neutrino puzzles

1
neutrino puzzles

• Ulrich Heintz
• Boston University
• http//physics.bu.edu/quarknet/2002/neutrinos.ppt

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outline

• the neutrino
• atmospheric neutrinos
• solar neutrinos
• accelerator neutrinos
• does it make sense?

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the neutrino in the standard model
The Standard Model
e ?e u d
0.511 MeV 0 a few MeV a few MeV
? ?? c s
106 MeV 0 1100 MeV 150 MeV
? ?? t b
1.8 GeV 0 175 GeV 4.2 GeV
spin ½ (fermions)
quarks
leptons
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neutrino properties

• how do we detect neutrinos?
• no charge, no color
• neutrinos interact only by the weak force
• can penetrate entire earth without interacting
• need lots of neutrinos and big detectors
• limits on the neutrino masses
• mass of ?e lt 3 eV (? decay of 3H)
• mass of ?? lt 0.19 MeV (?!???)
• mass of ?? lt 18 MeV (?- ! ?- ?- ? ??)

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origin of atmospheric neutrinos

• cosmic rays
• interact in upper atmosphere
• ??? decay
• ??e decay
• expect two ?? per ?e
• energy ¼ 1 GeV

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neutrino detection

• neutrino interaction with matter
• electron neutrinos (?e) produce electrons (e)
• muon neutrinos (??) produce muons (?)
• tau neutrinos (??) produce taus (?)

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water Cerenkov detector
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Super Kamiokande
50 ktons H2O
inner detector 11146 20 tubes
41 m
outer detector 1867 8 tubes
1 km
39 m
3 km
2 km
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Super Kamiokande
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?e in SuperK
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?? in SuperK
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whats this?
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?e and ?? flux versus zenith angle
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neutrino oscillations
mass difference
strength of mixing
momentum
distance travelled
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neutrino oscillations

• p 400 MeV
• range of momenta centered on 400 MeV

p(?? ! ?e)
distance traveled (m)
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atmospheric neutrinos

• what does this mean?
• ?? disappear
• ????e
• would see e
• ?????
• ? is hard to see
• ?? from top
• no oscillations
• ?? from bottom
• oscillations
• limit parameters

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?e and ?? flux versus zenith angle
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neutrino mixing parameters

• maximal mixing
• sin22? ¼ 1
• small ?m2
• ?m2 ¼ 10-3 eV2

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K2K

• to check Super-K results
• shoot ?? beam from KEK to Kamiokande (K2K)
• ?? energy ¼ 1.3 GeV
• count ?? events at Super-K
• if there are oscillations expect a deficit of
  ??s (disappearance)
• not enough energy to make ?s (appearance)

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how to make a neutrino beam?
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K2K
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do they oscillate?

• ? beam events at Super-K
• observe 56
• expect 80
• probability for this without oscillations ¼ 1

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Super-K accident

• on November 12, 2001
• 6779 of 11146 inner tubes collapsed
• rebuild with 47 of tubes by fall 2002
• complete rebuild after that

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solar neutrinos
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reactions in the sun
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standard solar model
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solar neutrino experiments

• SAGE, GALLEX
• ?e 71Ga?71Gee ? flux 0.558 SSM
• Homestake
• ?e37Cl?37Are- ? flux 0.33 SSM
• Super-K
• ?x e- ??x e- ? flux 0.46 SSM

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solar neutrino in Super-K
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the solar neutrino puzzle
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Sudbury Neutrino Observatory

• Creighton Mine, Sudbury, Ontario
• 1000 tonnes D2O in 12 m diameter acrylic vessel
• 9500 PMTs in 17 m diameter support
• 7000 tonnes H2O
• Surrounded by norite rock

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Sudbury Neutrino Observatory
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neutrino reactions in SNO

• charged current
• neutral current
• elastic scattering

electron neutrinos only
all neutrinos
mostly electron neutrinos
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observed neutrino flux
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observed neutrino flux

• Fsno 5.09

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neutrino oscillation parameters

• maximal mixing
• sin22? ¼ 1
• small ?m2
• ?m2 lt 10-4 eV2

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accelerator neutrinos

• LSND (Los Alamos)
• ? ?? ??
• ? ?e ?e ??
• observe ?e
• oscillations from ??
• Karmen (Rutherford Lab)
• no oscillation signal
• Miniboone (Fermilab)
• starts 2002
• will resolve issue

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does it make sense?

• three oscillation signals
• atmospheric neutrinos ? ? m2 ¼ 10-3 eV2
• solar neutrinos ? ? m2 ¼ 10-4 eV2
• accelerator neutrinos ? ? m2 ¼ 0.1 eV2
• incompatible with three neutrinos
• one of the experiments is wrong
• there is a 4th neutrino

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conclusion

• thank you!

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summary

• strong evidence for neutrino oscillations
• from atmospheric neutrinos (????? ?)
• from solar neutrinos (?e??? or ?? ?)
• at least one neutrino must have mass
• accelerator neutrino oscillation signal
• mildly inconsistent experiments
• not compatible with these and three neutrinos
• is there a 4th (sterile) neutrino?