OZI rule violation in p¯p annihilation into φππ by two step processes

The φπ⁺π⁻ production in pˉp annihilation at rest is strongly enhanced by a two step mechanism with intermediate KˉKππ states. The relative yield of the φ production due to the resonant final state interaction decreases with increasing total energy of the pˉp system. Received: 4 August 1997     

Scales in nuclear matter: Chiral dynamics with pion nucleon form factors<Superscript>⋆</Superscript>

A systematic calculation of nuclear matter is performed which includes the long-range correlations between nucleons arising from one- and two-pion exchange. Three-body effects from 2π exchange with excitations of virtual Δ(1232)-isobars are also taken into account in our diagrammatic calculation of the energy per particle ˉ(k _f). In order to eliminate possible high-momentum components from the interactions we introduce at each pion-baryon vertex a form factor of monopole type. The empirical nuclear matter saturation point, ρ₀ ≃ 0.16fm^-3, ˉ₀ ≃ - 16MeV, is well reproduced with a monopole mass of Λ ≃ 4πf _π ≃ 1.16GeV. As in the recent approach based on the universal low-momentum NN potential V _low-k, the inclusion of three-body effects is crucial in order to achieve saturation of nuclear matter. We demonstrate that the dependence of the pion exchange contributions to ˉ(k _f) on the “resolution” scale Λ can be compensated over a wide range of Λ by counterterms with two “running” contact couplings. As a further application we study the in-medium chiral condensate 〈ˉq〉(ρ) beyond the linear density approximation. For ρ ⩽ 1.5ρ₀ we find small corrections from the derivative dˉ(k _f)/dm _π, which are stable against variations of the monopole regulator mass Λ.     

¯N interaction from meson-exchange and quark-gluon dynamics

We investigate the ˉN interaction at low energies using a meson exchange model supplemented with a short-distance contribution from one-gluon exchange. The model is developed in close analogy to the meson-exchange KN interaction of the Jülich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (ρ , ω exchange and higher-order box diagrams involving ˉ^* N , ˉΔ , and ˉ^*Δ intermediate states. The short-range part is assumed to receive additional contributions from genuine quark-gluon processes. The predicted cross-sections for ˉN for excess energies up to 150MeV are of the same order of magnitude as those for KN but with average values of around 20mb, roughly a factor two larger than for the latter system. It is found that the ω -exchange plays a very important role. Its interference pattern with the ρ -exchange, which is basically fixed by the assumed SU(4) symmetry, clearly determines the qualitative features of the ˉN interaction --very similiar to what happens also for the KN system.     

ππ scattering and the meson resonance spectrum

A ππ, ˉKK, and ρρ(ωω) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities for elastic ππ scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the meson resonance table of the Particle Data Group. As expected, the ππ inelasticity is very strongly related to the opening of the ˉK channel near 1 GeV, and the opening of ρρ(4π) and ωω(6π) channels in the 1.5 GeV region. The predictions of this model are compared to the various elastic ππ→ππ amplitudes, that were obtained from analyses of π⁻ p →π⁻π⁺n data. The role of the various resonances, in particular the glueball candidate f ₀(1500) and the f _J(1710) is investigated. Received: 19 November 1997     

Testing the nature of the Λ(1520)-resonance in proton-induced production

The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of the pp → pK⁺K^-p and pp → pK⁺π⁰π⁰Λ reactions. In particular, we show that the ratio between the π⁰π⁰Λ and K^-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at Jülich or the developing CSR facility at Lanzhou.     

Multiquark picture for Σ (1620)

In this work we report on a new QCD sum rule analysis to predict masses of the excited baryon states (e.g. Σ (1620) and Λ (1405)) by using multiquark interpolating fields ((qˉq)(qqq)). For the Σ (1620) we consider the ˉKN, πΣ, and πΛ (I = 1) multiquark interpolating fields. The calculated mass from those multiquark states is about 1.592 GeV. For the Λ (1405) we first show the result using the π⁺Σ⁻+π⁰Σ⁰+π⁻Σ⁺ (I = 0) multiquark interpolating field, and compare the calculated mass to that of our previous result using the π⁰Σ⁰ multiquark state. We then show that the mass 1.405 GeV is well reproduced when using the ˉKN (I = 0) multiquark state. The uncertainties in our sum rules are also discussed. Received: 7 September 1998 / Revised version: 5 January 2000     

Self-consistent treatment of the quark condensate and hadrons in nuclear matter

We calculate the contribution of pions to the $\bar qq$-expectation value κ(ρ) =<M|ˉq q|M> in symmetric nuclear matter. We employ exact pion propagator renormalized by nucleon-hole and isobar-hole excitations. Conventional straightforward calculation leads to the “pion condensation” at unrealistically small values of densities, causing even earlier restoration of chiral symmetry. This requires a self-consistent approach, consisting in using the models, which include direct dependence of in-medium mass values on κ(ρ), e.g. the Nambu–Jona-Lasinio–model. We show, that in the self-consistent approach the ρ-dependence of the condensate is described by a smooth curve. The “pion condensate” point is removed to much higher values of density. The chiral restoration does not take place at least while ρ < 2.8ρ₀ with ρ₀ being the saturation value. Validity of our approach is limited by possible accumulation of heavier baryons (delta isobars) in the ground state of nuclear matter. For the value of effective nucleon mass at the saturation density we found m ^*(ρ₀) = 0.6m, consistent with nowadays results of other authors. Received: 8 October 1998     

SU(3) classification of p-wave ηπ and π systems

An exotic meson, the π₁(1400) with J ^PC = 1^{- +}, has been seen to decay into a p-wave ηπ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ( qˉq + qˉq) belonging to a flavor ˉ10 representation of SU(3). In contrast, the π₁(1600) with a substantial decay mode into π is likely to be a member of a flavor octet. Received: 27 March 2002 / Accepted: 8 August 2002 / Published online: 10 December 2002 RID="b" ID="b"e-mail: klempt@iskp.uni-bonn.de Communicated by V. Vento     

Target fragmentation in pp, ep and γp collisions at high energies

We calculate target fragmentation in pp→nX and γp→nX reactions in the meson cloud picture of the nucleon. The pp→nX reaction is used to fix the pnπ⁺ form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small x _Bj electroproduction of forward neutrons at HERA. Here the qˉq dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the hadronic reaction. For deep inelastic events (Q ² > 10 GeV²) screening is weaker but still present at large Q ². The signature for this absorptive rescattering is a shift of the dσ/dE_n distribution to higher neutron energies for photofragmentation. Received: 12 June 1999 / Revised version: 12 October 1999     

Electromagnetic polarizabilities of the nucleon and properties of the σ-meson pole contribution

The t-channel contribution to the difference of electromagnetic polarizabilities of the nucleon, (α - β)^t, can be quantitatively understood in terms of a σ-meson pole in the complex t-plane of the invariant scattering amplitude A ₁(s, t) with properties of the σ-meson as given by the quark-level Nambu-Jona-Lasinio model (NJL). Equivalently, this quantity may be understood in terms of a cut in the complex t-plane where the properties of the σ-meson are taken from the ππ → σ → ππ, γγ → σ → ππ and Nˉ → σ → ππ reactions. This equivalence may be understood as a sum rule where the properties of the σ-meson as predicted by the NJL model are related to the f ₀(600) particle observed in the three reactions. In the following, we describe details of the derivation of (α - β)^t making use of predictions of the quark-level NJL model for the σ-meson mass. An erratum to this article is available at .     

The process p¯↦γπwithin the handbag approach

We analyse the exclusive channel pˉ↦γπ⁰, assuming handbag dominance. The soft parts are parametrized in terms of CGLN amplitudes for the qˉ↦γπ⁰ transition and form factors for the pˉ↦qˉ ones; the latter represent moments of Generalized Distribution Amplitudes. We present a combined fit to Fermilab data from E760 taking simultaneously into account information from other exclusive reactions, especially from pˉ↦γγ data. Overall a nicely consistent picture emerges, such that one can hope, that our theoretical analysis will be reliable also for the kinematics of GSI/FAIR, which, hopefully, will provide much more precise and complete data. Consequently, data from this facility should improve our knowledge both on the proton-antiproton distribution amplitudes and the pion production mechanism.     

Forward dispersion relations and Roy equations in <Emphasis Type="Italic">ππ</Emphasis> scattering

We first review the results of an analysis of ππ interactions in S, P and D waves for the two-pion effective mass from threshold to about 1.4GeV. In particular, we show a recent improvement of this analysis above the Kˉ threshold using more data for phase shifts and including the S0-wave inelasticity from ππ→Kˉ. In addition, we have improved the fit to the f ₂(1270)-resonance and used a more flexible P-wave parametrization above the Kˉ threshold and included an estimation of the D2-wave inelasticity. The better accuracy thus achieved also required a refinement of the Regge analysis above 1.42GeV. Finally, in this work we check that the ππ scattering amplitudes obtained in this approach satisfy remarkably well forward dispersion relations and Roy's equations.     

K-matrix analysis of the (IJ<Superscript>PC</Superscript> = 00<Superscript>+ +</Superscript>)-wave in the mass region below 1900 MeV

We present the results of the current analysis of the partial wave IJ ^PC = 00^{+ +} based on the available data for meson spectra ( ππ, KˉK,ηη,η,ππππ). In the framework of the K-matrix approach, the analytical amplitude has been reconstructed in the mass region 280 MeV < < 1900 MeV. The following scalar-isoscalar states are seen: comparatively narrow resonances f ₀(980), f ₀(1300), f ₀(1500), f ₀(1750) and the broad state f₀(1200-1600). The positions of the amplitude poles (masses and total widths of the resonances) are determined as well as pole residues (partial widths to meson channels ππ, KˉK,ηη,η,ππππ). The fitted amplitude gives us the positions of the K-matrix poles (bare states) and the values of bare-state couplings to meson channels thus allowing the quark-antiquark nonet classification of bare states. On the basis of the obtained partial widths to the channels ππ, KˉK,ηη,η, we estimate the quark/gluonium content of f ₀(980), f ₀(1300), f ₀(1500), f ₀(1750), f₀(1200-1600). For f ₀(980), f ₀(1300), f ₀(1500) and f ₀(1750), their partial widths testify the qˉq origin of these mesons though being unable to provide precise evaluation of the possible admixture of the gluonium component in these resonances. The ratios of the decay coupling constants for the f₀(1200-1600) support the idea about the gluonium nature of this broad state. Received: 14 May 2002 / Accepted: 20 August 2002 / Published online: 11 February 2003 RID="a" ID="a"e-mail: anisovic@thd.pnpi.spb.ru Communicated by A. Sch?fer     

Exotic states X ±(1600, I G (J PC)=2+ (2++)) in photoproduction reactions

It is shown that the list of unusual mesons that are planned to be studied in photoproduction reactions can be supplemented with I ^G (J ^PC)=2⁺ (2⁺⁺) exotic states X ^±(1600), which are natural to seek as manifestations of the ρ^±ρ⁰ decay channels in the reactions γN → ρ^±ρ⁰ N and γN → ρ^±ρ⁰Δ. A classification of the ρ^±ρ⁰ states according to their quantum numbers is presented. A model for the spin structure of the amplitudes for the reactions γp → f ₂(1270)p, γp → a ₂ ⁰ (1320)p, and γN → X ^±(N, Δ) is proposed, and estimates are obtained for the corresponding cross sections. At E _γ≈6 GeV, it is found that σ(γP → f ₂(1270)p)≈0.12 μb, σ(γp → a ₂ ⁰ (1320)p)≈0.25 μb, σ(γN → X ^± N → ρ^±ρ⁰ N) ≈ 0.018 μb, and σ(γp → X ⁻Δ⁺⁺ → ρ⁻ρ⁰Δ⁺⁺≈0.031 μb. The problem of isolating signals from X ^± states against the natural background that is associated with other channels of π^±π⁰π⁺π⁻ production is discussed. It is deduced that searches for exotic states X ^±(2⁺ (2⁺⁺)) in experiments at JLAB will be quite efficient—for example, the yield of about 2.8×10⁶ events per month is expected to correspond to the estimated cross sections for the reactions γN → X ^± N → ρ^±ρ⁰ N. __________ Translated from Yadernaya Fizika, Vol. 63, No. 10, 2000, pp. 1904–1912. Original Russian Text Copyright ? 2000 by Achasov, Shestakov.     

Three-body hadronic structure of low-lying 1/2+ Σ and Λ resonances⋆

We discuss the dynamical generation of some low-lying 1/2⁺ Σ 's and Λ 's in two-meson one-baryon systems. These systems have been constructed by adding a pion in the S -wave to the ˉN pair and its coupled channels, where the 1/2^- Λ(1405) -resonance gets dynamically generated. We solve Faddeev equations in the coupled-channel approach to calculate the T -matrix for these systems as a function of the total energy and the invariant mass of one of the meson-baryon pairs. This squared T -matrix shows peaks at the energies very close to the masses of the strangeness -1 , 1/2⁺ resonances listed in the particle data book.     

Partial widths for the decays η:(1295) →γγ and η:(1440) →γγ

We discuss γγ partial widths of pseudoscalar/isoscalar mesons η:(M) in the mass region M∼ 1000–1500 MeV. The transition amplitudes η:(1295) →γγ and η:(1440) →γγ are studied within an assumption that the decaying mesons are the members of the first radial excitation nonet 2¹ S ₀qˉq. The calculations show that partial widths being of the order of 0.1 keV are dominantly due to the nˉn meson component while the contribution of the sˉs component is small. Received: 24 September 1999     

QCD Coulomb gauge approach to exotic hadrons

The Coulomb gauge Hamiltonian model is used to calculate masses for selected J^PC states consisting of exotic combinations of quarks and gluons: ggg glueballs (oddballs), qˉg hybrid mesons and qˉqˉ tetraquark systems. An odderon Regge trajectory is computed for the J^- glueballs with intercept much smaller than the pomeron, explaining its nonobservation. The lowest 1^-+ hybrid-meson mass is found to be just above 2.2GeV while the lightest tetraquark state mass with these exotic quantum numbers is predicted around 1.4GeV consistent with the observed π(1400).     

Manifestations of hidden polarized strangeness of the nucleon in polarization phenomena for the process p +¯p → P0+ V0

The sensitivities of the one-spin and two-spin polarization observables for p+ˉp→P⁰+V⁰, with P⁰=π⁰, η,η′ and V⁰=ρ,ω,φ, based on the triplet enhancement hypothesis for strangeness production in pˉp collisions are analyzed. The analysis is carried out under special kinematical conditions where the P⁰ meson production angle in the CMS is equal to π/2, for which C-invariance of strong interactions reduces the number of independent amplitudes to three. Received: 17 September 1997     

Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions

Antiproton proton annihilation reactions allow unique access to the moduli and phases of nucleon electromagnetic form factors in the time-like region. We present the helicity amplitudes for the unequal-mass single-photon reaction pˉ → l ⁺ l ^- in the s channel including the lepton mass. The relative signs of these amplitudes are determined using simple invariance properties. Helicity amplitudes for one-photon exchange annihilation reaction pˉ → Bˉ are also given, where B is any spin-one-half particle with structure. Crossing relations between the ep → ep scattering and the pˉ → l ⁺ l ^- annihilation channels are discussed and the crossing matrix for the helicity amplitudes is given. This matrix may be used to verify known expressions for the space-like helicity amplitudes due to one-photon exchange.     

Electrical resistivity of microinhomogeneous PdMnxFe1−x alloys

The electronic band-structure calculations of the PdFe ferromagnet and the PdMn antiferromagnet performed in this work permit one to conclude that the specific features of the electrical resistivity observed in the ternary PdMn_xFe_1−x alloy system [the deviation from the Nordheim-Kurnakov rule ρ₀(x)∼x(1−x), which is accompanied by a high maximum of residual resistivity (not typical of metals) ρ ₀ ^m ∼220 μΩ cm at x _C∼0.8 and a negative temperature resistivity coefficient in the interval 0.5≤x≤1] are due to the microinhomogeneous (multiphase) state of the alloys and a variation in the band-gap parameter d spectrum caused by antiferromagnetic ordering of a PdMn-type phase. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 2, 2002, pp. 193–197. Original Russian Text Copyright ? 2002 by Kourov, Korotin, Volkova.