arXiv subjects
Publications and source records attributed to D. V. Bugg.
The phase variation of the sigma -> pi-pi amplitude is accurately determined as a function of mass from BES II data for J/Psi -> omega-pi-pi. The determination arises from interference with the strong b1(1235)-pi amplitude. The observed phase variation agrees within errors with that in pi-pi elastic scattering.
The threshold pbar-p peak in BES data for J/Ψto gamma-pbar-p may be fitted as a cusp. It arises from the well known threshold peak in pbar-p elastic scattering due to annihilation. Several similar examples are discussed. The PS185 data for pbar-p to Lambdabar-Lambda require an almost identical cusp at the Lambdabar-Lambda threshold. There is also a cusp at the Sigma-N threshold in Kminus-d to piminus-Lambda-p. Similar cusps are likely to arise at thresholds for all 2-body de-excitation processes, providing the interaction is attractive; likely examples are Lambda-pbar, Sigma-pbar, and Kbar-Lambda. The narrow peak observed by Belle at 3872 MeV in piplus-piminus-J/Psi may be a 1++ cusp due to the Dbar-D* threshold. The narrow Xi*(1862) observed by NA49 may be due to a threshold cusp in Sigma(1385)-Kbar coupled to Xi-pi and Sigma-Kbar. The relation of cusps to known resonances such as fo(980) is discussed.
A correct understanding and description of the I=2 pi-pi S-wave interaction is important for the extraction of the I=0 pi-pi S-wave interaction from experimental data and for understanding the I=0 pi-pi S-wave interaction theoretically. With t-channel rho, f2(1270) exchange and the pi pi -> rho rho -> pi pi box diagram contribution, we reproduce the pi-pi isotensor S-wave and D-wave scattering phase shifts and inelasticities up to 2.2 GeV quite well in a K-matrix formalism.
We describe the spectra and decays of pi pi and pi K atoms within a non-relativistic effective field theory. The evaluations of the energy shifts and widths are performed at next-to-leading order in isospin symmetry breaking. We provide general formulae for all S-states, and discuss the states with angular momentum one in some detail. The prediction for the lifetime of the pi K atom in its ground-state yields tau = (3.7 \pm 0.4) * 10^{-15} sec.
The latest $πN$ elastic scattering data are re-analysed to determine the coupling constant $g_c$ of the charged pion, using the dispersion relation for the invariant amplitude $B^{(+)}$. Depending on the choice of data-base, values $g^2_c/4π= 13.80$ to 13.65 are obtained with errors of $\pm 0.12$. We re-examine the well known discrepancy with the Goldberger-Treiman relation. After allowing for the mass dependence of the pion decay constant $f_π$, a (2-3)% discrepancy is predicted, hence $g^2_c/4π= 13.74 \pm 0.10$ in the prior case. The mass difference between charge states of $Δ(1232)$ is $M^0 -M^{++} = 2.0 \pm 0.4$ MeV, close to twice the mass difference between neutron and proton. The difference in widths on resonance is $Γ^0 - Γ^{++} =3.8 \pm 1.0$ MeV. One may account for a width difference of 4.5 MeV from phase space for decays and the extra channel $Δ^0 \to γn$.
With t-channel rho, f2(1270) exchange and the pi pi -> rho rho -> pi pi box diagram contribution, we reproduce the pi pi isotensor S-wave and D-wave scattering phase shifts and inelasticities up to 2.2 GeV quite well in a K-matrix formalism. The t-channel rho exchange provides repulsive negative phase shifts while the t-channel f2(1270) gives an attractive force to increase the phase shifts for pi pi scattering above 1 GeV, and the coupled-channel box diagram causes the inelasticities. The implication to the isoscalar pi pi S-wave interaction is discussed.
J/psi and psi' decay to mesons are a good place to look for glueballs, hybrids and for extracting strange and nonstrange components in mesons. Abundant J/psi and psi' events have been collected at the Beijing Electron Positron Collider (BEPC). More data will be collected at upgraded BEPC and CLEO-C. Here we provide explicit PWA formulae for many interesting channels in the covariant tensor formalism.
Mass ratios of glueballs predicted by the latest Lattice QCD calculations in the quenched approximation agree well with four prime experimental candidates.
We calculate partial widths for the decays a_0(980)\toγγand f_0(980)\toγγunder the assumption that a_0(980) and f_0(980) are members of the basic 1^3P_0 q\bar q nonet. The results are in a reasonable agreement with data thus giving an argument for a q\bar q origin of these mesons. We also calculate the γγpartial widths for the other scalar mesons, members of the 2^3P_0 q\bar q nonet.
We discuss a mechanism by which a set of $q\bar q$-states mixes with an exotic one, so that the exotic state accumulates the widths of the overlapping $\bar qq$ resonances. The broad state created this way acts as a 'locking' state for the others. Using results of a previous analysis of the $(IJ^{PC}=00^{++})$-wave, we estimate the mean radius squared of the broad state $f_0 (1530^{+90}_{-250})$; it appears to be distinctly larger than the mean squared radii of the locked narrow states. This supports an idea about the constructive role of broad states in forming the confinement barrier.
We present a dissenting view of some aspects of the work of the Crystal Barrel collaboration.
We discuss the mechanism of broad state formation when one of several overlapping resonances accumulates the widths of others. This mechanism may be important in the mixing of quark states with exotic ones. The broad resonance acts as a locking state for other states which mix with it; we consider the role of the broad state in the formation of the confinement barrier.
The background due to the direct diffractive dissociation of the photon into the $π^+π^-$-pair to the "elastic" diffractive $ρ^0$-meson production in electron-proton collisions is calculated. The amplitude for the background process $γp \to π^+ π^- p$ is proportional to the $π$-meson - proton cross section. Therefore, describing the HERA data, we can estimate $σ(πp)$ at energy $s_{πp}\sim (2 - 3) 10^{3} GeV^2$ that is considerably higher the existing data. At large $Q^2$ the interference between resonant and non-resonant $π^+ π^-$ production leads also to the more slow increase of the $σ^L/σ^T$ ratio with the mass of the $2π$ (i.e. $ρ^0$-meson) state.
Data on $J/Ψ\to γ(ρρ)$ demand a broad $0^-$ $ρρ$ signal, attributable to a glueball with a mass of 1750--2100 MeV. Decays of this broad state to $ρρ$, $ωω$, $K^*\bar K^*$ and $ϕϕ$ channels agree well with flavour blindness. The narrow $ι(1440)$ may be attributed to mixing between the glueball and the $s\bar s$ radial excitation. The latter is pushed down in mass by repulsion between the two levels. We conjecture that the $2^+$ glueball may likewise be broad. Mixing between it and the $2^3P_2~q\bar q$ and $s\bar s$ radial excitation can explain the appearance of $f_2(1565)$ and a $2^+$ $Θ(1710)$ at masses lower than anticipated. Mixing with higher $q\bar q$ states can explain the $2^+$ resonance at 1920 MeV and also $ϕϕ$ signals observed by Etkin et al. and by the JETSET collaboration.
High partial waves for $pp$ and $np$ elastic scattering are examined critically from 210 to 800 MeV. Non-OPE contributions are compared with predictions from theory. There are some discrepancies, but sufficient agreement that values of the $πNN$ coupling constants $g_0^2$ for $π^0$ exchange and $g^2_{c}$ for charged $π$ exchange can be derived. Results are $g^2_0 = 13.91 \pm 0.13 \pm 0.07$ and $g^2_c = 13.69 \pm 0.15 \pm 0.24$, where the first error is statistical and the second is an estimate of the likely systematic error, arising mostly from uncertainties in the normalisation of total cross sections and $dσ/dΩ$.