Conveners
Parallel 2: Jets & high-pT: High-pT hadrons
- Magdalena Djordjevic (Institute of Physics Belgrade)
Parallel 2: Jets and High-pT Hadrons
- Helen Caines (Yale University (US))
Parallel 2: Jets & high-pT: Jet quenching
- Urs Wiedemann (CERN)
Parallel 2: Jets & high-pT: Jet-medium interactions
- Henner Buesching (Johann-Wolfgang-Goethe Univ. (DE))
Parallel 2: Jets & high-pT: Jet substructure
- Gunther Roland (Massachusetts Inst. of Technology (US))
Parallel 2: Jets & high-pT: Jet substructure
- Jorn Henning Putschke (Wayne State University (US))
Parallel 2: Jets & high-pT
- Constantinos Loizides (ORNL)
Parallel 2: Jets & high-pT
- Rainer Fries (Texas A&M University)
We present the measurement of charged particle production at mid-rapidity ($|\eta| < 0.9$) in pp ($\sqrt{s}$ = 2.76 TeV, 5.02 TeV), p-Pb ($\sqrt{s_{\rm NN}}$ = 5.02 TeV), Xe-Xe ($\sqrt{s_{\rm NN}}$ = 5.44 TeV) and Pb-Pb ($\sqrt{s_{\rm NN}}$ = 2.76 TeV and 5.02 TeV) collisions with ALICE at the LHC. The transverse momentum ($p_{\rm T}$) spectra are measured in the broad range $0.15 < p_{\rm T}...
The spectra of charged particles in XeXe and PbPb collisions at $\sqrt{s_{NN}} = 5.44$ TeV and $\sqrt{s_{NN}} = 5.02$ TeV, respectively, are presented in six ranges of collision centrality. The PbPb nuclear modification factor is constructed with a measured pp reference, and the XeXe nuclear modification factor is formed with an extrapolated pp reference. Both are found to be heavily...
Measurements of charged-particle production in heavy-ion collisions and their comparison to $pp$ data provide insight into the properties of the quark-gluon plasma. In 2015, the ATLAS detector at the LHC recorded 0.49 nb$^{-1}$ of Pb+Pb collisions and 25 pb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. In addition, around 3 $\mu$b$^{-1}$ of Xe+Xe...
The $p_\perp$ dependence of the nuclear modification factor $R_{AA}$ measured in PbPb collisions at the LHC exhibits a universal shape, which can be very well reproduced in a simple energy loss model based on the BDMPS medium-induced gluon spectrum. The scaling is observed for various hadron species ($h^\pm$, D, $J/\psi$) in different centrality classes and at both colliding energies, √s=2.76...
Neutral mesons, namely neutral pions and $\eta$-mesons, are abundantly produced in AA collisions and can be reconstructed and identified via two-photon decays in wide range of transverse momenta. This makes them excellent probe of the parton energy loss in heavy ion collisions.
Photons in ALICE can be reconstructed via several complementary methods, using either the central tracking system...
The nuclear modification factor, $R_{AA}$, has been satisfactorily described by various jet quenching models. Nonetheless, all these formalisms seemed to underpredict the high $p_T$ ($>10$ GeV/c) elliptic flow, $v_2$. Recently, it has been argued that by the inclusion of event-by-event fluctuations in the soft sector the $R_{AA} - v_2$ problem may be solved. In order to confirm that this is...
STAR has previously reported significant transverse momentum imbalance of a specific set of di-jets selected with "hard cores", i.e. with a constituent cut of 2 GeV/$c$. After reclustering these same di-jets with a lower constituent cut of 200 MeV/$c$, the di-jet balance is restored to the level of p+p collisions within the original cone size of $R=0.4$.
The interpretation of these results as...
Energetic heavy quarks passing through the hot and dense medium of a quark-gluon plasma (QGP), represented by the resulting mesons, are viewed as a suitable probe for the interactions inside of the QGP, in particular the mechanisms of energy loss, as they are less likely to thermalize within the medium and are mostly created at early stages of the medium evolution.
However, models of both,...
The production of deuterons in high-energy collisions is particularly sensitive to the space and time evolution of the system, as well as the baryon production and transport mechanisms. Recent ALICE measurements of spectra and anisotropic flow of (anti-)deuterons provide insight into the production mechanisms of particles in heavy-ion collisions thanks to a critical comparison with the...
The two-prong substructure of the leading subjets inside a reconstructed jet opens new windows on precision constraints on the in-medium modification of parton showers. We present the first resumed calculation of the groomed soft-dropped subjet momentum sharing distribution in heavy ion collisions, and demonstrate that both the STAR data at RHIC and the CMS results at LHC can be understood in...
Most studies of medium-induced jet modification rely on the comparison of jet properties measured in heavy ion collisions with a proton-proton baseline of the same reconstructed jet $p_T$. Migration of jets from higher to lower $p_T$ due to energy loss, together with the steepness of the jet spectrum, lead to a heavy ion jet sample with a given $p_T$ range which is dominated by the jets that...
The phenomenon of jet quenching in ultra-relativistic heavy ion collisions reveals the effect of substantial final state interactions that cause QCD jets to lose energy to the quark-gluon plasma (QGP), mainly by induced gluon radiation. In standard analytic approaches to energy loss, jets are approximated by single partons and thus higher-order effects in the strong coupling constant are...
With our coupled jet-fluid model [1, 2, 3], we study the nuclear modifications of full jets and jet structures for single inclusive jet, dijet and gamma-jet events in relativistic heavy-ion collisions. The evolution of full jet shower is studied via a set of coupled transport equations including the effects of collisional energy loss, transverse momentum broadening and medium-induced splitting...
In this talk we study jets in non-equilibrium quark-gluon plasma using new theoretical tools developed for photons [1]. Jets broaden through radiation which is suppressed because of coherent interaction with the medium. We analyze this radiation when the medium is not in thermal equilibrium. Jet observables can then be used to gain direct access to non-equilibrium properties of the QGP, such...
Jet substructure analysis has the promise to reveal the details of the QCD shower beyond existing jet cross section and coincidence measurements in hadron collider QCD and heavy-ion. Traditional jet substructure variables have been constructed using expert knowledge, and are largely transplanted, unmodified, from the high-energy physics to heavy-ion, thus inhibiting its performance as a QCD...
One of the widely used kinematic assumptions in calculating hard probe radiative energy loss within QGP, is the soft-gluon approximation, which considers that energy loss of the parent parton via gluon's bremsstrahlung is small compared to its initial energy. However, diverse theoretical formalisams obtained a notable energy loss of high $p_{\perp}$ particles, implicitly suggesting inadequacy...
A strongly coupled quark-gluon plasma (QGP) is created in relativistic heavy-ion collisions. Jets are a good probe of the energy loss properties of the QGP experienced by hard partons traversing the medium. Experimentally we take high transverse momentum ($p_{T}$) trigger particles as proxies of jets. The jet-like yield of high-$p_{T}$ particles found in correlations with respect to highly...
The productions of inclusive b-jet and $b\bar{b}$ dijets in Pb+Pb collisions have been investigated by considering the heavy quark and the light quark in-medium evolution simultaneously. The initial hard processes of inclusive b-jet and $b\bar{b}$ dijets productions are described by a next-to-leading order (NLO) plus parton shower Monte Carlo (MC) event generator SHERPA which can be well...
When traversing hot and dense QCD matter energetic partons lose energy by both elastic collisions and medium-induced gluon radiation. Several analytic calculations of radiative jet energy loss demonstrated the importance of the non Abelian Landau-Pomeranchuk-Migdal (LPM) effect, a coherence effect resulting from the finite formation time of emitted gluons. While in these calculations it is...
We present a novel setup of an antenna splitting inside the medium taking into account the finite formation time of the dipole, which turns out to be an important scale. In particular, we consider the splitting of a color-singlet dipole, studying in detail its formation and subsequent propagation through the medium. We discuss the role of coherence and the relevant time scales which control...
Studies of fully reconstructed QCD jets in heavy-ion collisions aim to extract properties of the created hot and dense nuclear matter. Recently, jet substructure observables have extended the plethora of established observables by introducing techniques that facilitate more differential measurements of jet modifications. This talk will summarize the main lines of discussion at the 5th Heavy...
Recent measurements of jet substructure provide insights
into how the hard and soft parts of the jets are modified
by jet-medium interaction. One can also learn the flavor
dependence of jet quenching via comparisons between boson
tagged jet and inclusive jet. In this study, with the
Linear Boltzmann Transport (LBT) model, we investigate
the jet shape, jet splitting function and groomed...
We present a variety of jet substructure measurements performed in pp collisions at $\sqrt{s} = 13$ TeV with the focus on grooming, among them $z_g$, $M_g$ and $R_g$, in a wide range of $p_{\rm T}$ between 20 and 200 GeV/$c$ and jet resolution $0.2 < R < 0.5$. Thanks to the capabilities of the ALICE apparatus jet substructure measurement are possible with an infrared constituent cutoff at 0.15...
Medium-induced jet splitting function is one of the central quantities in studying the interaction of hard jets with the dense nuclear medium. Soft-drop groomed jet measurements provide a direct tool to probe jet splitting function and its medium modification. Based on higher-twist formalism, we study the nuclear modification of groomed jet splitting in heavy-ion collisions at RHIC and the LHC...
I will present a calculation of jet mass distributions for small-radius jets in proton-proton and heavy ion collisions using soft-collinear effective theory (SCET). A process-independent groomed jet mass function is defined which captures the soft-collinear radiation inside jets. The factorization expression simplifies significantly, allowing one to calculate jet mass distributions for jets in...
Measurements of jet yields in heavy-ion collisions can be used to constrain jet energy loss models, and in turn provide information about the physical properties of deconfined QCD matter. ALICE reconstructs charged particle jets (charged jets) with high-precision tracking of charged particles down to $p_{\rm T}^{track} = 150$ MeV/$c$, and jets (full jets) with the addition of particle...
Uncovering the inner working of the quark-gluon plasma requires comprehensive jet substructure information. I will discuss the study of jet quenching utilizing quark and gluon jet substructures as independent probes of heavy ion collisions. Jet and subjet features are exploited to highlight differences between quark and gluon jets in vacuum and in a medium. I will first discuss a...
Measurements of jet substructure have augmented substantially the scope
of jet quenching studies by arguably giving experimental access to
single splitting jet properties and possibly allowing for the
identification of QGP response contributions to a jet. We show that jet
substructure observables provide a path to measure how quenched a jet is
without the need for comparison with other...
The JETSCAPE Collaboration (Jet Energy-loss Tomography with a Statistically and Computationally Advanced Program Envelope) has developed and released an innovative, modular and flexible event generator to be used by the heavy-ion community. The modifications of jet substructure in relativistic heavy-ion collisions represent a new class of quenching observables, which are sensitive to the...
Jets represent an important tool allowing to access the information about the hot and dense medium created in heavy ion collisions. Both jet yields and jet internal structure are observed to be modified in heavy-ion collisions compared to proton-proton reference. This talk presents latest measurements of the nuclear modification factor, $R_{AA}$, for $R=0.4$ jets in Pb+Pb collisions at...
High-Twist approach has been used to calculate parton energy loss and medium modified fragmentation function due to multiple parton scattering. We revisit this problem in deeply inelastic scattering (DIS) process, with a generalized high-twist approach. In this approach, the differential radiated gluon number distribution can be expressed in terms of unintegrated gluon distribution function,...
Event-by-event jet suppression, anisotropy and hard-soft tomography
Xin-Nian Wang$^{1,2,3}$ , Shanshan Cao$^4$, Yayun He$^1$ and Tan Luo$^1$
A consistent description of high $p_T$ particle suppression ($R_{AA}$) and azimuthal anisotropy $v_2$ has been a puzzle in the study of jet quenching, pointing to some non-perturbative native of jet transport. Event-by-event single inclusive jet...
Although quark/gluon single parton energy loss is theoretically well established and under control by the corresponding Casimir color factor (CF/CA), quark/gluon initiated jets will wash out the corresponding color factor ratio due to the parton shower evolution. As such, for phenomenological studies in heavy-ions, it is not only mandatory to take into account the corresponding deviation from...
We investigate the radiative break-up of a highly energetic quark or gluon in a high-temperature QCD plasma. We find that, as a result of the turbulent nature of the underlying parton cascade the quark to gluon ratio of the soft fragments tends to a universal constant value that is independent of the initial conditions, within an inertial range of momenta T ≪ ω ≪ E, where E denotes the energy...
Recent measurements of jet structure modifications at RHIC and LHC highlight the importance of differential measurements to study the nature of jet quenching. Since these jet structure observables are intimately dependent on parton evolution in both the angular and energy scale, measurements are needed to disentangle these two scales in order to probe the medium at difference length scales to...
A consistent modelling of back reaction of the medium on the jet evolution is important for understanding the jet structure. Majority of existing models implement only one-way jet-medium interaction by coupling jets to a fixed hydrodynamic expansion and not including the energy deposition in the medium itself.
In this talk we show the first results of jet observables from a parton cascade...
The JETSCAPE Collaboration (Jet Energy-loss Tomography with a Statistically and Computationally Advanced Program Envelope) has developed and released an innovative, modular and flexible event generator to be used by the heavy-ion community. High-energy jet evolution through deconfined QCD matter is a multi-scale problem that involves different stages, whose physics should be addressed by...
Jets are known to be strongly modified when propagating through a hot and dense medium. Current LHC and RHIC results in heavy-ion systems show a strong suppression of the total jet yield, increase of dijet and boson-jet momentum imbalance and modification of the jet substructure. The description of the later is challenging for all event Monte Carlo event generators that describe jet...
