- The paper extends experimental limits on hidden sector models by exploiting LHC data from 2011–2012.
- The analysis applies kinetic mixing and diphoton resonance searches to set robust bounds on U(1) gauge boson and axion-like interactions.
- The study pioneers LHC searches for minicharged particles, complementing constraints from astrophysical and low-energy experiments.
Analysis of LHC Constraints on Hidden Sector Models
This paper presents a systematic investigation into the constraints that Large Hadron Collider (LHC) experiments impose on several foundational models of hidden sector physics. The paper utilizes LHC data from 2011 and 2012 to extend the previously established limits on these models, particularly focusing on extra U(1) gauge bosons, often referred to as "hidden photons," scalar and pseudo-scalar particles, and minicharged particle (MCP) scenarios. These investigations are crucial in exploring physics beyond the Standard Model (SM), particularly in regimes that are inaccessible to lower energy experiments and astrophysical observations.
Hidden Gauge Bosons
The paper first targets hidden U(1) gauge bosons, which do not directly interact with SM particles at the tree level. Their primary interaction with the visible sector occurs through kinetic mixing or via higher-dimensional operators. The kinetic mixing is analyzed through an extra U(1) model that introduces a new gauge boson, which mixes with the hypercharge U(1) gauge boson of the SM. The authors provide constraints on the kinetic mixing parameter with calculated bounds from the LHC data competing with and extending upon those set by existing low-energy experiments.
The results reveal that current LHC limits extend the accessible mass range significantly, suggesting that hidden photons with masses from the GeV to TeV scale could be observable at the LHC. These findings motivate further experimental searches focused on narrow Z′-like resonances in various final states, including dileptons.
Scalar and Pseudo-Scalar Particles
The paper then assesses scalar and pseudo-scalar particles, focusing on axion-like particles that interact via higher-dimensional operators. Two main forms of interactions are considered: coupling with gauge boson bilinears and derivative (or Yukawa) interactions with fermions. Axion-like particles could manifest through a distinctive diphoton signature, produced via gluon fusion, thereby mimicking Higgs-like signals. The authors exploit photon pair production spectra at the LHC to set unprecedented limits in the high-mass regime.
Furthermore, the paper investigates the implications of derivative couplings where pseudo-scalars couple to SM fermions via dimension-five operators, translating into effective Yukawa interactions. These couplings provide potential signatures in the form of dilepton resonances. The derived constraints are presented graphically, depicting the exclusion regions for the involved parameters.
Minicharged Particles
Finally, the paper explores the field of particles with small unquantized electric charges. These MCPs arise naturally in extensions of the SM that include massless hidden photons. The CMS experiment’s search for MCPs elucidates a previously unexplored mass range, thus complementing astrophysical bounds. The distinctive experimental signature of faint tracks in the muon chamber is highlighted, showcasing the ability of LHC experiments to fill notable gaps in the explorations of new physics.
Conclusion and Future Directions
This paper effectively integrates several corners of hidden sector physics, offering comprehensive and novel LHC constraints that extend over a wide mass range. These results are pivotal for developing a more robust understanding of possible SM extensions and have highlighted the necessity of further LHC data to build on these exploratory foundations.
The authors' approach capitalizes on LHC's capacity to probe weakly coupled hidden sector particles, underscoring the importance of continued, high-luminosity LHC operations to refine these exclusions further. As the energy and integrated luminosity increase in future runs, progressively stringent limits can be set, potentially mapping out even broader regions of parameter space. This work lays critical groundwork for subsequent experimental investigations, especially as we advance into the high-luminosity phase of the LHC in search of hidden new physics phenomena.