Observation of a new boson with mass near 125 GeV in pp collisions at sqrt(s) = 7 and 8 TeV (1303.4571v2)

Abstract: A detailed description is reported of the analysis used by the CMS Collaboration in the search for the standard model Higgs boson in pp collisions at the LHC, which led to the observation of a new boson. The data sample corresponds to integrated luminosities up to 5.1 inverse femtobarns at sqrt(s) = 7 TeV, and up to 5.3 inverse femtobarns at sqrt(s) = 8 TeV. The results for five Higgs boson decay modes gamma gamma, ZZ, WW, tau tau, and bb, which show a combined local significance of 5 standard deviations near 125 GeV, are reviewed. A fit to the invariant mass of the two high resolution channels, gamma gamma and ZZ to 4 ell, gives a mass estimate of 125.3 +/- 0.4 (stat) +/- 0.5 (syst) GeV. The measurements are interpreted in the context of the standard model Lagrangian for the scalar Higgs field interacting with fermions and vector bosons. The measured values of the corresponding couplings are compared to the standard model predictions. The hypothesis of custodial symmetry is tested through the measurement of the ratio of the couplings to the W and Z bosons. All the results are consistent, within their uncertainties, with the expectations for a standard model Higgs boson.

• The paper demonstrates the observation of a new boson at 125 GeV with a 5σ local significance using combined decay channel analysis.
• It employs multivariate event selection and a modified frequentist framework to robustly analyze 7 and 8 TeV proton-proton collision data.
• The results confirm the SM Higgs boson's properties with precise mass and coupling measurements, paving the way for future high-energy physics research.

Observation of a New Boson with Mass Near 125 GeV in pp Collisions

The document provides a comprehensive description of the CMS Collaboration's efforts to search for and eventually observe a new boson, hypothesized to be the Standard Model (SM) Higgs boson, in proton-proton collisions at the Large Hadron Collider (LHC) with center-of-mass energies of 7 and 8 TeV. The collected data corresponds to integrated luminosities of 5.1 fb$^\text{-1}$ and 5.3 fb$^\text{-1}$, respectively.

Experimental Context and Methodology

The LHC was designed with the ambition of discovering the SM Higgs boson, a particle postulated to confer mass to other particles via the Higgs mechanism. The search for this particle has focused on several decay channels: $\gamma\gamma$, $\cPZ\cPZ$, $\PW\PW$, $\tau\tau$, and $\cPqb\cPqb$. Each channel offers different advantages in terms of signal significance and background reduction, exploiting the distinct signatures and kinematic features in the CMS detector.

The CMS experiment employs a complex and multifaceted approach to event selection, utilizing multivariate analysis techniques to enhance the sensitivity of the search. The combined results from multiple decay channels are used within a modified frequentist framework ($CL_s$) to set exclusion limits and evaluate the presence of a signal.

Observation and Results

The analysis reveals a combined local significance of 5 standard deviations near 125 GeV, thereby providing compelling evidence for the existence of a new boson. A fit to the invariant mass peak in the high-resolution channels ($\gamma\gamma$ and $\cPZ \cPZ \to 4\ell$) yields a mass estimate of $125.3 \pm 0.4_{\text{stat}} \pm 0.5_{\text{syst}}$ GeV.

The results are consistent with the theoretical predictions for a SM Higgs boson. The measurements of the boson's couplings to fermions and gauge bosons are in agreement with the expected values, supporting the hypothesis that the observed particle is indeed the SM Higgs boson.

Implications and Future Prospects

The discovery of a new boson marking a mass consistent with the SM Higgs boson has profound implications for particle physics, confirming a crucial element of the SM and opening new avenues for exploring beyond-the-standard-model physics. The results lay the groundwork for future studies aimed at measuring the properties of this particle with higher precision and investigating potential deviations from SM predictions.

Continued experiments at the LHC with increased luminosity and refined detector capabilities will further elucidate the properties of the Higgs boson and potentially reveal new physics phenomena that could lead to a deeper understanding of fundamental forces and particles. This research represents a significant milestone in high-energy physics, supporting the framework of the SM while simultaneously motivating the search for new physics beyond it.