Local approximations for polarization potentials

We discuss the derivation of an equivalent polarization potential independent of angular momentum l for use in the optical Schrodinger equation that describes the elastic scattering of heavy ions. Three different methods are used for this purpose. Application of our theory to the low energy scattering of light heavy-ion systems at near-barrier energies is made. It is found that the notion of an l-independent polarization potential has some validity but cannot be a good substitute for the l-dependent local equivalent Feshbach polarization potential.

Magnetic ordering of EuTe/PbTe multilayers determined by x-ray resonant diffraction

In this work we use resonant x-ray diffraction combined with polarization analysis of the diffracted beam to study the magnetic ordering in EuTe/PbTe multilayers. The presence of satellites at the (1/2 1/2 1/2) magnetic reflection of a 50 /repetition EuTe/PbTe superlattice demonstrated the existence of magnetic correlations among the alternated EuTe layers. The behavior of the satellites intensity as T increases toward the Neel temperature T(N) indicates that these correlations persist nearly up to T(N) and suggests the preferential decrease of the magnetic order parameter of external monolayers of each EuTe layer within the superlattice. (C) 2008 American Institute of Physics.

(7,9,10)Be elastic scattering and total reaction cross sections on a (12)C target

Elastic scattering angular distributions for (7)Be, (9)Be, and (10)Be isotopes on (12)C target were measured at laboratory energies of 18.8, 26.0, and 23.2 MeV, respectively. The analysis was performed in terms of optical model potentials using Woods-Saxon and double-folding form factors. Also, continuum discretized coupled-channels calculations were performed for (7)Be and (9)Be + (12)C systems to infer the role of breakup in the elastic scattering. For the (10)Be + (12)C system, bound states coupled-channels calculations were considered. Moreover, total reaction cross sections were deduced from the elastic scattering analysis and compared with published data on other weakly and tightly bound projectiles elastically scattered on the (12)C target, as a function of energy.

Measurement of the Bottom Quark Contribution to Nonphotonic Electron Production in p plus p Collisions at root s=200 GeV

The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at root s = 200 GeV has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of p(T) >= 5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high p(T).

Comparison of (120)Sn((6)He, (6)He)(120)Sn and (120)Sn(alpha,alpha)(120)Sn elastic scattering and signatures of the (6)He neutron halo in the optical potential

Cross sections of (120)Sn(alpha,alpha)(120)Sn elastic scattering have been extracted from the alpha-particle-beam contamination of a recent (120)Sn((6)He,(6)He)(120)Sn experiment. Both reactions are analyzed using systematic double-folding potentials in the real part and smoothly varying Woods-Saxon potentials in the imaginary part. The potential extracted from the (120)Sn((6)He,(6)He)(120)Sn data may be used as the basis for the construction of a simple global (6)He optical potential. The comparison of the (6)He and alpha data shows that the halo nature of the (6)He nucleus leads to a clear signature in the reflexion coefficients eta(L) : The relevant angular momenta L with eta(L) >> 0 and eta(L) << 1 are shifted to larger L with a broader distribution. This signature is not present in the alpha-scattering data and can thus be used as a new criterion for the definition of a halo nucleus.

alpha-particle production in (6)He+(120)Sn collisions

The collision (6)He+ (120)Sn has been investigated at four energies near the Coulomb barrier. A large yield of a particles has been detected, with energies around the energy of the scattered (6)He beam. The energy and angular distributions of the a particles have been analyzed and compared with breakup and neutron transfer calculations.

Higher Moments of Net Proton Multiplicity Distributions at RHIC

200 GeV corresponding to baryon chemical potentials (mu(B)) between 200 and 20 MeV. Our measurements of the products kappa sigma(2) and S sigma, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long-range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the root s(NN) dependence of kappa sigma(2). From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for mu(B) below 200 MeV.

Charged and strange hadron elliptic flow in Cu plus Cu collisions at root s(NN)=62.4 and 200 GeV

We present the results of an elliptic flow, v(2), analysis of Cu + Cu collisions recorded with the solenoidal tracker detector (STAR) at the BNL Relativistic Heavy Ion Collider at root s(NN) = 62.4 and 200 GeV. Elliptic flow as a function of transverse momentum, v(2)(p(T)), is reported for different collision centralities for charged hadrons h(+/-) and strangeness-ontaining hadrons K(S)(0), Lambda, Xi, and phi in the midrapidity region vertical bar eta vertical bar < 1.0. Significant reduction in systematic uncertainty of the measurement due to nonflow effects has been achieved by correlating particles at midrapidity, vertical bar eta vertical bar < 1.0, with those at forward rapidity, 2.5 < vertical bar eta vertical bar < 4.0. We also present azimuthal correlations in p + p collisions at root s = 200 GeV to help in estimating nonflow effects. To study the system-size dependence of elliptic flow, we present a detailed comparison with previously published results from Au + Au collisions at root s(NN) = 200 GeV. We observe that v(2)(p(T)) of strange hadrons has similar scaling properties as were first observed in Au + Au collisions, that is, (i) at low transverse momenta, p(T) < 2 GeV/c, v(2) scales with transverse kinetic energy, m(T) - m, and (ii) at intermediate p(T), 2 < p(T) < 4 GeV/c, it scales with the number of constituent quarks, n(q.) We have found that ideal hydrodynamic calculations fail to reproduce the centrality dependence of v(2)(p(T)) for K(S)(0) and Lambda. Eccentricity scaled v(2) values, v(2)/epsilon, are larger in more central collisions, suggesting stronger collective flow develops in more central collisions. The comparison with Au + Au collisions, which go further in density, shows that v(2)/epsilon depends on the system size, that is, the number of participants N(part). This indicates that the ideal hydrodynamic limit is not reached in Cu + Cu collisions, presumably because the assumption of thermalization is not attained.

Elastic scattering and total reaction cross section of (6)He+(120)Sn

The elastic scattering of (6)He on (120)Sn has been measured at four energies above the Coulomb barrier using the (6)He beam produced at the RIBRAS (Radioactive Ion Beams in Brasil) facility. The elastic angular distributions have been analyzed with the optical model and three- and four-body continuum-discretized coupled-channels calculations. The total reaction cross sections have been derived and compared with other systems of similar masses.

J/psi production at high transverse momenta in p plus p and Cu plus Cu collisions at root s(NN)=200 GeV

The STAR Collaboration at the Relativistic Heavy Ion Collider presents measurements of J/psi e(+) e(-) at midrapidity and high transverse momentum (pT > 5 GeV/c) in p + p and central Cu + Cu collisions at root s(NN) = 200 GeV. The inclusive J/psi production cross section for Cu + Cu collisions is found to be consistent at high p(T) with the binary collision-scaled cross section for p + p collisions. At a confidence level of 97%, this is in contrast to a suppression of J/psi production observed at lower p(T). Azimuthal correlations of J/psi with charged hadrons in p + p collisions provide an estimate of the contribution of B-hadron decays to J/psi production of 13% +/- 5%.

Elastic scattering and total reaction cross sections for the (8)Li+(12)C system

The elastic-scattering angular distribution for (8)Li on (12)C has been measured at E(LAB) = 23.9 MeV with (8)Li radioactive nuclear beam produced by the Radioactive Ion Beams in Brazil facility. This angular distribution was analyzed in terms of optical-model with Woods-Saxon and double-folding Sao Paulo potential. The roles of the breakup and inelastic channels were also investigated with cluster folding and deformed potentials, respectively, through coupled-channels calculations. The angular distribution for the proton-transfer (12)C((8)Li, (9)Be)(11)B reaction was also measured at the same energy. The spectroscopic factor for the <(9)Be|(8)Li + p > bound system was obtained and compared with shell-model calculations and with other experimental values. Total reaction cross sections for the present system were also extracted from the elastic-scattering analysis. A systematic of the reduced reaction cross sections obtained from the present and published data on (6,7,8)Li isotopes on (12)C was performed as a function of energy.

Possible hyperdeformed band in (36)Ar observed in (12)C+(24)Mg elastic scattering

Fifteen strongly oscillating angular distributions of the elastic scattering of (12)C + (24)Mg at energies around the Coulomb barrier (E(c.m). = 10.67-16.00 MeV) are reproduced by adding five Breit-Wigner resonance terms to the l = 2, 4, 6, 7, and 8 elastic S matrix. The nonresonant, background elastic scattering S matrix S(l)(0) is calculated using the Sao Paulo potential. The J = 2, 4, 6, 7, and 8 (h) over bar molecular resonances fit well into a rotational molecular band, together with other higher lying resonances observed in the (16)O + (20)Ne elastic scattering. We propose that the presently observed, largely deformed molecular band corresponds to the hyperdeformed band, which has been found previously in alpha-cluster calculations, as well as in a new Nilsson model calculation. Systematic study of its possible clusterizations predicts the preference of the (12)C + (24)Mg and (16)O + (20)Ne molecular structure, in accordance with our present results.

Reaction cross sections for (8)B, (7)Be, and (6)Li+(58)Ni near the Coulomb barrier: Proton-halo effects

Elastic scattering of (8)B, (7)Be, and (6)Li on a (58)Ni target has been measured at energies near the Coulomb barrier. Optical-model fits were made to the experimental angular distributions, and total reaction cross sections were deduced. A comparison with other systems provides striking evidence for proton-halo effects on (8)B reactions. As opposed to the situation for the neutron-halo nucleus (6)He, for which particle transfer dominates, the ""extra"" cross section observed for (8)B appears to result entirely from projectile breakup.

Effects of the target spin on the reaction mechanism of the (16)O+(63)Cu system

Precise quasielastic and alpha-transfer excitation functions, at theta(lab) = 161 degrees, have been measured at energies near the Coulomb barrier for the (16)O + (63)Cu system. This is the first time reported quasielastic barrier distribution for a medium odd-A nucleus target deduced from the data. Additional elastic scattering angular distributions data available in the literature for this system were also used in the investigation of the role of several individual channels in the reaction dynamics, by comparing the data with free-parameter coupled-channels calculations. In order to do so, the nucleus-nucleus bare potential has a double-folding potential as the real component and only a very short-range imaginary potential. The quasielastic barrier distribution has been shown to be a powerful tool in this analysis at the barrier region. A high collectivity of the (63)Cu was observed, mainly due to the strong influence of its 5/2-and 7/2-states on all reaction channels investigated. A striking influence of the reorientation of the ground-state target-spin on the elastic cross sections, taken at backward angles, was also observed.

The (9)Be((8)Li, (9)Be)(8)Li elastic-transfer reaction

Angular distributions for the (9)Be((8)Li, (9)Be) (8)Li elastic-transfer reaction have been measured with a 27-MeV (8)Li radioactive nuclear beam. Spectroscopic factors for the <(9)Be vertical bar(8)Li + p > bound system were obtained from the comparison between the experimental differential cross sections and finite-range distorted-wave Born approximation calculations made with the code FRESCO. The spectroscopic factors so obtained are compared with shell-model calculations and other experimental values. Using the present value for the spectroscopic factors, cross sections and reaction rates for the (8)Li(p,gamma) (9)Be direct proton-capture reaction of astrophysical interest were calculated in the framework of the potential model.