Observation of theBs0→η′η′Decay

Abstract

The first observation of the B(s)(0)→η'η' decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb(-1) of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [3.31±0.64(stat)±0.28(syst)±0.12(norm)]×10(-5), where the third uncertainty comes from the B(±)→η'K(±) branching fraction that is used as a normalization. In addition, the charge asymmetries of B(±)→η'K(±) and B(±)→ϕK(±), which are control channels, are measured to be (-0.2±1.3)% and (+1.7±1.3)%, respectively. All results are consistent with theoretical expectations.

Threshold cusps and triangle singularities in hadronic reactions

“…Another interesting occurrence of TSs [157,158] is related to the hidden-charm pentaquark candidate P c (4450), observed in the J/ψp invariant mass distribution of the decay Λ 0 b → J/ψpK − by the LHCb Collaboration in 2015 [35]. It was regarded as a candidate of hidden-charm pentaquark states with masses above 4 GeV that were first predicted in Ref.…”

“…. GeV Λ + c → π + π 0 πΣK * NK I [144,145] a N (1700) [10] N (1700) → π∆ ρN π I [146] N (1875) [10] N (1875) → πN (1535) Σ * KΛ I [147] ∆(1700) [148][149][150] γp → ∆(1700) → πN (1535) → pπ 0 η ∆ηp I [151] 2.2 GeV [152] Λ + c → π 0 φp Σ * K * Λ F [153] 1.66 GeV [154,155] Λ + c → π + K − p a 0 Λη, Σ * ηΛ F [156] P c (4450) [35] Λ 0 b → K − J/ψp Λ(1890)χ c1 p F [157][158][159][160]…”

“…For example, the Argand plots of the ψ π, J/ψp, and D 0 p distributions were presented recently by the LHCb Collaboration in Refs. [35,134,294], respectively.…”

“…Here we follow the XY Z naming scheme that is still used in most of the relevant publications.2 A conventional explanation of the observed peaks was given in Refs. [26,27].3 region Z c (4430) [30], Z c (3900) [31,32] and Z c (4020) [33], the charged bottomonium-like structures Z b (10610) and Z b (10650) [34], and the pentaquark candidates with hidden charm P c (4312), P c (4440) and P c (4457) [35,36]. Most of these new structures were observed in the heavy-flavor sector.…”

The BESIII physics programme

“…These latter charmonium-like states are collectively referred to as the XYZ mesons to indicate that their underlying structure is still not well understood. During the same time period, the Belle group discovered candidates for nonstandard mesons in the bottom-quark sector [30] and the LHCb group found strong candidates for five-quark (pentaquark) baryons [31].…”