Measurement of Higgs boson production and properties in the WW decay channel with leptonic final states

Abstract: A search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 and 19.4 inverse femtobarns collected with the CMS detector in pp collisions at sqrt(s) = 7 and 8 TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for m[H] = 125.6 GeV. The observed signal cross section times the branching fraction to WW for m[H] = 125.6 GeV is 0.72+0.20-0.18 times the standard model expectation. The spin-parity J(P)=0(+) hypothesis is favored against a narrow resonance with J(P)=2(+) or J(P)=0(-) that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair.

Measurement of Higgs Boson Production and Properties in the $WW$ Decay Channel

This paper provides a comprehensive account of the measurements concerning the production and properties of the Higgs boson in the $WW$ decay channel, specifically focusing on leptonic final states, as analyzed using data from the CMS detector at the Large Hadron Collider (LHC). The study leverages an integrated luminosity of 24.3 $\text{fb}^{-1}$, encompassing proton-proton collisions at center-of-mass energies of 7 and 8 TeV.

The research begins with a robust introduction to the role of the Higgs boson in the electroweak theory, underscoring the significance of confirming its spin-parity and verifying its decay channels. The significance of these measurements is amplified by the observed excess of $WW$ production events, consistent with a Higgs boson having a mass near 125 GeV and spin-parity $J^P = 0^+$.

Methodology and Analysis

The study stratifies the analysis across eight categories based on the final states and jet multiplicities, with two-lepton decays and three-lepton final states being focal points. A combination of counting analysis methodologies and sophisticated shape-based analyses, including binned template fits in multidimensional observables, is employed to optimize signal extraction.

1. Two-Lepton Final States:
   • The two-lepton analysis explores both same-flavor and different-flavor categories, segmented further by jet multiplicities into 0, 1, and 2 jets, with a sub-selection for VBF and VH tags.
   • In 0-jet and 1-jet categories, integrated analyses leveraging $m_{\ell\ell}$, $m_T$, and other kinematic variables are implemented. The template fits reveal that the $WW$ signature aligns with SM predictions, yielding a best-fit for signal strengths consistent with SM expectations.
2. Three-Lepton Final States:
   • Analyses of three-lepton events target the associated production with additional bosons, offering distinct signatures that include moderate $\text{MET}$ and minimal hadronic activity.
   • The spin-parity analysis, dismissing alternative hypotheses of $J^P = 2^+$ or $J^P = 0^-$, effectively consolidates the interpretation of the observed Higgs boson as $J^P = 0^+$.

Results and Implications

The paper reports a significant observation consistent with a Higgs boson defined by the Standard Model at $m_{\text{H}} = 125.6$ GeV, with a signal significance of 4.3 standard deviations against the background-only hypothesis. The observed cross section times branching ratio is measured to be 0.72 of the SM expectation, reinforcing the existence of a Higgs-like boson in this $WW$ channel.

The exclusion limits set by the analyses are expanded beyond the immediate detection scope, addressing a broader mass range up to 600 GeV while demonstrating the methodology's sensitivity and robustness. The constraints placed on spin and parity parameters significantly strengthen the validity of the SM description of the Higgs boson.

Conclusions and Future Directions

This paper elucidates strong evidence for Higgs boson decay into $WW$ boson pairs, consistent with the SM hypothesis. These findings enrich understanding of electroweak symmetry breaking and consolidate the comprehension of Higgs boson properties, including spin-parity configurations.

Future research ventures may explore granular explorations of the decay mechanisms, potentially examining systematic uncertainties in greater depth or augmenting statistical data with upcoming LHC runs at higher luminosities. Further theoretical development could explore beyond-standard-model implications, adapting methodologies to search for potential anomalies in decay patterns or develop models that accommodate new particle interactions or couplings not yet observed.