Showing papers by "German Martinez published in 2005"

Systematic studies of the centrality and √sNN dependence of the dET/dη and dNch/dη in heavy ion collisions at midrapidity

Abstract: The PHENIX experiment at the relativistic heavy ion collider (RHIC) has measured transverse energy and charged particle multiplicity at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at center-of-mass energies $\sqrt{{s}_{\mathrm{NN}}}=19.6,130$, and $200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ as a function of centrality. The presented results are compared to measurements from other RHIC experiments and experiments at lower energies. The $\sqrt{{s}_{\mathrm{NN}}}$ dependence of $dE{}_{T}/d\ensuremath{\eta}$ and $dN{}_{\mathrm{ch}}/d\ensuremath{\eta}$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE{}_{T}/d\ensuremath{\eta}$ and $dN{}_{\mathrm{ch}}/d\ensuremath{\eta}$ is similar at all measured incident energies. At RHIC energies, the ratio of transverse energy per charged particle was found to be independent of centrality and growing slowly with $\sqrt{{s}_{\mathrm{NN}}}$. A survey of comparisons between the data and available theoretical models is also presented.

Production of phi mesons at midrapidity in root S-NN=200 GeVAu+Au collisions at relativistic energies

Abstract: We present the results of phi meson production in the K+K- decay channel from Au+Au collisions at root s(NN) =200 GeV as measured at midrapidity by the PHENIX detector at Brookhaven National Laboratory's Relativistic Heavy Ion Collider. Precision resonance centroid and width values are extracted as a function of collision centrality. No significant variation from the Particle Data Group accepted values is observed, contrary to some model predictions. The phi transverse mass spectra are fitted with a linear exponential function for which the derived inverse slope parameter is seen to be constant as a function of centrality. However, when these data are fitted by a hydrodynamic model the result is that the centrality-dependent freeze-out temperature and the expansion velocity values are consistent with the values previously derived from fitting identified charged hadron data. As a function of transverse momentum the collisions scaled peripheral-to-central yield ratio R-CP for the phi is comparable to that of pions rather than that of protons. This result lends support to theoretical models that distinguish between baryons and mesons instead of particle mass for explaining the anomalous (anti) proton yield.

Deuteron and Antideuteron Production inAu+AuCollisions atsNN=200GeV

Abstract: The production of deuterons and antideuterons in the transverse momentum range $1.1l{p}_{T}l4.3\text{ }\text{ }\mathrm{GeV}/c$ at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{GeV}$ has been studied by the PHENIX experiment at RHIC. A coalescence analysis, comparing the deuteron and antideuteron spectra with that of proton and antiproton, has been performed. The coalescence probability is equal for both deuterons and antideuterons and it increases as a function of ${p}_{T}$, which is consistent with an expanding collision zone. Comparing (anti)proton yields, $\overline{p}/p=0.73\ifmmode\pm\else\textpm\fi{}0.01$, with (anti)deuteron yields, $\overline{d}/d=0.47\ifmmode\pm\else\textpm\fi{}0.03$, we estimate that $\overline{n}/n=0.64\ifmmode\pm\else\textpm\fi{}0.04$. The nucleon phase space density is estimated from the coalescence measurement.

Measurement of single electron event anisotropy in Au+Au collisions at √sNN = 200 GeV

Abstract: The transverse momentum dependence of the azimuthal anisotropy parameter v(2), the second harmonic of the azimuthal distribution, for electrons at midrapidity (vertical bar eta vertical bar < 0.35) has been measured with the PHENIX detector in Au+Au collisions at root s(NN) = 200 GeV. The measurement was made with respect to the reaction plane defined at high rapidities (vertical bar eta vertical bar = 3.1-3.9). From the result we have measured the v(2) of electrons from heavy flavor decay after subtraction of the v(2) of electrons from other sources such as photon conversions and Dalitz decay from light neutral mesons. We observe a nonzero single electron v(2) with a 90% confidence level in the intermediate-p(T) region. The precision of the present data set does not permit us to conclude definitively that heavy quarks exhibit thermalization with the transverse flow of the bulk matter.

Jet structure of baryon excess in Au+Au collisions at root SNN=200 GeV

Abstract: Two particle correlations between identified meson and baryon trigger particles with 2.5

Midrapidity direct-photon production in p + p collisions at √s=200 GeV

Abstract: A measurement of direct photons in p+p collisions at root s=200 GeV is presented. A photon excess above background from pi(0)->gamma+gamma, eta ->gamma+gamma and other decays is observed in the transverse momentum range 5.5 < p(T)< 7 GeV/c. The result is compared to a next-to-leading-order perturbative QCD calculation. Within errors, good agreement is found between the QCD calculation and the measured result.

Midrapidity direct-photon production inp+pcollisions ats=200GeV

Abstract: A measurement of direct photons in $p+p$ collisions at $\sqrt{s}=200\text{ }\text{ }\mathrm{GeV}$ is presented. A photon excess above background from ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}+\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}+\ensuremath{\gamma}$ and other decays is observed in the transverse momentum range $5.5l{p}_{\mathrm{T}}l7\text{ }\text{ }\mathrm{GeV}/c$. The result is compared to a next-to-leading-order perturbative QCD calculation. Within errors, good agreement is found between the QCD calculation and the measured result.

What Happens to Wages After Displacement

Abstract: Faced with limited resources, policymakers need to know when and where to target support for displaced workers. The academic literature offers little support, presenting wide-ranging results with no consistent explanation for the observed differences in wages after workers are displaced. In this paper, we demonstrate that the heterogeneity found in the literature is consistent with varying market conditions. The results suggest that support for displaced workers can be more efficiently allocated by considering the timing and location of displacement.

Constraints on the time-scale of nuclear breakup from thermal hard-photon emission

Abstract: Measured hard photon multiplicities from second-chance nucleon-nucleon collisions are used in combination with a kinetic thermal model, to estimate the break-up times of excited nuclear systems produced in nucleus-nucleus reactions at intermediate energies. The obtained nuclear break-up time for the $^{129}${Xe} + $^{nat}${Sn} reaction at 50{\it A} MeV is $\Delta$$\tau$ $\approx$ 100 -- 300 fm/$c$ for all reaction centralities. The lifetime of the radiating sources produced in seven other different heavy-ion reactions studied by the TAPS experiment are consistent with $\Delta$$\tau$ $\approx$ 100 fm/$c$, such relatively long thermal photon emission times do not support the interpretation of nuclear breakup as due to a fast spinodal process for the heavy nuclear systems studied.

The Ring Imaging Cherenkov detector (RICH) of the AMS experiment

Abstract: The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring Imaging Cherenkov (RICH) detector for measuring the electric charge and velocity of the charged cosmic particles. A RICH prototype consisting of 96 photomultiplier units, including a piece of the conical reflector, was built and its performance evaluated with ion beam data. Preliminary results of the in-beam tests performed with ion fragments resulting from collisions of a 158 GeV/c/nuc primary beam of Indium ions (CERN SPS) on a Pb target are reported. The collected data included tests to the final front-end electronics and to different aerogel radiators. Cherenkov rings for a large range of charged nuclei and with reflected photons were observed. The data analysis confirms the design goals. Charge separation up to Fe and velocity resolution of the order of 0.1% for singly charged particles are obtained.