FLUCTUATIONS AND INITIAL STATE GRANULARITY IN HEAVY ION COLLISIONS AND THEIR EFFECTS ON OBSERVABLES FROM HYDRODYNAMICS

A comparison is made between results obtained using smooth initial conditions and event-by-event initial conditions in the hydrodynamical description of relativistic nuclear collisions. Some new results on directed flow are also included.

Measurement of neutrino oscillations with the MINOS detectors in the NuMI beam

This Letter reports new results from the MINOS experiment based on a two-year exposure to muon neutrinos from the Fermilab NuMI beam. Our data are consistent with quantum-mechanical oscillations of neutrino flavor with mass splitting vertical bar Delta m(2)vertical bar = (2.43 +/- 0.13) x 10(-3) eV(2) (68% C.L.) and mixing angle sin(2)(2 theta) > 0.90 (90% C.L.). Our data disfavor two alternative explanations for the disappearance of neutrinos in flight: namely, neutrino decays into lighter particles and quantum decoherence of neutrinos, at the 3.7 and 5.7 standard-deviation levels, respectively.

Identifying Multiquark Hadrons from Heavy Ion Collisions

Identifying hadronic molecular states and/or hadrons with multiquark components either with or without exotic quantum numbers is a long-standing challenge in hadronic physics. We suggest that studying the production of these hadrons in relativistic heavy ion collisions offers a promising resolution to this problem as yields of exotic hadrons are expected to be strongly affected by their structures. Using the coalescence model for hadron production, we find that, compared to the case of a nonexotic hadron with normal quark numbers, the yield of an exotic hadron is typically an order of magnitude smaller when it is a compact multiquark state and a factor of 2 or more larger when it is a loosely bound hadronic molecule. We further find that some of the newly proposed heavy exotic states could be produced and realistically measured in these experiments.

Transition in Yield and Azimuthal Shape Modification in Dihadron Correlations in Relativistic Heavy Ion Collisions

Hard-scattered parton probes produced in collisions of large nuclei indicate large partonic energy loss, possibly with collective produced-medium response to the lost energy. We present measurements of pi(0) trigger particles at transverse momenta p(T)(t) = 4-12 GeV/c and associated charged hadrons (p(T)(a) = 0.5-7 GeV/c) vs relative azimuthal angle Delta phi in Au + Au and p + p collisions at root s(NN) = 200 GeV. The Au + Au distribution at low p(T)(a), whose shape has been interpreted as a medium effect, is modified for p(T)(t) < 7 GeV/c. At higher p(T)(t), the data are consistent with unmodified or very weakly modified shapes, even for the lowest measured p(T)(a), which quantitatively challenges some medium response models. The associated yield of hadrons opposing the trigger particle in Au + Au relative to p + p (I(AA)) is suppressed at high p(T) (I(AA) approximate to 0.35-0.5), but less than for inclusive suppression (R(AA) approximate to 0.2).

High-p(T) pi(0) production with respect to the reaction plane in Au plus Au collisions at s(NN)=200 GeV

Measurements of the azimuthal anisotropy of high-p(T) neutral pion (pi(0)) production in Au+Au collisions at s(NN)=200 GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of pi(0) mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v(2)) of the angular distributions are presented as a function of pi(0) transverse momentum (p(T)) for different bins in collision centrality. Measured reaction plane dependent pi(0) yields are used to determine the azimuthal dependence of the pi(0) suppression as a function of p(T), R(AA)(Delta phi,p(T)). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the pi(0) suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.

Hydro-kinetic approach to relativistic heavy ion collisions

We develop a combined hydro-kinetic approach which incorporates a hydrodynamical expansion of the systems formed in A + A collisions and their dynamical decoupling described by escape probabilities. The method corresponds to a generalized relaxation time (tau(rel)) approximation for the Boltzmann equation applied to inhomogeneous expanding systems; at small tau(rel) it also allows one to catch the viscous effects in hadronic component-hadron-resonance gas. We demonstrate how the approximation of sudden freeze-out can be obtained within this dynamical picture of continuous emission and find that hypersurfaces, corresponding to a sharp freeze-out limit, are momentum dependent. The pion m(T) spectra are computed in the developed hydro-kinetic model, and compared with those obtained from ideal hydrodynamics with the Cooper-Frye isothermal prescription. Our results indicate that there does not exist a universal freeze-out temperature for pions with different momenta, and support an earlier decoupling of higher p(T) particles. By performing numerical simulations for various initial conditions and equations of state we identify several characteristic features of the bulk QCD matter evolution preferred in view of the current analysis of heavy ion collisions at RHIC energies.

Bilayer graphene dual-gate nanodevice: An ab initio simulation

We study the electronic transport properties of a dual-gated bilayer graphene nanodevice via first-principles calculations. We investigate the electric current as a function of gate length and temperature. Under the action of an external electrical field we show that even for gate lengths up 100 angstrom, a nonzero current is exhibited. The results can be explained by the presence of a tunneling regime due the remanescent states in the gap. We also discuss the conditions to reach the charge neutrality point in a system free of defects and extrinsic carrier doping.

High density flux of Co nanoparticles produced by a simple gas aggregation apparatus

Gas aggregation is a well known method used to produce clusters of different materials with good size control, reduced dispersion, and precise stoichiometry. The cost of these systems is relatively high and they are generally dedicated apparatuses. Furthermore, the usual sample production speed of these systems is not as fast as physical vapor deposition devices posing a problem when thick samples are needed. In this paper we describe the development of a multipurpose gas aggregation system constructed as an adaptation to a magnetron sputtering system. The cost of this adaptation is negligible and its installation and operation are both remarkably simple. The gas flow for flux in the range of 60-130 SCCM (SCCM denotes cubic centimeter per minute at STP) is able to completely collimate all the sputtered material, producing spherical nanoparticles. Co nanoparticles were produced and characterized using electron microscopy techniques and Rutherford back-scattering analysis. The size of the particles is around 10 nm with around 75 nm/min of deposition rate at the center of a Gaussian profile nanoparticle beam.

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.

Parton energy loss in heavy-ion collisions via direct-photon and charged-particle azimuthal correlations

Charged-particle spectra associated with direct photon (gamma(dir)) and pi(0) are measured in p + p and Au + Au collisions at center-of-mass energy root(S)(NN) = 200 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A shower-shape analysis is used to partially discriminate between gamma(dir) and pi(0). Assuming no associated charged particles in the gamma(dir) direction ( near side) and small contribution from fragmentation photons (gamma(frag)), the associated charged-particle yields opposite to gamma(dir) (away side) are extracted. In central Au + Au collisions, the charged-particle yields at midrapidity (vertical bar eta vertical bar < 1) and high transverse momentum (3 < (assoc)(PT) < 16 GeV/c) associated with gamma(dir) and pi(0) (vertical bar eta vertical bar < 0.9, 8 < (trig)(PT) < 16 GeV/c) are suppressed by a factor of 3-5 compared with p + p collisions. The observed suppression of the associated charged particles is similar for gamma(dir) and pi(0) and independent of the gamma(dir) energy within uncertainties. These measurements indicate that, in the kinematic range covered and within our current experimental uncertainties, the parton energy loss shows no sensitivity to the parton initial energy, path length, or color charge.

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.

Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy-ion collisions

Parity (P)-odd domains, corresponding to nontrivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in noncentral collisions. To study this effect, we investigate a three-particle mixed-harmonics azimuthal correlator which is a P-even observable, but directly sensitive to the charge-separation effect. We report measurements of this observable using the STAR detector in Au + Au and Cu + Cu collisions at root s(NN) = 200 and 62 GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators and discuss in detail possible contributions from other effects that are not related to P violation.

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.

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.

Hadronic resonance production in d+Au collisions at root S(NN) = 200 GeV measured at the BNL Relativistic Heavy Ion Collider

We present the first measurements of the rho(770)(0),K(*)(892),Delta(1232)(++),Sigma(1385), and Lambda(1520) resonances in d+Au collisions at s(NN)=200 GeV, reconstructed via their hadronic decay channels using the STAR detector (the solenoidal tracker at the BNL Relativistic Heavy Ion Collider). The masses and widths of these resonances are studied as a function of transverse momentum p(T). We observe that the resonance spectra follow a generalized scaling law with the transverse mass m(T). The < p(T)> of resonances in minimum bias collisions are compared with the < p(T)> of pi,K, and p. The rho(0)/pi(-),K(*)/K(-),Delta(++)/p,Sigma(1385)/Lambda, and Lambda(1520)/Lambda ratios in d+Au collisions are compared with the measurements in minimum bias p+p interactions, where we observe that both measurements are comparable. The nuclear modification factors (R(dAu)) of the rho(0),K(*), and Sigma(*) scale with the number of binary collisions (N(bin)) for p(T)> 1.2 GeV/c.