Constraints on light scalars from PS191 results

TL;DR

This paper reanalyzes the PS191 experiment data to set new constraints on hypothetical light scalars, excluding certain mass and coupling ranges, and demonstrates the experiment's sensitivity beyond its original sterile neutrino search purpose.

Contribution

It provides the first reinterpretation of PS191 results to constrain light scalars coupled via Higgs mixing, extending the experimental sensitivity to new parameter regions.

Findings

Excluded scalar masses between 100-150 MeV with mixing above 4×10^{-4}

Demonstrated PS191's sensitivity to light scalars beyond sterile neutrino searches

Provided a framework for extending analysis to other scalar coupling models

Abstract

We argue that the fixed target experiment PS191 operating on a proton beam of 19.2 GeV at CERN in the eighties was sensitive to hypothetical light scalars produced by mesons and decaying to charged particles. The experiment was dedicated to searches for sterile neutrinos produced in weak meson decays and decaying into final states with pairs of charged particles: electrons and muons. Two charged tracks from the same point have been adopted as the signal signature. Exploiting the same signature we use the negative results of searches at PS191 and place new limits on the light scalars coupled to the Standard Model (SM) particles via mixing with the Higgs boson. In particular, previously allowed region of masses 100--150 MeV and mixing above 4$\times 10^{-4}$ is disfavored. Our analysis can be extended straightforwardly to models with other patterns of scalar couplings to SM particles.