Novel Tools and Observables for Jet Physics in Heavy-Ion Collisions
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Jet Quenching in Quark Gluon Plasma: flavor Tomography at RHIC and LHC by the CUJET Model
Jet quenching in Quark Gluon Plasma: flavor tomography at RHIC and LHC by the CUJET model Alessandro Buzzatti Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences Columbia University 2013 c 2013 Alessandro Buzzatti All Rights Reserved Abstract Jet quenching in Quark Gluon Plasma: flavor tomography at RHIC and LHC by the CUJET model Alessandro Buzzatti A new jet tomographic model and numerical code, CUJET, is developed in this thesis and applied to the phenomenological study of the Quark Gluon Plasma produced in Heavy Ion Collisions. Contents List of Figures iv Acknowledgments xxvii Dedication xxviii Outline 1 1 Introduction 4 1.1 Quantum ChromoDynamics . .4 1.1.1 History . .4 1.1.2 Asymptotic freedom and confinement . .7 1.1.3 Screening mass . 10 1.1.4 Bag model . 12 1.1.5 Chiral symmetry breaking . 15 1.1.6 Lattice QCD . 19 1.1.7 Phase diagram . 28 1.2 Quark Gluon Plasma . 30 i 1.2.1 Initial conditions . 32 1.2.2 Thermalized plasma . 36 1.2.3 Finite temperature QFT . 38 1.2.4 Hydrodynamics and collective flow . 45 1.2.5 Hadronization and freeze-out . 50 1.3 Hard probes . 55 1.3.1 Nuclear effects . 57 2 Energy loss 62 2.1 Radiative energy loss models . 63 2.2 Gunion-Bertsch incoherent radiation . 67 2.3 Opacity order expansion . 69 2.3.1 Gyulassy-Wang model . 70 2.3.2 GLV . 74 2.3.3 Multiple gluon emission . 78 2.3.4 Multiple soft scattering . -
News from the Precision Frontier at the LHC
News from the Precision Frontier at the LHC Doreen Wackeroth [email protected]ffalo.edu Colloquium @ McMaster University Hamilton, Ontario, January 25, 2017 HEPCOS@UB is a member of the LHC CMS collaboration and gratefully acknowledges funding by the U.S. National Science Foundation The Standard Model in a nutshell The physical world at the very fundamental level follows a symmetry principle: the strong and electroweak interactions of matter particles (leptons and quarks) are prescribed by gauge symmetries, i. e. the Lagrangian L = LQCD + LEW is form-invariant, L!L, under SU(3)color and SU(2)I =isospin × U(1)Y =hypercharge transformations of the matter and gauge fields. 1 a µν;a LQCD = − 4 Gµν G Pf j µ a λa j + j=1 q¯ (x)iγ (@µ + igs Gµ(x) 2 )q (x) P ¯ µ Yf b b LEW = f ΨL;f γ (i@µ − g1 2 Bµ + g2I Wµ )ΨL;f P µ (±1+yf ) + f a¯R;f γ (i@µ + g1 2 Bµ)aR;f 1 µν 1 b µν;b − 4 Bµν B − 4 Wµν W Glashow (1961) b Bµ : U(1) gauge field, Wµ; b = 1; 2; 3 : SU(2) gauge fields ΨL;f (aR;f ): SU(2) doublet(singlet) for left(right)-handed fermions Electroweak symmetry breaking in the Standard Model The mediators of the weak interaction, the W and Z bosons, are massive, but 2 b µ,b naively introducing mass terms in L such as M Wµ W breaks the electroweak symmetry of LEW . The mechanism of spontaneous symmetry breaking allows for simultaneously generating W and Z boson masses and preserving the gauge symmetry of LEW . -
Search for New Physics in Dijet Resonant Signatures and Recent Results from Run 2 with the CMS Experiment
138 Proceedings of the LHCP2015 Conference, St. Petersburg, Russia, August 31 - September 5, 2015 Editors: V.T. Kim and D.E. Sosnov Search for new physics in dijet resonant signatures and recent results from Run 2 with the CMS experiment GIULIA D’IMPERIO Universit`aLa Sapienza and INFN Roma On behalf of the CMS Collaboration Abstract. A search for narrow resonances in proton-proton collisions at a center-of-mass energy of √s = 13 TeV is presented. The dijet invariant mass distribution of the two leading jets is measured with the CMS detector using early data from Run 2 of the Large Hadron Collider. The dataset presented here was collected in July 2015 and corresponds to an integrated luminosity of 42 1 pb− . The highest observed dijet mass is 5.4 TeV. The spectrum is well described by a smooth parameterization and no evidence for new particle production is observed. Upper limits at a 95% confidence level are set on the cross section of narrow resonances with masses above 1.3 TeV. When interpreted in the context of specific models the limits exclude: string resonances with masses below 5.1 TeV; scalar diquarks below 2.7 TeV; axigluons and colorons below 2.7 TeV; excited quarks below 2.7 TeV; and color octet scalars below 2.3 TeV. Introduction Deep inelastic proton-proton (pp) collisions often produce two or more energetic jets when the constituent partons are scattered with large transverse momenta (pT ). The invariant mass of the two jets with the largest pT in the event (the dijet) has a spectrum that is predicted by quantum chromodynamics (QCD) to fall steeply and smoothly with increasing dijet mass (m jj) [1]. -
Measurements of Photon-And Z-Tagged Jet Quenching by ATLAS
Measurements of photon- and Z-tagged jet quenching by ATLAS Jeff Ouellette, on behalf of the ATLAS Collaboration0,∗ 0University of Colorado Boulder, Boulder, CO, 80302 E-mail: [email protected] The latest measurements of jet quenching by ATLAS with photon- and /-tagged events are presented, as described during a parallel talk in the Hard Probes 2020 conference. Emphasis is on the newest measurement using /-tagged events. ATL-PHYS-PROC-2020-053 08 September 2020 HardProbes2020 1-6 June 2020 Austin, Texas ∗Speaker © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/ Measurements of photon- and Z-tagged jet quenching by ATLAS Jeff Ouellette, on behalf of the ATLAS Collaboration 1. Introduction Studies of jets produced in events tagged by an electroweak boson have proven a useful way to study bulk properties of the Quark-Gluon Plasma created in heavy ion collisions. Due to the colorless nature of the electroweak bosons, such events provide an experimental handle on the initial ?T of the hard-scattered parton before parton-medium interactions begin (i.e. at the very beginning of the post-collision evolution). This provides both an initial-state snapshot of the parton as well as a final-state measurement of the modified shower, which helps understand the nature of parton- medium interactions. Previous measurements at the LHC by ATLAS have used photon-tagged events to study partonic energy loss in this manner, including studies of the photon-jet momentum balance GjW [1] and the fragmentation pattern of jets in photon-tagged events [2] with the 2015 collision data. -
Introduction to Jet Finding and Jetography (1)
Introduction to Jet Finding and Jetography (1) Gavin Salam CERN, Princeton University and LPTHE/Paris (CNRS) 2011 IPMU-YITP School and Workshop on Monte Carlo Tools for LHC Yukawa Institute for Theoretical Physics, Kyoto University, Japan September 2011 [Introduction] [Background knowledge] Jets Jets are everywhere in QCD But not the same as partons: Our window on partons Partons ill-defined; jets well-definable Jets lecture 1 (Gavin Salam) MC tools for LHC school September 2011 2 / 30 [Introduction] [Background knowledge] Why do we see jets? Parton fragmentation Gluon emission: dE dθ α ≫ 1 quark Z s E θ At low scales: αs → 1 Jets lecture 1 (Gavin Salam) MC tools for LHC school September 2011 3 / 30 [Introduction] [Background knowledge] Why do we see jets? Parton fragmentation Gluon emission: dE dθ α ≫ 1 quark Z s E θ θ At low scales: gluon αs → 1 Jets lecture 1 (Gavin Salam) MC tools for LHC school September 2011 3 / 30 [Introduction] [Background knowledge] Why do we see jets? Parton fragmentation Gluon emission: dE dθ α ≫ 1 quark Z s E θ At low scales: αs → 1 Jets lecture 1 (Gavin Salam) MC tools for LHC school September 2011 3 / 30 [Introduction] [Background knowledge] Why do we see jets? Parton fragmentation Gluon emission: dE dθ α ≫ 1 quark Z s E θ At low scales: αs → 1 hadronisation non−perturbative Jets lecture 1 (Gavin Salam) MC tools for LHC school September 2011 3 / 30 [Introduction] [Background knowledge] Why do we see jets? Parton fragmentation Gluon emission: π+ dE dθ α ≫ 1 quark Z s E θ KL π0 At low scales: K+ − αs → 1 hadronisation -
Pos(EPS-HEP 2009)044 Jet − Γ 5 Tev Allowing High
CMS Experiment at LHC: Detector Status and Physics Capabilities in Heavy Ion Collisions PoS(EPS-HEP 2009)044 Ivan Amos Cali∗ for the CMS Collaboration Massachusetts Institute of Technology E-mail: [email protected] p The Large Hadron Collider at CERN will collide lead ions at SNN = 5:5 TeV allowing high statistics studies of the dense partonic system with hard probes: heavy quarks and quarkonia 0 with an emphasis on the b and ¡, high-pT jets, photons, as well as Z bosons. The Compact Muon Solenoid (CMS) detectors will allow a wide range of unique measurements in nuclear collisions. The CMS data acquisition system, with its reliance on a multipurpose, high-level trigger system, is uniquely qualified for efficient triggering in high-multiplicity heavy ion events. The excellent calorimeters combined with tracking will allow detailed studies of jets, particularly medium effects on the jet fragmentation function and the energy and pT redistribution of particles within the jet. The large CMS acceptance will allow detailed studies of jet structure in rare g − jet and Z-jet events. The high resolution tracker will tag b quark jets. The muon chambers combined with tracking will study production of the Z0 , J=y and the ¡ family in the central rapidity region of the collision. In addition to the detailed studies of hard probes, CMS will measure charged multiplicity, energy flow and azimuthal asymmetry event-by-event. The 2009 Europhysics Conference on High Energy Physics, July 16 - 22 2009 Krakow, Poland ∗Speaker. ⃝c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. -
Soft Modifications to Jet Fragmentation in High Energy Proton-Proton
Soft modifications to jet fragmentation in high energy proton–proton collisions Christian Bierlicha,b,∗ aNiels Bohr Institute, University of Copenhagen, Blegdamsvej 19, 21000 København Ø, Denmark. bDepartment of Astronomy and Theoretical Physics, Lund University, S¨olvegatan 14A, S 223 62 Lund, Sweden. Abstract The discovery of collectivity in proton–proton collisions, is one of the most puzzling outcomes from the first two runs at LHC, as it points to the possibility of creation of a Quark–Gluon Plasma, earlier believed to only be created in heavy ion collisions. One key observation from heavy ion collisions is still not observed in proton–proton, namely jet-quenching. In this letter it is shown how a model capable of describing soft collective features of proton–proton collisions, also predicts modifications to jet fragmentation properties. With this starting point, several new observables suited for the present and future hunt for jet quenching in small collision systems are proposed. Keywords: Quark–Gluon Plasma, QCD, Collectivity, Jet quenching, Hadronization, Monte Carlo generators 1. Introduction to study its influence also on events containing a Z and a hard jet. One of the key open questions from Run 1 and Run 2 at The non-observation of jet quenching in pp and pPb colli- the LHC, has been prompted by the observation of collective sions is, though maybe not surprising due to the vastly different features in collisions of protons, namely the observation of a geometry, one of the most puzzling features of small system near–side ridge [1], as well as strangeness enhancement with collectivity. If collectivity in small systems is due to final state multiplicity [2]. -
Theoretical Aspects of Jet Substructure
Theoretical aspects of jet substructure Mrinal Dasgupta University of Manchester Karlsruhe, July 6th 2017 Based mainly on work with Gavin Salam, Simone Marzani, Alessandro Fregoso, Andrzej Siodmok, Gregory Soyez, Lais Schunk and Alexander Powling Outline • Introduction to boosted particle searches and jet substructure • Theoretical issues in substructure studies • Jet substructure from theory first principles • Some recent progress and developments • Conclusions Boosted object hadronic decays X AT REST BOOSTED X Boosted regime implies studying particles with pT >> MX. Important at the LHC with access to TeV scales in pT. Decay products are collimated. M 2 ✓2 = p2 z(1 z) T − Hadronic two-body decays often reconstructed in single jet. Jets from QCD vs boosted heavy particles What jet do we have here? Jets from QCD vs boosted heavy particles A gluon jet ? Jets from QCD vs boosted heavy particles A quark jet ? Jets from QCD vs boosted heavy particles A W/Z/H ? Jets from QCD vs boosted heavy particles A top quark? Source: An ATLAS boosted top candidate The boosted regime implies a change in paradigm in that jets can be more than quarks and gluons. Isn’t the jet mass a clue? Looking at jet mass is not enough! Jet substructure for LHC searches Since 2008 a vibrant research field emerged based on developing and exploiting jet substructure. Butterworth, Davison Rubin, Salam 2008. Published in PRL. Builds on work by Seymour 1993. BDRS paper has over 600 citations. “Jet substructure” title search on arXiv gives > 100 papers post BDRS. BDRS method results Mass drop method + filtering Signal significance of 4 . -
Study of Jet Quenching with Z+Jet Correlations in Pbpb and Pp
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-EP-2017-002 2017/08/29 CMS-HIN-15-013 Study of jet quenching with Z+jetp correlations in PbPb and pp collisions at sNN = 5.02 TeV The CMS Collaboration∗ Abstract The production of jets in association with Z bosons, reconstructed via the m+m− and e+e− decay channels, is studied in pp and, for the first time, in PbPb collisions. Both data samples were collected by the CMS experiment at the LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The PbPb collisions were analyzed in the 0–30% centrality range. The back-to-back azimuthal alignment was studied in both pp and Z PbPb collisions for Z bosons with transverse momentum pT > 60 GeV/c and a re- jet jet Z coiling jet with pT > 30 GeV/c. The pT imbalance, xjZ = pT /pT, as well as the Z average number of jet partners per Z, RjZ, were studied in intervals of pT. The RjZ is found to be smaller in PbPb than in pp collisions, which suggests that in PbPb colli- sions a larger fraction of partons associated with the Z bosons fall below the 30 GeV/c jet pT threshold because they lose energy. Published in Physical Review Letters as doi:10.1103/PhysRevLett.119.082301. arXiv:1702.01060v2 [nucl-ex] 26 Aug 2017 c 2017 CERN for the benefit of the CMS Collaboration. CC-BY-3.0 license ∗See Appendix B for the list of collaboration members 1 The correlated production of vector bosons and jets in hard parton scatterings occurring in ul- trarelativistic heavy ion collisions provides an ideal probe of the quark-gluon plasma (QGP), a deconfined state of quarks and gluons [1, 2]. -
Disentangling Heavy Flavor at Colliders
MIT-CTP/4880 Disentangling Heavy Flavor at Colliders Philip Ilten,1, ∗ Nicholas L. Rodd,2, y Jesse Thaler,2, z and Mike Williams1, x 1Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. 2Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. We propose two new analysis strategies for studying charm and beauty quarks at colliders. The first strategy is aimed at testing the kinematics of heavy-flavor quarks within an identified jet. Here, we use the SoftDrop jet-declustering algorithm to identify two subjets within a large-radius jet, using subjet flavor tagging to test the heavy-quark splitting functions of QCD. For subjets containing a J= or Υ, this declustering technique can also help probe the mechanism for quarkonium production. The second strategy is aimed at isolating heavy-flavor production from gluon splitting. Here, we introduce a new FlavorCone algorithm, which smoothly interpolates from well-separated heavy- quark jets to the gluon-splitting regime where jets overlap. Because of its excellent ability to identify charm and beauty hadrons, the LHCb detector is ideally suited to pursue these strategies, though similar measurements should also be possible at ATLAS and CMS. Together, these SoftDrop and FlavorCone studies should clarify a number of aspects of heavy-flavor physics at colliders, and provide crucial information needed to improve heavy-flavor modeling in parton-shower generators. I. INTRODUCTION The production of charm and beauty quarks at the Large Hadron Collider (LHC) is studied both as a fun- damental probe of Standard Model (SM) phenomenology, and as an important component of searches for physics beyond the SM. -
Jet Quenching in Small Systems
Jet Quenching in Small Systems Bruno Miguel Tavares Lopes da Silva Under supervision of Guilherme Milhano and Liliana Apolin´ario Departamento de F´ısica and LIP, Instituto Superior T´ecnico, Lisboa, Portugal (Date: October 2019) Ever since the discovery of the Quark-Gluon Plasma in heavy-ion collisions, the study of jet quenching (i.e. the energy loss and modified branching of partons transversing dense media) has been at the forefront of current theoretical and experimental efforts in QCD. Experimental data from both PbPb and XeXe collisions show significant signs of jet quenching, which is a strong indicator for QGP production. However, the question of whether these effects remain when we go to smaller colliding systems is still open. With this in mind, several light-ion collisions were simulated within the JEWEL framework, in order to fill the gap between what is already known from experiments. Therefore, the results will serve as predictions for future experi- ments involving these systems, like the OO collisions planned for the run 3 of the LHC. The results show that the level of jet quenching remains rather similar across all simulated systems, until HeHe collisions, where a significant decrease in quenching is visible, but still not entirely negligible, like in pp collisions. The results also found a lower bound to the initial mean temperature of the medium for significant signs of quenching (Ti ∼ 300 MeV). Finally, a sophisticated analysis of jet substructure is presented by looking at the kinematic Lund plane. This plane, even in a qualitative way, proves to be a powerful tool to distinguish between high and low quenched systems. -
Commissioning of the CMS Tracker and Preparing for Early Physics at the LHC
Commissioning of the CMS tracker and preparing for early physics at the LHC Matthew Wingham Blackett Laboratory Department of Physics Imperial College London A thesis submitted for the degree of Doctor of Philosophy of Imperial College London and the Diploma of Imperial College. July 2008 Abstract The Compact Muon Solenoid (CMS) experiment is a general purpose detector at the Large Hadron Collider. It has been designed and optimised to discover the Higgs boson and physics beyond the Standard Model. An early discovery of the Higgs boson is the collaboration's top priority and will require a good understanding of both the detector and the physics of the background processes, with a small integrated luminosity. This principle has been the driving force behind the work presented in this thesis. The Silicon Strip Tracker (SST) sits at the heart of the CMS detector. The de- velopment of core algorithms to commission the SST are reviewed and the process of live commissioning at the Tracker Integration Facility is described. A crowning success of this study is the calibration of 1.6 M channels and their synchronisation to a cosmic muon trigger to within 1 ns. The SST is expected to produce ¯ve times more zero-suppressed data than any other CMS sub-detector. As such its e±cient handling within High-Level Trigger algorithms is paramount. The performance of the online hit reconstruction software is pro¯led, the ine±ciencies are characterised and a new scheme to focus on physics regions-of-interest only is proposed. As an example of its success, when running the single ¿ trigger path over H § ¿ §º¿ events, hit reconstruction times were reduced from 838 5 ms to only 5.13! 0.05 ms without any loss in tracking e±ciency.