In high energy particle collisions the shape of the event, i.e. the relative distribution of particles in momentum space, is often used to try to select events with certain topologies. It is claimed that an event shape observable like transverse sphericity is able to discriminate between jet-like events and events that are dominated by soft production from the underlying event.
In this paper we investigate the relationship between the shape of the event and the number of jets found in the respective event for both $e^{+}e^{-}$ and pp collisions using the PYTHIA model. In $e^{+}e^{-}$ collisions, we find that the transverse sphericity of the event can be used effectively to either enhance or suppress the fraction of jets found in the selected sample, and can even discriminate between single, two, and multi-jet topologies. However, contrary to current literature, we find that in pp collisions this does not hold. It is shown that the transverse sphericity as well as the particle multiplicity is sensitive to the number of multi-parton interactions.
The ALICE collaboration recently reported high-statistics $\bf p_t$ spectra from 5 TeV and 13 TeV p-p collisions with intent to determine the role of jets in high-multiplicity collisions. In the present study a two-component (soft + hard) model (TCM) of hadron production in p-p collisions is applied to ALICE $\bf p_t$ spectra. As in previous TCM studies of A-B collision systems jet and nonjet contributions to $\bf p_t$ spectra are accurately separated over the entire $\bf p_t$ acceptance. The statistical significance of data-model differences is established leading to insights concerning selec…
We present predictions for the inclusive production of charm jets in proton-proton collisions at 2.76 and 5.02 TeV. The charm-quark is considered massless. In this scheme we find that the ratio of the next-to-leading order to the leading order cross section (K factor) is almost equal to one depending essentially on the choice of the renormalization and factorization scale. Adding non-pertubative corrections obtained from Pythia Monte Carlo calculations lead to reasonable agreement with experimental c-jet cross sections obtained by the CMS collaboration.
We present predictions for the inclusive production of bottom jets in proton-antiproton collisions at 1.96 TeV and proton-proton collisions at 7 TeV. The bottom quark is considered massless. In this scheme, we find that at small transverse momentum (p_T) the ratio of the next-to-leading order to the leading-order cross section (K factor) is smaller than one. It increases with increasing p_T and approaches one at larger p_T at a value depending essentially on the choice of the renormalization scale. Adding non-perturbative corrections obtained from PYTHIA Monte Carlo calculations leads to reaso…
Cross section predictions of W and Z bosons in association with jets (up to 6 jets, $W\to\ell^{\pm}ν$ and $Z\to\ell^{\pm}$ where $\ell^{\pm}$=$e^{\pm}$ or $μ^{\pm}$) in proton-proton collisions at $\sqrt{s}$=14 TeV is performed using Alpgen MC generator with CTEQ6L1 leading order parton distribution function. In addition, W and Z boson cross sections are obtained up to next to next to leading order (NNLO) QCD corrections using MCFM MC generator. To validate the predictions, a detailed comparison of NNLO QCD calculations with 8 TeV CMS results for total cross section is performed and a fiducial…
Study on the Energy Dependence of the Radii of Jets by the HBT Correlation Method in e+e- collisions
用HBT关联方法，利用蒙特卡罗模拟发生器Jetset7.4，在$\sqrt s =30$、50、70、91.2、110、130、150和170 GeV产生了40，000，000个$^+$-$^-$碰撞事例，详细研究了喷注半径大小与能量的关系.喷注半径的测量使用HBT关联方法与相同的末态π介子的不可分辨性。发现夸克喷注和胶子喷注的平均半径与c. m无关。e $^+$ e $^-$碰撞的能量。夸克喷注的平均半径明显大于胶子喷注。在部分子演化结束时，得到了e $^+$ e $^-$碰撞中夸克喷注和胶子喷注的平均半径不变的结果。
The discriminators of quark-gluon jets developed for $pp$ collisions at the LHC can be used to measure the gluon jet fraction in a jet sample. It allows to measure various characteristics of the quark and gluon jets. The methodology of such measurements for modern hadron colliders is discussed.
Hard probes created through large momentum transfers are used to study the properties of QCD matter created in heavy-ion collisions, by comparing the measurements to those in p+p collisions. Jets, and the "quenching" or suppression of jets in the medium created in heavy-ion collisions, are studied through various different observables. We present the most recent measurements from $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions, with p+p collisions as the reference, by the STAR Collaboration. The observables are semi-inclusive charged jets and di-jet transverse momentum imbalance. Additionally, corr…
In this paper, we investigate the medium modifications of $p_{T}$ dispersion($p_{T}D$) of inclusive jets with small radius ($R=0.2$) in Pb+Pb collisions at $\sqrt{s}=2.76$~TeV. The partonic spectrum in the initial hard scattering of elementary collisions are obtained by an event generator POWHEG+PYTHIA, which matches the next-to-leading (NLO) matrix elements with parton showering, and energy loss of fast parton traversing in hot/dense QCD medium is calculated by Monte Carlo simulation within Higher-Twist formalism of jet quenching in heavy-ion collisions. We present the model calculations of n…
We carry out a detailed calculations of W+jets production in Pb+Pb collisions at the Large Hadron Collider (LHC). In our calculations, the production of W+jet in p+p reference is obtained from Sherpa, which matches next-to-leading-order matrix elements to the resummation of parton shower calculations. Jet propagation and medium response in the quark-gluon plasma is simulated with the Linear Boltzmann Transport (LBT) model. We calculate five observables of W+jets productions with jet quenching effect in Pb+Pb collisions: event distribution as a function of the vector sum of the lepton and jets …
We report the first measurement of fully corrected semi-inclusive charged recoil jets for both direct-photon ($γ_{dir}$) and $π^{0}$ triggers, within two trigger transverse energy ranges between 9 GeV and 15 GeV, in central Au+Au collisions at $\sqrt {s_{\rm NN}}$ = 200 GeV using data with an integrated luminosity of 13 $\rm nb^{-1}$ collected by the STAR experiment. A comparison between $π^{0}$-triggered recoil jets in p+p collisions and PYTHIA is discussed. A comparison is also presented between the suppression of $γ_{dir}$- and $π^{0}$-triggered recoil jets in central Au+Au collisions with …
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…
We carry out the first detailed calculations of jet production associated with $W$ gauge bosons in Pb+Pb collisions at the Large Hadron Collider (LHC). In our calculations, the production of $W$+jet in p+p collisions as a reference is obtained by Sherpa, which performs next-to-leading-order matrix element calculations matched to the resummation of parton shower simulations, while jet propagation and medium response in the quark-gluon plasma are simulated with the Linear Boltzmann Transport (LBT) model. We provide numerical predictions on seven observables of $W$+jet production with jet quenchi…
In this paper we investigate the medium modifications of girth distributions for inclusive jets and $Z^0$ tagged jets with small radius ($R=0.2$) in Pb+Pb collisions with $\sqrt{s}=2.76$ TeV at the LHC. The partonic spectrum in the initial hard scattering of elementary collisions are obtained by a event generator POWHEG+PYTHIA, which matches the next-to-leading (NLO) matrix elements with parton showering, and energy loss of faster parton traversing in hot/dense QCD medium is calculated by Monte Carlo simulation within Higher-Twist formalism of jet quenching in heavy-ion collisions. We present …
Collectivity, as interpreted to mean flow of a dense medium in high-energy A-A collisions described by hydrodynamics, has been attributed to smaller collision systems -- p-A and even p-p collisions -- based on recent analysis of LHC data. However, alternative methods reveal that some data features attributed to flows are actually manifestations of minimum-bias (MB) jets. In this presentation I review the differential structure of single-particle $p_t$ spectra from SPS to LHC energies in the context of a two-component (soft + hard) model (TCM) of hadron production. I relate the spectrum hard co…
In this work we show that the proper analysis and interpretation of the experimental data on the multiplicity distributions of charged particles produced in jets measured in the ATLAS experiment at the LHC indicates their sub-Poissonian nature. We also show how, by using the recurrent relations and combinants of these distributions, one can obtain new information contained in them and otherwise unavailable, which may broaden our knowledge of the particle production mechanism.
Di-jet observables are excellent probes to study the effect of jets in dense systems. Interacting Lund strings will affect jet observables and suggests a new common mechanism responsible for jet modification in p-A and A-A. In this proceeding, we present our new implementation of the string shoving mechanism in PYTHIA8 which lets us study the effects on jet observables in p-p and nuclear collisions. We also present preliminary results showing the effects in hadron-jet correlation studies.
We study nuclear modification of the photon-tagged jets in $AA$ collisions within the jet quenching scheme based on the light-cone path integral approach to the induced gluon emission. The calculations are performed for running coupling. Collisional energy loss is treated as a perturbation to the radiative mechanism. We obtain a reasonable agreement with the recent data from the STAR Collaboration on the mid-rapidity nuclear modification factor $I_{AA}$ for Au+Au collisions at $\sqrt{s}=200$ GeV for parametrization of running $α_s$ consistent with that necessary for description of the data on …
Reconstructed jets initiated from heavy quarks provide a powerful tool to probe the properties of the quark-gluon plasma (QGP) and to explore the mass hierarchy of jet quenching. In this article, we review the recent theoretical progresses on heavy-flavour jets in high-energy nuclear collisions at the RHIC and LHC. We focus on the yields and substructures of charm and bottom quark jets with jet quenching effect, such as the nuclear modification factors, transverse momentum imbalance, angular correlation, radial profiles, fragmentation functions, the "dead-cone" effect, etc.
我们提出了一个模型来描述强子-强子碰撞中的衍射事件，其中一个快度间隙被两个喷流包围。在t通道中交换的硬色单重态对象和快度间隙由pQCD Balitsky-Fadin-Kuraev-Lipatov Pomeron描述，包括由于下一个领先的修正。我们允许快度间隙小于喷流间的快度间隔，并使用HERWIG Monte Carlo模拟了相应的软辐射。我们的模型是能够重现所有的Tevatron数据，并允许估计在大型强子对撞机的喷流-间隙-喷流截面。
Unveiling the jet angular broadening with photon-tagged jets in high-energy nuclear collisions
College of Science, China Three Gorges University（三峡大学理学院）；Center for Astronomy and Space Sciences and Institute of Modern Physics, China Three Gorges University（三峡大学天文与空间科学中心暨现代物理研究所）
