Observation of an exotic narrow doubly charmed tetraquark

Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. The observation of a new type of hadronic state, a doubly charmed tetraquark containing two charm quarks, an anti-u and an anti-d quark, is reported using data collected by the LHCb experiment at the Large Hadron Collider. This exotic state with a mass of about 3875 MeV/c 2 manifests itself as a narrow peak in the mass spectrum of D0D0π + mesons just below the D∗+D0 mass threshold. The near-threshold mass together with a strikingly narrow width reveals the resonance nature of the state.

Features of the distribution of events by the multiple of secondary particles depending on the energy of collision and the assymetricity of collising relativistic nuclei

To search for signals of the phase transition of matter from the hadronic state to the quark­gluon plasma, interactions with extreme characteristics are studied. The study of the dependence of the av­erage multiplicity on the projectile energy for sulfur and silicon nuclei with energies of 3.7 AGeV, 14 AGeV, and 200 AGeV has been carried out. Experimental data on inelastic interactions with the nuclei of the NIKFI BR­2 emulsion obtained at the SPS at CERN and at the Synchrophasotron at JINR. To take into account fluctuations in the initial conditions of the nucleus­nucleus interaction, the events were divided into central and peripheral ones. A comparative analysis of the average multiplicity with heavy and light nuclei of the photographic emulsion is presented. The multiplicity increase factor has an almost linear increase in energy (on the logarithmic axis) for all events, except for the central interactions of sulfur nuclei with heavy emulsion nuclei at 200 AGeV. These events are explosive events, which give a flux of secondary particles in a narrow range of average pseudo­rapidity and significantly shifted towards low values <η>. The analysis of events of complete destruction of the projectile nucleus is presented. Such events are considered as events in which the most favorable conditions are created for the formation of a quark­gluon plasma.

Deciphering the recently discovered tetraquark candidates around 6.9 GeV

Recently a novel hadronic state of mass 6.9 GeV, that decays mainly to a pair of charmonia, was observed in LHCb. The data also reveals a broader structure centered around 6490 MeV and suggests another unconfirmed resonance centered at around 7240 MeV, very near to the threshold of two doubly charmed $$\Xi _{cc}$$ Ξ cc baryons. We argue in this note that these exotic hadrons are genuine tetraquarks and not molecules of charmonia. It is conjectured that they are V-baryonium , namely, have an inner structure of a baryonic vertex with a cc diquark attached to it, which is connected by a string to an anti-baryonic vertex with a $${\bar{c}} {\bar{c}}$$ c ¯ c ¯ anti-diquark. We examine these states as the analogs of the V-baryonium states $$\Psi (4360)$$ Ψ ( 4360 ) and Y(4630)/$$\Psi (4660)$$ Ψ ( 4660 ) which are charmonium-like tetraquarks. One way to test these claims is by searching for a significant decay of the state at 7.2 GeV into $$\Xi _{cc}{\overline{\Xi }}_{cc}$$ Ξ cc Ξ ¯ cc . Such a decay would be the analog of the decay of the state Y(4630) into to $$\Lambda _c{\overline{\Lambda }}_c$$ Λ c Λ ¯ c . We further argue that there should be trajectories of both orbital and radial excited states of the X(6900). We predict their masses. It is possible that a few of these states have already been seen by LHCb.

The Rapidity Distributions and the Thermalization Induced Transverse Momentum Distributions in Au-Au Collisions at RHIC Energies

It is widely believed that the quark-gluon plasma (QGP) might be formed in the current heavy ion collisions. It is also widely recognized that the relativistic hydrodynamics is one of the best tools for describing the process of expansion and hadronization of QGP. In this paper, by taking into account the effects of thermalization, a hydrodynamic model including phase transition from QGP state to hadronic state is used to analyze the rapidity and transverse momentum distributions of identified charged particles produced in heavy ion collisions. A comparison is made between the theoretical results and experimental data. The theoretical model gives a good description of the corresponding measurements made in Au-Au collisions at RHIC energies.

THERMOFIELD DYNAMICS AND e+e- REACTIONS

The thermofield dynamics, a real-time formalism for finite temperature quantum field theory, is used to calculate the rates for e+e- reactions at finite temperature. The results show the role of temperature in defining a hadronic state after the plasma has been cooled down.

WEAK RADIATIVE DECAYS OF PSEUDOSCALAR CHARMED MESONS

We consider here radiative weak decays of charmed mesons such as [Formula: see text] and [Formula: see text] in a quark model where in general a translationally invariant SU(6) hadronic state is described by constituent quark field operators satisfying equal time algebra and a harmonic oscillator wave function. The model had its earlier success during its application to a variety of hadronic phenomena, and here also, without any free parameters, it calculates the branching ratios as [Formula: see text] and [Formula: see text]. Such calculations are very close to the estimations of Asthana and Kamal, and thus is consistent with the QCD enhancement of the latter branching ratio with respect to the former.

J/Ψ SUPPRESSION IN EXPANDING HADRONIC MATTER WITH A PHASE TRANSITION

J/Ψ propagation in hadronic matter expanding longitudinally and transversely in the central rapidity region of a nucleus-nucleus collision is examined. During the expansion, a first order transition from the quark-gluon plasma to the hadronic state occurs. The J/Ψ suppression in matter is due to the combined effects of the plasma, the mixed phase and hadrons on the resonance. Finally, J/Ψ momentum distributions for the model which assumes a J/Ψ formation time and for the one where J/Ψ dissolution is described on the quantum level are presented.