Neutrinos

1
Neutrinos

• Theoretically proposed by W.Pauli in the 1930s.
• First detected by Frederick Reines and Clyde
  Cowan in 1953, Hanford Experiment
• Neutral
• Spin ½
• Rarely Interacting
• Massless

2
First Solar Neutrino Experiment
----but not to study neutrinos

• Our motivation was to use neutrinos to look into
  the interior of the sun and thereby test directly
  the theory of stellar evolution and nuclear
  energy generations in stars.
• ------John
  Bahcall Raymond Davis

3
Solar Neutrino Mystery

• Observed solar neutrino flux (ue)
• 1/3
• standard solar model prediction

Neutrino Oscillations!! ue ----gt um ut
4
Oscillation Formalism

• Two Flavor Mixing
• n1 n2
• na cosq sinq
• nb -sinq cosq
• P(na ? nb) sin22q sin2(1.27 Dm2 L/E)
• Dm2 m22 - m12

5
Experimental Status

• Solar Neutrino Experiments
• SNO (Sudbury Neutrino Observatory)
• D20 detector to measure total solar neutrino
  flux
• Total flux Standard Solar Model Predicted
• Reactor Neutrino Experiments
• KamLAND
• Anti-neutrino Disappearance
• Solar and KamLAND combined (3s)
• 0.23ltsin2qsollt0.37
• 7.310-5eV2ltDm2sollt9.110-5eV2.

6
Experimental Status

• Atmospheric Neutrino Experiments
• Super-K
• A Huge Water Cherenkov Detector in Japan
• L/E distribution of atomspheric nm survival prob
• Accelerator Neutrino Experiments
• K2K (KEK to Kamioka)
• A Long base line neutrino oscillation experiment
• nm disappearance
• Atmospheric and K2K combined
• 0.34ltsin2qATMlt0.66
• 1.410-3eV2ltDm2ATMlt3.310-3eV2
• nm ---gtnt

7
Signal Identification

• Principle nt N ? t- X t- decay
• Kink Tau decay length mm.

t- ? m- nt nm
t- ? e- nt ne
nt CC ? 9 BF to 3 charged pions
t- ? p- 2pnt
8
Design Concern

• High energy
• Tau Mass 1.78 GeV
• Threshold to produce a tau 3.5 GeV
• Long Distance
• P(na ? nb) sin22q sin2(1.27 Dm2 L/E)
• High position resolution of the detector
• Tau lifetime 29010-15s
• Decay length mm
• gt85 tau decays involve only one charged track