8/5/2002 Ulrich Heintz - Quarknet 2002 1

neutrino puzzlesUlrich 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

e e u d0.511 MeV 0 a few MeV a few MeV

c s106 MeV 0 1100 MeV 150 MeV

t b1.8 GeV 0 175 GeV 4.2 GeV

leptons quarksspin = ½ (fermions)

The Standard Model

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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 < 3 eV ( decay of 3H)

– mass of < 0.19 MeV (+!++)

– mass of < 18 MeV (- ! - - + )

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origin of atmospheric neutrinos• cosmic rays

• interact in upper atmosphere

decaye decay

• expect two per e

• energy ¼ 1 GeV

+

p

+

e+

e

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neutrino detection• neutrino interaction with matter

– electron neutrinos (e) produce electrons (e)

– muon neutrinos () produce muons ()

– tau neutrinos () produce taus ()

e

ee

e

W

ee

W

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water Čerenkov detector

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Super Kamiokande

41 m

39 m3 km 2 km

1 km

outer detector:1867 8” tubes

50 ktons H2O

inner detector:11146 20” tubes

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Super Kamiokande

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e in SuperK

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in SuperK

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what’s this?

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e and flux versus zenith angle

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neutrino oscillations

e

x

c

p

mmp e

222

212

2cos12sin

2

1)(

strength of mixing

distance travelled

momentum

mass difference

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neutrino oscillations• p = 400 MeV

• range of momenta centered on 400 MeV

p(

!

e)

distance traveled (m)

0.00

0.20

0.40

0.60

0.80

1.00

0 50 100 150 200 250 300 350 400 450

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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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earth

how to make a neutrino beam?

+

p

+

e+

e

p+

+

target

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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

p+p2H+e++ep+e-+p2H+e

2H+p3He+

3He+3He4He+2p 3He+p4He+e++e

3He+4He7Be+

7Be+p8Be+8Be8B* +e+ +e

8B*4He+4He

7Be+e-7Li+e

7Li+p4He+4He

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standard solar model

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solar neutrino experiments• SAGE, GALLEX

– e +71Ga71Ge+e flux = 0.558 SSM

• Homestake– e+37Cl37Ar+e- 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

2039m to surface.

1011m to sun.

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Sudbury Neutrino Observatory

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neutrino reactions in SNO• “charged current”

• “neutral current”

• “elastic scattering”

ee

W

n pp

pxx

Z

nnp

p

electron neutrinos only

all neutrinos

e

ee

e

Z mostly electron neutrinos

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observed neutrino flux

154.0

154.0 eeseees

encenc

cceecc

/s /cm66.041.3/s /cm27.039.2

/s /cm64.009.5

/s /cm11.076.1/s /cm11.076.1

22

2

22

es

nc

ecc

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observed neutrino flux

ssm = 5.05+1.01-0.81 sno = 5.09+0.44

-0.43+0.46-0.43

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neutrino oscillation parameters• maximal mixing

– sin22 ¼ 1

• small m2

– m2 < 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?