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Register a new userIs the existence of a $J/psi J/psi$ bound state plausible?
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In a recent measurement LHCb reported pronounced structures in the $J/psi J/psi$ spectrum. One of the various possible explanations of those is that they emerge from non-perturbative interactions of vector charmonia. It is thus important to understand whether it is possible to form a bound state of two charmonia interacting through the exchange of gluons, which hadronise into two pions at the longest distance. In this paper, we demonstrate that, given our current understanding of hadron-hadron interactions, the exchange of correlated light mesons (pions and kaons) is able to provide sizeable attraction to the di-$J/psi$ system, and it is possible for two $J/psi$ mesons to form a bound state. As a side result we find from an analysis of the data for the $psi(2S)to J/psi pipi$ transition including both $pipi$ and $Kbar K$ final state interactions an improved value for the $psi(2S)to J/psi$ transition chromo-electric polarisability: $|alpha_{psi(2S)J/psi}|= (1.8pm 0.1)~mbox{GeV}^{-3}$, where the uncertainty also includes the one induced by the final state interactions.
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The two exotic $P_c^+(4380)$ and $P_c^+(4450)$ discovered in $2015$ by the LHCb Collaboration, together with the four resonances $X(4140)$, $X(4274)$, $X(4500)$ and $X(4700)$, reported in $2016$ by the same collaboration, are described in a constituent quark model which has been able to explain the properties of charmonium states from the $J/psi$ to the $X(3872)$. Using this model we found a $bar DSigma_c^*$ bound state with $J^P=frac{3}{2}^-$ that may be identified with the $P_c^+(4380)$. In the $bar D^*Sigma_c$ channel we found three possible candidates for the $P_c^+(4450)$ with $J^P=frac{1}{2}^-$, $frac{3}{2}^-$ and $frac{3}{2}^+$ with almost degenerated energies. The $X(4140)$ resonance appears as a cusp in the $J/psiphi$ channel due to the near coincidence of the $D_{s}^{pm}D_{s}^{astpm}$ and $J/psiphi$ mass thresholds. The remaining three $X(4274)$, $X(4500)$ and $X(4700)$ resonances appear as conventional charmonium states with quantum numbers $3^{3}P_{1}$, $4^{3}P_{0}$ and $5^{3}P_{0}$, respectively; and whose masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds.
Motivated by a recent successful dynamical explanation for the newly observed fully-charm structure $X(6900)$ in the mass spectrum of di-$J/psi$ by LHCb [J.~Z.~Wang textit{et al.} arXiv:2008.07430], in this work, we extend the same dynamical rescattering mechanism to predict the line shape of more potential fully-heavy structures in the invariant mass spectrum of $J/psi psi(3686)$, $J/psi psi(3770)$, $psi(3686) psi(3686)$, and $J/psi Upsilon(1S)$ at high energy proton-proton collisions, whose verification in experiments should be helpful to further clarify the nature of $X(6900)$. The above final states of vector heavy quarkonia can be experimentally reconstructed more effectively by a $mu^+mu^-$ pair in the muon detector compared with $Qbar{Q}$ meson with other quantum numbers. Furthermore, the corresponding peak mass positions of each of predicted fully-heavy structures are also given. Our theoretical studies here could provide some valuable information for the future measurement proposals of LHCb and CMS, especially based on the accumulated data after completing Run III of LHC in the near future.
We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $cbar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.
The products of the electron width of the J/psi meson and the branching fraction of its decays to the lepton pairs were measured using data from the KEDR experiment at the VEPP-4M electron-positron collider. The results are Gamma_{ee}(J/psi)*Br(J/psi->e^+e^-)=(0.3323pm0.0064pm0.0048) keV, Gamma_{ee}(J/psi)*Br(J/psi->mu^+mu^-)=(0.3318pm0.0052pm0.0063) keV. Their combinations Gamma_{ee}times(Gamma_{ee}+Gamma_{mumu})/Gamma=(0.6641pm0.0082pm0.0100) keV, Gamma_{ee}/Gamma_{mumu}=1.002pm0.021pm0.013 can be used to improve theaccuracy of the leptonic and full widths and test leptonic universality. Assuming emu universality and using the world average value of the lepton branching fraction, we also determine the leptonic Gamma_{ll}=5.59pm0.12 keV and total Gamma=94.1pm2.7 keV widths of the J/psi meson.
In two recent reactions by Belle producing $Dbar D$ and $Dbar D^*$ meson pairs, peaks above threshold have been measured in the differential cross sections, possibly indicating new resonances in these channels. We want to study such reactions from the point of view that the $D$ meson pairs are produced from already known or predicted resonances below threshold. Our study shows that the peak in the $Dbar D^*$ production is not likely to be caused by the X(3872) resonance, but the peak seen in $Dbar D$ invariant mass can be well described if the $Dbar D$ pair comes from the already predicted scalar X(3700) resonance.
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