The CMS Collaboration at CERN has published a landmark review in Physics Reports on April 17, presenting the most comprehensive search so far for Higgs boson production through heavy resonance decays, using data from LHC Run 2 and outlining prospects for the High-Luminosity LHC (HL-LHC).

The group led by Prof. WANG Jin at the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences contributed to key analysis channels, development of the statistical combination framework, and interpretation of results in a wide range of new physics models. Dr. WANG Chu, a postdoctoral fellow at IHEP, gave the approval report in CMS.

Since the discovery of the Higgs boson at CERN in 2012, its properties have been highly consistent with the predictions of the Standard Model. However, the scientific community generally believes that the Standard Model is not the ultimate theory, and there may still be unknown particles or interactions at higher energy scales.

The study focuses on signatures where heavy new particles decay into final states containing Higgs bosons—specifically, into two Higgs bosons, a Higgs and a vector boson (W or Z), or a Higgs and another potential new resonance. These scenarios are motivated by theories beyond the Standard Model, such as extended Higgs sectors, supersymmetry, extra dimensions, and heavy vector bosons.

As shown in Figure 1, the results indicate that the observed data are overall consistent with Standard Model expectations, with no significant evidence of new physics emerging thus far. Nevertheless, this study places the most stringent exclusion limits to date across a broad range of theoretical models.

Figure 1: The upper limits on the production cross section times branching ratio for a spin-0 resonance X across various mass hypotheses. The observed data are in good agreement with Standard Model background expectations, and no significant excess is seen. (Credit: CMS Collaboration)

Advanced machine learning techniques were introduced in several analysis channels of this study, significantly enhancing signal discrimination and overall analysis performance.

Looking ahead to the HL-LHC phase, the study provides forward-looking projections on the sensitivity to a variety of key physics processes. As shown in Figure 2, with an expected twentyfold increase in data, the sensitivity across multiple analysis channels will be significantly enhanced over a broad mass range. These improvements may allow coverage of currently inaccessible regions of the model parameter space, further extending the boundaries of potential new physics discoveries.

Figure 2: Projected sensitivity for the X → HH process at the High-Luminosity LHC (HL-LHC, 3000 fb⁻¹). The figure demonstrates the expected reach of different sub-analyses and their combination across a wide mass range, showing strong potential for probing new physics processes in the HL-LHC era. (Credit: CMS Collaboration)

This research was supported by the Excellence Research Group Program of the National Natural Science Foundation of China and the National Key Research and Development Program of China.

Physics Reports, founded in 1971, is one of the most prestigious international review journals in the field of physics. With a current impact factor of 23.9, it reflects both top-tier research standards and long-term academic influence.

Full article: https://www.sciencedirect.com/science/article/pii/S0370157324003223