η mesons in hot magnetized nuclear matter

\begin{document}$\eta N$\end{document} interactions are investigated in hot magnetized asymmetric nuclear matter using the chiral SU(3) model and chiral perturbation theory (ChPT). In the chiral model, the in-medium properties of η-mesons are calculated using medium modified scalar densities under the influence of an external magnetic field. Further, in a combined chiral model and ChPT approach, off-shell contributions of the \begin{document}$\eta N$\end{document} interactions are evaluated from the ChPT effective \begin{document}$\eta N$\end{document} Lagrangian, and the in-medium effect of scalar densities are incorporated from the chiral SU(3) model. We find that the magnetic field has a significant effect on the in-medium mass and optical potential of η mesons, and we observe a deeper mass-shift in the combined chiral model and ChPT approach than in the solo chiral SU(3) model. In both approaches, no additional mass-shift is observed due to the uncharged nature of η mesons in the presence of a magnetic field.     

Search for narrow resonances lighter than ? mesons

We report a search for narrow resonances, produced in collisions at  TeV, that decay into muon pairs with invariant mass between 6.3 and 9.0 GeV/c ². The data, collected with the CDF II detector at the Fermilab Tevatron collider, correspond to an integrated luminosity of 630 pb⁻¹. We use the dimuon invariant mass distribution to set 90% upper credible limits of about 1% to the ratio of the production cross section times muonic branching fraction of possible narrow resonances to that of the ϒ(1S) meson.     

Scalar mesons in the decays η′ → 3π0 and η′ → π0π+π?

The decays η → 3π ⁰ and η → π ⁰ π ⁺ π ⁻ are considered within the isobar model. It is shown that, in order to explain the branching ratio and the shape of the Dalitz plot for the decay η′ → 3π ⁰, it is sufficient to take into account the contributions of the σ and a ₀ mesons. The inclusion of the σ meson is necessary for reproducing the shape of the distribution over the Dalitz plot. The branching ratio for the decay η′ → π ⁰ π ⁺ π ⁻ is obtained. The predictions for the distributions over the Dalitz plot for this decay are presented. These predictions depend strongly on model parameters.     

Systematic study on QCD interactions of heavy mesons with ρ meson

The strong interactions of the negative-parity heavy mesons with ρ   meson may be described consistently in the context of an effective Lagrangian, which is invariant under isospin SU(2)$\mathit{SU}(2)$ transformation. Four coupling constants g_HHρ$g_{HH\rho }$, f_H∗Hρ$f_{H^{\ast }H\rho }$, g_H∗H∗ρ$g_{H^{\ast }{H}^{\ast }\rho }$ and f_H∗H∗ρ$f_{H^{\ast }{H}^{\ast }\rho }$ enter the effective Lagrangian, where H  (H^∗)$(H^{\ast })$ denotes a pseudoscalar bottom or charm meson (the corresponding vector meson). Using QCD light cone sum rule (LCSR) method and, as inputs, the hadronic parameters updated recently, we give an estimate of g_H∗H∗ρ$g_{H^{\ast }{H}^{\ast }\rho }$ and f_H∗H∗ρ$f_{H^{\ast }{H}^{\ast }\rho }$, about which little was known before, and present an improved result for g_HHρ$g_{HH\rho }$ and f_H∗Hρ$f_{H^{\ast }H\rho }$. Also, we examine the heavy quark asymptotic behavior of these nonperturbative quantities and assess the two low energy parameters β and λ of the corresponding effective chiral Lagrangian.     

Study of charm fragmentation into D *?± mesons in deep-inelastic scattering at HERA

The process of charm quark fragmentation is studied using D ^* ± meson production in deep-inelastic scattering as measured by the H1 detector at HERA. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to D ^* ± mesons. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the D ^* ± meson in the event. The fragmentation parameters extracted for the two phase space regions are found to be different. Deceased. Also at Physics Department, National Technical University, Zografou Campus, 15773 Athens, Greece. Also at Rechenzentrum, Universit?t Wuppertal, Wuppertal, Germany. Also at University of P.J. Šafárik, Košice, Slovak Republic. Also at CERN, Geneva, Switzerland. Also at Max-Planck-Institut für Physik, München, Germany. Also at Comenius University, Bratislava, Slovak Republic. Also at DESY and University Hamburg, Hamburg, Germany. Also at Faculty of Physics, University of Bucharest, Bucharest, Romania. Also at Ulaanbaatar University, Ulaanbaatar, Mongolia. Supported by the Bundesministerium für Bildung und Forschung, FRG, under contract numbers 05 H1 1GUA/1, 05 H1 1PAA/1, 05 H1 1PAB/9, 05 H1 1PEA/6, 05 H1 1VHA/7 and 05 H1 1VHB/5. Supported by the UK Science and Technology Facilities Council, and formerly by the UK Particle Physics and Astronomy Research Council. Supported by FNRS-FWO-Vlaanderen, IISN-IIKW and IWT and by Interuniversity Attraction Poles Programme, Belgian Science Policy. Partially supported by Polish Ministry of Science and Higher Education, grant PBS/DESY/70/2006. Supported by the Deutsche Forschungsgemeinschaft. Supported by VEGA SR grant no. 2/7062/27.     

Electromagnetic decays of radially excited mesons π0′, ρ0′, ω0′, and production of π0′ at lepton colliders

Radiative decays π ⁰(π ^0′) → γ + γ, π ^0′ → ρ ⁰(ω) + γ, ρ ^0′(ω′) → π ⁰ + γ, ρ ^0′(ω′) → π ^0′ + γ, and some processes of π ^0′ production at lepton colliders are considered in the framework of the nonlocal SU(2) × SU(2) Nambu-Jona-Lasinio model. Mixing of the radially excited and the ground meson states is taken into account. Numerical results for the decay and production processes are presented.     

Perspectives for the measurement of Ds+ mesons via?the?Ds+ →K+K?π+ channel in the ALICE experiment

Heavy quarks, such as charm, are produced in hard scatterings in the early stages of high energy nucleus-nucleus collisions and are expected to be a powerful tool to investigate the properties of the quark gluon plasma (QGP). The tracking detectors of the ALICE apparatus will allow to track and identify particles in central rapidity range down to low P _t . Among D mesons it would be particularly interesting to measure D _s yield via an exclusive hadronic decay channel because it could help to disentangle different hadronization mechanisms. The possibility of reconstructing the D _s meson through its D _s ⁺→K ⁺ K ⁻ π ⁺ decay channel in the central barrel was studied. The problem considered is characterized by the comparatively low yield of the D _s mesons against the huge amount of combinatorial background. Different kinematic and topological cuts have been studied in order to increase the signal-to-background ratio and the statistical significance. In addition, D _s mesons preferentially decay through intermediate resonant states and this fact can improve the separation of signal from background. Results of cut parameters tuning and values of significance for an analysis performed on simulated data are presented.     

Near-threshold production of a0(980) mesons in πN and NN collisions and a0-f0 mixing

We consider near-threshold a ₀(980)-meson production in πN and NN collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from πN reactions are used to calculate the contribution of the a ₀ meson to the cross sections and invariant mass distributions of the reactions and pp → ppK ⁺ K ⁻. It is found that the experimental observation of a ₀ ⁺ mesons in the reaction is much more promising than the observation of a ₀ ⁰ mesons in the reaction pp → ppK ⁺ K ⁻. Effects of isospin violation in the reactions pN → da ₀, pd → ³He(³H)a ₀, and dd → ⁴Hea ₀, which are induced by a ₀(980)-f ₀(980) mixing, are also analyzed. From Yadernaya Fizika, Vol. 66, No. 1, 2003, pp. 155–174. Original English Text Copyright ? 2003 by Kondratyuk, Bratkovskaya, Grishina, Büscher, Cassing, Str?her. This article was submitted by the authors in English.     

Measurement of the forward-backward asymmetry of charm and bottom quarks at theZ pole usingD*± mesons

The forward-backward asymmetries for the processes and at theZ resonance are measured using identifiedD ^*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D ^*+D ⁰⁺ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be:

2γ decays of scalar mesons (σ(600), f0(980), and a0(980)) in the Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f ₀(980), and a ₀(980) are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N _c approximation, where N _c is the number of colors) are taken into account. These contributions, as we show, are the values of the same order of magnitude. For the f ₀ decay the K-loop contribution turns out to play the dominant role. The results are in satisfactory agreement with modern experimental data.     

Production off2(1270) andf0(975) mesons by photons and hadrons of energy 65–175 GeV

Measurements are reported of inclusive production of -mesons in the beam fragmentation region in p, p andKp collisions. Results include a small but significant departure from VMD, and a pronounced rise in the/ ⁰ ratio with increasingp _T .     

Photoproduction of πmesons from nuclei

Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead) has been studied for incident-photon energies from 200 MeV to 800 MeV with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data were obtained for the inclusive photoproduction of neutral pions and the partial channels of quasifree single- , double- , and photoproduction. They have been analyzed in terms of the in-medium behavior of nucleon resonances and the pion-nucleus interaction. They are compared to earlier measurements from the deuteron and to the predictions of a Boltzmann-Uehling-Uhlenbeck (BUU) transport model for photon-induced pion production from nuclei.PACS: 13.60.Le Meson production - 25.20.Lj Photoproduction reactions     

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f0(980), a0(980) scalar mesons

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f₀ and a₀ resonances. The ππ → ππ, phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the π⁰η and mass distributions in the T = 1 channel. Furthermore, the total and partial strong decay widths of the f₀ and a₀ resonances are properly reproduced. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below GeV.     

Photoformation of π mesons in carbon

A calculation is made of the total cross section of the¹²C(,^–)¹²N reaction as a function of the energy of the quanta, by means of the technique of nonrelativistic diagrams, which permitted the differential cross sections of this reaction and the electroexcitation of the 15.11-MeV level in¹²C to be directly related. For the amplitude of the photocreation of-mesons in the nucleons we take the relativistic- and gradient-invariant expression, which follows from the model of the algebra of currents with physical pions. An analysis is made of the effect of the contributions of (1232) resonance and vector mesons to the amplitude, and also the different choice of the reaction kinematics in the nucleon.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 46–50, September, 1979.     

Nuclear bound states of ω mesons

Models based on chiral SU(3)_l ⊗ SU(3)_r symmetry and vector meson dominance suggest an attractive potential for the ω meson in a nuclear medium. We discuss the feasibility of producing nuclear bound states of ω mesons using (d, ³He) and pion induced reactions on selected nuclear targets.     

合成反铁磁Ni81Fe19/Co90Fe10/Ru/Co90Fe10/Ni81Fe19的研究

采用直流磁控溅射方法制备了一系列的合成反铁磁及以其为自由层的自旋阀.研究发现,在Ni₈₁Fe₁₉与Ru层之间插入适当厚度的Co₉₀Fe₁₀层后,可有效地提高合成反铁磁两磁性层间的反铁磁耦合强度,得到具有饱和场H_s更高、饱和磁化强度M_s更低、热稳定性更好的合成反铁磁.另外,以这种合成反铁磁作自旋阀的自由层时,可有效提高自旋阀的稳定性. 关键词： 合成反铁磁 退火 自旋阀     

High-resolution study of the ν1/ν5 and 2ν1/ν1+ν5 P-H stretching bands of PH2D

The P-H stretching bands ν₁/ν₅ and 2ν₁/ν₁+ν₅ were recorded using a Bruker 120 HR interferometer with a resolution of 0.0042 and 0.0088 cm⁻¹, respectively, and analyzed. From the fits 33 and 50, respectively, vibrational, rotational, centrifugal distortion, and resonance interaction parameters were obtained. These reproduce 668 and 497 rovibrational energies of the pairs of states ν₁/ν₅ and 2ν₁/ν₁+ν₅ with experimental accuracies, rms=0.00016 and , respectively. “Local mode” behavior of the PH₂ fragment is established and discussed in detail.