Showing papers on "Pion published in 1987"
TL;DR: A detailed study of high-energy processes in solar flares is reported, including the production of neutrons and pions, and incorporating isobaric and scaling models and a recent compilation of pion production data as mentioned in this paper.
Abstract: A detailed study of high-energy processes in solar flares is reported, including the production of neutrons and pions, and incorporating isobaric and scaling models and a recent compilation of pion production data (Dermer, 1986). The broad-band gamma-ray spectrum resulting from the decay of neutral pions, the bremsstrahlung of positrons and electrons from the decay of charged pions, and the annihilation in flight of positrons is evaluated. Also evaluated is the 0.511 MeV gamma-ray line resulting from the annihilation of the positrons which survive annihilation in flight. Calculations were based on an isotropic, thick-target model using the best available nuclear data and models. Results are compared with extensive observation of the June 3, 1982 flare (10-120 MeV gamma rays), 0.511 and 2.2 MeV line emission, nuclear line emission, high-energy neutrons, and interplanetary charged particles. 75 references.
203 citations
TL;DR: In this paper, the electromagnetic and axial currents and corresponding form factors of solitons resulting from a non-linear chiral theory of pions, ρ and ω mesons are investigated.
127 citations
TL;DR: In this paper, the temperature dependence of physical properties of the pion and σ-meson in the Nambu-Goldstone phase is examined on the basis of an effective lagrangian for quarks.
126 citations
TL;DR: The Nambu--Jona-Lasinio model at finite temperature and density is used to investigate the static and dynamical properties of the pion and near the chiral phase transition the pions decouple from matter.
Abstract: We use the Nambu--Jona-Lasinio model at finite temperature and density to investigate the static and dynamical properties of the pion. Near the chiral phase transition the pion is found to decouple from matter. The relevance of this result for hadronic matter is discussed.
104 citations
TL;DR: In this article, the authors compare the differential cross sections of high-mass muon pair production on deuterium and tungsten by incident negative pions of 140 and 286 GeV.
96 citations
TL;DR: Negative pion multiplicity was measured over the range of participant nucleon number 80 ~A < 270 for incident energies from 530 to 1350 MeV/n in the La+ La system to require a stiff nuclear matter equation of state.
Abstract: Negative pion multiplicity was measured over the range of participant nucleon number 80 ~A < 270 for incident energies from 530 to 1350 MeV/n in the La+ La system. Th~ is proportional to A and increases linearly with the c.m. energy. Thermal and potential energies, and temperatures of the maximum density phase of the collision are extracted from the data. The results require a stiff nuclear matter equation of state.
84 citations
TL;DR: This work calculates the nucleon self-energy and the density-dependent effective NN and N..delta.. cross sections in a nuclear medium and shows a sizable reduction of the pion production cross section and important changes in theelta.. absorption cross sections.
Abstract: Within the relativistic Dirac-Brueckner approach we discuss the properties of highly-energetic nucleons and deltas in dense nuclear matter. The effective NN and N..delta.. interactions are constructed in a fully self-consistent way and reproduce all known properties of nuclear matter. We calculate the nucleon self-energy and the density-dependent effective NN and N..delta.. cross sections in a nuclear medium. Results show a sizable reduction of the ..delta.. (pion) production cross section and important changes in the ..delta.. absorption cross sections.
83 citations
CERN1
TL;DR: In this article, the valence quarks in a pion were computed on the lattice using Wilson fermions in the quenced approximat, and they were found to be 0.49±0.08 and 0.02 at a scale μ ≅ 7 GeV, in good agreement with experimental data.
75 citations
TL;DR: In this article, it was shown that the nuclear dependence of transverse momentum distribution of massive muon pairs produced in hadronic interactions increases with the magnitude of the muon transversal momentum.
64 citations
TL;DR: The circular polarization of the 1.081 MeV γ rays from 18F has been measured to be (1.7±5.8)×10-4.4), which is significantly smaller than recent theoretical predictions based on the Weinberg-Salam model.
Abstract: The circular polarization of the 1.081 MeV γ rays from 18F has been measured to be (1.7±5.8)×10-4. 18F was produced by a 4.05 MeV 3He+ beam impinging on a recirculating water target with a thin entrance window. The circular polarization was measured with four magnetic transmission polarimeters, each backed by a 150 cm3 n-type Ge detector. A fast data acquisition system limited overall peak losses to 30% at a count rate of 60 kHz per detector. Supplementary experiments were carried out to investigate the sensitivity of the circular polarization measurement to systematic variations of beam position and intensity. These effects were found to be negligible relative to the statistical uncertainty. The experimental result is interpreted in terms of an isovector parity-nonconserving matrix element between the ‖0+,T=1,1.042 MeV〉 and ‖0-,T=0,1.081 MeV〉 states in 18F that is dominated by the weak pion exchange contribution. The present result for the weak pion-nucleon coupling strength is ‖fπ1‖=(0.4-0.4+1.4)×10-7, which is significantly smaller than recent theoretical predictions based on the Weinberg-Salam model.
61 citations
CERN1
TL;DR: In this paper, the second moment of the pion's distribution amplitude on a 103×20 lattice with Wilson fermions in the quenched approximation and at β = 6.0.
TL;DR: In this paper, the authors derived the relativistic quantum transport and constraint equations for the Vlasov-Uehling-Uhlenbeck approach for baryons coupled to scalar and vector mesons.
Abstract: We derive the relativistic quantum transport- and constraint equations for a relativistic field theory of baryons coupled to scalar and vector mesons. We extract a selfconsistent momentum dependent Vlasov term and the structure of quantum corrections for the Vlasov-Uehling-Uhlenbeck approach. The inclusion of pions and deltas into this transport theory is discussed.
TL;DR: In this paper, the authors report results of an inclusive measurement of the charmed baryon, Λc, in the forward direction of proton-proton interactions with s =63 GeV.
TL;DR: Pion production in heavy ion reactions, especially near pion production threshold energies, are reviewed in this article. And nuclear collective models and models incorporating Pion production from nucleon-nucleon interactions are compared with existing data.
Abstract: Pion production in heavy ion reactions, especially near pion production threshold energies, are reviewed. Nuclear collective models and models incorporating pion production from nucleon-nucleon interactions are compared with existing data. (AIP)
University of Tokyo1, Lawrence Berkeley National Laboratory2, Johns Hopkins University3, University of California, Santa Barbara4, University of California, Los Angeles5, University of California, San Diego6, Carnegie Mellon University7, University of California, Berkeley8, University of California, Riverside9, Ames Laboratory10, University of California, Davis11, University of Massachusetts Amherst12, New York University13
TL;DR: The multiplicities per event of π± and K± were measured separately for e+e- annihilation into c c, b b, and light quark pairs at Ecm=29 GeV as mentioned in this paper.
TL;DR: In this paper, the dominant resonance excitation is dynamically described by a semirelativistic quark model and the background is considered to arise from Born-terms diminuished by the lowest order partial waves.
Abstract: A partial wave decomposition of\({v \mathord{\left/ {\vphantom {v {\bar v}}} \right. \kern-
ulldelimiterspace} {\bar v}}\) single pion production is used for studying resonant and nonresonant contributions. The dominant resonance excitation is dynamically described by a semirelativistic quark model. Nonresonant background is considered to arise from Born-terms diminuished by the lowest order partial waves (which are determined by resonances alone.) The method permits evaluation of interferences between resonance and background amplitudes as well as, more importantly, among resonances themselves. Predicted interference patterns are reflected by the pion angular distribution coefficients which compare well with recent data. Results obtained this way are also in agreement with momentum transfer measurements if higher resonance excitation form factors are chosen to resemble those tested in pion photoproduction, rendering simultaneously any nonresonant background small.
TL;DR: In this article, the relative amounts of K ∗ π, Kϱ and non-resonant Kππ in each decay mode are determined, and isospin amplitudes and phases are derived.
TL;DR: In this paper, the experimental and theoretical results for intermediate energy nucleus-nucleus collisions (E / A =20-200 MeV ) are reviewed, including incomplete fusion reactions, linear momentum transfer measurements, non-equilibrium light and complex particle emission, sub-threshold pion production, high energy photon emission, and particle correlations at large and small relative momenta.
TL;DR: The phase structure of the nonlinear mean-field meson theory of baryonic matter (nucleons plus delta resonances) is analyzed and it is shown that the equation of state cannot be derived unambiguously from pion data.
Abstract: We analyze the phase structure of the nonlinear mean-field meson theory of baryonic matter (nucleons plus delta resonances). Depending on the choice of the coupling constants, we find three physically distinct phase transitions in this theory: a nucleonic liquid-gas transition in the low temperature, T, < 20 MeV, low density, p=0.5po, regime, a high-temperature ( T z 150 MeV) finite density transition from a gas of massive hadrons to a nearly massless baryon, antibaryon plasma, and, third, a strong phase transition from the nucleonic fluid to a resonance-dominated "deltamatter'' isomer at p 12po and T, < 50 MeV. All three phase transitions are of first order. It is shown that the occurrence of these different phase transitions depends critically on the coupling constants. Since the production of pions also depends strongly on the coupling constants, it is Seen that the equation of state cannot be derived unambiguously from pion data.
TL;DR: In this paper, it is argued that chemically bonddeltaIchemically bond = (1/2 K decays are dominated by transitions to virtual diquark-antidiquark states which then evolve into mesons.
Abstract: It is argued that chemically bonddeltaIchemically bond = (1/2 K decays are dominated by transitions to virtual diquark-antidiquark states which then evolve into mesons Virtual diquark formation also contributes significantly to the relatively short lifetime of the D/sup 0/ meson It gives rise to a modified picture of the D/sup +/ width and of some baryon-antibaryon decays of B mesons The CP-violating parameter epsilon' of the K system remains small and unaffected even though the corresponding operator transforms as an isospin doublet
TL;DR: In this paper, the two-body photo break-up of the deuteron above pion threshold is calculated treating the final state interaction in a coupled channel approach with inclusion of Δ degrees of freedom.
TL;DR: A bosonization of quantum chromodynamics is employed to derive a meson effective action, thus providing a direct link between QCD and meson phenomenology, and motivates a divergence-free, global color-symmetry model for mesons, which is seen to be a generalization of various phenomenological models.
Abstract: A bosonization of quantum chromodynamics (QCD) is employed to derive a meson effective action, thus providing a direct link between QCD and meson phenomenology. As an example of this approach expressions are obtained for the meson parameters associated with the analysis of \ensuremath{\omega}\ensuremath{\rightarrow}3\ensuremath{\pi} decay. The bosonization also directly motivates a divergence-free, global color-symmetry model for mesons, which is seen to be a generalization of various phenomenological models. Good estimates are obtained for the values of several of the meson parameters.
TL;DR: The hypothesis of chiral anomalies and the color-SU(3) quark symmetry are confirmed and the Wess-Zumino-Witten effective Lagrangian is confirmed.
Abstract: The vertex ..gamma -->..3..pi.. has been investigated in the reaction of pion pair production by pions in the nuclear Coulomb field, ..pi../sup -/+(Z,A)..--> pi../sup -/+..pi../sup 0/+(Z,A), in the region of low-invariant-mass ..pi../sup -/..pi../sup 0/ pairs. The experiment has been carried out in the 40-GeV pion beam of the IHEP accelerator (Serpukhov) with the SIGMA spectrometer. We have measured for the first time the cross section of the reaction in the region of momentum transfer squared q/sup 2/ ..3..pi.. coupling constant F/sup 3//sup ..pi../ = 12.9 +- 0.9 +- 0.5 GeV/sup -3/, where the first (second) error is statistical (systematic). The obtained result agrees with the calculations based on the Wess-Zumino-Witten effective Lagrangian. The hypothesis of chiral anomalies and the color-SU(3) quark symmetry are confirmed.
TL;DR: In this paper, three independent two-current nucleon observables are studied within the two-flavor Skyrme model for the παω system and the results are compared with existing quark model results as well as with empirical determinations.
TL;DR: The measured Q2 dependence and decay distribution support the f1( 1285) spin and parity assignment and both the JPC=1++ f1 (1285) and theJPC=0-+ (958) in tagged two-photon interactions and the (957) in untagged interactions are observed.
Abstract: We observe both the J/sup P//sup C/ = 1/sup + +/ f/sub 1/(1285) and the J/sup P//sup C/ = 0/sup - +/ eta'(958) in tagged two-photon interactions and the eta'(958) in untagged interactions. The measured Q/sup 2/ dependence and decay distribution support the f/sub 1/(1285) spin and parity assignment. The radiative width of the f/sub 1/(1285) is measured as (M/sup 2//Q/sup 2/)GAMMA/sub ..gamma..//sub ..gamma..//sub */ = 9.4 +- 2.5 +- 1.7 keV, on the assumption of a rho-pole form factor.
TL;DR: In this article, the authors show that general analytic and unitarity properties make such an enhancement a priori unlikely, and that either experimental data and its modelled explanations violate these general principles or some experiments are wrong.
TL;DR: Upper limits for the branching ratio are given as a function of mass and lifetime of the A/sup 0/ for lifetimes shorter than 10/sup -13/ sec.
Abstract: We have searched for the decay process K/sup +/..--> pi../sup +/A/sup 0/, where A/sup 0/ is any particle of mass less than 100 MeV/c/sup 2/ decaying into e/sup +/e/sup -/. Upper limits for the branching ratio are given as a function of mass and lifetime of the A/sup 0/. For lifetimes shorter than 10/sup -13/ sec, a limit of 4.5 x 10/sup -7/ at the 90% confidence level is obtained.
TL;DR: The theory of analog pion double charge exchange on semimagic even-even nuclei is examined and it is shown that the amplitude for the reaction can be expressed as the sum of two independent functions for an entire shell.
Abstract: The theory of analog pion double charge exchange on semimagic even-even nuclei is examined from the point of view of the nuclear shell model. It is shown that the amplitude for the reaction can be expressed as the sum of two independent functions for an entire shell. A more general relation is also discussed which is true for any shell in which the generalized seniority scheme is valid.