Pseudoscalar States Research Articles

New resonance production in e +e − collisions

Based on the large rate of radiative Z decays, estimates for production and subsequent γ decay of possible narrow scalar or vector resonances are derived for e +e − colliders. From this, also model-independent lower bounds on their total production rates can be deduced. γγ experiments could set stringent limits on masses and widths of (pseudo) scalar states.

Mechanism of chiral symmetry breakdown in quantum chromodynamics

Abstract A specific dynamical mechanism is proposed of chiral symmetry breakdown in QCD according to which a light pseudoscalar bound state is formed out of every color-neutral quark-antiquark combination of light quarks for which the associated axial current q γ μ γ 5 q is conserved exactly in the limit of vanishing quark masses. The pseudoscalar meson mass is of order m Λ s where Λ s is the QCD mass scale and m the quark mass assumed much smaller than Λs. No light scalar or vector meson is formed by this mechanism.

Identification of a Pseudoscalar State at 1440 MeV INJψRadiative Decays.

Identification of a Pseudoscalar State at 1440 MeV IN<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mi>J</mml:mi></mml:mrow><mml:mrow><mml:mi>ψ</mml:mi></mml:mrow></mml:mfrac></mml:math>Radiative Decays.

Self-consistent meson mass spectrum

A dual-topological-unitarization (or dual-fragmentation) approach to the calculation of hadron masses is presented, in which the effect of planar ''sea''-quark loops is taken into account from the beginning. Using techniques based on analyticity and generalized ladder-graph dynamics, we first derive the approximate ''generic'' Regge-trajectory formula ..cap alpha..(t) = max (S/sub 1/+S/sub 2/, S/sub 3/+S/sub 4/)-(1/2) +2alpha-circumflex'(s/sub a/ +(1/2)(t-summationm/sub i/ /sup 2/)) for any given hadronic process 1+2..-->..3+4, where S/sub i/ and m/sub i/ are the spins and masses of i = 1,2,3,4, and ..sqrt..s/sub a/ is the effective mass of the lowest nonvanishing contribution (a) exchanged in the crossed channel. By requiring a minimization of secondary (background, etc.) contributions to a, and demanding simultaneous consistency for entire sets of such processes, we are then able to calculate the masses of all the lowest pseudoscalar and vector qq-bar states with q = u,d,s and the Regge trajectories on which they lie. By making certain additional assumptions we are also able to do this with q = u,d,c and q = u,d,b. Our only arbitrary parameters are m/sub rho/, m/sub K/*, m/sub psi/, and m/sub Upsilon/, one of which merely serves to fix the energy scale. In contrast to many other approaches,more » a small m/sub ..pi../ /sup 2//m/sub rho/ /sup 2/ ratio arises quite naturally in the present scheme.« less

Anomalous Ward identities and ψ→γη(η′), ψ′ →ψπ0(η) decay rates

Anomalous Ward identities saturated with one-particle pseudoscalar states, together with π0, η and η′ → 2γ decay amplitudes and Γ(ψ → η′γ)/Γ(ψ → ηγ), Γ(ψ′ → ψπ0)/Γ(ψ′ → ψη) branching ratios, provide a set of equations which can be solved for the axial-vector couplings and the topological charge components.

The glueball G(1440) and radially excited pseudoscalar states

It is pointed out that there exist two isoscalar 0 −+ states near 1.4 GeV besides the axial-vector E(1420), one is a glueball and the other is a member of the radially excited pseudoscalar nonet. The relationship between the (2 1S 0)- and (1 3P 1)- trajectories is discussed.

Pseudoscalars and vector mesons in a unitary and self-consistently broken SU(6) W scheme

We estimate hadronic self-energy effects to “bare” pseudoscalar (P) and vector (V) meson states due to theP→PV→P, P→VV→P, V→ PP→V, V→PV→V andV→VV→V loops. We simulate higher order diagrams by consistently requiring external and internal particles to have the same mass. We find good agreement with all the experimental masses (exceptmπ), widths and mixing angles. The “bare”P andV states are heavy (≈1.26 GeV) and degenerate up to a smallms−mu quark mass difference term. The “bare” coupling constants for thePPV, PVV andVVV vertices obey exact OZI rule and almost exact SU(6)W symmetry. We use a common cut-off ofkcm≃0.7 GeV/c corresponding to a harmonic oscillator radius of ≃0.7 fm for all SU(6)W related thresholds except for the pion.

Relativistic Wave Equation and Mass Spectrum of Gluonium

A relativistic wave equation is derived for gauge-invariant J=0 gluonium amplitudes, and show that its reduced eigenvalue equation is identical with that for a quark-antiquark system in /sup 3/P/sub 1/ states. Analysing relations between potentials in the two respective systems, I obtain an upper limit of 2 GeV to the ground-state mass if I take light quarkonium as a reference system, whereas I estimate the ground state to lie between 2.5 and 3 GeV if I use charmonium potential parameters. The scalar and the pseudoscalar gluonium states are degenerate in the present approach.

In search of scalar gluonium

We discuss a scalar meson coupled strongly to gluons. Radiative decays of the J/ψ are taken as a source of gluons so that our aim is to calculate Γ(J/ ψ→ σγ), where σ is the presumed scalar gluonium. We use QCD sum rules to find both 〈0| α s G μν a G μν a | σ〉 (where G μν a is the gluon field strength tensor) and Γ(J/ ψ→ σγ) in terms of 〈0| α s G μν a G μν a | σ〉. The final prediction for the width is expected to be valid within a factor of two and gives Γ( J/ψ→σγ→ two pions in S-wave + γ) ⋍ 25 eV for m σ = 700 MeV . Non-perturbative QCD naturally explains the observed asymmetry between scalar and pseudoscalar states in the radiative decays of the J/ψ. Some general remarks on gluonium in QCD are made.

Heavy quarkonium decay in the presence of instantons

The instanton contribution to the on-shell quark-antiquark annihilation amplitude is investigated by means of the dilute gas approximation in the limit of large quark masses. We find that the instanton correction - evaluated with an instanton scale size cut off ρc - to the decay rate of pseudoscalar states is not necessarily positive and decreases with the inverse of the quark mass squared. There is no instanton contribution to the decay of vector states.

Charmed meson spectra

We have done a relativistic computation of charmed meson spectra using an effective quark-quark interaction (with a scalar confining interaction and the asymptotic freedom constraint in the short-range part), which gives a good description of the charmomium and bottomium properties up to the problems related to the pseudoscalar states. The mass of D 0 is correctly reproduced using a light quark mass of 0.31 GeV, the hyperfine splitting is slightly too large (by about 30%). Radiative decays are computed as well as π-decays using PCAC. The results have been extended to the new-flavoured mesons. We have also explicitly verified the necessity of a relativistic treatment of the light quark.

A phenomenological model for pseudoscalar meson mixing

Conventional models of η-η′ mixing are extended to include radial excitations in the mass matrix. The number of free parameters is minimized by using the Quigg-Rosner logarithmic potential to obtain properties of radially excited states. The remaining parameters are fixed by fitting observed masses. The wave functions obtained by diagonalizing the mass matrix give an η similar to the conventional description, 99% ground state and mainly octet but a very different η′ with a 50% admixture of radial excitations, and the s s configuration dominant in the ground-state component. This η′ wave function modifies the bad quark-model predictions for peripheral production by introducting form factors which lead to new predictions in agreement with experiment. Additional isoscalar pseudoscalar states are predicted around 1280 and 1500 MeV. Applications to radiative vector meson decays and charmonium are also discussed.

Radiative decays of heavy particles in the geometrodynamical approach

We calculate the radiative decays of the new particles in the geometrodynamical theory of hadrons. Very good results are obtained forE1 transitions, while theM1 transitions fail in describing the J/ψ and ψ′ transitions to the X(2830) and the χ(3455) interpreted as pseudoscalar states. On this basis we speculate that the X(2830) might be interpreted as nonrelativistic bound states «molecules» of $$\left( {D\bar D} \right)$$ and the χ(3455) might be called η c (3340).

New-particle spectroscopy, The Lorentz structure of the confining quark-quark interaction and asymptotic freedom

In this work we investigate the information which can be found on the Lorentz structure of the confining interaction from the new-particle spectroscopy. Although not conclusive, some slight evidence in favour of a scalar-type confining interaction can be found in charmonium. We have also treated exactly the asymptotic freedom constraint on the one-gluon exchange interaction and found some significant improvements on the theoretical interpretation of charmonium properties, as well as a good description of upsilon spectroscopy. However, the problems related to the pseudoscalar states remain unsolved.

Remarks about asymptotic freedom and upsilon

Assuming a universal confining interaction which increases linearly with the distance between the quarks and treating exactly the asymptotic freedom constraint on αs, we find a consistent description of the new particle spectroscopy (up to the problems related to the pseudoscalar states) for an effective value of αs at small Q2 of the order of 0.4. In charmonium, a scalar-type confining interaction could be slightly preferred.

Duality constraints for charmed-particle spectroscopy

Constraints on the charmed-meson mass spectrum and couplings are obtained from pole-saturated FESR. The Regge-trajectory slopes are predicted to vary inversely with respect to the mass of the lowest pseudoscalar state, while the asymptotic energy scale factors show no sign of becoming greater than the canonical 1.0 (GeV)2. Strong couplings are found to be larger than naiveSU4 predictions.

Decay widths of vector mesons in a relativistic quark model

The relativistic quark model of B6HM, Joos and KRAMMER (1) has been successfully applied to many meson decays: radiative, leptonie, semileptonie and nonleptonic decays (2). In this model the mesons are quark (q)-antiquark (~) bound-state solutions of the Wick-rotated Bethe-Salpeter (BS) equation with a 4-dimensional harmonic oscillator kernel. The advantage of this model is that all quark loop diagrams which contain at least one BS amplitude are convergent. I n this note we wish to report on dynamical calculations of the decay widths of vector mesons. The BS amplitudes for the pseudoscalar (P) and vector (V) meson ground states are given by

SU(3) breaking in the two-body decays of the Ψ(3100)

Motivated by the experimental fact that the ψ(3100) does not appear to behave like an SU(3) singlet when it decays into a vector pseudoscalar final state, we propose a model for SU(3) breaking in ψ decays. In the model we envision the ψ decay as a two-stage'process. In the first stage the quark-antiquark pair which comprises the ψ annihilate via a Zweig rule violating interaction to create a pair of “ordinary” quarks. We allow this interaction to violate SU(3) invariance so that all quarks may not be created equally. In stage two the quark pair turns itself into hadrons via a Zweig-allowed, SU(3)-invariant interaction. The data for the vector-pseudoscalar decays seem to indicate that the intermediate quark pair behaves like a heavy ω. We then use this “fact”. to make predictions for the baryon-antibaryon and the tensor-vector decays.

Radiative decays of the new mesons in the Harari quark model

The Harari quark model is used to analyse the radiative decays of the narrow resonances in the spirit of an earlier investigation for the “old” mesons due to Van Royen and Weisskopf. We find Γ( Ψ(3.1)→ η(2.8) γ)=6.2 keV as against 30 keV predicted by the charm model. The spectroscopy of the pseudoscalar states and their radiative decays are also briefly discussed.

Space reflection symmetry and the pseudo-scalar magnetic charge

Conserved angular momentum and generalized space reflection operators are built for the non-relativistic dyonium with the pseudo-scalar magnetic charge and states diagonalizing them are found. These states belong to different spinor classes provided one uses integer or half-integer numbers in the charge quantization condition.