ELEMENTARY PARTICLE PHYSICS Current Topics in Particle Physics Laurea Magistrale in Fisica, curriculum Fisica Nucleare e Subnucleare Lecture 1 Simonetta Gentile ∗ ∗ Università Sapienza,Roma,Italia. October 14, 2018 S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 1 / 49
Preliminaries Simonetta Gentile terzo piano Dipartimento di Fisica Gugliemo Marconi Tel. 0649914405 e-mail: simonetta.gentile@roma1.infn.it pagina web:http://www.roma1.infn.it/people/gentile/simo.html S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 2 / 49
Bibliography ♠ Bibliography K.A. Olive et al. (Particle Data Group), The Review of Particle Physics , Chin. Phys. C, 38, 090001 (2014)(PDG) update 2015, http://pdg.lbl.gov/ F. Halzen and A. Martin, Quarks and Leptons: An introductory course in Modern Particle Physics , Wiley and Sons, USA(1984). ♠ Other basic bibliography: A.Das and T.Ferbel, Introduction to Nuclear Particle Physics World Scientific,Singapore, 2 nd Edition(2009)(DF). D. Griffiths, Introduction to Elementary Particles Wiley-VCH,Weinheim, 2 nd Edition(2008),(DG) B.Povh et al. , Particles and Nuclei Springer Verlag, DE, 2 nd Edition(2004).(BP) D.H. Perkins, Introduction to High Energy Physics Cambridge University Press, UK, 2 nd Edition(2000). Y.Kirsh & Y. Ne’eman, The Particle Hunters Cambridge University Press, UK, 2 nd Edition(1996).(KN) S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 3 / 49
♠ Particle Detectors bibliography: William R. Leo Techniques for Nuclear and Particle Physics Experiments , Springer Verlag (1994)(LEO) C. Grupen, B. Shawartz Particle Detectors , Cambridge University Press (2008)(CS) The Particle Detector Brief Book ,(BB) http://physics.web.cern.ch/Physics/ParticleDetector/Briefbook/ Specific bibliography is given in each lecture S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 4 / 49
Lecture Contents - 1 part 1. Introduction. Lep Legacy 2. Proton Structure 3. Hard interactions of quarks and gluons: Introduction to LHC Physics 4. Collider phenomenolgy 5. The machine LHC 6. Inelastic cros section pp 7. W and Z Physics at LHC 8. Top Physics: Inclusive and Differential cross section t ¯ t W, t ¯ t Z 9. Top Physics: quark top mass, single top production 10. Dark matter Indirect searches Direct searches S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 5 / 49
Specific Bibliography ♠ Bibliography of this Lecture ALEPH Collaboration, the DELPHI Collaboration, the L3 Collaboration, the OPAL Collaboration, the SLD Collaboration, the LEP Electroweak Working Group, the SLD electroweak, heavy flavour groups, Precision electroweak measurements on the Z resonance , CERN-PH-EP/2005-041, SLAC-R-774, arXiv:hep-ex/0509008,https://arxiv.org/abs/hep-ex/0509008 Physics Reports. 2006, vol. 427, no. 5-6, p. 257-454 J. Mnich, Experimental Tests of the Standard Model in e + e − → f ¯ f Z Resonance , Phys. Rep. 271 (1996) 181 S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 6 / 49
Contents 1 Introduction 2 Lep legacy S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 7 / 49
Introduction The aim of the course is to provide students with a general overview of the current topics in experimental particle physics either accelerator either astroparticle quests. The aim is very ambitious and challenging for the lecturer and the students. The course will begin with an overview of LEP results. Introduction to LHC Physics. Proton structure hard interactions of quarks and gluons (reminder) Tool for this study will be shortly discussed as.Detector performances, identification of particles ( e, µ „) of jets, background subtraction techniques. To prove to understand the well established physics is necessary before any claim any discovery. Proton-proton collisions For such purpose: W and Z Physics at LHC will be reviewed. Top Physics: Inclusive and Differential cross section t ¯ t W, t ¯ t Z and quark top mass, single top production will be discussed. The main discovery Higgs boson as already discussed in previous . I was asked not discuss. Heavy Ions collisions S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 8 / 49
Introduction Dark matter: direct and indirect search. Antimatter at origin of Universe. Neutrino physics or High energy cosmic rays Requested skills: Fisica nucleare e subnucleare I e II, Meccanica quantistica. Seminars Laboratory Exams for attending to lectures and not attending students Introducing ourselves... S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 9 / 49
Contents 1 Introduction 2 Lep legacy S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 10 / 49
Lep legacy The Large Electron Positron collider (LEP) gave a fundamental contribution to particle physics in particularly on the understanding of the Standard Model (SM) of the Electroweak (EW) and Strong (SI) Interactions . LEP yielded a very large number of important experimental results (see the Particle Data Books) and has placed the SM on a solid experimental ground. He was housed in 27 km tunnel, actually used from the Large Hadron Collider(LHC) 4 experiments: ALEPH, DELPHI, L3 and OPAL LEP1: √ s ≈ 91 GeV (1989 -1995) LEP2: √ s ≈ 130-209 GeV (1995 -2000) LEP had luminosities of 10 31 − 10 32 cm − 2 s − 1 which yielded collision rates of ≈ 1 event/s at LEP1 and ≈ 0.01 event/s at LEP2. S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 11 / 49
Physics e + e − colliders • Weak mixing angle relates the masses of the heavy gauge bosons: cos ϑ W = M W M Z • ρ parameter is the ratio of neutral to charged current coupling strength or equivalently boson mass relation: M 2 W ρ = Z cos 2 θ W M 2 ρ = 1 in SM with one Higgs doublet. • Deviation from ρ = 1 can originate from radiative corrections. • The contribution of the vector and axialvector part to the interactions is different and their relative strength denoted by the vector and axialvector coupling constants g V and g A . • In SM these coupling constants g V , g A are universal for all generations: Lepton Universality. S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 12 / 49
Electron positron annihilation The cross section for massless fermions summing over all helicity states as function of θ scattering angle, between incoming electron e − and outgoing fermion f can be written as m Z : d σ f (1 + cos 2 θ ) πα 2 = N f 2 s { Q 2 γ exchange c d θ � V (1 + cos 2 θ ) + 4 g e � V g f A g f 2 g e − Q f A cos θ R{ χ } Interference �� V ) 2 + ( g e A ) 2 � � V ) 2 + ( g f A ) 2 � (1 + cos 2 θ ) ( g f ( g e + + A g f V g f +8 g e V g e A cos θ | χ | 2 } Z exchange S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 13 / 49
Electron positron annihlilation N f c = 1 for leptons, = 3 for quarks 1 s χ = 4 sin 2 ϑ W cos 2 ϑ W s − m 2 Z + i Γ Z m Z Total width Γ Z is the sum of the partial decay width into fermions Γ f : � Γ Z = Γ f f αm Z � V ) 2 + ( g f A ) 2 � ( g f Γ f = N f e 12 sin 2 ϑ W cos 2 ϑ W S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 14 / 49
Electron positron annihlilation: cross section • The total cross section e + e − → f ¯ f is : σ f = 4 πα 2 V g f 3 s N f c { Q 2 f − 2 Q f g e V R{ χ } � V ) 2 + ( g e A ) 2 � � V ) 2 + ( g f A ) 2 � ( g f ( g e | χ | 2 } + + For √ s = m Z the interference term(second) vanishes and photon term(first) is very small.At Lowest Order (LO): σ f ( √ s = m Z ) ≈ 12 π Γ e Γ f m 2 Γ 2 Z Z Z BR ( Z → e + e − ) · BR ( Z → f ¯ 12 π = f ) m 2 The peak cross section is thus the product of the branching ratio of the Z decaying into initial an final state fermions times a dimensional factor. S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 15 / 49
Electron positron annihlilation: cross section The Br calculated from lowest order Γ f (Eq.1) Table : Lowest Br at Z BR = Γ f / Γ Z e, µ, τ 3.5% ν e , ν µ , ν τ 7% hadrons � � = � q q ¯ q 69% About 20% of Z bosons decay into neutrinos and are not de- Figure : Lowest order cross section tected. for e + e − → hadrons as function of center-of-mass- energy S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 16 / 49
Electron positron annihlilation: asymmetry • Straight forward derivation of other observables as : N F − N B asymmetries A FB = N F + N B F="forward" means that the produced fermion (as opposed to anti-fermion) is in the hemi-sphere defined by the direction of the electron beam (polar scattering angle θ < π/ 2) � 1 � 0 ∂σ ∂σ N F = ∂ cos θd cos θ N B = ∂ cos θd cos θ 0 − 1 Integrating Eq. 1 at √ s = m Z : A g f V g f A g f − 4 Q f g e A R{ χ } + 8 g e A g e V | χ | 2 F B ( s ) = 3 A f A ) 2 + ( g e A ) 2 + ( g f 8 V ) 2 ][( g f Q 2 f − 2 Q f g e V g e f R{ χ } + [( g e V ) 2 ] | χ | 2 g f V g f F B ( √ s = m Z ) = 3 g e V g e A f A A V ) 2 + ( g e V ) 2 + ( g f ( g e A ) 2 ( g f A ) 2 S. Gentile (Sapienza) ELEMENTARY PARTICLE PHYSICS October 14, 2018 17 / 49
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