K2K ： KEK-to-Kamioka Long

Baseline Neutrino Oscillation

Experiment Kenzo NAKAMURA

KEKFor the K2K Collaboration

Les Houches EuroConference on Neutrino Masses and Mixings

June 21, 2001Les Houches Physics Center, France

K2K Collaboration

Chonnum National Univ.

Donshin Univ.

Seoul National Univ.

ICRR, Univ. of Tokyo

KEK

Kobe Univ.

Kyoto Univ.

Niigata Univ.

Okayama Univ.

Osaka Univ.

Science Univ. of Tokyo

Tohoku Univ.

Boston Univ.

Univ. of California at Irvine

Univ. of Hawaii at Manoa

SUNY at Stony Brook

Univ. of Washington at Seattle

Warsaw Univ.

•Accelerator ： 12 GeV proton synchrotron•Beam intensity ： 61012 protons / pulse•Repetition ： 1 pulse / 2.2 sec•Pulse width ： 1.1 s (9 bunches)

•Horn-focused wide-band beam•Average neutrino energy ： 1.3 GeV

•Near detector ： 300 m from the target•Far detector (Super-Kamiokande) ： 250 km from the target•Goal ： 1020 protons on target

Water Cherenkov detector Total mass ： 50 kton Inner mass ： 32 kton Fiducial mass: 22.5 kton

K2K (KEK-to-Kamioka)

Pion Monitor

200m

Near Detector

Pion Monitor

MuonMonitor

• Horn current: 250 kA

• Production target: Al 66cm×3cmφ

Beam Line and Magnetic Horn

K2K Near Detector

Measure flux, spectrum, profile

Measure e contamination

Study interactions at 1 GeV

1 kton water Cherenkov detector

Same structure and systematics as SuperK

Common water target

Scintillating-Fiber tracker

Active area: 2.4 m 2.4 m 20 (x,y) layer

Water target

19 layers of 60-mm thick water

Lead-glass counter

Muon/Fe

12 layers of iron plates (total mass 1,000 tons interleaved with muon drift chambers

Reconstructed Neutrino Energy

Spectra with 1020 POT

l + n l + p

l-

p

( El , pl )

μμμN

μμNν θpEm

mEmE

cos

2/2

The neutrino energy is reconstructed by assuming quasi-elastic (QE) scattering.

Oscillated/Non-oscillated with

1020 POT

non QE Bkg

Expected Sensitivity

1020 protons on target in 4～ 5 years

Profile and Spectrum at the Near

Detector

R 100cmR 200cmR 300cm

E (GeV)R (cm)

MRD (Muon Range Detector)

MRD fiducial vol. for monitor-ing the rate.

Neutrino profile at 300 m

Neutrino spectrum averaged within a given R

Num

ber

of

neu

trin

os/

cm2/1

02

0

PO

T

Num

ber

of

neu

trin

os/

cm2/1

02

0

PO

T

Profile and Spectrum at the Far

Detector

Num

ber

of

neu

trin

os/

cm2/1

02

0

PO

T

Far/Near(R 300 cm) Flux

Ratio

It is vitally important to predict the far spectrum model-independently from the spectrum measured at the near site.

Measure momentum and angular distribution of pions, N(p, ).

Neutrino flux (E) at any distance using only decay kinematics.

E (GeV)

Pion Monitor

Pion monitor is a gas-Cherenkov counter which measures the pion p- distribution just after the magnetic horn.Sensitive to p >2 GeV (E > 1 GeV) to

avoid background from 12 GeV protons.

Predict far/near flux ratio above 1 GeV

Normally retracted from the beam line

Special low-intensity runs for measurement

Pion Monitor Results and

Fitting

p

w1w2 w3 w4 …..: :

: :

Pion Monitor: Unfolded

Result

- 5

- 4

- 3

- 2

- 1

0

1

2

3

4

5

2 3 4 5 6 7P i o n m o m e n t u m ( G e V / c )

Pio

n an

gle

(*10

mra

d)

beam axis

+

Relative Pion Population in p- plane

Spectra from Pion Monitor

Measurement

Flux Ratio from Pion Monitor

Measurement

Good agreement between the pion monitor results and the beam Monte Carlo above 1 GeV.

Thus, for the extrapolation of the event rate, MC calculation is used.

Systematic error estimated from pion monitor:

R(E)=SK(E)/FD(E)

%6%7

R

Muon Monitor

Sensitive to initially high energy (>5.5 GeV)

Spill-by-spill monitoring of Beam intensity

Targetting Horn stability

Profile Beam direction

Segmented ionization chamber

K2K Experiment: Schematic

1ktWater Cherenkov

MRD Lead Glass SciFi

Super-KamiokandeN

expectedSK N

observedSK

Far/near flux ratio

Nobserved1ktN

observedMuon/Fe NobservedSciFi

Consistency checkComparison This talk ： Number of events Future ： Spectrum

Near Detector Beam Monitors

Muon monitor

•Primary beam stability•Targetting

Pion monitor

•Pion kinematics

P －

Current Transformer

•Primary beam

intensity

Beam Monte Carlo

Uncertainties in the absolute flux normalization and cross section cancel out between 1kton and SK

Confirm above1 GeV

MRD•Rate stability•Directional stability•Spectrum stability

1 kton Event

H2O target (same as SK)

Same detection principle as SK

Rate normalization in calculating the epected number of nm events at the far site.

Fid. Mass: 25 ton Event selection:

Qtot>1000p.e. ～ 2events/100 spill

MRD Event

Neutrino int. in MRD iron plates (CC inclusive)

Large area coverage (8m)

profile (vertex dist.) Large mass (fid. Mass =

329 ton) high rate ( ～ 5/100spill)

Monitor neutrino direction intensity spectrum

1 0 0 c m

R u n 124 4 S p il l 20 799 T R G ID 1 9 9 6 2 2 17 4 8 5 6 0

N v tx 0

8mBeam

SciFi Event

Neutrino int. in SciFi H2O target (+Al 20%)

Pos. resolution ～1mm

well defined fid. vol. multitrack resolution

Fiducial mass = 5.9 ton

Event selection: matching SCIFI & MRD track

1 event/1000 spill Study neutrino

interaction, e.g. inelastic/elastic

Beam

Protons Delivered onto the

Target

H o rn 2 0 0 k ATa rg e t 2 c m

H o r n 2 5 0 k ATa r g e t3 c m

- m o n

- m o n

0

2

4

6

A p r 9 9 J u l9 9 O c t 9 9 J a n 0 0 A p r 0 0 J u n 0 0

Pro

ton

s/P

uls

e (

10

^12

)

D a t e

0

5

1 0

1 5

2 0

2 5

Acc

um

ula

ted

PO

T (

10

^18

)

Accumulated POT

Protons / pulse

Beam Direction

Arb

. un

it H o r iz o n ta l

x (c m )0 20 0 40 0-200-400

y (c m )0 20 0 40 0-200-400

Ve rt ic a l

0

20 00

40 00

60 00

80 00

Vertex distribution of MRD events (Nov99)

MRD MRD

Centered within sys. err. of 20cm (0.7mrad)

Fitted center x: 1±5cmy: － 10±4cm from SK dir.

(stat)

SK SK

Stability of the Profile Center

Measured with the Muon Range Detector

Stable to within 1 mrad Well within the

required 3 mrad- 1 0 0

- 8 0

- 6 0

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

1 0 0

prof

ile

cent

er x

i n t e g r a t e d d a y ( 1 d a t a p o i n t / 5 d a y s )

- 1 0 0

- 8 0

- 6 0

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

pro

file

cen

ter

y

i n t e g r a t e d d a y ( 1 d a t a p o i n t / 5 d a y s )

1mrad

1mrad

1mrad

1mrad

MRD

MRD

Stability of the Muon Profile

Center

1mrad

1mrad

Jun‘99

Jun‘00

Nov‘99

Jan‘00

Feb‘00

Mar‘00

May‘00

Spill-by-spill measurement with the muon monitor

Stable within 1 mrad

Stability of the MRD Event

Rate

Measured with the MRD

Good stability

Fe

even

ts/5

x1012

PO

T

～ 5.5events/100spillMRD

Horn 250kA

Target 3cm

Horn 200kA

Target 2cm

MRD MRD

Stability of Muon Energy and Angle

E (GeV) (deg)

Arb

itra

ry U

nit

s

Measured with MRD

Stable within statistical error

Expected Number of SK

Events

SKkt

ktSK R

NN

obsexp

dEEE

dEEE

M

MR

kt

SK

kt

SK

OH

OH

2

2

obsktN : observed events in 1kt

kt detection eff. of 1kt

SK : detection eff. of SK

kt

SKM

M fiducial mass ratio

(syst.) (stat.)2.08.37 5.38.3

exp SKN from 1 kton events

events SCIFI from 2.37 :

events MRD from 0.41:c.f.6.4

5.0-exp

0.66.6-

exp

SK

SK

N

N These results are consistent with each other.

Systematic Error

(syst.) (stat.)2.08.37 5.38.3

exp SKN

1kt (mainly V/V) %5

Near/Far Ratio %67

Total %910

SK(mainly V/V) %3

SK Event

K2K event selection at SK1. No pre-activity in 30sec

2. p.e. in 300ns window > 200

3. OD Nhit in largetst cluster<10

4. Deposite Energy > 30MeV

5. Fiducial cut (distance from wall>2m)

Detection efficiency

=79%

for CC:93%,

for NCinel:68%

SK Event Category

FC (Fully Contained; Light in ID only) Vertex inside the 22.5 kton fiducial volume Vertex outside the fiducial volumeOD contained （ Light in OD only)Crossing (Light in both ID and OD ）

Events vs POT

FC events in 22.5 kton fiducial volume

KS prob. = 7% KS prob. = 12 %

All events (FC + OD)

Arrival Time Distribution

(s)

1

10

1 02

1 03

-500 -250 0 250 500

0

10

-5 0 5

5

No pre. act

> 200 p.e.

Exp’ed Atm BG<10-3 in 1.5s win.

28 observed.

Tspill TSK

sec3.1TOF2.0 SpillSK TTTTSpill, TSK: Abs. time of spill start, SK event measured with GPS

TOF: 0.83ms(Time of flight from KEK to Kamioka)

Observed vs Expected at SK

cos KEK Distribution

Preliminary

Data

MC w/o osc.

Need to estimate syst. err. in MC expect.

1-ring -like

Reconstructed Momentum

F. C . 1 - r i n g - l i k e M e V / c

0

2

4

6

8

1 0

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0

PreliminaryDataMC w/o osc.

Need to estimate syst. err. in MC expect.

Reconstructed E

M e V / c

0

2

4

6

8

1 0

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0

Fully contained 1-ring -like (22.5kt)

Preliminary

DataMC w/o osc.

Need to estimate syst. err. in MC expect.

Visible Energy

DataMC w/o osc.

Preliminary

need to estimate syst. err. in MC expect.

K2K Run in 2001

Until July 12

Conclusions

Methodology of a long-baseline neutrino experiment established.

Beam steering (direction)

Time synchronization between near site and far site

Monitoring of the neutrino beam at near site

Prediction of neutrino beam properties at far site from near site measurements

2.29 x 1019 POT accumulated from Jun ’99 to Jun ’00.

# of fully contained events in fiducial volume @ SK

Observed : 28

Expected : 37.8 +3.5-3.8 (w/o osc.)

Deficit of ~1GeV after 250km flight at 90% significance

Statistics doubled this summer

Future

Spectrum analysis

e appearance

Study of interactions at 1GeV region

Upgrade of the near detector in summer, 2003

Upgrade of the near detector

Upgrade of the Near Detector

(Segmented Liquid Scintillator with WLS Fiber Readout)

4m

2m

4m

Large Volume: 4×4×2m3

~30tonsFine segment: 20×20×20mm3

One cell is read-out to both X and Ydirections by X,Y fibers.

Large Light Yield:20~30 photo-electrons/cell for MIP

Particle ID: p/ : dE/dx / : range

#channels : ～ 40,000

cellstructure

Upgraded Near Detector

Liquid

Scintillator

Event Simulation

Neutrino Energy spectrum and the ratio

w/ and w/o oscillation

Uncertainty (now)Uncertainty (upgrade)

Spectrum ratio

2.6

JHF-to-SK Neutrino Project

http://neutrino.kek.jp/jhfnu/

Letter of Intent: hep-ex/0106019

Overview

~1GeV beamKamioka

JAERI(Tokaimura)

→ → xx disappearance （ m232 ）～ 10-4 eV2, （ sin2223 ）～ 0.01

→ → ee appearance sin2213 ）～ 0.01 NC measurement → →s

～ 1 MW 50 GeV PS

( conventional beam)

Super-K: 50 ktonWater Cherenkov

JHK Accelerator Complex

JAERI@Tokai-mura(60km N.E. of KEK)

(Approved in Dec.2000)

0.00520.410.77Power(MW)

0.450.530.292Rate(Hz)

640330Int.(1012ppp)

1212050E(GeV)

K2KMINOSJHF

Construction2001 - 2006

Construction of neutrino beam lines is not yet approved.

Comparison of Three Beams

WBBLE2OA2°

Linear Log

OAB/WBB long HE tailPeak @ 800MeV~1GeVSharp peak for NBB/OABOAB produce very intense “NBB”

Target: Cu. 1cm, 30cm rodSK size: ±500m

Number of CC Events with

Various Beams

WBBWBB

LE1.5LE2LE3 OA3°

OA2°OA1°

WBB:5200 CC int./22.5kt/yrNBB: 620 CC int./22.5kt/yr (2GeV/c tune)OAB: 2200 CC int./22.5kt/yr (2degree)

MNS Matrix and Parameters

MNS mixing matrix

three mixing parameters

a cp violating phase

mass-squared differences

e

c12c13 s12c13 s13e

i

s12c23 c12s13s23ei c12c23 s12s13s23e

i c13s23

s12s23 c12 s13c23ei c12s23 s12 s13c23e

i c13c23

1

2

3

12, 13,23

m21

2 ,m32

2

12

DisappearanceDisappearance

1ring FC -like

Reconstructed E (MeV)Fit with 1-sin22 ・ sin2(1.27m2L/E)

Oscillation with m2=3×10-3

sin22=1.0

No oscillation

Non-QE

(linear)

(log)

m2=3×10-3

sin22=1.0

~3%

Ratio after BG subtraction

Precision of the Parameters

(sin22) ～ 0.01 in 5 years(m2) ～ <1×10-4 in 5 years

(sin22) (m2 )

NBB-3GeV, OAB-2degree, NBB-1.5GeV

0.01 1×10-4

e Appearance: Expected Signal

and Background

OAB2o 5year

Reconstruct E as Quasi-Elastic

interaction

Apply Energy Cut

0.4GeV< E <1.2GeV (OAB2o)

e Appearance: Sensitivities

In the SK allowed region1.510-3<m2<510-3

eV2:

sin22e ～ 0.005or sin2213 ～ 0.01

NC Measurement

NC/CC sensitive tos

NC Enriched Sample

sterileactiveNC PPN 1

# of NC events

logm2)

#0 + #e-like

3.2×10-3

JHF-to-SK Second Phase Hyper-Kamiokande: 1 Mton water Cherenkov detector JHF beam power upgrade: 4MW

200 statistics Goal of the 2nd phase

sin2213 sensitivity below 10-3 (if 13 not discovered in the 1st phase)

CP phase to 10 – 20 degrees (if the solution to the solar neutrino problem is MSW-LMA)

Proton decay (p K, e+0)

5JHF20SK 5 year

Hyper-Kamiokande: A Next-Generation Nucleon Decay Detector

at Kamioka

0.5 Mton

1 Mton: Total Length 400m (8 Compartments)

CP Violation

CP Sensitivity