Elementary scalar mesons and Regge poles

We show, for the annihilation amplitude of π⁺π^? → two vector mesons, that parity conservation and rotational symmetry demand the existence of a triplet of Regge singularities crossing at t = 0. In the usual scalar-vector field theory, calculations of the leading terms of this amplitude up to the eight order show that these singularities are moving Regge poles. Contrary to common belief, the elementary scalar meson lies on one of them.     

Masses of heavy-light mesons in Regge phenomenology

The masses of some orbitally and radially excited heavy-light mesons are calculated in Regge phenomenology. The results are in reasonable agreement with the experimental data and those given in many other theoretical approaches. Based on the calculation, we suggest that the recently observed D(2550), D(2600) and D(2760) can be assigned as the charmed members of the 2¹S₀, 2³S₁ and 1³D₁ multiplets, respectively. D_s1^*(2700)^± may be assigned as the charm-strange member of the 2³S₁ state. The results may be helpful in understanding the nature of current and future experimentally observed heavy-light mesons.     

Spectroscopy ofQ\bar Qg hybrid mesons

Hybrid mesons composed of a quark, an antiquark, and a gluon are studied in the case of heavy quarks. Their masses are calculated with the potential model which can interpret heavy quarkonium spectroscopy. The ground state of the hybrid mesons \(c\bar cg\) and \(b\bar bg\) is found to be almost spherically symmetric, whereas that of \(t\bar tg\) is two-centered as anH ₂ ⁺ molecule. The \(b\bar bg\left[ {t\bar tg} \right]\) ground state turns out to have a mass below the \(B\bar B\left[ {T\bar T} \right]\) threshold. The excited states contain 0^??, 1^?+ exotic states and 1^?? states which may be examined bye ⁺ e ^? colliders.     

Evidence for non-q \bar q mesons

The non-Abelian nature of QCD suggests that particles that have a gluon constituent, such as glueballs or hybrids, should exist. In addition,q q states are also predicted. This paper describes a search for these non-q q mesons performed by experiment WA 76 using the CERN Omega Spectrometer and discusses three candidates which have been observed.Invited talk at HEXAM 89, Bechyn Castle, Czechoslovakia, June 25–30, 1989.     

Hadroproduction of High-Transverse-Momentum B c mesons within the k T -Factorization approach

With the k _T -factorization approach, the transverse-momentum spectra of B _c mesons at the energies of the Tevatron and LHC hadron colliders are calculated on the basis of the fusion and fragmentation models. In the fusion model, the calculations are performed under the assumption of charm excitation in the proton.     

Elastic electroproduction of \rho mesons at HERA

The elastic electroproduction of mesons is studied at HERA with the H1 detector for a photon virtuality in the range and for a hadronic centre of mass energy in the range GeV. The shape of the () mass distribution in the resonance region is measured as a function of . The full set of spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on , W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large , the cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron–hadron cross sections. Received: 22 February 1999 / Published online: 25 February 2000     

4\pi-decays of scalar and vector mesons

Two different annihilation modes, and , are used to study the 4–decays of scalar and vector mesons. The data are dominated by 4 scalar isoscalar interactions. At least two states are needed, the and the . The 4–decay width of the is more than 6 times larger than the sum of all observed partial decay widths to two pseudoscalar mesons. The state has important couplings to and to . The 4-decays of the (1500) represent about half of its total width. The and the are observed in several 4 decay modes. The ratio of the relative to the decay of the is in contradiction to its proposed interpretation as a pure hybrid state but it suggests that it is not a pure –state either. Our results favour the assignment of the as state, its interpretation as -state is less plausible. Received: 7 December 2000 / Published online: 19 July 2001     

Determination of radiative widths of scalar mesons from experimental results on \gamma\gamma\to\pi\pi

The scalar mesons in the 1 GeV region constitute the Higgs sector of the strong interactions. They are responsible for the masses of all light flavour hadrons. However, the composition of these scalar states is far from clear, despite decades of experimental effort. The two photon couplings of the 's are a guide to their structure. Two photon results from Mark II, Crystal Ball and CELLO prompt a new Amplitude Analysis of , cross-sections. Despite their currently limited angular coverage and lack of polarized photons, we use a methodology that provides the nearest one can presently achieve to a model-independent partial wave separation. We find two distinct classes of solutions. Both have very similar two photon couplings for the and . Hopefully these definitive results will be a spur to dynamical calculations that will bring us a better understanding of these important states. Received: 10 Decmeber 1998 / Published online: 27 April 1999     

N \bar N Annihilation creates two mesons

N \(\bar N\) annihilation is assumed to occur exclusively via two-meson production, with nearest threshold dominance. A phenomenological expression for the branching ratios, implementing the rule, contains two parameters. The set ofs- andp-wave (q \(\bar q\) ) mesons is used. Reasonable results are obtained for rates measured inp \(\bar p\) annihilation at rest. The numerous channels are projected into the multipion and kaon final states for comparison with in-flight experiments. A good overall agreement is reached up top _lab～3 GeV/c; beyond, more mesons should be included to provide new thresholds.     

Spectroscopy,decay properties and Regge trajectories of the B and B_s mesons

A Gaussian wave function is used for detailed study of the mass spectra of the B and BS mesons using a Cornell potential incorporated with a O(1/m) correction in the potential energy term and expansion of the kinetic energy term up to O p~(10) for relativistic correction of the Hamiltonian.The predicted excited states for the B and B_s mesons are in very good agreement with results obtained by experiment.We assign B_2(5747) and B_(s2()5840) as the 1~3P~2 state,B1(5721) and Bs1(5830) as the 1P_1 state,B0(5732) as the 1~3P_0 state,B_(s1)(5850) as the 1~P 1 state and B(5970) as the 2~3S_1 state.We investigate the Regge trajectories in the(J,M~2) and(nr,M~2) planes with their corresponding parameters.The branching ratios for leptonic and radiative-leptonic decays are estimated for the B and BS mesons.Our results are in good agreement with experimental observations as well as outcomes of other theoretical models.     

Spectra and decays of $\pi \pi$ and $\pi K$ atoms

We describe the spectra and decays of and 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 atom in its ground state yields s.Received: 9 May 2004, Published online: 23 July 2004     

$VA\widetilde{V}$ correlator within the instanton vacuum model

The correlator of vector and non-singlet axial-vector currents in the external electromagnetic field is calculated within the instanton liquid model of the QCD vacuum. In general the correlator has two Lorentz structures: longitudinal, w_L, and transversal, w_T, with respect to the axial-vector index. Within the instanton model the saturation of the anomalous w_L structure is demonstrated. It is known that in the chiral limit the transversal structure w_T is free from perturbative corrections. In this limit within the instanton model we calculate the transversal invariant function w_T at arbitrary space-like momentum transfer q and show the absence of power corrections to this structure at large q². Instead there arise exponential corrections to w_T at large q² reflecting non-local properties of the QCD vacuum. The slope of w_T at zero virtuality, the QCD vacuum magnetic susceptibility of the quark condensate and its momentum dependence are estimated.Received: 7 May 2005, Published online: 6 July 2005     

Towards a model-independent determination of the $\phi\to \gamma f_0$ coupling

A guide to the composition of the enigmatic f ₀(980) and a ₀(980) states is their formation in -radiative decays. Precision data are becoming available from the KLOE experiment at the DA NE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f ₀(980) to this channel can be extracted from these, independently of the background provided by production. To do this we use the fact that the behaviour of both the f ₀(980) and cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the is GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f ₀(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the branching ratio which can only be fixed by further precision data on the f ₀(980). Nevertheless, the is now the same order of magnitude as the experimental .Received: 25 March 2003, Published online: 5 September 2003