TheThe problematicproblematic particleparticle AnAn introductoryintroductory coursecourse onon neutrinoneutrino physicsphysics (IV)(IV) J.J. Gómez-Cadenas CERN Summer Student School Geneve, August,2004 Outline Where (almost all) the various anomalies, puzzles and problems created by neutrinos are explained. The sun also rises Detecting solar neutrinos Radiochemical •Only event rates •No time & no direction Scintillation •Event timing Cherenkov •Event timing & direction Radiochemical experiments − νe + N → N′ + e Proposed by Pontecorvo in 1946. N' (unstable) is separated from the target with physical-chemical techniques and quantitatively measured by observing its decay back in N. dΦi(E) Interaction Rate (R) = Ntarget ⋅ ∑ ∫σ i(E)⋅ dE i dE -46 2 10 2 -1 σ i ~ 10 cm ; Φi ~ 6 × 10 [s cm ] Detector masses 1 Solar Neutrino Unit [SNU] = 1 ν interaction/day each 1030 targets 29 30 Ntarget = 10 -10 nuclei, namely O(10-100) tons of target to have O(1) ν interaction/day The chlorine experiment Cl37 →25% of all natural chlorine Inverse beta decay (0.86 Mev threshold) Cl37+ν →Ar37+e- Ar is chemically very different from Chlorine. An inert gas that can be eventually removed from chlorine. It is radioactive and reverts to Cl37 emitting an Auger electron The hero in the mine Concept: Count the atoms of Only a few atoms 37 Ar37 produced by neutrinos of Ar per run! 380 000 liters of C2Cl4 (a cleaning fluid) deep inside Homestake mine to shield from natural radiation (a olimpic swimming pool) Let Argon-37 accumulate from 1 to 3 months. Flush with He gas to remove Ar from fluid. Let the Ar condensate in a 77 K charcoal trap. Collect and purify Ar. Count the number of Auger electrons from Ar37 Chlorine by numbers 3737Cl(ν ,e)3737Ar (E = 813 keV) Cl(νee,e) Ar (Ethrthr = 813 keV) K EC τ = 50.5 d Kshellshell EC τ = 50.5 d 3737ClCl + + 2.82 2.82 keV keV ((AugerAuger e e-,- ,X X)) ExpectsExpects 8.28.2 SNUSNU ±±1.81.8 ObservsObservs 2.562.56 SNUSNU ±±0.230.23 The solar neutrino problem •Also called “paradox”, “dilemma”, “puzzle” and other nice words that showed that every body (secretly) believed that: •Davis (Chlorine experiment) was wrong •Bahcall (The solar model) was wrong Or, more likely: Both were wrong! Gallium experiments 7171Ga(ν ,e)7171Ge (E = 233 keV) Ga(νee,e) Ge (Ethrthr = 233 keV) K,LK,L shell shell ECEC τ τ = = 16.5 16.5 dd 7171 GaGa + + 10 10 keV, keV, 1 1 keV keV - (Auger(Auger e e,- ,X) X) ExpectsExpects 127127 SNUSNU ±±1212 ObservsObservs 68.168.1 SNUSNU ±±3.753.75 Water detectors: Principle Water detectors: Concept Water detectors: Concept Super-K The cathedral of light The cathedral of light The eyes of Super-Kamiokande Super-Kamiokande solar results Super-Kamiokande by numbers A neutrino picture of the sun Super-K observation Neutrinos come from the sun indeed! The solar neutrino problem after Super Kamiokande So Davis was not wrong after all! SNO SNO detector Signals in SNO Neutron detection (SNO) SNO observations − CC ν e + d ⇒ p + p + e − − ES ν x + e ⇒ν x + e NC ν x + d ⇒ p + n +ν x ΦCC = φe Φ ES = φe + 0.15⋅φµτ Φ NC = φe +φµτ The solar neutrino problem So the sun is shining the expected number of neutrinos but many of them are νµ and/or ντ! Not only Davis, but also Bahcall was right! Atmospheric neutrinos Atmospheric flux prediction Ingredientes: •Primary proton flux •Hadronic production models •Hadron propagation (geomagnetic effects) Zenith angle measures ν path lengt Notice: Three decades of path length from O(104) to O(10) km. Super-K sees also atmospheric neutrinos Atmospheric ν interactions Correlation between lepton energy and ν energy Sub-Gev sample contains neutrinos of below 1 GeV energy. Multi-GeV sample: all the way to 100 GeV and more. So one has a very large range of neutrino path length and Energies available Atmospheric ν sample The atmospheric neutrino problem Energy dependence Effect depends no only on the path length but also on the energy Solar & Atmospheric neutrino problems •The combination of all solar neutrino experiments (before SNO) implied that solar neutrinos were disappearing between production (in the sun core) and detection in the earth. •SNO shows that the sun is shining the expected ν flux but most of them are νµ and/or ντ •The zenith dependence observed by Super-Kamiokande experiment showed that νµ (but not νe) produced in the atmosphere were also disappearing. The effect depends on the zenith angle, that is on the neutrino path length, between production and detection and on the energy.