Observation of new excited $${B} ^0_{s} $$ B s 0 states

Abstract

Abstract A structure is observed in the

$${B} ^{\pm }{K} ^{\mp }$$

B

±

K

∓

mass spectrum in a sample of proton–proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9

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

fb

- 1

. The structure is interpreted as the result of overlapping excited

$${B} ^0_{s} $$

B

s 0

states. With high significance, a two-peak hypothesis provides a better description of the data than a single resonance. Under this hypothesis the masses and widths of the two states, assuming they decay directly to

$${B} ^{\pm }{K} ^{\mp }$$

B

±

K

∓

, are determined to be

$$\begin{aligned} m_1&= 6063.5 \pm 1.2 \text { (stat)} \pm 0.8\text { (syst)}\,\text {Me}\text {V}, \\ \Gamma _1&= 26 \pm 4 \text { (stat)} \pm 4\text { (syst)}\,\text {Me}\text {V}, \\ m_2&= 6114 \pm 3 \text { (stat)} \pm 5\text { (syst)}\,\text {Me}\text {V}, \\ \Gamma _2&= 66 \pm 18 \text { (stat)} \pm 21\text { (syst)}\,\text {Me}\text {V}. \end{aligned}$$

m 1

= 6063.5 ± 1.2

(stat) ± 0.8

(syst)

Me

,

Γ 1

= 26 ± 4

(stat) ± 4

(syst)

Me

,

m 2

= 6114 ± 3

(stat) ± 5

(syst)

Me

,

Γ 2

= 66 ± 18

(stat) ± 21

(syst)

Me

.

Alternative values assuming a decay through

$${B} ^{*\pm }{K} ^{\mp }$$

B

∗ ±

K

∓

, with a missing photon from the

$$B^{*\pm } \rightarrow B^{\pm }\gamma $$

B

∗ ±

→

B ±

γ

decay, which are shifted by approximately 45

$$\,\text {Me}$$

Me

V, are also determined. The possibility of a single state decaying in both channels is also considered. The ratio of the total production cross-section times branching fraction of the new states relative to the previously observed

$$B_{s2}^{*0}$$

B

s 2

∗ 0

state is determined to be

$$0.87 \pm 0.15 \text { (stat)} \pm 0.19 \text { (syst)}$$

0.87 ± 0.15

(stat) ± 0.19

(syst)

.