共查询到20条相似文献,搜索用时 437 毫秒
1.
Elena Bruna 《The European Physical Journal C - Particles and Fields》2009,62(1):133-137
The measurement of jet fragmentation functions in p+p collisions at 200 GeV is of great interest because it provides a baseline
to study jet quenching in heavy-ion collisions. It is expected that jet quenching in nuclear matter modifies the jet energy
and multiplicity distributions, as well as the jet hadrochemical composition. Therefore, a systematic study of the fragmentation
functions for charged hadrons and identified particles is a goal both in p+p and Au+Au collisions at RHIC. Studying fragmentation
functions for identified particles is interesting in p+p by itself because it provides a test of NLO calculations at RHIC
energies. We present a systematic comparison of jet energy spectra and fragment distributions using different jet-finding
algorithms in p+p collisions in STAR. Fragmentation functions of charged and neutral strange particles are also reported for
different jet energies. 相似文献
2.
Xin Dong 《The European Physical Journal C - Particles and Fields》2009,61(4):659-664
I report the most recent measurements on open heavy flavor production at RHIC on behalf of the STAR collaboration. The total
charm production cross section in midrapidity at RHIC energy is found to approximately scale by number of binary collisions
in d + Au, Cu + Cu and Au + Au collisions. The nuclear modification factor of non-photonic electrons is strongly suppressed in
central Au + Au collisions, suggesting substantial heavy quark energy loss at RHIC. The bottom decay contribution to non-photonic
electrons was studied via the e–h and e–D
0 azimuthal angular correlations. The bottom contribution is found to be important at p
T
>5 GeV/c, and is consistent with the FONLL calculation within uncertainties. Charm production through gluon jet splitting was measured
by studying the D
*± contents in the fully reconstructed jets in p+p collisions. This rate is consistent with pQCD evaluation of gluon splitting into a pair of charm quarks and subsequent hadronization. 相似文献
3.
N. Borghini 《The European Physical Journal C - Particles and Fields》2007,49(1):327-331
The explanation of the suppression of high-pT hadron yields at RHIC in terms of jet-quenching implies that the multiplicity distributions of particles inside a jet and
jet-like particle correlations differ strongly in nucleus–nucleus collisions at RHIC or at the LHC from those observed at
e+e- or hadron colliders. We present a framework for describing the medium-induced modification, which has a direct interpretation
in terms of a probabilistic medium-modified parton cascade, and which treats leading and subleading partons on an equal footing.
We show that our approach can account for the strong suppression of single inclusive hadron spectra measured in Au–Au collisions
at RHIC, and that this implies a characteristic distortion of the single inclusive distribution of soft partons inside the
jet. We determine, as a function of the jet energy, to what extent the soft fragments within a jet can be measured above some
momentum cut.
PACS 12.38.Mh; 25.75.-q 相似文献
4.
L. Bravina A. Capella E. G. Ferreiro A. B. Kaidalov K. Tywoniuk E. Zabrodin 《The European Physical Journal C - Particles and Fields》2009,61(4):865-870
One observes strong suppression effects for hard probes, e.g. the production of J/ψ or high-p
T
particles, in nucleus–nucleus (AA) collisions at RHIC. Surprisingly, the magnitude of the suppression is quite similar to that at SPS. In order to establish
whether these features arise due to the presence of a thermalized system of quarks and gluons formed in the course of the
collision, one should investigate the impact of suppression mechanisms which do not explicitly involve such a state. We calculate
shadowing for gluons in the Glauber–Gribov theory and propose a model invoking a rapidity-dependent absorptive mechanism motivated
by energy-momentum conservation effects. Furthermore, final-state suppression due to interaction with comoving matter (hadronic
or pre-hadronic) has been shown to describe the data at SPS. We extend this model by including the backward reaction channel,
i.e. recombination of open charm, which is estimated directly from pp data at RHIC. Strong suppression of charmonium both in pA and AA collisions at LHC is predicted. This is in stark contrast with the predictions of models assuming QGP formation and thermalization
of heavy quarks. 相似文献
5.
F. Noferini 《The European Physical Journal C - Particles and Fields》2007,52(1):247-251
The aim of this work is to extend to LHC the results observed for two-particle correlations at RHIC, especially in terms of
jet quenching effects. In this study a parton quenching model developed in the BDMPS-Z-SW framework is considered and implemented
as an afterburner for PYTHIA and HIJING. A simplified parametrization of the quenching mechanism at the parton level is included
in one of the most popular Monte Carlo event generators for AA collisions, HIJING. The simulation method, tuned on the RHIC
data, is then used to make predictions for the LHC energy regime in order to probe the scenario we will study in the ALICE
experiment. 相似文献
6.
We show that partons traversing a quark–gluon plasma can lose substantial amounts of energy also by scatterings, and not only through medium-induced radiation as mainly considered previously. Results from Monte Carlo simulations of soft interactions of partons, emerging from a hard scattering, through multiple elastic scatterings on gluons in an expanding relativistic plasma show a sizeable jet quenching which can account for a substantial part of the effect observed in RHIC data. 相似文献
7.
8.
Sevil Salur 《The European Physical Journal C - Particles and Fields》2009,62(1):119-125
Jets can be used to probe the physical properties of the high energy density matter created in collisions at the Relativistic
Heavy Ion Collider (RHIC). Measurements of strong suppression of inclusive hadron distributions and di-hadron correlations
at high p
T
have already provided evidence for partonic energy loss. However, these measurements suffer from well-known geometric biases
due to the competition of energy loss and fragmentation. These biases can be avoided if the jets are reconstructed independently
of their fragmentation details—quenched or unquenched. In this paper, we discuss modern jet reconstruction algorithms (cone
and sequential recombination) and their corresponding background subtraction techniques required by the high multiplicities
of heavy ion collisions. We review recent results from the STAR experiment at RHIC on direct jet reconstruction in central
Au+Au collisions at
GeV. 相似文献
9.
We discuss one of the most prominent features of the very recent preliminary elliptic flow data of J/ψ-mesons from the PHENIX Collaboration (PHENIX Collaboration (C. Silvestre), arXiv:0806.0475 [nucl-ex]). Even within the
rather large error bars of the measured data a negative elliptic flow parameter (v2) for J/ψ in the range of p
T = 0.5-2.5 GeV/c is visible. We argue that this negative elliptic flow at intermediate pT is a clear and qualitative signature for the collectivity of charm quarks produced in nucleus-nucleus reactions at RHIC.
Within a parton recombination approach we show that a negative elliptic flow puts a lower limit on the collective transverse
velocity of heavy quarks. The numerical value of the transverse flow velocity for charm quarks that is necessary to reproduce the data is (charm) ∼ 0.55-0.6c and therefore compatible with the flow of light quarks. 相似文献
10.
The rate of high energy photons produced from energetic jets during their propagation through the QGP at RHIC and LHC is studied by taking into account the contribution of jet quenching in the medium. It is shown that the jet quenching effect reduces the rate of jet-photon conversion at large transverse momemtum by about 40% at RHIC with √S= 200 AGeV, and by about 80% at LHC with √S = 5500 AGeV. 相似文献
11.
The current status of the understanding of jet quenching in nuclear collisions at RHIC is reviewed. The experimentally large
level of suppression of jets in Au+Au collisions at RHIC is a success, but also introduces a challenge in terms of quantitative
understanding of the properties of the collision zone. The medium appears to be equally black to all interacting probes utilized
to date, limiting the amount of tomographic information that can be obtained from quenching phenomena. In order to recover
this information, a probe to which the medium is gray needs to be found.
PACS 25.75.-q 相似文献
12.
A. Dainese 《The European Physical Journal C - Particles and Fields》2007,49(1):135-141
At LHC energy, heavy quarks will be abundantly produced and the design of the ALICE detector will allow us to study their
production using several channels. The expected heavy-quark in-medium energy loss in nucleus-nucleus collisions at the LHC
is calculated within a model, that is compared to the available heavy-quark quenching measurements at RHIC. The nuclear modification
factors and heavy-to-light ratios of charm and beauty mesons are considered. The capability of the ALICE experiment for addressing
this phenomenology is discussed.
PACS 25.75.-q; 14.65.Dw; 13.25.Ft 相似文献
13.
Alejandro?Ayala Eleazar?Cuautle Isabel?Domínguez Antonio?Ortiz Guy?Pai? 《The European Physical Journal C - Particles and Fields》2009,62(3):535-540
The experimental results on transverse momentum azimuthal hadron correlations at RHIC have opened a rich field for parton
energy loss analysis in heavy-ion collisions. Recently, a considerable amount of work has been devoted to study the shapes
of the “away-side” jet which exhibit an interesting and unexpected “double hump” structure not observed in the analogous treatment
of the pp data. Driven by the possibility that the latter result might just mean that such a structure exists already in the case of
pp collisions, but that its relative intensity could be small, here we use the Event Shape Analysis to show that it is possible
to identify and select well defined event topologies in pp collisions, among which a double hump structure for the away-side jet emerges. Using two shape parameters, the sphericity
in the transverse plane and the recoil to analyze a sample of PYTHIA generated pp collisions at
GeV, we show that this structure corresponds to two jets emitted in the backward hemisphere. Finally, we show that Q-PYTHIA
qualitatively reproduces the decrease in the yield of dijet events and the increase of the double hump structure in the away
side observed in heavy-ion collisions. The implications for the treatment of parton energy loss in heavy-ion collisions are
discussed. 相似文献
14.
V. A. Okorokov 《Physics of Atomic Nuclei》2009,72(1):147-160
Experimental results obtained by studying the azimuthal anisotropy of final states in nucleus-nucleus interactions at the energies of the relativistic heavy-ion collider (RHIC) are systematized. The medium is found to exhibit a pronounced collective behavior, which is likely to be formed at an early, parton, stage of the spacetime evolution of product hot and dense matter. Experimental data on the azimuthal anisotropy indicate that strongly interacting matter produced in the final state under extreme conditions behaves as a nearly ideal liquid rather than an ideal gas of quarks and gluons. The experimentally observed suppression of high-transverse-momentum jets and substantial modification of jetlike azimuthal correlations in heavy-ion collisions suggest that the energy loss of partons propagating in high-temperature matter featuring a high density of color charges is extremely large. The dependence of the amount of hardjet suppression in nucleus-nucleus collisions on the orientation of a jet with respect to the reaction plane was first discovered experimentally at RHIC. A strong suppression of the production of high-transverse-momentum particles and jets at RHIC is a unique phenomenon, which was discovered experimentally at lower energies. 相似文献
15.
A. Gehrmann-De Ridder T. Gehrmann E. Poulsen 《The European Physical Journal C - Particles and Fields》2006,47(2):395-411
The production of final state photons in deep inelastic scattering originates from photon radiation off leptons or quarks
involved in the scattering process. Photon radiation off quarks involves a contribution from the quark-to-photon fragmentation
function, corresponding to the non-perturbative transition of a hadronic jet into a single, highly energetic photon accompanied
by some limited hadronic activity. Up to now, this fragmentation function was measured only in electron–positron annihilation
at LEP. We demonstrate by a dedicated parton-level calculation that a competitive measurement of the quark-to-photon fragmentation
function can be obtained in deep inelastic scattering at HERA. Such a measurement can be obtained by studying the photon energy
spectra in γ+(0+1)-jet events, where γ denotes a hadronic jet containing a highly energetic photon (the photon jet). Isolated
photons are then defined from the photon jet by imposing a minimal photon energy fraction. For this so-called democratic clustering
approach, we study the cross sections for isolated γ+(0+1)-jet and γ+(1+1)-jet production as well as for the inclusive isolated
photon production in deep inelastic scattering. 相似文献
16.
M. J. Leitch 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):868-874
At the Relativistic Heavy-Ion Collider (RHIC) collisions of heavy ions at nucleon-nucleon energies of 200GeV appear to have
created a new form of matter thought to be a deconfined state of the partons that ordinarily are bound in nucleons. We discuss
the evidence that a thermalized partonic medium, usually called a Quark Gluon Plasma (QGP), has been produced. Then, we discuss
the effect of this high-density medium on the production of jets and their pair correlations. Next, we look at direct photons
as a clean electro-magnetic probe to constrain the initial hard scatterings. Finally, we review the developing picture for
the effect of this medium on the production of open heavy quarks and on the screening by the QGP of heavy-quark bound states. 相似文献
17.
Guangyou QIN 《原子核物理评论》2020,37(3):317-328
简要回顾了高能核碰撞中夸克胶子等离子体的软探针和硬探针的一些最新进展,主要内容集中在相对论重离子对撞机和大型强子对撞机实验中各向异性集体流和喷注淬火的理论和唯象研究,对小系统中集体流的来源也做了简要的讨论。对于软探针,讨论了初态三维涨落和碰撞几何各向异性、相对论流体力学演化、末态各向异性集体流以及集体流的涨落、关联和纵向去关联等。通过与实验数据作系统的比较,可以探测重离子碰撞中夸克胶子等离子体的动力演化和各种输运性质。对于硬探针,集中讨论了部分子能量损失和喷注淬火对部分子味道的依赖性、重味夸克在夸克胶子等离子体中的强子化、整体喷注在核介质中的演化以及核介质对喷注的响应等。细致分析相关的观测量,可以帮助我们更全面地了解相对论核碰撞中喷注与核介质的相互作用以及重味粒子的生成。对于小系统,讨论初态和末态效应在解释小系统中轻强子和重味强子的集体流方面的贡献,这有助于我们理解大碰撞系统中集体流的起源成因。 相似文献
18.
We extract the transverse momentum distribution of effective partons using the spectra of Ω, Ξ, Λ and ϕ hadrons measured by the STAR Collaboration from Au + Au collisions at $
\sqrt {s_{NN} }
$
\sqrt {s_{NN} }
= 200 GeV at RHIC. The extracted momentum distribution of strange quarks is flatter than that of up/down quarks consistent
with hydrodynamics expansion in partonic phase prior to hadronization. Consistency in quark ratios derived from various hadron
spectra gives clear evidence for hadron production as suggested by quark coalescence or recombination model. 相似文献
19.
Gouranga C. Nayak 《Physics of Particles and Nuclei Letters》2017,14(1):18-27
Theoretical understanding of the observed jet quenching measurements at RHIC and LHC is challenging in QCD because it requires understanding of parton to hadron fragmentation function in non-equilibrium QCD. In this paper, by using closed-time path integral formalism, we derive the gauge invariant definition of the gluon to hadron fragmentation function in non-equilibrium QCD which is consistent with factorization theorem in non-equilibrium QCD from first principles. 相似文献
20.
B. Sahlmuller 《Indian Journal of Physics》2011,85(6):981-985
The π
o meson has been a crucial probe for observing jet quenching in ultrarelativistic heavy-ion collisions at RHIC. Measurements
of the η meson in the same collisions have also shed light on a possible dependence of the observed suppression on the particle species.
The preliminary π
0 nuclear modification factor R
AA
from the 2004 RHIC run allowed a first systematic comparison between a precise measurement with high statistics and theoretical
calculations, constraining model parameters such as the initial gluon density dNg/dy, and the transport coefficient [^(q)]\hat q. The final π
0 spectra and R
AA
are shown as well as the first η results obtained with both PHENIX electromagnetic calorimeters. 相似文献