Determination of meson resonance contributions to pion and kaon inclusive spectra

π- andK-meson inclusive spectra with low transverse momenta inK-meson fragmentation region inKp-interactions are determined on the basis of the assumption on a recombination mechanism of hadron production. It is shown that the pion and kaon spectra (both “direct” and from resonance decay) inK-meson fragmentation region can be expressed by structure functions of initialK-meson. Contributions from resonance decays from different meson multiplets (vector, axial and tensor) to pion and kaon inclusive spectra are determined. α=(3A _T /5A _V )=0.28±0.02 is found for the suppression factor ofP-wave meson state production as compared to theS-wave one. It is shown that with decreasing final meson mass the relative contribution of direct production to meson inclusive spectrum increases. In the limits of available experimental errors in meson resonance spectra there is found no dependence of meson yields on the value of summary spin of quark and antiquark producing meson (β=3A _P /A _V =1). It is shown that analysis of meson resonance inclusive spectra allows one to determine not only the parameters of valence quark distribution in the initialK-meson but also the sea parton distributions. For the strange sea quark distribution inK-meson there is founds _S(x) ～(1?x) ^ns wheren _S =4.8±1.0, which agrees with the prediction of the quark counting rules for this quantity.     

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.     

Situation around thea 0(980) meson after the experimentγγ→a 0→π 0 η

Based on the four-quark interpretation of the scalara ₀(980) meson a model for theγγ→a ₀→π ⁰ η reaction amplitude is constructed which describes well the experimental data. The ideas about the nature of thea ₀(980) meson which appeared after the Crystal Ball measurement of the two-photon production of thea ₀ meson are discussed briefly.     

Effect of a meson cloud on the jet nuclear modification factor in <Emphasis Type="Italic">pA</Emphasis> collisions

We study the effect of the nucleon meson cloud on centrality dependence of the jet nuclear modification factor R _pA. We find that the meson–baryon Fock components may lead to a noticeable deviation of R _pA from unity. Our results for R _pA show the same tendency as that observed by ATLAS in p + Pb collisions at √s = 5.02 TeV. The meson cloud suppresses the central jet events and enhances the peripheral jet events. However, quantitatively the effect is somewhat smaller than in the data.     

Vector mesons in asymmetric nuclear matter

The propagation of a vector meson (ϱ and ω) in dense asymmetric nuclear matter (with the number density of protons and neutrons different) is studied. Of particular interest is the density dependence of the vector meson masses, as also their variation with the asymmetry parameter, mass splitting among the ϱ isospin multiplets and the change of the form of the ϱ meson self-energy or the polarization tensor (II_μν) when the p ↔ n symmetry is broken. Contributions of both the Fermi sea and Dirac vacuum have been considered. It is shown that while the density dependent dressing of the vector meson propagator lifts the dispersion characteristics into the region of instability, the Dirac vacuum on the other hand contributes with opposite sign, thereby enhancing the possibility of stable collective modes even for higher values of vector meson momenta. The role of tensor coupling on the dispersion characteristics is also presented.     

Construction of local meson operator from the path-ordered operator in QCD2

A local meson operator is constructed from the path-ordered operator on QCD₂. The meson operator satisfies the Klein-Gordon equation with the mass identical to the eigenvalue of the 't Hooft equation. The interaction of the meson is shown to be nonlocal and to have a coupling proportional to 1/N_c.     

Some rare processes in a model of composite quarks and leptons

The branching ratios of some rare processes, i.e. meson →μe, meson →meson μe, baryon → baryon μe, are calculated in a composite quark and lepton model. Use is made of an effective Hamiltonian which originates from hypercolor singlet 0^? and 1^? bound state exchange mechanism, acting at a mass scaleM _P andM _V respectively. Under the reasonable assumptionM _P =M _V onlyK _L →μe puts a significant limit on the composite scale.     

Solitons bound to heavy mesons

We improve the bound state approach of the Skyrme model applied to the heavy baryons by adopting a static heavy meson picture where the soliton moves around the fixed heavy meson. This allows to take into account the center of mass corrections in a more consistent way. The bound state masses so obtained are comparable to the experimentally observed Λ _c and Λ _c ^* masses. A loosely bound state of a soliton with an antiflavored heavy meson is found, which leaves a possibility of the nonstrange pentaquark baryon(s).     

Broadening of ρ(→ e+e−) meson produced coherently in the photonuclear reaction

The e ⁺ e ^? invariant mass distribution spectra are calculated to estimate the hadron parameters of the ρ meson produced coherently in the photonuclear reaction. The elementary reaction occurring in the nucleus is considered to proceed as γN → ρ ⁰ N; ρ ⁰ → e ⁺ e ^?. We describe the elementary ρ meson photoproduction by the experimentally determined reaction amplitude $f_{\gamma {\rm N} \to \rho ^0 {\rm N}}$ . The ρ meson propagator is presented by the eikonal form, and the ρ meson nucleus optical potential V _Oρ appearing in it is estimated using the “t?” approximation. The ρ meson nucleon scattering amplitude f _ρN extracted from the measurements is used to generate this potential. The calculated e ⁺ e ^? invariant mass distribution spectra are compared with those measured at Jefferson Laboratory. The calculated results for the transparency ratio are also presented.     

Absolute γ-decay rates of the fc(3.55) from tensor meson dominance and QCD-potentials

We compute the coupling gf_c of the 2⁺⁺ cc? meson f_c(3.55) to the energy-2-momentum tensor, 〈0|T_μν|f_c〉·√ = gf_c?μν, from the QCD-potential of Barbieri, Gatto, Kögerler and Kunszt. Vector meson and tensor dominance then imply, including color, Γ(Ψ' → γf_c) = 20 keV in good agreement with experiment. Other potentials available in the literature yield widths which are larger by up to a factor 2. A naive formulation of vector meson dominance for both γ's in f_c → γγ yields A width which is an order of magnitude above the experimental limit.     

On the electromagnetic couplings of the f and σ mesons

We use the Ward identities for the θ_μνV_?V_λ vertex and the assumptions of f and σ meson dominance of the stress energy momentum tensor θ_μν, and of vector meson dominance of the electromagnetic currents V_? to present estimates for the electromagnetic couplings of the f and σ mesons. A comparison is made with results obtained by other methods.     

Lepton-number violating decays of heavy mesons

The experimental observation of lepton-number violating processes would unambiguously indicate the Majorana nature of neutrinos. Various ΔL=2 processes for pseudoscalar meson M ₁ decays to another pseudoscalar meson M ₂ and two charged leptons ? ₁, ? ₂ (\(M_{1}^{+}\rightarrow \ell_{1}^{+}\ell_{2}^{+}M_{2}^{-}\)) have been studied extensively. Extending the existing literature on the studies of these kinds of process, we consider the rare decays of heavy mesons to a vector meson or a pseudoscalar meson. These processes have not been searched for experimentally, while they may have sizable decay rates. We calculate their branching fractions and propose to search for these decay modes in the current and forthcoming experiments, in particular at the LHCb.     

Probabilistic quark-model approach to proton fragmentation

A probabilistic approach is formulated to study the behaviour of the incident hadron quark flavours in the fragmentation process of high energy protons in lowp _T reactions. Analysis of available data onpp collisions, mainly on hyperon and antibaryon multiplicities, leads to estimates of the probabilities for the different ways in which the incident valence quarks recombine into final hadrons. We find that all three incident quarks emerge in one and the same outgoing nucleon (or nucleon resonance) with probabilityA ₃=0.35–0.4, that two of them emerge in one baryon and the third in another hadron (mostly a meson or meson resonance) with probabilityA ₂=0.6–0.5, and that they emerge in three distinct hadrons (mostly mesons or meson resonances) with probabilityA ₁=0.05–0.1. We find good support for a very simple probabilistic picture of the fragmentation process.     

The QCD sum rule approach for the semileptonic decay of the D or B meson into a light meson and leptons

We use the method of QCD sum rules to treat the semileptonic weak decay of the D or B meson into a light meson and leptons. To obtain the transition form factors, we adopt the two-point Green’s function in the presence of an external vector or axial-vector field. We find that this method can be related approximately to the traditional three-point Green’s function in the heavy quark limit (m _Q → ∞). Unlike some existing QCD sum rule calculations, our results indicate that the form factors have simple dipole or monopole behavior. We obtain results on the various form factors of the semileptonic decay of D and B mesons into a light meson and investigate various decay processes such as B?⁰ → π ⁺ τ _^?ν?_τ and B?⁰ → ρ ⁺ τ^～ν?_τ. The method allows us to take into account nonperturbative strong interaction effects, thereby providing a more reliable determination of the Cabibbo-Kobayashi-Maskawa matrix elements from the experimental data.     

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.     

On the decayK L 0 →l + l −

Using one of the models of Gell-Mannet al. the intermediate vector meson mass is estimated by using the upper limit for the decay of theK _L ^Emphasis>/0 meson into a lepton pair. This mass turns out to be very large. Therefore only the leading terms are taken into account.     

Nuclear bound states of ω mesons

Models based on chiral SU(3)_l ⊗ SU(3)_r symmetry and vector meson dominance suggest an attractive potential for the ω meson in a nuclear medium. We discuss the feasibility of producing nuclear bound states of ω mesons using (d, ³He) and pion induced reactions on selected nuclear targets.     

Monte Carlo Glauber wounded nucleon model with meson cloud

We study the effect of the nucleon meson cloud on predictions of the Monte Carlo Glauber wounded nucleon model for AA, pA, and pp collisions. From the analysis of the data on the charged multiplicity density in AA collisions we find that the meson–baryon Fock component reduces the required fraction of binary collisions by a factor of ~2 for Au + Au collisions at √s = 0.2 TeV and ~1.5 for Pb + Pb collisions at √s = 2.76 TeV. For central AA collisions, the meson cloud can increase the multiplicity density by ~16–18%. We give predictions for the midrapidity charged multiplicity density in Pb + Pb collisions at √s = 5.02 TeV for the future LHC run 2. We find that the meson cloud has a weak effect on the centrality dependence of the ellipticity ?₂ in AA collisions. For collisions of the deformed uranium nuclei at √s = 0.2 TeV, we find that the meson cloud may improve somewhat agreement with the data on the dependence of the elliptic flow on the charged multiplicity for very small centralities defined via the ZDCs signals. We find that the meson cloud may lead to a noticeable reduction of ?₂ and the size of the fireball in pA and pp collisions.     

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.