Measurement of the properties of a Higgs boson in the four-lepton final state

TL;DR

This CMS study analyzes H→ZZ→4l data from 7 and 8 TeV LHC runs to precisely measure the Higgs boson’s mass, width, cross section, and spin-parity. Using a multidimensional likelihood framework that combines mass, kinematic discriminants, and production-category information, the analysis confirms a narrow resonance near 125.6 GeV, with a width limit ΓH<3.4 GeV and a signal strength consistent with SM expectations (μ≈0.93). Spin-parity tests robustly exclude pseudoscalar and all tested spin-1 hypotheses, while most spin-2 scenarios are disfavored, underscoring the SM Higgs interpretation. The work demonstrates the power of the 4l channel and complex discriminants (MELA) to probe Higgs properties, including potential CP-odd admixtures, and solidifies the Higgs boson’s role in electroweak symmetry breaking with high-precision measurements and stringent tests of alternative models.

Abstract

The properties of a Higgs boson candidate are measured in the H to ZZ to 4l decay channel, with l = e, mu, using data from pp collisions corresponding to an integrated luminosity of 5.1 inverse femtobarns at the center-of-mass energy of sqrt(s) = 7 TeV and 19.7 inverse femtobarns at sqrt(s) = 8 TeV, recorded with the CMS detector at the LHC. The new boson is observed as a narrow resonance with a local significance of 6.8 standard deviations, a measured mass of 125.6 +- 0.4 (stat) +- 0.2 (syst) GeV, and a total width less than 3.4 GeV at the 95% confidence level. The production cross section of the new boson times its branching fraction to four leptons is measured to be 0.93 +0.26 -0.23 (stat) +0.13 -0.09 (syst) times that predicted by the standard model. Its spin-parity properties are found to be consistent with the expectations for the standard model Higgs boson. The hypotheses of a pseudoscalar and all tested spin-one boson hypotheses are excluded at the 99% confidence level or higher. All tested spin-two boson hypotheses are excluded at the 95% confidence level or higher.

Figures (27)

• Figure 1: (top) Expected four-lepton mass distribution for ${H}\xspace\to{Z}{Z}\to 4\mathrm{e}$ for $m_{{H}\xspace} = 126\,\text{Ge\spaceV}\xspace$ using ECAL-only electron momentum estimation (green open points: $\mathrm{ECAL}_\text{std.}$ only), and using the method employed in this analysis (black full points: $E_\text{regr}-p$ combination). The fitted standard deviation, $\sigma_\mathrm{dCB}$, of the double-sided Crystal-Ball CrystalBall function and effective width $\sigma_\text{eff}$ defined in the text are indicated. Electrons with $p_{\mathrm{T}}\xspace^\mathrm{e} > 7$$\,\text{Ge\spaceV}$ in the full $\eta^\mathrm{e}$ range are used. (bottom) Expected effective momentum resolution $\sigma_\text{eff}/p$ for electrons in the EB as a function of the momentum for the ECAL-only, the tracker-only, and the combined estimates.
• Figure 2: Relative difference between the dilepton mass peak positions in data and simulation as obtained from ${Z}$, ${J}\space/\space\psi\xspace$ and $\Upsilon(\mathrm{nS})$ resonances as a function of (top) the transverse momentum of one of the electrons regardless of the second for dielectron events, and (bottom) the average muon $p_{\mathrm{T}}\xspace^{\mu}$ for dimuon events for the 8$\,\text{Te\spaceV}$ data.
• Figure 3: (top) Relative difference between the dielectron $\sigma_\text{eff}$ in data and simulation, as measured from ${Z}\to\mathrm{e}^+\mathrm{e}^-$ events, where the electrons are classified into different categories (B: barrel, E: end caps, G: golden, S: showering). (bottom) Relative difference between the dimuon mass resolutions in data and simulation as measured from ${J}\space/\space\psi\xspace$, $\Upsilon(\mathrm{nS})$, and ${Z}$ decays as functions of the average muon $p_{\mathrm{T}}\xspace^{\mu}$. The uncertainties shown are statistical only. Results are presented for data collected at $\sqrt{s}= 8$$\,\text{Te\spaceV}$.
• Figure 4: Efficiency, as a function of the lepton $p_{\mathrm{T}}\xspace^\ell$, for reconstructing and selecting (top) electrons and (bottom) muons, measured with a ${Z}\to\ell\ell$ data sample by using a tag-and-probe method.
• Figure 5: Geometrical acceptance times selection efficiency for the SM Higgs boson signal as a function of $m_{{H}\xspace}$ in the three final states for gluon fusion production. Points represent efficiency estimated from full CMS simulation; lines represent a smooth polynomial curve interpolating the points, used in the analysis. The vertical dashed line represents $m_{{H}\xspace} = 126\,\text{Ge\spaceV}\xspace$.