Search for Higgs and $Z$ Boson Decays to $J/\psi\gamma$ and $\Upsilon(nS)\gamma$ with the ATLAS Detector

TL;DR

This paper reports a search for rare Higgs and Z boson decays into quarkonium plus photon using ATLAS data, setting upper limits on their branching fractions due to no observed excess.

Contribution

First search for Higgs and Z decays to quarkonium plus photon with ATLAS, establishing upper limits on branching fractions at 8 TeV.

Findings

No significant excess observed above background.

Upper limits set on branching fractions for Higgs and Z decays.

Constraints improve understanding of rare boson decay modes.

Abstract

A search for the decays of the Higgs and $Z$ bosons to $J/\psi\gamma$ and $\Upsilon(nS)\gamma$ ($n=1,2,3$) is performed with $pp$ collision data samples corresponding to integrated luminosities of up to $20.3\mathrm{fb}^{-1}$ collected at $\sqrt{s}=8\mathrm{TeV}$ with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95\% CL upper limits are placed on the branching fractions. In the $J/\psi\gamma$ final state the limits are $1.5\times10^{-3}$ and $2.6\times10^{-6}$ for the Higgs and $Z$ boson decays, respectively, while in the $\Upsilon(1S,2S,3S)\,\gamma$ final states the limits are $(1.3,1.9,1.3)\times10^{-3}$ and $(3.4,6.5,5.4)\times10^{-6}$, respectively.