Status of Super-Kamiokande, K2K and JHF ACFA LC Yuichi Oyama (KEK) for Super-Kamiokande collaboration, K2K collaboration and JHF collaboration Dec

Super-Kamiokande ● 50kt water Cherenkov detector with inch  PMTs. ● Located at 1000m underground in Kamioka mine, Japan ● Operation since April ● Discovery of neutrino mass using atmospheric neutrinos. Precise study of solar neutrino oscillations. ●

Super-Kamiokande accident on November 12, 2001 ● 6661 inner PMTs and 1017 outer PMTs were broken. ● The implosion of one PMT created shock waves which triggered a chain reaction to destroy the other PMTs. ● Remaining ~5200 PMTs are covered by Acrylic + FRP vessels. The experiment was restarted with about half PMT density in December 2002.

Present status of Super-Kamiokande ● Enjoying interesting topics of SK-I data: The experiment is successfully in operation !  -ray burst, relic supernova neutrino, e from the Sun, ● Calibration and modification of analysis tools for SK-II are in progress. ● Super-Kamiokande -II Jan.-2003, fully contained event 3 flavor oscillation, WIMP search, solar neutrino modulation,  0 /  ratio, upward-going muon astronomy,    search, correlation with solar flare, neutrino magnetic moment, exotic mode of nucleon decay… A paper rush is coming!

Overview of the K2K experiment ● ● ● First long-baseline neutrino oscillation experiment Muon neutrino beam generated at KEK is shot toward the Super- Kamiokande detector, which is 250km away from KEK Search for neutrino oscillations in the parameter region  m 2 > 2×10 -3 eV 2 is possible. It covers the parameter regions suggested by the atmospheric neutrino anomaly.

P Primary Beam-line 12GeV/c proton beam Al Target Front Detectors  Decay pipe (200m) TRISTAN RING (B-factory) Muon Pit K2K neutrino beamline in KEK 1.1  sec beam duration 2.2sec accelerator cycle 12GeV PS Intensity 6~7x10 12 ppp To Kamioka   ->   +  Total p.o.t.

profile at SK mrad /cm 2 (x10 6 ) distance (km) SK(0.2mrad) spectrum at SK Neutrino energy (GeV) /cm 2 /0.1GeV(x10 6 ) 0 5 Property of the neutrino beam ● The mean energy is about 1.3GeV and the peak energy is about 1.0GeV. ● Almost pure muon neutrino beam. e /  ratio is about 1%. ● Nearly the same energy spectrum and flux within 3 mrad. (The size of SK is ~50m/250km = 0.2mrad) ● Neutrino flux at SK (250km downstream) is 1.3x10 6 /cm 2 for p.o.t. and ~170 events are expected in the 22.5kton of fiducial volume in the case of null oscillation. ● The direction of the beam is adjusted within 1mrad.

K2K Front Detectors at 300m from the target (a)1kt water Cherenkov detector (1kt) An 1/50 miniature of SK detector. Direct comparison with SK data (b)Fine-Grained Detector (FGD) Consists of 4 detector elements. Precise measurement of neutrino beam property. Trigger counters

Study of the Neutrino beam in the Front Detectors 100cm 1kt detectorFine-Grained detector ● The excellent agreements between data and expectations in KEK site ensure the reliability of the expected beam at SK site. ● Data recorded in the Front Detectors are used to study properties of the neutrino beam. ● The beam direction, stability of the beam intensity, energy spectrum, e /  ratio well agree with expectations.

Summary of data-taking in K2K-I ● First neutrino beam: January 27, 1999 ● Physics run: June 4, 1999 – July 12, 2001 ● First neutrino event: June ● Total successful physics run: days ● Total POT for analysis: 47.8x10 18 p.o.t. ● Total spill numbers: 9.22x10 6 spill  M.H.Ahn et al., PRL 90, (2003)

1.5  s GPS KamiokaKEK Neutrino events in Super-Kamiokande ● E vis > 30 MeV and no signal in the outer detector time correlation with the neutrino beam Number of events in the fiducial volume is 56. ● Expected atmospheric neutrino background is 1.3x10 -3 events. Events within 1.5  sec time window are selected because neutrino beam width is 1.1  sec and accuracy of the absolute time determination by GPS is 0.2  sec. ● The rate of the neutrino events is uniform. ● Selection Results Number of events P.O.T. (x10 18 ) History of event accumulation

E (GeV) Number of events data  m=2.8x10 -3 eV 2 no oscillation Number of neutrino events is considerably smaller than the expectation. (1)We observed 56 neutrino events where the expectation is 80.1  (2)Neutrino energy distribution is  -   oscillation analysis for K2K-I data calculated from 29 single ring  -like events. The result shows a slight discrepancy in GeV range. If null oscillation is assumed, such poor agreements happen with a probability of less than 1%.

Constraints on   -   oscillation The best fit parameters are (  m 2,sin 2 2  )=(2.8x10 -3 eV 2, 1.0). ● The expectation of the total SK events is ~54, where data is 56.  m 2 ranges (1.5~3.9)x10 -3 eV 2 for sin 2 2  ● Agreement with the SK atmospheric neutrino results is excellent. ● K2K SK

Status of K2K-II ● K2K-II data taking is started in January 2003 and successfully in progress. K2K-IK2K-II (~Apr.03)total POT (x10 18 ) # of events The event rate is consistent with K2K-I. Number of events POT (x10 18 ) ● Further data-taking is scheduled in ● Oct.2003 – Feb.2004 and Oct.2004 – Mar.2005.

JHF experiment 295km KEK Kamioka Tokai ● Next generation long-baseline neutrino-oscillation experiment ● High intensity neutrino beam from JHF 50GeV Proton Synchrotron in J-PARC is shot toward the Super-Kamiokande detector 295km away. ● Nominal beam intensity is about 100 times larger than K2K. J-PARC in JAERI Letter of Intent : hep-ex/

The name of the entire project. It includes JAERI : Japan Atomic Energy Research Institute. Tokai : the name of the village where JAERI is located. What is J-PARC, JAERI, Tokai, JHF J-PARC : Japan Proton Accelerator Research Complex. The host institute of J-PARC J-PARC in JAERI, Tokai To SK 400MeV Linac 3GeV PS 50GeV PS Pacific Ocean Decay Volume Target High Energy Physics, Nuclear Physics, Life Science, Material Science, Nuclear Technology. Accelerators consist of 400MeV Linac, 3GeV PS and 50GeV PS. ● J-PARC is under construction since ● JHF has not been approved yet. If it will be approved in end of this December, the construction will start in April 2004, and the experiment will start in JHF : Japan Hadron Facility. 50GeV Proton Synchrotron Official name is not fixed. JHF = J-PARC = T2K : Name of the neutrino experiment.

K2K JHF E proton (GeV)1250 Beam Power (kW) Protons per second3x x10 14 p  140m0m280m2 km295 km on-axis off-axis JHF Beamline and Detectors ● Muon ~140m downstream First near ~280m downstream (boundary of the JAERI site) Second near ~2km downstream Far 295km downstream (Super-Kamiokande) ● ● ● Detectors Beamline Off Axis beam ● The center of the beam direction is adjusted to be 2 o ~ 3 o off from the SK direction. “Off axis beam” and “2km detector” Comparison of the proton beam

 m 23 2 and  23 were determined by atmospheric/K2K neutrino oscillation. ● Remaining unknown parameters are  13 and . ● (3)Observation of  by JHF upgrade (4MW) + Hyper-Kamiokande If neutrinos have mass, the flavor eigenstates are mixtures of the mass eigenstates. The neutrino mass matrix, U, has 6 parameters. 1 () 2 3 e ()   = U ● 1 CP violation phase,  2 square mass differences (  m 12 2,  m 23 2 ), 3 mixing angles (  12,  23,  13 )  m 12 2 and  12 were determined by solar/reactor neutrino oscillation. ●  m 12 2 ~ (6~8)x10 -5 eV 2, sin 2 2  12 ~ 0.8  m 23 2 ~ (2~3)x10 -3 eV 2, sin 2 2  Neutrino mass matrix and physics goal of JHF ~ > (1)First observation of finite  13 if sin 2 2  (2)Precise measurements of  m 23 2 and  23 ~ >  (  m 23 2 )~0.1x10 -3 eV 2,  (sin 2 2  23 )~0.025 Complete understanding of neutrino mass matrix

Measurement of  13 by e appearance It is 110m and e /  ratio is 0.2%. (In K2K, 200m and 1.3%) ● e background is generated with muon decay in the decay pipe.  +  + +  e + + e +  ● e background To reduce the e fraction in the  beam, a short decay pipe is used. P(  e ) y sin 2  23 sin 2 2  13 sin 2 (1.27  m 23 2 L/E )  m 23 2 ~ (2~3)x10 -3 eV 2  13 can be determined by observing e appearance. sin 2  23 ~0.5  13 is expected to be small because it is the mixing angle between 1 st and 3 rd generation. Present upper limit is sin 2 2  13 ~ 0.1. The oscillation probability should be maximized. Neutrino beam energy is adjusted according to  m  the same  m 2 as atm. oscillation) Small e appearance signal must be searched for. ● To increase e appearance signal To reduce background Excellent e/  identification in SK. Identification of neutral current  0 background in water Cherenkov detector is also under study. ●

Neutrino cross section quasi-elastic scattering Requirements for Neutrino Energy  + n  + p Neutrino energy is calculated from quasi-elastic scattering; ●  + N  +  ’s + N’ The oscillation probability is maximum for E = 0.5~1.0 GeV ● E P     )  m 2 =2.5x10 -3 eV 2, sin 2 2  =1.0, L=295km Survival probability Neutrino interactions with  productions are background to select quasi-elastic scattering. They are recognized as single ring muon events in SK, and neutrino energy can be calculated by simple 2-body kinematics. Neutrinos of E =0.5~1.0GeV are desired. ● Fraction of quasi-elastic scattering is smaller for high energy neutrinos.

1° 0° 2° 3° Off Axis Angle E peak(GeV)  m 23 2 (x10 -3 eV 2 )  beamline SK ● ● Off Axis beam The center of the beam direction is adjusted to be 2 o ~ 3 o off from the SK direction. Although neutrino intensity at SK is lower, the peak energy is low and high energy neutrinos are suppressed. We want to adjust the peak energy to the oscillation maximum, which has still large uncertainty. Keep a tunability of the beam direction and wait other experiments.

SK ~10km HK Tunability of the beam direction and shape of the decay pipe ● To satisfy this condition, the cross section of the decay pipe should be rectangular, and the height of the pipe is larger in downstream. ● Hyper-Kamiokande is proposed to construct about 10km away from SK. The beam direction can be adjusted to 2 o ~ 3 o off both from SK and HK. 2.0 o Beam eye 3.0 o 2.5 o 2.0 o SKHK Map in Kamioka Side view of decay pipe

2km target ●  SK ● ● 2km detector ● A water Cherenkov detector is definitely needed as a front detector. Neutrino beam intensity is too high. The rate is 60 events/spill/1kt at the 280m detector site. 110m of neutrino production point must be viewed as “point like” for reliable flux extrapolation to SK. ● Construct a water Cherenkov detector at an appropriate distance. Muon range counter Water Cherenkov Fine grained detector

Summary ● After the recovery in December 2002, Super-Kamiokande-II is successfully in operation. ● Super-Kamiokande K2K ● Analysis based on data (47.9x10 18 p.o.t.) was published. Probability of null oscillation is less than 1%  m 2 ranges (1.5~3.9)x10 -3 eV 2 for sin 2 2  JHF ● Complete understanding of neutrino mass matrix ● Keywords: ~100 x K2K e appearance for  13 measurement 2km detectorOff-axis beam ● Hopefully, start in The experiment has taken data corresponding to more than 70x10 18 p.o.t. Data-taking will continue at least until March 2005.

Milestones of Super-Kamiokande, K2K and JHF Today SK accident SK-II SK-I JHF construction Since Apr K2K-I K2K-II Half recover Full recover SK-III JHF

SUPPLIMENT

A typical K2K neutrino event in Super-Kamiokande   n    p 

Detector upgrade in K2K-II ● For more precise study of neutrino interactions in sub-GeV range, a new detector SciBar has been installed. ● Full active solid scintillator tracker channels of 1.3cm x 2.5cm x 3m scintillator bar which contain wavelength shifting fibers inside. ● Even short track of less than 4cm can be recognized.

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