J/Psi Production by Charm Quark Coalescence

Production of $c\bar c$ pairs in elementary hadron-hadron collisions is introduced in a simulation of relativistic heavy ion collisions. Coalescence of charmed quarks and antiquarks into various charmonium states is performed and the results are compared to PHENIX J$/\psi$ Au+Au data. The $\chi$ and $\psi$' bound states must be included as well as the ground state J$/\psi$, given the appreciable feeding from the excited states down to the J$/\psi$ via gamma decays. Charmonium coalescence is found to take place at relatively late times: generally after $c$($\bar c$)-medium interactions have ceased. Direct production of charmonia through hadron-hadron interactions, {\it ie.} without explicit presence of charm quarks, occurring only at early times, is suppressed by collisions with comoving particles and accounts for some $\sim 5\%$ of the total J$/\psi$ production. Coalescence is especially sensitive to the level of open charm production, scaling naively as $n_{c\bar c}^2$. The J$/\psi$ transverse momentum distribution is dependent on the charm quark transverse momentum distribution and early charm quark-medium interaction, thus providing a glimpse of the initial collision history.Comment: 19 pages, 10 figure

Large scale shell model calculations for odd-odd 58−62^{58-62}Mn isotopes

Large scale shell model calculations have been carried out for odd-odd $^{58-62}$Mn isotopes in two different model spaces. First set of calculations have been carried out in full $\it{fp}$ shell valence space with two recently derived $\it{fp}$ shell interactions namely GXPF1A and KB3G treating $^{40}$Ca as core. The second set of calculations have been performed in ${fpg_{9/2}}$ valence space with the $fpg$ interaction treating $^{48}$Ca as core and imposing a truncation by allowing up to a total of six particle excitations from the 0f$_{7/2}$ orbital to the upper $\it{fp}$ orbitals for protons and from the upper $\it{fp}$ orbitals to the 0g$_{9/2}$ orbital for neutron. For low-lying states in $^{58}$Mn, the KB3G and GXPF1A both predicts good results and for $^{60}$Mn, KB3G is much better than GXPF1A. For negative parity and high-spin positive parity states in both isotopes $fpg$ interaction is required. Experimental data on $^{62}$Mn is sparse and therefore it is not possible to make any definite conclusions. More experimental data on negative parity states is needed to ascertain the importance of 0g$_{9/2}$ and higher orbitals in neutron rich Mn isotopes.Comment: 5 pages, 4 figures, Submitted to Eur. Phys. J.

Electrophysiological correlates of high-level perception during spatial navigation

We studied the electrophysiological basis of object recognition by recording scalp\ud electroencephalograms while participants played a virtual-reality taxi driver game.\ud Participants searched for passengers and stores during virtual navigation in simulated\ud towns. We compared oscillatory brain activity in response to store views that were targets or\ud nontargets (during store search) or neutral (during passenger search). Even though store\ud category was solely defined by task context (rather than by sensory cues), frontal ...\ud \u

Shell Model Study of the Neutron-Rich Nuclei around N=28

We describe the properties of the neutron rich nuclei around N=28 in the shell mode framework. The valence space comprises the $sd$ shell for protons an the $pf$ shell for neutrons without any restriction. Good agreement is found with the available experimental data. The N=28 shell closure, even if eroded due to the large neutron excess, persists. The calculations predict that $^{40}$S and $^{42}$S are deformed with $\beta=0.29$ and $\beta=0.32$ respectively.Comment: 17 pages and 19 figures, LateX, RevTe

Probing hadronic formation times with antiprotons in p+A reactions at AGS energies

The production of antiprotons in $p+A$ reactions is calculated in a microscopic transport approach employing hadronic and string degrees of freedom (HSD). It is found that the abundancies of antiprotons as observed by the E910 Collaboration in $p+A$ reactions at 12.3 GeV/c as well as 17.5 GeV/c can approximately be described on the basis of primary proton-nucleon and secondary meson-baryon production channels for all targets. The transport calculations demonstrate that the antiproton rapidity distributions for heavy targets are sensitive to the $\bar{p}$ (or hadron) formation time in the nuclear medium. Within our analysis the data from the E910 Collaboration are reasonably described with a formation time of $0.4-0.8$ fm/c in the hadron rest frame.Comment: 18 pages, LaTeX, 8 postscript figures; submitted to Nucl. Phys.

Instability of the hedgehog shape for the octet baryon in the chiral quark soliton model

In this paper the stability of the hedgehog shape of the chiral soliton is studied for the octet baryon with the SU(3) chiral quark soliton model. The strangeness degrees of freedom are treated by a simplified bound-state approach, which omits the locality of the kaon wave function. The mean field approximation for the flavor rotation is applied to the model. The classical soliton changes shape according to the strangeness. The baryon appears as a rotational band of the combined system of the deformed soliton and the kaon.Comment: 24 pages, LaTeX, 8 eps file

Baryon Structure and the Chiral Symmetry of QCD

Beyond the spontaneous chiral symmetry breaking scale light and strange baryons should be considered as systems of three constituent quarks with an effective confining interaction and a chiral interaction that is mediated by the octet of Goldstone bosons (pseudoscalar mesons) between the constituent quarks.Comment: Lecture given at the 35. Universit\"atswochen f\"ur Kern- und Teilchenphysik, Schladming, Austria, March 1996 (Perturbative and Nonperturbative Aspects of Quantum Field Theory, ed. by H. Latal and W. Schweiger, Springer 1996). Paper (23 pages) with 2 figures and the required macro lamuphy

Strangeness, charm and bottom in a chiral quark-meson model

In this paper we investigate an SU(3) extension of the chiral quark-meson model. The spectra of baryons with strangeness, charm and bottom are considered within a "rigid oscillator" version of this model. The similarity between the quark part of the Lagrangian in the model and the Wess-Zumino term in the Skyrme model is noted. The binding energies of baryonic systems with baryon number B=2 and 3 possessing strangeness or heavy flavor are estimated. The results obtained are in good qualitative agreement with those obtained previously in the topological soliton (Skyrme) model.Comment: 12 pages, no figures. Journal ref: submitted to Nucl.Phys.

Subthreshold antiproton production in proton-carbon reactions

Data from KEK on subthreshold antiproton as well as on pi(+-) and K(+-) production in proton-nucleus reactions are described at projectile energies between 3.5 and 12.0 GeV. We use a model which considers a hadron-nucleus reaction as an incoherent sum over collisions of the projectile with a varying number of target nucleons. It samples complete events and allows thus for the simultaneous consideration of all particle species measured. The overall reproduction of the data is quite satisfactory. It is shown that the contributions from the interaction of the projectile with groups of several target nucleons are decisive for the description of subthreshold production. Since the collective features of subthreshold production become especially significant far below the threshold, the results are extrapolated down to COSY energies. It is concluded that an antiproton measurement at ANKE-COSY should be feasible, if the high background of other particles can be efficiently suppressed.Comment: 15 pages, 5 figures, gzipped tar file, submitted to J. Phys. G v2: Modification of text due to demands of referee

Quantum Kinks: Solitons at Strong Coupling

We examine solitons in theories with heavy fermions. These ``quantum'' solitons differ dramatically from semi-classical (perturbative) solitons because fermion loop effects are important when the Yukawa coupling is strong. We focus on kinks in a $(1+1)$--dimensional $\phi^4$ theory coupled to fermions; a large-$N$ expansion is employed to treat the Yukawa coupling $g$ nonperturbatively. A local expression for the fermion vacuum energy is derived using the WKB approximation for the Dirac eigenvalues. We find that fermion loop corrections increase the energy of the kink and (for large $g$) decrease its size. For large $g$, the energy of the quantum kink is proportional to $g$, and its size scales as $1/g$, unlike the classical kink; we argue that these features are generic to quantum solitons in theories with strong Yukawa couplings. We also discuss the possible instability of fermions to solitons.Comment: 21 pp. + 2 figs., phyzzx, JHU-TIPAC-92001