Search for a Higgs boson in the decay channel H to ZZ(*) to q qbar l-l+ in pp collisions at sqrt(s) = 7 TeV

TL;DR

This CMS study searches for the SM Higgs boson in the H->ZZ(*)->qqll channel using 4.6 fb⁻¹ of 7 TeV data. It leverages full kinematic reconstruction, five angular observables, and jet-flavor discrimination (including b-tagging and quark-gluon tagging) with data-driven background sidebands to extract a signal from the mZZ distributions across multiple categories and mass hypotheses. No evidence for a SM-like Higgs is found, and 95% CL upper limits on the production cross section relative to the SM are reported for mH from 130 to 600 GeV, with SM4 interpretations excluding several mass ranges. The approach demonstrates the value of semileptonic ZZ final states in constraining Higgs properties and beyond-Standard-Model scenarios at the LHC.

Abstract

A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into a final state containing two quark jets and two leptons, H to ZZ(*) to q q-bar l-l+ is presented. Results are based on data corresponding to an integrated luminosity of 4.6 inverse femtobarns of proton-proton collisions at sqrt(s)=7 TeV, collected with the CMS detector at the LHC. In order to discriminate between signal and background events, kinematic and topological quantities, including the angular spin correlations of the decay products, are employed. Events are further classified according to the probability of the jets to originate from quarks of light or heavy flavor or from gluons. No evidence for the Higgs boson is found, and upper limits on its production cross section are determined for a Higgs boson of mass between 130 and 600 GeV.

Figures (5)

• Figure 1: Diagram describing the process $\mathrm{p}\mathrm{p}\to{H}\xspace+\mathrm{X}\to{Z}{Z}^{(*)}+\mathrm{X}\to{q}\overline{{q}}\,\ell^-\ell^++\mathrm{X}$ in terms of the angles $(\theta^*, \Phi_1, \theta_1, \theta_2, \Phi)$ defined in the parent particle rest frames (${H}\xspace$ or ${Z}$), where $\mathrm{X}$ indicates other products of the $\mathrm{p}\mathrm{p}$ collision not shown on the diagram Gao:2010qx.
• Figure 2:
• Figure 3: The $m_{{Z}{Z}}$ invariant mass distribution after final selection in three categories: 0 ${b}$-tag (top), 1 ${b}$-tag (middle), and 2 ${b}$-tag (bottom). The low-mass range $120<m_{{Z}{Z}}<170\,\text{Ge\spaceV}\xspace$ is shown on the left and the high-mass range $183<m_{{Z}{Z}}<800\,\text{Ge\spaceV}\xspace$ is shown on the right. Points with error bars show distributions of data and solid curved lines show the prediction of background from the sideband extrapolation procedure. In the low-mass range, the background is estimated from the $m_{{Z}{Z}}$ sideband for each Higgs mass hypothesis and the average expectation is shown. Solid histograms depicting the background expectation from simulated events for the different components are shown. Also shown is the SM Higgs boson signal with the mass of 150 (400)$\,\text{Ge\spaceV}$ and cross section 5 (2) times that of the SM Higgs boson, which roughly corresponds to expected exclusion limits in each category.
• Figure 4: Observed (solid) and expected (dashed) 95% CL upper limit on the ratio of the production cross section to the SM expectation for the Higgs boson obtained using the $\mathrm{CL_s}$ technique. The 68% (1$\sigma$) and 95% (2$\sigma$) ranges of expectation for the background-only model are also shown with green (darker) and yellow (lighter) bands, respectively. The solid line at 1 indicates the SM expectation. Left: low-mass range, right: high-mass range.
• Figure 5: Observed (dashed) and expected (solid) 95% CL upper limit on the product of the production cross section and branching fraction for ${H}\xspace\rightarrow{Z}{Z}$ obtained with the $\mathrm{CL_s}$ technique. The 68% (1$\sigma$) and 95% (2$\sigma$) ranges of expectation for the background-only model are also shown with green (darker) and yellow (lighter) bands, respectively. The expected product of the SM Higgs production cross section and the branching fraction is shown as a red solid curve with a band indicating theoretical uncertainties at 68% CL. The same expectation in the fourth-generation model is shown with a red dashed curve with a band indicating theoretical uncertainties. Left: low-mass range, right: high-mass range.