Abstract
Searches for the exclusive decays of the Higgs and Z bosons into a J/ψ, ψ(2S), or ϒ(nS) (n=1,2,3) meson and a photon are performed with a pp collision data sample corresponding to an integrated luminosity of 36.1fb−1 collected at s=13TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above the expected backgrounds, and 95% confidence-level upper limits on the branching fractions of the Higgs boson decays to J/ψγ, ψ(2S)γ, and ϒ(nS)γ of 3.5×10−4, 2.0×10−3, and (4.9,5.9,5.7)×10−4, respectively, are obtained assuming Standard Model production. The corresponding 95% confidence-level upper limits for the branching fractions of the Z boson decays are 2.3×10−6, 4.5×10−6 and (2.8,1.7,4.8)×10−6, respectively.
Highlights
Following the observation of a Higgs boson H with a mass of approximately 125 GeV by the ATLAS and CMS collaborations [1,2], detailed measurements of its properties show no deviations from the Standard Model (SM) [3]
Decays of the Higgs boson into a heavy, vector quarkonium state, Q ≡ J /ψ or Υ(nS), and a photon were searched for by t√he ATLAS Collaboration with up to 19.2 fb−1 of data collected at s = 8 TeV [28], resulting in 95% confidence level (CL) upper limits of 1.5 × 10−3 for B (H → J /ψ γ ) and (1.3, 1.9, 1.3) × 10−3 for B (H → Υ(nS) γ ) (n = 1, 2, 3)
To maintain a single search region, while ensuring near-optimal sensitivity for both the Higgs and Z boson analyses, the transverse momentum of the Q candidate pQT is required to be greater than a value that varies as a function of the invariant mass of the three-body system mQγ
Summary
Following the observation of a Higgs boson H with a mass of approximately 125 GeV by the ATLAS and CMS collaborations [1,2], detailed measurements of its properties show no deviations from the Standard Model (SM) [3]. Deviations of the c- and b-quark Yukawa couplings from the SM expectations can lead to significant increases in the branching fractions for exclusive decays These deviations can arise in beyondthe-SM theories; for example, the quark masses might not originate entirely from the Higgs mechanism but could be induced by other subdominant sources of electroweak symmetry breaking [21]. Decays of the Higgs boson into a heavy, vector quarkonium state, Q ≡ J /ψ or Υ(nS), and a photon were searched for by t√he ATLAS Collaboration with up to 19.2 fb−1 of data collected at s = 8 TeV [28], resulting in 95% confidence level (CL) upper limits of 1.5 × 10−3 for B (H → J /ψ γ ) and (1.3, 1.9, 1.3) × 10−3 for B (H → Υ(nS) γ ) (n = 1, 2, 3). Throughout the remainder of this Letter, where no distinction is relevant, the J /ψ and ψ(2S) states are referred to collectively as the ψ(nS) states
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