Search for hidden-sector bosons in $B^0 \!\to K^{*0}μ^+μ^-$ decays (1508.04094v2)

Abstract: A search is presented for hidden-sector bosons, $\chi$, produced in the decay ${B^0!\to K^*(892)^0\chi}$, with $K^*(892)^0!\to K^{+}\pi^{-}$ and $\chi!\to\mu^+\mu^-$. The search is performed using $pp$-collision data corresponding to 3.0 fb$^{-1}$ collected with the LHCb detector. No significant signal is observed in the accessible mass range $214 \leq m({\chi}) \leq 4350$ MeV, and upper limits are placed on the branching fraction product $\mathcal{B}(B^0!\to K^*(892)^0\chi)\times\mathcal{B}(\chi!\to\mu^+\mu^-)$ as a function of the mass and lifetime of the $\chi$ boson. These limits are of the order of $10^{-9}$ for $\chi$ lifetimes less than 100 ps over most of the $m(\chi)$ range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.

• The paper reports a search for hidden-sector bosons in B0 → K*0μ+μ- decays, setting upper limits on the branching fraction product at the order of 10⁻⁹ for lifetimes below 100 ps.
• It employs a profile likelihood ratio test with Gaussian constraints across a mass range of 214 to 4350 MeV from 3.0 fb⁻¹ of pp-collision data.
• The study constrains scalar and axial-vector portal models, refining theoretical efforts in dark matter research and explanations of cosmic-ray anomalies.

Search for Hidden-Sector Bosons in B⁰ → K*⁰μ⁺μ⁻ Decays

The paper presented by the LHCb collaboration focuses on an investigative search for hidden-sector bosons, denoted as $\chi$, within the decay process $B^0 \to K^{*0}\chi$. Here, the $K^{*0}$ decays to $K^+\pi^-$, and the boson $\chi$ further decays to $\mu^+\mu^-$. The research utilizes $pp$-collision data amounting to 3.0 fb⁻¹, collected with the LHCb detector at CERN. The significance of such a search lies in the potential discovery of new particles that fail to interact strongly with known particles and thus may account for unresolved phenomena such as dark matter.

Methodology

The paper explores the mass range of $\chi$ from 214 MeV to 4350 MeV. Despite extensive searches, no significant signals of the hidden-sector bosons were observed within this mass range. The paper constrains the branching fraction product $$\mathcal{B}(B^0 \to K^{*0}\chi) \times \mathcal{B}(\chi \to \mu^+\mu^-)$$, setting upper limits that reach the order of $10^{-9}$ for $\chi$ lifetimes less than 100 ps.

The statistical methodology employs a profile likelihood ratio test across a spectrum of potential $\chi$ masses to rigorously determine signal presence, with systematic uncertainties incorporated via Gaussian constraints in the likelihoods.

Results and Constraints

The constraints specified claim greater stringency than previous studies, particularly over the axial-vector and scalar portal parameters which remain pivotal in theories aiming to explain cosmic-ray anomalies and dark matter via these hidden-sector interactions.

Notably, this investigation provides constraints across a breadth of theoretical models:

• The search limits the possible contribution of $\chi$ in theories involving scalar portal models postulating early universe inflation or baryon asymmetry.
• Furthermore, implications on the axial-vector portal models, specifically those attempting to expound phenomena such as suppression of charge-parity violation and the existence of axions, are deduced.

Implications and Future Directions

While no hidden-sector bosons were detected, the research delivers valuable exclusions that refocus theoretical effort towards mass ranges and parameter spaces uncharted by these constraints. The continuing advancements of particle detection methods coupled with increased luminosity in future collider runs may improve sensitivity and potentially reveal evidence of hidden-sector bosons.

The research underscores a critical intersection of experimental particle physics and cosmological theory, encouraging further explorations into the mechanics of dark matter and other exotic phenomena. As the integration of more sophisticated detection techniques and analytical models progresses, it is likely that the unexplored domains of particle physics may yield insights previously obscured by experimental limitations.