Production of a0-mesons in the reactions πN↦a0N and pp↦da0 + at GeV energies

We investigate the reactions πN↦a ₀ N and pp↦da ₀ ⁺ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross-section of the reaction πN↦a ₀ N. These results are used to calculate the differential and total cross-sections of the reaction pp↦da ₀ ⁺ within the framework of the two-step model in which two nucleons produce an a₀-meson via π-meson exchange and fuse to a deuteron. The necessity of new measurements on a₀ production and branching fractions (of its decay to the K and πη channels) is emphasized for clarifying the a₀ structure. Detailed predictions for the reaction pp→da ₀ ⁺ are presented for the energy regime of the proton synchrotron COSY-Jülich. Received: 4 August 2000 / Accepted: 17 September 2000     

Dynamical chiral-symmetry breaking at T = 0 and T ≠ 0 in the Schwinger-Dyson equation with lattice QCD data

Dynamical chiral-symmetry breaking (DCSB) in QCD is investigated in the Schwinger-Dyson (SD) formalism based on lattice QCD data. From the quenched lattice data for the quark propagator in the Landau gauge, we extract the SD integral kernel function, the product of the quark-gluon vertex and the polarization factor in the gluon propagator, in an Ansatz-independent manner. We find that the SD kernel function exhibits the characteristic behavior of nonperturbative physics, such as infrared vanishing and strong enhancement at the intermediate-energy region around p 0.6GeV. The infrared and intermediate energy region (0.4GeV < p < 1.5GeV) is found to be most relevant for DCSB from analysis on the relation between the SD kernel and the quark mass function. We apply the lattice-QCD-based SD equation to thermal QCD, and calculate the quark mass function at the finite temperature. Spontaneously broken chiral symmetry is found to be restored at high temperature above 110 MeV.     

Measurement of the single-spin asymmetry in the reaction π − d ↑ → π 0 X in the beam-fragmentation region at 40 GeV and p T of up to 2 GeV/c

The single-spin asymmetry A _N in the reaction π ^? + d _↑ → π ⁰ + X in the beam-fragmentation region at the energy of 40 GeV was investigated by using the PROZA setup installed at the U-70 accelerator of the Institute for High Energy Physics (IHEP, Protvino). It was measured to be A _N = (13.6 ± 2.6(stat.) ± 2.0(syst.))% in the intervals 0.7 < x _F < 1.0 and 1.0 < p _T < 1.8 GeV/c. The results agree with the asymmetry of π ⁰ mesons in the charge-exchange reaction π ^? + p _↑ → π ⁰ + n at the same values of the transverse momentum and beam energy. The asymmetry in the reaction K ^? + d _↑ → π ⁰ + X was simultaneously measured and found to be A _N = (11 ± 14)% for p _T > 1.2 GeV/c.     

The ππ S-wave in the 1 to 2 GeV region from a ππ,\bar K K and ρρ(ωω) coupled channel model

A simpleππ, $\bar K$ K, andρρ(ωω) fully coupled channel model is proposed to predict the isoscalarS-wave phase shifts and inelasticities forππ scattering in the 1.0 to 2.0 GeV region. TheS- matrix is required to exhibit poles corresponding to the established isoscalarJ ^π=0⁺ resonancesf ₀(975),f ₀(1400), andf ₀(1710). A dominant feature of the experimentalππ inelasticity is the clear opening of the $\bar K$ K channel near 1 GeV, and the opening of another channel in the 1.4–1.5 GeV region. The success of our model in predicting this observed dramatic energy dependence indicates that the effect of multipion channels is adequately described by theππ coupling to the $\bar K$ K channel, theρρ(4π) andωω(6π) channels.     

Measurement of the reaction γp → K0Σat photon energies up to 2.6 GeV⋆

The reaction p K⁰⁺ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the ⁺ as a function of the kaon production angle in the centre-of-mass system, cos^c.m._K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of p K⁺⁰. The ⁺ is polarized predominantly at cos^c.m._K 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.     

Search for e + e − → f 0(600)γ, f 0(980)γ, f 0(1350)γ, and f 2(1270)γ processes in the energy range from 1.05 to 1.38 GeV

In the energy range from 1.05 to 1.38 GeV, the upper limits for the cross sections of e ⁺ e ^? → f ₀(600)γ, f ₀(980)γ, f ₀(1350)γ, and f ₂(1270)γ → π⁰π⁰γ processes have been established. Measurements are performed in accordance with the statistics gathered in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider. The resultant upper limits vary from 6 to 42 pb depending on the energy and the model.     

Observation of the spin alignment of the ϱ0-meson produced in ¯pp interactions at 22.4 and 5.7 GeV/c

Studying the ⁰-meson production in ¯pp interactions at 22.4 GeV/c and in 4-prong anníhilation channels of ¯pp interactions at 5.7 GeV/c, we have observed an essential ⁰-meson spin alignment. The values of the ₀₀ element of the ⁰-meson spin density matrix (thez-axis is directed along the normal to the production plane) are equal to 0.08 ± 0.07 and 0.55 ± 0.03, respectively, i.e. the ⁰-meson spin lies preferably in the production plane. The absence of such an effect in pp interactions at 12 and 24 GeV/c and also the essentially larger ⁰ production cross section in ¯pp interactions at these energies make it possible to connect the observed ⁰-meson spin alignment with the annihilation processes. The character of the observed spin alignment is unexpected from the point of view of usual models, e.g. multiperipheral models. This effect could be described by the spontaneous polarization of quarks and antiquarks during the state preceding their recombination into mesons.Dedicated to Professor Ivan Úlehla on the occasion of his sixtieth birthday.The authors would like to express their gratitude to the CERN-Prague collaboration for permission to use their data on ¯pp interactions at 5.7 GeV/c. The authors are also indebted to A. M. Baldin, S. B. Gerasimov and H. I. Miettinen for valuable discussions, to the technicians and assistants at all laboratories for their work.     

The σK coupling in the chiral unitary approach and the isoscalar ¯N , ¯A interaction

We evaluate the “σ " exchange contribution to the ˉN → ˉN scattering within a chiral unitary approach. We show that the chiral transition potentials for ππ → Kˉ in the t -channel lead to a “σ " contribution that vanishes in the ˉ forward direction and, hence, would produce a null “σ " exchange contribution to the K^- optical potential in nuclear matter in a simple impulse approximation. This is a consequence of the fact that the leading-order chiral Lagrangian gives an I = 0 ππ → Kˉ amplitude proportional to the squared momentum transfer, q². This finding poses questions on the meaning or the origin of “σ " exchange potentials used in relativistic mean-field approaches to the K^- nuclear self-energy. This elementary “σ ” exchange potential in ˉN → ˉN is compared to the Weinberg-Tomozawa term and is found to be smaller than the present theoretical uncertainties but will be relevant in the future when aiming at fitting increasingly more accurate data.     

Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

Erratum to: Analytic Calculations of the Branching Ratio and CP Violation in $$B_s^0 \to {K^{*0}}{\overline K ^{*0}}$$ B s 0 → K * 0 K ¯ * 0 Decay

Physics of Atomic Nuclei -     

Angular distribution and polarization of K*(890) in ¯pp annihilation at 5.7 GeV/c

We have studied angular distributions ofK ^*(890) and found strong angular asymmetry forward-backward in ¯K ^*/K ^* in the centre of mass system. The ¯K ^* are produced predominantly in original direction of ¯p while theK ^* follow the proton directions. We also looked for angular distributions and-matrix elements in the rest system ofK ^*. We did not find any strong deviation from the isotropy distributions. In our research the corresponding matrix element for the angular distribution acoording to transversity axis has been found, ₀₀=0·37 ±0·05.     

Measurement of the pion form factor for Mππ^2 between 0.1 and 0.85 GeV2 with the KLOE detector

The KLOE experiment at the φ-factory DAФPNE has measured the pion form factor in the range between 0.1 〈 Mππ^2 〈 0.85 GeV^2 using events taken at √s = 1 GeV with a photon emitted at large polar angles in the initial state. This measurement extends the Mππ^2 region covered by KLOE ISR measurements of the pion form factor down to the two pion production threshold. The value obtained in this measurement of the dipion contribution to the muon anomalous magnetic moment of △αμ^ππ= （478.5±2-0stat±4.8syst±2.9theo）·10^-10 further confirms the discrepancy between the Standard Model evaluation for αμ and the experimental value measured by the （g-2） collaboration at BNL.     

τ → K–π0ντ Decay in the Nambu–Jona-Lasinio Model Including the Final-State Interaction of Mesons

JETP Letters - The $$\tau \to {{K}^{ - }}{{\pi }^{0}}{{\nu }_{\tau }}$$ decay has been described within the Nambu–Jona-Lasinio model including the contact term and the contribution from an...     

Pressure and temperature dependence of the structure of liquid Sn up to 5.3 GPa and 1373 K

Pressure and temperature dependence of the structure of liquid Sn has been measured up to 5.3?GPa and 1373?K using multi-angle energy-dispersive X-ray diffraction in Paris–Edinburgh cell. Under nearly isobar condition at ～1?GPa, liquid Sn displays a normal behavior with gradual structural changes with temperature up to 1373?K. Under isothermal compressions at 850 and 1373?K, however, the structure factors of liquid Sn both show a turn-over at ～3?GPa in the height of the first diffraction peak. According to the hard sphere cluster model, the structure of liquid Sn may be viewed as two different types of clusters. Below ～3?GPa, it is shown that the packing fraction of the dominant cluster (occupying ～0.94 fraction) changes with compression, while above ～3?GPa, the packing fractions and the hard sphere diameters of both clusters start to influence the structure, causing significant changes with increasing pressure. Our results suggest that the compression behavior of liquid Sn changes from localized densification only in one cluster below ～3?GPa to homogeneous structural changes in both clusters above ～3?GPa.     

On polarization of strange baryons in reactions p + p↦p + Λ0 + K+ and p + p↦p + Σ0 + K+ near thresholds

Polarization properties of strange baryons produced in pp reactions, p + p↦p + Λ⁰ + K⁺ and p + p↦p + Σ⁰ + K⁺, near thresholds of the final states pΛ⁰K⁺ and pΣ⁰K⁺ are analysed relative to polarizations of colliding protons. The cross-sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)). Received: 22 October 2001 / Accepted: 14 November 2001     

Medium effects in the production and π0γ decay of ω-mesons in pA collisions in the GeV region

The ω resonance production and its π⁰γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π⁰γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively. The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the π⁰ and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated π⁰'s and γ's are produced. Received: 2 April 2001 / Accepted: 5 June 2001     

Observation of the f 2(1525) resonance in the ηη system produced in K − p interactions at a momentum of 32.5 GeV/c

The reaction K ^? p → ηη(Λ/Σ⁰) at a momentum of 32.5 GeV/c was studied for the first time. The experiment was performed by using the GAMS-4π spectrometer at the 70-GeV accelerator of the Institute for High Energy Physics (IHEP, Protvino). The f ₂(1525) resonance was observed in the effective-mass spectrum of the ηη system at a low background level. The cross section for f ₂(1525) production was measured. The branching ratio for f ₂(1525)-meson decay to ηη and K $\bar K$ was found to be R = 0.119 ± 0.015(stat.) ± 0.036(syst.), which is in agreement with the world-average value.     

A search for excited electrons in the e+e− reactions up to the √s of 56 GeV

Excited electrons, e^1's, have been searched for by making use of the processes e⁺e⁻→e⁺e⁻γγ and eγ(e) (quasi-real Compton scattering). From the former process, we have obtained the lower limit for the mass of e^1', 27.9 GeV/c. A good agreement with QED is observed in the latter process, and new upper limits have been set for the coupling strength λ as a function of the mass of e¹.