arXiv subjects

V. Riquer

Publications and source records attributed to V. Riquer.

41 records · Page 3Linked to original sources

arXiv2004

Diquark-Antidiquarks with Hidden or Open Charm and the Nature of X(3872)

Heavy-light diquarks can be the building blocks of a rich spectrum of states which can accommodate some of the newly observed charmonium-like resonances not fitting a pure c-cbar assignment. We examine this possibility for hidden and open charm diquark-antidiquark states deducing spectra from constituent quark masses and spin-spin interactions. Taking the X(3872) as input we predict the existence of a 2++ state that can be associated to the X(3940) observed by Belle and re-examine the state claimed by SELEX, X(2632). The possible assignment of the previously discovered states D_s(2317) and D_s(2457) is discussed. We predict X(3872) to be made of two components with a mass difference related to (m_u-m_d) and discuss the production of X(3872) and of its charged partner X^(+-) in the weak decays of B^(+,0).

hep-ph↗

arXiv2004

A new look at scalar mesons

Light scalar mesons are found to fit rather well a diquark-antidiquark description. The resulting nonet obeys mass formulae which respect, to a good extent, the OZI rule. OZI allowed strong decays are reasonably reproduced by a single amplitude describing the switch of a qbar-q pair, which transforms the state into two colourless pseudoscalar mesons. Predicted heavy states with one or more quarks replaced by charm or beauty are briefly described; they should give rise to narrow states with exotic quantum numbers.

hep-ph↗

arXiv2004

J/psi Absorption in Heavy Ion Collisions II

Using the methods introduced in a previous paper, we consider the dissociation of J/psi by the lowest-lying pseudoscalar and vector mesons in the hadronic fireball formed in heavy ion collisions, assumed to be a hadron gas at temperature T. Absorption by nuclear matter is accounted for as well. We compare with the S-U and Pb-Pb data presented by the NA50 Collaboration. From data at low centrality we find T=160-180 MeV, close to the predicted temperature of the transition to quark-gluon plasma and to the temperatures measured by hadron abundances. We extrapolate to higher centralities with the approximation of scaling the energy density of the fireball with the average baryon density per unit transverse area. Using the energy-temperature relation of the hadron gas made by the same pseudoscalar and vector mesons, the fall off of J/psi production shown by the NA50 data, can be marginally reproduced only for the highest temperature, T=180 MeV. If we use the energy-temperature relation of a Hagedorn gas with limiting temperature T_H=173 MeV, predictions fall short from reproducing the data. These results suggest that a different mechanism is responsible for the J/psi suppression at large centralities, which could very well be the formation of quark-gluon plasma.

hep-ph↗

arXiv2004

Is the anomalous decay ratio of D_{sJ}(2632) due to isospin breaking?

Quark pair annihilation into gluons is suppressed at large momenta due to the asymptotic freedom. As a consequence, mass eigenvalues of heavy states should be almost diagonal with respect to up and down quark masses, thereby breaking isospin. We suggest the particle observed by the SELEX Collaboration, D_{sJ}(2632) to be to a good extent a [cd][dbar sbar] state, which would explain why its D^0 K^+ mode is anomalously suppressed with respect to D_s eta. Predictions for the rates of the yet unobserved modes D_s pi^0 and D^+ K^0 are given.

hep-ph↗

arXiv2004

J/psi Absorption in Heavy Ion Collisions

We present a new calculation of the pi-J/psi dissociation cross sections within the Constituent Quark-Meson Model recently introduced. To discuss the absorption of J/psi in heavy-ion collisions, we assume the J/psi to be produced inside a thermalized pion gas, as discussed by Bjorken, and introduce the corrections due to absorption by nuclear matter as well. We fit the absorption length of the J/psi to the data obtained at the CERN SPS by the NA50 Collaboration for Pb-Pb collisions. Collisions of lower centrality allow us to determine the temperature and the energy density of the pion gas. For both these quantities we find values close to those indicated by lattice gauge calculations for the transition to a quark-gluon plasma. A simple extrapolation to more central collisions, which takes into account the increase of the energy deposited due to the increased nucleon flux, fails to reproduce the break in J/psi absorption indicated by NA50, thus lending support to the idea that an unconfined quark-gluon phase may have been produced. This conclusion could be sharpened by analysing in a similar way, as a function of centrality, other observables such as strange particle production.

hep-ph↗