Search for a Standard Model Higgs boson in the decay channel H to ZZ(∗) to 4l

This is a condensed description with plots for the analysis CMS-HIG-11-004

Abstract

A search for a Higgs boson in the decay channel H → ZZ(∗) with each Z boson decaying to an electron or muon pair is presented using pp collisions from the LHC at sqrt(s)= 7 TeV. The data analyzed correspond to an integrated luminosity of 1.13 ± 0.07 fb−1 recorded by the CMS detector in 2010 and 2011. The search covers Higgs boson mass (mH) hypotheses of 110 < mH < 600 GeV/c2 with an expected sensitivity varying between one and five times the standard model cross section at 95% CL over most of the mass range. Fifteen events are observed, while 14.4 ± 0.6 events are expected from standard model background processes. Six of the events are below the kinematic threshold of two on-shell Z's (m_H < 180 GeV/c2), while 1.9 ± 0.1 background events are expected. The probability that the background fluctuates to the observed number of events is 1.3%. The events are not clustered in mass excluding interpretation as the standard model Higgs boson. The distribution of events is consistent with the expectation of standard model continuum production of ZZ(∗) pairs and the production cross section for 60 < m_Z < 120 GeV/c2 is measured to be in agreement with the predicted value. Upper limits at 95% CL on the cross section×branching ratio for a Higgs boson with standard model-like decays exclude cross sections from about one to two times the expected standard model cross section for masses in the range 180 < mH < 420 GeV/c2. Reinterpreted in the context of the standard model with four fermion generations a Higgs boson with a mass in the range 138 -162 GeV/c2 and 178-502 GeV/c2 is excluded at 95% CL.

Main Results

We find no evidence of Standard Model Higgs boson production. Fifteen events are observed in the 2e2mu, 4e and 4mu channels for an integrated luminosity of 1.13 ± 0.07 fb−1, while 14.4 ± 0.6 events are expected from standard model background processes. The distribution of events is compatible with the expectation from the standard model continuum production of Z boson pairs from q\bar{q} annihilation and gg fusion. No clustering of events is observed in the measured m_4l mass spectrum.

Using the high-mass selection which contains eight events, a total cross section for a pair of Z bosons in the mass range 60 < m_Z < 120 GeV/c2 has been measured to be in agreement with the predicted value.

Upper limits obtained at 95\% CL on the cross section×branching ratio for a Higgs boson with standard model-like decays exclude cross sections from about one to two times the expected standard model cross section for masses in the range 180 < mH < 420 GeV/c2.

Upper limits obtained in the context the standard model with a fourth fermion generation, exclude a Higgs boson with a mass in the ranges 138 -162 GeV/c2 and 178-502 GeV/c2 at 95% CL.

Figures from HIG-11-004

Figure	Label	Description
	Figure 1 a) left pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed mZ1 mass for the 4e channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 a) center pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed mZ2 mass for the 4e channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 a) right pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed four-lepton invariant mass for the 4e channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 b) left pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed mZ1 mass for the 4mu channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 b) center pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed mZ2 mass for the 4mu channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 b) right pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed four-lepton invariant mass for the 4mu channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 c) left pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed mZ1 mass for the 2e2mu channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 3 c) center pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed mZ2 mass for the 2e2mu channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 1 c) right pdf,eps,png	Comparison between data and MC at an early stage of the event selection where the four lepton combination is chosen. Reconstructed four-lepton invariant mass for the 2e2mu channel. Points with statistical uncertainties represent the data. Shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 2 pdf,eps,png	Distribution of the best reconstructed Z candidate invariant mass for the events in the four-lepton background control region defined by a pair of identified leptons with opposite charge and matching flavour and another pair of leptons with isolation cut relaxed, flavour and charge requirements removed and large impact parameters. Solid points represent the data, shaded histograms represent the MC expectations, the signal and the ZZ background contribute negligibly. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 3 a) pdf,eps,png	Distribution of the four-lepton reconstructed mass for the baseline selection in the 4e channel. Points represent the data, shaded histograms represent the signal and background expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 3 b) pdf,eps,png	Distribution of the four-lepton reconstructed mass for the baseline selection in the 4mu channel. Points represent the data, shaded histograms represent the signal and background expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 3 c) pdf,eps,png	Distribution of the four-lepton reconstructed mass for the baseline selection in the 2e2mu channel. Points represent the data, shaded histograms represent the signal and background expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 3 d) pdf,eps,png	Distribution of the four-lepton reconstructed mass for the baseline selection in the sum of the 4l channels. Points represent the data, shaded histograms represent the signal and background expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 4 pdf,eps,png	Distribution of the four-lepton reconstructed mass for the sum of the 4l channels in the high-mass selection. Points represent the data, shaded histograms represent the signal and background expectations. The samples correspond to an integrated luminosity of L = 1.13 fb−1.
	Figure 5 a) pdf, eps, png	The mean expected and the observed upper limits at 95% C.L. on σ(pp → H + X) × B(ZZ → 4l) for a Higgs boson in the mass range 120-600 GeV/c2, for an integrated luminosity of 1.13 fb−1 using the CLs approach. The expected ratios for (a) the SM and for (b) the SM with a fourth-fermion family (SM4) are presented. The results are obtained using a shape analysis method.
	Figure 5 b)pdf, eps, png	The mean expected and the observed upper limits at 95% C.L. on σ(pp → H + X) × B(ZZ → 4l) for a Higgs boson in the mass range 120-600 GeV/c2, for an integrated luminosity of 1.13 fb−1 using the CLs approach. The expected ratios for (a) the SM and for (b) the SM with a fourth-fermion family (SM4) are presented. The results are obtained using a shape analysis method.
	Figure 6 a) pdf,eps,png	Event yields in the 4e channel as a function of the event selection steps. Black points with uncertainties represent the data, other symbols represent the MC expectations The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 6 b) pdf,eps,png	Event yields in the 4mu channel as a function of the event selection steps. Black points with uncertainties represent the data, other symbols represent the MC expectations The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Figure 6 c) pdf,eps,png	Event yields in the 2e2mu channel as a function of the event selection steps. Black points with uncertainties represent the data, other symbols represent the MC expectations The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Table 1 pdf, eps, png	Event yields in the (a) 4e, (b) 4mu and (c) 2e2\mu channel for the trigger and the seven event selection steps (see text) with steps three and four regrouped as "4l" for the choice of the best four leptons. The samples correspond to an integrated luminosity of L = 1.13 fb−1
	Table 2 pdf, eps, png	Number of ZZ background events and relative uncertainties in the signal region in a mass range from 100 to 600 GeV/c2, estimated from normalization to the measured Z rate and from Monte Carlo simulation, for baseline and high-mass event selections.
	Table 3 pdf, eps, png	Number of background events and relative uncertainties for baseline and high-mass event selections in the signal region in a m4l range from 100 to 600 GeV/c2, estimated from data as described in the text. Upper three rows: t¯t and Z b¯b /c ¯ c estimated from the control region with inverted SIP3D, relaxed isolation, charge and flavour requirements for two leptons. Lower three rows: Z+jets estimated from the control region with relaxed isolation and identification requirements for two leptons.
	Table 4 pdf, eps, png	Summary of the magnitude of systematic uncertainties in percent
	Table 5 pdf, eps, png	Number of events observed, background and signal rates for each final state in a mass range from m1 = 100 GeV/c2 to m2 = 600 GeV/c2 both for the baseline and high-massselections. For ZZ, Z+jets, t¯t and Zb¯b /c ¯ c the data driven estimations are used, for WZ the Monte Carlo estimation is used.
	Table 6 pdf, eps, png	Properties of the four-lepton combinations satisfying the baseline selection for the Higgs boson search.

Additional Figures

Figure	Label	Description
	pdf, eps, png	The mean expected and the observed upper limits at 95% C.L. on σ(pp → H + X) × B(ZZ → 4l) for a Higgs boson in the mass range 120-600 GeV/c2, for an integrated luminosity of 1.13 fb−1 using the CLs approach. The results are obtained using a shape analysis method.
	pdf, eps, png	The mean expected and the observed upper limits at 95% C.L. on σ(pp → H + X) × B(ZZ → 4l) for a Higgs boson in the mass range 110-200 GeV/c2, for an integrated luminosity of 1.13 fb−1 using the CLs approach. The results are obtained using a shape analysis method.
	pdf, eps, png	Per-lepton probability to go from reco electron to electron with full ID and Isolation requirements, as measured in 2011 DATA using a Z+1 electron sample and as a function of pT. Electron is in Barrel. Data are shown as blue points and error bars. A parametrization is superimposed (dashed blue line) with statisical uncertainties shown as shaded yellow band.
	pdf, eps, png	Per-lepton probability to go from reco electron to electron with full ID and Isolation requirements, as measured in 2011 DATA using a Z+1 electron sample and as a function of pT. Electron is in Endcaps. Data are shown as blue points and error bars. A parametrization is superimposed (dashed blue line) with statisical uncertainties shown as shaded yellow band.
	pdf, eps, png	Per-lepton probability to go from tracker muon to muon with full ID and Isolation requirements, as measured in 2011 DATA using a Z+1 muon sample and as a function of pT. Muon is in Barrel. Data are shown as blue points and error bars. A parametrization is superimposed (dashed blue line) with statisical uncertainties shown as shaded yellow band.
	pdf, eps, png	Per-lepton probability to go from tracker muon to muon with full ID and Isolation requirements, as measured in 2011 DATA using a Z+1 muon sample and as a function of pT. Muon is in Endcaps. Data are shown as blue points and error bars. A parametrization is superimposed (dashed blue line) with statisical uncertainties shown as shaded yellow band.
	pdf, eps, png	Data-MC comparison of electron reconstruction efficiency as a function of pT
	pdf, eps, png	Data-MC comparison of electron reconstruction efficiency as a function of pT (zoom on y range)

Event Displays

	Candidate A (phi view): white.png, black.png
	Candidate A (eta view): white.png, black.png
	Candidate A (3D view): white.png, black.png
	Candidate O (phi view): white.png, black.png
	Candidate O (eta view): white.png, black.png
	Candidate O (3D view): white.png, black.png
	Candidate N (phi view): white.png, black.png
	Candidate N (eta view): white.png, black.png
	Candidate N (3D view): white.png, black.png