Background Fluctuations in Heavy Ion Jet Reconstruction

Reconstruction of Jet Properties in Pb-Pb Collisions with the ALICE-Experiment

The study of the hot and dense medium created in heavy-ion collisions via the effect of parton energy loss is one of the major goals of jet and high-\pt\ measurements in these reactions. In particular the modifications of the longitudinal and transverse jet structure. Here the subtraction of the underlying heavy-ion event, as well as a precise knowledge of the background induced fluctuations of the reconstructed jet energy is required. We extract the modification of the near- and away-side jet yield in heavy-ion collisions at the LHC and present a detailed assessment of background fluctuations…

Jet reconstruction and jet background classification with the ALICE experiment in PbPb collisions at the LHC

For a quantitative interpretation of reconstructed jet properties in heavy-ion collisions it is paramount to characterize the contribution from the underlying event and the influence of background fluctuations on the jet signal. In addition to the pure number fluctuations, region-to-region correlated background within one event can enhance or deplete locally the level of background and modify the jet energy. We show a first detailed assessment of background effects using different probes embedded into heavy-ion data and quantify their influence on the reconstructed jet spectrum.

Machine Learning based jet momentum reconstruction in Pb-Pb collisions measured with the ALICE detector

The precise reconstruction of jet transverse momenta in heavy-ion collisions is a challenging task. A major obstacle is the large number of uncorrelated (mainly) low-$p_\mathrm{T}$ particles overlaying the jets. Strong region-to-region fluctuations of this background complicate the jet measurement and lead to significant uncertainties. We developed a novel approach to correct jet momenta (or energies) for the underlying background in heavy-ion collisions. The approach allows the measurement of jets down to extremely low transverse momenta and for large resolution $R$ by making use of common Ma…

Data-driven analysis methods for the measurement of reconstructed jets in heavy ion collisions at RHIC and LHC

We present data-driven methods for the full reconstruction of jets in heavy ion collisions, for inclusive and co-incidence jet measurements at both RHIC and LHC. The complex structure of heavy ion events generates a large background of combinatorial jets, and smears the measured energy of the true hard jet signal. Techniques to correct for these background effects can induce biases in the reported jet distributions, which must be well controlled for accurate measurement of jet quenching. Using model studies, we evaluate the proposed methods for measuring jet distributions accurately while mini…

Experimental Status of Jets in Heavy-Ion Collisions

Jet quenching has been one of the most important indicators that ultra-relativistic heavy-ion collisions produce a deconfined state of quarks and gluons, known as the Quark-Gluon Plasma. While the quenching of jets traditionally refers to the energy loss of high-momentum partons, the study of jet quenching has grown into a multi-pronged field where the measurement of jets and their modification in heavy-ion collisions is used as an important tool to study many aspects of QCD deconfinement. This contribution reviews the current experimental status of jets at the LHC and RHIC, and reports recent…

Jets in heavy ion collisions with ATLAS

The energy loss of high-p_T partons provides insight into the transport properties of the medium created in relativistic heavy ion collisions. Evidence for this energy loss was first experimentally established through observation of high-p_T hadron suppression at RHIC. More recently, measurements of fully reconstructed jets have been performed at the LHC. In this summary the latest experimental results from the ATLAS collaboration on jet suppression are presented. In particular the jet suppression in inclusive jet yields, path length dependence of the jet suppression, photon-jet and Z^0-jet co…

Jet Reconstruction at RHIC

Full jet reconstruction in heavy-ion collisions is expected to provide more sensitive measurements of jet quenching in hot QCD matter at RHIC. In this paper we review recent studies of jets utilizing modern jet reconstruction algorithms and their corresponding background subtraction techniques.

Inclusive Distribution of Fully Reconstructed Jets in Heavy Ion Collisions at RHIC: Status Report

We present an update to the analysis of fully reconstructed jets in heavy ion collisions by the STAR Collaboration at RHIC. We analyse the response of the anti-$k_{T}$ algorithm in the presence of background, and present a new observable for the measurement of inclusive jet production that is expected to be more robust against background model assumptions than previous jet analyses at RHIC and LHC.

Jet reconstruction in hadronic collisions by Gaussian filtering

A new algorithm for jet finding in hadronic collisions is presented. The algorithm, based on a Gaussian filter in $(η,ϕ)$, is specifically intended for use in heavy ion collisions and/or for detectors with limited acceptance. The performance of the algorithm is compared to two conventional algorithms, a seedless cone algorithm and a $k_\perp$ algorithm, for Pythia simulated di-jet events in $\sqrt{s} = 200 \mathrm{GeV}$ $p + p$ collisions with $4 \mathrm{GeV}/c \le \sqrt{Q^2} \le 16 \mathrm{GeV}/c$. The Gaussian filter is found to perform as well as, and in some instances better than, the conv…

Fast embedding of jets in heavy-ion collisions for background studies with ALICE

Jet reconstruction in heavy-ion collisions is strongly affected by soft background from the underlying event. For an appropriate interpretation of the jet observables it is essential to understand the influence of the background and its fluctuations on the reconstructed jets. With this purpose we study random cones and the response of a known probe embedded in a heavy-ion events. The embedded probe can be a single high-p_T track or a jet from a simulated or real pp event. This allows a detailed study of background fluctuations and verification of the performance of background subtraction metho…

Jet substructure measurements in heavy-ion collisions with ALICE

Jet substructure, defined by observables constructed from the distribution of constituents within a jet, provides the versatility to tailor observables to specific regions of QCD radiation phase space. This flexibility provides exciting new opportunities to study jet quenching in heavy-ion collisions and to ultimately help reveal the nature of the quark-gluon plasma. The ALICE detector is particularly well-suited to jet substructure measurements in heavy-ion collisions due to its high-precision tracking system. In these proceedings, we report several new jet substructure measurements in Pb-Pb …

Latest CMS Heavy-Ion Results on Jets

Jet studies provide an experimental method to explore the features of energy loss in the strongly interacting quark-gluon plasma. Recent jet results from 2.76 TeV PbPb and pp collisions measured with the CMS detector are presented. Jets in the most head-on (central) PbPb collisions are quenched in comparison to pp, and the jets fragment in different ways in the two systems. Measurements from pPb collisions at 5.02 TeV show that the jet and charged particle suppression seen in central PbPb measurements are not due to initial state nuclear effects.

New results on the modification of jet structure in Heavy Ion collisions

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.

应用于重离子碰撞中喷注背景扣除的可解释机器学习方法

Interpretable Machine Learning Methods Applied to Jet Background Subtraction in Heavy Ion Collisions

针对重离子碰撞喷注测量受背景限制的问题，提出用符号回归提取背景扣除深度神经网络的函数表示，发现其等效于喷注粒子多重数方法，证明可解释机器学习可揭示物理过程。

重离子碰撞中基于多重数的喷注背景扣除方法

Multiplicity Based Background Subtraction for Jets in Heavy Ion Collisions

本文将基于喷注多重数的背景扣除方法扩展到广泛的分辨率参数范围，并用低复杂度浅层神经网络学习喷注多重数与背景波动的关系，证明了可解释方法的有效性。

Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV

The effect of event background fluctuations on charged particle jet reconstruction in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV has been measured with the ALICE experiment. The main sources of non-statistical fluctuations are characterized based purely on experimental data with an unbiased method, as well as by using single high $p_{\rm T}$ particles and simulated jets embedded into real Pb-Pb events and reconstructed with the anti-$k_{\rm T}$ jet finder. The influence of a low transverse momentum cut-off on particles used in the jet reconstruction is quantified by varying the minimum…

Jet Reconstruction with Particle Flow in Heavy-Ion Collisions with CMS

In the particle-flow approach information from all available sub-detector systems is combined to reconstruct all stable particles. The global event reconstruction has been shown to improve, in particular, the resolution of jet energy and missing transverse energy in pp collisions compared to purely calorimetric measurements. This improvement is achieved primarily by combining the precise momentum determination of charged hadrons in the silicon tracker with the associated energy depositions in the calorimeters. By resolving individual particles inside jets, particle flow reduces the sensitivity…

Full Jet Reconstruction in Heavy Ion Collisions

Full jet reconstruction has traditionally been thought to be difficult in heavy ion events due to large multiplicity backgrounds. The search for new physics in high luminosity p+p collisions at the LHC similarly requires the precise measurement of jets over large backgrounds caused by pile up; this has motivated the development of a new generation of jet reconstruction algorithms which are also applicable in the heavy ion environment. We review the latest results on jet-medium interactions as seen in A+A collisions at RHIC, focusing on the new techniques for full jet reconstruction.

Jet Measurements in Heavy-ion Collisions with CMS

The production of a strongly interacting medium in heavy-ion collisions is identified through suppression of high transverse momentum jets leading to an effect known as jet quenching. Detailed measurements of nuclear modification factors and energy flow of the aforementioned quenched jets are performed with the CMS detector. These new results extend previous measurements to large angles with respect to the quenched jets and increase reach in the transverse momentum range. High statistics pp, pPb and PbPb data taken in 2011-13 are used in the following analysis. A new data-driven method to esti…

Nuclear k_T in d+Au Collisions from Multiparticle Jet Reconstruction at STAR

This paper presents the most recent nuclear k_T measurements from STAR derived from multiparticle jet reconstruction of d+Au and p+p collisions at sqrt(s)=200 GeV. Since jets reconstructed from multiple particles are relatively free of fragmentation biases, nuclear k_T can be measured with greater certainty in this way than with traditional di-hadron correlations. Multi-particle jet reconstruction can also be used for a direct measurement of the fragmentation function.

Jet Reconstruction in Heavy Ion Collisions

Measurements of strong suppression of inclusive hadron distributions and di-hadron correlations at high $p_{T}$, while providing evidence for partonic energy loss, also suffer from geometric biases due to the competition of energy loss and fragmentation. The measurements of fully reconstructed jets is expected to lack these biases as the energy flow is measured independently of the fragmentation details. In this article, we review the recent results from the heavy ion collisions collected by the STAR experiment at RHIC on direct jet reconstruction utilizing the modern sequential recombination …

Jet reconstruction in heavy ion collisions (emphasis on Underlying Event background subtraction)

A modification of the internal structure of jets is expected due to the production of a dense QCD medium, the Quark Gluon Plasma, in heavy-ion collisions. We discuss some aspects of jet reconstruction in p+p and A+A collisions and emphasize the dramatically increased contribution of the underlying event in nucleus-nucleus collisions as compared with the vacuum case. We conclude with its consequences on the full jet spectrum and fragmentation function extraction at LHC.

Measurements of jet structure and fragmentation from full jet reconstruction in heavy ion collisions at RHIC

Measurements of inclusive hadron suppression and di-hadron azimuthal correlations have provided important insights into jet quenching in hot QCD matter. However, they do not provide access to the energy of the hard scattering and are limited in their sensitivity since they can be affected by biases toward hard fragmentation and small energy loss. Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss, but is challenging due to the high-multiplicity environment. We present measurements of fully reconstructed di-jets at mi…

Searching for Jets in Heavy Ion Collisions

Jet quenching measurements using leading particles and their correlations suffer from known biases, which can be removed via direct reconstruction of jets in central heavy ion collisions. In this talk, we discuss several modern jet reconstruction algorithms and background subtraction techniques that are appropriate to heavy ion collisions.

Heavy ion jet physics studies using precision jet substructure and quark-gluon jet classification

In the first talk I discuss the usefulness of jet grooming for testing jet quenching mechanisms, and I present a calculation of soft-drop jet mass distribution in proton-proton and heavy ion collisions. In the second talk I discuss the comprehensive studies of quark and gluon jet substructure as a way to search for qualitatively new jet modification signatures. I emphasize the importance of precise understanding of jet substructure as well as powerful analysis tools in future heavy ion jet physics studies, with direct applications to hard probes using heavy flavors and hadronically-decaying el…

Elucidating Jet Energy Loss in Heavy Ion Collisions

Very soon the LHC will provide beams for heavy ion collisions at 5.52 TeV/nucleon. This center-of-mass energy results in a large cross-section for producing high-$E_T$ ($>$ 50 GeV) jets that are distinct from the soft, underlying event. This brings with it the possibility of performing full jet reconstruction to directly study jet energy loss in the medium produced in heavy ion collisions. In this note, we present the current state of jet reconstruction performance studies in heavy ion events using the ATLAS detector. We also discuss the possibilities of energy loss measurements available with…

Jet Fragmentation Function Moments in Heavy Ion Collisions

The nature of a jet's fragmentation in heavy-ion collisions has the potential to cast light on the mechanism of jet quenching. However the presence of the huge underlying event complicates the reconstruction of the jet fragmentation function as a function of the momentum fraction z of hadrons in the jet. Here we propose the use of moments of the fragmentation function. These quantities appear to be as sensitive to quenching modifications as the fragmentation function directly in z. We show that they are amenable to background subtraction using the same jet-area based techniques proposed in the…

Full Jet Reconstruction in d+Au and p+p Collisions at RHIC

The STAR detector is well suited for investigating jet production at RHIC. It has a large acceptance for both charged particles and electromagnetic radiation, so that reconstructed jets contain a large fraction of the particles descending from an initial hard scattered parton. Inclusive jets can be used to measure $j_T$, which characterizes the transverse jet shape. Di-jet angular distributions in d+Au and p+p collisions at RHIC provide a determination of intrinsic and nuclear $k_{T}$. The most recent results from this analysis based on year 2003 d+Au and p+p data are presented and compared to…

RHIC和LHC实验中重离子碰撞的喷注淬火

Jet Quenching in Heavy-Ion Collisions at RHIC and the LHC experiments

本文综述了RHIC和LHC实验中重离子碰撞喷注淬火的最新结果，揭示喷注能量损失、共面性偏离及其味道和路径长度依赖性，为约束QGP性质和理论模型提供关键依据。

Jet Analysis in Heavy Ion Collisions in CMS

At the Relativistic Heavy Ion Collider, jets have been a useful tool to probe the properties of the hot, dense matter created. At the Large Hadron Collider, collisions of Pb+Pb at $\sqrt{s_{NN}}$ = 5.5 TeV will provide a large cross section of jets at high $E_T$ above the minimum bias heavy ion background. Simulations of the Compact Muon Solenoid (CMS) experiment's capability to measure jets in heavy ion collisions are presented. In particular, $γ$-jet measurements can estimate the amount of energy lost by a jet interacting strongly with the medium, since the tagged photon passes through unaff…

Jets in heavy ion collisions at RHIC

Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss in hot and dense QCD matter, but is challenging due to the high multiplicity environment. The STAR and PHENIX collaborations at RHIC have recently presented measurements of fully reconstructed jets from p+p, Cu+Cu and Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 200 \mathrm{GeV}$. We review the first results on inclusive jet spectra, di-jets and fragmentation functions and discuss their implications on understanding of jet quenching.

Jet-Underlying Event Separation Method for Heavy Ion Collisions at the Relativistic Heavy Ion Collider

Reconstructed jets in heavy ion collisions are a crucial tool for understanding the quark-gluon plasma. The separation of jets from the underlying event is necessary particularly in central heavy ion reactions in order to quantify medium modifications of the parton shower and the response of the surrounding medium itself. There have been many methods proposed and implemented for studying the underlying event substructure in proton-proton and heavy ion collisions. In this paper, we detail a method for understanding underlying event contributions in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV …

First fragmentation function measurements from full jet reconstruction in heavy-ion collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV by STAR

Measurements of inclusive hadron suppression and di-hadron azimuthal correlations in ultra-relativistic nuclear collisions at RHIC have provided important insights into jet quenching in hot QCD matter, but are limited in their sensitivity due to well-known biases. Full jet reconstruction in heavy-ion collisions would conceptually provide a direct measurement of the energy of the scattered parton before energy loss, alleviating such biases and allowing a measurement of the energy loss probability distribution in a model-independent way from hard probes. In these proceedings we utilize recent pr…

Tagged jets and jet reconstruction as a probe of QGP induced partonic energy loss

Recent experimental advances at the Relativistic Heavy Ion Collider (RHIC) and the large center-of-mass energies available to the heavy-ion program at the Large Hadron Collider (LHC) will enable strongly interacting matter at high temperatures and densities, that is, the quark-gluon plasma (QGP), to be probed in unprecedented ways. Among these exciting new probes are fully-reconstructed inclusive jets and the away-side hadron showers associated with a weakly or electromagnetically interacting boson, or, tagged jets. Full jet reconstruction provides an experimental window into the mechanisms of…

Full jet reconstruction in 200 GeV p+p, d+Au and Au+Au collisions by STAR

Measurements of inclusive hadron suppression and di-hadron azimuthal correlations have provided important insights into jet quenching in hot QCD matter. However, they do not provide access to the energy of the hard scattering and are limited in their sensitivity since they can be affected by biases toward hard fragmentation and small energy loss. Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss, but is challenging due to the high multiplicity environment. Study of jet production and properties in d+Au and p+p colli…

Jet-based measurements of Sivers and Collins asymmetries at the future Electron-Ion Collider

We present predictions and projections for hadron-in-jet measurements and electron-jet azimuthal correlations at the future Electron-Ion Collider (EIC). These observables directly probe the three-dimensional (3D) structure of hadrons, in particular, the quark transversity and Sivers parton distributions and the Collins fragmentation functions. We explore the feasibility of these experimental measurements by detector simulations and discuss detector requirements. We conclude that jet observables have the potential to enhance the 3D imaging EIC program.

重离子碰撞中喷注产生的因子化

Factorization for jet production in heavy-ion collisions

该研究将喷注建模为与QCD介质相互作用的开放量子系统，建立有效场论并推导含辐射子喷注函数与微扰匹配系数卷积的喷注产生因子化公式。

推进重离子碰撞中的喷注内部结构测量

Pushing forward jet substructure measurements in heavy-ion collisions

该工作通过解析和蒙特卡洛模拟，提出利用前向快度区喷注内部结构变窄效应作为颜色退相干动力学的明确实验信号，以克服选择偏差影响。

Factorization of jet cross sections in heavy-ion collisions

We propose a new phenomenological approach to establish QCD factorization of jet cross sections in the heavy-ion environment. Starting from a factorization formalism in proton-proton collisions, we introduce medium modified jet functions to capture the leading interaction of jets with the hot and dense QCD medium. A global analysis using a Monte Carlo sampling approach is performed in order to reliably determine the new jet functions from the nuclear modification factor of inclusive jets at the LHC. We find that gluon jets are significantly more suppressed due to the presence of the medium tha…

Jet studies with STAR at RHIC: jet algorithms, jet shapes, jets in AA

Hard scattered partons are predicted to be well calibrated probes of the hot and dense medium produced in heavy ion collisions. Interactions of these partons with the medium w ill result in modifications of internal jet structure in Au+Au events compared to that observed in the p+p/d+Au reference. Full jet reconstruction is a promising tool to measu re these effects without the significant biases present in measurements with high-$\pT$ hadrons. One of the most significant challenges for jet reconstruction in the heavy ion environment comes from the correct characterization of the background fl…

Jets as precision probes in electron-nucleus collisions at the Electron-Ion Collider

We discuss the prospects of using jets as precision probes in electron-nucleus collisions at the future Electron-Ion Collider. Jets produced in deep-inelastic scattering can be calibrated by a measurement of the scattered electron. Such electron-jet "tag and probe" measurements call for an approach that is orthogonal to most HERA jet measurements as well as previous studies of jets at the future EIC. We present observables such as the electron-jet momentum balance, azimuthal correlations and jet substructure, which can provide constraints on the parton transport coefficient in nuclei. We compa…

Supersonic Jets in Relativistic Heavy-Ion Collisions

Mach-cone shock waves were proposed to explain the broad and perhaps double-peaked away-side 2-particle jet-correlations at RHIC; however, other mechanisms cannot be ruled out. Three-particle jet-correlation is needed in order to distinguish various physics mechanisms. In this talk the 3-particle jet-correlation measurements are presented and their implications are discussed.

Methodology for the study of modified jet-like topologies in heavy ion collisions via three particle correlation functions

Methodology is presented for analysis of three-particle correlation functions obtained in heavy ion collisions at ultra-relativistic energies. We show that harmonic correlations can be removed and jet driven correlations reliably extracted. Results from detailed Monte Carlo simulations are used to demonstrate the efficacy of this technique for the study of modifications to away-side jet topologies. Such modifications are an essential probe of the properties of the quark gluon plasma produced in heavy ion collisions.

Identifying groomed jet splittings in heavy-ion collisions

Measurements of jet substructure in heavy-ion collisions may provide key insight to the nature of jet quenching in the quark-gluon plasma. Jet grooming techniques from high-energy physics have been applied to heavy-ion collisions in order to isolate theoretically controlled jet observables and explore possible modification to the hard substructure of jets. However, the grooming algorithms used have not been tailored to the unique considerations of heavy-ion collisions, in particular to the experimental challenge of reconstructing jets in the presence of a large underlying event. We report a se…

Spin asymmetries in electron-jet production at the future electron ion collider

We study all the possible spin asymmetries that can arise in back-to-back electron-jet production, $ep\rightarrow e+\text{jet}+X$, as well as the associated jet fragmentation process, $ep\rightarrow e+ \text{jet} (h)+X$, in electron-proton collisions. We derive the factorization formalism for these spin asymmetries and perform the corresponding phenomenology for the kinematics relevant to the future electron ion collider. In the case of unpolarized electron-proton scattering, we also give predictions for azimuthal asymmetries for the HERA experiment. This demonstrates that electron-jet product…

First Direct Measurement of Jets in $\sqrt{s_{NN}}=200$ GeV Heavy Ion Collisions by STAR

We present the first measurement of reconstructed jets in ultra-relativistic heavy ion collisions. Utilizing the large coverage of the STAR Time Projection Chamber and Electromagnetic Calorimeter, we apply several modern jet reconstruction algorithms and background subtraction techniques and explore their systematic uncertainties in heavy ion events. The differential spectrum for inclusive jet production in central Au+Au collisions at $\sqrt {s_{NN}}= 200$ GeV is presented. In order to assess the jet reconstruction biases, this spectrum is compared with the jet cross section measured in $\sqrt…

Jet Modification in Heavy Ion Collisions at RHIC

These proceedings present a brief overview of the main results on jet-modifications in heavy ion collisions at RHIC. In heavy ion collisions, jets are studied using single hadron spectra and di-hadron correlations with a high-\pt{} trigger hadrons. At high pt, a suppression of the yields due to parton energy loss is observed. A quantitative confrontation of the data with various theoretical approaches to energy loss in a dense QCD medium is being pursued. First results from $γ$-jet events, where the photon balances the initial jet energy, are also presented and compared to expectations from mo…

Machine Learning based jet momentum reconstruction in heavy-ion collisions

The precise reconstruction of jet transverse momenta in heavy-ion collisions is a challenging task. A major obstacle is the large number of (mainly) low-$p_{\rm T}$ particles overlaying the jets. Strong region-to-region fluctuations of this background complicate the jet measurement and lead to significant uncertainties. In this paper, a novel approach to correct jet momenta (or energies) for the underlying background in heavy-ion collisions is introduced. The proposed method makes use of common Machine Learning techniques to estimate the jet transverse momentum based on several parameters, inc…

Measurement of the Shared Momentum Fraction $z_g$ using Jet Reconstruction in p+p and Au+Au Collisions with STAR

One key difference in current energy loss models lies in the treatment of the Altarelli-Parisi, AP, splitting functions. It has been shown that the shared momentum fraction, henceforth called Jet Splitting Function $z_g$ as determined by the SoftDrop grooming process can be made a Sudakov-safe measurement of the symmetrized AP functions in p+p collisions. The STAR collaboration presents the first z_g measurements at $\sqrt{s_{NN}}=200$ GeV in p+p and Au+Au collisions, where in Au+Au we use the specific di-jet selection introduced in our previous momentum imbalance measurement. For a jet resolu…

Measurement of the Shared Momentum Fraction $z_g$ using Jet Reconstruction in p+p and Au+Au Collisions with STAR

One key difference in current energy loss models lies in the treatment of the Altarelli-Parisi, AP, splitting functions. It has been shown that the shared momentum fraction, henceforth called Jet Splitting Function $z_g$ as determined by the SoftDrop grooming process can be made a Sudakov-safe measurement of the symmetrized AP functions in p+p collisions. The STAR collaboration presents the first $z_g$ measurements at $\sqrt{s_{NN}}=200$ GeV in p+p and Au+Au collisions, where in Au+Au we use the specific di-jet selection introduced in our previous momentum imbalance measurement. For a jet reso…

Background subtraction and jet quenching on jet reconstruction

In order to assess the ability of jet observables to constrain the characteristics of the medium produced in heavy-ion collisions at the LHC, we investigate the influence of background subtraction and jet quenching on jet reconstruction, with focus on the dijet asymmetry as currently studied by ATLAS and CMS. Using a toy model, we examine the influence of different background subtraction methods on dijet momentum imbalance and azimuthal distributions. We compare the usual jet-area based background subtraction technique and a variant of the noise-pedestal subtraction method used by CMS. The pur…

Physics with the ALICE Electromagnetic Calorimeter

I will present physics measurements which are achievable in the ALICE experiment at the LHC through the inclusion of a new electromagnetic calorimeter. I will focus on jet measurements in proton proton and heavy ion collisions. Detailed simulations have been performed on jet reconstruction, jet triggering, heavy flavor jet reconstruction through electron identification, gamma-jet reconstruction and the measurements of identified hadrons and resonances in jets. I will show the physics capabilities which are made possible through the combination of calorimeter information with the other detector…

重离子碰撞中的喷注子结构测量

Jet substructure measurements in heavy-ion collisions

本文介绍了LHC的ATLAS、ALICE、CMS实验近期的重离子碰撞喷注子结构测量结果，涵盖软滴修整喷注半径等多项测量内容。

Identification and Rejection of Fake Reconstructed Jets From a Fluctuating Heavy Ion Background in ATLAS

Full jet reconstruction in relativistic heavy ion collisions provides new and unique insights to the physics of parton energy loss. Because of the large underlying event multiplicity in $A+A$ collisions, random and correlated fluctuations in the background can result in the reconstruction of fake jets. These fake jets must be identified and rejected to obtain the purest jet sample possible. A large but reducible fake rate of jets reconstructed using an iterative cone algorithm on HIJING events is observed. The absolute rate of fake jets exceeds the binary-scaled p+p jet rate below 50 GeV and i…