Search for a resonance decaying into a scalar particle and a Higgs boson in the final state with two bottom quarks and two photons in proton-proton collisions at a center of mass energy of 13 TeV with the ATLAS detector (2404.12915v2)

Abstract: A search for the resonant production of a heavy scalar $X$ decaying into a Higgs boson and a new lighter scalar $S$, through the process $X \to S(\to bb) H(\to \gamma\gamma)$, where the two photons are consistent with the Higgs boson decay, is performed. The search is conducted using an integrated luminosity of 140 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The search is performed over the mass range 170 $\leq$ $m_{X}$ $\leq$ 1000 GeV and 15 $\leq$ $m_{S}$ $\leq$ 500 GeV. Parameterised neural networks are used to enhance the signal purity and to achieve continuous sensitivity in a domain of the ($m_{X}$, $m_{S}$) plane. No significant excess above the expected background is found and 95% CL upper limits are set on the cross section times branching ratio, ranging from 39 fb to 0.09 fb. The largest deviation from the background-only expectation occurs for ($m_{X}$, $m_{S}$) = (575, 200) GeV with a local (global) significance of 3.5 (2.0) standard deviations.

• The paper demonstrates the search for a heavy scalar resonance X decaying into a Higgs boson and a lighter scalar S using 140 fb⁻¹ of 13 TeV ATLAS data.
• Advanced parameterized neural networks are employed to optimize signal discrimination across a mass range of 170–1000 GeV for X and 15–500 GeV for S.
• The analysis sets 95% CL upper limits on production cross-sections, with a notable 3.5σ local deviation observed at X = 575 GeV and S = 200 GeV.

Search for a Resonance Decaying into a Scalar Particle and a Higgs Boson at 13 TeV with the ATLAS Detector

This paper presents a detailed paper conducted by the ATLAS Collaboration, focusing on the search for a hypothetical heavy scalar resonance (denoted as X) decaying into a Standard Model Higgs boson (H) and a lighter scalar particle (S) in proton-proton collisions at a center-of-mass energy of 13 TeV. Employing data from the ATLAS detector at the Large Hadron Collider (LHC), this research aims to investigate a specific decay process of X to S and H, leading to a final state characterized by two bottom quarks (b-jets) and two photons.

Overview and Methodology

The paper analyzes an extensive dataset representing an integrated luminosity of 140 fb$^{-1}$. The search covers a broad mass range for X (170–1000 GeV) and S (15–500 GeV), assessing the possibility of the coupling of the observed 125 GeV Higgs boson with additional scalar states, as predicted by various beyond the Standard Model (BSM) theories.

To confront the challenges posed by background processes that can mimic the expected signal, advanced analysis techniques were utilized. Notably, parameterized neural networks (PNNs) were implemented to optimize signal discrimination across the investigated mass parameter space, thus maintaining continuous sensitivity. The PNNs were trained to adapt to varying kinematic profiles associated with different mass hypotheses of X and S, allowing the generation of a dedicated discriminant for each hypothesis.

Experimental Results

The research results did not reveal any significant excess over the predicted Standard Model background. Consequently, the paper establishes 95% confidence level (CL) upper limits on the cross-section for the production of X, factoring in the decay to S and H, and subsequently the b$\bar{b}\gamma\gamma$ final state. The limits range from 39 fb at lower X mass (170 GeV) to 0.09 fb at higher X mass (1000 GeV), with the most notable deviation noted for masses X = 575 GeV and S = 200 GeV, yielding a local significance of 3.5σ, although the global significance reduces this to 2.0σ.

Theoretical and Practical Implications

The research extends the frontier of exploration for extended Higgs sectors implied by BSM theories, investigating the complex landscape where additional scalar resonances might exist. It adds significant value by probing mass regions previously unexplored with such precision, thereby enhancing the understanding of potential scalar sector extensions.

From a theoretical viewpoint, this work informs future theoretical models and potential refinements necessary to accommodate or refute the presence of additional scalar states based on collider evidence. Pragmatically, it enriches the framework for detector-level analysis techniques in high-energy physics, underpinning future experiments with refined analytical tools such as the described neural network methodologies.

Speculation on Future Developments

Efforts such as these lay the groundwork for garnering further experimental insight into Higgs-like scalars. Progress in this domain would potentially require collecting more data at higher luminosities or energies and refining analytical techniques to discern subtle signals in complex collision environments.

The engagement of complementary experiments and advancements in detector technology may yield breakthroughs necessary for the resolution of current ambiguities in the scalar sector. The techniques demonstrated here may also transition to probing other elusive particles or interactions at the LHC or future colliders.