4 ± 3.3 39.1 ± 6.3 2.1 ± 0.3 56.6 ± 3.7 7.1 ± 3.1 0.6 ± 0.6 105.5 ± 8.0 96

  • cut based approach in the 1-jet category, ee/mumu final state *:
mH H→WW pp→WW WZ+ZZ+Z/gamma* Top W+jets W&gamma* all bkg. data
125 4.4 ± 1.3 9.7 ± 1.9 8.7 ± 4.9 9.5 ± 1.1 3.9 ± 1.7 1.3 ± 1.2 33.1 ± 5.7 43
130 7.1 ± 2.2 11.2 ± 2.2 9.1 ± 5.4 10.7 ± 1.2 3.7 ± 1.7 1.3 ± 1.2 36.0 ± 6.3 53
160 37.9 ± 10.9 13.8 ± 2.8 28.4 ± 10.7 16.2 ± 1.6 3.8 ± 2.1 0.0 ± 0.0 62.3 ± 11.4 65
400 7.4 ± 2.2 19.6 ± 3.2 7.9 ± 2.4 33.4 ± 2.4 1.6 ± 1.3 4.4 ± 1.8 66.8 ± 5.1 67

  • cut based approach in the 2-jet category, emu final state *:
mH H→WW pp→WW WZ+ZZ+Z/gamma* Top W+jets W&gamma* all bkg. data
125 1.5 ± 0.2 0.4 ± 0.1 0.1 ± 0.0 3.4 ± 1.9 0.3 ± 0.3 0.0 ± 0.0 4.1 ± 1.9 6
130 2.5 ± 0.4 0.5 ± 0.2 0.1 ± 0.0 3.0 ± 1.8 0.3 ± 0.3 0.0 ± 0.0 3.9 ± 1.9 6
160 9.9 ± 1.3 0.8 ± 0.2 0.1 ± 0.0 4.2 ± 2.2 0.6 ± 0.4 0.0 ± 0.0 5.6 ± 2.2 11
400 2.3 ± 0.4 1.9 ± 0.8 0.2 ± 0.0 9.1 ± 2.7 0.5 ± 0.4 0.0 ± 0.0 11.7 ± 2.9 22

  • cut based approach in the 2-jet category, ee/mumu final state *:
mH H→WW pp→WW WZ+ZZ+Z/gamma* Top W+jets W&gamma* all bkg. data
125 0.8 ± 0.1 0.3 ± 0.1 3.1 ± 1.8 2.0 ± 1.2 0.0 ± 0.0 0.0 ± 0.0 5.4 ± 2.2 7
130 1.3 ± 0.2 0.4 ± 0.2 3.8 ± 2.2 2.0 ± 1.2 0.0 ± 0.0 0.0 ± 0.0 6.2 ± 2.5 7
160 6.0 ± 0.8 0.7 ± 0.3 4.7 ± 2.7 2.4 ± 1.2 0.2 ± 0.4 0.0 ± 0.0 8.0 ± 3.0 9
400 1.6 ± 0.2 1.5 ± 0.7 6.6 ± 2.8 4.9 ± 1.9 0.7 ± 0.7 0.0 ± 0.0 13.8 ± 3.5 15

Selections definition

WW selection

The following cuts constitute what in the paper is called WW selection

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

(*) For Higgs masses below 140 GeV in 0 and 1 jet categories no cut is applied in Δφ(ll-jetmax) and the projected MET cut in ee,μμ channel is set to 20 GeV. Additionally a dedicated multivariate selection combining missing transverse momentum, kinematic and topological variables, is used to reject Drell-Yan events and maximize the surviving signal yield. DYMVA variable has to be greater than 0.6 for 0 jet bin and above 0.3 for the 1 jet bin.

(**) For the VBF selection, Particle Flow MET is used.

Higgs selection

The following cuts constitute what in the paper is called Higgs selection
mH pTmax pTmin mll Δφll mT
[GeV/c2] [GeV/c] [GeV/c] [GeV/c2] dg. [GeV/c2]
120 20 10 40 115 [80,120]
130 25 10 45 90 [80,125]
160 30 25 50 60 [90,160]
200 40 25 90 100 [120,200]
250 55 25 150 140 [120,250]
300 70 25 200 175 [120,300]
400 90 25 300 175 [120,400]

Other figures

Kinematic variables at the WW selection level

mll_ALL_CommonCuts_WWsel_Lin.png dilepton invariant mass in the 0-jet bin at WW selection level
mll_ALL_CommonCuts_WWsel_Lin_1j.png dilepton invariant mass in the 0-jet bin at WW selection level

leading lepton pT 0-jet / 1-jet / at WW selection level
pdf pdf [pdf] other formats

trailing lepton pT 0-jet / 1-jet / at WW selection level
pdf pdf [pdf] other formats

Fraction of 0-jet events as a function of jet pT threshold

jetveto_0jet_vtxcomp_wrt_loPU.png Fraction of 0-jet events as a function of jet pT threshold measured in a sample of same-flavour lepton pairs consistent with Z decay, showing stability of jet selection in different pile-up conditions. A jet pT threshold of 30 GeV is used in the analysis

Kinematic variables final selection

dPhi_N-2_mh125_nj0.png Δφ ll in the 0-jet bin one step before the final selection (no cuts on Δφ(ll) and m(ll)) for mh=125 GeV
dPhi_N-2_mh125_nj1.png Δφ ll in the 1-jet bin one step before the final selection (no cuts on Δφ(ll) and m(ll)) for mh=125 GeV

dilepmass_N-1_mh125_nj0.png dilepton invariant mass in the 0-jet bin at final selection (all other selection applied) for mh=125 GeV
dilepmass_N-1_mh125_nj1.png dilepton invariant mass in the 1-jet bin at final selection (all other selection applied) for mh=125 GeV

leading lepton pT the 0-jet / 1-jet / bins for mh=125 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

trailing lepton pT the 0-jet / 1-jet / bins for mh=125 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

dilepton invariant mass in the 0-jet and 1-jet bins for mh=160 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

Δφ ll in the 0-jet / 1 jet bins for mh=160 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

leading lepton pT the 0-jet / 1-jet / bins for mh=160 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

trailing lepton pT the 0-jet / 1-jet / bins for mh=160 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

transverse mass in the 0-jet bin for mh=125 GeV and mh=160 GeV at final selection (all other selection applied)
pdf pdf [pdf] other formats

Exclusion limits at low masses

limit_cut_data.png Limits from 2012 at low masses
limit_cut_inj125.png Signal injection using prediction at 5.1/fb 8 TeV
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