Searches for exclusive Higgs and Z boson decays into J/ψ γ, ψ(2S) γ, and ϒ(nS) γ at s=13TeV with the ATLAS detector

Pseudoscalar quarkonium+γ production at NLL+NLO accuracy

“…where Ψ P (0) is the wavefunction at the origin and is defined by 4 The relativistic correction agrees with the result in Ref. [37] with x 0 =x 0 = 1/2.…”

“…The definition of fP is different from that of Ref [14]. by a multiplicative factor i 4. We take the nonrelativistic normalization for the LDME while Ref [14].…”

Rare and exotic Higgs decays, including new scalars

“…Table 1 reports the branching fractions of the aforementioned processes as predicted by the SM. Searches for the exclusive decays of the Higgs boson into a J/ψ, ψ(2S), or ϒ(nS) (with n = 1, 2, 3) meson and a photon have been performed by the ATLAS collaboration, using a pp collision data sample corresponding to an integrated luminosity L = 36.1 fb −1 , collected at √ s = 13 TeV [7].…”

“…In Figure 1 (left) the mass of the µ + µ − γ system of the ϒ(nS)γ candidates selected in the barrel is represented in both data and simulation. Given that no significant excess of events is observed above the background expectations in any of the channels under study, 95% confidence level (CL) upper limits are extracted and are able to exclude branching fraction down to The m µ + µ − γ distribution for the selected ϒ(nS)γ candidates detected in the barrel of the ATLAS experiment along with the results of the maximum-likelihood fits with background-only models [7]. Right: The four-muon invariant mass distribution, for J/ψ J/ψ candidates, with superimposed maximum likelihood fit (solid blue line) [8].…”

Charm-quark Yukawa coupling in h→cc¯γ at LHC

“…A second approach used exclusive decays of the Higgs into a J/ψ and a photon [23]. While this final state can be well-separated from backgrounds in the J/ψ → µ + µ − channel [24][25][26], it suffers from a small branching ratio and modeling assumptions to extract the Higgs-charm Yukawa. In particular, the leading contribution to this process is via the vector meson dominance γ * → J/ψ, which is an order of magnitude larger than that involving the charm-quark Yukawa coupling [23,27,28], leading to a less sensitive upper bound on y c of about 50 times of the SM prediction at the HL-LHC [29].…”