Página 19 dos resultados de 19478 itens digitais encontrados em 0.161 segundos

Probing the Nuclear Symmetry Energy with Heavy-Ion Reactions Induced by Neutron-Rich Nuclei

Chen, Lie-Wen; Ko, Che Ming; Li, Bao-An; Yong, Gao-Chan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/04/2007
Relevância na Pesquisa
45.84%
Heavy-ion reactions induced by neutron-rich nuclei provide a unique means to investigate the equation of state of isospin-asymmetric nuclear matter, especially the density dependence of the nuclear symmetry energy. In particular, recent analyses of the isospin diffusion data in heavy-ion reactions have already put a stringent constraint on the nuclear symmetry energy around the nuclear matter saturation density. We review this exciting result and discuss its implications on nuclear effective interactions and the neutron skin thickness of heavy nuclei. In addition, we also review the theoretical progress on probing the high density behaviors of the nuclear symmetry energy in heavy-ion reactions induced by high energy radioactive beams.; Comment: 29 pages, 35 figures. Invited review article for Frontiers of Physics in China

Higher order bulk characteristic parameters of asymmetric nuclear matter

Chen, Lie-Wen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.84%
The bulk parameters characterizing the energy of symmetric nuclear matter and the symmetry energy defined at normal nuclear density $\rho_0 $ provide important information on the equation of state (EOS) of isospin asymmetric nuclear matter. While significant progress has been made in determining some lower order bulk characteristic parameters, such as the energy $E_0(\rho_0)$ and incompressibility $K_0$ of symmetric nuclear matter as well as the symmetry energy $E_{sym}(\rho_0)$ and its slope parameter $L$, yet the higher order bulk characteristic parameters are still poorly known. Here, we analyze the correlations between the lower and higher order bulk characteristic parameters within the framework of Skyrme Hartree-Fock energy density functional and then estimate the values of some higher order bulk characteristic parameters. In particular, we obtain $J_0=-355 \pm 95$ MeV and $I_0=1473 \pm 680$ MeV for the third-order and fourth-order derivative parameters of symmetric nuclear matter at $\rho_0 $ and $K_{sym} = -100 \pm 165$ MeV, $J_{sym} = 224 \pm 385$ MeV, $I_{sym} = -1309 \pm 2025$ MeV for the curvature parameter, third-order and fourth-order derivative parameters of the symmetry energy at $\rho_0 $, using the empirical constraints on $E_0(\rho_0)$...

Plans for a Neutron EDM Experiment at SNS

Ito, Takeyasu M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/02/2007
Relevância na Pesquisa
45.84%
The electric dipole moment of the neutron, leptons, and atoms provide a unique window to Physics Beyond the Standard Model. We are currently developing a new neutron EDM experiment (the nEDM Experiment). This experiment, which will be run at the 8.9 A Neutron Line at the Fundamental Neutron Physics Beamline (FNPB) at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory, will search for the neutron EDM with a sensitivity two orders of magnitude better than the present limit. In this paper, the motivation for the experiment, the experimental method, and the present status of the experiment are discussed.; Comment: 9 Pages, 4 Figures, submitted to the proceedings of the Second Meeting of the APS Topical Group on Hadronic Physics, Nashville, TN, October 22-24, 2006

Nuclear effects on the longitudinal structure function at small x

Armesto, N.; Paukkunen, H.; Salgado, C. A.; Tywoniuk, K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.84%
We discuss the longitudinal structure function in nuclear DIS at small $x$. We work within the framework of universal parton densities obtained in DGLAP analyses at NLO. We show that the nuclear effects on the longitudinal structure function closely follow those on the gluon distribution. The error analyses available from newest sets of nuclear PDFs also allow to propagate the uncertainties from present data. In this way, we evaluate the minimal sensitivity required in future experiments for this observable to improve the knowledge of the nuclear glue. We further discuss the uncertainties on the extraction of $F_2$ off nuclear targets, introduced by the usual assumption that the ratio $F_L/F_2$ is independent of the nuclear size. We focus on the kinematical regions relevant for future lepton-ion colliders.; Comment: LaTeX, 12 pages, 4 eps figures; v2: reference added; v3: comments and references added, results and conclusions unchanged, final version

Nuclear three-body problem in the complex energy plane: Complex-Scaling-Slater method

Kruppa, A. T.; Papadimitriou, G.; Nazarewicz, W.; Michel, N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.84%
The physics of open quantum systems is an interdisciplinary area of research. The nuclear "openness" manifests itself through the presence of the many-body continuum representing various decay, scattering, and reaction channels. As the radioactive nuclear beam experimentation extends the known nuclear landscape towards the particle drip lines, the coupling to the continuum space becomes exceedingly more important. Of particular interest are weakly bound and unbound nuclear states appearing around particle thresholds. Theories of such nuclei must take into account their open quantum nature. To describe open quantum systems, we introduce a Complex Scaling (CS) approach in the Slater basis. We benchmark it with the complex-energy Gamow Shell Model (GSM) by studying energies and wave functions of the bound and unbound states of the two-neutron halo nucleus 6He viewed as an $\alpha$+ n + n cluster system. In the CS approach, we use the Slater basis, which exhibits the correct asymptotic behavior at large distances. To extract particle densities from the back-rotated CS solutions, we apply the Tikhonov regularization procedure, which minimizes the ultraviolet numerical noise. While standard applications of the inverse complex transformation to the complex-rotated solution provide unstable results...

Irradiation of Nuclear Track Emulsions with Thermal Neutrons, Heavy Ions, and Muons

Artemenkov, D. A.; Bradnova, V.; Zaitsev, A. A.; Zarubin, P. I.; Zarubina, I. G.; Kattabekov, R. R.; Mamatkulov, K. Z.; Rusakova, V. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
Exposures of test samples of nuclear track emulsion were analyzed. Angular and energy correlations of products originating from the thermal-neutron-induced reaction n$_{th} + ^{10}$B $\rightarrow ^{7}$Li $+ (\gamma) + \alpha$ were studied in nuclear tack emulsions enriched in boron. Nuclear track emulsions were also irradiated with $^{86}$Kr$^{+17}$ and $^{132}$Xe$^{+26}$ of energy about 1.2 MeV per nucleon. Measurements of ranges of heavy ions in nuclear track emulsions made it possible to determine their energies on the basis of the SRIM model. The formation of high-multiplicity nuclear stars was observed upon irradiating nuclear track emulsions with ultrarelativistic muons. Kinematical features studied in this exposure of nuclear track emulsions for events of the muon-induced splitting of carbon nuclei to three alpha particles are indicative of the nuclear-diffraction interaction mechanism.; Comment: Pleiades Publishing, Ltd., 2015. 7 pages, 9 figures

Particle production at forward rapidity in d+Au and Au+Au collisions in STAR experiment at RHIC

Mohanty, Bedangadas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
We present the recent results from the STAR experiment on charged and neutral particle measurements at the forward rapidity in d+Au collisions at sqrt{s_{NN}} = 200 GeV and Au+Au collisions at sqrt{s_{NN}} = 62.4 GeV. The nuclear modification factor for charged and neutral hadrons in d+Au collisions are presented. Measurements of Lambda and anti-Lambda production at forward rapidity and the variation of net baryon density as a function of collision centrality are discussed. We have also studied the limiting fragmentation of photons and charged particles in Au+Au collisions. The photons and charged particles separately follow the energy independent limiting fragmentation behaviour. However they have been observed to follow a different centrality dependence of limiting fragmentation.; Comment: Talk give at 18th International conference on nucleus-nucleus collisions (Quark Matter 2005), August 4 -9, Budapest, Hungary. 4 pages and 6 figures

Nuclear Modification of Electron Spectra and Implications for Heavy Quark Energy Loss in Au+Au Collisions at sqrt(s_NN)=200 GeV

PHENIX Collaboration; Adler, S. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/10/2005
Relevância na Pesquisa
45.85%
The PHENIX experiment has measured mid-rapidity transverse momentum spectra (0.4 < p_T < 5.0 GeV/c) of electrons as a function of centrality in Au+Au collisions at sqrt(s_NN)=200 GeV. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi^0 and eta mesons, were removed. The resulting non-photonic electron spectra are primarily due to the semi-leptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to non-photonic electrons in p+p collisions. A significant suppression of electrons at high p_T is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.; Comment: 330 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

Recent Results from the BRAHMS Experiment

Staszel, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/10/2005
Relevância na Pesquisa
45.85%
We present recent results obtained by the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the systems of Au + Au and Cu + Cu at \rootsnn{200} and at 62.4 GeV, and p + p at \rootsnn{200}. Nuclear modification factors for Au + Au and Cu + Cu collisions are presented. Analysis of anti-particle to particle ratios as a function of rapidity and collision energy reveal that particle populations at the chemical freeze-out stage for heavy-ion reactions at and above SPS energies are controlled by the baryon chemical potential. From the particle spectra we deduce significant radial expansion ($\beta \approx $ 0.75), as expected for systems created with a large initial energy density. We also measure the elliptic flow parameter $v_2$ versus rapidity and \ptn. We present rapidity dependent $p/\pi$ ratios within $0 < y < 3$ for Au + Au and Cu + Cu at \rootsnn{200}. \Raa is found to increase with decreasing collision energy, decreasing system size, and when going towards more peripheral collisions. However, \Raa shows only a very weak dependence on rapidity (for $0 < y < 3.2$), both for pions and protons.; Comment: 16 pages and 14 figures, proceedings for plenary talk at Quark Matter 2005, Budapest, Hungary

First measurement of the strange particles Rcp nuclear modification factors in heavy-ion collisions at the SPS

Bruno, G. E.; Dainese, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
The NA57 experiment has measured the pt distributions of K0s, Lambda, and antiLambda particles in fixed-target Pb-Pb interactions at sqrt(s_{NN})=17.3 GeV as a function of the collision centrality. In this paper we study the central-to-peripheral nuclear modification factors and compare them to other measurements and to theoretical predictions.; Comment: Contribution to the poster session of the Quark Matter 2005 Conference. To be published in Acta Physica Hungarica A, Heavy Ion Physics

Systematic Study of Particle Production at High p_T with the PHENIX Experiment

Klein-Boesing, Christian
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/06/2006
Relevância na Pesquisa
45.85%
A systematic study of particle production at large transverse momentum with the PHENIX experiment at RHIC is shown. We demonstrate that the suppression of the yield of high p_T hadrons in central Au+Au collisions compared to the scaled p+p reference persists up to highest p_T for neutral pions and eta mesons. A similar suppression pattern is also observed in Cu+Cu collisions at the same energy. In addition we present the first RHIC results on high-p_T particle production close to SPS energies.; Comment: 8 pages, 5 figures, to appear in the Proceedings of the 22nd Workshop on Nuclear Dynamics, La Jolla California, March 2006

High Rapidity Physics with the BRAHMS Experiment

Debbe, R.; Collaboration, for the BRAHMS
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/08/2006
Relevância na Pesquisa
45.85%
We report the study of the nuclear modification factor R_{AuAu} as function of pT and pseudo-rapidity in Au+Au collisions at top RHIC energy. We find this quantity almost independent of pseudo-rapidity. We use the pbar/pi- ratio as a probe of the parton density and the degree of thermalization of the medium formed by the collision. The pbar/pi- ratio has a clear rapidity dependence. The combination of these two measurements suggests that the pseudo-rapidity dependence of the R_{AuAu results from the competing effects of energy loss in a dense and opaque medium and the modifications of the wave function of the high energy beams in the initial state.; Comment: 5 pages, four figures, to appear in the proceedings of the 9th Conference on the Intersections of Particle and Nuclear Physics (CIPANP 2006), Puerto Rico, 30 May - 3 June 2006

Direct Photon Production in Au+Au Collisions at RHIC-PHENIX Experiment

Isobe, Tadaaki
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
Direct photons have been measured with the PHENIX experiment in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV. The direct photon result obtained with PHENIX-EMCal up to 18 GeV/$c$ is consistent with the NLO pQCD calculation scaled by the nuclear overlap function. The measurement using internal conversion of photons into $e^+e^-$ shows the enhancement of the yield comparing with NLO pQCD calculation.; Comment: 4 pages, 5 figures. Contributed parallel talk at Hard Probes 2006, Asilomar CA USA, Jun. 9-16, 2006

Direct photons measured by the PHENIX experiment at RHIC

Bathe, Stefan; Collaboration, for the PHENIX
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/09/2006
Relevância na Pesquisa
45.85%
Results from the PHENIX experiment at RHIC on direct photon production in p+p, d+Au, and Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. In p+p collisions, direct photon production at high p_T behaves as expected from perturbative QCD calculations. The p+p measurement serves as a baseline for direct photon production in Au+Au collisions. In d+Au collisions, no effects of cold nuclear matter are found within the large uncertainty of the measurement. In Au+Au collisions, the production of high p_T direct photons scales as expected for particle production in hard scatterings. This supports jet quenching models, which attribute the suppression of high p_T hadrons to the energy loss of fast partons in the medium produced in the collision. Low p_T direct photons, measured via e+e- pairs with small invariant mass, are possibly related to the production of thermal direct photons.; Comment: 5 pages, 5 figures, Proceedings of the Hot Quarks 2006 Workshop for young scientists on the physics of ultra-relativistic nucleus-nucleus collisions, Villasimius, Sardinia, Italy, May 15--20, 2006

Nuclear Modification Factor for Charged Pions and Protons at Forward Rapidity in Central Au+Au Collisions at 200 GeV

al., I. Arsene et
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/10/2006
Relevância na Pesquisa
45.85%
We present spectra of charged pions and protons in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at mid-rapidity ($y=0$) and forward pseudorapidity ($\eta=2.2$) measured with the BRAHMS experiment at RHIC. The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both $y=0$ and $\eta=2.2$ exhibit suppression for charged pions but not for (anti-)protons at intermediate $p_T$. The $\bar{p}/\pi^-$ ratios have been measured up to $p_T\sim 3$ GeV/$c$ at the two rapidities and the results indicate that a significant fraction of the charged hadrons produced at intermediate $p_T$ range are (anti-)protons at both mid-rapidity and $\eta = 2.2$.

Search for the QCD critical point in nuclear collisions at the CERN SPS

The NA49 Collaboration; Antoniou, N. G.; Diakonos, F. K.; Mavromanolakis, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
Pion production in nuclear collisions at the SPS is investigated with the aim to search, in a restricted domain of the phase diagram, for power-laws in the behavior of correlations which are compatible with critical QCD. We have analyzed interactions of nuclei of different size (p+p, C+C, Si+Si, Pb+Pb) at 158$A$ GeV adopting, as appropriate observables, scaled factorial moments in a search for intermittent fluctuations in transverse dimensions. The analysis is performed for $\pi^+\pi^-$ pairs with invariant mass very close to the two-pion threshold. In this sector one may capture critical fluctuations of the sigma component in a hadronic medium, even if the $\sigma$-meson has no well defined vacuum state. It turns out that for the Pb+Pb system the proposed analysis technique cannot be applied without entering the invariant mass region with strong Coulomb correlations. As a result the treatment becomes inconclusive in this case. Our results for the other systems indicate the presence of power-law fluctuations in the freeze-out state of Si+Si approaching in size the prediction of critical QCD.; Comment: 31 pages, 11 figures

The ASY-EOS experiment at GSI: investigating the symmetry energy at supra-saturation densities

Russotto, P.; Chartier, M.; De Filippo, E.; Févre, A. Le; Gannon, S.; Gašparić, I.; Kiš, M.; Kupny, S.; Leifels, Y.; Lemmon, R. C.; Łukasik, J.; Marini, P.; Pagano, A.; Pawłowski, P.; Santoro, S.; Trautmann, W.; Veselsky, M.; Acosta, L.; Adamczyk, M
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/09/2012
Relevância na Pesquisa
45.85%
The elliptic-flow ratio of neutrons with respect to protons in reactions of neutron rich heavy-ions systems at intermediate energies has been proposed as an observable sensitive to the strength of the symmetry term in the nuclear Equation Of State (EOS) at supra-saturation densities. The recent results obtained from the existing FOPI/LAND data for $^{197}$Au+$^{197}$Au collisions at 400 MeV/nucleon in comparison with the UrQMD model allowed a first estimate of the symmetry term of the EOS but suffer from a considerable statistical uncertainty. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration in May 2011.; Comment: Talk given by P. Russotto at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS)

Quarkonia production in the STAR experiment

Barbara Trzeciak for the STAR Collaboration
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/02/2013
Relevância na Pesquisa
45.85%
In this proceedings the recent STAR results of $J/\psi$ and $\Upsilon$ production in $p+p$, $d$+Au and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at mid-rapidity are reported. $J/\psi$ $p_{T}$ spectra in $p+p$ and Au+Au collisions for both low and high $p_{T}$ are shown. $J/\psi$ nuclear modification factor ($R_{AA}$) in $d$+Au and Au+Au collisions and $\Upsilon$ $R_{AA}$ in Au+Au collisions are reported. Also, $J/\psi$ polarization in $p+p$ collisions and $J/\psi$ $v_{2}$ for semi-central Au+Au collisions are presented.; Comment: Quark Matter 2012 proceedings, 4 pages, 8 figures

Result of the search for neutrinoless double-$\beta$ decay in $^{100}$Mo with the NEMO-3 experiment

Arnold, R.; Augier, C.; Baker, J. D.; Barabash, A. S.; Basharina-Freshville, A.; Blondel, S.; Blot, S.; Bongrand, M.; Brudanin, V.; Busto, J.; Caffrey, A. J.; Calvez, S.; Cerna, C.; Cesar, J. P.; Chapon, A.; Chauveau, E.; Duchesneau, D.; Durand, D.; Egoro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double $\beta$ ($0\nu\beta\beta$) decay. We report final results of a search for $0\nu\beta\beta$ decays with $6.914$ kg of $^{100}$Mo using the entire NEMO-3 data set with a detector live time of $4.96$ yr, which corresponds to an exposure of 34.3 kg$\cdot$yr. We perform a detailed study of the expected background in the $0\nu\beta\beta$ signal region and find no evidence of $0\nu\beta\beta$ decays in the data. The level of observed background in the $0\nu\beta\beta$ signal region $[2.8-3.2]$ MeV is $0.44 \pm 0.13$ counts/yr/kg, and no events are observed in the interval $[3.2-10]$ MeV. We therefore derive a lower limit on the half-life of $0\nu\beta\beta$ decays in $^{100}$Mo of $T_{1/2}(0\nu\beta\beta)> 1.1 \times 10^{24}$ yr at the $90\%$ Confidence Level, under the hypothesis of light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range $\langle m_{\nu} \rangle < 0.33$--$0.62$ eV. We also report constraints on other lepton-number violating mechanisms for $0\nu\beta\beta$ decays.

Nuclear constraints on the momenta of inertia of neutron stars

Worley, Aaron; Krastev, Plamen G.; Li, Bao-An
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.85%
Properties and structure of neutron stars are determined by the equation of state (EOS) of neutron-rich stellar matter. While the collective flow and particle production in relativistic heavy-ion collisions have constrained tightly the EOS of symmetric nuclear matter up to about five times the normal nuclear matter density, the more recent experimental data on isospin-diffusion and isoscaling in heavy-ion collisions at intermediate energies have constrained considerably the density dependence of the nuclear symmetry energy at subsaturation densities. Although there are still many uncertainties and challenges to pin down completely the EOS of neutron-rich nuclear matter, the heavy-ion reaction experiments in terrestrial laboratories have limited the EOS of neutron-rich nuclear matter in a range much narrower than that spanned by various EOSs currently used in astrophysical studies in the literature. These nuclear physics constraints could thus provide more reliable information about properties of neutron stars. Within well established formalisms using the nuclear constrained EOSs we study the momenta of inertia of neutron stars. We put the special emphasis on the component A of the extremely relativistic double neutron star system PSR J0737-3039. Its moment of inertia is found to be between 1.30 and 1.63 $(\times10^{45}g$ $cm^2)$. Moreover...