11-September-2005 C2CR2005, Prague 1 Super-Kamiokande Atmospheric Neutrino Results Kimihiro Okumura ICRR Univ. of Tokyo ( [email protected]) 11-September-2005

11-September-2005 C2CR2005, Prague 1

Super-Kamiokande AtmospheSuper-Kamiokande Atmospheric Neutrino Resultsric Neutrino Results

Kimihiro Okumura ICRR Univ. of Tokyo

([email protected])

11-September-2005C2CR2005, Prague


OutlineOutline

Super-Kamiokande-I Results new → oscillation analysis search for tau neutrinos search for 13

neutrino flux study

Status of Super-Kamiokande-II Analysis


Super-KamiokandeSuper-Kamiokande

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

SK-I SK-IIIreconstruction

SK-III will start on June 2006.

• 50kton cylindrical water Cherenkov detector (22.5kt fiducial vol.)

• 1000m underground (2700m water equiv.)

• optically separated into ID and ODSK-I

40% Photocathod coverage 11146 Num. of inner detector PMTs

SK-IIaccident

PMT enclosure :Acrylic (front) andFiberglass (back)

SK-II

518219%


Observation of Atmospheric NeutrinoObservation of Atmospheric Neutrino

Fully Contained (E ~1GeV, e )

Stopping (E~10GeV, )

Partially Contained (E ~10GeV, )

Through-going (E~100GeV, )

Event classification

sensitive energy: 0.1GeV ~ 10TeV


Zenith Angle Distributions (SK-I)Zenith Angle Distributions (SK-I)

< <

> >

– oscillation (best fit)

null oscillatione-like -like FC and PC : 1489 days

Up-going : 1646 days

Preliminary


Previous oscillation analysisPrevious oscillation analysis

Question: Can single analysis give the best sin2(2) and m2 ?

Zenith angle analysis : UP/DOWN ~ sin2(2) good for sin2(2)

L/E analysis : dip ~ /2 good for m2

Allowed region ofprevious zenith and L/E

cos

Nu

mb

er

of

eve

nts

Da

ta /

MC


Oscillation analysis with finer binningOscillation analysis with finer binning

Important energy range to see the oscillation dip = multi-GeV

Finer energy bins for multi-GeV events

Important energy range to see the oscillation dip = multi-GeV

Finer energy bins for multi-GeV events

Full

oscillation 1/2 osci.

Expected sensitivity with 5yr MC (sin22, m2)truth = (1.00, 2.510-3 eV2)

previous zenith (180bins)

L/E

finer binning (370bins)

zenith angle analysis with finer energy binning

gives better sensitivity for both sin2(2) and m2


Allowed region with finer binningAllowed region with finer binning

Previous zenith-angle analysisL/E analysis

90% CL allowed region:sin22> 0.93

2.0 < m2 < 3.0×10-3eV2

90% CL allowed region:sin22> 0.93

2.0 < m2 < 3.0×10-3eV2

Preliminary


Search for CC Search for CC events events

CC events

hadrons

Only ～ 1.0 CC

FC events/kton ・ yr Only ～ 1.0 CC

FC events/kton ・ yr

hadrons CC MC

appears only for up-going events

use down-going events for control sample

events are accompanied with many hadronsevent topology similar to other hadronic events

likelihood (or NN) analysis


Tau-like events selection criteriaTau-like events selection criteria

Visible energy > 1.33 GeV (multi-GeV energy)

Multi-ring events (event w/ hadron particles)

Most energetic ring is e-like (showering event)

log(likelihood) > 0 or

NN > 0.5


Likelihood variablesLikelihood variables

visible energy

Max. momentum for -like ring

Clustered sphericity in the center of mass frame

Max distance from primary and decay-e vertex

Sphericity in the lab fame

Number of candidate rings

MC

Down-going data

Down-going , e MC

Preliminary


Tau likelihood distributionsTau likelihood distributions

downwarddownward

DATABG-MCtau-MC

Cut

likelihood

upwardupward

MC)

DATABG-MCtau-MC

Cut

likelihood

Num

ber

of e

vent

s

Tau-like events : Likelihood > 0

Preliminary


Likelihood analysis NN analysis

, e, & NC background

, e, & NC background

Data Data ×1.82 MC ×1.93 MC

coszenith coszenith

Nu

mb

er

of e

vent

s

145±48(stat)+9 / -36 (osc. para. uncertainty)

152±47(stat)+12 / -27 (osc. para. uncertainty)

79±31(syst) 79±31 (syst)

Fitted # of events

Expected # of events

Preliminary

Zenith angle dist. and fit resultsZenith angle dist. and fit results


Search for non-zero Search for non-zero 1313

Non-zero 13 will enhance →e oscillation in multi-GeV energy due to matter effect in Earth

Electron appearance is expected in upward-going events

s213=0.05 s213=0.00 null oscillation

Electron appearance

1+multi-ring, e-like, 2.5 - 5 GeV

P(→e)

coszenithNeutrino Energy (GeV)

cos

zen

ith

E

LmP e

22

132

232 27.1

sin2sinsin)(

Three flavor oscillation analysis with m2solar=0 assumption :


MMulti-GeV electronsulti-GeV electronsUP/DOWN asymmetryZenith angle

single-Ring electron

multi-Ring electron

Preliminary

No significant excess due to matter effect in upward-going multi-GeV electron sample

Data

No oscillation

Three flavor best fit(normal hierarchy)


Allowed region for Allowed region for 1313

Distributions are best fitted when sin2(13)=0

Consistent with two flavor oscillation

sin2(13)<0.14 allowed in 90% C.L. from SK-I data

Normal hierarchy (m2>0)

2min/ndf = 376.82/368 @(2.5x10-3, 0.5, 0.0)

Preliminary

90%CL

99%CLexcluded by CHOOZexcluded by CHOOZ

m2

(eV

2 )

sin2

13

sin223 sin213


Atmospheric Atmospheric flux measurement flux measurement

Recent neutrino flux calculations have improved due to accurate measurement of comic-ray protons / muons

Approximately 20% difference still exists among flux models in higher energies

Neutrino flux calculation

cosmic-ray proton flux


ee and and energy spectrum energy spectrum

SK-Ie and event rates are compared with expectation in each energy range

Neutrino energies are estimated from simulation

Neutrino oscillation included for expected

→(m2, sin22) = (2.5x10-3 eV2,1.0) assumed

expectation

data

sub-GeV

multi-GeV

sub-GeV

multi-GeV

PC

upmu-stopupmu-thru

Eve

nts

/ yr

/ G

eVE

vent

s /

yr /

GeV

Neutrino energy(GeV)

e

Preliminary


Comparison with flux modelsComparison with flux models

Neutrino flux models: HKKM04 Phys. Rev. D70 043008 (2004)

Bartol Phys. Rev. D70 023006 (2004)

Fluka hep-ph/0305208

Systematic uncertainties: detector efficiency cross section ~10% oscillation ~4% for

Results: absolute flux and spectrum are

consistent within systematic errors

HKKM04 and Fluka under-estimated high energy flux

Dat

a /

Exp

ecta

tion

e

Preliminary

Error bar : (stat.)2+(sys.)2


New HKKM flux calculationNew HKKM flux calculation

HKKM flux revised: modified hadron interaction

model see Dr. Honda’s talk

Agreement in high energy becomes better

Dat

a /

Exp

ecta

tion

e

Preliminary

Error bar : (stat.)2+(sys.)2


Zenith Angle Distributions (SK-II)Zenith Angle Distributions (SK-II)

< <

> >

– oscillation (best fit)

null oscillatione-like -like

FC and PC : 627 daysUp-going : 609 days

Preliminary


Preliminary

Preliminary

Contours for SK-IIContours for SK-IISK-II SK-I

SK-II data are consistent with SK-I data

SK-I + SK-II combined analysis : next step


SK-II L/E analysisSK-II L/E analysisL/E analysis was carried out for the SK-II data with the identical selection criteria as those in SK-I.

SK-II SK-I

Osc.

Decay

Decoh.

Consistent with SK-I.Oscillation still gives the best fit to the data.

Consistent with SK-I.Oscillation still gives the best fit to the data.

Preliminary


SummarySummary

SK-I analysis results: New → oscillation analysis with finer binning give

s more stringent constraint :• sin22 > 0.93, 2.0<m2<3.0x10-3 eV2 (90%C.L.)

Data are consistent with appearance

No evidence for multi-GeV electron appearance due to non-zero 13

Neutrino flux calculation models are compared and consistent with data

SK-II data was analyzed independently and consistent with SK-I

End

Documents

11-September-2005 C2CR2005, Prague 1 Super-Kamiokande Atmospheric Neutrino Results Kimihiro Okumura ICRR Univ. of Tokyo ( [email protected]) 11-September-2005