Search results for "Nucleon"
showing 10 items of 1041 documents
Chiral unitary model for the kaonic atom
2000
We study kaonic atoms over the periodic table using a kaon self-energy in the nuclear medium derived from the SU(3) chiral unitary model. This model is quite successful in reproducing the scattering amplitude of meson meson and the strangeness $S=\ensuremath{-}1$ meson baryon reactions. In particular the properties of the $\ensuremath{\Lambda}(1405)$ resonance are well reproduced. In the nuclear medium the properties of this resonance are appreciably modified, and consequently the kaon nucleon scattering amplitudes, leading to an attractive kaon nucleus self-energy for densities higher than ${\ensuremath{\rho}}_{0}/25.$ With this interaction we are able to reproduce shifts and widths of kao…
Two-meson cloud contribution to the baryon antidecuplet self-energy
2005
We study the self-energy of the SU(3) antidecuplet coming from two-meson virtual clouds. Assuming that the exotic Theta+ belongs to an antidecuplet representation with N(1710) as nucleon partner, we derive effective Lagrangians that describe the decay of N(1710) into N pi pi with two pions in s- or p-wave. It is found that the self-energies for all members of the antidecuplet are attractive, and the larger strangeness particle is more bound. From two-meson cloud, we obtain about 20 % of the empirical mass splitting between states with different strangeness.
Neutrino-nucleon scattering rate in proto-neutron star matter
2002
We present a calculation of the neutrino-nucleon scattering cross-section which takes into account the nuclear correlations in the relativistic random phase approximation (RPA). Our approach is based on a quantum-hadrodynamics model with exchange of sigma, omega, pi, rho and delta mesons. In view of applications to neutrino transport in the final stages of supornova explosion and proto-neutron star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-noutron asymmetry and temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor channel, coupling to the delta-meson and meson mixin…
Meson exchange currents in theHe3(γ,π+)3H reaction
1996
We generate meson exchange currents mechanisms for the (\ensuremath{\gamma},${\mathrm{\ensuremath{\pi}}}^{+}$) reaction in nuclei starting from the \ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}N amplitude on one nucleon and allowing one of the pions to be produced off shell and be absorbed by a second nucleon. Detailed calculations are presented for the \ensuremath{\gamma} $^{3}\mathrm{\ensuremath{\pi}}^{+3}$H reaction, where we show that the cross section at large momentum transfers is dominated by these mechanisms, helping improve the agreement with experimental data. It is also shown that the meson exchange currents produce important effects in the photon a…
φ, ϱ, and ω production in pU, OU and SU reactions at 200 GeV per nucleon
1991
Abstract Low mass muon pair production at high P T and low X F studied in pU, OU and SU 200 GeV per nucleon react ions. When energy density or projectile mass are increased, φ production is enhanced as compared with the yield of muon pairs in the mass continuum (1.7 M μμ c 2 ), whereas the production of ω and ϱ, experimentally unresolved, remains approximately constant. This φ enhancement is in agreement with predictions based on quark-gluon plasma formation and, together with the previously reported J/Ψ suppression, puts severe constraints on a purely hadronic description of nucleus-nucleus collisions.
Transverse energy distributions in nucleus-nucleus collisions at 200 GeV/nucleon
1990
Abstract The transverse energy ET distributions of nucleus-nucleus collisions are studied in the framework of a simple geometrical model. The distributions for inclusive production of J ψ and muon pairs in the mass continuum are analyzed. The shape of the ET distribution of the continuum agreed with the model. The previously oberved decrease of the ratio ( J ψ )/continuum with increasing ET is due to the behavior of the J ψ .
J/ψ suppression at forward rapidity in Pb–Pb collisions at sNN=5.02 TeV
2017
The inclusive J/$\psi$ production has been studied in Pn-Pb and pp collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV, using the ALICE detector at the CERN LHC. The J/$\psi$ meson is reconstructed, in the centre-of-mass rapidity interval $2.5<y<4$ and in the transverse-momentum range $p_{\rm T}<12$ GeV/$c$, via its decay to a muon pair. In this Letter, we present results on the inclusive J/$\psi$ cross section in pp collisions at $\sqrt{s}=5.02$ TeV and on the nuclear modification factor $R_{\rm AA}$. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum $p_{\rm T}$ of…
The spin of the nucleon in deep inelastic lepton scattering experiments
1992
The current experimental status of the spin dependent structure functions as measured in polarized deep inelastic scattering of charged leptons from nucleons is reviewed. The proposals for new experiments at CERN, SLAC and HERA are discussed with special emphasis on the experiment of the Spin Muon collaboration at CERN which has started data taking.
Study of J/$\psi$ production in p-U, O-U and S-U interactions at 200 GeV per nucleon
1991
Abstract In a search for quark-gluon plasma formation, the production of J/ψ and muon pairs in the mass continuum region is studied in oxygen-uranium and sulphur-uranium interactions. The yield of J/ψ relative to the continuum is measured to be a decreasing function of the neutral transverse energy produced in the collision, i.e. of the energy density. A comparison is made with proton-uranium reactions.
High energy neutrino yields from astrophysical sources II: Magnetized sources
2007
We calculate the yield of high energy neutrinos produced in astrophysical sources for arbitrary interaction depths $\tau_0$ and magnetic field strengths $B$. We take into account energy loss processes like synchrotron radiation and diffusion of charged particles in turbulent magnetic fields as well as the scattering of secondaries on background photons and the direct production of charm neutrinos. Meson-photon interactions are simulated with an extended version of the SOPHIA model. Diffusion leads to an increased path-length before protons leave the source of size R_s and therefore magnetized sources lose their transparency below the energy $E\sim 10^{18}{\rm eV} (R_s/{\rm pc}) (B/{\rm mG})…