Many body modes of antiproton annihilation tested with antiproton production

We study the inclusive (y,¯ p) and (p,p) reactions in nuclei and check the sensitivity to the¯p annihilation mechanisms. We find that including the many body annihilation mechanisms in nuclei reduces appreciably the cross section of these reactions with respect to the evaluation considering only the one body mechanism of¯p annihilation. This shows that the¯p production reactions are more sensitive to¯p annihilation than the direct¯p annihilation reactions and makes the production experiments very useful tools to investigate the complex mechanisms of¯p annihilation in nuclei.     

Photoproduction of π+ p-pairs on the 16O nucleus and isobar configurations

The yield of the ¹⁶O(γ, π⁺ p) reaction has been measured in the region of the excitation of the Δ(1232) isobar at high momentum transfers to the residual nuclear system. The experimental data are interpreted within the model taking into account manifestations of isobar configurations in the ground state of the ¹⁶O nucleus. Direct and exchange mechanisms of the production of pions with emission of one and two nucleons, which follow from the structures of the density matrices for these reactions, have been considered. The probability of the production of the Δ-isobar in the ground state of the ¹⁶O nucleus has been empirically estimated as P _Δ = 0.019 ± 0.003 ± 0.003.     

Multichannel effective range approach to low energy nucleon-antinucleon interactions

MultichannelM-matrix method is applied to an N¯N-system with taking into account elasticp¯ p-scattering, charge-exchangep¯ p → n¯ n reaction andp¯ p annihilation. The isospin breaking in theM-matrix is discussed. We describe the differential and total cross-sections forp¯ p → p¯ p andp¯ p → n¯ n processes, cross-section σ_tot(p¯ p) and the real-to-imaginary ratio of the forward amplitude of elasticp¯ p scattering. The fitting leads to bound state in thep-wave near thep¯ p-threshold, which elucidates a significant role of this wave at small energies.     

Hadron spectra from nuclear collisions

We describe high energy nuclear collisions by a superposition of isotropically decaying thermal sources (“fireballs”) of freeze-out temperature T = 0.15 GeV. The longitudinal fireball superposition is taken as boost-invariant, in a rapidity range determined by the average energy loss of nucleons in p?p collisions. The transverse fireball motion is assumed to be due to random walk initial state collisions; it is determined by p?A data and then extrapolated to central A?B interactions. We thus obtain parameter-free predictions for the rapidity and transverse momentum spectra of hadrons produced in high energy nucleus-nucleus collisions. The results account fully for the observed broadening of transverse momentum distributions, so that single-particle spectra require neither collective flow nor temperature increase.     

Two nucleon emission following bound pion absorption

The absorption of a bound 2p pion in¹⁶O with the emission of two fast nucleons leading to low excitation of the residual nucleus has been studied. In our calculation, the following important effects have been considered simultaneously: (i) correlations in the initial nuclear wave function are treated on the basis of the Brueckner theory, (ii) the mutual final state scattering of the emitted pair and (iii) the nucleon-nucleus scattering are taken into account by the use of eikonal model wave function. Results are compared with other calculations and experiments. It is found that inspite of our elaborate treatments serious discrepancies between theory and experiments still remain. A more careful study of the absorption mechanism is emphasized.     

Quark condensate in the nuclear matter

We calculate the quark condensate in the nuclear matter, taking into account the single-pion and two-pion exchanges between nucleons. We find the dependence of the averaged value of the quark operator¯qq on the density of the matterρ. At very low density the nonlinear terms are proportional toρ ² and increase the tendency to restoration of the chiral symmetry. At larger values of density the account of interaction inside the matter slower down the restoration of chiral symmetry compared to the gas approximation law. The leading nonlinear term in Fermi momentum power expansion becomes of the orderρ ^4/3 . The value of the condensate at the saturation value of density is obtained. The role of multinucleon effects is analyzed.     

Rescattering mechanisms for\bar pd \to pX reactions

Inclusive proton spectra for the reactions¯pd→3πp, ¯pd→5πp, and¯p d →K¯Kmπp are calculated. In addition to nucleon exchange, the rescattering of pions and kaons, and the production and absorption of heavy mesons is evaluated. In the proton spectator momentum regime of 200 to 600 MeV/c, the role of heavy mesons is found to be negligible. The proper counting of the topological variants of pion and kaon rescattering can explain the cross sections with the exception of the¯pd→3πp channel.     

A measurement of neutron-proton bremsstrahlung near 130 MeV

We have measured the double differential cross section for bremsstrahlung production in neutron-proton collisions near 130 MeV. Outgoing nucleons were detected at eight pairs of angles simultaneously. The cross sections agree with several theoretical predictions for those four angle pairs in which the proton emerged at 20° (θ = 20°), but are larger than expected in the four cases that θ_p = 32°. The method of data reduction, and the sources of uncertainty, are discussed in detail.     

Using nuclei to probe hadronization in QCD

The behavior of quasi-exclusive and inclusive ϱ and J/ψ photoproduction, electroproduction and hadroproduction in nuclei are discussed for small and large p_⊥. In particular we argue that J/ψ production in ion-ion collisions is likely to be suppressed relative to the background lepton pair production, independent of whether or not a QCD plasma is formed. We point out that previous extractions of the J/ψ inelastic cross section do not actually measure the cross section for the interaction of physical J/ψ's with nucleons.     

Production of hypernuclei with hadronic and electromagnetic probes

We present an overview of a fully covariant formulation for describing hypernuclear production with hadronic and electromagnetic probes. This theory is based on an effective Lagrangian picture and it focuses on production amplitudes that are described via creation, propagation and decay into relevant channels of N^∗(1650), N^∗(1710) and N^∗(1720) intermediate baryonic resonance states in the initial collision of the projectile with one of the target nucleons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Specific examples are discussed for reactions which are of interest in current and future experiments on hypernuclear production.     

Search for narrow p¯p resonances in the reaction p¯p → p¯pπ+π−.

The reaction p¯p → p¯pπ⁺π^?. has been studied with high statistics at CERN-LEAR with incident p¯ momenta from 1.65 to 2.0 GeV/c by the JETSET (PS202) experiment. The aim of this paper is to search for narrow resonances decaying to p¯p. No evidence for such structures is found. In particular, an upper limit for the production of a 2.02 GeV state with a width of Γ = 20 MeV, having been seen in other hadroproduction experiments, is established. Our results restrict the cross section for such a peak to be below 200 nb at the 95% confidence level.     

Formation of η′(958) Meson Bound States and Chiral Symmetry In-Medium

We theoretically discuss the feasibility to observe the η′(958)-mesic nuclei by using the missing mass spectroscopy. We evaluate the η′-nucleus optical potential including the contribution of lowest order in density together with the second order terms account for η′ absorption by two nucleons, based on a recent model of the η′N interaction. We show the calculated formation cross section of the η′ bound states from (π, N) reaction with pion beam momentum p _π = 1.8 GeV/c and (p, d) reaction with proton kinetic energy T _p = 2.5 GeV.     

The differential cross section and polarization in p + p → d + π+

A coupled-channels approach is used for incorporating NΔ configurations into the mechanism of the meson production reaction p + p → d + π⁺. The differential cross section and the polarization asymmetry are calculated for lab energies ranging from threshold to 750 MeV including the partial waves up to f-wave pions and ³F state nucleons. It is found that the pp state ³F₃ is important in obtaining a reasonable agreement with the existing experimental data. We find a remarkable insensitivity of the differential cross section to the D-state probability of the deuteron, whereas the polarization is somewhat dependent on this.     

Antiproton production inp+A andd+A reactions at subthreshold energies

The production of antiprotons in proton-nucleus and deuteron-nucleus collisions is analyzed with respect to one-step nucleon-nucleon (NN → NNp¯ p) and secondary Δ-nucleon (ΔN → NNN¯ p) production channels within a phase-space model incorporating the selfenergies of the baryons. It is found that contrary to nucleus-nucleus collisions the Δ induced reaction channels are of minor importance except at very low bombarding energies. The data from KEK are approximately reproduced when accounting for the internal momentum distribution of the deuteron which provides a natural explanation for the large enhancement of the ¯p cross section ind+A as compared top+A.     

Thermal hadron production in Si-Au collisions

The most abundantly produced hadron species in Si - Au collisions at the BNL-AGS (nucleons, pions, kaons, antikaons and hyperons) are shown to be in accord with emission from a thermal resonance gas source. Within the uncertainties of the present data, two freeze-out points are possible. The best agreement is obtained for a temperature T ? 110 MeV and a baryochemical potential μ_B ? 540 MeV, corresponding to about 1/3 standard nuclear density. Another possible point lies at about twice nuclear density, with T ? 160 MeV and μ_B ? 620 MeV. Our analysis takes the isopin asymmetry of the initial state fully into account.     

Charmonium production in proton-nucleon and proton-nucleus collisions

Systematic nuclear effects discovered in the production ofJ/ψ particles in high-energy proton-nucleus collisions cannot be explained within the conventional picture in which a heavy color singlet $Q\bar Q$ pair, after its production, experiences multiple scattering from nucleons of the residual nucleus. We propose to take into account color octet intermediate states formed in the primary production of the heavy-quark pairs. Using a perturbative QCD analysis we study the microscopic production mechanism for $Q\bar Q$ pairs through gluon-gluon fusion with subsequent color neutralization in a strongly interacting medium. The influence of the surrounding matter on this process is investigated.     

Asymptotic properties of regge trajectories and elastic pseudoscalar-meson scattering on nucleons at high energies

A phenomenological Regge-eikonal model featuring nonlinear monotonic parametrizations of vacuum Regge trajectories, where their asymptotic behavior in the perturbative sector is taken explicitly into account, is proposed for describing the elastic diffractive scattering of light pseudoscalar mesons on nucleons. In analyzing available experimental data on angular distributions, it is shown that, at collision energies in the region √s > 13 GeV, the diffraction pattern of the processes π ^± p → π ^± p and K ^± p → K ^± p at low momentum transfers can be described qualitatively by using the same phenomenological approximations to vacuum Regge trajectories as in the case of nucleon-nucleon scattering. This fact is indicative of the possibility of explicitly relating Regge phenomenology of various hadron-hadron processes to fundamental results obtained within QCD.     

How much charm can \bar PANDA produce?

We consider the production of charmed baryons and mesons in the proton-antiproton binary reactions at the energies of the future $\bar P$ ANDA experiment. To describe these processes in terms of hadronic interaction models, one needs strong couplings of the initial nucleons with the intermediate and final charmed hadrons. Similar couplings enter the models of binary reactions with strange hadrons. For both charmed and strange hadrons we employ the strong couplings and their ratios calculated from QCD light-cone sum rules. In this method finite masses of c and s quarks are taken into account. Employing the Kaidalov??s quark-gluon string model with Regge poles and adjusting the normalization of the amplitudes in this model to the calculated strong couplings, we estimate the production cross-section of charmed hadrons. For $p\bar p \to \Lambda _c \bar \Lambda _c$ it can reach several tens of nb at p _lab = 15 GeV, whereas the cross-sections of ?? _c and D pair production are predicted to be smaller.     

A new diquark model for deep inelastic structure functions

The bulk of data from deep inelasticep, eD, μp, μN, νp and νN scattering is fitted with a new diquark model of nucleons. The proton is found to be mostly in au(ud) ₀ state, where the (ud)₀ diquark has spin and isospin zero. There is hence no trace ofSU(6) symmetry among diquarks in nucleons.