612 research outputs found
Indication for scattering in collisions at 200 GeV
A mass shift of about -40 MeV/ was measured in
collisions at 200 GeV at RHIC. Previous mass shifts have
been observed at CERN-LEBC-EHS and CERN-LEP. We will show that phase space does
not account for the mass shift measured at RHIC, CERN-LEBC-EHS
and CERN-LEP and conclude that there are significant scattering interactions in
collisions.Comment: 11 pages and 7 figure
A microscopic approach to heating rate of ferrofluid droplets by a magnetic field
CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORIn this work, we study the heating process of colloidal ferrofluids by a magnetic field. The heating of the fluid occurs by the magnetic relaxation of the nanoparticles which provide thermal energy for the host liquid. In the limit of small volumes, the relaxation process occurs through the Neel mechanism since the magnetic nanoparticles present superparamagnetic behavior. Within this limit, we have used a microscopic model for the coupling to phonons and external magnetic field in order to model the relaxation mechanism and to obtain an expression for the heating rate of the fluid as a function of microscopic parameters. The analysis allows determining appropriate conditions for an optimal heating rate for ferrofluids based on superparamagnetic nanoparticles.1254111CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIOR307466/2016-7PNPD 028/2010E.C.S. acknowledges support from the CNPq agency under Grant No. 307466/2016-7. P.A.O. acknowledges financial support from FONDECYT under Grant No. 1140571. F.F.F. and E.C.S. acknowledge CAPES agency financial support (No. CAPES PNPD 028/2010)
Production in Au+Au and pp Collisions at = 200GeV at STAR
Mid-rapidity and are
measured in Au+Au and pp collisions at =200GeV using the STAR
detector at RHIC. The mass is systematically shifted at small
transverse momentum for both Au+Au and pp collisions. The
transverse mass spectra are measured in Au+Au collisions at different
centralities and in pp collisions. The mean transverse momentum
as a function of the collision centrality is compared to those of identified
, and . The and ratios are
compared to measurements in A+A, , , collisions at
various colliding energies. The physics implications of these measurements are
also discussed.Comment: 6 pages, 4 figures, proceedings of Strange Quarks in Matter
(SQM2003), Atlantic Beach, USA, to be published in J. Phys.
Técnicas pra caracterização dos estoques de carbono e humificação da matéria orgânica em diferentes sistemas de manejo de solos na região de Mococa (SP).
Devido à crescente preocupação com o meio ambiente, o estudo de solos tem ganho destaque estudos nos últimos anos. O solo é o maior reservatório de Carbono terrestre, assim desempenha papel fundamental no ciclo deste elemento. O estudo do estoque de Carbono no solo é importante pois diferentes tipos de manejo e culturas podem aumentar a concentração deste elemento no solo e assim diminuir o efeito estufa. O objetivo desse estudo foi avaliar as variações dos estoques de carbono no solo e humificação da matéria orgânica do solo (MOS) devido às mudanças de uso do solo em áreas agrícolas e mata nativa. Foram utilizadas as técnicas de Análise Elementar (CHN) e Espectroscopia de Fluorescência Induzida por Laser (LIFS) para análises da concentração de Carbono e do grau de humificação da MOS respectivamente. Foram avaliadas amostras de solo de áreas de mata nativa, café e uma área de café convertida para cana de açúcar sob regime de colheita crua, coletadas na região de Mococa, SP. Os resultados mostram que áreas de mata nativa estocam mais Carbono do que áreas agrícolas, além disso, também foi possível concluir que o estoque de Carbono é mais estável em horizontes mais profundos. Dentre os manejo agrícolas, o Café-CanaCrua foi o que melhor apresentou quantidade de Carbono estável
Thermal analysis of production of resonances in relativistic heavy-ion collisions
Production of resonances is considered in the framework of the
single-freeze-out model of ultra-relativistic heavy ion collisions. The
formalism involves the virial expansion, where the probability to form a
resonance in a two-body channel is proportional to the derivative of the
phase-shift with respect to the invariant mass. The thermal model incorporates
longitudinal and transverse flow, as well as kinematic cuts of the STAR
experiment at RHIC. We find that the shape of the pi+ pi- spectral line
qualitatively reproduces the preliminary experimental data when the position of
the rho peak is lowered. This confirms the need to include the medium effects
in the description of the RHIC data. We also analyze the transverse-momentum
spectra of rho, K*(892), and f_0(980), and find that the slopes agree with the
observed values. Predictions are made for eta, eta', omega, phi, Lambda(1520),
and Sigma(1385).Comment: minor modifications, a reference adde
Dynamics and freeze-out of hadron resonances at RHIC
Yields, rapidity and transverse momentum spectra of ,
, and the meson resonances ,
, and are predicted. Hadronic rescattering leads to a
suppression of reconstructable resonances, especially at low . A mass
shift of the of 10 MeV is obtained from the microscopic simulation, due
to late stage formation in the cooling pion gas.Comment: Proceedings of the Strange Quark Matter 2003, eprint version differs
from published versio
, K and f Production in Au-Au and pp Collisions at = 200 GeV
Preliminary results on , KK and production using the mixed-event
technique are presented. The measurements are performed at mid-rapidity by the
STAR detector in = 200 GeV Au-Au and pp interactions at RHIC.
The results are compared to different measurements at various energies.Comment: 4 pages, 6 figures. Talk presented at Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
A comparison of statistical hadronization models
We investigate the sensitivity of fits of hadron spectra produced in heavy
ion collisions to the choice of statistical hadronization model. We start by
giving an overview of statistical model ambiguities, and what they tell us
about freeze-out dynamics. We then use Montecarlo generated data to determine
sensitivity to model choice. We fit the statistical hadronization models under
consideration to RHIC data, and find that a comparison fits can shed
light on some presently contentious questions.Comment: Proceedings for SQM2003 [7th Int. Conf. on Strangeness in Quark
Matter (Atlantic Beach, NC, USA, Mar 12-17, 2003)], to be published in
Journal of Physics G (Typos corrected, reference added
What do we learn from Resonance Production in Heavy Ion Collisions?
Resonances with their short life time and strong coupling to the dense and
hot medium are suggested as a signature of the early stage of the fireball
created in a heavy ion collision \cite{rap00,lut01,lut02}. The comparison of
resonances with different lifetimes and quark contents may give information
about time evolution and density and temperature of during the expanding of
fireball medium. Resonances in elementary reactions have been measured since
1960. Resonance production in elementary collisions compared with heavy ion
collisions where we expect to create a hot and dense medium may show the direct
of influence of the medium on the resonances. This paper shows a selection of
the recent resonance measurements from SPS and RHIC heavy ion colliders.Comment: 10 pages, 8 figures, HotQuarks 2004 conference proceeding
Resonance production in heavy ion collisions
Recent results of resonance production from RHIC at
200 GeV and SPS at 17 GeV are presented and discussed in
terms of the evolution and freeze-out conditions of a hot and dense fireball
medium. Yields and spectra are compared with thermal model predictions at
chemical freeze-out. Deviations in the low transverse momentum region of the
resonance spectrum of the hadronic decay channel, suggest a strongly
interaction hadronic phase between chemical and kinetic freeze-out. Microscopic
models including resonance rescattering and regeneration are able to describe
the trend of the data. The magnitude of the regeneration cross sections for
different inverse decay channels are discussed. Model calculations which
include elastic hadronic interactions between chemical freeze-out and thermal
freeze-out based on the K(892)/K and (1520)/ ratios suggest a
time between two freeze-outs surfaces of 4 fm/c. The difference
in momentum distributions and yields for the (1020) resonance
reconstructed from the leptonic and hadronic decay channels at SPS energy are
discussed taking into account the impact of a hadronic phase and possible
medium modifications.Comment: 8 pages, 4 figures, conference proceedings (SQM2004
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