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

Abstract

A search for a Higgs boson in the four-lepton decay channel H → ZZ, with each Z boson decaying to an electron or muon pair, is reported. The search covers Higgs boson mass hypotheses in the range 110 < mH < 600 GeV. The analysis uses data corresponding to an integrated luminosity of 4.7 fb−1 recorded by the CMS detector in pp collisions at √s = 7 TeV from the LHC. Seventy-two events are observed with four-lepton invariant mass m4l > 100 GeV (with thirteen below 160 GeV), while 67.1 ± 6.0 (9.5 ± 1.3) events are expected from background. The four-lepton mass distribution is consistent with the expectation of standard model background production of ZZ pairs. Upper limits at 95% confidence level exclude the standard model Higgs boson in the ranges 134–158 GeV, 180–305 GeV, and 340–465 GeV. Small excesses of events are observed around masses of 119, 126, and 320 GeV, making the observed limits weaker than expected in the absence of a signal.

• Selected numbers

Figures

Figure	Label	Description
	pdf,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 = 4.7 fb−1.

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Zoom on the low mass range with existing exclusion limits at 99\% CL; also shown are the central values and event-by-event mass measurement uncertainties. Points represent the data, shaded histograms represent the background and opened histogram the signal expectations. The results are presented for an integrated luminosity of 4.7 fb−1.

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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 110-600 GeV/c2, the limits are calculated relative to their expected SM Higgs boson prediction σSM, for an integrated luminosity of 4.7 fb−1 using the CLs approach. The expected ratios for the SM is presented. The results are obtained using a shape analysis method.

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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 110-180 GeV/c2, the limits are calculated relative to their expected SM Higgs boson prediction σSM, for an integrated luminosity of 4.7 fb−1 using the CLs approach. The expected ratios for the SM is presented. The results are obtained using a shape analysis method.

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The significance of the local fluctuations with respect to the standard model expectation as a function of the Higgs boson mass in the range 110-600 GeV/c2, for an integrated luminosity of 4.7 fb−1, obtained both without (blue) or with (red) event-by-event measurement uncertainties, and for the combination of the three channels.

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The significance of the local fluctuations with respect to the standard model expectation as a function of the Higgs boson mass in the range 110-160 GeV/c2, for an integrated luminosity of 4.7 fb−1, obtained both without (blue) or with (red) event-by-event measurement uncertainties, and for the combination of the three channels.

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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 110-600 GeV/c2, for an integrated luminosity of 4.7 fb−1 using the CLs approach. The cross section of σ(pp → H + X) × B(ZZ → 4l) is also shown. The results are obtained using a shape analysis method.

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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 110-180 GeV/c2, for an integrated luminosity of 4.7 fb−1 using the CLs approach. The cross section of σ(pp → H + X) × B(ZZ → 4l) is also shown. The results are obtained using a shape analysis method.

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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 = 4.7 fb−1.

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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 = 4.7 fb−1.

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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 =4.7 fb−1.

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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 = 4.7 fb−1.

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Distribution of transverse momentum of four-lepton system (p_{T,4l}) 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 = 4.7 fb−1.

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Distribution of the reconstructed mass of the first lepton pair (M_{Z1}) 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 = 4.7 fb−1.

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Distribution of the reconstructed mass of the second lepton pair (M_{Z2}) 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 = 4.7 fb−1.

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Distribution of transverse momentum of four-lepton system (p_{T,4l}) versus the four-lepton reconstructed mass (M_{4l}) for the 4e (green circle), 4mu (green triangle) and 2e2mu (blue cross). The samples correspond to an integrated luminosity of L = 4.7 fb−1.

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Distribution of the reconstructed mass of the second lepton pair (M_{Z2l}) versus the four-lepton reconstructed mass (M_{4l}) for the 4e (green circle), 4mu (green triangle) and 2e2mu (blue cross). The samples correspond to an integrated luminosity of L = 4.7 fb−1.

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Distribution of the reconstructed mass of the second lepton pair (M_{Z2l}) versus the reconstructed mass of the first lepton pair (M_{Z1}) for the 4e (green circle), 4mu (green triangle) and 2e2mu (blue cross). The samples correspond to an integrated luminosity of L = 4.7 fb−1.

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Errors on the M_{4l} measurement versus the M_{4l} in the data for the 4e (green circle), 4mu (green triangle) and 2e2mu (blue cross). The samples correspond to an integrated luminosity of L = 4.7 fb−1.

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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 = 4.7 fb−1.

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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 = 4.7 fb−1.

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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 = 4.7 fb−1.

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Number of event candidates observed, and background and signal rates for each final state for 100 < m_{4l} < 600 GeV/c2 for the baseline selection. For the Z+X background, data driven estimations are used.

Additional Material

Figure	Label	Description
	pdf,png	Mean measurement efficiency for the Higgs boson signal within the geometrical acceptance. The efficiency determined for the signal selection is obtained using Monte Carlo signal samples,  and plotted as a function of the Higgs boson mass hypothesis mH separately for the  4e, 4mu, and 2e2mu channels.

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Distribution of the transverse momentum (pT) for each of the four leptons (ordered in pT) from H to 4l signal events and for a mass hypothesis of mH = 120 or mH = 140. The distributions are obtained using MC signal samples and shown at generator level within eta acceptance (empty histograms), and for selected events (shaded histograms) in the 4e, 4mu, and 2e2mu channels.

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Electron identification efficiencies computed with the tag-and-probe method as a function of the probe eta in the 7-10 GeV/c p_T bin. Errors shown are statistical only.

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Electron identification efficiencies computed with the tag-and-probe method as a function of the probe $p_{T}$ in the eta bins 0 < eta < 0.78

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mll distributions and fits for tags plus passing and failing probes used for the electron identification efficiency measurement in the barrel, 7-10 GeV/c transverse momentum bin. The samples correspond to an integrated luminosity of L = 4.7 fb−1.

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Distribution of the four-lepton reconstructed mass in the sum of the 4l channels applying a relaxed selection to illustrate the single resonance Z->4l peak. The lower cut of m_{Z2} is relaxed from 12 GeV/c2 to 4 GeV/c2 and the minimum cut on m_{4l} in not applied. Points represent the data, shaded histograms represent the MC expectations. The samples correspond to an integrated luminosity of L = 4.7 fb−1.

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Electron isolation efficiencies computed with the tag-and-probe method in the bin 7 < p_T < 100 GeV/c as a function of the isolation cut R_{iso} in the bin of number of reconstructed vertices, N_{vxt} > 12.

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Muon isolation efficiencies computed with the tag-and-probe method in the bin 5 < p_T < 100 GeV/c as a function of the isolation cut R_{iso} in the bin of number of reconstructed vertices, N_{vxt} > 12.

Event Display

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4e candidate: m4l= 125.7 GeV/c2 mZ1= 92.3 GeV/c2 mZ2= 27.2 GeV/c2.

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4μ candidate m4l= 238.5 GeV/c2 mZ1= 91.0 GeV/c2 mZ2= 93.2 GeV/c2.

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2e2mu candidate: m4l= 244.6 GeV/c2 mZ1= 91.2 GeV/c2 mZ2= 93.2 GeV/c2.