QCD Multipole Expansion and Hadronic Transitions in Heavy Quarkonium Systems

Observation of ϒ(4S)→η^{'}ϒ(1S)

We report the first observation of the hadronic transition ϒ(4S)→η^{'}ϒ(1S), using 496  fb^{-1} data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We reconstruct the η^{'} meson through its decays to ρ^{0}γ and to π^{+}π^{-}η, with η→γγ. We measure B(ϒ(4S)→η^{'}ϒ(1S))=[3.43±0.88(stat)±0.21(syst)]×10^{-5}, with a significance of 5.7σ.

First Observation of the Hadronic Transition ϒ(4S)→ηh(b)(1P) and New Measurement of the h(b)(1P) and η(b)(1S) Parameters

Using a sample of 771.6×10(6) ϒϒ(4S) decays collected by the Belle experiment at the KEKB e(+)e(-) collider, we observe, for the first time, the transition ϒ(4S)→ηh(b)(1P) with the branching fraction B[ϒ(4S)→ηh(b)(1P)]=(2.18±0.11±0.18)×10(-3) and we measure the h(b)(1P) mass M(h(b)(1P))=(9899.3±0.4±1.0)  MeV/c(2), corresponding to the hyperfine (HF) splitting ΔM(HF)(1P)=(0.6±0.4±1.0)  MeV/c(2). Using the transition h(b)(1P)→γη(b)(1S), we measure the η(b)(1S) mass M(η(b)(1S))=(9400.7±1.7±1.6)  MeV/c(2), corresponding to ΔM(HF)(1S)=(59.6±1.7±1.6)  MeV/c(2), the η(b)(1S) width Γ(η(b)(1S))=(8(-5)(+6)±5)  MeV/c(2) and the branching fraction B[h(b)(1P)→γη(b)(1S)]=(56±8±4)%.

Observation of e+e- → π+π-π(0)(χbJ) and Search for X(b) → ωϒ(1S) at sqrt[s] = 10.867 GeV

The e(+)e(-) → π(+)π(-)π(0)χ(bJ) (J = 0,1,2) processes are studied using a 118 fb(-1) data sample acquired with the Belle detector at a center-of-mass energy of 10.867 GeV. Unambiguous π(+)π(-)π(0)χ(bJ) (J = 1,2), ωχ(b1) signals are observed, and indication for ωχ(b2) is seen, both for the first time, and the corresponding cross section measurements are presented. No significant π(+)π(-)π(0)χ(b0) or ωχ(b0) signals are observed, and 90% confidence level upper limits on the cross sections for these two processes are obtained. In the π(+)π(-)π(0) invariant mass spectrum, significant non-ω signals are also observed. We search for the X(3872)-like state (named X(b)) decaying into ωϒ(1S); no significant signal is observed with a mass between 10.55 and 10.65 GeV/c(2).

Extracting the light quark mass ratio m(u)/m(d) from bottomonia transitions

We propose a new method to extract the light quark mass ratio m(u)/m(d) using the Υ(4S)→h(b)π⁰(η) bottomonia transitions. The decay amplitudes are dominated by the light quark mass differences, and the corrections from other effects are rather small, allowing for a precise extraction. We also discuss how to reduce the theoretical uncertainty with the help of future experiments. As a by-product, we show that the decay Υ(4S)→h(b)η is expected to be a nice channel for searching for the h(b) state.

Tetraquark interpretation of the BELLE data on the anomalous Upsilon(1S)pi+ pi- and Upsilon(2S)pi+ pi- production near the Upsilon(5S) resonance

We analyze the Belle data [K. F. Chen (Belle Collaboration), Phys. Rev. Lett. 100, 112001 (2008); I. Adachi (Belle Collaboration), arXiv:0808.2445] on the processes e+ e- --> Upsilon(1S)pi+ pi-, Upsilon(2S)pi+ pi- near the peak of the Upsilon(5S) resonance, which are found to be anomalously large in rates compared to similar dipion transitions between the lower Upsilon resonances. Assuming these final states arise from the production and decays of the J(PC)=1(--) state Y(b)(10,890), which we interpret as a bound (diquark-antidiquark) tetraquark state [bq][bq], a dynamical model for the decays Y(b) --> Upsilon(1S)pi+ pi-, Upsilon(2S)pi+ pi- is presented. Depending on the phase space, these decays receive significant contributions from the scalar 0(++) states, f0(600) and f0(980), and from the 2(++) qq-meson f(2)(1270). Our model provides excellent fits for the decay distributions, supporting Y(b) as a tetraquark state.

Extraction of the light quark mass ratio from the decays psi'-->J/psipi0(eta)

Light quark masses are important fundamental parameters of the standard model. The decays psi'-->J/psipi0(eta) were widely used in determining the light quark mass ratio m(u)/m(d). However, there is a large discrepancy between the resulting value of m(u)/m(d) and the one determined from the light pseudoscalar meson masses. Using the technique of nonrelativistic effective field theory, we show that intermediate charmed meson loops lead to a sizable contribution to the decays and hence make the psi'-->J/psipi0(eta) decays not suitable for a precise extraction of the light quark mass ratio.

Implications of heavy-quark spin symmetry on heavy-meson hadronic molecules

In recent years, many heavy mesons and charmonia were observed which do not fit in the conventional quark model expectations. Some of them are proposed to be hadronic molecules. Here we investigate the consequences of heavy-quark spin symmetry on these heavy-meson hadronic molecules. Heavy-quark spin symmetry enables us to predict new heavy-meson molecules and provides us with a method to test heavy-meson molecule assumptions of some newly observed states. In particular, we predict an eta_{c};{'}f_{0}(980) bound state as the spin-doublet partner of the Y(4660) proposed as a psi;{'}f_{0}(980) bound state with a mass of 4616_{-6};{+5} MeV and the prominent decay mode eta_{c};{'}pipi. The width is predicted to be Gamma(eta_{c};{'}pipi) = 60 +/- 30 MeV. The pi;{+}pi;{-} invariant mass spectrum and the line shape are calculated. We suggest searching for this state in B;{+/-} --> eta_{c};{'}K;{+/-}pi;{+}pi;{-}, whose branching fraction is expected to be large.

Observation of Upsilon(2S)-->etaUpsilon(1S) and search for related transitions

We report the first observation of Upsilon(2S)-->etaUpsilon(1S), with a branching fraction B=(2.1(-0.6)+0.7(stat)+/-0.3(syst)) x 10(-4) and a statistical significance 5.3sigma. Data were acquired with the CLEO III detector at the CESR e+e(-) symmetric collider. This is the first process observed involving a b-quark spin flip. For related transitions, 90% confidence limits in units of 10(-4) are B(Upsilon(2S)-->pi0Upsilon(1S)) < 1.8, B(Upsilon(3S)-->etaUpsilon(1S)) < 1.8, B(Upsilon(3S)-->pi0Upsilon(1S)) < 0.7, and B(Upsilon(3S)-->pi0Upsilon(2S)) < 5.1.