“The Story of the neutrino” Does the missing matter matter? or

21st/22nd March 2002Particle Physics Masterclass Oxford University 2 An Introduction Sudbury Neutrino Observatory (SNO) 2km underground To observe the Sun !

21st/22nd March 2002Particle Physics Masterclass Oxford University 3 Discovery of Radioactivity Henri Becquerel, 1896 Accidentally left photographic plates in a dark drawer with some uranium salts... The plates became “fogged” The Uranium was emitting something which was interacting with the film...

21st/22nd March 2002Particle Physics Masterclass Oxford University 4 Radioactivity and momentum conservation Unstable nucleus Recoiling (more) stable nucleus A* is at rest (P TOTAL = 0) A and B must have equal and opposite momenta: p + (-p) = 0 But, E 2 = p 2 + m 2 and the total energy loss is fixed... So, there can be only one value of the energy of the escaping particle... A* A B p -p MAMA mBmB Conservation of momentum Einstein: Relativity

21st/22nd March 2002Particle Physics Masterclass Oxford University 5 The Beta-decay puzzle A* A e-e- Beta-particle energy N A nucleus decays giving out an electron... Something must be wrong with the picture...? The electron has a range of energies Energy and momentum aren’t conserved!?

21st/22nd March 2002Particle Physics Masterclass Oxford University 6 The “neutrino” hypothesis What Pauli “saw”: “What if the missing energy is carried off by an otherwise “invisible” particle...?” Wolfgang Pauli, 1930 A* A e-e- C

21st/22nd March 2002Particle Physics Masterclass Oxford University 7 The birth of the neutrino Pauli: “I have done a terrible thing. I have invented a particle which cannot be detected...” very light It must be very light, possibly massless: (sometimes, the electron takes all the energy in the decay) electrically neutral It must be electrically neutral: (charge conservation in beta decay) It is produced along with an electron: (they can’t be made on their own...) interact very rarely It must interact very rarely: (it always escapes the detector without being seen)

21st/22nd March 2002Particle Physics Masterclass Oxford University 8 25 years later: Hard but not impossible Beta decay in a nuclear reactor np e-e- e “Inverse” Beta decay pn e+e+ e It would take m (300 light years) of water to absorb a single neutrino. Therefore we need many neutrinos... …and a very large detector...and it’s the same type of reaction in “reverse”

21st/22nd March 2002Particle Physics Masterclass Oxford University 9 Neutrinos from the Sun p p p n e e+e+ The biggest nuclear reactor of them all... Two protons fuse to give a “deuteron”, a positron and an electron neutrino 10 billion neutrinos from the sun pass through your finger tip every second!

21st/22nd March 2002Particle Physics Masterclass Oxford University ,000 bottles of cleaning fluid Neutrinos can change chlorine atoms to argon atoms by Inverse Beta Decay Cl + e  Ar + e - Measure the amount of argon produced in one month......find 10 atoms in ! e  p + e - n + e  p + e -

21st/22nd March 2002Particle Physics Masterclass Oxford University 11 Some of our neutrinos are missing... We “understand” how each nuclear reaction works... We can measure how much energy the sun gives out... We can accurately predict the number of neutrinos we expect! p + p  p + n + e + e + (Energy) Sun Total energy  “Light detector” N neutrinos = Total energy Reaction energy Something must be wrong with the neutrinos...

21st/22nd March 2002Particle Physics Masterclass Oxford University 12 Neutrinos as waves... Oscillations! What if neutrinos were made up of two quantum waves with different wavelengths...? These waves would interfere Electron neutrinos disappear depending on the distance and mass difference of the neutrinos Quantum waves interfering over 100 million miles!

21st/22nd March 2002Particle Physics Masterclass Oxford University 13 SNO - two measurements at once 1000 tonnes of heavy water (D 2 0) 10,000 light detectors 100 million km to the sun 2039m to surface

21st/22nd March 2002Particle Physics Masterclass Oxford University 14 Sudbury Neutrino Observatory

21st/22nd March 2002Particle Physics Masterclass Oxford University 15 SNO - two measurements at once Reaction like beta decay to detect electron neutrinos e e + d  p + p + e All neutrinos can break up deuterons (electron, muon or tau) n any + d  p + any + n enSee e or n from flash of light If oscillation occurs: Number of e Number of any <1

21st/22nd March 2002Particle Physics Masterclass Oxford University 16 Cosmic encounters... proton High energy protons from space in all directions Hit the atmosphere and produce a “shower” of particles This shower includes muons These particles decay like beta decay to give......neutrinos! 100 particles m -2 s -1 This is why all neutrino detectors are underground

21st/22nd March 2002Particle Physics Masterclass Oxford University 17 Atmospheric neutrinos “Shower particle” muon neutrino e electron neutrino muon neutrino Muons and electrons can’t just be made or decay on their own... Particle “type” must be conserved A shower particle produces a muon and a muon neutrino. The muon decays to a muon neutrino......and an electron along with an electron neutrino 2  : 1 e

21st/22nd March 2002Particle Physics Masterclass Oxford University 18 Detecting neutrino oscillations... Knowing what ratio of neutrino types to expect......count neutrinos after different distances See how many neutrinos of each type have disappeared (oscillated) Atmospheric neutrinos Compare “up” and “down” Soudan 2

21st/22nd March 2002Particle Physics Masterclass Oxford University 19 Soudan 2: Disappearing neutrinos... e  1000 tonnes of iron! What do electron and muon neutrino interactions look like? Interacting electron neutrinos produce electrons Electrons create e + e - pairs “Electromagnetic Showers” Interacting muon neutrinos produce muons Muons are heavier than electrons  Straight track until it runs out of energy muon e

21st/22nd March 2002Particle Physics Masterclass Oxford University 20 What we (don’t) know... There are three types of neutrino, each associated with a “lepton” They appear to change (oscillate) between neutrino types Real quantum waves in action over millions of miles! e nu-e mu nu-mu tau nu-tau