Repositório RCAAP
Recent results from PHOBOS at RHIC
PHOBOS is one of the four heavy ion experiments currently running at the Relativistic Heavy Ion Collider (RHIC). In this paper we will present some of the current results from PHOBOS: the study of charged multiplicity distribution as function of pseudorapidity and centrality at <IMG SRC="/img/revistas/bjp/v34n3a/a32img01.gif" > or = 19.6, 130 and 200 GeV, a discussion of multiplicity scaling, and a measurement of transverse momentum spectra (pT) of charged hadrons produced in d+Au and Au+Au interactions at <IMG SRC="/img/revistas/bjp/v34n3a/a32img01.gif" > or = 200 GeV. The dependence of the Au+Au yields as function of centrality is found to be independent of pT. A strong suppression in the Au+Au hadron spectra relative to p<IMG SRC="/img/revistas/bjp/v34n3a/a32img05.gif"> at high pT is observed. The spectral shape for d+Au collisions is significantly different from the observations in Au+Au, the yield suppression is not observed in d+Au.
2004
Back,B.B. Baker,M.D. Ballintijn,M. Barton,D.S. Becker,B. Betts,R.R. Bickley,A.A. Bindel,R. Budzanowski,A. Busza,W. Carroll,A. Decowski,M.P. García,E. Gburek,T. George,N. Gulbrandsen,K. Gushue,S. Halliwell,C. Hamblen,J. Harrington,A.S. Heintzelman,G.A. Henderson,C. Hofman,D.J. Hollis,R.S. Hoynski,R. Holzman,B. Iordanova,A. Johnson,E. Kane,J.L. Katzy,J. Khan,N. Kucewicz,W. Kulinich,P. Kuo,C.M. Lee,J.W. Lin,W.T. Manly,S. McLeod,D. Mignerey,A.C. Nouicer,R. Olszewski,A. Pak,R. Park,I.C. Pernegger,H. Reed,C. Remsberg,L.P. Reuter,M. Roland,C. Roland,G. Rosenberg,L. Sagerer,J. Sarin,P. Sawicki,P. Sedykh,I. Skulski,W. Smith,C.E. Steinberg,P. Stephans,G.S.F. Sukhanov,A. Tang,J.- L. Tonjes,M.B. Trzupek,A. Vale,C. Nieuwenhuizen,G.J.van Verdier,R. Veres,G.I. Wolfs,F.L.H. Wosiek,B. Wozniak,K. Wuosmaa,A.H. Wysouch,B. Zhang,J.
Relativistic equations of state at finite temperature
In this work we study the effects of temperature on the equations of state within a relativistic model, with the inclusion of the baryons of the octet over a wide range of densities. We compare the results of the equation of state, effective mass and strangeness fraction for the TM1, NL3 and GL sets of parameters.
2004
Santos,A. M. S. Menezes,D. P.
Pseudo-SU(4) model and beta decay of pf-shell nuclei
The spectra and the beta decay of the Ni-Cu-Zn isotopes with A=58, 59 and 60 are studied by using the pseudo-SU(4) model.
2004
Valencia,J. P. Wu,H.C.
137Cs distribution in guava trees
This paper presents results of 137Cs concentration measured from a guava tree cultivated after the first decontamination work of one of the sites where the worst Brazilian radiological accident occurred. The present work aims to verify how the 137Cs is transported and distributed along the tropical trees. Bi-dimensional analyses of the radial distribution of 137Cs in the main trunk are also presented. Neither symmetrical nor homogeneous behaviors of the specific activity distribution in the tree rings were observed.
2004
Mosquera,B. Veiga,R. Mangia,L. Carvalho,C. Estellita,L. Uzeda,D. Facure,A. Violini,B. Anjos,R. M.
The nucleon-nucleon interaction
Recent developements in our understanding of the fundamental nucleon-nucleon interaction are reviewed. Among the topics considered are (1) the so-called high-precision nucleon-nucleon potentials that emerged in the mid 1990s, (2) progress in the microscopic description of the intermediate-range part of the nucleon-nucleon interaction in terms of correlated pion-pion and rho-pion exchange and (3) efforts towards a quantitative descripton of the nucleon-nucleon interaction utilizing methods based on effective field theory.
2004
Haidenbauer,J.
Beta decay and structure of exotic nuclei in the mass regions N=Z, A ~ 70 and near the N=20 closed shell
This paper describes two beta decay experiments performed at the CERN/ISOLDE mass separator. The structure of 74Kr has been studied using a total absorption gamma spectrometer (TAgS). The measured Gamow-Teller strength is presented and compared to HFBCS+QRPA calculations. The 33Na decay is also presented. The structure of the 33Mg daughter nucleus is compared to shell-model calculations, showing for the first time an inversion of states in the A~35 mass region.
2004
Courtin,S. Baumann,P. Dessagne,Ph. Maréchal,F. Miehé,Ch. Perrot,F. Poirier,E. Ramdhane,M.
Monte Carlo simulation of activity measurements by means of 4pb-g coincidence system
The methodology for simulating all detection processes in a 4<FONT FACE=Symbol>pb-g</FONT> coincidence system by means of the Monte Carlo technique is described. The goal is to predict the behavior of the observed activity as a function of the 4<FONT FACE=Symbol>pb</FONT> detector efficiency. In this approach, the information contained in the decay scheme is used for determining the contribution of all radiations emitted by the selected radionuclide, to the measured spectra by each detector. This simulation yields the shape of the coincidence spectrum, allowing the choice of suitable gamma-ray windows for which the activity can be obtained with maximum accuracy. The simulation can predict a detailed description of the extrapolation curve, mainly in the region where the 4<FONT FACE=Symbol>pb</FONT> detector efficiency approaches 100%, which is experimentally unreachable due to self absorption of low energy electrons in the radioactive source substrate. The theoretical work is being developed with MCNP Monte Carlo code, applied to a gas-flow proportional counter of 4pi geometry, coupled to a pair of NaI(Tl) crystals. The calculated efficiencies are compared to experimental results. The extrapolation curve can be obtained by means of another Monte Carlo algorithm, being developed in the present work, to take into account fundamental characteristics of a complex decay scheme, including different types of radiation and transitions. The present paper shows preliminary calculated values obtained by the simulation and compared to predicted analytical values for a simple decay scheme.
2004
Takeda,Mauro N. Dias,Mauro S. Koskinas,Marina F.
Dirac-Hartree-Bogoliubov approximation for finite nuclei with blocking
We have extended the Dirac-Hartree-Bogoliubov (DHB) approximation developed in a previous work [1] with the inclusion of blocking terms in order to study the pairing properties of both even and odd nuclei. We have concentrated our attention in the isotope chains of 12-26O, 34-56Ca, 48-78Ni and 100-132Sn as well as on the alpha-decay of the new superheavy element (277)112.
2004
Baldini-Neto,E. Carlson,B. V. Hirata,D.
Semiclassical Coulomb excitation matrix elements
Coulomb excitation matrix elements are often expressed in terms of the scalar electric potential and the electromagnetic fields. We show that, through an appropriate gauge transformation, the excitation matrix elements can always be expressed in terms of the electromagnetic fields alone. This change in representation becomes important when the widths of the excited states are taken into account.
2004
Carlson,B.V. Canto,L.F. Hussein,M.S.
A formalism for weak interactions in nuclei
The neutrino-nucleus cross-section and the muon capture rate are discussed within a simple formalism which facilitates the nuclear structure calculations. The corresponding formulae only depend on four types of nuclear matrix elements, which are currently used in the nuclear beta decay. We have also considered the non-locality effects arising from the velocity-dependent terms in the hadronic current. We show that for both observables in 12C the higher order relativistic corrections are of the order of ~ 4% only, and therefore do not play a significant role.
2004
Samana,A. Krmpotic,F. Mariano,A.
Fusion cross section measurements for systems 6Li + 27Al,64Zn at near-barrier energies
Fusion cross-sections were measured for the 6Li+27 Al,64 Zn and 9Be+64Zn systems at energies around the Coulomb barrier, in order to study the influence of the break-up of weakly bound nuclei on the fusion process.
2004
Rodríguez,M.D. Padron,I. Martí,G.V. Anjos,R.M. Gomes,P.R.S. Lubian,J. Veiga,R.S.L. Pacheco,A.J. Capurro,O.A. Fernández Niello,J.O. Testoni,J.E. Arazi,A. Ramírez,M.
Nucleon magnetic moments in light-front models with quark mass asymmetries
We show that the systematic inconsistence found in the simultaneous fit of the neutron and proton magnetics moments in light-front models, disappears when one allows an asymmetry in the constituent quark masses. The difference between the constituent quarks masses is an effective way to include in the nucleon model the effect of the attractive short ranged interaction in the singlet spin channel.
2004
Araújo,W. R. B. de Trevisan,L. A. Frederico,T. Tomio,L. Dorokhov,A. E.
Topological charge screening and pseudoscalar glueballs
Topological charge screening in the QCD vacuum is found to provide crucial nonperturbative contributions to the short-distance expansion of the pseudoscalar (0-+) glueball correlator. The screening contributions enter the Wilson coefficients and are an indispensable complement to the direct instanton contributions. They restore consistency with the anomalous axial Ward identity and remedy several flaws in the 0-+ glueball sum rules caused by direct instantons in the absence of screening (lack of resonance signals, violation of the positivity bound and of the underlying low-energy theorem). The impact of the finite width of the instanton size distribution and the (gauge-invariant) renormalization of the instanton contributions are also discussed. New predictions for the 0-+ glueball mass and decay constant are presented.
2004
Forkel,Hilmar
Hadron polarization in semi-inclusive reactions involving photons
A phenomenological model which has had some success in explaining polarization phenomena and left-right asymmetry in inclusive proton-proton scattering is considered for reactions involving photons. In particular, the reactions (a) gamma + p -> H + X; (b) gamma + p(<IMG SRC="/img/revistas/bjp/v34n3a/a46img01.gif">) <FONT FACE=Symbol>® p</FONT>± + X and (c) p(<IMG SRC="/img/revistas/bjp/v34n3a/a46img01.gif">) -> + p <FONT FACE=Symbol>® g</FONT> + X are considered where gamma = resolved photon and hyperon H = lambda, sigma, xi etc. Predictions for hyperon polarization in (a) and the asymmetry (in (b) and (c)) provide further tests of this particular model. Feasibility of observing (b) at HERA and the effect of the polarization of the sea in the proton in p(<IMG SRC="/img/revistas/bjp/v34n3a/a46img01.gif">) + p <FONT FACE=Symbol>® p</FONT>± + X is briefly discussed.
2004
Solano Salinas,C.J. Gupta,V.
Spin-1 particle in the light-front approach
The electromagnetic current of spin-1 composite particles does not transform properly under rotations if only the valence contribution is considered in the light-front model. In particular, the plus component of the current, evaluated only for the valence component of the wave function, in the Drell-Yan frame violates rotational symmetry, which does not allow a unique calculation of the electromagnetic form-factors. The prescription suggested by Grach and Kondratyuk [Sov. J. Nucl. Phys. 38, 198 (1984)] to extract the form factors from the plus component of the current, eliminates contributions from pair diagrams or zero modes, which if not evaluated properly cause the violation of the rotational symmetry. We address this problem in an analytical and covariant model of a spin-1 composite particle.
2004
Melo,J. P. B. C. de Frederico,T.
Measurement of inelastic-scattering cross sections in the 16O+28Si system to discriminate regular and chaotic regimes
A new experiment to measure differential cross sections as a function of the bombarding energy and scattering angle for the 16O + 28Si system in order to discriminate regular and chaotic regimes, was performed using the particle spectrometer CHICO combined with the multidetector array Gammasphere. In this contribution we summarize the characteristics of the method developed to analyze the experimental data and present the preliminary results.
2004
Martí,G. V. Pacheco,A. J. Testoni,J. E. Abriola,D. Capurro,O. A. DiGregorio,D. E. Fernández Niello,J.O. Macchiavelli,A.O. Clark,R.M. Fallon,P. Goergen,A. Ward,D. Wu,C.Y. Hayes,A. Cline,D. Teng,R.
Vacuum polarization effects in relativistic nuclear pairing
In the present work we discuss the contribution of the vacuum polarization on the nuclear pairing, in the context of the relativistic Hartree-Fock-Bogoliubov (HFB) approximation. The polarization effects on the pairing, as a function of Fermi momentum, is shown with the scalar and vector meson-nucleon coupling constants scaled by a parameter x. We have obtained that the nuclear pairing is affected by the vacuum polarization.
2004
Batista,E. F. Carlson,B.V. Frederico,T.
A Dirac description of ¹S0+³ S1-³ D1 pairing in nuclear matter
We develop a Dirac-Hartree-Fock-Bogoliubov description of nuclear matter pairing in ¹S0 and ³S¹-³ D¹ channels. Here we investigate the density dependence ot the ¹S0 and ³S¹-³ D¹ pairing fields in asymmetric nuclear matter, using a Bonn meson-exchange interaction between Dirac nucleons. In this work, we present preliminary results.
2004
Haas,B. Funke Carlson,B. V. Frederico,Tobias
Heavy ion interactions from Coulomb barrier to few GeV/n: Boltzmann Master Equation theory and FLUKA code performances
Results which have been recently obtained with the Boltzmann master equation and the FLUKA code in the analysis of heavy ion interactions at relative energies ranging from Coulomb barrier up to a few GeV/n are discussed.
2004
Battistoni,G. Cavinato,M. Cerutti,F. Clivio,A. Fabrici,E. Gadioli,E. Erba,E. Gadioli Garzelli,M. V. Mairani,A. Empl,A. Pinsky,L. S. Ballarini,F. Ottolenghi,A. Fassò,A. Ferrari,A. Ranft,J. Sala,P. R.
Study of neutron-DNA interaction at the IPEN BNCT research facility
Our group at the Laboratorio do Acelerador Linear (IFUSP- USP) is currently developing several studies related to the interaction of different kinds of radiation with DNA. Initially, our plan is to study the interactions proton-DNA, gamma-DNA and neutron-DNA. In this work we describe the most important features of the neutron-DNA study, which we plan to perform by selecting thermal, epithermal and fast neutrons. To improve the information about radiation-DNA interaction is important in order to achieve more secure and efficient cancer treatments by using radiation therapy. Nowadays, one important technique is the boron neutrons capture therapy, where neutrons are used to initiate a nuclear reaction at the tumor site. The effects of the neutrons on the health tissue, however, must be better understood. The study of neutron-DNA interaction, in this scenario, is of great importance. The research facility for Boron Neutron Capture Therapy (BNCT) in the IEA-R1 Reactor of the IPEN-CNEN/SP[1] will be used for studying the neutron-induced DNA damage. At present, we are evaluating the characteristics of the neutron flux at the biological sample, and we are carrying out simulations of the experimental procedure through Monte Carlos N Particle transport code system version 4C (MCNP-4C)[2] to find the experimental conditions necessary to minimize such contamination, and also verify the effects of those gamma's on the DNA molecule. The first step is the selection of filters configurations, which will allow us to irradiate the DNA sample with thermal, epithermal and fast neutrons. We present the results of our simulations, and describe the experimental setup show the best sets of materials necessary to obtain neutron spectra for different neutrons energies.
2004
Gual,M. R. Rodriguez,O. Guzman,F. Deppman,A. Arruda Neto,J. D.T. Likhachev,V.P. Coelho,Paulo R. P. Siqueira,P.T.D.