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Showing papers by "German Martinez published in 2006"


Journal ArticleDOI
Pietro Cortese, G. Dellacasa, Luciano Ramello, M. Sitta  +975 moreInstitutions (78)
TL;DR: The ALICE Collaboration as mentioned in this paper is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC.
Abstract: ALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. It currently involves more than 900 physicists and senior engineers, from both the nuclear and high-energy physics sectors, from over 90 institutions in about 30 countries.The ALICE detector is designed to cope with the highest particle multiplicities above those anticipated for Pb–Pb collisions (dNch/dy up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and pA), which primarily provide reference data for the nucleus–nucleus collisions. In addition, the pp data will allow for a number of genuine pp physics studies.The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2004. The experiment is currently under construction and will be ready for data taking with both proton and heavy-ion beams at the start-up of the LHC.Since the comprehensive information on detector and physics performance was last published in the ALICE Technical Proposal in 1996, the detector, as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) provides an updated and comprehensive summary of the performance of the various ALICE subsystems, including updates to the Technical Design Reports, as appropriate.The PPR is divided into two volumes. Volume I, published in 2004 (CERN/LHCC 2003-049, ALICE Collaboration 2004 J. Phys. G: Nucl. Part. Phys. 30 1517–1763), contains in four chapters a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, the experimental conditions at the LHC, a short summary and update of the subsystem designs, and a description of the offline framework and Monte Carlo event generators.The present volume, Volume II, contains the majority of the information relevant to the physics performance in proton–proton, proton–nucleus, and nucleus–nucleus collisions. Following an introductory overview, Chapter 5 describes the combined detector performance and the event reconstruction procedures, based on detailed simulations of the individual subsystems. Chapter 6 describes the analysis and physics reach for a representative sample of physics observables, from global event characteristics to hard processes.

587 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala1, N. N. Ajitanand3  +341 moreInstitutions (43)
TL;DR: The PHENIX experiment as mentioned in this paper measured midrapidity of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT] and removed contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons.
Abstract: The PHENIX experiment has measured midrapidity ([FORMULA: SEE TEXT]) transverse momentum spectra ([FORMULA: SEE TEXT]) of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT]. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in p+p collisions. A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.

249 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala1, N. N. Ajitanand3  +340 moreInstitutions (43)
TL;DR: Azimuthal correlations of jet-induced high-p(T) charged hadron pairs are studied at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV in this article.
Abstract: Azimuthal correlations of jet-induced high-p(T) charged hadron pairs are studied at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The distribution of jet-associated partner hadrons (1.0

244 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala3, N. N. Ajitanand4  +339 moreInstitutions (44)
TL;DR: In this article, the cross sections and nuclear dependence of J/psi production versus rapidity, transverse momentum, and centrality were obtained and compared to lower energy p+A results and to theoretical models.
Abstract: J/{psi} production in d+Au and p+p collisions at {radical}(s{sub NN})=200 GeV has been measured by the PHENIX experiment at rapidities -2.2

110 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala1, N. N. Ajitanand3  +342 moreInstitutions (44)
TL;DR: In this paper, the authors measured the transverse momentum spectra of eta mesons within 2-10 GeV/c at midrapidity by the PHENIX experiment in Au+Au collisions.
Abstract: Inclusive transverse momentum spectra of eta mesons have been measured within p(T)=2-10 GeV/c at midrapidity by the PHENIX experiment in Au+Au collisions at root s(NN) = 200 GeV. In central Au+Au the eta yields are significantly suppressed compared to peripheral Au+Au, d+Au, and p+p yields scaled by the corresponding number of nucleon-nucleon collisions. The magnitude, centrality, and p(T) dependence of the suppression is common, within errors, for eta and pi(0). The ratio of eta to pi(0) spectra at high p(T) amounts to 0.40 < R-eta/pi(0)< 0.48 for the three systems, in agreement with the world average measured in hadronic and nuclear reactions and, at large scaled momentum, in e(+)e(-) collisions.

109 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the nuclear dependence of the PHENIX experiment at high energy collisions at a rate of 2.2lyl+2.4 and showed that the absorption in the final state is weak and the shadowing of the gluon distributions is small.
Abstract: $J/\ensuremath{\psi}$ production in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{GeV}$ has been measured by the PHENIX experiment at rapidities $\ensuremath{-}2.2lyl+2.4$. The cross sections and nuclear dependence of $J/\ensuremath{\psi}$ production versus rapidity, transverse momentum, and centrality are obtained and compared to lower energy $p+A$ results and to theoretical models. The observed nuclear dependence in $d+\mathrm{Au}$ collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parametrizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.

94 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala3, N. N. Ajitanand4  +338 moreInstitutions (45)
TL;DR: In this article, the properties of jets produced in p+p collisions at root s = 200 GeV were measured using the method of two-particle correlations, where the trigger particle is a leading particle from a large transverse momentum jet while the associated particle comes from either the same jet or the away-side jet.
Abstract: The properties of jets produced in p+p collisions at root s=200 GeV are measured using the method of two-particle correlations. The trigger particle is a leading particle from a large transverse momentum jet while the associated particle comes from either the same jet or the away-side jet. Analysis of the angular width of the near-side peak in the correlation function determines the jet-fragmentation transverse momentum j(T). The extracted value, root =585 +/- 6(stat)+/- 15(sys) MeV/c, is constant with respect to the trigger particle transverse momentum, and comparable to the previous lower root s measurements. The width of the away-side peak is shown to be a convolution of j(T) with the fragmentation variable, z, and the partonic transverse momentum, k(T). The is determined through a combined analysis of the measured pi(0) inclusive and associated spectra using jet-fragmentation functions measured in e(+)e(-) collisions. The final extracted values of k(T) are then determined to also be independent of the trigger particle transverse momentum, over the range measured, with value of root =2.68 +/- 0.07(stat)+/- 0.34(sys) GeV/c.

79 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala3, N. N. Ajitanand4  +338 moreInstitutions (45)
TL;DR: In this article, the centrality dependence of midrapidity pion, kaon, and proton transverse momentum distributions in d+Au and p+p collisions at root s(NN) = 200 GeV was measured.
Abstract: PHENIX has measured the centrality dependence of midrapidity pion, kaon, and proton transverse momentum distributions in d+Au and p+p collisions at root s(NN) = 200 GeV. The p+p data provide a reference for nuclear effects in d+Au and previously measured Au+Au collisions. Hadron production is enhanced in d+Au, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti)protons is larger than that for pions. The difference increases with centrality but is not sufficient to account for the abundance of baryon production observed in central Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). The centrality dependence in d+Au shows that the nuclear modification factor increases gradually with the number of collisions encountered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production.

78 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala3, N. N. Ajitanand4  +338 moreInstitutions (45)
TL;DR: In this paper, the root-mean-squared transverse momentum of fragmenting hadrons with respect to the jet root was measured at the PHENIX experiment at the Relativistic Heavy Ion Collider.
Abstract: Dihadron correlations at high transverse momentum p(T) in d+Au collisions at root s(NN)=200 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. From these correlations, we extract several structural characteristics of jets: the root-mean-squared transverse momentum of fragmenting hadrons with respect to the jet root , the mean sine-squared of the azimuthal angle between the jet axes , and the number of particles produced within the dijet that are associated with a high-p(T) particle (dN/dx(E) distributions). We observe that the fragmentation characteristics of jets in d+Au collisions are very similar to those in p+p collisions and that there is little dependence on the centrality of the d+Au collision. This is consistent with the nuclear medium having little influence on the fragmentation process. Furthermore, there is no statistically significant increase in the value of from p+p to d+Au collisions. This constrains the effect of multiple scattering that partons undergo in the cold nuclear medium before and after a hard collision.

51 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala1, N. N. Ajitanand3  +340 moreInstitutions (43)
TL;DR: The invariant differential cross section for inclusive electron production in p+p collisions at [FORMULA: SEE TEXT] has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4
Abstract: The invariant differential cross section for inclusive electron production in p+p collisions at [FORMULA: SEE TEXT] has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4

48 citations


Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala1, N. N. Ajitanand3  +341 moreInstitutions (43)
TL;DR: In this paper, the azimuthal distribution of identified π0 and inclusive photons has been measured in VsNN=200 GeV Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC).
Abstract: The azimuthal distribution of identified π0 and inclusive photons has been measured in VsNN=200 GeV Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter (v2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon v2 is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured pT range 1–6 GeV/c. An attempt is made to extract v2 of direct photons.

Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala3, N. N. Ajitanand4  +338 moreInstitutions (44)
TL;DR: In this paper, the two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged particles at mid-rapidity in d+Au and p+p collisions at the Relativistic Heavy Ion Collider were investigated.
Abstract: Deuteron-gold (d+Au) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction (x) predict modifications to jet production at forward rapidity (deuteron-going direction) in d+Au collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in d+Au and p+p collisions at root s(NN)=200 GeV. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with x similar to 0.1 to similar to 0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.

Journal ArticleDOI
S. S. Adler1, S. Afanasiev2, Christine Angela Aidala3, N. N. Ajitanand4  +407 moreInstitutions (46)
TL;DR: In this paper, an improved measurement of the double helicity asymmetry for pi(0) production in polarized proton-proton scattering at root s=200 GeV employing the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) was presented.
Abstract: We present an improved measurement of the double helicity asymmetry for pi(0) production in polarized proton-proton scattering at root s=200 GeV employing the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The improvements to our previous measurement come from two main factors: Inclusion of a new data set from the 2004 RHIC run with higher beam polarizations than the earlier run and a recalibration of the beam polarization measurements for the earlier run, which resulted in reduced uncertainties and increased beam polarizations. The results are compared to a Next to Leading Order (NLO) perturbative Quantum Chromodynamics (pQCD) calculation with a range of polarized gluon distributions.

Posted Content
TL;DR: 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.
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.