H. A. TANAKA PHYSICS 489/1489 INTRODUCTION TO HIGH ENERGY PHYSICS

Transcription

1 H. A. TANAKA PHYSICS 489/1489 INTRODUCTION TO HIGH ENERGY PHYSICS

2 SOME LOGISTICS Instructor: Hirohisa Tanaka Hiro Offic Hours (MP801A) TBA: w ll do a doodl poll TA: Randy Conklin MP920 rconklin@physics.utoronto.ca Pr-rquisits: PHY354, PHY356 spcial rlativity Lagrangian Mchanics quantum mchanics Dirac Notation, prturbation thory, commutators, spin/angular momntum multivariat calculus, matrix/linar algbra

3 SOME MORE LOGISTICS Cours wbsit: undr construction! lcturs, problm sts, solutions, postd hr. Txtbook: Modrn Particl Physics, M. Thomson lcturs gnrally follow th txt, but not xhaustivly it is ssntial to rad th txtbook... it may not hav bn covrd in lctur! Grading: 4 problm sts (40%) 1 midtrm xamination on 3 Novmbr (20%) 1 final xamination (40%) For homwork: it is fin and ncouragd to work togthr, but ach prson must fully show thir work submit in drop box in basmnt bfor 1700 on du day solutions will b postd at that tim lat assignmnts will not accptd aftr solutions ar postd if you anticipat any issus with turning in th assignmnt, plas tll m in advanc

4 CLASS OUTLINE D. J. Griffiths: Introduction to Elmntary Particls Good altrnativ rfrnc for class

5 CLASS OBJECTIVES: Larn th taxonomy of th lmntary particls/intractions what ar th fundamntal constitunts and thir intractions? what ar th basic proprtis and ruls which govrn thm? (what is allowd/forbiddn)? dpict basic procsss through Fynman diagrams Undrstand th basic principls of how w produc/dtct lmntary particls and study thir proprtis Kinmatics of particl intractions Us spcial rlativity, consrvation laws Calculat th amplitud of an lmntary procsss using th Fynman diagrams/ruls, and calculat cross sctions/dcay rats

6 STUDY GROUP I v ntrd this class for a Rgistrd Study Group

7 Participat in Rcognizd Study Groups By joining or coordinating a study group, you will: Guarant rgular study tim Gain motivation and undrstanding Mt your prs Gt quick accss rsourcs and supports Rciv Co-Curricular crdit for participating and lading Visit studygroups.artsci.utoronto.ca

8 Startd from a study group Now h passd. Rcognizd Study Groups Guarant rgular study tim Gain motivation and undrstanding Mt your prs Gt quick accss rsourcs and supports Rciv Co-Curricular crdit for participating and lading Visit studygroups.artsci.utoronto.ca

9 #comtogthr and study Rcognizd Study Groups Guarant rgular study tim Gain motivation and undrstanding Mt your prs Gt quick accss rsourcs and supports Rciv Co-Curricular crdit for participating and lading Visit studygroups.artsci.utoronto. ca

10 HIGH ENERGY PHYSICS Particl physics Elmntary particls fundamntal intractions/particls What dos high nrgy hav to do with fundamntal particls/intractions?

11 THE STANDARD MODEL ν νµ ντ no charg, no color ν νµ ντ no charg, no color - µ - τ - -1 charg, no color + µ + τ + +1 charg, no color particls u c t +2/3 charg, color u c t -2/3 charg, color d s b -1/3 charg, color d s b +1/3 charg, color Z W ± Mdiators of EM intraction antiparticls γ Mdiator of EM intraction H agnt of spontanous symmtry braking g Mdiator of strong intraction

12 INTERACTIONS Fundamntal building block of an intraction is th vrtx lctromagntism quantum lctrodynamics x x wak chargd currnt i j wak nutral currnt y y α (α EM )~1/137 g W ~1/30 g Z ~1/30 γ W Z x is any chargd particl strong intraction quantum chromodynamics q α S ~1 q is any quark (colord objct) q i:+2/3 quark, j: -1/3 quark or i: νl, j: l - arrows: dirction mattrs! backward arrow mans antiparticl don t mix up arrow and labl sam lttr mans sam particl vrtx factor coupling constant y is quark or lpton not part of diagram but indicats strngth of intraction

13 THE STANDARD MODEL ν νµ ντ wak intractions No EM/strong intraction µ τ EM and wak intractions No strong intraction u c t EM and wak intractions strong intractions d s b EM and wak intractions strong intractions Z W ± Mdiators of EM intraction γ Mdiator of EM intraction H agnt of spontanous symmtry braking g Mdiator of strong intraction

14 BUILDING UP INTERACTIONS Vrtics can b rotatd and connctd by common particls ( propagator ) γ γ γ γ γ γ γ γ γ γ γ

15 Prson: Why dos your van hav Fynman diagrams on it? Fynman: Bcaus I AM Richard Fynman!

16 MULTIPLE DIAGRAMS: In fact, any allowd procss has an infinit numbr of possibl diagrams Rcall th coupling constant: diagrams with mor vrtics hav vrtx factors if this is small, diagrams with mor vrtics contribut lss w do calculation at ordr N whr N is th numbr of vrtics. must considr all diagrams of ordr N if w want mor prcis calculation w go to highr ordr

17 HADRONS In th laboratory, w nvr s fr quarks but bound systms: msons : quark and antiquark pair baryons : thr quarks bound togthr antibaryons : thr antiquarks bound togthr Collctivly thy ar calld hadrons To undrstand th undrlying mchanism for a procss involving hadrons, considr th constitunt quarks B 0 D B ν ν b W c b W u d d d d

18 WEAK CHARGED CURRENT This is probably th most complicatd procss it is th only on that can chang th idntity of a particl For lptons (nutrinos) it is rlativly asy: chang a nutrino into its corrsponding lpton ν l l - For quarks, any transition from top to bottom row is possibl: crossing columns ( gnrations is disfavourd Cabibbo-supprssd

19 THE PENGUIN DIAGRAM

20 STUDYING PARTICLES Dcays: disintgration of particls into othr particls rat of dcay, typ of particls mittd, and kinmatics of dcay can tll us about undrlying mchanism. nrgy/momntum consrvation can tll us its mass Scattring collision of particls outgoing particls may or may not b th sam cross sction ( probability ) of intraction and outgoing particls can tll us about undrlying mchanism Dcay vs. Scattring: in som cass, dcays ar scattring of constitunt particls many particls of short livd; thy can on

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25 WHAT WE WILL NOT COVER In som sns, this class is pdagogically misplacd A mor logical approach might b to study th fundamntal framwork of quantum fild thory first consistnt quantum mchanical framwork for trating rlativistic particls byonds th scop of this class..... W hav othr fundamntal principls (consrvation laws, symmtry, tc.) to work with. But a larg part of th class will com out of nowhr without a full xplanation Fynman ruls for calculating th amplitud of a procss

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27 NOTE ON UNITS Standard unit of nrgy in particl physics is V kv, MV, GV, TV, V ~ 1.6 x J Rcall E=mc 2 Mass can b xprssd in units of [E]/c 2 V/c 2 For rfrnc, m p = MV/c 2 =1.672x10-27 kg p = (γ)mv momntum can b xprssd in units of [m]c V/c Txtbook gnrally uss ħ = c =1 Us V as th units for mass, momntum, nrgy I will oftn carry around units of c

28 NEXT TIME Plas rad Chaptr 1, Chaptr Problm st 1 is postd

29 First lmntary particl wikipdia Thomson s vacuum tub cathod ray studis: What is a cathod ray? appars to b chargd, but what is it? Sris of xprimnts: Dmonstratd that lctric charg follows th cathod ray Dflctd by lctric fild Masurd charg/mass ratio: dtrmin vlocity by balancing E/B forcs Points to particl-natur of th lctron

30 PARTICLE VERSUS WAVE Photon: firmly ingraind blif in wav natur Planck s quantum hypothsis: first clu of particl natur. Photolctric ffct: lctrons from a matrial ar libratd only whn th wavlngth of light is short Einstin (1905): light is composd of particls, whos nrgy is proportional to frquncy (Nobl Priz 1921) Compton scattring (1923): Knock-out of lctrons by light γ(λ).... θ γ(λ ) Rlation btwn λ, λ and θ is prcisly that of a particl with mass = 0 and nrgy hc/λ (hc/λ ) striking th lctron

31 wikipdia INTO THE ATOM High nrgy physics in th Radioactivity: α ( 4 H nuclus) β (lctron) γ (photon/light) transmutation of lmnts into othr lmnts! Discovry of th atomic nuclus: vry concntratd chargd mass at th cntr of th atom scattring α particls Scattring xprimnts: α + 12 N 17 O + 1 H (=p) first indication that protons ar containd within th nuclus (and = hydrogn nucli) Ruthrford also postulatd nutrons...

32 PHYSICS IN THE 1930S In th tumultuous ra that gav birth to: spcial/gnral rlativity quantum mchanics within ~30 yars, th basic building blocks of ordinary mattr wr idntifid. p - γ atoms ar som numbr of protons bound togthr in th nuclus, with an qual numbr of lctrons bound to thm lctromagntically A fw dvlopmnts thn compltly disruptd this simpl pictur

33 Th Yukawa Hypothsis EM (photon) binds lctron to nuclus Yukawa: som forc (=particl) must bind th nuclus togthr short rang = massiv H calld this th π particl (300 x m ) wikipdia Th π is sought in cosmic rays using photographic mulsions Svral things ar discovrd th μ mson th π mson strang particls K, Λ, Σ What ar ths things?

34 Antiparticls In th 1920 s, physicists try to put togthr: Quantum Mchanics Spcial Rlativity Dirac s attmpt at this lads to th nd for: wikipdia positivly chargd countrpart of th lctron Such a particl is actually obsrvd just lik th lctron, but positivly chargd in du cours, find vry particl has an antiparticl (In som cass,.g. γ, it is itslf) antiparticls ar dnotd by a bar CERN

35 A C C E L E R AT O R S

36 HADRON ZOO As nrgis of acclrators incrasd, a prolifration of nw particls (hadrons) wr discovrd: Msons: psudoscalar msons: π +, π 0, π -, η, η, K +, K -,K 0, K 0 vctor msons: ρ +, ρ 0, ρ -, ω, φ, K* +, K* -, K* 0, K* 0 Baryons p, n, Λ, Σ +, Σ 0, Σ -, Ξ +, Ξ 0, Ξ - strang particls Δ ++, Δ +, Δ 0, Δ --, Σ* +, Σ* 0, Σ* -, Ξ* 0, Ξ* -, Ω - and many mor.... what ar all ths particls? Strang = copiously producd, but long liftim

37 Willis Lamb (1955): th findr of a nw lmntary particl usd to b rwardd by a Nobl Priz, but such a discovry now ought to b punishd by a $10,000 fin.

38 PARTICLE PHYSICS IN THE 1970S ν νµ ντ wak intractions No EM/strong intraction µ τ EM and wak intractions No strong intraction p u c t EM and wak intractions strong intractions n d s b EM and wak intractions strong intractions γ Mdiator of EM intraction π g Mdiator of strong intraction?

39 DISCOVERY OF NC, W, Z NC raction of nutrinos in bubbl chambr µ + µ + W production in pp collisions. Obsrv W + ν Z particl by obsrving Z + W, Z ar xtrmly massiv W ~ 80 GV/c 2 Z ~ 91 GV/c 2 S latr that this is rsponsibl for th waknss of th wak intraction At first sight thr may b littl or no similarity btwn lctromagntic ffcts and th phnomna associatd with wak intractions. Yt crtain rmarkabl parallls mrg with th supposition that th wak intractions ar mdiatd by unstabl bosons. Both intractions ar univrsal, for only a singl coupling constant suffics to dscrib a wid class of phnomna: both intractions ar gnratd by vctorial Yukawa couplings of spin-on filds t*. S.L. Glashow, 1960

40 PARTICLE PHYSICS IN THE 1970S ν νµ ντ wak intractions No EM/strong intraction µ τ EM and wak intractions No strong intraction p u c t EM and wak intractions strong intractions n d s b EM and wak intractions strong intractions Z W Mdiators of EM intraction π γ g Mdiator of EM intraction Mdiator of strong intraction?

41 NOTE ON UNITS Standard unit of nrgy in particl physics is V kv, MV, GV, TV, V ~ 1.6 x J Rcall E=mc 2 Mass can b xprssd in units of [E]/c 2 V/c 2 For rfrnc, m p = MV/c 2 =1.672x10-27 kg p = (γ)mv momntum can b xprssd in units of [m]c V/c Txtbook gnrally uss ħ = c =1 Us V as th units for mass, momntum, nrgy

42 NEXT TIME Plas rad Chaptr 1, Chaptr Start looking at problm st.