Glueball spectrum from N_f=2 lattice QCD study on anisotropic lattices

The lowest-lying glueballs are investigated in lattice QCD using N_f = 2 clover Wilson fermions on anisotropic lattices. We simulate at two different and relatively heavy quark masses, corresponding to physical pion masses of mπ～938 MeV and 650 MeV. The quark mass dependence of the glueball masses has not been investigated in the present study. Only the gluonic operators built from Wilson loops are utilized in calculating the corresponding correlation functions. In the tensor channel, we obtain the ground state mass to be 2.363(39) GeV and 2.384(67)GeV at mπ～938 MeV and 650 MeV, respectively. In the pseudoscalar channel, when using the gluonic operator whose continuum limit has the form of ∈_ijkTrB_iD_jB_k, we obtain the ground state mass to be 2.573(55) GeV and 2.585(65) GeV at the two pion masses. These results are compatible with the corresponding results in the quenched approximation. In contrast, if we use the topological charge density as field operators for the pseudoscalar, the masses of the lowest state are much lighter(around 1 GeV) and compatible with the expected masses of the flavor singlet qq meson. This indicates that the operator ∈ijk TrBiDjBk and the topological charge density couple rather differently to the glueball states and qq mesons. The observation of the light flavor singlet pseudoscalar meson can be viewed as the manifestation of effects of dynamical quarks. In the scalar channel, the ground state masses extracted from the correlation functions of gluonic operators are determined to be around 1.4-1.5 GeV, which is close to the ground state masses from the correlation functions of the quark bilinear operators. In all cases, the mixing between glueballs and conventional mesons remains to be further clarified in the future.     

Octet-decuplet baryon mass splittings from self-consistent one-loop perturbation theory

The bag model of confined relativistic quarks in chiral-invariant interaction with scalar, pseudoscalar, vector, and pseudovector mesons, as well as gluons, is used to calculate the masses and wave functions of the spin-1/2 baryon octet and spin-3/2 decuplet, using selfconsistent Brillouin-Wigner bound state perturbation theory. Chiral symmetry breaking is invoked with the sigma model. SU (6) and SU (3) symmetries are broken by the experimental meson spectrum, and a strange quark mass. Mass corrections are calculated to one loop order, limited to the baryons of the octet and decuplet and the lowest lying mesons. Encouraging results are obtained, especially for theΔ — N and theΣ — Λ splittings. Convergence and stability have not been demonstrated, but are evidently improved by the self-consistency requirement. An initial parameter tuning gives a fit to all the octet and decuplet masses within ≦0.02 GeV, at the price of choosing the bag radius, the non-strange baryon input bag mass, and the strange quark mass. Even these small discrepancies can be dramatically reduced by fine-tuning the vector meson coupling and including an instanton contribution peculiar to theΛ.     

The mixing of scalar mesons and the baryon-baryon interaction

By introducing the mixing of scalar mesons in the chiral SU(3) quark model, we dynamically investigate the baryon-baryon interaction. The hyperon-nucleon and nucleon-nucleon interactions are studied by solving the resonating group method (RGM) equation in a coupled-channel calculation. In our present work, the experimental lightest pseudoscalar p \pi, K,h \eta,h^￠ \eta^{{\prime}}_{} mesons correspond exactly to the chiral nonet pseudoscalar fields p \pi, K,h \eta,h^￠ \eta^{{\prime}}_{} in the chiral SU(3) quark model. The h \eta,h^￠ \eta^{{\prime}}_{} mesons are considered as the mixing of singlet and octet mesons, and the mixing angle q_ps \theta_{{ps}}^{} is taken to be -23^° . For scalar nonet mesons, we suppose that there exists a correspondence between the experimental lightest scalar f ₀(600) , k \kappa , a ₀(980) , f ₀(980) mesons and the theoretical scalar nonet s \sigma , k \kappa , s^￠ \sigma^{{\prime}}_{} , e \epsilon fields in the chiral SU(3) quark model. For scalar mesons, we consider two different mixing cases: one is the ideal mixing and another is the q_s \theta_{s}^{} = 19^° mixing. The masses of the s^￠ \sigma^{{\prime}}_{} and e \epsilon mesons are taken to be 980MeV, which are just the masses of the experimental a ₀(980) , f ₀(980) mesons. The mass of the s \sigma meson is an adjustable parameter and is decided by fitting the binding energy of the deuteron, the masses of 560MeV and 644MeV are obtained for the ideal mixing and the q_s \theta_{s}^{} = 19^° mixing, respectively. We find that, in order to reasonably describe the YN interactions, the mass of the k \kappa meson is near 780MeV for the ideal mixing. However, we must enhance the mass of the k \kappa meson for the q_s \theta_{s}^{} = 19^° mixing, the 1050MeV is favorably used in the present work. The experimental s \sigma and k \kappa scalar mesons are very strange, both have larger widths. Hence, no matter what kind of mixing is considered, all the masses of scalar mesons we used in the present work seem to be consistent with the present PDG information.     

Q1(1290) and Q2 (1400) decay rates and their SU(3) implications

We summarize and combine the known information on the decay rates of the strangeness-one axial vector mesons, Q₁ and Q₂. From this information and the rate for B→ωπ, we determine the Q_A?Q_B mixing angle and the S-wave, symmetric and antisymmetric octet couplings for vector-pseudoscalar decays of axial vector mesons. If we assume the D(1285) and the E(1420) belong to the J^PC=1⁺⁺ nonet, we find the A₁ to have a mass of ～1.47 GeV and a large (>0.3 GeV) width.     

Excited flux tube from q¯g hybrid mesons

In the framework of quark models, hybrid mesons are either seen as two-body qˉ systems with an excited flux tube connecting the quark to the antiquark or as three-body qˉg systems including a constituent gluon. In this work we show that, starting from the three-body wave function of the qˉg hybrid meson in which the gluonic degrees of freedom are averaged, the excited flux tube picture emerges as an equivalent qˉ potential. This equivalence between the excited flux tube and the constituent-gluon approach is confirmed for heavy hybrid mesons but, for the first time, it is shown to hold in the light sector too, provided the contribution of the quark dynamics is correctly taken into account.     

Phenomenology of composite colored weak bosons

In composite models of quarks, leptons and weak bosons whereW-constituents are colored objects, color octet partners ofW ^± andZ ⁰ are predicted. We study in detail the phenomenology of these particles. Independent of the specific model one expects a color octet isotriplet of vector bosons (W ₈ ^± ,Z ₈ ⁰ ) with mass in the range of 100–200 GeV, and a color octet isosinglet vector bosonV ₈ ⁰ with substantially larger mass, due to mixing with the gluon. Moreover, relatively light color octet excitations of the leptons appear, while the existence of “color exotic” partners of the quarks is model dependent. These particles decay mainly into a lepton (quark) and a gluon. We construct the couplings ofW ₈ ^± ,Z ₈ ⁰ andV ₈ ⁰ to ordinary and “color exotic” fermions. The signals of color octet weak bosons in low energy weak reactions are explored in detail. The production cross section ofW ₈ ^± (Z ₈ ⁰ ) in hadron-hadron collisions is calculated for \(0.54TeV \leqq \sqrt s \leqq 20TeV\) . Various decay modes of colored weak bosons are studied. The most prominent decay signatures ofW ₈ ^± andZ ₈ ⁰ are events of the type (l ^+-: charged lepton;j: hadronic jet; : missing transverse momentum). The present CERN \(p\bar p\) collider data on such events are discussed in the light ofW ₈ ^± andZ ₈ ⁰ decays. If colored weak bosons are not found with a mass less than ～250 GeV composite model building will be strongly restricted.     

Renormalization-group analysis of the cosmological constraint on the Higgs scalar mass

The standard Model Higgs scalar boson minimally coupled to gravity does not take part in the inflation of the early universe if its mass exceeds a threshold value, which is m _H ^min = 142 GeV in the tree approximation for the potential of the scalar. Two-loop corrections modify this estimate, which becomes m _H ^min = 150 ± 3 GeV. Therefore, higher order corrections of perturbation theory have quite a controllable moderate character, but they are numerically important for experiments.     

Investigation of the decay η′ → 3 π 0 with the GAMS-4π spectrometer

An experiment performed with the GAMS-4π spectrometer resulted in observing 235 ± 45 events of the decay η′ → 3π ⁰. The respective charge-exchange reaction at a momentum of 32.5 GeV/c was used as a source of η′ mesons. The decay branching ratio was found to be Br(η′ → 3π ⁰) = (1.8 ± 0.4) × 10^?3. The slope parameter of the square of the respective matrix element in the linear approximation proved to be β = ?0.59 ± 0.18.     

On the particle multiplicity distributions at high energy

An experiment has been performed to study the inclusive photoproduction of π⁰ mesons. Photoproduced π⁰'s were detected in a hodoscope consisting of 14 lead glass Cerenkov counters. To obtain the cross sections at a photon energy of 6 GeV we used the photon-difference method. Data are presented in terms of the Feynman variable $\text{x = q}{}_6{}^1\text{(√s/2)}$ and the trnasverse momentum q⊥. We have measured four q⊥ distributions at x = 0.2, 0.4, 0.6 and 0.8. The results dhow that the π⁰ rate at small values of q⊥ is smaller than the π± rate. The data can be fitted smoothly by a form A exp (?Bq_⊥²) with a value about 3.5 GeV^?2 for the slope parameter B.     

Real gauge singlet scalar extension of the Standard Model: A possible candidate for cold dark matter

The simplest extension of Standard Model (SM) is considered in which a real SM gauge singlet scalar with an additional discrete symmetry Z ₂ is introduced to SM. This additional scalar can be a viable candidate of cold dark matter (CDM) since the stability of S is achieved by the application of Z ₂ symmetry on S. Considering S as a possible candidate of CDM, Boltzmann’s equation is solved to find the freeze-out temperature and relic density of S for Higgs mass 120 GeV in the scalar mass range 5 GeV to 1 TeV. As HHSS coupling δ ₂ appearing in Lagrangian depends upon the value of scalar mass m _S and Higgs mass m _h, the m _S???δ ₂ parameter space has been constrained by using the Wilkinson microwave anisotropy probe (WMAP) limit on the relic density of DM in the Universe and the results of recent ongoing DM direct search experiments, namely CDMS-II, CoGeNT, DAMA, EDELWEISS-II, XENON-10 and XENON-100. From such analyses, two distinct mass regions are found (a lower and higher mass domain) for such a DM candidate that satisfy both the WMAP limit and the experimental results considered here. The possible differential direct detection rates and annual variation of total detection rates have been estimated for this scalar DM candidate S for two detector materials, namely Ge and Xe. Finally, the γ-ray flux has been calculated from the galactic centre due to annihilation of two 130 GeV scalar DM into two monoenergetic γ-rays.     

J/Psi production in pp collisions at square root = 200 GeV at the BNL relativistic heavy ion collider

We study J/psi production in pp collisions at BNL Relativistic Heavy Ion Collider (RHIC) within the PHENIX detector acceptance range using the color singlet and color octet mechanism which are based on perturbative QCD and nonrelativistic QCD. Here we show that the color octet mechanism reproduces the RHIC data for J/psi production in pp collisions with respect to the p(T) distribution, the rapidity distribution, and the total cross section at square root = 200 GeV. The color singlet mechanism leads to a relatively small contribution to the total cross section when compared to the octet contribution.     

Production of η mesons in e+e− annihilations at √s=29 GeV

Data from e⁺e⁻ annihilations at 29 GeV have been used to measure the production cross section and fragmentation function of η mesons. The signal is observed in the η→γγ decay channel. The fragmentation for p_η>1.5 GeV/c agrees well with the prediction of the Lund model, whereas the prediction of the Webber model lies above the data. The mean multiplicity is measured to be 〈n_η〉=0.58±0.10 η mesons per hadronic event, of which 0.51 represents the direct production of η and η′ mesons in the fragmentation chain.     

Momentum analysis of kaon and pion pairs produced from time-like photons at 1.6 GeV energy

We present results for the total cross section of e⁺e^? annihilation into two hadrons at 1.6 GeV: σ_ππ = σ_KK = (1.8 ± 1.1) × 10^-33 cm².From these values we obtain the time-like electromagnetic form factors these mesons: |F_π|² = 0.24 ± 0.14 and |F_K|² = 0.46 ± 0.26.     

Towards a quantitative description of hadronic weak decays: Evolution equations for heavy flavour mesons

We develop a formalism for describing hadronic weak annihilation decays in analogy to the treatment of deep inelastic lepton-nucleon scattering: we write down evolution equations for colour singlet and octet $\text{(}\text{Q}\text{q}\text{)}$ systems inside mesons of increasing mass. Using D decays as input we can predict weak annihilation decay rates of heavier mesons in a semiquantitative fashion despite our ignorance on bound-state dynamics.     

Resonance structure in the γγ invariant mass spectrum in pC, dC, and dCu interactions

Along with ?? ⁰ and ?? mesons, a resonance structure in the invariant mass spectrum of two photons atM _??? = 360 ± 7 ± 9 MeV is observed in dC interactions at momentum 2.75 GeV/c per nucleon. This resonance structure is not observed in pC collisions at the beam momentum 5.5 GeV/c. The result obtained in the reaction dC is confirmed by the second experiment carried out on the deuteron beam at momentum 3.83 GeV/c per nucleon with a copper target. Some other checks of the observed effect are presented.     

Resonances in the ωω system

Results of a partial-wave analysis for the reaction π ^? → ωωn studied at the VES spectrometer (Institute for High Emergy Physics, Protvino) are presented. The behavior of the J ^PC = 2⁺⁺ amplitudes in the ωω system is described by the f ₂(1565) and f ₂(1910) resonances, whose parameters were fixed at M = 1.590 ± 0.010 GeV and Γ = 0.140 ± 0.011 GeV for the former and at M = 1.890 ± 0.010 GeV and Γ = 0.165 ± 0.019 GeV for the latter. The decay f ₄(2050) → ωω was observed at parameters values of M = 1.960 ± 0.015 GeV, Γ = 0.290 ± 0.020 GeV.     

Color octet contribution in exclusive P-wave charmonium decay into octet and decuplet baryons

In the last years, the need for the color octet state in inclusive P-wave charmonium decay has been firmly established. However, the implications of this in the corresponding exclusive reactions have not been fully recognized. We argue for the necessity of the color octet in P- and higher-wave quarkonium decay. Using a set of phenomenologically constructed baryon wave functions, we consider the decay into an octet and decuplet baryon–antibaryon pair. By doing so, we subject the wave functions to a test of applicability. We show that the color singlet component alone is insufficient to account for the experimental measurements, and only by including the color octet contribution can the partial theoretical decay widths be brought into the range of the data. By the present and earlier applications of the set of wave functions, these show themselves to be reasonable model wave functions at around the scale –20 GeV. Received: 1 March 1999 / Published online: 18 May 2000