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1. chinaXiv:201711.02316 [pdf]

Effects of Zb states and bottom meson loops on γ(4S)→γ(1S, 2S)π+π? transitions

Yun-Hua Chen; Martin Cleven; Johanna T. Daub; Feng-Kun Guo; Christoph Hanhart; Bastian Kubis; Ulf-G. Mei遪er; Bing-Song Zou
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We study the dipion transitions (4S) → (nS)π+π? (n = 1, 2). In particular, we consider the effects of the two intermediate bottomoniumlike exotic states Zb(10610) and Zb(10650) as well as bottom meson loops. The strong pion–pion final-state interactions, especially including channel coupling to K ?K in the S-wave, are taken into account modelindependently 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 Zb-exchange terms. For the (4S) → (2S)π+π? decay, the result shows that including the effects of the Zb-exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the ππ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the (4S) → (1S)π+π? decay, we show that there is a narrow dip around 1GeV in the ππ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower 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 (4S) → (1S)K+K? process.

submitted time 2017-11-10 Hits1192Downloads645 Comment 0

2. chinaXiv:201609.01010 [pdf]

The nature of near-threshold XYZ states

Martin Cleven; Feng-Kun Guo; Christoph Hanhart; Qian Wang; Qiang Zhao
Subjects: Physics >> Nuclear Physics

We demonstrate that the recently observed X,Y,Z states cannot be purely from kinematic effect. Especially the narrow near-threshold structures in elastic channels call for nearby poles of the S-matrix which are qualified as states. We propose a way to distinguish cusp effects from genuine states and demonstrate that (not all of) the recently observed X,Y,Z states cannot be purely from kinematic effects. Especially, we show that the narrow near-threshold structures in elastic channels call for nearby poles of the S-matrix, since the normal kinematic cusp effect cannot produce that narrow structures in the elastic channels in contrast to genuine S-matrix poles. In addition, it is also discussed how spectra can be used to distinguish different scenarios proposed for the structure of those poles, such as hadro-quarkonia, tetraquarks and hadronic molecules. The basic tool employed is heavy quark spin symmetry.

submitted time 2016-09-14 Hits1250Downloads731 Comment 0

3. chinaXiv:201609.00927 [pdf]

Employing spin symmetry to disentangle different models for the XYZ states

Martin Cleven; Feng-Kun Guo; Christoph Hanhart; Qian Wang; Qiang Zhao
Subjects: Physics >> Nuclear Physics

In order to test different models proposed for some states discovered recently in the charmonium mass range that do not fit into the pattern predicted by the conventional quark model, we derive predictions for the spectrum within the hadro-charmonium picture, the tetraquark picture as well as the hadronic molecular approach. We exploit heavy quark spin symmetry for the hadro-charmonium and hadronic molecule scenarios. The patterns that emerge from the different models turn out to be quite distinct. For example, only within the hadro-charmonium picture a pseudoscalar state emerges that is lighter than the Y(4260). Possible discovery channels of these additional states are discussed.

submitted time 2016-09-13 Hits1415Downloads837 Comment 0

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