Full Jet Research Articles

Jet modification in the next decade: A pedestrian outlook

In this review, we recount the current status of the theory of jet modification in dense matter. We commence with an outline of the ‘traditional’ observables which may be calculated without recourse to event generators. These include single- and double-hadron suppression, nuclear modification factor vs. reaction plane etc. All these measurements are used to justify both the required underlying physical picture of jet modification as well as the final obtained values of jet transport coefficients. This is followed by a review of the more modern observables which have arisen with the ability to reconstruct full jets, and the challenges faced therein. This is followed by a preview of upcoming theoretical developments in the field and an outlook on how the interface between these developments, phenomenological improvements, and upcoming data will allow us to quantitatively determine properties of the medium which effect the modification of hard jets.

Visual characterization of heated water spray jet breakup induced by full cone spray nozzles

The present work with specific objectives places a greater emphasis on measurements of the breakup lengths and phenomenological analysis of a hot water jet under reduced pumping pressures in still environment. Therefore, visual and comparative studies are conducted on full cone jet disintegration of heated water for low pumping pressures. A further analysis of the grabbed images confirms the strong influence of the input processing parameters on full cone spray patternation. It is also predicted that the heated liquids generate a dispersed spray pattern by utilizing partial evaporation of the spraying medium. The radial spray cone width and angle do not vary significantly with increasing Reynolds and Weber numbers at early injection phases, leading to enhanced macroscopic spray propagation. The discharge coefficient, mean flow rate, and mean flow velocity are significantly influenced by the load pressure, but less affected by the temperature. The fine scale image analysis also predicts toroidal-shaped vortex formation in the spray structure near the water boiling point.

Properties of Full Jet in High-Energy Heavy-Ion Collisions from Parton Scatterings

The properties of fully reconstructed jet are investigated in p + p and Pb + Pb collisions atsNN= 2.76 TeV within a multiphase transport (AMPT) model with both partonic scatterings and hadronic rescatterings. A large transverse momentum (pT) asymmetry of dijet or photon-jet arises from the strong interactions between jet and partonic matter. Theξ-dependent jet fragmentation function in Pb + Pb collisions is decomposed into two contributions from different jet hadronization mechanisms, that is, fragmentation versus coalescence. The medium modification of differential jet shape displays that the jet energy is redistributed towards a larger radius owing to jet-medium interactions in heavy-ion collisions. Jet triangular azimuthal anisotropy coefficient,v3jet, which shows a smaller magnitude than the elliptic coefficientv2jet, decreases more quickly with increasing jetpT, which can be attributed to a path-length effect of jet energy loss. All of these properties of full jet are consistent with the jet energy loss mechanism in a stronglyinteracting partonic matter in high-energy heavy-ion collisions.

Theory of jet quenching in ultra-relativistic nuclear collisions

We present a short overview of recent progress in the theory of jet quenching in ultra-relativistic nuclear collisions, including phenomenological studies of jet quenching at RHIC and the LHC, development in NLO perburbative QCD calculation of jet broadening and energy loss, full jet evolution and modification, medium response to jet transport, and lattice QCD and AdS/CFT studies of jet quenching.

The tricky azimuthal dependence of jet quenching at RHIC and LHC via CUJET2.0

High transverse momentum neutral pion and charged hadron suppression pattern with respect to reaction plane at RHIC and LHC energies in central and semi-peripheral AA collisions are studied in a perturbative QCD based model, CUJET2.0. CUJET2.0 has dynamical DGLV radiation kernel and Thoma-Gyulassy elastic energy loss, with both being generalized to including multi-scale running strong coupling as well as energy loss probability fluctuations, and the full jet path integration is performed in a low $p_T$ flow data constrained medium which has 2+1D viscous hydrodynamical expanding profile. We find that in CUJET2.0, with only one control parameter, $\alpha_{max}$, the maximum coupling strength, fixed to be 0.26, the computed nuclear modification factor $R_{AA}$ in central and semi-peripheral AA collisions are consistent with RHIC and LHC data at average $\chi^2/d.o.f.<1.5$ level. Simultaneous agreements with high $p_T$ azimuthal anisotropy $v_2$ data are acquired given average $\alpha_{max}$ over in-plane and out-of-plane paths varying as little as 10\%, suggesting a non-trivial dependence of the high $p_T$ single particle $v_2$ on the azimuthally varied strong coupling.

Improvement in secondary cooling of continuous casting of round billets through analysis of heat flux distribution

A mathematical model of heat transfer and solidification for a continuous casting of round billets was developed. The water flux density of the secondary cooling zone was experimentally measured, using an apparatus in industrial scale with two types of nozzles, flat jet and full cone jet. The profiles of water distribution were applied on the mathematical model. The results showed that the water distribution is not uniform in both longitudinal and angular directions owing to the unevenness of the spray and to the curvature effect of the round billet. This non-uniformity causes important variation of the heat transfer coefficients and superficial temperature of the billet, especially in the first cooling zones, where the temperature is higher. The mathematical model was used to simulate a change of nozzle type in the first cooling zone. The results showed that the heat flux and superficial temperature variations were reduced with a full cone jet nozzle in comparison with the flat jet nozzles.

NON-UNIFORM WATER FLUX DENSITY APPROACH APPLIED ON A MATHEMATICAL MODEL OF HEAT TRANSFER AND SOLIDIFICATION FOR A CONTINUOUS CASTING OF ROUND BILLETS

In the present work, the water flux densities of nozzles with flat jet and full cone jet were experimentally measured using an apparatus in industrial scale that reproduces the secondary cooling of the continuous casting of round billets of Vallourec Tubos do Brasil. A mathematical model for heat transfer and solidification for the continuous casting of round billets was developed applying the experimental water flux density profile, establishing a non-uniform water distribution approach. The mathematical model was validated by experimental measurements of the billet superficial temperature, performed at the industrial plant. The results of the mathematical model using both uniform and non-uniform water flux density approaches were compared. The non-uniform water distribution approach enabled to identify important variations of the heat transfer coefficients and the billet temperatures, especially in the first cooling zone, and to assess more accurately the local effects of the water distribution on the thermal behavior of the strand. The non-uniform water flux density approach applied to the mathematical model was a useful and more accurate tool to improve the comprehension of the thermal behavior of the steel along the secondary cooling

Full Jet Reconstruction in 2.76 TeV pp and Pb-Pb collisions in the ALICE experiment

Measurements of the suppression of high-pT particles and the away-side jets from heavy-ion collisions at RHIC have shown that medium-induced energy loss affects partons produced in the early stage of a heavy-ion collision. At LHC energies the initial production cross-section is much higher, which allows jets to be reconstructed with a wide kinematic range. Measuring fully reconstructed jets by taking advantage of the ALICE Electromagnetic Calorimeter allows for a more differential investigation of the parton energy loss. Parton energy loss will allow us to access key observables of the hot, dense matter created in heavy ion collisions. The data presented was collected during the 2.76 TeV Pb-Pb runs, as well as baseline measurements from the 2.76 TeV pp run. The procedures used to reconstruct jets and extract them from a fluctuating background will be discussed. The procedure for quantifying the background with a limited acceptance will also be discussed. These results are compared to pp measurements and simulations.

Measurement of jet pT spectra in Pb–Pb collisions at = 2.76 TeV with the ALICE detector at the LHC

Reconstruction of jets in high-energy heavy-ion collisions is challenging due to the large and fluctuating background coming from the underlying event. We report results on full jet reconstruction, obtained from data collected in 2011 by the ALICE detector at LHC for Pb-Pb collisions at = 2.76 TeV. The analysis makes use of the tracking system and the electromagnetic calorimeter. Signal jets, which come from hard scattered partons, are reconstructed using the anti-kT jet finder algorithm. The average background is subtracted on a jet-by-jet basis to reduce the contribution to the jet reconstructed energy coming from the underlying event. The jet spectrum is corrected to account for fluctuations in the background momentum density and detector effects through unfolding.

The Physics of sPHENIX

Jet related observables have been some of the most powerful and exciting probes for understanding the matter produced in ultra-relativistic heavy ion collisions. Full jet reconstruction was begun at RHIC, and the LHC experiments have shown the power and kinematic reach of these observables. Here we discuss the sPHENIX detector and physics program which aims to bring full calorimetric based jet reconstruction to RHIC in order to explore the temperature dependence of the strongly interacting Quark Gluon Plasma.

Recent results on jet physics from ALICE at the LHC

An overview of recent results on jet physics from the ALICE collaboration is presented. We mainly discuss azimuthal correlations and nuclear modification factors for both hadrons and jets. The very low pT tracking (> 150 MeV/c) capabilities of the ALICE detector associated to its electromagnetic calorimetry, allow to reconstruct both charged jets and full jets, with minimum bias on the jet fragmentation. A detailed measurement of the underlying event fluctuations will be discussed, as well as, jet spectra measurements, in pp and Pb-Pb collisions, using low constituent pT cuts and hadron-recoil jet correlations, which give a controlled way to subtract the combinatorial background.

Results on Jet Spectra and Structure from ALICE

Full jet reconstruction in ALICE uses the combined information from charged and neutral particles. Essentially all jet constituents can be measured with large efficiency down to very low transverse momenta (pT > 150 MeV/c). This has the advantage to introduce a minimum bias on the jet fragmentation, in particular for low jet momenta and in the presence of quenching. In this article, we present preliminary results from reconstruction of charged jets in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. The inclusive charged jet spectrum, the jet nuclear modification factors (R_AA, R_CP), the ratio of spectra measured with different resolution parameters and hadron-jet correlations are discussed. For pp data at the same center of mass energy, the inclusive spectrum of fully reconstructed jets and its resolution parameter dependence are reported.

Calculating jetvnand the event plane in the presence of a jet

Advances in measurements of jets and collective phenomena in ultrarelativistic heavy ion collisions have led to further understanding of the properties of the medium created in such collisions. Measurements of the correlations between the axes of reconstructed jets and the reaction plane or second-order participant plane of the bulk medium (defined as jet ${v}_{2}$), as well as the higher-order participant planes (jet ${v}_{n}$), provide information on medium-induced parton energy loss. Additionally, knowledge of jet ${v}_{n}$ as well as the ability to reconstruct the event plane in the presence of a jet are necessary in analyses of jet-triggered particle correlations, which are used to study medium-induced jet shape modification. However, the presence of a jet can bias the event plane calculation, leading to an overestimation of jet ${v}_{2}$. This paper proposes a method for calculating jet ${v}_{2}$ (and by extension, the higher jet ${v}_{n}$ harmonics) and the event plane in an unbiased way, using knowledge of the azimuthal angle of the jet axis from full jet reconstruction.

Calculating the charge of a jet

Jet charge has played an important role in experimentally testing the Parton Model and the Standard Model, and has many potential LHC applications. The energy-weighted charge of a jet is not an infrared-safe quantity, so hadronization must be taken into account. Here we develop the formalism to calculate it, cleanly separating the nonperturbative from the perturbative physics, which we compute at one-loop order. We first study the average and width of the jet charge distribution, for which the nonperturbative input is related to (dihadron) fragmentation functions. In an alternative and novel approach, we consider the full nonperturbative jet charge distribution and calculate its evolution and jet algorithm corrections, which has a natural Monte Carlo-style implementation. Our numerical results are compared to Pythia and agree well in almost all cases. This calculation can directly be extended to similar track-based observables, such as the total track momentum generated by an energetic parton.

Composite octet searches with jet substructure

Abstract Many new physics models with strongly interacting sectors predict a mass hierarchy between the lightest vector meson and the lightest pseudoscalar mesons. We examine the power of jet substructure tools to extend the 7 TeV LHC sensitivity to these new states for the case of QCD octet mesons, considering both two gluon and two b-jet decay modes for the pseudoscalar mesons. We develop both a simple dijet search using only the jet mass and a more sophisticated jet substructure analysis, both of which can discover the composite octets in a dijet-like signature. The reach depends on the mass hierarchy between the vector and pseudoscalar mesons. We find that for the pseudoscalar-to-vector meson mass ratio below approximately 0.2 a simple dijet analysis with only the jet mass variable provides the best discovery limit; for a ratio between 0.2 and the QCD-like value of 0.3, the full jet substructure analysis has the best discovery potential; for a ratio above approximately 0.3, the standard four-jet analysis is more suitable.

High-$\pt$ processes measured with ALICE at the LHC

From studies of single-particle spectra, particle correlations, and jet production in heavy-ion collisions we can obtain information about the density and the dynamic properties of the Quark-Gluon Plasma (QGP). The observed suppression of high-pT particle production (RAA) and away-side jets (IAA) is generally attributed to energy loss of partons as they propagate through the plasma. We present the results obtained from the analysis of Pb-Pb collisions at sqrt (sNN) = 2.76 TeV recorded by ALICE in November 2010. The nuclear modification factors RAA and IAA, and the status of full jet reconstruction in Pb-Pb is presented. Comparison with the RHIC measurements at lower collision energy and with theory models is shown.

Hard dihadron correlations in heavy-ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and CERN Large Hadron Collider

High transverse momentum (${P}_{T}$) processes are considered to be an important tool to probe and understand the medium produced in ultrarelativistic heavy-ion collisions via the interaction of hard, perturbatively produced partons with the medium. In this context, triggered hard dihadron correlations constitute a class of observables set between hard single inclusive hadrons (dominated by the leading jet fragments) and fully reconstructed jets; while they probe some features of the perturbative QCD evolution of a parton shower in the medium, they do not suffer from the problem of finding a suitable separation between soft hadrons coming from perturbative jets and soft hadrons coming from the nonperturbative medium as the identification of full jets does. On the other hand, the trigger requirement introduces nontrivial complications to the process, which makes the medium modification of the correlation pattern difficult and nonintuitive to understand. In this work, we review the basic physics underlying triggered dihadron correlations and make a systematic comparison of several combinations of medium evolution and parton-medium interaction models with the available data from 200-AGeV Au-Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). We also discuss the expected results for 2.76-ATeV Pb-Pb collisions at the CERN Large Hadron Collider (LHC).

Measurement of jets and jet suppression in TeV lead–lead collisions with the ATLAS detector at the LHC

The first results of single jet observables in Pb+Pb collisions at TeV measured with the ATLAS detector at the LHC are presented. Full jets are reconstructed with the anti-kt algorithm with R = 0.2 and 0.4, using an event-by-event subtraction procedure to correct for the effects of the underlying event including elliptic flow. The geometrically-scaled ratio of jet yields in central and peripheral events, RCP, indicates a clear suppression of jets with ET > 100 GeV. The transverse and longitudinal distributions of jet fragments are also presented. We find little or no substantial change to the fragmentation properties and no significant change in the level of suppression when moving to the larger jet definition.

Jet–hadron correlations in STAR

Advancements in full jet reconstruction have made it possible to use jets as triggers in azimuthal angular correlations to study the modification of hard-scattered partons in the medium created in ultrarelativistic heavy-ion collisions. This increases the range of parton energies accessible in these analyses and improves the signal-to-background ratio compared to dihadron correlations. Results of a systematic study of jet–hadron correlations in central Au–Au collisions at GeV are indicative of a broadening and softening of jets which interact with the medium. Furthermore, jet–hadron correlations suggest that the suppression of the associated hadron yield at high-pT is balanced in large part by low-pT enhancement.

High-pT particle correlations in pp collisions at LHC/ALICE**Supported by NSFC (10875051, 11020101060), the Program of Introducing Talents of Discipline to Universities of China (QLPL200909, B08033 and CCNU09C01002).

Two-particle correlation triggered by high-pT particles allows us to study hard scattering phenomena when full jet reconstruction is challenging. An analysis of the first ALICE pp data where charged and neutral particles isolated or not are used as trigger particles is presented. The two-particle correlation between the trigger (t) and the associate (a) particles is studied as a function of the imbalance parameter and interpreted in terms of the jet fragmentation function.