Charmonium states in quark-gluon plasma

We discuss how the spectral changes of quarkonia at T _c can reflect the ‘critical’ behaviour of QCD phase transition. Starting from the temperature dependencies of the energy density and pressure from lattice QCD calculation, we extract the temperature dependencies of the scalar and spin-2 gluon condensates near T _c. We also parametrize these changes into the electric and magnetic condensate near T _c. While the magnetic condensate hardly changes across T _c, we find that the electric condensate increases abruptly above T _c. Similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules, we show that these sudden changes induce equally abrupt changes in the mass and width of J/ψ, both of which are larger than 100 MeV at slightly above T _c.      

QCD sum rule for Λ(1405)

Motivated by the recently constructed interpolation field for S₁₁(1535), we propose a new interpolating field for Λ(1405). Using this current, we calculate the mass of Λ(1405) based on the conventional QCD sum rule analysis. By calculating the Wilson coefficients up to dimension 8 operators and taking into account the mass corrections from s-quark, we find the calculated mass of Λ(1405) to be very close to its experimental value.     

Couplings between pion and charmed mesons

We compute the couplings , and using QCD sum rules. These couplings are important inputs in the meson-exchange model calculations used to estimate the amount of absorption due to pions and rho mesons in heavy-ion collisions. Our sum rules are constructed at the first order in the pion momentum , which give the couplings that are not trivially related to the soft-pion theorem. Our calculated couplings, which somewhat depend upon the values of the heavy meson decay constants, are , , and . Received: 10 October 2001 / Revised version: 25 October 2001 / Published online: 7 December 2001     

The thermal width of heavy quarkonia moving in quark–gluon plasma

The velocity dependence of the thermal width of heavy quarkonia traveling with respect to the quark–gluon plasma is calculated up to the NLO in perturbative QCD. At the LO, the width decreases with increasing speed, whereas at the NLO it increases with a magnitude approximately proportional to the expectation value of the relative velocity between the quarkonium and a parton in thermal equilibrium. Such an asymptotic behavior is due to the NLO dissociation cross section converging to a nonvanishing value in the high energy limit.     

Uncommon ferromagnetic interactions in a homometallic Co(II) chain bridged by a single end-to-end azide

A new one-dimensional heterochiral coordination polymer [Co(bmdt)(N3)2].MeCN (1.MeCN) with well-isolated chains was prepared via a self-assembly process. Magnetic data show that intrachain ferromagnetic couplings via the single end-to-end azide group are observed, which is an extraordinary case among the azide-bridged Co(II) systems.     

Charmed exotics in heavy ion collisions

Based on the color–spin interaction in diquarks, we argue that charmed multiquark hadrons are likely to exist. Because of the appreciable number of charm quarks produced in central nucleus–nucleus collisions at ultrarelativistic energies, the production of charmed multiquark hadrons is expected to be enhanced in these collisions. Using both the quark coalescence model and the statistical hadronization model, we estimate the yield of charmed tetraquark mesons, T_cc, and pentaquark baryons, Θ_cs, in heavy ion collisions at RHIC and LHC. We further discuss the decay modes of these charmed exotic hadrons in order to facilitate their detections in experiments. PACS 25.75.Dw; 14.20.Lq; 14.40.Lb     

Identifying multiquark hadrons from heavy ion collisions

Identifying hadronic molecular states and/or hadrons with multiquark components either with or without exotic quantum numbers is a long-standing challenge in hadronic physics. We suggest that studying the production of these hadrons in relativistic heavy ion collisions offers a promising resolution to this problem as yields of exotic hadrons are expected to be strongly affected by their structures. Using the coalescence model for hadron production, we find that, compared to the case of a nonexotic hadron with normal quark numbers, the yield of an exotic hadron is typically an order of magnitude smaller when it is a compact multiquark state and a factor of 2 or more larger when it is a loosely bound hadronic molecule. We further find that some of the newly proposed heavy exotic states could be produced and realistically measured in these experiments.     

Self-consistent simulation on the modal gain of graded-index separate-confinement-heterostructure quantum-well lasers

The effective guide index directly causes the mutual influences in determining the complex refractive index of quantum well and the complex propagation constant of a guided mode. In this paper, self-consistent model (SCM) working on both density matrix theory and transfer matrix method is applied to investigate the modal gain of AlGaAs/GaAs graded-index separate-confinement-heterostructure single quantum-well (GRIN-SCH-SQW) lasers. Based on SCM, the simulated modal gain spectrum shows good agreement with the experimental result. Although varying with the thickness of SCH region or aluminum mole fraction, the percentage change of optical gain is much smaller than that of optical confinement factor. On the other hand, thin well width of QW results in a relative high optical gain but poor optical field confinement. Such opposing effects tend to balance each other and cause the modal gain almost insensitive to the well width change before 60 Å. Further increase of well thickness, the percentage change of optical gain is obviously larger than that of optical confinement factor. Therefore the optical gain becomes the dominant parameter that directly decreases the magnitude of modal gain.