what have we learned from super-k? before super-k sk-i (1996-2001) atmospheric solar sno & sk-i

G. Sullivan - Princeton - Mar 2002

What Have We Learned from Super-K?

– Before Super-K– SK-I (1996-2001)

• Atmospheric• Solar

– SNO & SK-I• Active solar

– SK Accident• Rebuild

Greg SullivanUniversity of Maryland


Why Super-Kamiokande?

• Solar Neutrinos “Problem”– 3 experiments showed a deficit of solar neutrinos.

• Going back ~30 years– About ½ of the expected number were observed– results can not be reconciled with the standard solar model

• Atmospheric Neutrino “Anomaly”

– IMB and Kamiokande saw less than expected ratio of e

• One Proposed Explanation was: Neutrino Oscillations

– Solar neutrinos might be e

– Atmospheric neutrinos might be


Neutrino Oscillations

• If neutrinos oscillate then “mixing” must occur between different type of neutrinos. Weak eigenstates of the neutrino are mixtures of the neutrinos with definite mass.– mass is not 0 and flavor is not absolutely conserved!

• Probability of electron neutrino to remain electron flavor

• Matter Effects will alter this vacuum expression– MSW effect

GeV

kmeVee E

LmP

222 27.1

sin2sin1)(


Super-Kamiokande Detector

Detector Characteristics 41 m h x 39 m dia. 50,000 ton (22,000 ton

fiducial) 11,200 20” PMTs inner

detector 1,850 8” PMTs anti-

detector 40% photo-cathode

coverage


Super-Kamiokande


Detecting neutrinos

Electron or

muon track

Electron or

muon track

Cherenkov ring on the

wall

Cherenkov ring on the

wall

The pattern tells us the energy and type of particle

We can easily tell muons from electrons

The pattern tells us the energy and type of particle

We can easily tell muons from electrons


A muon going through the detector


Stopping Muon


Stopping Muon – Decay Electron


Atmospheric Neutrino Production

Ratio predicted to ~ 5%

Absolute Flux Predicted to ~20% :

2

ee


Atmospheric Oscillations

about 13,000 km

about 15

km

Neutrinos produced in

the atmosphere

Neutrinos produced in

the atmosphere

We look for transformations

by looking at s with different distances from production

SK


Atmospheric Neutrino Interactions

n p

W+

Reaction Thresholds

Electron: ~1.5 MeV

Muon: ~110 MeV

Tau: ~3500 MeV

Charged Current Neutral Current

e e

n p

W +


Telling particles apart

MuonElectronMuonElectron


Muon - Electron Identification

PID Likelihood

sub-GeV, Multi-GeV, 1-ring

Monte Carlo (no oscillations)

We expect

about twice as

many as e


Super-K Atmospheric Data Set

• 1289.4 days of data (22.5 kilotons fiducial volume)• Data Set is divided into:

– Single and Multi Ring events– Electron-like and Muon-like– Energy Intervals

• 1.4 GeV< Evis >1.4 GeV• Also Evis< 400MeV (little or no pointing)

– Fully or partially contained muons (PC)– Upward going muons - stopping or through going

• Data is compared to Atmospheric Monte Carlo– Angle (path length through earth)– Visible energy of the Lepton


Low Energy Sample

No Oscillations

Oscillations (1.0, 2.4x10-3eV2)


Moderate Energy Sample


Multi-GeV Sample

Oscillations (1.0, 2.4x10-3eV2)

No Oscillations

UP going Down UP Down


Multi-Ring Events


Upward Going Muons


Summary of Atmospheric Results

Best Fit for to

Sin22 =1.0,

M2=2.4 x 10-3eV2

2min=132.4/137 d.o.f.

No Oscillations

2min=316/135 d.o.f.

99% C.L.

90% C.L.

68% C.L.

Best Fit

Compelling evidence for to atmospheric neutrino oscillations


Tau vs Sterile Neutrino Analysis


Tau Appearance?

• Tau’s require greater than 3 GeV in neutrino energy– This eliminates most events

• Three correlated methods were used– All look for enhanced upward going multi-ring events

• All show slight evidence for Tau appearance• None are statistically significant


The 0 sample

• For to s the rate of NC events is reduced as

compared to to which is the same as no

oscillations.• The SK NC enriched sample is only about 1/3

from NC interactions.

• The 0 sample is the cleanest NC signal

• Until K2K the error in (0) (~1-2 Gev) has been as large as the effect!


0 Peaks


New Results


Neutrinos From Solar Reactions


The Solar Neutrino Problem


Oscillation Parameter Space

LMA

LOW

VAC

SMA


Expected Day – Night Asymmetry

Bahcall


Solar Neutrinos in Super-K

• The ratio of NC/CC cross section is ~1/6.5

W

e

-

e

e

- e

-

Charged Current (electron ’s only)


Solar Neutrinos in Super-K

• Super-K measures:– The flux of 8B solar neutrinos (electron type)– Energy, Angles, Day / Night rates, Seasonal

variations• Super-K Results:

– We see the image of the sun

from 1.6 km underground

– We observe a lower than predicted

flux of solar neutrinos (45%)


Low Energy Electron in SK


Solar Neutrinos

From SunFrom SunToward SunToward Sun

)s cm 10 x (syst)0.03(stat) (2.35

ssm) (syst) )0.005(stat (0.465

1-2-608.00.07

0.0160.015 -

e

SSM:Bachall 2000 Flux:

8B 5.05x106 /cm2/s

Spectrum Ortiz et al


Global Flux allowed parameter space


Energy Spectrum


Day / Night - BP2000+New 8B SpectrumPreliminary

(syst)(stat)0.0200.021N)(D

21

DN 0.0130.012-


Seasonal Variation


Combined Results


SNO Results - Summer 2001

• SNO measures just e

• SK measures mostly e but also other flavors (~1/6 strength)

• From the difference we see oscillations!

}This is from

&

neutral current


Combining SK and SNO

• SNO measures e= (35 ± 3 )% ssm

• SK Measures es= (47 ± .5 ± 1.6)% ssm

• No Oscillation to active neutrinos:– ~3 difference

• If Oscillation to active neutrinos:– SNO Measures just e

• This implies that ssm (~2/3 have oscillated)

– SK measures es =(e + ( /6.5)

• Assuming osc. SNO predicts that SK will see es ~ (35%+ 65%/6.5) ssm = 45% ± 3% ssm


SK & SNO Flux Measurements


Super-K Disaster - Nov 12, 2001

• Chain reaction destroyed 7000 ID and 1000 OD Tubes

• The cause is not completely understood, but it started with a bottom pmt collapse.

• The energy release comes from a 4 T column of water falling

• There are plans to rebuild…


Disaster (Continued)


Rebuild at ½ of Original Coverage


What Have We Learned?

• Neutrinos undergo flavor oscillations– Neutrinos have mass– Flavor mixing

• 3 mixing angles, 2 m2 & 1 mass (or 3 masses)

• Atmospheric– Maximal mixing ()– m23 2 ~ 2 x 10-3 eV2

• Solar– Looks like active not sterile neutrinos– m12 2 ~ ? – Mixing angle ?


What We’ll Hopefully Know Soon

• Kamland, Borexino,SNO,SK,Cl,Ga– Which solution for solar neutrinos

• first m122

• first

• Accelerator (MINOS, JHF, K2K,…)– Better m23

2 , better

– First measurement of

• If not zero

– CP Violation in neutrinos possible


Questions

• Neutrino Mass– Majorana or Dirac?

• Lepton Number Violation?• GUTs?

– What is the absolute Mass Scale? • Why neutrinos have such small mass?• Which mass Hierarchy of 3 mass states?• Cosmology?

• Mixing Matrix– Why mixing structure different then CKM in quarks?

• GUTs?– CP Violation?

what have we learned from super-k? before super-k sk-i (1996-2001) atmospheric solar sno & sk-i

Documents