Showing papers by "German Martinez published in 2004"
TL;DR: In this paper, the authors measured the centrality dependence of transverse momentum distributions and particle yields at the PHENIX experiment at the Relativistic Heavy Ion Collider (HIC).
Abstract: The centrality dependence of transverse momentum distributions and yields for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},{K}^{\ifmmode\pm\else\textpm\fi{}},p$, and $\overline{p}$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$ in ${p}_{T}$. Both mean transverse momenta and particle yields per participant pair increase from peripheral to midcentral and saturate at the most central collisions for all particle species. We also measure particle ratios of ${\ensuremath{\pi}}^{\ensuremath{-}}∕{\ensuremath{\pi}}^{+}$, ${K}^{\ensuremath{-}}∕{K}^{+}$, $\overline{p}∕p$, $K∕\ensuremath{\pi}$, $p∕\ensuremath{\pi}$, and $\overline{p}∕\ensuremath{\pi}$ as a function of ${p}_{T}$ and collision centrality. The ratios of equal mass particle yields are independent of ${p}_{T}$ and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta $\ensuremath{\sim}1.5--4.5\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$, proton and antiproton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.
622 citations
TL;DR: The PHENIX experiment at the Relativistic Heavy Ion Collider has measured charged hadron yields at midrapidity over a wide range of transverse momenta in this article.
Abstract: The PHENIX experiment at the Relativistic Heavy Ion Collider has measured charged hadron yields at midrapidity over a wide range of transverse momenta $(0.5l{p}_{T}l10\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c)$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\text{GeV}$. The data are compared to ${\ensuremath{\pi}}^{0}$ measurements from the same experiment. For both charged hadrons and neutral pions, the yields per nucleon-nucleon collision are significantly suppressed in central compared to peripheral and nucleon-nucleon collisions. The suppression sets in gradually and increases with increasing centrality of the collisions. Above $4--5\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$ in ${p}_{T}$, a constant and almost identical suppression of charged hadrons and ${\ensuremath{\pi}}^{0}$'s is observed. The ${p}_{T}$ spectra are compared to published spectra from $\text{Au}+\text{Au}$ at $\sqrt{{s}_{NN}}=130$ in terms of ${x}_{T}$ scaling. Central and peripheral ${\ensuremath{\pi}}^{0}$ as well as peripheral charged spectra exhibit the same ${x}_{T}$ scaling as observed in $p+p$ data.
214 citations
TL;DR: In this article, the Bertsch-Pratt radius parameters were determined as a function of the transverse momentum of the pair, and the centrality of the collision, using the standard core-halo partial Coulomb fits, and a new parametrization which constrains the Coulomb fraction as determined from the unlike sign pion correlation.
Abstract: Bose-Einstein correlations of identically charged pion pairs were measured by the PHENIX experiment at midrapidity in Au+Au collisions at roots(NN)=200 GeV. The Bertsch-Pratt radius parameters were determined as a function of the transverse momentum of the pair and as a function of the centrality of the collision. Using the standard core-halo partial Coulomb fits, and a new parametrization which constrains the Coulomb fraction as determined from the unlike-sign pion correlation, the ratio R-out/R-side is within 0.8-1.1 for 0.25 similar to0.45 GeV/c is approximately constant at unity as a function of centrality.
150 citations
TL;DR: In this paper, the PHENIX collaboration measured the transverse momentum spectra and yields of hadrons in Au+Au collisions at √s NN =130 GeV at the Relativistic Heavy Ion Collider.
Abstract: Transverse momentum spectra and yields of hadrons are measured by the PHENIX collaboration in Au+Au collisions at √s NN =130 GeV at the Relativistic Heavy Ion Collider. The time-of-flight resolution allows identification of pions to transverse momenta of 2 GeV/c and protons and antiprotons to 4 GeV/c. The yield of pions rises approximately linearly with the number of nucleons participating in the collision, while the number of kaons, protons, and antiprotons increases more rapidly. The shape of the momentum distribution changes between peripheral and central collisions. Simultaneous analysis of all the p T spectra indicates radial collective expansion, consistent with predictions of hydrodynamic models. Hydrodynamic analysis of the spectra shows that the expansion velocity increases with collision centrality and collision energy. This expansion boosts the particle momenta, causing the yield from soft processes to exceed that for hard to large transverse momentum, perhaps as large as 3 GeV/c.
137 citations
TL;DR: In this paper, the PHENIX Collaboration measured event-by-event fluctuations of the average transverse momentum of produced particles near midrapidity and observed that the fluctuations exhibited a dependence on both the centrality of the collision and on the pT range over which the average is calculated.
Abstract: Event-by-event fluctuations of the average transverse momentum of produced particles near midrapidity have been measured by the PHENIX Collaboration in square root of (sNN)=200 GeV Au+Au, and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the pT range over which the average is calculated. Both the centrality and pT dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard-scattering processes.
64 citations
TL;DR: In this article, the PHENIX experiment at the Relativistic Heavy Ion Collider was used to measure the J/psi production in proton-proton collisions at roots = 200 GeV over a wide rapidity and transverse momentum range.
Abstract: J/psi production has been measured in proton-proton collisions at roots=200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 4.0+/-0.6(stat)+/-0.6(syst)+/-0.4(abs) mub. The mean transverse momentum is 1.80+/-0.23(stat)+/-0.16(syst) GeV/c.
58 citations
TL;DR: In this article, the double longitudinal spin asymmetry of the proton was measured at the Relativistic Heavy Ion Collider with average beam polarizations of 0.27 and 1.5 GeV/c at midrapidity.
Abstract: We present a measurement of the double longitudinal spin asymmetry in inclusive pi(0) production in polarized proton-proton collisions at roots=200 GeV. The data were taken at the Relativistic Heavy Ion Collider with average beam polarizations of 0.27. The measurements are the first in a program to study the longitudinal spin structure of the proton, using strongly interacting probes, at collider energies. The asymmetry is presented for transverse momenta 1-5 GeV/c at midrapidity, where next-to-leading-order perturbative quantum chromodynamic (NLO pQCD) calculations well describe the unpolarized cross section. The observed asymmetry is small and is compared to a NLO pQCD calculation with a range of polarized gluon distributions.
42 citations
TL;DR: In this article, the Charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) is analyzed as a function of collision centrality.
Abstract: First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of $J∕\ensuremath{\psi}$'s measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for $\text{Au-Au}$ reactions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ is analyzed as a function of collision centrality. For this analysis we have studied $49.3\ifmmode\times\else\texttimes\fi{}{10}^{6}$ minimum bias $\text{Au-Au}$ reactions. We present the $J∕\ensuremath{\psi}$ invariant yield $dN∕dy$ for peripheral and midcentral reactions. For the most central collisions where we observe no signal above background, we quote $90%$ confidence level upper limits. We compare these results with our $J∕\ensuremath{\psi}$ measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.
25 citations
TL;DR: A patient is reported showing complete histological resolution of NASH after iron depletion therapy, highlighting the importance of iron overload in the occurrence of both liver fat accumulation and inflammatory changes seen in NASH.
Abstract: After its description in the early eighties (1), nonalcoholic steatohepatitis (NASH) has become a well-defined clinical entity with potentially dangerous consequences including progression to cirrhosis (2). The pathogenesis of NASH considers the occurrence of fat accumulation in the liver cell followed by a sequential series of events including an inflammatory response leading to hepatocellular injury which may lead to a fibrogenic response (3). While fat accumulation has been mainly related to insulin resistance, factors that trigger inflammation and fibrosis progression are less clear. Iron overload has been regarded as an important factor related to both insulin resistance and oxidative stress (4, 5). In fact, it has been reported that patients with hepatic steatosis have increased ferritin and transferrin saturation reflecting iron overload (6) and that iron depletion may have an insulin-sparing effect (7), which suggests a significant role of iron in the pathogenesis of fatty liver and NASH. Albeit it has been suggested that phlebotomy might be a useful treatment for NASH with concomitant iron overload, published data on the effects of iron depletion on both biochemical and histological alterations in these patients are limited.
25 citations
TL;DR: In this article, the yield of J/psi's measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au-Au reactions at roots(NN) = 200 GeV is analyzed as a function of collision centrality.
Abstract: First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of J/psi's measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au-Au reactions at roots(NN) = 200 GeV is analyzed as a function of collision centrality. For this analysis we have studied 49.3x10(6) minimum bias Au-Au reactions. We present the J/psi invariant yield dN/dy for peripheral and midcentral reactions. For the most central collisions where we observe no signal above background, we quote 90% confidence level upper limits. We compare these results with our J/psi measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.
8 citations