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Register a new userEffects of $Z_b$ states and bottom meson loops on $Upsilon(4S) to Upsilon(1S,2S) pi^+pi^-$ transitions
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We study the dipion transitions $Upsilon(4S) rightarrow Upsilon(nS) pi^+pi^-$ $(n=1,2)$. In particular, we consider the effects of the two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$ as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to $Kbar{K}$ in the $S$-wave, are taken into account model-independently by using dispersion theory. Based on a nonrelativistic effective field theory we find that the contribution from the bottom meson loops is comparable to those from the chiral contact terms and the $Z_b$-exchange terms. For the $Upsilon(4S) rightarrow Upsilon(2S) pi^+pi^-$ decay, the result shows that including the effects of the $Z_b$-exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the $pipi$ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the $Upsilon(4S) rightarrow Upsilon(1S) pi^+pi^-$ decay, we show that there is a narrow dip around 1 GeV in the $pipi$ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower $Upsilon$ states, and needs to be verified by future data with high statistics. Also we predict the decay width and the dikaon mass distribution of the $Upsilon(4S) rightarrow Upsilon(1S) K^+ K^-$ process.
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In this work, we study the contributions of the intermediate bottomoniumlike $Z_b$ states and the bottom meson loops in the heavy quark spin flip transitions $Upsilon(4S) to h_b(1P,2P) pi^+pi^-$. Depending on the constructive or destructive interferences between the $Z_b$-exchange and the bottom meson loops mechanisms, we predict two possible branching ratios for each process: BR$_{Upsilon(4S) to h_b(1P)pi^+pi^-}simeqbig(1.2^{+0.8}_{-0.4}times10^{-6}big)$ or $big( 0.5^{+0.5}_{-0.2}times10^{-6}big)$, and BR$_{Upsilon(4S) to h_b(2P)pi^+pi^-}simeq big(7.1^{+1.7}_{-1.1}times10^{-10}big)$ or $big( 2.4^{+0.2}_{-0.1}times10^{-10}big)$. The bottom meson loops contribution is found to be much larger than the $Z_b$-exchange contribution in the $Upsilon(4S) to h_b(1P) pipi$ transitions, while it can not produce decay rates comparable to the heavy quark spin conserved $Upsilon(4S) to Upsilon(1S,2S) pipi$ processes. We also predict the branch fractions of $psi(3S,4S) to h_c(1P)pi^+pi^-$ contributed from the charm meson loops.
The dipion transitions $Upsilon(2S,3S,4S) to Upsilon(1S,2S)pipi$ are systematically studied by considering the mechanisms of the hadronization of soft gluons, exchanging the bottomoniumlike $Z_b$ states, and the bottom-meson loops. The strong pion-pion final-state interaction, especially including the channel coupling to $Kbar{K}$ in the $S$-wave, is taken into account in a model-independent way using the dispersion theory. Through fitting to the available experimental data, we extract values of the transition chromopolarizabilities $|alpha_{Upsilon(mS)Upsilon(nS)}|$, which measure the chromoelectric couplings of the bottomonia with soft gluons. It is found that the $Z_b$ exchange has a slight impact on the extracted chromopolarizablity values, and the obtained $|alpha_{Upsilon(2S)Upsilon(1S)}|$ considering the $Z_b$ exchange is $(0.29pm 0.20)~text{GeV}^{-3}$. Our results could be useful in studying the interactions of bottomonium with light hadrons.
Within the framework of dispersion theory, we analyze the dipion transitions between the lightest $Upsilon$ states, $Upsilon(nS) rightarrow Upsilon(mS) pipi$ with $m < n leq 3$. In particular, we consider the possible effects of two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$. The $pipi$ rescattering effects are taken into account in a model-independent way using dispersion theory. We confirm that matching the dispersive representation to the leading chiral amplitude alone cannot reproduce the peculiar two-peak $pipi$ mass spectrum of the decay $Upsilon(3S) rightarrow Upsilon(1S) pipi$. The existence of the bottomoniumlike $Z_b$ states can naturally explain this anomaly. We also point out the necessity of a proper extraction of the coupling strengths for the $Z_b$ states to $Upsilon(nS)pi$, which is only possible if a Flatte-like parametrization is used in the data analysis for the $Z_b$ states.
Using data collected in the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider we search for transitions $Upsilon(4S) rightarrow eta_b(1S)omega$, $Upsilon(5S) rightarrow eta_b(1S)omega$ and $Upsilon(5S) rightarrow eta_b(2S)omega$. No significant signals are observed and we set 90% confidence level upper limits on the corresponding visible cross sections: $0.2 ~textrm{pb}, 0.4 ~textrm{pb}$ and $1.9 ~textrm{pb}$, respectively.
We report the first observation of the hadronic transition $Upsilon(4S)toetaUpsilon(1S)$, using 496 fb$^{-1}$ data collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We reconstruct the $eta$ meson through its decays to $rho^0gamma$ and to $pi^+pi^-eta$, with $etatogammagamma$. We measure: ${cal B}(Upsilon(4S)toetaUpsilon(1S))=(3.43pm 0.88 {rm(stat.)} pm 0.21 {rm(syst.)})times10^{-5}$, with a significance of 5.7$sigma$.
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