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(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
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Antiparticles Cambridge, 1928 : The Dirac Equation Quantum Mechanics
Special Relativity The Dirac Equation
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the positron, e+ e- e+ Dirac’s equation predicted the existence of
Same mass but opposite charge to e- e- e+
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Discovery of the Positron
Anderson, 1933 Cosmic ray track in cloud chamber: (trail of water droplets)
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g + N e+ + e- + N
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e+e- pair creation is commonplace :
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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 )
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OPAL experiment at LEP Collider
e+ + e- g + g OPAL experiment at LEP Collider Eg = 45 GeV
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(e.g. fluorine doped glucose)
The PET Scanner Inject a positron-emitting radioactive isotope : (e.g. fluorine doped glucose) study metabolic activity
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e+ + e- g + g Eg = mec2 = 511 keV
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e+ + e- m+ + m-
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e+ + e- W+ + W-
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UA1 experiment at CERN SppS Collider
p + p Z0 + stuff e+ + e- UA1 experiment at CERN SppS Collider (1984)
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Particle Antiparticle e- e+ ne ne p p u u u u d d p- p+ u u d d
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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
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Matter e- p n Antimatter e+ p n … but where is it ?
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Neutral Kaons Neutral particles containing a strange quark or antiquark : K0 K0 s s d d “K-zero” “K-zero bar” Size : ~ m Mass :
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Discovery of K0 1946 Butler and Rochester Manchester K0 p+ + p-
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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
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A mechanical analogy …. K0 K0 KS KL
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K0 K0
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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
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DAPHNE “phi factory”, Frascati, Italy
KS and KL in KLOE DAPHNE “phi factory”, Frascati, Italy
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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
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The NA48 Detector
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A different experiment
The NA48 Experiment A different experiment (NA50)
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Magnetic Spectrometer
Detects charged particles Consists of 4 drift chambers …. …. and a magnet
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LKr Electromagnetic Calorimeter
Mainly for photons and electrons 10 m3 liquid krypton
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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
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Contact is made with aliens ….
The President of the World is sent to greet them ….
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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)
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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
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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
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~ 109 photons for every proton
The Universe ~ protons ~ antiprotons ~ 109 photons for every proton
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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)
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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
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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 ?)
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