arXiv subjects
Publications and source records attributed to T. Barnes.
In this talk I summarize the status of exotic mesons, including both theoretical expectations and experimental candidates. The current experimental candidates are ``spin-parity exotics''; since these are most often considered possible hybrid mesons, the theoretical discussion will be mainly concerned with hybrids. The exotic meson candidates discussed are the surprisingly light pi_1(1400) and pi_1(1600).
We apply a quark interchange model to spin-dependent and exotic meson-meson scattering. The model includes the complete set of standard quark model forces, including OGE spin-orbit and tensor and scalar confinement spin-orbit. Scattering amplitudes derived assuming SHO and Coulomb plus linear plus hyperfine meson wavefunctions are compared. In I=2 pi pi we find approximate agreement with the S-wave phase shift from threshold to 1.5 GeV, where we predict an extremum that is supported by the data. Near threshold we find rapid energy dependence that may reconcile theoretical estimates of small scattering lengths with experimental indications of larger ones based on extrapolation of measurements at moderate kpi^2. In PsV scattering we find that the quark-quark L*S and T forces map into L*S and T meson-meson interactions, and the P-wave L*S force is large. Finally we consider scattering in J^PC-exotic channels, and note that some of the Deck effect mechanisms suggested as possible nonresonant origins of the pi_1(1400) signal are not viable in this model.
In this contribution we summarize experimental information and theoretical results for the dissociation cross sections of charmonium by light hadrons. Theoretical predictions for these RHIC-related processes differ by orders of magnitude over the physically relevant energy range. The results found by the author and collaborators using a constituent interchange model, which predicts cross sections in the mb region near threshold, are discussed in more detail.
We report measurements of the two-magnon states in a dimerized antiferromagnetic chain material, copper nitrate (\QTR{group}{Cu(NO$_{3}$)$_{2}\cdot 2.5$D$_{2}$O}). Using inelastic neutron scattering, we have studied the one- and two-magnon excitation spectra in a large single crystal of this material. We compare this new data with perturbative expansions of the alternating Heisenberg chain and find good agreement with these calculations. The data may also show evidence for the recently proposed S=1 two-magnon bound state (Phys. Rev. B54, R9624 (1996)).
We evaluate the cross sections for the dissociation of $J/ψ$ and $ψ'$ by $π$ and $ρ$ at low collision energies, using the quark-interchange model of Barnes and Swanson. The dissociation cross section for $J/ψ$ by $π$ is found to be relatively small with a maximum of about 1 mb and a kinetic energy threshold of 0.65 GeV. The pion-induced $ψ'$ dissociation cross section is found to be much larger, with a maximum of about 5 mb and a lower threshold. Dissociation cross sections for $J/ψ$ and $ψ'$ by $ρ$ mesons are also evaluated and are found to be large near threshold.
Using the quark-interchange model of Barnes and Swanson, we evaluate the dissociation cross sections for $J/ψ$ and $ψ'$ by $π$ and $ρ$ at low collision energies. In collisions with $π$ mesons near threshold the $π+ J/ψ$ dissociation cross section is predicted to be small, but the $π+ψ'$ cross section is found to be quite large, in qualitative agreement with experimental data on $J/ψ$ and $ψ'$ production in high-energy heavy-ion collisions. The $ρ+ J/ψ$ and $ρ+ ψ'$ dissociation cross sections are both predicted to be large numerically and are divergent near threshold. These $ρ+ J/ψ$ and $ρ+ ψ'$ cross sections show considerable sensitivity to the mass of the $ρ$ meson if it is off energy shell.
In this contribution I discuss recent developments in light meson spectroscopy, and note specific areas in which DAFNE is an especially appropriate tool for future experiments. One topic of special relevance is the spectroscopy of excited vector mesons; quite narrow vector hybrids are predicted by the flux-tube model, which could be produced by DAFNE when operating in the $M_{e^+e^-}\approx 1.5-2$ GeV range. A second topic, which would be appropriate for a later date because it requires a rather higher beam energy, is the production of C=(+) mesons in $γγ$ collisions.
In this contribution I review recent experimental developments in the spectroscopy of higher-mass mesons, especially candidate radial excitations discussed at the WHS99 meeting in Frascati.
In this contribution I discuss prospects for photoproducing hybrid mesons at CEBAF, based on recent model results and experimental indications of possible hybrids. One excellent opportunity appears to be a search for the I=1, JPC=2+-, neutral "(b2)o" hybrid in (a2 pi)o through diffractive photoproduction. Other notable possibilities accessible through pi+ or pio exchange photoproduction are I=1, JPC=1-+, charged "pi1+" in f1 pi+, (b1 pi)+ and (rho pi)+; piJ(1770)+ in f2 pi+ and (b1 pi)+; pi(1800)+ in f0 pi+, f2 pi+, omega rho+ and (rho pi)+; a1 in f1 pi+ and f2 pi+; and omega in (rho pi)o, omega eta and (K1 K)o.
We present V(RI)sub data for thirteen Cepheids in the Large Magellanic Cloud ans fifty-five in each wavelength band. The median uncertainty in the photometry iy Moffett, Gieren & Barnes (1998) which contained 1000 measures ($\pm 0.01$ mag) in each wavelength band on 22 variables with periods in the range 8--133 days.
In this paper we derive quark model results for scattering amplitudes and equivalent low energy potentials for heavy meson pairs, in which each meson contains a heavy quark. This "BB" system is an attractive theoretical laboratory for the study of the nuclear force between color singlets; the hadronic system is relatively simple, and there are lattice gauge theory (LGT) results for V_BB(r) which may be compared to phenomenological models. We find that the quark model potential (after lattice smearing) has qualitative similarities to the LGT potential in the two B*B* channels in which direct comparison is possible, although there is evidence of a difference in length scales. The quark model prediction of equal magnitude but opposite sign for I=0 and I=1 potentials also appears similar to LGT results at intermediate r. There may however be a discrepancy between the LGT and quark model I=1 BB potentials. A numerical study of the two-meson Schrodinger equations in the (bqbar)(bqbar) and (cqbar)(cqbar) sectors with the quark model potentials finds a single "molecule", in the I=0 BB* sector. Binding in other channels might occur if the quark model forces are augmented by pion exchange.
In this paper we present results for the ground state and low-lying excitations of the $S=1/2$ alternating Heisenberg antiferromagnetic chain. Our more conventional techniques include perturbation theory about the dimer limit and numerical diagonalization of systems of up to 28 spins. A novel application of multiple precision numerical diagonalization allows us to determine analytical perturbation series to high order; the results found using this approach include ninth-order perturbation series for the ground state energy and one magnon gap, which were previously known only to third order. We also give the fifth-order dispersion relation and third-order exclusive neutron scattering structure factor for one-magnon modes and numerical and analytical binding energies of S=0 and S=1 two-magnon bound states.
Magnetic excitations have been investigated in the spin dimer material VODPO_4 \cdot 1/2 D_2O using inelastic neutron scattering. A dispersionless magnetic mode was observed at an energy of 7.81(4) meV. The wavevector dependence of the scattering intensityfrom this mode is consistent with the excitation of isolated V^{4+} spin dimers with a V-V separation of 4.43(7) Å. This result is unexpected since the V-V pair previously thought to constitute themagnetic dimer has a separation of 3.09 Å. We identify an alternative V-V pair as the likely magnetic dimer, which involves superexchange pathways through a covalently bonded PO_4 group. This surprising result casts doubt on the interpretation of (VO)_2P_2O_7 as a spin ladder.
Magnetic excitations in an array of (VO)_2P_2O_7 single crystals have been measured using inelastic neutron scattering. Until now, (VO)_2P_2O_7 has been thought of as a two-leg antiferromagnetic Heisenberg spin ladder with chains running in the a-direction. The present results show unequivocally that (VO)_2P_2O_7 is best described as an alternating spin-chain directed along the crystallographic b-direction. In addition to the expected magnon with magnetic zone-center energy gap Δ= 3.1 meV, a second excitation is observed at an energy just below 2Δ. The higher mode may be a triplet two-magnon bound state.
We discriminate gluonic hadrons from conventional $q\bar q$ states by surveying radial and orbital excitations of all I=0 and I=1 $n\bar n$ systems anticipated up to 2.1 GeV. We give detailed predictions of their quasi-two-body branching fractions and identify characteristic decay modes that can isolate quarkonia. Several of the ``missing mesons'' with L$_{q\bar q}=2$ and L$_{q\bar q}=3$ are predicted to decay dominantly into certain S+P and S+D modes, and should appear in experimental searches for hybrids in the same mass region. We also consider the topical issues of whether some of the recently discovered or controversial meson resonances, including glueball and hybrid candidates, can be accommodated as quarkonia.
In this letter we report results from inelastic neutron scattering experiments on powder samples of vanadyl pyrophosphate, (VO)2P2O7. We see evidence for three magnetic excitations, at 3.5 meV, 6.0 meV and 14 meV. The intensity of the 3.5 meV mode is strong near Q=0.8 A-1, consistent with the one-magnon gap mode reported previously and predicted by the spin-ladder model. The magnetic scattering at 14 meV may be due to the top of the one-magnon band or the two-magnon continuum predicted in the ladder model. The 6.0 meV mode also peaks in intensity at Q=0.8 A-1. This mode has not been reported previously and was not anticipated by existing theoretical treatments of the spin ladder.
We argue that an experimental search for an $η_c'$, the first radial excitation of the $η_c(2980)$, may be carried out using the two photon process $e^+e^- \to e^+e^- γγ\ra e^+e^-η_c'$. We estimate the partial width $Γ_{γγ}(η_c')$ and the branching fraction $B(η_c' \to h)$, where $h$ is an exclusive hadronic channel, and find that for $h = K^o_s K^\pm π^\mp$ it may be possible to observe this state in two photon collisions at CLEO-II.
Open-flavor strong decays are mediated by $q\bar q$ pair production, which is known to occur dominantly with \3p0 quantum numbers. The relation of the phenomenological \3p0 model of these decays to ``microscopic" QCD decay mechanisms has never been clearly established. In this paper we investigate $q\bar q$ meson decay amplitudes assuming pair production from the scalar confining interaction (sKs) and from one gluon exchange (OGE). sKs pair production predicts decay amplitudes of approximately the correct magnitude and D/S amplitude ratios in $b_1\toωπ$ and $a_1\toρπ$ which are close to experiment. The OGE decay amplitude is found to be subdominant in most cases, a notable exception being $^3$P$_0\to{}^1$S$_0+{}^1$S$_0$. The full sKs~+~OGE amplitudes differ significantly from \3p0 model predictions in some channels and can be distinguished experimentally, for example through an accurate comparison of the D/S amplitude ratios in $b_1\toωπ$ and $a_1\toρπ$.