Search for Higgs and $Z$ Boson Decays to $J/ψγ$ and $Υ(nS)γ$ with the ATLAS Detector

Abstract

A search for the decays of the Higgs and $Z$ bosons to $J/ψγ$ and $Υ(nS)γ$ ($n=1,2,3$) 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 $J/ψγ$ 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 $Υ(1S,2S,3S)\,γ$ final states the limits are $(1.3,1.9,1.3)\times10^{-3}$ and $(3.4,6.5,5.4)\times10^{-6}$, respectively.

Figures (2)

• Figure 1: (color online) The $m_{\mm\gamma}$ and $p_{\rm T}^{\mm\gamma}$ distributions of the selected $\Jpsi\,\gamma$ candidates, along with the results of the unbinned maximum likelihood fit to the signal and background model (S+B fit). The error bars on the data points correspond to the statistical uncertainties. The Higgs and $Z$ boson contributions as expected for branching fraction values of $10^{-3}$ and $10^{-6}$, respectively, are also shown.
• Figure 2: (color online) The $m_{\mm\gamma}$, $p_{\rm T}^{\mm\gamma}$ and $m_{\mm}$ distributions of the selected $\Upsilon(nS)\,\gamma$ candidates, along with the results of the unbinned maximum likelihood fit to the signal and background model (S+B fit). The error bars on the data points correspond to the statistical uncertainties. The Higgs and $Z$ boson contributions as expected for branching fraction values of $10^{-3}$ and $10^{-6}$, respectively, for each of the $\Upsilon(nS)$ are also shown.