Hc 5: Outline. Book by Tipler, chapter 12.2

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2 Hc 5: Outline Introduc:on Produc:on and iden:fica:on of par:cles Basic concepts: par:cle- an:par:cle, leptons and hadrons Fundamental interac:ons and force carriers Conserva:on laws and symmetries The Standard model: Quark model Book by Tipler, chapter

3 Ordering scheme for elementary par:cles (repe::on) Baryons have half- integer spin proton, an:- proton, neutron Δ(1232) resonances, Λ(1116), Mesons have integer spin π 0, π ± (140) η(547), σ(600), ρ(770), ω(782), φ(1019), K ± (493), K 0 s (498), Leptons do not interact strongly electron, muon, tau and neutrinos Note: Leptons are elementary par:cles, hadrons not Baryons and mesons are hadrons 42

4 Structure of ma5er Building blocks: Elementary par:cles Interac:ons between par:cles This lecture 43

5 Concept of interac:ons Force between two objects Descrip:on of an effect of unknown cause In general a central force: F(r) = 1/r 2 Informa:on exchange with finite velocity (v c) Describe interac:on by exchange of par:cle(s) Four fundamental interac:ons 44

6 Fundamental interac:ons (1) are coupled to a certain par:cle property Interac(on Gravita:onal Electromagne:c Strong Weak Par(cle property mass charge colour charge flavour (or weak charge) 45

7 Fundamental interac:ons (2) Interac:on is mediate by exchange par:cle - boson with integer spin Interac(on Gravita:onal Electromagne:c Strong Weak Force carrier or exchange par(cle graviton photon gluon W ± and Z 0 boson Graviton is postulated and not discovered yet. 46

8 Fundamental interac:ons (3) Underlying field theory (more in dedicated quantum field theory courses) Interac(on Gravita:onal Electromagne:c Strong Weak Field theory (Quantum- ) Gravity Quantum Electrodynamics Quantum Chromo- dynamics Electro- weak theory 47

9 Feynman diagrams Rules Line for par:cle; ver:ces for interac:on Par:cle considered in :me - 1- dimensional space frame Par:cle (right arrow) and an:- par:cle (lel arrow) Feynman diagrams give computa:onal rules (more in quantum- field theory courses) t x Compton effect Annihila:on process Book Tipler, page

$Baryons (q, q, q) Mesons (q, an:- q) Strong interac:on between quarks, not between leptons No evidence for free (frac:onally charged) quarks Why?$

10 Strong interac:on: Quarks Hadrons have substructure Evident from deep- inelas:c electron sca5ering experiments Hadrons consist of quarks q (more in the lecture Quark model ) Baryons (q, q, q) Mesons (q, an:- q) Strong interac:on between quarks, not between leptons No evidence for free (frac:onally charged) quarks Why? Deep- inelas6c electron sca7ering 49

11 Quark proper:es Quark flavour Quarks have different flavours: up, down, charm, As for the leptons, three genera:on of quarks exist 50

Colour charge states: red, blue and green and their an:- colour

12 Strong interac:on: Gluons Quarks have an addi:onal property: colour (or strong charge ) Why needed? Colour charge states: red, blue and green and their an:- colour Hadrons are colour neutral states Gluons also carry colour (special!) à They interact with each other 51

Gluon colour charge Possible combina:ons of red, blue and green (an:- ) colour states An:- symmetric colour wave func:on required à 8 Independent colour

13 Gluon colour charge Possible combina:ons of red, blue and green (an:- ) colour states An:- symmetric colour wave func:on required à 8 Independent colour states Colour singlet (rr +bb +gg)/ 3 (rb +br )/ 2 (rg +gr )/ 2 (bg +gb )/ 2 (rr bb )/ 2 Colour octet i(rb br )/ 2 i(rg gr )/ 2 i(bg gb )/ 2 (rr +bb 2gg )/ 6 52

14 Feynman diagram of interac:on between quarks and gluons Gluons are represented as spirals carry (colour, an:- colour) charge 53

15 Poten:al of the strong interac:on Strong force described by Quantum Chromo- dynamics Poten:al is not pure 1/r (gluons massless) since gluons interact with each other linear increase of the field at long distances r Field energy of the string is k = 1 GeV/fm Electromagne:c Field lines Strong interac:on 54

16 (Running) coupling constant α s Asympto:c freedom at short distance the coupling is weak at large distances it is strong quarks only in bound states α s 0.2 at E = 30 GeV Confinement Free quarks not observed in nature Remember in QED: α = e 2 4πε 0!c = Q: momentum transfer 55

17 Quark confinement At short distance, e.g., inside a proton, α s is small and the quarks are free Pull one quark out, α s increases and the force tries to keep it in 56

process is called hadronisation and leads to a reduction of the field

18 Hadronisa:on Primary produced quarkanti-quark pair (QCD string) forms more quark- anti-quark pairs, which fragments into hadrons This process is called hadronisation and leads to a reduction of the field energy The produced hadrons are seen as two back-to-back orientated jets 57

19 Jets A jet is a collimated spray of par:cles JADE experiment, DESY-HERA ALICE experiment, CERN-LHC 58

20 Weak interac:on New interac:on necessary to describe β and strange par:cle decays Weak interac:on happens for all quarks (having flavour) and leptons changes only quark flavour but not lepton flavour The process is therefore not possible. Exchange par:cles µ e +γ charge current: W ± boson (mass = 80 GeV/c 2 ) neutral current: Z 0 boson (mass = 91 GeV/c 2 ) Electro- weak field theory (more in quantum field theory course) 59

21 Weak interac:on (cont d) Charged vector bosons change flavour of quarks and leptons A à B + W + 60

22 Dominant weak decays of quarks quark Each downward arrow emits e + + ν e Each upwards arrow emits e - + ν e Two less possible path are shown with dashed arrows 61

23 Weak interac:on (cont d) Charged vector bosons change flavour of quarks and leptons A à B + W + Neutral vector boson causes change of energy A à A + Z 0 A = quark or lepton 62

24 Feynman diagrams for weak interac:ons β decay 63

25 Feynman diagrams for weak interac:ons β - decay n p+e +ν e Decay of Λ 0 par-cle Λ 0 p+e +ν e 64

26 Discovery of W ± and Z 0 bosons Produced in proton- an6- proton collisions: Z 0 à e + e - decay Predicted by S. Glashow, S. Weinberg and A. Salam (1973) Discovered by C. Rubbia (and S. van der Meer), UA1 experiment at CERN (1983) W ± (80) and Z 0 (91) are one of the heaviest elementary par:cles 65

27 Three genera:ons of par:cles Shape and height of the signal of the Z 0 boson are theore:cal related to the number of quark and lepton genera:ons But why? 66

28 How many elementary par:cle states exist? Answer: Quarks (incl. colour) 36 Leptons 12 Exchange par:cles ======================== 67

29 Summary Hc 5 Strong interac:on colour charge gluons (carry colour!) colour field and strings Weak interac:on flavour charge Outlook: Why are certain interac:ons possible and other not? à Addi:onal quantum numbers à Conserva:on laws and symmetries W ± and Z 0 bosons Feynman diagrams 68

30 Ques:ons? 69

Overview. The quest of Particle Physics research is to understand the fundamental particles of nature and their interactions.

Overview. The quest of Particle Physics research is to understand the fundamental particles of nature and their interactions. Overview The quest of Particle Physics research is to understand the fundamental particles of nature and their interactions. Our understanding is about to take a giant leap.. the Large Hadron Collider