A high statistics study of high-$p_t$ two-particle azimuthal correlations in Pb-Au at $\sqrt{s_{\rm NN}}=17.2$ GeV, performed by the CERES experiment at the CERN-SPS, is presented. A broad away-side correlation with significant dip at $Δϕ\approxπ$ is observed. The shape and magnitude of the correlation is similar to measurements at RHIC. In comparison to PYTHIA calculations, we observe a significant excess of soft particles at the away-side. A study of charge correlations between trigger and associated particles disfavors vacuum fragmentation of the away-side jet and suggests significant energy transfer of the hard-scattered parton to the medium.
Energy dependence of transverse particle production from SPS to RHIC
Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity in Pb+Pb collisions at sqrt{ s_{NN} }=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-}, by the NA49 experiment. The nuclear modification factors R_{AA} , R_{AA/pA} and R_{CP} were extracted and are compared to RHIC results at sqrt{ s_{NN} }=200 GeV. The modification factor R_{AA} shows a rapid increase with transverse momentum in the covered region. The modification factors R_{AA/pA} and R_{CP} shows a saturation well below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200 GeV RHIC results closely i…
The energy dependence of $p_t$ angular correlations inferred from mean-$p_{t}$ fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
The STAR collaboration presents measurements of semi-inclusive distributions of charged jets recoiling from high transverse energy ($E_{\text{T}}$) direct photon and $π^{0}$ triggers in $p$+$p$ and central Au+Au collisions at $\sqrt{s_{\text{NN}}} = 200$ GeV. Jets are reconstructed from charged particles using the anti-$k_{\text{T}}$ algorithm with jet resolution parameters $R = 0.2$ and 0.5. The large uncorrelated background in central Au+Au collisions is corrected using a mixed-event technique. This enables a jet measurement extending to low transverse momentum and large $R$ with well-contro…
We present measurements of the nuclear modification factors RAA and RpA(PYTHIA) of b jets in lead-lead and proton-lead collisions, respectively, using the CMS detector. Jets from b-quark fragmentations are found by exploiting the long lifetime of the b-quark through tagging methods using distributions of the secondary vertex displacement. From these, b-jet cross-sections are calculated and compared to the pp cross-section from the 2.76 TeV pp data collected in 2013 and to a PYTHIA simulation at 5.02 TeV, where these center-of-mass energies correspond to those of the PbPb and pPb data. We obser…
Probing jet hadrochemistry modification with measurements of $\mathbfπ$, K, and p in jets and the underlying event in pp and Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV
Jet Radius Dependence of Energy Loss in Pb+Pb Collisions: A Comparative Analysis of the Ratio of Nuclear Modification Factors and Fractional Energy Loss
University of Illinois（伊利诺伊大学）；Dipartimento di Fisica, Università and INFN Torino（都灵大学物理系及意大利国家核物理研究所都灵分部）
通过比较ATLAS和ALICE在5.02 TeV Pb+Pb碰撞中不同喷注半径下的核修正因子比值和分数能量损失，研究了喷注淬火的半径依赖性，揭示了单喷注和双喷注测量以及不同探测器之间的差异。
With our coupled jet-fluid model, we study the nuclear modifications of full jets and jet structures for single inclusive jet and $γ$-jet events in relativistic heavy-ion collisions. The evolution of full jet showers is studied via a set of coupled transport equations including the effects of collisional energy loss, transverse momentum broadening and medium-induced splitting. The dynamics of the jet energy and momentum deposited into the medium is described by hydrodynamic equations with source terms. Our detailed analysis indicates that collisional absorption (energy loss) tends to narrow th…
The first evidence of jet quenching was observed at RHIC via suppression of single high $p_T$ hadron $R_{AA}$ and the disappearance of the away-side jet peak in two-particle correlations. Since then, hadron $R_{AA}$ and two-particle correlations continue to be useful probes of the QGP in heavy ion collisions, since the particles involved are fragments of the jets produced in the initial hard scattering. PHENIX recently improved the width measurements extracted from $π^0$-hadron correlations after removing the higher order flow terms in the underlying event subtraction. Measurements of the away…
These proceedings report recent studies performed by the ALICE, ATLAS and CMS experiments on jet substructure in pp and Pb+Pb collisions at 5.02 TeV. The dependence of the modification of the jet shape on the dijet transverse moment um asymmetry is presented. Measurements of particles recoiling against the Z boson without being constrained to jet cone delimitations are shown. Fully-corrected measurements of the N-subjettiness within anti-kt R = 0.4 charged-particle jets are also described.
The characterization of the jet substructure can give insight into the microscopic nature of the modification induced on high-momentum partons by the Quark-Gluon Plasma that is formed in ultra-relativistic heavy-ion collisions. Jet shapes allow us to study the modification of parton to jet fragmentation and virtuality, probing jet energy redistribution, intra-jet broadening or collimation and possible flavour hierarchy. Results of a selected set of jet shapes will be presented for $\mbox{p--Pb}$ collisions at $\sqrt{s_{\scriptscriptstyle \rm NN}}= 5.02~\mathrm{TeV}$ and for $\mbox{Pb--Pb}$ col…
We study the medium modification of jets correlated with large transverse momentum photons at the LHC via a transport and perturbative QCD hybrid model which incorporates the contributions from both elastic collisions and radiative energy loss experienced by the parton showers. Calculations are performed for the modification of the photon-tagged jet yield, the photon-jet energy imbalance, and the azimuthal distribution of away-side jets. The modifications of photon-tagged jets with different $x_T = p_{T, J}/p_{T, γ}$ values are studied and they exhibit different centrality and jet cone size de…
Within a multiphase transport model, medium modifications of differential jet shapes are investigated in Pb+Pb collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV. The differential jet shapes are significantly modified by the strong interactions between jets and a partonic medium in Pb+Pb collisions relative to that in p+p collisions. The modifications are slightly weakened by the hadronization of coalescence, but strengthened by resonance decays in hadronic rescatterings. Subleading jets display larger medium modifications than leading jets, especially in central Pb+Pb collisions with large dijet…
Highly energetic jets are sensitive probes for the kinematics and the topology of nuclear collisions. Jets are collimated sprays of charged and neutral particles, which are produced in the fragmentation of hard scattered partons in the early stage of the collision. The measurement of nuclear modification of charged jet spectra in p-Pb collisions provides an important way of quantifying the effects of cold nuclear matter in the initial state on jet production, fragmentation, and hadronization. Unlike in Pb-Pb collisions, modifications of jet production due to hot nuclear matter effects are not …
With our coupled jet-fluid model, we study the nuclear modifications of full jets and jet structures for single inclusive jets and $γ$-jets in Pb+Pb collisions at $5.02$~ATeV and $2.76$~ATeV. The in-medium evolution of full jet shower is described by a set of coupled transport equations including the effects of collisional energy loss, transverse momentum broadening and medium-induced splitting process. The dynamical evolution of bulk medium is simulated by solving relativistic hydrodynamic equation with source term which accounts for the energy and momentum deposited by hard jet shower to sof…
Jet energy transported to quark-gluon plasma during jet-medium interaction excites the QGP medium and creates energetic thermal partons -- recoil particles or recoils. Modification of the jet structure in heavy ion collisions is studied using \textsc{martini}, in which recoil simulation is enabled. In large systems such as central Pb-Pb collisions, the recoil effect is expected to be critical due to strong jet-medium interaction. We show the results of the jet mass function and jet shape function are improved when the recoil particles are included in the reconstructed jets. We conclude that th…
We study the evolution of full jet shower in quark-gluon plasma via solving a set of coupled differential transport equations for the three-dimensional momentum distributions of quarks and gluons contained in the full jets. In our jet evolution equations, we include all partonic splitting processes as well as the collisional energy loss and transverse momentum broadening for both the leading and radiated partons of the full jets. Combining with a realistic (2+1)-dimensional viscous hydrodynamic simulation for the space-time profiles of the hot and dense nuclear medium produced in heavy-ion col…
We present a coherent model that combines jet production from perturbative QCD with strongly-coupled jet-medium interactions described in holography. We use this model to study the modification of an ensemble of jets upon propagation through a quark-gluon plasma resembling central heavy ion collisions. Here the modification of the dijet asymmetry depends strongly on the subleading jet width, which can therefore be an important observable for studying jet-medium interactions. We furthermore show that the modification of the shape of the leading jet is relatively insensitive to the dijet asymmet…
We present the measurement of a new set of jet shape observables for track-based jets in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV. The set of jet shapes includes the first radial moment or angularity, $g$; the momentum dispersion, $p_{\rm T}D$; and the difference between the leading and sub-leading constituent track transverse momentum, $LeSub$. These observables provide complementary information on the jet fragmentation and can constrain different aspects of the theoretical description of jet-medium interactions. The jet shapes were measured for a small resolution param…
Based on a multiphase transport model, medium modifications of prompt photon-tagged jet fragmentation function are investigated by comparing prompt photon-tagged hadron azimuthal correlation in Au+Au collisions (0-40\%) with that in p+p collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV. The measured modification factor, $I_{AA}$, increases with the increasing integration range of the away side, which reveals a medium-modified jet shape in which the medium enhancement of soft particles is preferentially located far away from the jet axis. The $I_{AA}$ largely results from strong interactions betwe…
The first measurement of jet shapes, defined as the fractional transverse momentum radial distribution, for inclusive jets produced in heavy-ion collisions is presented. Data samples of PbPb and pp collisions, corresponding to integrated luminosities of 150 inverse microbarns and 5.3 inverse picobarns respectively, were collected at a nucleon-nucleon centre-of-mass energy of sqrt(s[NN]) = 2.76 TeV with the CMS detector at the LHC. The jets are reconstructed with the anti-kt algorithm with a distance parameter R = 0.3, and the jet shapes are measured for charged particles with transverse moment…
Charged jet production cross sections in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV measured with the ALICE detector at the LHC are presented. Using the anti-$k_{\rm T}$ algorithm, jets have been reconstructed in the central rapidity region from charged particles with resolution parameters $R = 0.2$ and $R = 0.4$. The reconstructed jets have been corrected for detector effects and the underlying event background. To calculate the nuclear modification factor, $R_{\rm pPb}$, of charged jets in p-Pb collisions, a pp reference was constructed by scaling previously measured charged jet spect…
The modification of jet substructure in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage jet evolution in JETSCAPE provides an integrated description of jet quenching by combining multiple models, with each becoming active at a different stage of the parton shower evolution. Jet substructure modification due to different aspects of jet quenching is studied using jet shape and jet fragmentation observables. Various combinations of jet energy loss models are exploed, with medium…
Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and PbPb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with p$_\mathrm{T}^\text{jet} >$ 30 GeV in events containing an isolated photon with p$_\mathrm{T}^γ>$ 60 GeV, using charged tracks with transverse momentum p$_\mathrm{T}^\text{trk} >$ 1 GeV in a cone around the jet axis. The association with an isolated photon constrains the initia…
We propose an extension to classify jet modification in heavy-ion collisions by including the jet mass along with its energy. The mass of a jet, as measured by jet reconstruction algorithms, is constrained by the jet's virtuality, which in turn has a considerable effect on such observables as the fragmentation function and jet shape observables. The leading parton, propagating through a dense medium, experiences substantial virtuality (or mass) depletion along with energy loss. Meaningful comparisons between surviving jets and jets produced in $p$-$p$ collisions require mass depletion to be ta…
The event generator based on the higher-twist energy loss formalism -- Modular All Twist Transverse-scattering Elastic-drag and Radiation (MATTER) -- is further developed and coupled to a hydrodynamic model for studying jet modification in relativistic nuclear collisions. The probability of parton splitting is calculated using the Sudakov form factor that is constructed by a combination of vacuum and medium-induced splitting functions; and the full parton showers are simulated, including both energy-momentum and space-time evolutions of all jet partons. With the assumption that partons below a…
Inclusive jet production in pPb collisions at a nucleon-nucleon (NN) center-of-mass energy of sqrt(s[NN]) = 5.02 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 35 inverse nanobarns is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range -2.0 < eta[CM] < 1.5 in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about eta[CM] = 0 is observed in the measured kinematic range. The measurements in t…
The CMS Collaboration presents the first measurement of the differential cross section of jets from charm quarks produced in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of sqrt(s[NN]) = 5.02 TeV, as well as results from charm quark jets in proton-proton (pp) collisions at sqrt(s) = 2.76 and 5.02 TeV. By comparing the yields of the pPb and pp collision systems at the same energy, a nuclear modification factor for charm jets from 55 to 400 GeV/c in pPb collisions at sqrt(s[NN]) = 5.02 TeV of R[pA] = 0.92 +/- 0.07 (stat) +/- 0.11 (syst) is obtained. This is consistent …
Measurements of the yield and nuclear modification factor, $R_\mathrm{ AA}$, for inclusive jet production are performed using 0.49 nb$^{-1}$ of Pb+Pb data at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV and 25 pb$^{-1}$ of $pp$ data at $\sqrt{s}=5.02$ TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti-$k_t$ algorithm with radius parameter $R=0.4$ and are measured over the transverse momentum range of 40-1000 GeV in six rapidity intervals covering $|y|<2.8$. The magnitude of $R_\mathrm{ AA}$ increases with increasing jet transverse momentum, reaching a value of approximately 0.6 …
A U.S.-based Electron-Ion Collider will provide the ultimate capability to determine both the structure and properties of nucleons and nuclei, as well as how matter and energy can be transported through a strongly interacting quantum mechanical environment. The production and propagation of long-lived heavy subatomic particles is a unique and critical part of this planned decade-long research program. In these proceedings we report the derivation of all branching processes in nuclei that lead to a modification of semi-inclusive hadron production, jet cross sections, and jet substructure when c…
