Jet substructure as a new Higgs search channel at the LHC (0802.2470v2)

Abstract: It is widely considered that, for Higgs boson searches at the Large Hadron Collider, WH and ZH production where the Higgs boson decays to b anti-b are poor search channels due to large backgrounds. We show that at high transverse momenta, employing state-of-the-art jet reconstruction and decomposition techniques, these processes can be recovered as promising search channels for the standard model Higgs boson around 120 GeV in mass.

• The paper presents jet substructure techniques that recover WH and ZH channels by isolating boosted Higgs boson decays into b-quarks.
• It utilizes a modified Cambridge/Aachen algorithm with mass-drop filtering to resolve fat jets into distinct subjets for improved mass resolution.
• Simulation studies indicate that these methods enhance the signal significance, potentially achieving over 4.5σ at an integrated luminosity of 30 fb⁻¹.

Essay on "Jet Substructure as a New Higgs Search Channel at the LHC"

The paper "Jet Substructure as a New Higgs Search Channel at the LHC," authored by Butterworth, Davison, Rubin, and Salam, addresses a critical challenge faced in the pursuit of detecting the Higgs boson within the energy environment of the Large Hadron Collider (LHC). The focus of the work is on the development and application of advanced jet substructure techniques to enhance the detection sensitivity for the Higgs boson, particularly in the context of its production in association with vector bosons ($WH$, $ZH$) and its subsequent decay into $b\bar{b}$ pairs.

Background and Motivation

The detection of a light Higgs boson, with a mass near 120 GeV, poses significant difficulties due to its relatively low production cross-section and the substantial backgrounds in proton-proton collision environments. Traditional search channels such as gluon fusion and vector boson fusion have been extensively studied, but the authors highlight the potential in the associated production of the Higgs with $W$ and $Z$ bosons, which had been largely disregarded due to overwhelming background noise, particularly from $t\bar{t}$ production.

Jet Substructure Techniques

The authors propose the utilization of jet substructure analysis as a means to recover the $WH$ and $ZH$ channels as viable search pathways. The methodology hinges on identifying "fat jets" which arise from boosted Higgs bosons decaying into $b\bar{b}$, which would typically manifest as a single massive jet. They apply a Cambridge/Aachen algorithm modified to incorporate mass-drop filtering, enabling them to dissect the fat jet into constituent subjets, thereby enhancing the mass resolution critical for distinguishing signal from background.

Key to this approach is the separation of the two $b$ quarks within the common jet environment, which involves adjusting the algorithm to recognize the angular separation that varies inversely with the transverse momentum of the Higgs. The paper delineates a filtering step which refines the jet by resolving it at a finer angular scale, removing soft radiation from the underlying event while retaining hard radiation characteristics pertinent to the Higgs decay.

Results and Numerical Impacts

Empirical investigations are conducted using MC simulation tools, with parameters tuned to reflect realistic LHC operational conditions, including underlying event models and parton distributions. The analysis assesses the signal significance by comparing the reconstructed Higgs mass peak within specified transverse momentum and rapidity ranges against backgrounds, particularly focusing on those arising from $Z$+jets and $t\bar{t}$ processes.

The numerical results emphasize that employing the proposed jet substructure techniques indeed improves the signal-to-background ratio in the challenging $120$ GeV region. Specifically, when associating $WH$ or $ZH$ with boosted kinematics, the identification method significantly reduces contamination from misidentified events, demonstrating a potential signal significance exceeding $4.5\sigma$ at an integrated luminosity of 30 fb$^{-1}$.

Implications and Future Directions

Practically, the findings suggest that with the enhanced jet substructure techniques, the $VH$ production channels could be elevated to have primary importance alongside traditional channels in Higgs searches at the LHC. Theoretically, this provides a nuanced approach for understanding Higgs couplings to vector bosons, opening new avenues for probing electroweak symmetry breaking parameters in the Standard Model.

Moving forward, the development articulated in this paper not only invites further experimental optimizations and validations but also calls for detailed theoretical explorations to refine the algorithmic parameters in non-ideal detector scenarios. The successful implementation of these strategies could profoundly impact the efficacy of Higgs boson searches, ultimately contributing to a more comprehensive mapping of the Standard Model landscape.

In summary, this paper articulates a sophisticated approach to utilizing jet substructure techniques to open up previously disregarded channels in the search for light Higgs bosons, proposing a combination of algorithmic innovation and empirical simulation which holds promise for advancing the frontier of particle physics research at the LHC.