Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the μμ b b and ττ b b final states

Abstract

A search for exotic decays of the Higgs boson (

$$\text {H}$$

H

) with a mass of 125

$$\,\text {Ge}\hspace{-.08em}\text {V}$$

Ge

V

to a pair of light pseudoscalars

$$\text {a}_{1} $$

a 1

is performed in final states where one pseudoscalar decays to two

$${\textrm{b}}$$

b

quarks and the other to a pair of muons or

$$\tau $$

τ

leptons. A data sample of proton–proton collisions at

$$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$

s

= 13

Te

V

corresponding to an integrated luminosity of 138

$$\,\text {fb}^{-1}$$

fb

- 1

recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (

$$\text {CL}$$

CL

) on the Higgs boson branching fraction to

$$\upmu \upmu \text{ b } \text{ b } $$

μ μ

b

b

and to

$$\uptau \uptau \text{ b } \text{ b },$$

τ τ

b

b

,

via a pair of

$$\text {a}_{1} $$

a 1

s. The limits depend on the pseudoscalar mass

$$m_{\text {a}_{1}}$$

m

a 1

and are observed to be in the range (0.17–3.3)

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

×

10

- 4

and (1.7–7.7)

$$\times 10^{-2}$$

×

10

- 2

in the

$$\upmu \upmu \text{ b } \text{ b } $$

μ μ

b

b

and

$$\uptau \uptau \text{ b } \text{ b } $$

τ τ

b

b

final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine upper limits on the branching fraction

$${\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} \rightarrow \ell \ell \text{ b } \text{ b})$$

B ( H →

a 1

a 1

→ ℓ ℓ

b

b )

at 95%

$$\text {CL}$$

CL

, with

$$\ell $$

ℓ

being a muon or a

$$\uptau $$

τ

lepton. For different types of 2HDM+S, upper bounds on the branching fraction

$${\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} )$$

B ( H →

a 1

a 1

)

are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space,

$${\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} )$$

B ( H →

a 1

a 1

)

values above 0.23 are excluded at 95%

$$\text {CL}$$

CL

for

$$m_{\text {a}_{1}}$$

m

a 1

values between 15 and 60

$$\,\text {Ge}\hspace{-.08em}\text {V}$$

Ge

V

.