Jan.-2002 @CERN

Review of experimental results on atmospheric neutrinos

Introduction Super-Kamiokande MACRO Soudan 2 Summary

Univ. of Tokyo, Kamioka ObservatoryMasato Shiozawa

Jan.-2002 @CERN

Super-Kamiokande detector

39.3 m

42 m

Water Cherenkovdetector

1000 m underground 50,000 ton (22,500 ton fid.) 11,146 20 inch PMTs 1,885 anti-counter PMTs

C Scientific American

Jan.-2002 @CERN

Phase-1 quick restart of K2K rebuild SK with about half PMT density by autumn of 2002 atmospheric ν, proton decay search solar ν, SN watch with higher energy threshold PMT vessel to prevent from chain reaction of explosion

Phase-2 full detector before the time of commissioning of JHF

Rebuilding Super-K

acrylic vessel acrylic+(FRP or stainless steel)

Jan.-2002 @CERN

Event classification of atmospheric ν

e/e/

Fully Contained (FC) Partially Contained (PC)

Upward through-going

Upward stopping

Contained event(sub-GeV, multi-GeV sample)

Eν ～ 1 GeV Eν ～ 10 GeV

Eν ～ 10 GeV (stop μ ） 100 GeV (through μ ）

Jan.-2002 @CERNZenith angle distributions(FC+PC+up-μ)

No oscillation (χ2

=393.4/172 d.o.f)

Best fit (m2=2.5x10-3eV2,sin22=1.00 χ2

min=157.5/170 d.o.f)νμ⇔ντ 2-flavor oscillations

～ 15km～ 13000km～ 500km ～ 13000km ～ 500km

Jan.-2002 @CERN

Combined allowed regions

→

Super-KamiokandeBest fit(Δm2=2.5×10-3,sin22θ=1.0

χ2min=157.5/170 d.o.f)

No oscillation

(χ2 =393.4/172 d.o.f)

Δm2 = (1.6 ～ 3.6)x10-3eV2

sin22θ > 0.9 @ 90%CL

Jan.-2002 @CERN

νμ⇔ντorνμ⇔νsterile?

Using MSW effect and enriched NC sample

→: No matter effect / NC interaction

→s : With matter effect / No NC interactionNeutrino oscillation in matter:

( ) = ( cosm

s

sinm

- sinm cosm ) 1 2( ) sin22m

sin22=

(cos2sin22= 2 GFnnE / m2 √

For sin22= 1

sin22m1~ + 1

And for E = 30~100 GeV ≫1 andsin22m≪1 Suppression !

Test zenith angle of NC enriched events, high energy PC and through-going muon events.

A

llow

ed

reg

ion

fro

m F

C s

ing

le-r

ing

sam

ple

Jan.-2002 @CERN

νμ⇔ντorνμ⇔νsterile?

→s

→Evis> 5 GeV

<E>=~25 GeV

Zenith angle of high-E PC

up

/dow

n r

ati

o

cosΘ

→s

→

１ checking matter effect (partially contained events)

Up/down ratio of high-E PC

10-3 10-2

Δm2

Jan.-2002 @CERN

νμ⇔ντorνμ⇔νsterile?

→s

→

2 checking matter effect (upward through going μ)

Zenith angle of up through μ

cosΘ

vert

ical/

hori

zon

tal ra

tio

→

→s

V/H ratio of up through μ

10-3 10-2

Δm2

Jan.-2002 @CERN

νμ⇔ντorνμ⇔νsterile?

→s

→

3 checking NC enriched sample (multi-ring events)

Zenith angle of NC sample Up/down ratio of NC sample

cosΘ

up

/dow

n r

ati

o →

→s

10-3 10-2

Δm2

pu

re ν

μ⇔

νste

rile o

scilla

tion

sare

dis

favore

d w

ith

ab

ou

t 9

9%

CL

99%

CL e

xclu

ded

90%

CL e

xclu

ded

E

xclu

ded

reg

ion

f

rom

th

ree t

est

sam

ple

s

Jan.-2002 @CERN

Neutrino Decay

Neutrino Decay is a possible solution of the atmospheric neutrino problem (V.Barger et al.)

2

3

322μμ ))

E

L

2τ

mexp(sin(cos)νP(ν Survival probability without

neutrino oscillation(Δm2<<1)

FC 1-ring + PC + up-μdata are consistentwith neutrino decayscenario χ2

min=147.0/152 dof

Jan.-2002 @CERNNeutrino Decay study with NC enriched sample

Deficit of up-going NCevents is expected forν decay scenario

)0.07(stat.1.06down

up

data

perform χ2 test to constrain neutrino decay parameters

Jan.-2002 @CERN

Result on neutrino decay study

The 99%CL allowed region by FC 1-ring+PC+up-μ sampleis excluded at 99%CL by the NC enriched sample.

Jan.-2002 @CERNUpdate of neutrino crosssection(very preliminary)

c22

F2N2

QE θcosGMdq

dσ

Update parameters GF=1.16639×10-5

sinθc=0.22 ↓σ is increased by 5.8% (energy indep.)

free proton target bound nucleon target

blue newMagenta old

μν

μν

μν

blue newMagenta old

Jan.-2002 @CERNUpdate of neutrino flux(very preliminary)

HONDA 1D (official)

Fluka 3D

HONDA 3D (new) 3D calculation dpmjet3 interaction model primary flux from BESS/AMS Ikenoyama effect

sub-GeV e

multi-GeV μmulti-GeV e

sub-GeV μ

Jan.-2002 @CERN

MACRO detector76.6m×12m×9.3m

streamer tubes

liq. scintillation counters(TOF system)

Jan.-2002 @CERN

Up throughgoing muons in MACRO

Obs. 863evObs. 809ev(BG sub.)Exp. 1122ev.(Bartol)

Obs./Exp.=0.721±0.026(stat)±0.043(sys)±0.123(th)

Jan.-2002 @CERN

90% allowed region from MACRO

χmin@(1.0,2.5×10-3eV2)

νμ⇔ντ

consistent with Super-K

Jan.-2002 @CERN

Low energy events in MACRO

Obs. 154ev.Exp. 285ev.Obs./Exp. = 0.54±0.04(stat)±0.05(sys)±0.13(th)

Obs. 262ev.(BG sub.)Exp. 375ev.Obs./Exp. = 0.70±0.04(stat)±0.07(sys)±0.17(th)

consistent with up throughgoing muon results

Th

e S

ou

dan

2

dete

cto

r

Fid

uci

al m

ass

: 7

70

ton

s

(Ar/

CO

2, 0.8

cm/μ

sec)

×224

Man

n@

neu

trin

o2

00

0

Jan.-2002 @CERN

HiRes event summary in Soudan 2

νμ νe

Obs. 114.0±10.7 140.0±11.8Obs.(Bgsub) 106.3±14.7 132.8±13.4Exp.(Bartol) 158.5±4.8 132.8±4.4 (renorm. to νe data)

HiRes sample Recoil proton + lepton(>150MeV/c) single lepton(>600MeV/c) multiprong (Evis>700MeV and |Σp|>450MeV/c)

R=(μ/e)data/ (μ/e)MC=0.67±0.12

Jan.-2002 @CERN

Soudan 2 allowed region

χmin@(0.9,7.9×10-3eV2)

consistent with Super-K

Jan.-2002 @CERNSummary of atmospheric ν observations

Atmospheric neutrinos are measured using various techniques in SK, MACRO, Soudan 2

→ all consistent with each other

Δm2=1.6 ～ 3.6×10-3, sin22θ>0.9 for νμ⇔ντ

sterile neutrino is disfavored as a prominent oscillation partner

neutrino decay scenario with Δm2<<1 is excluded at

99% C τ likelihood distributions