(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, 21 - 22 April 2005

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

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

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

g + N  e+ + e- + N

e+e- pair creation is commonplace :

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 )

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

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

e+ + e-  g + g Eg = mec2 = 511 keV

e+ + e-  m+ + m-

e+ + e-  W+ + W-

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

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

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

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

Neutral Kaons Neutral particles containing a strange quark or antiquark : K0 K0 s s d d “K-zero” “K-zero bar” Size : ~ 10-15 m Mass :

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

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

A mechanical analogy …. K0 K0 KS KL

K0 K0

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

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

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

The NA48 Detector

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

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

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

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

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

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  1019 Joules (1 Megaton of TNT = 4.2 x 1015 Joules)

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

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

~ 109 photons for every proton The Universe ~ 1080 protons ~ 0 antiprotons ~ 109 photons for every proton

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)

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 : 109 + 1 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

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 ?)