Electromagnetic signals of quark gluon plasma

Successive equilibration of quark degrees of freedom and its effects on electromagnetic signals of quark gluon plasma are discussed. The effects of the variation of vector meson masses and decay widths on photon production from hot strongly interacting matter formed after Pb + Pb and S + Au collisions at CERN SPS energies are considered. It has been shown that the present photon spectra measured by WA80 and WA98 Collaborations can not distinguish between the formation of quark matter and hadronic matter in the initial state.     

Central photoproduction ofJ/ψ andϒ as a test of QCD

Central photoproduction ofJ/ψ and Υ are calculated using the QCD structure functions of the real photon and compared with the back-grounds arising from Bethe-Heitler production of μ pairs andJ/ψ and Υ production coming from the hadronic (vector meson) part of the real photon. It is shown that in principle central photoproduction ofJ/ψ can be used to obtain information on the QCD structure function of the real photon.     

矢量介子的辐射衰变

介子的辐射衰变是低能强子物理研究的重要方向, 通过它能够揭示介子的结构和性质。从有效场论的观点来看,介子衰变主要包含光子和强子之间的相互作用。使用SU(3)对称性和VMD模型分别对矢量介子的辐射衰变进行了研究。 通过对实验数据进行拟和,给出了在两种情形下V→Pγ的衰变宽度的理论值,并得到赝标量混合角θP 为－6°。 Radiative decay of mesons is an important aspect in low energy hadronic physics,through which structures and properties of mesons can be revealed. In view of effective field theories, the radiative decay of mesons involves mainly interactions between photons and hadrons. In this paper,we investigate the decay of vector mesons by using SU(3) symmetry and the vector meson dominance model respectively. By fitting with experiments, we give the theoretic widths for V→Pγ in both cases and the mixing angle of pseudoscalars θP is －6°.     

Meson Lagrangians in a superconductor quark model

On the basis of a effective “superconductivity”-type four-quark interaction, phenomenological Lagrangians are obtained for interactions of scalar, pseudoscalar, vector, and axial vector meson nonets. The Lagrangians include mass terms breaking chiral and U(3) invariance and corresponding to the quark masses m_u ≠ m_d ≠ m_s. It is shown that upon introducing boson fields the masses of current quarks in the initial Lagrangian are replaced by the masses of constituent quarks in the phenomenological boson Lagrangians. Estimates of these masses are presented. Electromagnetic interactions are considered, and the vector dominance model is derived. The widths of various meson decays are calculated.     

Influence of In-medium properties of vector mesons on dilepton production in heavy ion collisions at SIS energies

Dileptons represent a unique probe for nuclear matter under extreme conditions reached in heavy ion collisions. They allow the study of meson properties, like mass and decay width, at various density and temperature regimes. Up to now, in the Tübingen model for dilepton production, modification of meson properties in nuclear medium has been accounted for by allowing a density dependence of the mass (Brown–Rho scaling) together with an ad hoc dependence of the meson decay widths on the same variable. We use the extended vector meson dominance (eVMD) model to extract meson properties in nuclear matter by computing the in-medium meson spectral functions. Dilepton spectra for C+C at 1.0 and 2.0 AGeV are calculated and compared with previous results.     

Decays of intermediate vector bosons,radiative corrections and QCD jets

We investigate decay properties of the intermediate vector bosons W^± and Z⁰. QED and QCD radiative corrections to leptonic and hadronic decay modes are calculated. Implications of the results for decay widths, branching ratios, determination of the number of neutrino species, e-μ-τ universality and properties of hadronic jets produced in W^± and Z⁰ decays are examined.     

Corrections to VMD in the photoproduction of vector mesons I: Mass dependence of amplitudes

We study the dependence of the vector meson scattering amplitudes on the external masses, assuming that the most important effects arise from the coupling of the vector mesons to low mass intermediate states which mediate the scattering. The consequence is that the amplitudes for ?⁰ and ø photoproduction are modified by approximately + 10% and ?15% respectively. This result is equivalent to naively using the coupling constants from the e⁺e^- decay widths and ignoring the mass variation effects. The analysis also calls attention to residual uncertainties at the several percent level.     

Spin effects in two-body hadronic decays of the B c mesons

Spin effects in the weak two-body hadronic decays of the B _c and B _c ^* mesons into J/ψ and ρ(π) mesons are considered within the model of hard one-gluon exchange between quarks at high momentum transfers. It is shown that the polarization of the J/ψ meson in the decays of the B _c ^* meson differs substantially from that in the decays of the B _c ^* meson. The decay widths of the B _c ^* meson differ significantly from the widths of the B _c ^* meson.     

Meson loops in the f0(980) and a0(980) radiative decays into ρ , ω

We calculate the radiative decay widths of the a ₀(980) and f ₀(980) scalar mesons into ργ and ωγ considering the dynamically generated nature of these scalar resonances within the realm of the chiral unitary approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two-meson loop function easily regularizable. We provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models and some version of vector meson dominance.     

Determinations of from inclusive semileptonic decays with reduced model dependence

We report two novel determinations of /|Vub/ with reduced model dependence, based on measurements of the mass distribution of the hadronic system in semileptonic B decays. Events are selected by fully reconstructing the decay of one B meson and identifying a charged lepton from the decay of the other B meson from Upsilon(4S)-->BB events. In one approach, we combine the inclusive B-->Xulambdav rate, integrated up to a maximum hadronic mass mX<1.67 GeV/c2, with a measurement of the inclusive B-->Xsgamma photon energy spectrum. We obtain /Vub/=(4.43+/-0.38stat+/-0.25syst+/-0.29theo) x 10-3. In another approach we measure the total B-->Xulambdav rate over the full phase space and find /Vub/=(3.84+/-0.70stat+/-0.30syst+/-0.10theo) x 10-3.     

Vector states in e+e− annihilation at 3.9–4.5 GeV

The structure observed at SPEAR in e⁺e^? annihilation in the energy range 3.9–4.5 GeV is explained in an SU(8) × SL(3, R) color quark model. The model can account for the mass differences, total hadronic and leptonic widths, as well as for the rise in, and the magnitude of, R. Main predictions are the SU(3) properties of these states, strong suppression of their decays into the ψ(3.1) and the existence of another vector meson around 6 GeV.     

Vector and Tensor Coupling Constants of SU(3) Baryons in a Chiral Soliton Model

We report in the present talk a recent investigation on the vector properties of SU(3) baryons, based on a chiral soliton model. All relevant parameters from the model are adjusted to the experimental data of the masses and magnetic moments of the baryon octet. We compute the electromagnetic transitions for the baryon octet, the decuplet, and the antidecuplet. The numerical predictions for transition magnetic moments and radiative partial decay widths are in a very good agreement with all data of existing experiment and the vector meson dominance being used, the coupling constants for the vector mesons and antidecuplet baryon vertices are determined from the calculated transition magnetic moments.     

Quark masses from the vector meson spectrum

We investigate a matching arrangement between the VMD and the quark model in which the structure of the latter determines the spectrum of vector meson masses and their couplings to the photon. Current quark masses are in turn determined by the spectrum of vector meson masses of the corresponding flavour family.     

A search for a narrow radial excitation of the $\mathrm{D}^{*\pm}$ Meson

A sample of 3.73 million hadronic Z decays, recorded with the OPAL detector at LEP in the years 1991–95, has been used to search for a narrow resonance corresponding to the decay of the meson into . The mesons are reconstructed in the decay channel with . No evidence for a narrow resonance is found. A limit on the production of narrow in hadronic Z decays is derived: Received: 16 January 2001 / Published online: 28 May 2001     

Do light colored scalars exist?

The general question of the properties of light, neutral colored spin-zero particles in QCD is examined. Models with spontaneous breaking of QCD at very large distances, such as that of DeRújula, Giles, and Jaffe and the SO(3) scheme of Slansky, Goldman, and Shaw, require such light colored Higgs scalars. These scalars will form color-singlet hadronic bound states at short distances and estimates are given of bound state masses, decay widths, and production rates in processes such as ψ → γ + X within the MIT bag model. The resulting states are expected in the mass neighborhood ～1.5 GeV and should resemble glueballs.     

The reaction γp → pπ+π−π+π− for photon energies from 25 to 70 GeV

Measurements of the reaction γp → pπ⁺π^?π⁺π^? are presented, in which π⁺π^?π⁺π^? systems with masses up to 3 GeV are produced from fragmentation of the incident photon. The reaction is dominated by production of the large peak of the ?′(1600) meson and, at higher masses ?2 GeV, y production of jet-like 4π systems. The ?′(1600) meson is produced by a predominantly s-channel helicity conserving mechanism. At higher masses there are also indications of ?π peaks, of masses 1.3 GeV (the A₂ meson) and 1.75 GeV, produced with a recoiling π meson by a mechanism consistent with the Deck effect.     

Mass Spectrum and Decay Properties of D Meson

A comparative study of the spectroscopy and decay properties of the D meson is carried out within the framework of phenomenological quark-antiquark potential (Coulomb plus power) model using hydrogenic and Gaussian wave function. The spin-hyperfine, spin-orbit and tensor interactions are employed to obtain the pseudoscalar and vector meson masses incorporating the effect of mixing. The decay constants (f _P/V ) are computed with QCD correction using the wave function at the origin. The leptonic branching fractions and electromagnetic transition rates are also calculated in this scheme. Our predictions at potential index ν=1 are in good agreement with experimental results as well as lattice and other theoretical models.