Searches for exclusive Higgs and Z boson decays into a vector quarkonium state and a photon using 139 fb ^{- 1} of ATLAS √s=13 TeV proton–proton collision data

Abstract

AbstractSearches for the exclusive decays of Higgs and Z bosons into a vector quarkonium state and a photon are performed in the $$\mu ^+\mu ^-,\gamma $$ μ +

μ -

γ

final state with a proton–proton collision data sample corresponding to an integrated luminosity of 139 fb$$^{-1}$$

- 1

collected at $$\sqrt{s}=13$$

s

= 13

 TeV with the ATLAS detector at the CERN Large Hadron Collider. The observed data are compatible with the expected backgrounds. The 95% confidence-level upper limits on the branching fractions of the Higgs boson decays into $$J/\psi \,\gamma $$

J / ψ

γ

, $$\psi (2S)\,\gamma $$

ψ ( 2 S )

γ

, and $$\Upsilon (1S,2S,3S)\,\gamma $$

Υ ( 1 S , 2 S , 3 S )

γ

are found to be $$2.0\times 10^{-4}$$

2.0 ×

10

- 4

, $$10.5\times 10^{-4}$$

10.5 ×

10

- 4

, and $$(2.5,4.2,3.4)\times 10^{-4}$$

( 2.5 , 4.2 , 3.4 )

×

10

- 4

, respectively, assuming Standard Model production of the Higgs boson. The corresponding 95% CL upper limits on the branching fractions of the Z boson decays are $$1.2\times 10^{-6}$$

1.2 ×

10

- 6

, $$2.4\times 10^{-6}$$

2.4 ×

10

- 6

, and $$(1.1,1.3,2.4)\times 10^{-6}$$

( 1.1 , 1.3 , 2.4 )

×

10

- 6

. An observed 95% CL interval of $$(-133,175)$$

( - 133 , 175 )

is obtained for the $$\kappa _c/\kappa _\gamma $$

κ c

/

κ γ

ratio of Higgs boson coupling modifiers, and a 95% CL interval of $$(-37,40)$$

( - 37 , 40 )

is obtained for $$\kappa _b/\kappa _\gamma $$

κ b

/

κ γ

.