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What is the matter? Where is the antimatter? Professor Michael G Green Royal Holloway University of London.

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Presentation on theme: "What is the matter? Where is the antimatter? Professor Michael G Green Royal Holloway University of London."— Presentation transcript:

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2 What is the matter? Where is the antimatter? Professor Michael G Green Royal Holloway University of London

3 Where the hell …? What is the matter?.... Where is the antimatter?

4 What is matter? What is the matter?.... Where is the antimatter?

5 Where is the antimatter? What is the matter?.... Where is the antimatter?

6 The concept of elements In Aristotle’s philosophy there were four elements Dalton (1808) listed, with weights, many elements we recognize today What is the matter?.... Where is the antimatter?

7 The periodic table Mendeleev (1869) introduced the periodic table What is the matter?.... Where is the antimatter?

8 The plum pudding model J J Thomson believed the electrons were embedded in a positively charged matrix - plum pudding What is the matter?.... Where is the antimatter?

9 The structure of atoms Rutherford (1912) showed that atoms contain a central nucleus Electrons orbit nucleus with well-defined energy and ill-defined positions m What is the matter?.... Where is the antimatter?

10 The structure of nuclei Nucleus contains protons with charge +e and uncharged neutrons m What is the matter?.... Where is the antimatter?

11 m The structure of nucleons Neutrons and protons contain quarks What is the matter?.... Where is the antimatter?

12 < m The structure of quarks? There is no evidence for further structure ? What is the matter?.... Where is the antimatter?

13 Evidence for substructure Atom absorbs energy Only certain energy levels (orbits) allowed Electron energy increases Later ‘de-excites’ What is the matter?.... Where is the antimatter?

14 Evidence for substructure Measure size of struck objects (Rutherford 1912) substructure of protons and neutrons discovered using electrons as projectiles What is the matter?.... Where is the antimatter?

15 The constituents of matter Protons contain uud - charge = +e Neutrons contain udd - charge = 0 quarks electron 2323 e e - -e charge u de What is the matter?.... Where is the antimatter?

16 Prediction of antimatter Paul Dirac predicted existence of the positron in 1928 The only equation in Westminster Abbey? Dirac’s equation implies: positron mass = electron mass positron charge = +e What is the matter?.... Where is the antimatter?

17 Discovery of antimatter Anderson (1932) discovered the positron predicted by Dirac What is the matter?.... Where is the antimatter?

18 What is antimatter? e + e - Electrons and positrons annihilate to produce  -rays (energy) E = mc 2 What is the matter?.... Where is the antimatter?

19 Production of e + e - pairs Inverse process also occurs, with  -rays becoming an electron-positron pair e + e - What is the matter?.... Where is the antimatter?

20 How to produce antimatter e - e - e - e + e + -  thin metal region of magnetic field E  > few MeV since m c = 0.5 MeV e 2 What is the matter?.... Where is the antimatter?

21 The neutrino ‘Invented’ by Pauli (1928), named by Fermi (1933) Discovered by Reines & Cowan (1956) quarksleptons 2323 e e --e u de 0 What is the matter?.... Where is the antimatter?

22 The muon Discovered in cosmic rays by Neddermeyer and Anderson (1936) Appears identical to electron but 200 times as heavy Decays within 2.2  sec ‘Who ordered that?’ - I I Rabi What is the matter?.... Where is the antimatter?

23 Strange particles In 1947 Rochester and Butler discovered yet more new objects, now known to contain a third quark By the early 1960s beautiful patterns of particles containing three quarks or a quark and an antiquark were seen which were predictive (recall Mendeleev) What is the matter?.... Where is the antimatter?

24 The fundamental particles (1963) u de s  quarksleptons What is the matter?.... Where is the antimatter?

25 The zoo grows larger u d tc sb six quarks e     e six leptons What is the matter?.... Where is the antimatter?

26 A particle accelerator Energy of electrons is about 20kV What is the matter?.... Where is the antimatter?

27 The LEP accelerator Energy of electrons and positrons is about 100GeV What is the matter?.... Where is the antimatter?

28 CERN Europe’s research laboratory for particle physics in Geneva. What is the matter?.... Where is the antimatter?

29 LEP What is the matter?.... Where is the antimatter?

30 Inside the LEP tunnel LEP is 27km in circumference Four bunches of electrons and positrons circulate inside the vacuum pipe 100  s for a complete circuit About one electron-positron collision per second What is the matter?.... Where is the antimatter?

31 Electron-positron collisions e-e- e+e+     Annihilation produces energy - mini Big Bang Electron (matter) Particles and antiparticles are produced Positron (antimatter) E = mc 2 What is the matter?.... Where is the antimatter?

32 The ALEPH detector End view What is the matter?.... Where is the antimatter?

33 Collisions in ALEPH What is the matter?.... Where is the antimatter?

34 ALEPH - a LEP particle detector What is the matter?.... Where is the antimatter?

35 Three neutrinos...  measures rate at which e+e- collisions occur Number of different neutrinos = ± u d tc sb   e e   What is the matter?.... Where is the antimatter?

36 … and no further substructure e + e - e e -  e * Excited states produced if substructure exists mass What is the matter?.... Where is the antimatter?

37 The story so far All particles have an antiparticle. u d tc sb e    e  The everyday world contains two quarks and the electron. Additional quarks and leptons have been observed with six of each in total; most decay very rapidly. When energy turns to mass equal numbers of particles and antiparticles are produced. What is the matter?.... Where is the antimatter?

38 Matter-antimatter asymmetry in the Universe What is the matter?.... Where is the antimatter? When energy turns to mass equal numbers of particles and antiparticles are produced. This observation creates problems for our understanding of the present day Universe, which appears to contain only matter and essentially no antimatter

39 What is the matter?.... Where is the antimatter? The Universe began with a “Big Bang” about 15 billion years ago -270 o ? heavy elements formed in stars stars and galaxies exist, atoms form neutrons quark "soup" 15 billion years 1 million years 1 second deg 10 deg 10 9 deg 6000 o -255 o 3 minutes helium nuclei formed microwave background radiation fills universe 300,000 years 4000 o life on earth, molecules form dominates matter and protons formed 1 billion years s Big Bang Evolution of the Universe

40 The Big Bang What happened at times less than s is uncertain What is the matter?.... Where is the antimatter?

41 Evolution with matter-antimatter symmetry Eventually such a universe contains only photons (almost true for our Universe - cosmic microwave background) What is the matter?.... Where is the antimatter?

42 The Sakharov conditions Antimatter can turn into matter if: (a) proton decay occurs (b) there is a matter-antimatter asymmetry (CP violation) (c) there is thermal non- equilibrium Sakharov (1964) What is the matter?.... Where is the antimatter?

43 Proton decay Life on earth implies protons exist, on average, for >10 23 seconds Searches for proton decay have set limits >10 32 seconds d u u X e+e+ u u - proton 00 Proton decay converts quarks into leptons - important only in early stages of the Big Bang but a small effect will remain However antiprotons will decay similarly What is the matter?.... Where is the antimatter?

44 Parity violation Macroscopic systems obey the same physical laws in a mirror system, e.g. planetary motion “parity conservation”.  -decay (weak interaction) does not conserve parity. Discovered in 1956 in polarized 60 Co decay. θθ  cos1)( c v I  What is the matter?.... Where is the antimatter?

45 P violation - CP conservation Parity violation leads to an asymmetry for neutrinos -only left-handed ones exist. L L R R CP C P Changing particle to antiparticle (C) then applying the parity operation (P) produces the right-handed antineutrino, which exists “CP conservation” What is the matter?.... Where is the antimatter?

46 Matter-antimatter asymmetry In 1964 it was discovered that the radioactive decay of antimatter differs by a tiny amount from the decay of matter. Since then progress in understanding has been very slow: experiments are very difficult; astronomy is an observational science, not experimental (cannot repeat the Big Bang). BUT we have learned that the matter-antimatter asymmetry can only occur if there are three pairs of quarks. What is the matter?.... Where is the antimatter?

47 CP violation in K 0 decays d s - s d - K0K0 K0K0 - WW u,c,t Phases of the amplitudes for the two processes are not equal ‘CP violation’ (1964) Occurs only because there are three families of quarks s - d d - s K0K0 K0K0 - u,c,t WW What is the matter?.... Where is the antimatter?

48 CP violation COUNTS / 0.5 x s  ( s)  ( s) k 0  +  - DISTRIBUTION Leads to beautiful interference effects and non-exponential decay distributions What is the matter?.... Where is the antimatter?

49 A universe with CP violation Perhaps one in every 10 9 antiquarks turned into a quark very early in the life of the Universe After the matter-antimatter annihilation a small amount of matter will be left (about one proton for 10 9 photons) What is the matter?.... Where is the antimatter?

50 Current problems 1. We have never observed proton decay 2. Precise measurements of CP violation in K 0 decay are difficult and there are uncertain theoretical corrections 3. Cosmological models do not easily explain the ratio of 10 9 photons for each proton in the Universe What is the matter?.... Where is the antimatter?

51 CP violation in B 0 decays Similar effect expected in B 0 d b - b d - B0B0 B0B0 - WW u,c,t First measurements starting 1999, Stanford, California d d - b B0B0 B0B0 - u,c,t b - WW What is the matter?.... Where is the antimatter?

52 Weak decay eigenstates What is the matter?.... Where is the antimatter? In the Standard Model the weak decay eigenstates are and where d ’ and s ’ are a mixture of d and s of the form d ’= d cosθ c + s sinθ c s ’= -d sinθ c + s cosθ c We write this as

53 CP violation parameters What is the matter?.... Where is the antimatter? Further, there are relations among the elements of V such as V ud V * ub + V cd V * cb + V td V * tb = 0 that can be represented by a triangle. It is a condition for CP violation to occur that  is non-zero.

54 CP violation parameters What is the matter?.... Where is the antimatter? Prior to 1999 the shape of this triangle had been approximately determined from measurement of several parameters of V. However the angle had not been measured directly.

55 BaBar experiment at SLAC What is the matter?.... Where is the antimatter?

56 The process e + e -  B 0 B 0 What is the matter?.... Where is the antimatter? 9.0 GeV e GeV e + Centre of mass energy = GeV - a resonance energy for the production of B 0 B 0 B 0 and B 0 are moving in the laboratory system B0B0 B0B0

57 B decays What is the matter?.... Where is the antimatter? The two particles decay We identify them and measure the separation of the decay points The separation (typically 1mm) is translated to a time difference (typically 1ps)

58 Predicted distributions What is the matter?.... Where is the antimatter? Without CP violation the distribution of  t is exponential We measure many examples of the process to produce a distribution in  t (a) CP violation makes the distribution asymmetric (b) experimental resolution modifies it

59 Evidence for CP violation What is the matter?.... Where is the antimatter? The data show clear evidence of CP violation The size of the effect is consistent with the prediction of the Standard Model of particle physics

60 Values of sin 2  What is the matter?.... Where is the antimatter? Recently direct measurements have been made (summer 2002 values) OPAL ±0.5 CDF ALEPH Belle0.72 ± 0.07 ± 0.04 BaBar0.75 ± 0.09 ± 0.04

61 Summary The everyday world is made from up and down quarks and the electron. Experiments tell us that six quarks and six leptons exist. The “extra” ones seem to be needed to explain why there is an asymmetry between matter and antimatter and hence why we exist. However it is likely to be a long time before we have a good understanding of what happened in the first fraction of a second of the Universe’s existence What is the matter?.... Where is the antimatter?

62 THE END There follows 6 slides showing a series of summary sheets which have been sent out to schools throughout the UK. What is the matter?.... Where is the antimatter? What is the matter? Where is the antimatter?

63 Particle Physics Summary Sheets - the story so far GO

64 Example of Poster No.1

65 Example of Poster No.2

66 Example of Poster No.3

67 Example of Poster No.4

68 Example of Poster No.5

69 Example of Poster No.6

70 Particle Physics Summary Sheets - the story so far Available as double sided A4 sheets for individual student use, or as a set of 6 single sided A3 wall posters, they are entitled 'Particle Physics - the story so far'. For details of how to get the summary sheets and posters call or


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