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Register a new userNew charm resonances and $J/psi$ interactions in a hadron gas
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In relativistic heavy ion collisions, after the quark gluon plasma (QGP) phase there is a hadron gas (HG) phase. In both phases $J/psi$ may be formed and destroyed. In this note we study the $J/psi$ interactions with other mesons in the hadron gas phase. Making use of effective field Lagrangians we obtain the cross sections for the production and absorption processes. With respect to the existing calculations, the improvements introduced here are the inclusion of $K$ and $K^*$s in the effective Lagrangian approach and the inclusion of processes involving the new exotic charmonium states $Z_c(3900)$ and $Z_c(4025)$. We conclude that the interactions between $J/psi$ and all the considered mesons reduce the original $J/psi$ abundance ( determined at the end of the quark gluon plasma phase ) by 20 % and 24 % in RHIC and LHC collisions respectively. Consequently, any really significant change in the $J/psi$ abundance comes from dissociation and regeneration processes in the QGP phase.
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The first observation of exotic states with a new quark content $c bar{c} u bar{s}$ decaying to the $J/psi K^+$ final state is reported with high significance from an amplitude analysis of the $B^+ to J/psi phi K^+$ decay. The analysis is carried out using proton-proton collision data corresponding to a total integrated luminosity of 9 fb$^{-1}$ collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV. The most significant state, $Z_{cs}(4000)^+$, has a mass of $4003pm6,^{+,phantom{0}4}_{-,14}$ MeV, a width of $131pm15pm26$ MeV, and spin-parity $J^P=1^+$, where the quoted uncertainties are statistical and systematic, respectively. A new $1^+$ $X(4685)$ state decaying to the $J/psi phi$ final state is also observed with high significance. In addition, the four previously reported $J/psi phi$ states are confirmed and two more exotic states, $Z_{cs}(4220)^+$ and $X(4630)$, are observed with significance exceeding five standard deviations.
A comment on the LHCb discovery of J/psi-pair resonances. To appear in Science Bulletin as a NEWS and VIEWS Paper.
We investigate the in-medium modification of pseudoscalar and vector mesons in a QCD motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature for a wide mass range of meson masses, from light (pi, rho) to open-charm (D, D*) states. At the chiral / deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (the hadronic Mott effect). We calculate the in-medium cross sections for charmonium dissociation due to collisions with light hadrons in a chiral Lagrangian approach, and show that the D and D* meson spectral broadening lowers the threshold for charmonium dissociation by pi and rho meson impact. This leads to a step-like enhancement in the reaction rate. We suggest that this mechanism for enhanced charmonium dissociation may be the physical mechanism underlying the anomalous J/Psi suppression observed by NA50.
We analyze two recent reactions of Belle, producing $Dbar D$ and $Dbar D^*$ states that have an enhancement of the invariant $Dbar D$, $Dbar D^*$ mass distribution close to threshold, from the point of view that they might be indicative of the existence of a hidden charm scalar and an axial vector meson states below $Dbar D$ or $Dbar D^*$ thresholds, respectively. We conclude that the data is compatible with the existing prediction of a hidden charm scalar meson with mass around 3700 MeV, though other possibilities cannot be discarded. The peak seen in the $Dbar D^*$ spectrum above threshold is, however, unlikely to be due to a threshold enhancement produced by the presence, below threshold, of the hidden charm axial vector meson X(3872).
We show that the distributions of outgoing protons and charged hadrons in high energy proton-nucleus collisions are described rather well by a linear extrapolation from proton-proton collisions. The only adjustable parameter required is the shift in rapidity of a produced charged meson when it encounters a target nucleon. Its fitted value is 0.16. Next, we apply this linear extrapolation to precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets which exhibit a deviation from linear scaling in the atomic number A. We show that this deviation can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quantum coherence. We infer an average proper coherence time of 0.4 +/- 0.1 fm/c, corresponding to a coherence path length of 8 +/- 2 fm in the rest frame of the nucleus. Finally, we apply the linear extrapolation to measured J/Psi production cross sections for 200 and 450 GeV/c protons incident on a variety of nuclear targets. Our analysis takes into account energy loss of the beam proton, the time delay of particle production due to quantum coherence, and absorption of the J/Psi on nucleons. The best representation is obtained for a coherence time of 0.5 fm/c, which is consistent with Drell-Yan production, and an absorption cross section of 3.6 mb, which is consistent with the value deduced from photoproduction of the J/Psi on nuclear targets.
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