Inclusive study of bottomonium production in association with an $$\eta $$ η meson in $$e^+e^-$$ e + e - annihilations near $$\varUpsilon (5S)$$ Υ ( 5 S )

Abstract

We study bottomonium production in association with an η meson in e + e − annihilations near the Υ (5S), at a centre-of-mass energy of √ s = 10.866 GeV. The results are based on the 121.4 fb −1 data sample collected by the Belle experiment at the asymmetric-energy KEKB collider. Only the η meson is reconstructed and the missing-mass spectrum of η candidates is investigated. We observe the e + e − → ηΥ J (1D) process and find evidence for the e + e − → ηΥ (2S) process, while no significant signals of Υ (1S), h b (1P), nor h b (2P) are found. Cross sections for the studied processes are reported.The treatment of the non-perturbative regime of Quantum Chromodynamics represents one of the major open problems in particle physics [1]. Quarkonia -bound states of either b andb or c andc quarks -are regarded as one of the most fertile environments in which new theoretical approaches to this quandary can be tested [2], thanks to the intrinsic multiscale nature of their dynamics, which are characterized by the coexistence of hard and soft processes [3]. The richness of this sector has been shown by the wave of new discoveries from the BaBar, Belle and CLEO experiments, and then BESIII and LHCb, that challenged the prevailing theoretical models for quarkonium spectra and transitions. Unexpected neutral and charged states have been observed in both charmonium and bottomonium, together with striking violations of the Okubo-Zweig-Iizuka (OZI) rule [4][5][6] and Heavy Quark Spin Symmetry (HQSS). These have demonstrated that the light-quark degrees of freedom play a crucial role in the description of spectral properties [7] and transitions [8]. For a recent review of the theoretical models of quarkonia, see Refs. [9,10].The study of transitions that violate HQSS, like those on which this work is focused, is therefore part of a broader topic of studying exotic quarkonium-like states. HQSS and the models based on it, like the QCD Multipole Expansion [11][12][13][14][15][16], have been long considered reliable for describing hadronic transitions in bottomonium. In this approach, the transitions can be classified into favoured non-spin flipping, like Υ (nS) → ππΥ (mS), and disfavoured spin-flipping, like Υ (nS) → η Υ (mS), which are suppressed by a factor of (Λ QCD /m b ) 2 . As a result of this suppression, the small ratio of branching fractionsis predicted [17,18] This paper is devoted to the study of one of the missing experimental pieces in the puzzle of the hadronic transitions in bottomonium: the single-η emission from the Υ (5S)The final states with Υ (1S) and Υ (2S) have been studied by theorists using rescattering models [24] or by considering intermediate hybrids [35]. The predictions are affected by large uncertainties but agree within one order of magnitude with a preliminary result reported by Belle [36] that was obtained via the exclusive reconstruction of the Υ (1S, 2S) decay into muons. In a recent work [37], the case of Υ (5S) → ηΥ J (1D) is analyzed in the context of a rescattering model where the Υ (5S) ...

Averages of $b$-hadron, $c$-hadron, and $τ$-lepton properties as of 2018

“…Ignoring the p T and η dependence, we have adjusted the published results to the latest branching fraction averages [21] and combined them under the constraints of Eq. (27), following the procedure and assumptions described in Ref. [4].…”

$D$ wave bottomonia production from $Z_b^{(\prime)}$ decay

“…Such a mechanism plays essential role in the light meson transitions between lower heavy quarkonia . However, the measured widths of the hidden bottom decays of Υ(5S ) are much larger than the QCDME expectations [1][2][3][4][5]. Since Υ(5S ) dominantly decays into a pair of bottom mesons [8], the bottom meson pair can transit into a bottomonia and a light meson by exchanging a proper bottom meson.…”

“…A large data sample of e + e − collision at the energy of the Υ(5S ) resonance has been collected by the Belle collaboration. Based on this large data sample, the collaboration has reported a series of precise analyses of Υ(5S ) decay and has observed some unexpected phenomena, such as the anomalous transition widths between Υ(5S ) and lower bottomonia [1][2][3][4][5], and the bottomonium-like exotic states Z (′) b [6,7]. Υ(5S ) has become one of intriguing sources to investigate lower bottomonia, such as χ bJ , h b , and Υ(1D).…”

Measurement of the energy dependence of the e+e− → $$ B\overline{B} $$, $$ B{\overline{B}}^{\ast } $$ and $$ {B}^{\ast }{\overline{B}}^{\ast } $$ exclusive cross sections

“…Belle reported preliminary results on the Υ(nS)η (n = 1, 2) and Υ(1D)π + π − transitions [25] that show that corresponding fractions are not large. There are also rather strict upper limits on fractions of the η b (nS)ω (n = 1, 2) [26] and h b (nP )η (n = 1, 2) [27] transitions. However, there are still channels for which no experimental information is available.…”