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The (Past &) Future of Neutrino Physics
Peter Ratoff Lancaster University
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The Vitality of Neutrino Physics
SPIRES: find title NEUTRINOS and date XX > Papers Reines Cowan Davis 68 Golden time (1) Koshiba 87 Golden time (2) ?? EXAMPLES: 1956 discovery of ’s 1968 solar anomaly 1987 supernova ’s 1998 atmospheric ’s
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The 1970’s “Gargamelle” Heavy Liquid Bubble Chamber,
PS/SPS Neutrino Beams, CERN, mid-1970’s The 1970’s Neutrinos were a very useful tool... Couple to matter only via weak interactions: Discovery of weak neutral currents (Z0), 1973 Clean probe of nucleon structure (DIS expts) ... but not particularly interesting themselves! (i.e. had simple, well understood properties)
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The neutrino story: 1930’s – 1960’s
“desperate remedy” to avoid non-conservation of energy in β decays Fermi 1933, “neutrino” & first theory of weak interactions Pauli, 1930 The neutrino story: 1930’s – 1960’s Lederman, Schwartz & Steinberger et al 1962, first accelerator ν beam, discovery of νμ Reines & Cowan 1956, reactor beam experiment, discovery of νe
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‘Known’ properties of neutrinos in the 1970’s
electrically neutral spin ½ maximal helicity: LH neutrinos & RH antineutrinos couple to matter via weak interactions (W/Z) 3 flavours: νe νμ (ντ) apparently massless (?)
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SSM prediction = 7.6+1.3-1.1 n .6+1.3-1.1 The solar neutrino anomaly
Homestake Mine, N. Dakota Davis & Bahcall νe + 37Cl 37Ar + e- Rate = 2.56 0.23 SNU (1SNU = captures/s/target atom ) SSM prediction = n
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Observed ratio ~1, Look at zenith angle distributions…
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SuperKamiokande ... proved that neutrinos have mass Oscillation dip
Decay/decoherence excluded upgoing neutrinos Oscillation dip 22.5 Ktons H2O
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The Sudbury Neutrino Observatory (SNO)
... demonstrated that solar neutrinos change flavour 1 kton D2O SSM
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Neutrino Oscillations
If neutrinos have mass, must consider two distinct types of neutrino state : the eigenstates of the weak interaction: nl = ne, nm, nt - the flavour eigenstates the eigenstates of the free particle Hamiltonian: ni = n1, n2, n3 - the mass eigenstates There is absolutely no reason to believe that these are the same thing. In general:
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If neutrinos have mass:
For three neutrinos: Maki, Nakagawa, Sakata & Pontecorvo (MNSP) Three Angles In a two-neutrino model, with one angle, the transition probability is
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If neutrinos have mass:
For three neutrinos: atmospheric solar Two squared-mass differences - each has a sign
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If neutrinos have mass:
For three neutrinos: CP violating phase!
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KamLAND reactor νe experiment
_ KamLAND reactor νe experiment 80% of flux from L = km 1 kton liquid scintillator ...probes same oscillation parameters as solar ν expts
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... KamLAND proved (with other results) that neutrinos oscillate
2005 KamLAND, 2008
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Long baseline νμ accelerator beam expts: probe same parameters as atmospheric ν
MINOS
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Consistent picture emerges from all experiments...
Solar/reactor neutrinos (small mass difference Δm12, mixing angle θ12 ~ ) Atmospheric/accelerator neutrinos (large mass difference Δm23, mixing angle θ23 ~ 450) Mixing angle θ13 < 140 CHOOZ Reactor ν
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...well, a nearly consistent picture emerges from all expts! “LSND region” – 4th sterile ν ? Atmos./ Accel. ν expts Solar/Reactor ν expts
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The current perspective
(Borexino)
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Strong UK effort/RAL
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The 6 ton ND280 Downstream ECAL module, Lancaster, November 2008
Lead & scintillator calorimeter; 33 x 1cm active layers
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Use ND280 to study these!
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sin22θ13 ~ 0.03 in 5 yrs?
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Super Beam Experiments: The Incremental Approach
Increased proton driver power 2-4 MW Targetry Longer Baseline FNAL-DUSEL 1300 km Very deep beam line 600’ Larger Detector 100 KT LAr 300+ KT H2O Control Systematics Near Detector Hadron production Alan Bross ICHEP July 30, 2008
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b Beam - CERN baseline scenario:
Flux 6He ( νe): 2.9 × 1018 ion decays/straight/year 18Ne (νe): 1.1 × 1018 ion MEMPHYS: 400 kT fiducial water Cherenkov At Frejus: 130 km Sensitivities: Combine with atmospheric neutrino data Baseline ion energies: 6He: γ = 60 18Ne: γ = 100 Alan Bross ICHEP July 30, 2008
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Neutrino Factory - International Design Study Baseline
Proton Driver 4 MW, 2 ns bunch Target, Capture & Phase Rotation Hg Jet 200 MHz train Cooling 30 pmm ( ^ ) 150 pmm ( L ) Acceleration 103 MeV ® 25 GeV Storage/Decay ring MICE Alan Bross ICHEP July 30, 2008
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The way ahead?
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Backup slides
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71±5
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Flavour content of solar flux (SNO + SK)
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