1,721,232 research outputs found
Comparing energy loss phenomenology
No full textHigh-pT particle production is suppressed in heavy ion collisions due to parton energy loss in dense QCD matter. Here we present a systematic comparison of two different theoretical approximations to parton energy loss calculations: the opacity expansion and the multiple-soft scattering approximation for the simple case of a quark traversing a homogeneous piece of matter with fixed length (the TECHQM 'brick problem'), with focus on the range of parameters that is relevant for interpreting RHIC measurements of high-pT hadron suppression
Elliptic flow: a brief review
No full textOne of the fundamental questions in the field of subatomic physics is the question of what happens to matter at extreme densities and temperatures as may have existed in the first microseconds after the Big Bang and exists, perhaps, in the core of dense neutron stars. The aim of heavy-ion physics is to collide nuclei at very high energies and thereby create such a state of matter in the laboratory. The experimental program began in the 1990s with collisions made available at the Brookhaven Alternating Gradient Synchrotron (AGS) and the CERN Super Proton Synchrotron (SPS), and continued at the Brookhaven Relativistic Heavy-Ion Collider (RHIC) with the maximum centerof- mass energies of p sNN = 4.75, 17.2 and 200 GeV, respectively. Collisions of heavy ions at the unprecedented energy of 2.76 TeV recently became available at the LHC collider at CERN. In this review, I give a brief introduction to the physics of ultrarelativistic heavy-ion collisions and discuss the current status of elliptic flow measurements
Studying the relative bottom contribution via heavy-quark decay electron measurements in STAR
No full textWe report measurements of the azimuthal angular correlation distribution of heavy-quark decay electrons and open charmed mesons in pp collisions at GeV in the STAR experiment at RHIC. This measurement in combination with current theoretical model calculations allows to extract the relative bottom contribution to the heavy-quark decay electrons, which is important for the interpretation of the observed strong suppression of the high-p T electron yield in central Au+Au collisions
High-pT physics in sTAR
No full textRecent results of the STAR collaboration related to high transverse momentum phenomena are reviewed, which profit greatly from increased statistical reach from the large data sample collected in 2004 and improvement of particle identification at high pT . Dijet structures are observed even in central Au+Au collisions. At sufficiently high momentum a fragmentation pattern as in elementary collisions is observed, however the probability of observing a dijet partner hadron is strongly reduced. Beyond pT = 6 GeV/c all hadron species measured show a similar suppression. At lower pT interesting modifications are seen. A jet-correlated enhancement of long range in pseudorapidity is observed close to a trigger hadron. On the opposite side of the trigger a broad correlation structure is visible with an enhanced yield, which for certain kinematic conditions exhibits a double peak in central Au+Au collisions, whose origin is still under discussion. First results in d+Au collisions demonstrating the potential of photon physics in STAR are also presented
Common suppression pattern of η and π0 mesons at high transverse momentum in Au+Au collisions at VsNN=200 GeV
No full textInclusive transverse momentum spectra of η mesons have been measured within pT=2–10 GeV/c at midrapidity by the PHENIX experiment in Au+Au collisions at VsNN=200 GeV. In central Au+Au the η 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 pT dependence of the suppression is common, within errors, for η and π0. The ratio of η to π0 spectra at high pT amounts to 0.4
Jet-like correlations of heavy-flavor particles – from RHIC to LHC
No full textMeasurements at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory have revealed strong modification of the jet structure in high-energy heavy-ion collisions, which can be attributed to the interaction of hard scattered partons with the hot and dense QCD matter. The study of heavy-quark (charm and bottom) production in such collisions provides key tests of parton energy-loss models and, thus, yields profound insight into the properties of the produced matter. The high-pT yield of heavy-flavor decay electrons exhibits an unexpected large suppression. Since those single electrons have contributions from charm and bottom decays an experimental method is needed to investigate them separately. Heavy-flavor particle correlations provide information about the underlying production mechanism. In this contribution, a review on recent measurements on azimuthal correlations of single electrons and open charmed mesons at RHIC and perspectives of such measurements at the CERN-Large Hadron Collider (LHC) are presented. Moreover, it has been shown that next-to-leading-order (NLO) QCD processes, such as gluon splitting, become important at LHC energies. It will be demonstrated how this contribution can be determined through the measurement of the charm content in jets
Measurement of identified π0 and inclusive photon second-harmonic parameter v2 and Implications for Direct Photon Production in VsNN=200 GeV Au+Au
No full textThe 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
Charm content in jets in proton-proton collisions with the ALICE experiment at CERN-LHC
No full textCharm and bottom quarks have been proposed as probes to study partonic matter produced in high-energy heavy-ion collisions. The detailed understanding of the production mechanisms in proton-proton collisions is of considerable interest as a QCD test tool and as reference calibration for heavy-ion studies. Measurements of the D meson yield in jets probe the production processes in which the observed D mesons are formed primarily from gluon splitting into c or b pairs. The charm content in jets is calculable in perturbative QCD, and the leading non-perturbative correction is expected to be significant at LHC energies. In this contribution we present a performance study of the reconstruction of charged D*± mesons in jets based on the first data collected by the ALICE experiment in minimum bias p+p collisions at = 7 TeV . D*+ mesons are reconstructed through the decay sequence D*+ → D0π+ and D0 → K−π+ (and its charge conjugate channel)
High-pT hadron production and triggered particle correlations
No full textThe STAR experiment at the Relativistic Heavy-Ion Collider has performed measurements of high transverse momentum particle production in ultra-relativistic heavy-ion collisions. High-pT hadrons are generated from hard parton scatterings early in the collision. The outgoing partons probe the surrounded hot and dense matter through interactions. Recent results on high-pT inclusive particle production and leading particle correlations in p+p, d+Au and Au+Au collisions at sqrt(s_NN) = 200 GeV are reviewed
Quarkmaterie onder extreme temperatuur en dichtheid
No full textAlle energie en materie van het heelal, evenals tijd en ruimte ontstonden zo’n veertien miljard jaar geleden tijdens de oerknal. Protonen en neutronen ontstonden een korte tijd daarna uit een extreem heet gas met een extreem hoge dichtheid waarin quasivrije quarks en gluonen voorkwamen. Deze nieuwe verschijningsvorm van fundamentele materie – het zogenoemde quark-gluonplasma – is onder gecontroleerde laboratoriumomstandigheden nagebootst en zorgvuldig bestudeerd door middel van hoogenergetische botsingen tussen atoomkernen in grote deeltjesversnellers. Momenteel worden de hoogste energieën bereikt met de Relativistic Heavy-Ion Collider (Brookhaven, VS). Nog veel hogere energiedichtheden zullen worden bereikt met de Large Hadron Collider (CERN). Dit artikel geeft een beeld van de kennis die op dit moment is opgebouwd over deze bijzondere materietoestand
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