Quark Model Predictions Research Articles

Weakly model dependent pion form factor with physically interpretable parameters

We have constructed the pion form factor model satisfying fundamental principles, providing some freedom for the asymptotic behaviour and depending only on the adjustable parameters with a definite physical interpretation. The explicit incorporation of the pion form factor left-hand cut from the second Riemann sheet into a model was carried out for the first time. As a result we have described (contrary to the previous attempts [18, 19]) the pion form factor data from the range of momenta −9·770 GeV2 ≦t ≦ 9·579 GeV2 and data on theP-wave isovectorππ phase shift in the elastic region simultaneously with the adjustable parameters acquiring very reasonable values. The asymptotic behaviour was enforced by the data to be consistent with the naive quark model prediction. The calculated values of the pion charge radius as well as theP-wave isovectorππ scattering length coincide with the world averaged values. With regard to these positive features of our pion form factor model it can be employed for the reliable calculation (via unitarity) of theP-wave isovectorππ scattering partial amplitude outside the physical region, which could be useful in a saturation of various sum rules inππ scattering physics.

The reactionsK ? p?? ? ?(1385)� at 8.25 GeV/c

The reactionsK−p→π∓Σ(1385)± are studied at an incident laboratory momentum of 8.25 GeV/c using data from a high statistics (≃180 events/μb) bubble chamber experiment. In the case of the reactionK−p→π−Σ(1385)+ an amplitude analysis is performed and the complete Σ(1385)+ spin density matrix is extracted as a function oft′. The results are compared with the predictions of the additive quark model. In the case of the reactionK−p→π+Σ(1385)− the cross-sections for forward and backward production are determined.

Dependence of multiplicity and rapidity distributions on the number of projectile collisions in 200-GeV/cproton-nucleus interactions

Interactions of 200-GeV/c protons on hydrogen, neon, argon, and xenon were studied with a streamer-chamber spectrometer. The number of projectile collisions inside the nucleus and the number of secondary collisions in the intranuclear cascade were estimated. The dependence of multiplicity and rapidity distributions on the number of projectile collisions was analyzed. The predictions of the additive quark model were found to be in qualitative agreement with the results of the experiment.

Non-leptonic decays of charmed baryons in the MIT bag model

Non-leptonic decays of lower mass charmed baryons are calculated by employing the QCD corrected weak hamiltonian of the Weinberg-Salam model and wave functions of the MIT bag model. The results are compared with quark model predictions.

Suppression ofV→Pγdecay rates due to the spin-spin force from quantum chromodynamics

It is shown that the discrepancy between the naive quark-model prediction and the experimental decay rate of $V\ensuremath{\rightarrow}P\ensuremath{\gamma}$ comes from the difference of the wave functions between $^{3}S_{1}$ and $^{1}S_{0}$ states due to the spin-spin force.

Charged-Current Neutrino Interactions

Deep inelastic ..nu..N interactions are reviewed. Quark model predictions are given and structure functions analyzed. (AIP)

Radiative width of the K ∗+ (1430)

Using the Primakoff formalism, we have extracted the radiative decay width of the K ∗+(1430) produced in coherent interactions of 200 GeV/ c K + mesons in nuclear targets. The width obtained is 240 ± 45 keV, a value reasonably consistent with quark-model predictions.

Radiative width of the A 2(1310)

Using the Primakoff formalism, we have extracted the radiative decay width of the A + 2(1310) produced in coherent interactions of 200 GeV/ c π + mesons in nuclear targets. The width obtained is 295 ± 60 keV, a value consistent with quark-model predictions.

Two-particle correlations in pion-nucleus interactions at 40 GeV/c

Multiplicity distributions and two-particle correlation functions are presented for shower particles with pseudorapidity η>1 produced in π- interactions on C, Al, Cu, Pb targets at 40 GeV/c. The results are in the correlation function berween the data on nuclei and on hydrogen. The data are compared with the predictions of the additive quark model and the quasi-eikonal model.

Inclusive resonance production in 7.3 GeV/c $$\bar pp$$ interactions

We present results on inclusive baryon and meson resonance production in\(\bar pp\) interactions at 7.3 GeV/c. Total inclusive and semi-inclusive cross sections are given for Δ(1232),∑*(1385), ϱ0,f andK*±(892) production. For the meson resonances separation into annihilation and non-annihilation components has been made, the annihilation component being dominant at this energy. We find that the energy dependence of inclusive cross sections for ϱ0 production inpp interactions and\(\bar pp\) non-annihilations shows a type of scaling behaviour previously reported for ϕ, ψ, ψ′ and ϒ production inpp interactions.Δ++, ϱ0 andK*± production are studied in terms of Feynmanx,y* andpT2. For the vector mesons we compare they* andx dependences with the predictions of simple quark models.

Partially conserved axial-vector current condition in the quark model:GAGVfor vector mesons and theωρπcoupling constant

The PCAC (partially conserved axial-vector current) condition is implemented at the quark level for hadrons considered as bound states of constituent quarks. Using the Goldberger-Treiman relation and the $\ensuremath{\omega}\ensuremath{\rho}\ensuremath{\pi}$ coupling constant, it is shown that $\frac{{G}_{A}}{{G}_{V}}$ for the $\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\rho}$ Gamow-Teller transition is lower than the quark-model prediction by 20%. This supports the current view that $\frac{{G}_{A}}{{G}_{V}}$ for bound quarks is reduced by confinement effects. With this reduction, the decay rates $\ensuremath{\Gamma}({D}^{*}\ensuremath{\rightarrow}D{\ensuremath{\pi}}^{0})$ are calculated and found to be more or less in agreement with measurements.

A phenomenological analysis of single pion photoproduction in the resonance region using fixed-t dispersion relations

Abstract An energy-dependent partial-wave analysis of single pion photoproduction from the first resonance region through the fourth resonance region has been made. 7768 data points on the processes γ p → π + n, γ p → π 0 p and γ n → π − p have been used. The method employed in this analysis is mostly similar to that of R.G. Moorhouse et al. (MOR), which is specified by using (i) fixed- t dispersion relations and (ii) K -matrix formalism. In addition to this framework, a Regge-like parametrization of the amplitudes was employed in the higher energy region and the partial waves from S-wave up to H-wave were included. The coupling constant for the radiative decay of the principal multiplets have been determined successfully and comparisons both with the results of previous analyses and with the quark model predictions are discussed.

Projectile fragmentation in hadron-nucleus collisions at high energies

Particle production in hadron-nucleus collisions at high energies is discussed in the projectile fragmentation region. The predictions of the constituent quark model are analyzed. The contribution of diffractive interactions is explicitly taken into account. Comparison with the recent Fermilab measurements shows good agreement with the quark model and strong effects of diffractive collisions in some of the analyzed reactions.

Baryon Magnetic Moments in the Quark Model and Pion Cloud Contributions

Baryon magnetic moment is studied paying attention to the effects of pion cloud which is surrounding the 'bare' baryon whose magnetic moment is given by the quark model with broken SU(6) symmetry. The precisely measured nucleon magnetic moments are reproduced by the pion cloud contributions from the distance larger than 1.4 fm. The effects of pion cloud on the hyperon magnetic moments are also discussed. It is shown that the pion cloud contributions largely reduce the discrepancies between the quark model predictions and the recent accurate experimental data on the hyperon magnetic moments.

Quark dynamics and the weak non-leptonic decays of K and D mesons

Quark model predictions for K → 2 π and D → K π decays were investigated in dynamical frameworks based on the separable approximation (SA), current algebra (CA), current algebra modified for the meson moment dependence (CAC) and current algebra with final-state interactions (CAF). Relativistic and non-relativistic quark model predictions were compared. The effective weak hamiltonian was modified by changing the relative strengths of its flavour 20 and 84 parts. All these approaches were also applied to hyperon and Ω − non-leptonic decays. When using standard QCD enhancement, the best approximation for K → 2 π (CAC) works poorly with D → K π. The best approximatiob for D→K π (CAF) fails in the case of K → 2 π. Only CAC with the 84 piece of the hamiltonian quenched might be in agreement with studied weak decays.

Spin-orbit coupling in Σ-hypernuclei

Single-particle energies of Σ-hyperons in Σ 16O are calculated within a relativistic mean-field theory. This model predicts a small spin-orbit splitting for Σ-hyperons in Σ 16O compared to ordinary nucleons in nuclei. Half of the small spin-orbit splitting is due to the anomalous magnetic moment of the Σ-hyperon. K and K ∗ exchange terms are negligible. This is to be seen in contrast to a previous quark-model prediction of a strong spin-orbit splitting for hyperons.

Comments on the recent lower bounds on the percentage D state of the deuteron

Discusses the consequences for the recently derived lower bounds on the percentage D state of the deuteron, PD, of (i) recent further measurements of the asymptotic D- to S-state ratio of the deuteron, eta , (ii) the experimental value of the root-mean-square radius of the deuteron, rd, recently deduced from low-energy electron scattering data and constrained by the experimental values of eta and a recent quark-model prediction for the neutron electric form factor, GEn, and (iii) the contribution to the experimental value of the quadrupole moment of the deuteron, QD, from meson-exchange currents, relativistic effects and isobar components of the deuteron wavefunction.

Radiative decay of the K ∗−(890)

We report a measurement of the radiative decay of the K ∗− (890). The width for the transition K ∗− → K − γ is 62 ± 14 keV. The resulting ratio of decay probabilities (K ∗0 → K 0γ)/(K ∗− → K −γ), while consistent with predictions of certain quark models, does not agree with expectations from unbroken SU(3) symmetry.

Production of charged hadrons, π0 and electron pairs in 70 GeV/c π−p interactions

Charged multiplicity and π 0 cross sections for π −p inelastic interactions at 70 GeV/ c are presented. The data were obtained from an exposure of the BEBC bubble chamber equipped with a track sensitive target (TST) to an unseparated negative beam at the CERN SPS. About 10 000 events were used for the charged multiplicity study, and about 2000 Dalitz pairs for the π 0 production analysis. A total of 12 e +e − pairs with a mass higher than the π 0 mass were found and analysed in terms of η or ω Dalitz pairs or decay pairs of vector mesons. Comparisons with data at other energies are made in terms of charged prong, π 0 cross sections, and of multiplicity parameters. The moments of longitudinal and transverse momentum distributions of the π 0 are determined and compared to the predictions of quark counting rule models.

Study of the reactionsπ − p→K 0(890) Λ,K 0(890)Σ 0 andK 0(890)Σ 0 at 3.95 GeV/c

The reactionsπ−p→K0(890) Λ,K0(890)Σ0 andK0(890)Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections, density matrix elements of the vector meson and hyperon polarizations are presented. A transversity amplitude analysis is performed for each of the reactions. The results are compared with those obtained for the SU(3) related processesK−p→ϕΔ, ϕΣ0, ϕΣ0(1385) andϱ−Σ+(1385) and with predictions of the additive quark model and SU(6) sum rules.