Search for dark photons produced in 13 TeV $pp$ collisions

TL;DR

This study searches for dark photons in proton-proton collisions at 13 TeV, using muon decay channels, setting new limits on their properties, and pioneering displaced-vertex detection for long-lived dark photons.

Contribution

It provides the first sensitivity to long-lived dark photons via displaced-vertex signatures and sets the most stringent limits to date on prompt-like dark photons in certain mass ranges.

Findings

No evidence for dark photon signals was observed.

Established the most stringent limits for prompt-like dark photons between 10.6 and 70 GeV.

First to use displaced-vertex signatures to search for long-lived dark photons.

Abstract

Searches are performed for both prompt-like and long-lived dark photons, $A^{\prime}$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using $A^{\prime}\to\mu^+\mu^-$ decays and a data sample corresponding to an integrated luminosity of 1.6 fb$^{-1}$ collected with the LHCb detector. The prompt-like $A^{\prime}$ search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived $A^{\prime}$ search is restricted to the low-mass region $214<m(A^{\prime})<350$ MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the $\gamma$-$A^{\prime}$ kinetic-mixing strength. The constraints placed on prompt-like dark photons are the most stringent to date for the mass range $10.6 < m(A^{\prime}) < 70$ GeV, and are comparable to the best existing limits for $m(A^{\prime}) < 0.5$ GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.