1 Introduction and Detector

Kamiokande and Super-Kami ok ande

Yoichiro Suzuki

Kamioka Observatory, Inst i t ut efor Cosmi c Ray Research, The Uni versi t yof Tokyo, Hi gashi -Mozumi ,

Kami oka- chou, Gi f u,560 Japan

Neutrino astrophysics has begun in 1987 when Kamiokande observ ed the neutrino

burst from a sup erno va SN1987A. Kamiok ande succeeded to observ e solar neutrinos

and demonstrated at the �rst time that the observ ed neutrinos are coming from the

direction of the sun and con�rmed the long standing solar neutrino problem. The

atmospheric neutrino anomaly was �rst pointed out by the Kamiok ande experimen t

in 1988 and is now though t to be an evidence of a neutrino oscil lation. Sup er-

Kamiok ande, the bigger successor of Kamiok ande, started its op eration in April

1996. The accum ulated data have already exceeded those of Kamiok ande in its

quality and quan tity. New insights into neutrino masses will be obtained from the

results of SK in very near future.

1 Introduction and Detector

The giganti c i magi ngwater Cherenkov detectorslocated1000 m underground (2,700m water equi va-

l ent), Kami okande [1] and Super-Kami okande [ 2] ,are the powerful tool to understand neutri noprop-

erti esand study proton decay. The vol ume of Kami ok ande (KM) i s 4, 500 tons (948 photo-mul ti pl i er

tubes (PMTs) are arrangedto watch i nnervol ume of 2, 140tons),and that of Super-Kami okande (SK)

i s 50, 000 tons (11, 146PMTs are arranged f or the i nner vol ume of 32, 000 tons). KM has startedi ts

operati oni n1984, pri mari l yto study nucl eondecay [ 3]and l ateri n1987, KM has upgraded to be abl e

to detect l ow energy events above 9. 3MeV to study sol arneutri nos.In February, 1987, just af terthe

upgrade, KM has observed the neutri nobursts f roma supernova SN1987A [ 4] expl oded i nthe Large

Magel l ani cCl oud, 160k l i ght years away. Thi s i sthe �rstobservati onof astrophysi calneutri nosother

than sol arneutri nos,and i sthe begi nni ngof neutri no- astronomy. KM has succeededto obtai na �ni te

sol arneutri no ux i n 1987, soon af terthe neutri noburst detecti on. Thi s observati onprovi ded the

�rst evi dencethat the sun createshi gh energy neutri nosproduced by the 8B decay and con�rmed the

sol arneutri noprobl em[ 5] .Unexpectedanomal y of the atmospheri c neutri nos,whi ch i s now thought

to be an i ndi cati onof a neutri noosci l l at i onwas �rst poi nted out by the KM experi ment i n1988 [ 6] .

KM has stopped ma j or physi csrun i nFebruary i n 1995 and stopped i tsoperati oni n summer 1997.

The l aststage of the experi ment i s sol el ydevoted to a supernova watch. The physi csachi evemen ts

and the hi storyof KM are summari zed i nref erences[ 7] [ 8] .

Si nce the space i s l i mi tedi n thi s paper, we mostl y di scuss about the SK experi ment i n the

f ol l owi ng parts and physi csdi scussi onwi l l al sobe l i mi tedto neutri noosci l l at i onstudi es.

The schemati c vi ewof the SK detectori sshown i n�gure 1. SK i snot onl ybi ggerthan KM i ni ts

s i ze,but al sohas betterenergy, posi t i onand di recti onalresol uti ons:14%(19%), 26o(27o) , 87cm(100cm)

f or10 MeV el ectrons,respecti vel y(thenumbersshown i nthe parenthesesare thosef orKM). The better

resol uti onsare achi eved by the i ncreasednumber densi ty of PMTs. The PMTs are arranged on the

i nner surf aceof the detectorwi th the densi ty of 2 PMTs / 1 m2 (1 PMT / 1 m2 f or KM) whi ch

covers the 40% of the i nner surf ace. Thi s arrangement more than comp ensates the l i ght l oss (due

to the attenuati on) of the l onger travel di stance of the Cherenkov l i ght than KM. Outsi de of the

Figure 1: A schematic vi ew of the 50,000 ton imagi ng water Cherenk ov detector, Super-Kami ok ande. The

detector i sa cyli ndri cal shap e, 39. 3m i ndi ameter and 42m inhei ght. The i nner vol ume of 32, 000 tons, 16. 9m

i n radi us and 36. 2m i n hei ght, i s vi ewed by 11, 146 photo-m ul ti pl i ertubes wi th 50 cm di ameter.

inner detector is surrounded by the outer detector of 2m thic k activ e water slab view ed by 1,185 20

cm PMTs. This provides the shield against the external gamma rays and neutrons, and positiv ely

iden ti�es incoming particles like through-going cosmic ray muons, particles exiting the detector and

so on.

The energy of neutrinos, whic h we are interested in detecting in SK, ranges from a few MeV to

more than 100 TeV. The interactions of neutrinos in the detector will be describ ed later for solar and

atmospheric neutrino cases.

The relativistic charged particles tra versing faster than the ligh t velo city in the water emit

Cherenk ov ligh ts with an angle of

cos� =1

�n;

where �=42 � for particles with �=1, and n is the refractiv e index of water. Those ring image Cherenk ov

ligh ts are detected by the PMTs. The hit pattern, pulse heigh t and timing information are used to

reconstruct event vertex, direction, energy and particle sp ecies. The details of the event reconstruction

can be found in one of those theses[9].

2 Operation and Cali brati on

Sup er-Kamiok ande (SK) has started the op eration on 1st of April in 1996 and been con tinuously taking

data with the cum ulativ e live-time close to 90%. Most of the time not for taking data are sp ent to

calibrations, esp ecially to those using electron LINAC [10].

Water is essen tial for the SK exp erimen t. It serv es as a target. But the ligh t scattering and

absorption a�ects on the energy resolution, vertex resolution and so on. For the �rst two mon ths after

the start-up, there was a rapid impro vemen t of the water transparency , since we had just started to

circulate the water a few da ys before the start-up. Therefore in the analysis presen ted here we ha ve

not used the data tak en in April and Ma y, 1996. There is a small change of the water transparency

during the exp erimen t. The water transparency , whic h is ab out 100m at 420nm no w, is monitored and

measured by sev eral metho ds: muon-deca y electrons, through-going muons and a direct measuremen t

beam energy = 16.315 MeV

energy distribution for each linac energy x=-813.1 y=-70.7 z= 27 1997 Sep

0200400600800

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25energy (MeV)

+ DATA- MC


0250500750

1000

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25energy (MeV)

+ DATA- MC


0250500750

1000

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25energy (MeV)

+ DATA- MC


0

500

1000

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25energy (MeV)

+ DATA- MC

Figure 2: The energy distri buti onof LINAC

data taken at the central hei ght of the detector,

but wi th about 8m o� the center towards the

si de wal l . The energi es of the el ectrons are at

16. 3,13. 7, 11. 0 and 8. 9MeV f romthe top �gure

to the bottom �gure. The resul ts f rom the MC

simul ati ons are al so shown by the sol i d l i nes.

The data and the MC agree very wel l .


angular distribution for each linac energy x=-813.1 y=-70.7 z= 27 1997 Sep

0

500

1000

0 20 40 60 80 100 120 140 160 180theta (degree)

+ DATA- MC


0

500

1000

0 20 40 60 80 100 120 140 160 180theta (degree)

+ DATA- MC


0250500750

1000

0 20 40 60 80 100 120 140 160 180theta (degree)

+ DATA- MC


0250500750

1000

0 20 40 60 80 100 120 140 160 180theta (degree)

+ DATA- MC

Fi g ur e3: Same as �gure 2, but for the angul ar

di stri buti ons.

usi nga Dye la s e ra nda CCD came r a .A Chang eof the wa t e rt r a ns pa r e nc ywa s t a ke n i nt oa c c o unt

whe nt hee ve nt e ne r g ywa s r e c o ns t r uc t e d.

Ano t he ri mpo r t a nt e l e me nt r e l a t e dt o t hewa t e rqua l i ty i sRa do nc o nc e nt r a t i o ni nt hewa t e r .

The da ug ht e ro f t heRado nde c ay (214Bi )e mi t s� r ays wi t ht hemaxi mum e ne r g yo f 3 . 2 6Me Vandt he

r e s o l ut i o nt a i lo ft hi sde c ay pr oduc t si st hema jo rba ckg r o undf o rt hes o l a rne ut r i nome a s ur e me nt .The

c ur r e nt c o nc e nt r a t i o no f Rn i nt hewa t e ri sme a s ur e dt obe l e s st ha na f e wmBq/m3 whi ch i sa l r e a dy

mo r et ha na no r de ro fma g ni t udel owe rt ha nt heKM l e ve l ,buti ss t i l la s o ur c eo f t heba ckg r o und.We

a r emaki nge xt e ns i ve e �o r t st omake f ur t he rr e duc t i o nso f Rn i nt hewa t e r .Ana l ys i st hr e s ho l do f 6 . 5

Me V c ur r e nt l ys e ti sma i nl yde t e r mi ne dby t hi sba ckg r o undl e ve l .

Tr i g g e ri smade by t henumbe ro f PMT hi t swi t hi n2 00 ns e ct i mewi ndow. Da t aa r ebe i ngt a ke n

wi t htwo t hr e s ho l dl e ve l s |t hel ow e ne r g y( LE)a ndt hes upe r -l ow e ne r g y( SLE)t r i g g e r .The t hr e s ho l d

o f t heLE t r i g g e ri s�2 9 hi t sc o r r e s po ndi ngt oa bo ut5 . 7Me V on a n ave r a g e .The SLE t r i g g e ri ss e t

a t 2 4 hi t s( 4 . 6Me V on a n ave r a g e ) .The e ve nt ve r t e xo f t ho s ee ve nt so nl yhav i nga SLE t r i g g e ra r e

qui ck l yr e c o ns t r uc t e da nda c r ude�duc i a lc uta r ea ppl i e di nt heo n- l i neho s tc omput e r .Thi ss e l e c t i o n

r e duc e st he10 0Hz SLE t r i g g e rt oa bo ut5 Hz whi ch i sa ddo n t o po f t he1 1Hz o f t heLE t r i g g e r .

The e ne r g yo f a n e ve nt i sde t e r mi ne ddi �e r e nt l yf o rhi g he ne r g y( a t mo s phe r i cne ut r i no )a nd

l ow e ne r g y( s o l a rne ut r i no )e ve nt s . In t hea t mo s phe r i cne ut r i noa na l ys i s ,t hee ne r g yi sde t e r mi ne d

ba s e do n t henumbe ro f pho t o - e l e c t r o ns( 9p. e .a ppr ox i ma t e l yc o r r e s po ndst o1 Me V) a ndi nt hes o l a r

neutrino analysi st he ener gyi sdet ermi nedby t he number of hi tPMTs s i ncei ns uch l ow ener gymos t

of t hePMT hi t sar eone phot oel ect r ons(5.6 hi t sappr oxi mat el ycor r es ponds t o 1 MeV).

The accur acyof t he ener gys cal ef orhi ghener gyevent s i ses t i mat edt o be �2. 4%by t hevar i ous

met hods by us i ngcosmi cr ay t hr ough-goi ngmuons , s t oppi ngmuons ,muon- decay el ect r ons ,i nvar i ant

mas s of �0s and s o on. The ener gyr es ol ut i onf orel ect r onsand muons ar e2. 5%/qE(GeV )+0. 5%and

3%, r es pect i vel y.

In t hes ol arneut r i noanal ys i s ,t heabs ol ut eener gyof t heevent si scal i br at edby us i ngt heel ect r on

beampr oducedby t heel ect r onLI NAC pl acedneart heSK t ank,whi ch cover st heener gyr angebetween

5 and 15 MeV, exact l ymat chi ngt o t he ener gys pect r umof t he s ol arneut r i nos .The LI NAC was al s o

us edt o obt ai nt he angul arr es ol ut i onand t he ver t exr es ol ut i on.The beam ener gyof t he LI NAC was

cal i br at edby t he germani umdet ect orwhi ch was cal i br at edby us i ngt he mono chr omat i cel ect r ons

s el ect edby a magnet i cs pect r o- met er .The typi calener gyand angul ardi s t r i but i onst aken at var i ous

ener gi esand at t he i nject i onpos i t i onof about 8 m f r omt hewal lar e s hown i n�gur es2 and 3.

The uni f ormi ty t hr oughoutt he ent i r e�duci alvol ume and t he di r ect i onaldependence wer e

checked by t he LI NAC dat a t aken at di �er ent pos i t i ons , - r ay s our cesus i ngNi ( n, )Ni0

r eact i ons

pl acedman y di �er ent pl acesi nt he det ect orand t he s pal l at i onevent swhi ch happen uni f orml yi nt he

det ect orvol ume. Af t ercons i der i ngt hos ee�ect s ,t he ener gys cal eer r orf ort he t ot al ux meas ur ement

i ses t i mat edt o be �0. 85%. The det ai l sof t he cal i br at i onwi l lbe f oundi nr ef [10],[ 18] .

3 Physics with Super-Kamiokande

The pr i mar i l yphys i css ubj ectof Kami okande (KM) i sa s ear ch f ornucl eondecay; t hename Kami oka-

NDE comes f r omKami oka Nucl eonDecay Exper i ment . Af t ert he obs er vat i onof t he neut r i nobur s t

f r omSN1987A and t he s ucces sof t he s ol arneut r i nomeas ur ement , peopl ewoul dcal lt he exper i ment

as Kami oka Neut r i noDet ect i onExper i ment .

The mai n pur pos esof Super - Kami okande ( SK) ar e,o� cour s e,t o s ear ch f ornucl eondecay wi t h

an or derof magni t udebet t ers ens i t i vi ty, t omeas ur eneut r i nosf r omt hes un and t o s t udyatmos pher i c

neut r i nos .

I f neut r i noshave �ni t emas s es and non- zer omi xi ngsamong mas s ei gen- s t at es ,t henneut r i nos

pr oducedat t he avor ei gen- s t at esma y os ci l l at eamong di �er ent s t at eswi t ht he f ol l owi ng pr obabi l i ty

( f ortwo neut r i noos ci l l at i oncas e) ,

P (�� ! ��) = sin22�si n2�1:27 ��m2 � L=E

�;

wher e E i st he ener gyof neut r i noand L i st he di s t ancebetween t he s our ceand t he det ect or :L and

E ar e det ermi nedby t he exper i ment al ar r angement . I f �m 2�E/L, t henP (�� ! ��) = 1

2si n22�,

and i f�m 2�E/L, t henexper i ment s har dl ys ee t he os ci l l at i one�ectand ar e abl et o s et t he upper

l i mi tby si n22� � �m2 � 0:8[E=L]qP (�� ! ��) . I f �m

2�E/L, exper i ment s ar e i na mos t opt i mum

pos i t i on.For exampl e,f ora con�gur at i onE�1GeV and L�10 t o 10, 000km ( i nt he cas eof t he s ub-

GeV atmos pher i cneut r i nos ) ,�m2 � 10�1 � 10�4eV 2 and f orE�10 MeV and L� 150, 000, 000km ( f or

'Jus t So' s ol arneut r i noos ci l l at i on[ 11] ) ,�m2 � 10�11��10eV 2.

When neut r i nospas s t hr ought he medi a, t he el ect r onneut r i nosobt ai nan addi t i onalpot ent i al ,p2GFne t hr ought he char gedcur r ent f orwar d s cat t er i ngampl i t ude.The equat i onof t he neut r i no

propagation for �e ! �� case i s ,

id

dt

0@ �e

��

1A =

0@ �

�m2cos2�

4p+p2GFne

�m2sin2�

4p

�m2sin2�4p

�m2sin2�4p

1A0@ �e

��

1A :

The mi xi ngangle i nt hemat t erbecomes ,

tan2�m =tan2�V

1 � (2pp2GFne)=�m2cos2�V

:

If ( 2pp2GFne)=(�m2cos2�V ) = 1 ( r es onancecondi t i on) ,t hent hemi xi ngangl ei nt hemat t erbecomes

maxi mal , even t hough t he vacuum mi xi ng angl ei s smal l . I f t he neut r i nopr opagat esadi abat i cal y

t hr ought he r es onancer egi on,el ect r onneut r i noconver t si nt o ��'s . For 10 MeV neut r i nospr oducedi n

t he s un s at i s f yt he r es onancecondi t i onwhen pas s t hr ought he s un ( 0< ne/NA < 100 ) i f

�m2 � 1:6 � 10�4eV 2:

Adi abat i ccondi t i onf ort he 10 MeV neut r i nosi s ,

�m2sin22�

cos2�� 6:3 � 10�8eV 2:

Thes e condi t i onsdet ermi nest he par amet err egi onexpl ai ni ngt he ' obs er ved' conver s i onr at e.

Sear ches f orneut r i nomas s es have beendone not onl yby t he neut r i noos ci l l at i ons ear ches ,but

al s oby ot hermet hods l i ke di r ectmas s s ear ches and doubl ebet a decay exper i ment s al t hought he

i ndi cat i onof t he �ni t eneut r i nomas s es onl ycome f r omos ci l l at i onexper i ment s . The cur r ent upper

l i mi ton t he neut r i nomas s f r omt he exper i ment s l ooki ngdi r ect l yf ort he evi denceof �ni t eneut r i no

mas s es ar e,

m�� 18:2MeV=c2[12]

m�� 170keV=c2[ 13]

m�e � 3:5 � 5:6MeV=c2[ 14]

The bes tl i mi t sf ort heMa jor ananeut r i nomas s es of 0. 48� 1. 5eV2 [ 15]was obt ai nedf r omt he

doubl ebet adecay exper i ment (We have i ncl udedt he uncer t ai nty of t he nucl earmat r i xel ement ) .

As you s eeabove, neut r i noos ci l l at i onsar e t he onl yway t o appr oach smal lmas s es ( di �er ence)

wel lbel ow 1eV: s ens i t i ve t o t he ver ywi de �m2 r angedown t o 10�12 eV2.

The neut r i noos ci l l at i ons t udi esi n SK wi l lbe done not onl ywi t h hi gh s t at i s t i csand bet t er

qual i t i esbut wi t hdi �er ent appr oaches :mo del i ndependent and ux cal cul at i oni ndependent anal ys es

ar et he key i s s uef ort he SK exper i ment .

3.1 Atmospheric Neutri nos

Atmos pher i cneut r i nosar epr oduced i nt he upper atmos pher et hr ought he decay of mes ons pr oduced

by i nt er act i onsof pr i mar ycosmi c r ays on nucl eii n t he atmos pher e. The neut r i noener gyr anges

f r ombel ow GeV t o over TeV and t he di s t ancef r omt he poi nt s wher e neut r i nosar epr oducedand t he

det ect orl ocat i onr angesf r om10 t o13, 000km.Ther ef or et he s ens i t i vi ty t o t hemas s di �er encei sdown

t o�m2 � 10�4eV 2.

At t he l ow ener gyl i mi twher e mos t of t he muons pr oduced i nt he atmos pher edecay, t he r at i o

of (��+ ��)=(�e + ��e) becomes�2. The mor e t he ener gyi ncr eas es ,t hemor e t he r at i obecomes l ar ger .

The uncertainty of the atmospheri c neutri no ux calcul ati ons i s mai nl y come f rom the uncertai nty

of the primary cosmi c ray ux, meson producti ons, and neutri no i nteracti ons,and i s estimated to be

�25% (20% f rom the ux and 15% f rom the i nteracti onuncertai nti es). In order to mi nimi ze those

uncertai nti esi nthe neutri no osci l l ati onstudi es,the doubl e rati oR=(�/e)data/(�/e)MC i susual l ytaken.

Another imp ortant approac h i s to study the zeni th angl e di stri buti onof the neutri no events

whi ch wi l l be descri bed l ater.

In SK the atmospheri c neutri nos are studi ed by two cl assesof the events: the contai ned events

and upward goi ng muons. The upward goi ng muons are produced by hi gh energy muon neutri no

i nteracti ons taken underneath of the detector and penetrati ng the detector enteri ng f rom the bottom

of the detector. We wi l l not di scuss the upward goi ng muons i n thi s pap er.

3.1.1 Contained even ts

The contai ned events are those produced i n the detector by neutri no i nteracti ons. Tradi ti onal l ywe

di vi de the contai ned events i nto sub-GeV (El < 1. 33 GeV) and mul ti -GeV (El > 1. 33 GeV). The

sub-GeV sampl es were used ori gi nal l yto search f or proton decay.

The strategyto study atmospheri c neutri nos i s to i denti f yneutri no avor through the i denti �ca-

ti onof the l epton avor of si ngl eri ng events (i nthe sub-GeV sampl e) and of most energeti cparti cl e(i n

the mul ti -GeV sampl e). In the mul ti -GeV sampl e we have al so i ncl uded so cal l edparti al l ycontai ned

events (PC)|events whi c h have one track exi ti ngf rom the i nner detector. For exampl e, 91. 1% of the

el ectronevents come f rom�e charged current i nteracti onsand 95. 9% of the muon events come f rom��

charged current i nteracti ons i n sub-GeV sampl e. For the mul ti -GeV sampl e, the correl ati oni s much

better. Theref ore the parti cl ei denti �cati oni s the key i ssue f or the neutri no osci l l ati onanal ysi s.

The data between May-27 i n1996 and Oct-16 i n1997 (414. 2 e�ecti ve l i ve days) are used f or the

present anal ysi s. The contai ned events are �rst sel ectedby appl yi ng simpl e computer al gori zmto the

raw data (�106 events/day): (1) no si gni �cant outer detector acti vi ty, (2) the i nner total charge i s

> 200 photo-el ectrons. We have al so appl i ed f urther cuts to remo ve stoppi ng muons, through goi ng

muons and el ectrons f rom stoppi ng muon decays. Thi s reducti on step yi el ds�30 events/day f or the

f ul l ycontai ned event (FC) sel ecti onand �20 events f or parti al l ycontai ned event (PC) sel ecti on.Then

the events were scanned by two i ndependen t physi ci stsand the remai ni ng background events were

rejected. We �nal l y obtai ned �8. 0 f ul l ycontai ned events/day and �0. 5 parti al l ycontai ned events/day

af ter appl yi ng the 2m cut f rom the i nner PMT surf ace (22. 5kton �duci al vol ume) and the mi nimum

energy cuts of 30 MeV (ful l ycontai ned) and 3, 000 photo-el ectrons (parti al l ycontai ned).

The i denti �cati onof el ectronand muons are done by usi ng the i nf ormati on of the di �useness of

the Cherenk ov ri ngs. The probabi l i ty i s de�ned by

P(1)e(�) =

Y�i<1:5�c

1p2��i

exp

24�1

2

p:e :i � p: e :ie(�)

�i

!235 ;

where �i i s the resol uti onof PMT i ncl udi ng al so an e�ect of the gai n spread. We have al so simi l ar

probabi l i ty f uncti on f or the angul ar di stri buti on,P (2)e(�). Then the l og- l i kel i hood functi on i s determi ned

by

L = log(P 1� � P 2

�)� log(P 1e � P 2

e ):

The l i kel i hood di stri buti onof the parti cl ei denti �cati oni sshown i n�gure 4 and you can cl earl ysee the

good separati on between the �- l i ke and e- l i ke events. The mi s- i denti �cati onprobabi l i ty i s estimated

PID likelihood, Sub-GeV, 1-ring event

0

20

40

60

80

100

120

-10 -8 -6 -4 -2 0 2 4 6 8 10

Figure 4: The distribution of the likeliho od to iden tify electrons and muons. The separation between �-like

and e-lik e events are clearly seen. The probabilit y of the mis-iden ti�cation is less than 1%

Table 1: The summary of the contai ned events caused by the atmospheri c neutri no i nteracti ons i n

Super-Kami ok ande f or 414.2 e�ecti ve days. Al sol i stedi s the predi cti ons by the Monte Cal roCal cul a-

ti on.

Sub-GeV Mul ti -GeV

DATA MC(Honda) DATA MC(Honda)

1R 1853 2001. 3 394 411. 6

e- l i ke 962 796. 1 218 182. 7

�- l i ke 891 1205. 2 176 229. 0

2R 594 657. 2 153 143. 7

�3R 155 190. 1 151 156. 3

PC 200 244. 8

to be l ess than 1 %. The val i di ty of the parti cl ei denti �cati onwas veri �ed by the test done at KEK

usi ng a 1kt water Cherenk ov detector by the el ectronand muon beam wi th known momen tum [16].

The resul tsaf ter the �nal data sel ecti onsare summari zed i n tabl e 1. Al l the events are used to

mak e the doubl e rati oof the muons and el ectrons:

(�=e)DATA(�=e)MC

= 0:635+0:029�0:028 � 0:009 � 0:048( sub�GeV );


= 0:665+0 :059�0:054 � 0:020 � 0:078(multi�GeV (FC));


= 0:664+0 :069�0:062 � 0:022 � 0:097(mul t i�GeV (FC + PC)):

The �rst, second and thi rd errors come f rom stati sti cs,MC stati sti csand systemati cs, respecti vel y.

The doubl e rati os,(�=e)DATA=(�=e)MC , as a f uncti onof the energy f or sub-GeV and mul ti -GeV sampl e

are shown i n�gures 5 and 6. The monotonous suppressi on of �60% i sseen over enti reenergy regi on.

The zeni th angl e di stri buti on,whi c h i s of most imp ortance to understand about neutri no osci l -

l ati ons,i s simi l ar to the E/L pl ot si nce the zeni th angl e, �z, appro ximatel y determi nes the di stance(L)

(µ/e)DATA/(µ/e)MC v.s. momentum, Sub-GeV 1ring

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 200 400 600 800 1000 1200 1400

Figure 5: The double ratios,(�=e)DATA=(�=e)MC , for the sub-GeVsampl e as a functi on of energy for 414.2days of data.

(µ/e)DATA/(µ/e)MC v.s. momentum, Multi-GeV 1ring

0

0.5

1

1.5

2

2.5

3

3.5

4

1 10 100

Entries 4024

Fi g ur e6: Same as �gure 5, but for themul ti -GeV data sampl e.

zenith angle, Sub-GeV e-like

0

100

200

300

-1 -0.5 0 0.5 1zenith angle, Sub-GeV µ-like

0

100

200

300

-1 -0.5 0 0.5 1

zenith angle, Multi-GeV e-like

0

20

40

60

80

-1 -0.5 0 0.5 1zenith angle, Multi-GeV µ-like (FC+PC)

0

50

100

150

-1 -0.5 0 0.5 1

Fi g ur e7: The zeni th angl e di stri buti onof the e- l i ke and �- l i ke events f or the sub-GeV and mul ti -GeV datasampl es. The sol i dbars show the predi cti on f rom the MC cal cul ati on(no osci l l ati on)bei ng symmetri c f or al lthe di stri buti ons. In the hi gh energy muon sampl e, the zeni th angl e di storti oni s promi nen t. The predi cteddi stri buti ons for the neutri no osci l l ati on,�� ! �� (�m2 = 5� 10�3eV 2; sin22� = 1:0) are al so shown by thedotted l i nes. For e- l i ke data, the di �erence between no osci l l ati on(sol i dbars) and the osci l l ati on(dotted)comes f rom the ux re-normal i zati on due to the absol ute ux uncertai nty of 25%.

Figure 8: The up/down ratio of theupward goi ng (�1 < cos�z < �0:2) anddownwaed goi ng (0:2 < c o s �z < 1:0)events f or the �-li ke events . The hori zon-tal axi s shows the 'neutr i no'energy est i -mated wi th the hel p of the MC cal cul a-t i ons .The l owest data l essthan 500 MeVshoul dal ways be symmetr i c (1 i nthi s�g-ure)s i ncetherei spoor angul arcorrel at i onbetween l eptonsand neutr i nosi nthi sen-ergyregi on.

νµ - ντ

10-5

10-4

10-3

10-2

10-1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

sin22θ

∆m2 (

eV2 )

Fi g ur e9: An Al l owed regi onassumi ng�� ! �� neutr i noosci l l at i on.

be twe e nt he de t e ct orand t hepla c ewhe r ene ut r i no sa r epr oduc e d.If yo u s e et hedi s t o r t i o ni nt he

di s t r i but i o n,yo uc a ni mme di a t e l yg e tc r udeg ui deo n t heva l uef o rt heo s c i l l a t i o npa r ame t e r .Ano t he r

i mpo r t a nt cha r a c t e r i s t i c si st ha tt heze ni t ha ng l edi s t r i but i o ns ho ul dbe s ymme t r i c .

Thi sna t ur eo f t hes ymme t r ydoe s no t de pe ndupo n a ny ux c a l c ul a t i o nse xc e ptf o ra s ma l l

di �e r e nc e(l e s st ha n3% f o rt hee ve nt s be l ow 1 Ge V: ne g l i g i bl ea bove 1 Ge V) o f t heg e o -ma g ne t i c

c ut - o �.The r e f o r e ,i fa ny up/down a s ymme t r yi sf o und,i ti ndi c a t e si mme di a t e l yt ha ts omeunknown

s i t ua t i o nmus te x i s t .I nt hi ss e ns et heda t as t a ndsby i t s e l f .

I n�g ur e7, we have s hown t henumbe r o f e - l i ke a nd�- l i ke e ve nt sa s a f unc t i o no f z e ni t ha ng l e

f o rt hes ub- Ge Vandmul t i - Ge Vda t as e t s .The pr e di c t i o nss hown by t hes o l i dba r sa r es ymme t r i c

f o ra l lo f t heda t as ampl e sa l t ho ug ht hepr e di c t i o nshave 25% s ys t e ma t i cunc e r t a i nt i e swhi ch a r eno t

s hown i n�g ur e7 . The e l e c t r o ns ampl e ss how mo r eo r l e s ss ymme t r i cdi s t r i but i o ns ,but i nt hemuon

s ampl ei ti se v i de nt i a lt ha tmo r ene ut r i no sc omef r omt o po f t hede t e c t o ra ndl e s sf r omt hebo t t omo f

t hede t e c t o r .The mul t i - Ge Vmuonda t aha smo s tpr omi ne nt cha r a c t e r i s t i c s .

I n o r de rt o ma g ni f yt hepr o bl e m,we have s hown i n�g ur e8 , t her a t i oo f t heupwa r dg o i ng

(�1 < cos�z < �0:2 ) a nddownwa e dg o i ng( 0:2 < c o s �z < 1:0 ) e ve nt s f o rt he�- l i ke e ve nt s .Al lt he

da t ae xc e pto nel e s st ha n5 0 0Me Va r e�5 0%. The l owe s tda t al e s st ha n5 0 0Me V s ho ul da l ways be

s ymme t r i cs i nc et he r ei spoo r a ng ul a rc o r r e l a t i o nbe twe e nl e pt o nsa ndne ut r i no si nt hi se ne r g yr e g i o n.

The r e f o r et heda t abe l ow 5 0 0Me V c a nbe us e da s a c o nt r o l l e ds ampl ea nds ho ul dbe 1 i n�g ur e8 .

By us i ngt ho s ei nf o r ma t i o no nt hee ne r g ya ndz e ni t ha ng l edi s t r i but i o n,we c a ng e ta nc o n�de nc e

c o nt o urf o rt hene ut r i noo s c i l l a t i o npa r ame t e r s( f o r�� ! �� c a s e )a s s hown i n�g ur e 9 .The e xpe c t e d

z e ni t ha ng l edi s t r i but i o nsf o r�m2 = 5 � 1 0�3eV 2, s in22� =1 a r es hown i n�g ur er e f �g : z e ni t hby t he

Figure 10: The solar neutrino spectra. KM and SK can onl y measure the 8B-neutri nos and the Chl ori ne

experiment can measure both the 8B and 7Be-neutri nos. The gal l i umexperimen ts have l owest energy threshol d

and are abl e to observe neutri nos from the pp-fusi on process whi c h produces most of the sol ar neutri nos.

dotted lines which quite agree with the data.

It is interesting that a part of the al lowed region can be accessible by planned long basel ine

neutrino osci l lation experiments.

3.2 Solar Neutrinos

The solar neutrinos are pro duced in the central part of the sun through the various nuclear reac-

tions [17]. The dominan t pro cesses pro ducing neutrinos are those in the pp-c hain:

p+ p! d + e+ + �e(E� � 0:420MeV );

p+ e�+ p! d + �e(E� = 1:442MeV );

3He+ p ! 4He+ �e(E� � 18 :77MeV );

7Be+ e� !7 Li+ �e(E� = 0:862MeV (89 :7%) ; 0:384MeV (10 :3%)) ;

8B !8 Be� + e+ + �e(E� � 15MeV );

The solar neutrino spectra predicted by a standard solar mo del is shown in �gure 10.

The presen t energy threshold of SK is 6.5 MeV, and we therefore can only detect 8B neutrinos,

maxim um energy of whic h is� 15 MeV.

The main interaction in this energy region is the neutrino electron elastic scattering, since the

neutrino nucleus scattering is suppressed by the Pauli principle. The cross sections of the � + e

interactions are well calculated by the standard theory of the electro-weak interactions:

d�

dEe

=2G2

Fme

�

24c2L + c2R

1 �

E0

e

E�

!2

+ cLcRme

E�

35 ;

where cL = 1=2 + sin2�W and cR=sin2�W for �ee scattering, and cL = �1=2 + sin2�W and cR=sin

2�W

for ��e scattering. The �ee interaction is mediated by both charged and neutral curren ts, and the ��e

interaction is mediated only by the neutral curren t. With sin2�W=0.225, the total cross sections are

�(�e + e! �e + e) = 0:920 � 10�43(E�=10MeV )cm2;

�(�� + e! �� + e) = 0:157 � 1 0�43(E�=1 0MeV )cm2:

The ��e ne utralcu r r e nt int e r a c t i onmu st be t a ke ni nt oa c c o u nt wh e nt h en e u t r i n oo s c i l l a t i o no ft h e

�e ! �� mode i sc o n s i d e r e d .

Al t h o u ght h ec r o s ss e c t i o n sa r es ma l l ,t h o s e�+ e i nt e r a c t i o n sh ave t h ef o l l owi n gg ood ch a r a c t e r -

i s t i c s .Th ed i r e c t i o no ft h er e c o i le l e c t r o ni sc o n s t r a i n e dt obe ve r yf o r wa r d :Ee�2 � 2me|1 8d e gf o r

1 0Me Vr e c o i le l e c t r o n s .Th e r e f o r et h ed i r e c t i o n so ft h en e u t r i n o sa r ewe l lke pti nt h ed i r e c t i o no ft h e

r e c o i le l e c t r o n s .Th er e c o i le l e c t r o ne n e r g yr e e c t st h ei n c i d e nt n e u t r i n oe n e r g y, t h e r e f o r et h es h a pe

o ft h en e u t r i n oe n e r g ys pe c t r u mc a nbe s t u d i e dby t h er e c o i le l e c t r o ne n e r g y.

Fo rs o mes c e n a r i o s ,l i ke t h es p i n - avo rp r e c e s s i o n ,�e may c o nve r ti nt o��e. Th e s e��e's a r ed e t e c t e d

t h r o u g ht h e��e+p! e++n i nt e r a c t i o n s .Th ec r o s ss e c t i o no ft h i si nt e r a c t i o ni s

�( ��e + p! e+ + n) =G2FE

2�

�

��cos2�c��2"1 + 3

gAgV

!#= 9:2 3� 1 0�42

�E�

1 0MeV

�2cm2:

Th e c r o s ss e c t i o ni nwa t e ri sa bo u t2 0 t i me sl a r g e rt h a nt h a to f t h e�ee s c a t t e r i n g .Th e i n c i d e nt

n e u t r i n oe n e r g yi se xa c t l yo b t a i n e dby E� = Ee+1:3MeV , h owe ve rt h ed i r e c t i o n a li n f o r ma t i o nwo u l d

be l o s t .Th ea n g u l a rd i s t r i b u t i o no ft h ei nt e r a c t i o ni sa l mo s t a t :

d�=d� � 1:� 0:1 0 3� cos�:

Th ep u r po s eo ft h es o l a rn e u t r i n os t u d yi nSK i sn o to n l yt oc o n �r mt h e u xd e � c i t s ,b u ta l s ot o

o b t a i na nc o n c l u s i ve e v i d e n c eo fn e u t r i n oo s c i l l a t i o ni n d e pe n d e nt f r o mt h es o l a rmod e lc a l c u l a t i o n s .

Th ed i s t o r t i o no ft h er e c o i le l e c t r o ne n e r g ys h a pe ,i ff o u n d ,i sa s t r o n ge v i d e n c ef o rt h eMSW

e �e c to r t h eJu s tS o n e u t r i n oo s c i l l a t i o n s .Th e d ay t i mea n dt h en i g ht - t i me u xd i � e r e n c ei st h e

e v i d e n c eo ft h er e g e n e r a t i o no fn e u t r i n o st h r o u g ht h ee a r t h :t h eMSW e � e c to nt h ee a r t h ' sma t t e r .

Ot h e rt i meva r i a t i o n sl i ke s e a s o n a la n ds e mi - a n nu a la r ea l s ot h eke yi s s u ea n da c o r r e l a t i o nwi t ht h e

s o l a ra c t i v i ty wo u l dbe a ne v i d e n c eo fa l a r g en e u t r i n oma g n e t i cmo me nt .

In o r d e rt os t u d yt h o s ep h e n o me n ai nd e t a i l ,t h ee x pe r i me nt mu s ta c qu i r eve r yh i g hs t a t i s t i c a l

d a t aa n dr e d u c es y s t e ma t i ce r r o r s .Th ee n e r g yd e t e r mi n a t i o ni so fmo s tc r u c i a la n dd i �c u l ta mo n g

t h e m.Th ee n e r g yi sb a s i c a l l yd e t e r mi n e dby nu mbe ro fh i tPMTs c o r r e c t e df o rt h el i g ht a b s o r p t i o n

t h r o u g ht h ewa t e ra n dPMT g e o me t r ya n dtwo p h o t o nh i ta n di sc a l i b r a t e dby u s i n gt h ee l e c t r o n

be a mp r od u c e dby t h ee l e c t r o nLI NAC a swa sa l r e a d ye x p l a i n e d .

Th ed a t ap r e s e nt e dh e r ei sb a s e do n3 7 4. 2d ay so fd a t at a ke nbe twe e nMay 3 1 , 1 9 9 6a n dOc t2 0 ,

1 9 9 7 .Th ee x pe c t e ds o l a rn e u t r i n oe ve nt r a t ei s3 7e ve nt spe rd ay f o rS S MBP95 wh i l et h enu mbe ro f

e ve nt t r i g g e r e dpe rd ay i sa bo u to n emi l l i o n .Mo s ts e r i o u sb a ck g r o u n di sc o s mi cr ay mu o n s(�3 Hz)

a n ds u b s e q u e nt � a n d r ay so r i g i n a t i n gf r o mt h ed e c ay o ft h es p a l l a t i o np r od u c t s .Th o s emu o n sc a n

be r e move de a s i l yby u s i n gt h ei n f o r ma t i o no f t h ev i s i b l ee n e r g yi nt h ei n n e rvo l u mea n dt h o s ei n

t h eo u t e rd e t e c t o r .Th es p a l l a t i o np r od u c t swe r er e move dby u s i n gt h ed i s t a n c ea n dt i mec o r r e l a t i o n

be twe e nt h es p a l l a t i o np r od u c t sa n dt h ep a r e nt mu o n s .Th e r ea r es i g n i � c a nt a mo u nt o fb a ck g r o u n d

e nt e r i n gf r o mo u ts i d eo ft h ed e t e c t o r :mo s t l y r ay s .Th o s eb a ck g r o u n dwe r er e move dby a p p l y i n g

t h e� d u c i a lvo l u mec u t( 2 mf r o mt h es u r f a c eo f t h ei n n e rPMTs ) .Af t e rs e l e c t i n gt h ed a t abe twe e n

6 . 5 Me Va n d2 0Me V,we o b t a i n e d1 9 6e ve nt s /d ay a sa � n a ls a mp l e .

Th ecos�sun d i s t r i b u t i o no ft h e� n a ls a mp l ei ss h own i n� g u r e1 1a n dt h etwo d i me n s i o n a lp l o t

o ft h o s ee ve nt s ,i na c oo r d i n a t es y s t e mwh e r et h es u na l way ss i t sa tt h ec e nt e r ,i ss h own i n� g u r e1 2 :

t h i s� g u r emay be c a l l e da sa Ne u t r i n oHe l i o g r a p h .Fo r m� g u r e1 1we o b t a i n e dt h enu mbe ro fs o l a r

n e u t r i n o sby u s i n ga ma x i mu ml i ke l i h ood me t h od .We a s s u me dt h es h a pe o ft h e8B n e u t r i n os pe c t r u m

cosθsun

0

0.05

0.1

0.15

0.2

0.25

0.3

-1 -0.5 0 0.5 1

SK 374day 6.5-20MeV 22.5kt ALLE

vent

s/da

y/kt

on/b

in

Figure 11: The cos�sun distribution. The for-

ward peak caused by the solar neutrino interac-

tion is prominan t.

Fi gure 12: The image of the sun measured by

the solar neutrino:Neutrino Hel iograph.

of ref erence[19] and f or the li kel i hood cal cul ati onthe data i n the cos�sun di str i buti onsare f urther

di vi dedi nto energy bi ns. The number of events thus obtai nedi s4,951. 8 events i n374. 2days between

6. 5and 20 MeV i n22. 5kton�duci al vol ume.

The sol ar8B neutri no ux i s:

�8B = 2:37+0:06�0:05(stat:)

+0 :09

�0:07(sy st:)� 106=cm2=s;

Note that KM observed 597 events i n 2079 days: the measured ux i s �8B = 2:80 � 0:19(stat: ) �

0:33(syst:)� 106=cm 2=s: The resul tf romSK agrees that f romKM wi thi nexperi mental errors.

The rati oto the predi cti onthe standard sol armo del of BP95 i s,

DATA

SSMBP95

= 0:358+0 :009�0:008(stat: )

+0 :014

�0:010(sy st:):

The dayti me and ni ght-t i me ux di �erencehas a sol armo del i ndependent i nf ormati onon the

l argeangl eMSW sol uti ons.The day and ni ght ux rati oobtai nedby SK i s,

(Day �Night)

(Day +Night )= �0:31 � 0:024(stat: )� 0:014(sy st:):

No si gni �cant overal l ux di �erencei sf ound. The e�ect of the regenerati onthrough the earthdepends

upon the path l engthand the densi ty pro�l e of the earthwhere the sol arneutri nospass through. We

theref oredi vi dedthe ni ghtdata(cos� z < 0:0: the nadi r i s the z- coordi nate)i nto �ve bi ns (�cos� z =

0:2). We have shown i n�gure 13 the uxes of day ti me and ni ght- t i medi vi dedi nto 5 bi ns. The typi cal

day/ni ght uxes expected f roma l argeangl e sol uti on(�m2 = 2:82 � 10�5eV 2, sin22� = 0:66) and a

smal l angl e sol uti on(�m2 = 6:31� 10�6eV 2, sin22� = 9:12� 10�3) of MSW e�ect are al sopl ottedi n

�gure 13.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-0.2 0 0.2 0.4 0.6 0.8 1

data

/SS

MB

P95

day

nigh

t1

nigh

t2

nigh

t3

nigh

t4

nigh

t5

Figure 13: The day and night-t i me uxes. The ni ght data are di vi dedi nto5 bi ns wi th �cos� = 0:2. The ex-pectedday- ni ght uxes for �m2 = 2:82�10�5eV 2, sin 22� = 0:66(dashed li ne)and�m

2 = 6:31� 10�6eV 2, sind 22� = 9:12�10�3(dottedl i ne)are shown.

0

0.2

0.4

0.6

0.8

1

1.2

7 8 9 10 11 12 13 14 15MeV

data

/SS

MB

P95

Fi g ur e1 4: The spectrum of the recoi lel ectrons.The thi ck parts show the sta-t i st i calerrors and the extens i ons wi ththe thi n bars show the combi ned errorof stat i st i csand systemati cs .Al soshownare a typi calsmal l angl esol ut i on(�m2 =6:31� 10�6eV 2 and sin 22� = 9:12� 10�3

(dottedl i ne))and a typi caljust sosol ut i on(�m2 = 7:08 � 10�11eV 2 and sin 22� =0:83(dashed l i ne)) .

By usi ngthe dat awe ca ns t udyne ut r i noo s c i ll a t i o nhypo t he s i s .The c o n�de nc ec o nt o uro bt a i ne d

i ss hown i n�g ur e1 5 a t 95%C. L.It i squi t ei nt e r e s t i ngt ha te ve nwi t ht hi s's ma l l 'da t as ampl ewe c a n

dr aw ane xc l ude dr e g i o nwhe r eha l fo f t hel a r g ea ng l ea l l owe dr e g i o nso bt a i ne dby Ha t ae ta l .[20] a r e

e xc l ude d.

The r e c o i le l e c t r o ne ne r g ys pe c t umi sa ke y i s s uet ount a ng l et hes o l ut i o no f t hes o l a rne ut r i no

pr o bl e m,s i nc et hene ut r i noo s c i l l a t i o nmay have a s t r o nge ne r g yde pe nde nc e .I ti ss e ns i t i ve e s pe c i a l l y

t ot hes oc a l l e ds ma l la ng l es o l ut i o nsa ndt heJus tSo va c uumo s c i l l a t i o ns .I n�g ur e1 4 ,t hes pe c t r um

o f t her e c o i le l e c t r o nsi s s hown. The c ur r e nt da t ai ndi c a t et ha tt hedi s t r i but i o ni sc o ns i s t e nt t o

be a t ,but have be t t e r�t t i ngf o ra s ma l la ng l eo r jus ts o s o l ut i o ns(name l yno n- a tdi s t r i but i o n),

a l t ho ug hs t a t i s t i c a l l yno ts i g ni �c a nt . I n�g ur e1 4 ,we a l s opl o t t e dt hee xpe c t e de ne r g ydi s t o r t i o nf o r

a typi c a ls ma l la ng l e( �m2 = 6:3 1� 1 0�6eV 2 a nd sin22� = 9:1 2� 1 0�3 ) a nd a j us ts o s o l ut i o n

( �m2 = 7:0 8� 1 0�11eV 2 a ndsin 22� = 0:8 3 ) .

Fr omt hee ne r g ys pe c t r um,we c a ng e tt hec o n�de nc ec o nt o urf o rt hene ut r i noo s c i l l a t i o npa -

r ame t e r s .Fo r t heMSW r e g i o ns ,we have o bt a i ne de xc l ude dr e g i o nwi t h9 5%C. L.whi ch i ss hown a s

r e g i o nss ur r o unde dby t hes o l i dc ur ve s i n�g ur e1 5 .Fo r t hej us ts or e g i o nwe have o bt a i ne de xc l ude d

r e g i o na t 9 9%c o n�de nc el e ve l ,butwe g e ta l l owe dr e g i o na t 9 5%C. L.a s s hown i n�g ur e1 6 .Howe ve r

we s ho ul dno tt a ke t hi st oo s e r i o us l ya tt hi st i meno to nl ybe c a us et hes t a t i s t i c si sno ts u�c i e nt a ndt he

i ndi c a t i o ni sve r yma r g i na lbut a l s obe c a us et heSK e xpe r i me nt wi l ls oo n i nc r e a s et hes t a t i s t i c sve r y

r a pi dl ya t l e a s tf o ra ne xtc o upl eo f ye a r s .We s ho ul dwa i ta no t he rye a ro r s obe f o r et hee xpe r i me nt

c a nmake a de �ni t ec o nc l us i o n.

-8

-7

-6

-5

-4

-3

-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0log(sin22θ)

log(

∆m2 (

eV2 ))

-8

-7

-6

-5

-4

-3

-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0log(sin22θ)

log(

∆m2 (

eV2 ))

day and night 5bins-8

-7

-6

-5

-4

-3

-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0log(sin22θ)

log(

∆m2 (

eV2 ))

spectrum

Figure 15: The con�dence contour for

the MSW e�ect by the SK data. Theday/night ux di �erence and the electron

energy di stri buti onare used. No absol ute ux i nformati onwas used. The sol i dl i ne

shows the 95% excl uded regi on by the en-ergy spectrum and the dotted l i ne shows

the 95% excl uded regi on by day/ni ghtdata. Shaded regi ons are those obtai ned

by Hata et al .

-11.2

-11

-10.8

-10.6

-10.4

-10.2

-10

-9.8

-9.6

-9.4

0 0.2 0.4 0.6 0.8 1sin22θ

log(

∆m2 (

eV2 ))

spectrum-11.2

-11

-10.8

-10.6

-10.4

-10.2

-10

-9.8

-9.6

-9.4

0 0.2 0.4 0.6 0.8 1sin22θ

log(

∆m2 (

eV2 ))

Fi g ur e1 6: The con�dence contour for

the Just So osci l l ati onobtai ned by theel ectron energy di stri buti on. The sol i d

l i ne shows the regi on excl uded by 99%C.L.and the dotted l i neshows the al l owed

regi on at 95% C.L.

References

[1 ] The KM(II +III )coll abo r a ti o nc o nsi s t so f Uni v.o f To kyo , I CRR( Uni v .o f To kyo ) ,KEK, To ka i

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I NS( Uni v .o f To kyo ) ,Mi ya g iUni v .o f Educ a t i o n,a ndUni v .o f Pe ns y l va ni a .

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( 1 9 8 6 ) ;K. S. Hi r a t ae ta l . ,Phys .Le t t .B2 2 0,3 0 8 ( 1 9 8 9 ) .

[ 4 ]K. Hi r a t ae ta l . ,Phys .Re v .Le t t .5 8 ,1 4 9 0 ( 1 9 8 7 ) .

[ 5 ]K. S. Hi r a t ae t a l . ,Phys . Re v . Le t t .6 5 , 1 2 9 7 ( 1 9 9 0 ) ;K. S. Hi r a t ae t a l . ,Phys . Re v . D4 4 ,

2 2 4 1 ( 1 9 9 1 ) ; D4 5 , 2 1 7 0E( 1 9 9 2 ) ;K. S. Hi r a t ae t a l . ,Phys . Re v . Le t t .6 6 , 9 ( 1 9 9 1 ) ;Y. Fukuda e t

a l . , Phys .Re v .Le t t .7 7 , 1 6 8 3 ( 1 9 9 6 ) .

[ 6 ]K. S. Hi r a t ae t a l . ,Phys .Le t t .B2 0 5 ,4 1 6 ( 1 9 8 8 ) ;K. S. Hi r a t ae t a l . ,Phys .Le t t .B2 0 8 ,1 4 6 ( 1 9 9 2 ) ;

Y. Fukudae ta l . , Phys .Le t t .B3 3 5 , 2 3 7 ( 1 9 9 4 ) .

[7] Physics and Astrophysics of Neutrinos., ed. by M.Fukugita and A. Suzuki, p249, Springer-V erlag

(1994).

[8] Ph ysics and Astroph ysics of Neutrinos. , ed. by M.F ukugita and A. Suzuki, p388, Springer-V erlag

(1994).

[9] These theses wil lbe avai lable in 6 months: Y. Koshio, Ph.D. thesis, University of Toky o(1998);

Y. Yamaguc hi, Ph.D. thesis, Osaka Univ ersity(1998); Ok azawa, PhD. thesis, Niigata Univ er-

sity(1998); Kasuga, Ph.D. thesis, Univ ersity of Toky o(1998); Hayato, Ph.D. these, Toky o Inst. of

Technology .

[10] Nak ahata et al . , to be published in Nucl. Instr. Metho ds.

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[14] Ch. Weinheimer et al . , Ph ys. Lett. B300, 210 (1993); A. I. Belesev et al . , Ph ys. Lett. B350, 263

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[15] See for example, H. V. Klap dor-Kleingrothaus, in pro ceedings of the International Conference on

Neutrino Ph ysics and Astroph ysics, Helsinki , 1996; Nucl. Ph ysics. B(Pro c. Suppl)48, 216 (1996).

[16] S.Kasuga et al . , Ph ys. Lett. B374, 238(1996).

[17] see for example J.N.Bahcal l and M.Pinsonneault, Rev.Mo d.Ph ys. 67,781(1995); S.Turck-Chieze

and I.Lop es, Ap. J. 408,347(1993).

[18] K.Inoue, in pro ceedings of TAUP97.

[19] J.N.Bahcal l et al . , Ph ys. Rev. C54, 411 (1996).

[20] N.Hata and P.Langac ker, IASSNS-ASR 97/29, UPR-751T, hep-ph/9705339, Ma y (1997).

Documents

1 Introduction and Detector