Heavy-flavor measurements by the PHENIX experiment at RHIC

In recent years, PHENIX has studied many important observables related to heavy-flavor physics through their leptonic decay measurements including the invariant yield of electrons from nonphotonic sources, and prompt single muons, both of which are dominated by D and B mesons. Charm and beauty cross-sections were measured and compared through single lepton, and lepton-hadron correlations in p+p collisions at root s = 200 GeV. Observables for quarkonia production such as invariant yield and polarization were also measured in p+p collisions. In Au+Au collisions, preliminary results for the R(AA) for single electrons and a 90% CL upper limit for the suppression of s were produced. And in d+Au collisions, a preliminary R(CP) study for J/psi production in different centrality ranges was extracted.

Fractal structures in nonlinear plasma physics

Fractal structures appear in many situations related to the dynamics of conservative as well as dissipative dynamical systems, being a manifestation of chaotic behaviour. In open area-preserving discrete dynamical systems we can find fractal structures in the form of fractal boundaries, associated to escape basins, and even possessing the more general property of Wada. Such systems appear in certain applications in plasma physics, like the magnetic field line behaviour in tokamaks with ergodic limiters. The main purpose of this paper is to show how such fractal structures have observable consequences in terms of the transport properties in the plasma edge of tokamaks, some of which have been experimentally verified. We emphasize the role of the fractal structures in the understanding of mesoscale phenomena in plasmas, such as electromagnetic turbulence.

Nuclear dependence of charm production

Using data taken by SELEX during the 1996-1997 fixed target run at Fermilab, we study the production of charmed hadrons on copper and carbon targets with Sigma(-), p, pi(-), and pi(+) beams. Parametrizing the dependence of the inclusive production cross section on the atomic number A as A(alpha), we determine alpha for D(+), D(0), D(s)(+), D(+)(2010), Lambda(+)(c), and their respective anti-particles, as a function of their transverse momentum p(t) and scaled longitudinal momentum x(F). Within our statistics there is no dependence of alpha on x(F) for any charm species for the interval 0.1 < x(F) < 1.0. The average value of alpha for charm production by pion beams is alpha(meson) = 0.850 +/- 0.028. This is somewhat larger than the corresponding average alpha(baryon) = 0.755 +/- 0.016 for charm production by baryon beams (Sigma(-), p).

D (sJ) (2317) meson production at RHIC

We study the production of D (sJ) (2317) mesons in relativistic heavy ion collisions using the quark coalescence model. The predicted D (sJ) (2317) abundance depends sensitively on the quark structure of the D (sJ) (2317) meson. We have also evaluated the absorption cross sections of the D (sJ) (2317) meson by pi, rho, kaon and K* in a phenomenological hadronic model. We find that the final yield of D (sJ) (2317) mesons remains sensitive to its initial number produced from the quark-gluon plasma, providing thus the possibility of studying the quark structure of the D (sJ) (2317) meson and its production mechanism in relativistic heavy ion collisions.

Dilepton mass spectra in p plus p collisions at root s=200 GeV

PHENIX has measured the electron-positron pair mass spectrum from 0 to 8 GeV/c(2) in p + p collisions at root s = 200 GeV. The contributions from light meson decays to e(+)e(-) pairs have been determined based on measurements of hadron production cross sections by PHENIX. Within the systematic uncertainty of similar to 20% they account for all e(+)e(-) pairs in the mass region below similar to 1 GeV/c(2). The e(+)e(-) pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) pb. which is consistent with QCD calculations and measurements of single leptons by PHENIX. (C) 2008 Elsevier BV. All rights reserved.

Spontaneous breaking of superconformal invariance in (2+1) D supersymmetric Chern-Simons-matter theories in the large N limit

In this work we study the spontaneous breaking of superconformal and gauge invariances in the Abelian N = 1,2 three-dimensional supersymmetric Chern-Simons-matter (SCSM) theories in a large N flavor limit. We compute the Kahlerian effective superpotential at subleading order in 1/N and show that the Coleman-Weinberg mechanism is responsible for the dynamical generation of a mass scale in the N = 1 model. This effect appears due to two-loop diagrams that are logarithmic divergent. We also show that the Coleman-Weinberg mechanism fails when we lift from the N = 1 to the N = 2 SCSM model. (C) 2010 Elsevier B.V All rights reserved.

Density profiles in the raise and peel model with and without a wall; physics and combinatorics

We consider the raise and peel model of a one-dimensional fluctuating interface in the presence of an attractive wall. The model can also describe a pair annihilation process in disordered unquenched media with a source at one end of the system. For the stationary states, several density profiles are studied using Monte Carlo simulations. We point out a deep connection between some profiles seen in the presence of the wall and in its absence. Our results are discussed in the context of conformal invariance ( c = 0 theory). We discover some unexpected values for the critical exponents, which are obtained using combinatorial methods. We have solved known ( Pascal`s hexagon) and new (split-hexagon) bilinear recurrence relations. The solutions of these equations are interesting in their own right since they give information on certain classes of alternating sign matrices.