Mid- term exam Content: Specified on Blackboard Date: Thursday, 5 March 2015 Time: 8:30 10:30 Educatorium/Alfa

Transcription

1 Mid- term exam Content: Specified on Blackboard Date: Thursday, 5 March 2015 Time: 8:30 10:30 Room: Educatorium/Alfa Ques/on hour today at 16:00 in room BBL 083 1

2 3. Par/cle Physics André Mischke Utrecht University 2

3 Hc 4: Outline IntroducPon ProducPon and idenpficapon of parpcles Basic concepts: parpcle- anpparpcle, leptons and hadrons Fundamental interacpons and force carriers ConservaPon laws and symmetries The Standard model: Quark model Book by Tipler, chapter

4 ParPcle Physics Structure of maker building blocks: elementary parpcles interacpons between them Elementary parpcles are point- like have no structure are non- excited objects 4

5 Chemistry in the 19 th century Mendeleev s Periodic Table of elements Natural maker: bound states of 92 elements Elementary parpcles in 92 different versions InteracPon: chemical interacpon 5

6 Beginning of the 20 th century 1930s Known elementary parpcles: proton (protos = first), neutron, electron and photon Known interacpons GravitaPon Electro- magnepc interacpon Nuclear interacpon 6

7 Today's Standard Model Elementary parpcles Quarks and leptons (fermions; half- integer spin) InteracPons Exchange parpcles (bosons; integer spin) What was discovered in between? 7

8 ParPcle producpon Cosmic rays: ParPcles from space Balloon experiments (1910s) First evidence for new parpcles = new form of maker ParPcle accelerators - Since 1930 s - Current highest collision energy (8 TeV) reached at the Large Hadron Collider at CERN (Geneva, Switzerland) 8

9 Results from cosmic- ray experiments Balloon experiments in heights up to 5.3 km, V. Hess (1912) Measurement of the ionisapon rate with electrometer RadiaPon increases with increasing height Discovery of AnPmaKer ExoPc parpcles with strange behaviour (= parpcular long life Pmes) 9

10 First apparatuses for arpficially accelerapng parpcles to high energies 27- inch Cyclotron E.O. Lawrence (1934) 3.6 MeV proton beam Cockcrok- Walton accelerator (1932) 300 kev proton beam University grant of

11 ParPcle producpon In parpcles collisions e.g., proton on proton collision at 8 TeV centre- of- mass (cms) energy (at CERN or in the atmosphere) InelasPc collision E = mc 2 ParPcle producpon threshold: cms energy 2 mass RelaPvisPc energy- momentum relaponship (RelaPvisPc mechanics) E 2 = (pc) 2 + (mc 2 ) 2 Lorentz factor (Pme dilatapon) pc = βγ mc 2 and E = γ mc 2 where β = v/c = pc/e and γ = (1- β 2 ) - ½ Book by Tipler, chapter

12 IdenPficaPon of long- lived parpcles Long- lived means that the flight way γτ βc (life Pme Pmes velocity) is at least a few cenpmetre (from observer view) E.g., for typical γ = 200 the life Pme is τ 10-2 m/( m/s) s 12

13 ParPcle idenpficapon methods Aim is to detect a large fracpon of the produced parpcles and its properpes Charge and neutral parpcles ConservaPon laws: momentum, energy and charge Relevant quanppes/properpes type of parpcle (mass/charge m/q) momentum p energy E life Pme τ spin s 13

14 Momentum measurement: DeflecPon of charge parpcle in magnepc field MagnePc field B [Tesla] ParPcle with charge q (negapve in this example) Book by Tipler, page 94 Lorentz force Collision vertex ParCcle trajectory is a helix in 3D space and a circle in the transverse plane p [MeV /c] = 300 q B R 14

15 Charged parpcle idenpficapon: Time of flight Measurement of the Pme of flight (β = v/c) with two scinpllapon counter/detector pc = βγ mc 2, where the momentum is determined in a magnepc field Real data from the ALICE experiment at the CERN- LHC 15

16 Charged parpcle idenpficapon: Specific ionisapon energy loss Specific ionisapon energy loss in maker; from strength of the track charged parpcles ionise material Bethe- Bloch formula: de/dx = - e 2 f(βγ) de/dx β 2 γ 0.7 β 16

17 Charged parpcle idenpficapon in the ALICE* experiment at CERN Specific ionisapon energy loss * Website: hrp://aliceinfo.cern.ch/public/welcome.html 17

18 Energy measurement ElectromagnePc (photon, electron) or hadronic calorimeter (proton, neutron) Several interacpons with detector material à parpcle shower DeterminaPon of the total parpcle energy, deposited in the calorimeter parpcle Detector material read- out sensors 18

19 ReconstrucPon of short- lived parpcle: Invariant mass method B field p (E, p 1 ) 1! Λ π -! (E, p ) 2 2 σ mass = 2.2 MeV The existence of the intermediate state is evident from the peak in the invariant mass distribupon m inv c 2 = (E 1 + E 2 ) 2 - (! p 1 c+! p 2 c) 2 Life Pme: Tipler, chapter 4-2! τ = = Γ σ 2! 2ln 2 19

20 Bubble chamber picture Main measuring device from 1950's to 1980's Beam comes in from this side Features - ParPcles bend in the magnepc field - Neutral parpcles leaves no track, then decays into charge parpcles - Atomic electrons knocked out by parpcles 20

21 Break?! 21

22 Discovery of the positron (first anp- parpcle) Existence of positron (= anp- electron) postulated by P. Dirac (1927): Two solupons of the relapvispc wave equapon Cloud chamber photographs of cosmic ray events; C. Anderson (1932) Electron ionisapon but opposite curvature Discovery of the anp- proton (1955) p + p p + p + p + p E 2 p 2 c 2 = m 2 c 4 E =± p 2 c 2 +m 2 c 4 positron 22

23 Tracks of electron- positron pairs 30 MeV x- ray interacpons with a lead plate MagnePc field points out of the page 23

24 AnPmaKer in medical applicapons Positron emission tomography (PET) (developed at MassachuseKs General Hospital, 1952) 1. Positron- emiyng isotopes ( 11 C, 13 N, 15 O, 18 F) are inserted into physiologically relevant molecules (oxygen, glucose, enzymes) and injected into papent 2. Positron annihilapon is detected with crystal calorimeter 24

25 AnP- hydrogen atom (AnP- ) hydrogen is the simplest atomic system Hot (excited) and cold (slow, using a parpcle trap) anp- hydrogen produced at CERN in 1995 and 2011, respecpvely High- precision spectroscopy Goal: deeper understanding of maker- anpmaker imbalance anpmaker gravity p vacuum wall y φ x z annihilation detector mirror coils electrodes Typical parccle trap octupole e + 25

26 Today s heaviest anpmaker nuclei 18 anp- helium- 4 nuclei, produced in collisions of heavy atomic nuclei STAR experiment at Brookhaven NaPonal Laboratory, USA (2011) 26

27 Discovery of the neutrino n p+e n p+e +ν e # events not this but this # events m n - m p - m e 17 kev E e E e Electron energy spectrum of the β decay Preserve energy and momentum conservapon Existence of neutrino postulated by W. Pauli Discovered by Cowan and F. Reines (1956) 27

28 Discovery of the muon: A surprise! In cosmic ray experiments; C. Anderson (1937) New parpcle behaves like a heavy electron (about 200 Pmes heavier) 28

29 Summary: properpes of electron- like parpcles and neutrinos 29

30 Discovery of the pion Yukawa s predicted meson exchange parpcle In cosmic ray experiments by C. Powel (1947) DetecPon with photo emulsion pictures e + μ + Pion decay π + µ + +ν µ e + +ν e π + 30

31 Discovery of the V 0 parpcle cosmic ray shower Cosmic ray experiment; G. Rochester and C. Butler (1947) 3 cm lead V 0 particle They are produced through strong interacpon but decay very slow (long life Pme τ) τ(strange parpcle) s τ(δ resonance) s CharacterisPc V- decay topology: Discovery of neutral kaon, the K 0 s Cloud chamber picture IndicaPon for a new force: weak force (later more) 31

32 Strange parpcle producpon 32

33 Hundreds of parpcles discovered What are the underlying building blocks? 33

34 Ordering scheme: fundamental consptuent versus Pme 34

35 Ordering scheme (cont d) Ordering of hadrons (hadros = robust) using their measurable properpes (mass, charge, spin, isospin) SeparaPon of light and heavy hadrons and call them baryons and mesons mass [GeV] vector meson (spin 1) pseudo-scalars (spin 0) 35

36 Ordering scheme (cont d) Baryons (baryos = heavy) have half- integer spin proton, anp- proton, neutron Δ(1232) resonances, Λ(1116), Mesons (mesos = middle) have integer spin π 0, π ± (140) η(547), σ(600), ρ(770), ω(782), φ(1019), K ± (493), K 0 s (498), Leptons (leptos = light) do not interact strongly electron, positron, muon, neutrino, Note: Leptons are elementary parpcles, hadrons (baryons and mesons) not; evident from its excitapon spectra. 36

37 Summary Hc 4 ProducPon and idenpficapon of parpcles Every parpcle has an anp- parpcle with exactly the same mass but opposite electrical charge (later: opposite charge, baryon and strange number) New parpcles, with masses between electron and proton mass ExoPc parpcles: strangeness Ordering scheme Hadrons (baryons and mesons) and leptons 37

38 QuesPons? 38