Search for the Standard Model Higgs Boson in the Decay Channel $H\to ZZ\to 4l$ in $pp$ Collisions at $\sqrt{s}=7\mathrm{TeV}$

A search for a Higgs boson in the four-lepton decay channel $H\to ZZ$, with each $Z$ boson decaying to an electron or muon pair, is reported. The search covers Higgs boson mass hypotheses in the range of $110<m_H<600\mathrm{GeV}$. The analysis uses data corresponding to an integrated luminosity of $4.7{\mathrm{fb}}^{-1}$ recorded by the CMS detector in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ from the LHC. Seventy-two events are observed with four-lepton invariant mass $m_{4\ell }>100\mathrm{GeV}$ (with 13 below 160 GeV), while $67.1\pm 6.0$ ($9.5\pm 1.3$) 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 of 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.

Figure 1

(a) Distribution of the four-lepton reconstructed mass for the sum of the $4e$, $4\mu$, and $2e2\mu$ channels. (b) Expansion of the low-mass range with existing exclusion limits at 95% C.L.; also shown are the central values and individual candidate mass measurement uncertainties. Points represent the data, shaded histograms represent the background, and the unshaded histogram the signal expectations.

Figure 2

(a) The significance of the local excesses with respect to the standard model expectation as a function of the Higgs boson mass, without (blue) or with (red) individual candidate mass measurement uncertainties. (b) The observed and the median expected upper limits at 95% C.L. on $\sigma =\sigma (pp\to H+X)\times \mathcal{B}(H\to 4\ell )$, relative to their standard model prediction ${\sigma }_{\mathrm{SM}}$, for a Higgs boson in the mass range of 110–600 GeV, using the ${\mathrm{CL}}_s$ approach. The insets expand the low-mass range.