Jet Physics at the LHC: The Strong Force beyond the TeV Scale PDF
Preview Jet Physics at the LHC: The Strong Force beyond the TeV Scale
Springer Tracts in Modern Physics 268 Klaus Rabbertz Jet Physics at the LHC The Strong Force beyond the TeV Scale Springer Tracts in Modern Physics Volume 268 Series editors Yan Chen, Department of Physics, Fudan University, Shanghai, China Atsushi Fujimori, Department of Physics, University of Tokyo, Tokyo, Japan William C. Stwalley, Storrs, CT, USA Ulrike Woggon, Institut für Optik und Atomare Physik, Technische Universität Berlin, Berlin, Germany SpringerTractsinModernPhysicsprovidescomprehensiveandcritical reviewsof topics of current interest in physics. The following fields are emphasized: – Elementary Particle Physics – Condensed Matter Physics – Light Matter Interaction – Atomic and Molecular Physics – Complex Systems – Fundamental Astrophysics Suitable reviews of other fields can also be accepted. The Editors encourage prospectiveauthorstocorrespondwiththeminadvanceofsubmittingamanuscript. Forreviewsoftopicsbelongingtotheabovementionedfields,theyshouldaddress the responsible Editor as listed in “Contact the Editors”. More information about this series at http://www.springer.com/series/426 Klaus Rabbertz Jet Physics at the LHC The Strong Force beyond the TeV Scale 123 KlausRabbertz Institute for Experimental NuclearPhysics Karlsruhe Institute of Technology (KIT) Karlsruhe Germany ISSN 0081-3869 ISSN 1615-0430 (electronic) SpringerTracts inModern Physics ISBN978-3-319-42113-1 ISBN978-3-319-42115-5 (eBook) DOI 10.1007/978-3-319-42115-5 LibraryofCongressControlNumber:2016946949 ©SpringerInternationalPublishingSwitzerland2017 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor foranyerrorsoromissionsthatmayhavebeenmade. Printedonacid-freepaper ThisSpringerimprintispublishedbySpringerNature TheregisteredcompanyisSpringerInternationalPublishingAGSwitzerland To my French and German family Preface The first physics conference I ever attended is the Workshop “QCD—20 Years Later”attheRWTHAacheninJune1992.IttookplacebetweenseminarsIhadto follow for my studies and the work for my diploma thesis. In both activities I successfully avoided topics too complicated to understand because of their close relation to the theory of the strong interaction i.e. quantum chromodynamics. Nevertheless, I found the concept of jets, presented by Bryan Webber at this workshop, quite intriguing and also the summary report on the strong coupling constant aS, given by Guido Altarelli, seemed to be rather interesting. Two years later, encouragedbymythesisadvisorChristoph Berger,Ifound myself venturing on a subject of pure QCD for my Ph.D. thesis: the determination of the strong coupling constant from jet measurements in deep-inelastic scattering with the H1 experiment at the HERA collider in Hamburg. However, I unfortunately could demonstrate that the theoretical calculation available to me at that time had severe shortcomings preventing a timely success of this initial Plan A. As a consequence andinstigatedbyanothertalkfromBryanWebber,IdugevendeeperintoQCDfor Plan B and analysed, this time successfully, the interplay of perturbative and nonperturbative aspects in the context of event shapes and power corrections. Almost 20 years and two experiments later, my fascination for QCD and its successeshasnotceasedtoincrease.ThankstotheCMSexperimentandnumerous students confiding in me for their thesis work I was able to contribute to the more recent successes of QCD at the LHC. Meanwhile, I also had the great pleasure to lectureonexperimentaljetphysicsjustafterBryanWebberintheGraduiertenkolleg ofKCETAin2014.Lastautumn,IwasalsoselectedtopresenttheresultsofCMSat a workshop dedicated to the strong coupling constant at future colliders—just beforethedistinguishedsummaryspeakerGuidoAltarelli.Unfortunately,hepassed away just some days before. The proceedings of this workshop are dedicated to hismemory.Iwouldhaveappreciatedverymuchtohavehisexpertopiniononthe latest developments and somehow “close the loop”. ToshareandconservetheknowledgegainedduringLHCRun1,Ifindittimely tosummarisemyresearchandtowriteupthelecturesthatIhavegivensince2012 vii viii Preface in the form of this book. I hope it proves to be a useful resource on the topic of QCD and jet physics for students and colleagues alike. Knowing that it is practically impossible to name all who contributed in one or another way to this work, I would like to express my sincere thanks to everybody enablingmetopursueandaccomplishmyresearchgoals.Ioffermyexcusestoall thoseIcannotmentionexplicitly.Firstofall,IthankmycolleaguesinCMSforthe opportunitytoanalysethedataofthisgreatexperiment.Inparticular,mythanksgo to my long-term collaborators Günther Dissertori, Mikko Voutilainen, Nikos Varelas, Len Apanasevich, Andreas Hinzmann, Panos Kokkas, Manjit Kaur, Katerina Lipka, Ringaile Plačakyte, and Maxime Gouzevitch. Of course, there are also many colleagues in other experiments and projects or from theory, to which I am indebted, and I would like to mention explicitly my friends from FASTNLO Markus Wobisch and Daniel Britzger, my HERAFITTER/XFITTER collaborators, and Sergey Alekhin, Johannes Blümlein, Sven-Olaf Moch, Marco Guzzi, Stefan Dittmaier, Alexander Huss, Peter Uwer, Stefan Tapprogge, Frank Ellinghaus, Tancredi Carli, Steffen Schumann, Enrico Bothmann, Simon Plätzer, Juan Rojo, Pavel Nadolsky, and Gavin Salam. At KIT, I most sincerely thank Günter Quastfor, well,everything, and Thomas Müller for his wholehearted and continuous support. Iamalso verygrateful tomy colleagues at KIT for all their support and for the possibility to habilitate. I particularly thank my co-lecturer Stefan Gieseke and all the students that have worked or are working with me for their studies at KIT or elsewhere: Andreas Oehler, Oliver Oberst, Michael Heinrich, Volker Büge, Benjamin Klein, Fred Stober,DaniloPiparo,GeorgSieber,DominikHaitz,CorinnaGünth,FrankPolgart, Daniel Săvoiu, Anna Friedel, Pooja Gupta, Manuk Zubin Mehta, Giannis Flouris, and Anterpreet Kaur. Financial support by the Helmholtz Alliance “Physics at the Terascale” and the German Ministry of Education and Research is gratefully acknowledged. Special thanks go to Dominik Haitz, Georg Sieber, Daniel Săvoiu, and Mikko Voutilainenforproofreading,andtoDominikHaitz,StefanGieseke,DaniloPiparo, Rick Field, Joram Berger, Markus Wobisch, Francesco Pandolfi, Fred Stober, Anterpreet Kaur, Christoph Berger, Eckhard Elsen, and Christophe Grojean for their permission to reuse their sketches and figures. Finally, I express very special thanks to Frau Ute Heuser and Springer for their patience and confidence in me despite missed deadlines. Lastbutnotleast,myfinalandmostcordialthanksgotoMonAmour,Corinne Béroujon, for all her support and patience. Collonges-sous-Salève Klaus Rabbertz June 2016 About this Book Particlejetsareproducedabundantlyinhadron–hadroncollisions.AttheLHC,they probe the highest energies for new phenomena. Likewise, owing to the unprece- dented accuracy attained by the LHC experiments, jet measurements have evolved into precision tests of QCD, the theory of the strong interaction. A key prediction, the running of the strong coupling constant, has been established up to energy scales three times larger than previously possible. This book reviews the latest experimental results on jet physics at the LHC by meansofamultitude ofobservablesilluminatingdifferent aspects ofQCDlikethe interplaywithpredictionsinvolvingnewcolouredmatter,thecoupling strength,or thegluoncontentoftheproton,whichconstitutesasignificantsourceofuncertainty inpredictionsofHiggsbosonproduction.Anovelapproachusedinthisbookisthe classification of these observables into the three categories of absolute, ratio, and shape measurements; the advantages of each category and the differences between themareclearlypointedout.Thesignificanceofeachobservableiselaboratedwith the help of numerous illustrations. ix Contents 1 Introduction.... .... .... ..... .... .... .... .... .... ..... .... 1 References.. .... .... .... ..... .... .... .... .... .... ..... .... 2 2 Theoretical Framework... ..... .... .... .... .... .... ..... .... 3 2.1 Historical Overview .. ..... .... .... .... .... .... ..... .... 4 2.2 Basic Elements of QCD.... .... .... .... .... .... ..... .... 9 2.3 Perturbative QCD.... ..... .... .... .... .... .... ..... .... 12 2.3.1 The Strong Coupling Constant . .... .... .... ..... .... 13 2.3.2 Cross-Section Predictions . .... .... .... .... ..... .... 16 2.3.3 Parton Luminosity... .... .... .... .... .... ..... .... 19 2.3.4 Final State.... ..... .... .... .... .... .... ..... .... 20 2.4 General-Purpose Monte Carlo Event Generators.. .... ..... .... 22 2.4.1 Non-perturbative Modelling ... .... .... .... ..... .... 23 2.4.2 Perturbative Concepts.... .... .... .... .... ..... .... 26 2.5 Jet Algorithms .. .... ..... .... .... .... .... .... ..... .... 27 2.5.1 General Desiderata .. .... .... .... .... .... ..... .... 29 2.5.2 Theoretical Desiderata.... .... .... .... .... ..... .... 30 2.5.3 Experimental Desiderata .. .... .... .... .... ..... .... 33 2.5.4 Sequential Recombination Algorithms.... .... ..... .... 35 2.6 Theoretical Uncertainties ... .... .... .... .... .... ..... .... 37 2.6.1 Scale Uncertainties .. .... .... .... .... .... ..... .... 38 2.6.2 PDF Uncertainties... .... .... .... .... .... ..... .... 40 2.6.3 a Uncertainties .... .... .... .... .... .... ..... .... 44 S 2.6.4 Non-perturbative Uncertainties . .... .... .... ..... .... 45 2.6.5 Fast Interpolation Techniques.. .... .... .... ..... .... 46 References.. .... .... .... ..... .... .... .... .... .... ..... .... 48 3 Jet Measurement.... .... ..... .... .... .... .... .... ..... .... 61 3.1 The Detectors... .... ..... .... .... .... .... .... ..... .... 62 3.1.1 The ATLAS Detector .... .... .... .... .... ..... .... 62 3.1.2 The CMS Detector .. .... .... .... .... .... ..... .... 65 xi
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