QCD, Structure Functions, Jets History of the Strong Interaction - PowerPoint PPT Presentation

Particle Physics with Highest Energy Accelerators (Tevatron and LHC) QCD, Structure Functions, Jets • History of the Strong Interaction • QCD / QED • Proton-structure: structure functions • hadronisation • factorisation • hadron jets • measurement of α s • search for new physics (BSM) 1 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

History of Strong Interactions (1) 1932 : discovery of neutrons p n e 1933 : µ ≅ 2.5 e σ ⇒ substructure of the protons ? 2 m p 1947 : discovery of π -mesons and long-living V-particles (K , Λ ) in cosmic rays 0 1953 : V-particles produced at accelerators new inner quantum number (“strangeness" ). 1964 : static quark-model; new inner quantum number: colo r u Baryon Meson (p,n, Λ ,...) ( π ,K,...) 2 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

History of Strong Interactions (2) ; 1964 : static quark model new inner quantum number: Far be. e e 1969 : dynamic parton model : γ * q N } X 1973 : concept of asymptotic freedom ; α s Quantum Chromo Dynamics. Q 2 _ 1975 : 2-Jet structure in e e - annihilation: + q confirmation of quark-parton-model. + e g 0 1979 : discovery of gluons in 3-Jet-events Z , γ * – e _ q of e e -annihilations. + 3 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

� � � � � �� � � � History of Strong Interactions (3) 40 L3 QCD 30 1991: exp. signature of the gluon self coupling 20 DATA Abelian 10 0 o o o o o 0 20 40 60 80 � � 1990-2000: confirmation of asymptotic freedom 2004: Nobel Prize (concept of A.F.) to D. Gross, H.D. Politzer und F. Wilczek 4 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

History of Strong Interactions (4) >2004: QCD as background in searches for New Physics (BSM) example: Higgs search γ γ 5 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

properties of QED and : QCD QED QCD fermions leptons (e, µ, τ ) quarks (u, d, s, c, b, t ) force 3 colo -charges r electric charge couples to g exchange photon ( γ ) gluons (g) is possible ⇒ g quantum (carries no charge) (carry 2 color charges) g α α Confinement coupling s 1 2 2 2 α (Q =0) = α s (Q = M ) ≈ 0.12 Z Asymptotic "constant" 137 freedom Q 2 2 Q free (color neutral bound leptons (e, µ, τ ) Hadronen particles states of q and q) theory α 5 perturbation theory up toO( ) α 4 perturbation theory up to O( ) s precision -7 -6 0.1% ... 20% 10 .... 10 achieved 6 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

Quarks in the proton: model and experiment model, theory Truth experiment: measurement of scattered electrons sandbag result: too many electrons with large scattering 
 angles (qualitatively similar to 
 experiments of Rutherford, 1911) explanation: the proton has „hard“ components: QUARKS (Ch. Kiesling) 7 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

Quarks in the proton ? p θ ‘ x 0 1 γ , Z θ , E e e ‘ x 0 1 measurement of scattering angle 1/3 and energy of electrons 
 (2 given entities): determine angle and momentum fraction x of scattering partner of electron 
 x 0 1 1/3 (2 unknowns) (Ch. Kiesling) 8 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

Quarks and gluons in the proton ! u measurement of momentum fraction demonstrates 
 complicated „Iinner life“ of the protons: Gluon only half of momentum is carried by quarks ; 
 d u the rest is carried by „force carriers“, 
 the gluons for higher resolution, see more and more gluons! 0 (Ch. Kiesling) 9 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

energy dependence of coupling “constants”: • verified by high precision measurements QCD Sept. 2013 τ decays (N 3 LO) (Q) α s Lattice QCD (NNLO) DIS jets (NLO) Heavy Quarkonia (NLO) 0.3 e + e – jets & shapes (res. NNLO) Z pole fit (N 3 LO) ( – ) pp –> jets (NLO) 0.2 0.1 QCD α s (M z ) = 0.1185 ± 0.0006 1 10 100 1000 Q [GeV] 10 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

theoretical description of hadronisation process • parametrisation of individual subprocesses : – f(x,Q 2 ) : parton density (q, g) im Proton [pdf] (probability for a parton with fraction x of proton momentum) – “hard” QCD cross section, e.g. for qq –> gg; qg –> q ’ g ’ – parton shower: QCD radiation / splitting q–>qg, g–>gg, g–>qq – hadronisation: parametrisation of transition of q,g to hadrons (models!) – decays: parametrisation according to exp. data and spin-statistics 11 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

factorisation (theorem!): σ ij = f i ( x 1 , Q 2 ) f j ( x 2 , Q 2 ) ) ij ( Q 2 ) σ plus sequential application of “parton shower” and “hadronisation” .processes structure functions: F 2 (x,Q 2 ) = 2 x f(x,Q 2 ) e q ∑ QCD pertubation theory: Leading order (LO) matrix elements e.g. for 2–>2 processes: (for precision measurements, at least next-to-leading order (NLO) or even NNLO calcuations required!) 12 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

proton structure 13 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

proton structure (HERA + LHC) 14 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

proton structure 15 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

kinematic regions accessible to experiments 16 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

2-Jet final state in proton-antiproton collision (Tevatron; D0 detector) 17 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

2-Jet final state in proton-antiproton collision (Tevatron; D0 detector) 18 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

high-mass (9 TeV) di-jet event at LHC (13 TeV) 19 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

Event with four reconstructed hadronic jets. The four jets have a calibrated p T > 50 GeV, and are found with the anti-kt algorithm with R=0.6. The highest p T jet has a calibrated jet p T of 144 GeV. Event collected on 10 April 2010. 4-jet event 20 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

Jet momenta are calibrated according to the "EM+JES" scheme. Event collected on 8 October 2010. The highest jet multiplicity event collected by the end of October 2010, counting jets with p T greater than 60 GeV: this event has eight. • 1st jet (ordered by p T ): p T = 290 GeV, η = -0.9, φ = 2.7 8-jet event • 2nd jet: p T = 220 GeV, η = 0.3, φ = -0.7 • Missing E T = 21 GeV, φ = -1.9 • Sum E T = 890 GeV 21 Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

„pile-up“: • 10-40 collisions per beam crossing • detectors and electronics must Z  μμ event with 20 cope with huge reconstructed vertices (ellipses have 20 σ size amounts of data for visibility reasons) • physics analyses must cope with extremely high background rates Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets

QCD- / Jet- production cross sections proton - (anti)proton cross sections 9 9 10 10 total QCD cross section 8 8 10 10 ! tot 7 7 10 10 Tevatron LHC 6 6 10 10 -1 5 5 10 10 -2 s ! b 33 cm 4 4 10 10 Jet cross section E Tjet > 100 GeV 3 3 10 10 events / sec for L = 10 jet > " s/20) ! jet (E T 2 2 10 10 !!!" nb # 1 1 ! W 10 10 ! !!!" ! Z Jet cross section E Tjet > √ s/20 0 0 10 10 jet > 100 GeV) ! jet (E T -1 -1 10 10 -2 -2 10 10 -3 -3 10 10 ! t -4 -4 10 10 ! Higgs (M H =120 GeV) -5 -5 10 10 200 GeV -6 -6 10 10 500 GeV WJS2010 -7 -7 10 10 0.1 1 10 " s (TeV) Tevatron and LHC WS17/18 TUM S.Bethke, F. Simon V7: QCD. Structur Functions, Jets