1. (and why it may one day save your life!)
Matter ? Antimatter ?
.… how to tell an alien
from an anti-alien
(and why it may one day save your life!)
Richard Batley
Particle Physics Masterclass
Cavendish Lab, April 2005

2. Antiparticles Cambridge, 1928 : The Dirac Equation Quantum Mechanics
Special Relativity
The Dirac Equation

5. the positron, e+ e- e+ Dirac’s equation predicted the existence of
Same mass but opposite charge to e- e- e+

6. Discovery of the Positron
Anderson, 1933
Cosmic ray track in cloud chamber:
(trail of water droplets)

9. g + N  e+ + e- + N

10. e+e- pair creation is commonplace :

11. e+e- annihilation Use g  e+ + e- to produce positron beams
e.g. LEP e+e- Collider at CERN
Collide ~1011 e+ with ~1011 e-
( ~10-12 kg of e+ in lifetime of LEP )

12. OPAL experiment at LEP Collider
e+ + e-  g + g
OPAL experiment at LEP Collider
Eg = 45 GeV

13. (e.g. fluorine doped glucose)
The PET Scanner
Inject a positron-emitting radioactive isotope :
(e.g. fluorine doped glucose)
study metabolic activity

14. e+ + e-  g + g
Eg = mec2 = 511 keV

16. e+ + e-  m+ + m-

17. e+ + e-  W+ + W-

18. UA1 experiment at CERN SppS Collider
p + p  Z0 + stuff
e+ + e-
UA1 experiment at CERN SppS Collider
(1984)

19. Particle
Antiparticle e- e+ ne ne p p u u u u d d p- p+ u u d d

20. Antiparticles Particles and antiparticles have : the same mass
opposite charge
and, if they are unstable :
the same lifetime
e.g. muons :
Particles and antiparticles coexist on an equal footing in the Standard Model

22. Matter e- p n
Antimatter e+ p n
… but where is it ?

23. Neutral Kaons
Neutral particles containing a strange quark or antiquark : K0 K0 s s d d
“K-zero”
“K-zero bar”
Size :
~ m
Mass :

24. Discovery of K0
1946
Butler and Rochester
Manchester
K0  p+ + p-

25. KS and KL K0 K0 KS KL The neutral kaons can “mix” : s s d d
The particles we see decaying are : KS KL
“K-short”
“K-long”
Quantum mechanical mixtures of K0 and K0

26. A mechanical analogy …. K0 K0 KS KL

27. K0 K0

28. KS and KL have very different lifetimes :
e.g. for a beam of energy 100 GeV :
Average distance travelled before decay is
KS :
5.4 m
KL :
3.1 km
The beam starts out as
an equal mix of KS and KL
Eventually: only K-long’s are left

29. DAPHNE “phi factory”, Frascati, Italy
KS and KL in KLOE
DAPHNE “phi factory”, Frascati, Italy

30. The NA48 Experiment K0 K0 K0 K0 KS KL + -
Create a beam of neutral kaons ….
proton beam B +
secondary
particles K0
target K0 - B
(mixture)
Let them decay …. K0 K0
(vacuum)
(mixture) KS KL
NA48 detector

31. The NA48 Detector

32. A different experiment
The NA48 Experiment
A different experiment
(NA50)

33. Magnetic Spectrometer
Detects charged particles
Consists of 4 drift chambers ….
…. and a magnet

34. LKr Electromagnetic Calorimeter
Mainly for photons and electrons
10 m3 liquid krypton

35. More e+ than e- in K-long decays
CP Violation
The K-Long has revealed subtle differences between matter and antimatter
For example, the decay
occurs slightly (0.3%) more often than
More e+ than e- in K-long decays 
allows unambiguous definition of matter and antimatter

36. Contact is made with aliens ….
The President of the World is sent to greet them ….

37. e+ + e-  g + g p + p  g + g, p + p, ... n + n  g + g, p + p, ...
But are they aliens or anti-aliens ??
e+ + e-  g + g
p + p  g + g, p + p, ...
n + n  g + g, p + p, ...
E = mc2 :
D.Beckham + anti-alien  Joules
(1 Megaton of TNT = 4.2 x 1015 Joules)

38. In an Anti-world : In the NA48 experiment at CERN ….
The neutral kaon beams starts out with opposite amounts of K0 and K0
But, just as in our world :
the neutral kaon beam still starts out as an equal mix of KS and KL
and eventually becomes pure K-long
And, the decay
still occurs slightly (0.3%) more often than

39. Our World An Anti-world p n e- more e+ than e- in K-long decays p n e+
DIFFERENT
more e+ than e- in K-long decays
An Anti-world p n e+
SAME
more e+ than e- in K-long decays

40. ~ 109 photons for every proton
The Universe
~ protons
~ antiprotons
~ 109 photons for every proton

41. The Big Bang the Universe was born with
equal amounts of matter and antimatter
(and B violation and phase transitions)
CP violation :
the Universe contains
slightly more matter than antimatter
Particles and anti- particles annihilate :
the Universe contains only matter (and lots of photons)

42. and ~ 109 photons for every proton
t ~ 1 msec :
A hot, expanding “particle soup” :
e+ , e- , g , p, p, n, n
T ~ 1013 K
with a small excess of particles :
protons
109
antiprotons
After particle - antiparticle annihilation :
p + p  g + g 1
proton
antiprotons
2 x 109
photons
Today :
the Universe contains ~ 1080 protons
and ~ 109 photons for every proton

43. Open Questions What is the origin of CP violation ? ( NA48, LHCb, …. )
Is the CP violation we see what is needed in the Big Bang ?
Do aliens exist ?
(or even anti-aliens ?)