Results from K2K and status of T2K Yuichi Oyama (KEK) Sep-11-2005 Crimea2005@Yalta

Overview of the K2K experiment First long-baseline neutrino oscillation experiment. (1999-2004) ● Confirmation of nm-nt oscillation reported by Super-Kamiokande using artificial neutrino beam. ● 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 Dm2 > 2×10-3 eV2 is possible. It covers the parameter regions suggested by the atmospheric neutrino anomaly. ●

K2K neutrino beamline in KEK TRISTAN RING (B-factory) 12GeV PS Primary Beam-line P 12GeV/c proton beam 1.1msec beam duration Al Target 2.2sec accelerator cycle Intensity 5~6x1012 ppp Decay pipe (200m) Total 1020 p.o.t. p+ -> m+ + nm Muon Pit Front Detectors nm To Kamioka

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. ne/nm ratio is about 1%. ● The direction of the beam is adjusted within 1mrad. ● Nearly the same energy spectrum and flux within 3 mrad. ● It covers the size of SK; ~50m/250km = 0.2mrad. Neutrino flux at SK (250km downstream) is 1.3x106n/cm2 for 1020p.o.t. and ~170 events are expected in the 22.5kton of fiducial volume in the case of null oscillation. ● profile at SK 1 3 2 3mrad n/cm2 (x106) distance (km) SK(0.2mrad) spectrum at SK 1 2 3 4 5 Neutrino energy (GeV) n/cm2 /0.1GeV(x106)

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.

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

Summary of data-taking in K2K First neutrino beam: January 27, 1999 ● Physics run: Jun 4, 1999 – Jul 12, 2001 (K2K-I) ● Super-Kamiokande accident Jan 17, 2003 – Nov 6, 2004 (K2K-II) ● Total physics run: 442.8 days　(233.7+209.1) ● Total spill numbers: 17.4x106 spill ● Total POT for analysis: 92.2x1018 p.o.t. (47.9x1018 + 44.3x1018) 1999 2000 2001 2002 2003 2004 Year protons/pulse (x1012) 5 Total POT (x1018) 100 Delivered Protons on Target (POT)

time correlation with the neutrino beam Neutrino events in Super-Kamiokande Selection Evis > 30 MeV and no signal in the outer detector ● Events within 1.5msec time window are selected because neutrino beam width is 1.1msec and accuracy of the absolute time determination by GPS is 0.2msec. History of event accumulation ● # of events time correlation with the neutrino beam Number of events GPS Kamioka KEK 1.5ms Results P.O.T. (x1018) Number of events in the fiducial volume is 112. ● Expected atmospheric neutrino background is 2.5x10-3 events. The rate of the neutrino events is uniform. ●

A typical K2K neutrino event in Super-Kamiokande The event seems to be quasi-elastic scattering interaction; ● nm + n m- + p Neutrino energy can be calculated from muon energy and opening angle from KEK direction. ● mNEm - mm2/2 En = mN - Em + Pmcosqm-KEK

nm-nt oscillation analysis for K2K data 1 2 3 4 5 En P(nm nm) Neutrino Survival probability (1)We observed 112 neutrino events where the expectation is 155.9　　　 .　Number of neutrino events is considerably smaller than expectation. Dm2=3.0x10-3eV2, sin22q=1.0, L=250km +13.6 -15.6 (2)Neutrino energy distribution is data calculated from 58 single ring m-like events. No oscillation Best fit The result shows a clear discrepancy in 0.5-1.0GeV range. It reflects energy dependence of neutrino survival probability Number of neutrino events No oscillation (normalized to data) If null oscillation is assumed, such poor agreements happen with a probability of 0.003%. Neutrino energy (GeV)

Constraints on nm-nt oscillation Dm2 ranges (1.88~3.48)x10-3eV2 for sin22q=1.0@90%C.L. ● The best fit parameters are (Dm2,sin22q)=(2.76x10-3eV2, 1.0). ● The expectation of the total SK events is 107.7, where data is 112. Agreement with the SK atmospheric neutrino results is excellent. ● Dm2 (eV2) 10-1 10-2 10-3 10-4 0.2 0.4 0.6 0.8 1 sin22q Shape of oscillation contours by two experiments are different. SK atmospheric neutrino data is high statistics (~10000 events), but poor L and En determination. Sensitive to sin22q. K2K data is low statistics (~100 events), but L is constant and good En determination. 　　　Sensitive to Dm2. SK atmospheric neutrino (90%C.L.) They play complementary roles in determination of the oscillation parameters.

T2K experiment 295km J-PARC in JAERI KEK Kamioka Tokai J-PARC in JAERI Next generation long-baseline neutrino-oscillation experiment; ● from Tokai to Kamioka 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. ● Letter of Intent : hep-ex/0106019

What is J-PARC, JAERI, Tokai, T2K….. J-PARC : Japan Proton Accelerator Research Complex. J-PARC in JAERI, Tokai To SK 400MeV Linac 3GeV PS 50GeV PS Pacific Ocean Decay Volume Target The name of the entire project. It includes High Energy Physics, Nuclear Physics, Life Science, Material Science, Nuclear Technology. Accelerators consist of 400MeV Linac, 3GeV PS and 50GeV PS. JAERI : Japan Atomic Energy Research Institute. The host institute of J-PARC Tokai : the name of the village where JAERI is located. JHF : Japan Hadron Facility. 50GeV Proton Synchrotron T2K = JHFn = J-PARC n : Name of the neutrino experiment. J-PARC is under construction since 2001. ● T2K experiment was officially approved in December 2003. The construction started in April 2004, and the experiment will start in 2009. ●

T2K Beamline and Detectors p n 140m 0m 280m 2 km 295 km on-axis off-axis Comparison of the proton beam Beamline The center of the beam direction is adjusted to be 2o ~ 3o off from the SK direction. K2K T2K Eproton (GeV) 12 50 Beam Power (kW) 5.2 750 Protons per second 3x1012 1x1014 ● Off Axis beam Detectors Muon monitors @ ~140m downstream ● First near detectors@ ~280m downstream (boundary of the JAERI site) ● Second near detectors@ ~2km downstream ● Far detector@ 295km downstream (Super-Kamiokande) ● “x100 high intensity” and “Off axis beam” and “2km detector”

Requirements for Neutrino Energy Neutrinos of En=0.5~1.0GeV are desired from 3 reasons. 1 2 3 4 5 En P(nm nm) (1) The oscillation probability is maximum for En = 0.5~1.0 GeV Neutrino Survival probability Dm2=2.5x10-3eV2, sin22q=1.0, L=295km (2) Neutrino energy is calculated from quasi-elastic scattering events; nm + n m + p Neutrino cross section quasi-elastic scattering by simple 2-body kinematics. Other neutrino interactions are background to select quasi-elastic scattering. Fraction of quasi-elastic scattering is smaller for high energy neutrinos. (3) Water Cherenkov detector has better performance for single ring events.

Off-axis beam How to adjust neutrino energy to 0.5~1.0GeV q OA2.5° ● The center of the beam direction is adjusted to be 2o ~ 3o off from the SK direction. Although neutrino intensity at SK is lower, the peak energy is low and high energy neutrinos are suppressed. Neutrino energy spectrum is quasi-monochromatic. OA3° OA0° OA2° OA2.5° Off Axis Beam Arbitrary Unit En (GeV) q beamline SK Oscillation study is most effective if neutrino peak energy is adjusted to the oscillation maximum; Epeak = Eoscmax. ● Off Axis Angle 2.0o 2.1o 2.4o 3.0o Epeak(GeV) 0.782 0.756 0.656 0.520 Dm232(x10-3eV2) 3.28 3.17 2.75 2.18 Dm232 is calculated from Dm232=pEoscmax/2.54L Present Dm232 from other experiments is Dm232 ~ (2~3)x10-3eV2 The problem is the oscillation maximum has still large uncertainty. ●

Tunability of the beam direction and shape of the decay pipe Keep a tunability of the beam direction and wait other experiments. ● Hyper-Kamiokande (1Mt WC) will be proposed at 10km away from SK. The beam direction can be adjusted to 2o ~ 3o off both from SK and HK. ● To satisfy this condition, the cross section of the decay pipe is rectangular, and the height of the pipe is larger in downstream. ● Map in Kamioka Side view of decay pipe SK 2.0o Beam eye 3.0o 2.5o SK HK ~10km We will fix the beam direction after knowing the MINOS results in 2008 summer conferences. ● ● HK Cross section of decay pipe

2km detector 2km detector q A water Cherenkov detector is definitely needed as a front detector. ● However…., we have two difficulties. (1) Neutrino beam intensity is too high. The event rate is 60 events/spill/1kt at the 280m detector site. (2) 110m of neutrino production point must be viewed as “point like” for reliable flux extrapolation to SK. q SK ● Construct a water Cherenkov detector at an appropriate distance. 2km detector Muon range counter (Not approved yet) Water Cherenkov Fine grained detector 2km target

= U Neutrino mass matrix and physics goal of T2K If neutrinos have mass, the flavor eigenstates are mixtures of the mass eigenstates. The neutrino mass matrix, U, has 6 parameters. ● ne n1 2 square mass differences (Dm122, Dm232), nm n2 = U 3 mixing angles (q12,q23,q13) nt n3 1 CP violation phase, d. Dm122 and q12 were determined by solar/reactor neutrino oscillation. ● Dm122 ~ (6~8)x10-5eV2, sin22q12 ~ 0.8 Dm232 and q23 were determined by atmospheric/K2K neutrino oscillation. ● Dm232 ~ (2~3)x10-3eV2, sin22q23 0.9 ~ > Remaining unknown parameters are q13 and d. ● Complete understanding of neutrino mass matrix (1)First observation of finite q13 from ne-nm oscillation (2)Precise measurements of Dm232 and q23 from nm-nt oscillation (3)Observation of d after a beam intensity upgrade (0.75MW ->4MW) and construction of Hyper-Kamiokande.

Measurement of q13 by ne appearance q13 can be determined by observing ne appearance. ● P(nm ne) ~ sin2q23sin22q13sin2(1.27Dm232L/En) sin2q23~0.5 Dm232 ~ (2~3)x10-3eV2 (the same Dm2 as atm. n oscillation) q13 is expected to be small because it is the mixing angle between 1st and 3rd generation. Present upper limit is sin22q13 ~ 0.1 (CHOOZ). Small ne appearance signal must be searched for. Preliminary results from K2K Only 1 Single ring e-like events remains after e/m particle ID algorithm and p0 2g rejection. ● We expect 1.63 background (nmNC and beam ne) and 1~2 oscillation signal for parameters around the CHOOZ limit. ● The limit is sin22qem (~sin22q13/2) < 0.18 for Dm2=2.5x10-3eV2. No impact on present limit. Obviously, statistics is too small. Prospects in T2K Beam intensity is 100 times higher and ~100 ne signals are expected. “Neutrino energy cut” can be applied because neutrino energy is quasi-monochromatic. ● Sensitive to sin22q13 > 0.006 region.

Prospect for nm-nt oscillation Dm232 and q23 were already measured by Super-Kamiokande/K2K. ● Dm232 ~ (2~3)x10-3eV2, sin22q23 0.9 ~ > More precise determination of oscillation parameters is attained from precise measurement of neutrino survival probability as a function of neutrino energy. ● Neutrino Survival probability 1 P(nm nm) sin22q23 Dm2=2.5x10-3eV2, sin22q=1.0, L=295km 1 2 3 4 5 Eoscmax En Dm232 can be determined from position of the oscillation maximum Eoscmax; ● pEoscmax Dm232 = 2.54L From ~ 5% accuracy of Eoscmax measurement, D(Dm232 )~0.1x10-3eV2 is possible. sin22q23 can be determined from depth of the dip, or reduction of the neutrino events. Because of ~10000 event statistics (5years), D(sin22q23)~0.025 is attainable. ●

Summary K2K (1999 - 2004) From 92.2x1018 p.o.t., 112 neutrino events are observed in SK, where expectation based on Front detector data is 155.9 ● +13.6 -15.6 A distortion of the neutrino energy spectrum is also obvious. Probability of null oscillation is 0.003% ● Dm2 ranges (1.88~3.48)x10-3eV2 for sin22q=1.0@90%C.L. This result is consistent with Super-Kamiokande Only 1 possible ne signal was found. ● It is consistent with nmNC + beam ne background; 1.63. No impact on the present limit from other experiments. T2K (2009 - ) Keywords: ● ~100 x K2K Tunable off-axis beam 2km detector Complete understanding of neutrino mass matrix ● (1)First observation of finite q13 if sin22q13 0.006. ~ > (2)Precise measurements of Dm232 and q23 D(Dm232 )~0.1x10-3eV2, D(sin22q23)~0.025

Milestones of Super-Kamiokande, K2K and T2K 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 SK-I SK-II Since Apr. 1996 SK-III Half recover SK accident Full recover K2K-I K2K-II T2K construction T2K MINOS CNGS Today

Thank you!

Super-Kamiokande 50kt water Cherenkov detector with 11146 20-inch F PMTs. ● Located at 1000m underground in Kamioka mine, Japan ● Operation since April 1996. ● Discovery of neutrino mass using atmospheric neutrinos. ● ● Precise study of solar neutrino oscillations.

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

K2K-I Front Detectors at 300m from the target Trigger counters (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.

Study of the Neutrino beam in the Front Detectors Data recorded in the Front Detectors are used to study properties of the neutrino beam. ● Fine-Grained detector(K2K-I) 1kt detector 100cm The beam direction, stability of the beam intensity, energy spectrum, ne/nm ratio well agree with expectations. ● The excellent agreements between data and expectations in KEK site ensure the reliability of the expected beam at SK site. ●

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. ● 14400 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. ●

Summary of K2K neutrino events in Super-Kamiokande Observed Expected (no oscillation) All (FCFV) 112 155.9 total event analysis Single Ring 67 99.0 m-like 58 90.8 energy spectrum e-like 9 8.2 (tight e-like) (1) (1.63) ne appearance Multi Ring 45 56.8 This is for the entire period including both K2K-I and K2K-II. Again, muon directions was stable within 1mrad. FCFV = Fully Contained, Fiducial Volume ● ● “tight e-like cut” requires absence of delayed electron signal from m->e decay, and also rejects possible p0-> 2g events by finding second e-like ring forcibly.

MINOS experiment (2004 - ) Long-baseline neutrino-oscillation experiment from Fermilab 120GeV main injector (0.4MW) to Soudan mine 735km away. ● ● The detectors are “sandwich” of 2.54cm thick steel plane and 1cm thick scintillator in 1.5Tesla toroidal magnets. Total mass are 5.4kt for far detector and 0.98kt for near detector Fermilab Soudan 735km ● In low energy (LE) beam configuration, the peak energy is about 3GeV and ~2500 nm charged current events are expected in the far detector in 1 year. If q13 is close to CHOOZ limit, ne appearance signal can be found with 3s significance with 3 years of operation. ● ● With 5 years operation, Dm232 can be measured with 10% accuracy.

CNGS project (2006 - ) CERN Neutrino to Gran Sasso. Wide band nm beam from CERN 400GeV SPS is shot toward Gran Sasso laboratory 732km away. ● ● The neutrino beam is optimized for nt appearance; <En>=17GeV. Two experiments are under preparation. ● (June 2006 - ) OPERA Emulsion+Pb sandwich and spectrometer. Total mass is 1700 tons. If Dm232 = 2.4x10-3eV2, 12.8 nt events are expected in 5 years of operation where background is 0.8. ICARUS (Summer 2006 - ) Liquid Ar detector of 5 x 600ton modules. If Dm232 = 2.5x10-3eV2, 11.9 nt events are expected in 5 years of 5 module (3000ton) operation, where background is 0.7. First 600ton module will be ready by summer 2006, and other two 600ton modules will be completed by end of 2007.