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Dijet correlations (circles with boxes for point-to-point systematic errors) in Au+Au and Cu+Cu collisions at sNN=62.4 and 200 GeV. Left panels show central collisions, while right panels show peripheral collisions.
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We present azimuthal angle correlations of intermediate transverse momentum (1-4 GeV/c) hadrons from dijets in Cu+Cu and Au+Au collisions at square root sNN=62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is broadened, non-Gaussian, and peaked away from Delta phi=pi in central and semicentral collisions in all the systems. The b...
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Citations
... In order to understand quantitatively the parton energy loss mechanisms in the QGP, experiments have sought to determine the pathlength dependence of partons traversing the QGP by measuring various correlations. Studies of high-p T hadron correlations [139][140][141][142][143] include short-and long-range correlations in azimuth and pseudo-rapidity. The results of these studies have led to tests of possible collectivity in high multiplicity events in smaller collision systems [144]. ...
We revisit the graphic table of QCD signatures in our 1996 Annual Reviews article "The Search for the Quark-Gluon Plasma" and assess the progress that has been made since its publication towards providing quantitative evidence for the formation of a quark-gluon plasma in relativistic heavy-ion collisions and its characteristic properties.
... Jet quenching leads to several observable consequences: parton energy loss, modification of the jet substructure, and medium-induced acoplanarity. Jet quenching has been measured via inclusive yield and correlation measurements of high-p T hadrons and reconstructed jets, semi-inclusive jet measurements, jet shapes, and recently via jet substructure measurements at RHIC [23][24][25][26][27][28][29][30][31][32][33][34][35][36] and at the LHC [7,15,16,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. ...
The ALICE Collaboration reports a new differential measurement of inclusive jet suppression using pp and PbPb collision data at center-of-mass energy per nucleon-nucleon collision TeV. Charged-particle jets are reconstructed using the anti- algorithm with resolution parameters 0.2, 0.3, 0.4, 0.5, and 0.6 in pp collisions and 0.2, 0.4, 0.6 in central (010%), semi-central (3050%), and peripheral (6080%) PbPb collisions. The analysis uses a novel approach based on machine learning to mitigate the influence of jet background in central heavy-ion collisions, which enables measurements of inclusive jet suppression for jet GeV/c in central collisions at a resolution parameter of . This is the lowest value of jet achieved for inclusive jet measurements at R=0.6 at the LHC, and is an important step for discriminating different models of jet quenching in the quark-gluon plasma. The transverse momentum spectra, nuclear modification factors, and derived cross section and nuclear modification factor ratios for different jet resolution parameters of charged-particle jets are presented and compared to model predictions. A mild dependence of the nuclear modification factor ratios on collision centrality and resolution parameter is observed. The results are compared to a variety of jet quenching models with varying levels of agreement, demonstrating the effectiveness of this observable to discriminate between models.
... This is a direct signature of a highly dense partonic medium, usually formed in high energy heavy-ion collisions. The first evidence of the jet quenching phenomenon has been observed at the Relativistic Heavy-Ion Collider (RHIC) [10][11][12][13][14][15][16][17][18][19][20][21][22][23] via the measurement of inclusive hadron and jet production at high transverse momentum (p T ), γ-hadron correlation, di-hadron angular correlations and the dijet energy imbalance. The jet quenching phenomena are also widely studied in heavy-ion collisions at the Large Hadron Collider (LHC) [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. ...
Within the color string percolation model (CSPM), jet transport coefficient, q^, is calculated for various multiplicity classes in proton-proton and centrality classes in nucleus-nucleus collisions at the Large Hadron Collider energies for a better understanding of the matter formed in ultra-relativistic collisions. q^ is studied as a function of final state charged particle multiplicity (pseudorapidity density at midrapidity), initial state percolation temperature and energy density. The CSPM results are then compared with different theoretical calculations from the JET Collaboration those incorporate particle energy loss in the medium.
... E-mail address: alice -publications @cern .ch. Jet quenching has been observed at RHIC [21][22][23][24][25][26][27][28][29][30][31][32][33][34] and at the LHC [8,16,17,[35][36][37][38][39][40][41][42][43][44][45][46][47], e.g. via inclusive yield and correlation measurements of high-p T hadrons and reconstructed jets. ...
The jet radial structure and particle transverse momentum (pT) composition within jets are presented in centrality-selected Pb–Pb collisions at sNN=2.76 TeV. Track-based jets, which are also called charged jets, were reconstructed with a resolution parameter of R=0.3 at midrapidity |ηch jet|<0.6 for transverse momenta pT,ch jet=30–120 GeV/c. Jet–hadron correlations in relative azimuth and pseudorapidity space (Δφ,Δη) are measured to study the distribution of the associated particles around the jet axis for different pT,assoc-ranges between 1 and 20 GeV/c. The data in Pb–Pb collisions are compared to reference distributions for pp collisions, obtained using embedded PYTHIA simulations. The number of high-pT associate particles (4<pT,assoc<20 GeV/c) in Pb–Pb collisions is found to be suppressed compared to the reference by 30 to 10%, depending on centrality. The radial particle distribution relative to the jet axis shows a moderate modification in Pb–Pb collisions with respect to PYTHIA. High-pT associate particles are slightly more collimated in Pb–Pb collisions compared to the reference, while low-pT associate particles tend to be broadened. The results, which are presented for the first time down to pT,ch jet=30 GeV/c in Pb–Pb collisions, are compatible with both previous jet–hadron-related measurements from the CMS Collaboration and jet shape measurements from the ALICE Collaboration at higher pT, and add further support for the established picture of in-medium parton energy loss.
... Under the two-source (flow + jet) model assumption [44], this underlying event is directly subtracted to obtain the jet contributions. In our previous measurements and most RHIC A + A results, the subtracted flow modulations of the underlying event were limited to contributions of v 2 and the fourth-order harmonic component with respect to the second-order event plane v 4 { 2 } [15,16,20,23,28,[44][45][46][47][48]. Only the recent STAR measurement [49] took into account contributions from v 3 and the fourth-order harmonic component uncorrelated to the second-order event-plane in addition to v 4 { 2 }. ...
... Only the recent STAR measurement [49] took into account contributions from v 3 and the fourth-order harmonic component uncorrelated to the second-order event-plane in addition to v 4 { 2 }. At low-to-intermediate p T in two-particle correlations, intricate features appear such as the near-side long-range rapidity correlations called the "ridge" [45,50] and the away-side "double-humped" structures [28,44,[46][47][48][49]51,52]. Across the large rapidity ranges available at the Large Hadron Collider, the rapidity-independence and hence the likely geometrical origin of most of these structures have been established. ...
We present measurements of azimuthal correlations of charged hadron pairs in
√
s
NN
=
200
GeV
Au
+
Au
collisions for the trigger and associated particle transverse-momentum ranges of
1
<
p
t
T
<
10
GeV
/
c
and
0.5
<
p
a
T
<
10
GeV
/
c
. After subtraction of an underlying event using a model that includes higher-order azimuthal anisotropy
v
2
,
v
3
, and
v
4
, the away-side yield of the highest trigger-
p
T
(
p
t
T
>
4
GeV
/
c
) correlations is suppressed compared with that of correlations measured in
p
+
p
collisions. At the lowest associated particle
p
T
(
0.5
<
p
a
T
<
1
GeV
/
c
), the away-side shape and yield are modified relative to those in
p
+
p
collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-
p
T
trigger correlations (
2
<
p
t
T
<
4
GeV
/
c
), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle
Ψ
2
and
Ψ
3
. The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the
Ψ
2
event plane. This asymmetry and the measured suppression of the pair yield out-of-plane is consistent with a path-length-dependent energy loss. No
Ψ
3
dependence can be resolved within experimental uncertainties.
... Additionally, the observed suppression of high transverse momentum (p T ) single-hadron production as well as dihadron correlations, in heavy-ion collisions, compared to elementary pp interactions, showed that the produced matter is rather opaque [9][10][11][12][13][14][15][16][17][18][19]. Furthermore, studies of two-and multi-particle correlation functions unravelled several unanticipated correlation features [11,[20][21][22][23][24][25][26][27], including a near-side correlation peak (i.e., the prominent and relatively narrow peak centered at ∆ϕ = 0, |∆η| = 0 observed in two-particle correlation functions) broadening, the appearance of a near-side elongated ridge in relative pseudorapidity, as well as a strong suppression or modification of the away-side correlation peak relative to the one observed in pp collisions [10,28,29]. Extensive studies were carried out, both at RHIC and LHC energies, to fully characterize and understand the underlying causes of these features. ...
We present measurements of two-particle differential number correlation functions and transverse momentum correlation functions , obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained using charged particles in the pseudorapidity range 1.0, and transverse momentum range GeV/c as a function of pair separation in pseudorapidity, , azimuthal angle, , and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in as a function of the pair separation . Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of non-flow contributions to flow coefficients measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated.
... The latter assumption is called the Zero-Yield-At-Minimum (ZYAM) method [119]. Early studies of di-hadron correlations fit the data near ∆φ ≈ 1 to determine the background level [111,[120][121][122]. Later studies typically use a few points around the minimum [116,123,124]. ...
... Several theoretical models proposed that a hard parton traversing the medium would lose energy similar to the loss of energy by a supersonic object traveling through the atmosphere [297][298][299]. Early di-hadron correlations studies observed a displaced peak in the awayside [116,121,123,132]. Three-particle correlation studies observed that this feature was consistent with expectations from a Mach cone [300]. ...
A hot, dense medium called a Quark Gluon Plasma (QGP) is created in ultrarelativistic heavy ion collisions. Hard parton scatterings generate high momentum partons that traverse the medium, which then fragment into sprays of particle called jets. Experimental measurements from high momentum hadrons, two particle correlations, and full jet reconstruction at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) continue to improve our understanding of energy loss in the QGP. Run 2 at the LHC recently began and there is a jet detector at RHIC under development. Now is the perfect time to reflect on what the experimental measurements have taught us so far, the limitations of the techniques used for studying jets, how the techniques can be improved, and how to move forward with the wealth of experimental data such that a complete description of energy loss in the QGP can be achieved. Measurements of jets to date clearly indicate that hard partons lose energy. Detailed comparisons of the nuclear modification factor between data and model calculations led to quantitative constraints on the opacity of the medium to hard probes. While there is substantial evidence for softening and broadening jets through medium interactions, the difficulties comparing measurements to theoretical calculations limit further quantitative constraints on energy loss mechanisms. We call for an agreement between theorists and experimentalists on the appropriate treatment of the background, Monte Carlo generators that enable experimental algorithms to be applied to theoretical calculations, and a clear understanding of which observables are most sensitive to the properties of the medium, even in the presence of background. This will enable us to determine the best strategy for the field to improve quantitative constraints on properties of the medium in the face of these challenges.
... The current debate of collectivity in small systems was triggered by the discovery of ridge like correlations that extend over a long range in rapidity in high multiplicity p+p collisions by the CMS collaboration [5]. Such long range structure of azimuthal correlations was previously seen in heavy ion collisions at RHIC [44][45][46] and LHC [47] and generally attributed to the nearly boost invariance structure of the azimuthal correlations driven by hydrodynamic flow. At the same time causality arguments suggest [48] that such correlations must develop at the very early stages of the collisions, indicating the strong influence of initial state dynamics on such observable. ...
... The associated yields predicted by this model exhibit a much faster increase with N offline trk than that seen in the data, suggesting that other other mechanisms may be active in this region. Hydrodynamic models also predict no energy dependence: they reproduce the collective flow effect in heavy-ion collisions, which is nearly unchanged from the RHIC to the LHC center-of-mass energies, although they differ by more than an order of magnitude [43][44][45]. However, it remains to be seen whether hydrodynamic models can quantitatively describe the behavior of the observables presented here. ...
Measurements of multi-particle correlations in the collisions of small systems such as p+p, show striking similarity to the observations in heavy ion collisions. A number of observables measured in the high multiplicity events of these systems resemble features that are attributed to collectivity driven by hydrodynamics. However alternative explanations based on initial state dynamics are able to describe many characteristic features of these measurements. In this brief review we highlight some of the recent developments and outstanding issues in this direction.
... The current debate of collectivity in small systems was triggered by the discovery of ridgelike correlations that extend over a long range in rapidity in high-multiplicity p+p collisions by the CMS collaboration [5]. Such long range structure of azimuthal correlations was previously seen in heavy-ion collisions at RHIC [43][44][45] and LHC [46] and generally attributed to the nearly boost invariance structure of the azimuthal correlations driven by hydrodynamic flow. At the same time, causality arguments suggest [47] that such correlations must develop at the very early stages of the collisions, indicating the strong influence of initial-state dynamics on such observable. ...
Measurements of multi-particle correlations in the collisions of small systems such as p+p, show striking similarity to the observations in heavy ion collisions. A number of observables measured in the high multiplicity events of these systems resemble features that are attributed to collectivity driven by hydrodynamics. However alternative explanations based on initial state dynamics are able to describe many characteristic features of these measurements. In this brief review we highlight some of the recent developments and outstanding issues in this direction.
... Figures 18 and 19 show the di-hadron azimuthal correlation between trigger and associate particles. The system size (Au + Au and Cu + Cu collisions) and beam energy (200 GeV and 62.4 GeV) dependence as well as the centrality dependence are shown in Fig. 18 [15]. The p T dependence and a comparison with the p+p results are shown in Fig. 19 [16]. ...
... Beam energy, system size, and centrality dependence of the di-hadron correlation[15]. ...
High-energy heavy-ion collisions at RHIC-BNL and LHC-CERN provide a unique opportunity to study the properties of the high-temperature
and high-density nuclear matter called the quark–gluon plasma (QGP), which is supposed to exist in the early universe or inside
neutron stars. The PHENIX experiment is one of the major experiments at RHIC to study the properties of QGP, especially focusing
on various particle identification capabilities including photons, leptons, and hadrons. This article summarizes the soft
physics results from the PHENIX experiment, such as (1) global properties like transverse energy and multiplicity measurements
as well as centrality determination, (2) transverse momentum distribution and the nuclear modification factor, which represents
the modification of the spectra in A+A collisions relative to the binary-collision-scaled superposition of p+p data, (3) space-time properties with Hanbury Brown
and Twiss (HBT) interferometry correlation measurement and source imaging, (4) elliptic collective expansion and higher-order
harmonic event anisotropy, and (5) di-hadron correlation, jet modification, and medium response known as jet-quenching from
the partonic energy loss and redistribution of the lost energy. These results are reviewed and discussed.
