The Neutrino World：中微子的世界.ppt

The Neutrino World：中微子的世界
The Neutrino Revolution(2019 – …)
Neutrinos have nonzero masses!
Leptons mix!
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ThThe Neutrino World：中微子的世界
The Neutrino Revolution(2019 – …)
Neutrinos have nonzero masses!
Leptons mix!
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These discoveries come from the observation of neutrino oscillation.
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The Physics of Neutrino Oscillation
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Neutrinos Come in at Least Three Flavors
The known neutrino flavors: e ,  , 
Each of these is associated with the corresponding charged-lepton flavor: e ,  , 
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The Meaning of this Association
e
Detector
e
e
W boson
Short Journey
e




W




W
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Over short distances, neutrinos do not change flavor.




W
Short Journey
Does Not Occur
But if neutrinos have masses, and leptons mix, neutrino flavor changes do occur during long journeys.
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Let Us Assume Neutrino Masses and Leptonic Mixing
Neutrino mass —
There is some spectrum of 3 or more neutrino mass eigenstates i:
(Mass)2
1
2
3
4
Mass (i)  mi
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Leptonic mixing —
When W+  l+ +  ,
the produced neutrino state |> is
| > =  U*i |i> .
Neutrino of flavor  Neutrino of definite mass mi Leptonic Mixing Matrix
le  e, l  , l  
e, , or 
i
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Experimental Evidence
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Evidence For Flavor Change
Neutrinos
Solar
Reactor(L ~ 180 km)
Atmospheric
Accelerator(L = 250 and 735 km)
Stopped + Decay LSND L  30 m
Evidence of Flavor Change
Compelling
Compelling
Compelling
Compelling
Unconfirmed
(
)
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Solar e   /  is now well established.
The mechanism for this flavor conversion is the —
Large Mixing Angle version of the —
Mikheyev Smirnov Wolfenstein
— Effect.
This occurs as the neutrinos stream outward through solar material. It requires both interactions with matter and neutrino mass and mixing.
What Happens To Solar Neutrinos
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How Does the Large Mixing Angle MSW Effect Work?
The solar matter effect is imp