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Register a new userCanonical interpretation of $Y(10750)$ and $Upsilon(10860)$ in the $Upsilon$ family
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Inspired by the new resonance $Y(10750)$, we calculate the masses and two-body OZI-allowed strong decays of the higher vector bottomonium sates within both screened and linear potential models. We discuss the possibilities of $Upsilon(10860)$ and $Y(10750)$ as mixed states via the $S-D$ mixing. Our results suggest that $Y(10750)$ and $Upsilon(10860)$ might be explained as mixed states between $5S$- and $4D$-wave vector $bbar{b}$ states. The $Y(10750)$ and $Upsilon(10860)$ resonances may correspond to the mixed states dominated by the $4D$- and $5S$-wave components, respectively. The mass and the strong decay behaviors of the $Upsilon(11020)$ resonance are consistent with the assignment of the $Upsilon(6S)$ state in the potential models.
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The dipion transitions $Upsilon(10860)topi^+pi^-Upsilon(nS)$ ($n=1,2,3$) are studied in the framework of a unitary and analytic coupled-channel formalism previously developed for analysing experimental data on the bottomoniumlike states $Z_b(10610)$ and $Z_b(10650)$ [Phys. Rev. D 98, 074023 (2018)] and predicting the properties of their spin partners [Phys. Rev. D 99, 094013 (2019)]. In this work we use a relatively simple but realistic version of this approach, where the scattering and production amplitudes are constructed employing only short-ranged interactions between the open- and hidden-flavour channels consistent with the constraints from heavy quark spin symmetry, for an extended analysis of the experimental line shapes. In particular, the transitions from the $Upsilon(10860)$ to the final states $pi pi h_b(mP)$ ($m=1,2$) and $pi B^{(*)}bar B^* $ already studied before, are now augmented by the $Upsilon(10860)topi^+pi^-Upsilon(nS)$ final states ($n=1,2,3$). This is achieved by employing dispersion theory to account for the final state interaction of the $pipi$ subsystem including its coupling to the $Kbar K$ channel. Fits to the two-dimensional Dalitz plots for the $pi^+pi^-Upsilon$ final states were performed. Two real subtraction constants are adjusted to achieve the best description of the Dalitz plot for each $Upsilon(nS)$ $(n=1,2,3)$ while all the parameters related to the properties of the $Z_b$s are kept fixed from the previous study. A good overall description of the data for all $Upsilon(10860)topi^+pi^-Upsilon(nS)$ channels achieved in this work provides additional strong support for the molecular interpretation of the $Z_b$ states.
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.
We report new measurements of the total cross sections for $e^+e^-to Upsilon(n{rm S})pi^+pi^-$ ($n$ = 1, 2, 3) and $e^+e^-to bbar b$ from a high-luminosity fine scan of the region $sqrt{s} = 10.63$-$11.05$ GeV with the Belle detector. We observe that the $Upsilon(n{rm S})pi^+pi^-$ spectra have little or no non-resonant component and extract from them the masses and widths of $Upsilon(10860)$ and $Upsilon(11020)$ and their relative phase. We find $M_{10860}=(10891.1pm3.2^{+0.6}_{-1.7})$ MeV/$c^2$ and $Gamma_{10860}=(53.7^{+7.1}_{-5.6},^{+1.3}_{-5.4})$ MeV and report first measurements $M_{11020}=(10987.5^{+6.4}_{-2.5},^{+9.0}_{-2.1})$ MeV/$c^2$, $Gamma_{11020}=(61^{+9}_{-19},^{+2}_{-20})$ MeV, and $phi_{rm 11020}-phi_{rm 10860} = (-1.0pm0.4,^{+1.4}_{-0.1})$ rad.
High-accuracy $Upsilon$-meson photoproduction data from EIC and EicC experiments will allow the measurement of the near-threshold total cross section of the reaction $gamma ptoUpsilon p$, from which the absolute value of the $Upsilon p$ scattering length, $|alpha_{Upsilon p}|$, can be extracted using a Vector-Meson Dominance model. For this evaluation, we used $Upsilon$-meson photoproduction quasi-data from the QCD approach (the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude). A comparative analysis of $|alpha_{Upsilon p}|$ with the recently determined scattering lengths for $omega p$, $phi p$, and $J/psi p$ using the A2, CLAS, and GlueX experimental data are performed. The role of the young vector-meson effect is evaluated.
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.
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