K2K: KEKtoKamioka Long Baseline Neutrino Oscillation Experiment

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K2K KEK-to-Kamioka Long Baseline Neutrino
Oscillation Experiment

• Kenzo NAKAMURA
• KEK
• For the K2K Collaboration
• Les Houches EuroConference on Neutrino Masses and
  Mixings
• June 21, 2001
• Les Houches Physics Center, France

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K2K Collaboration
ICRR, Univ. of Tokyo KEK Kobe Univ. Kyoto
Univ. Niigata Univ. Okayama Univ. Osaka
Univ. Science Univ. of Tokyo Tohoku Univ.
Chonnum National Univ. Donshin Univ. Seoul
National Univ.
Boston Univ. Univ. of California at Irvine Univ.
of Hawaii at Manoa SUNY at Stony Brook Univ. of
Washington at Seattle Warsaw Univ.
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K2K (KEK-to-Kamioka)

• Accelerator 12 GeV proton synchrotron
• Beam intensity 6?1012 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
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Beam Line and Magnetic Horn

• Horn current 250 kA
• Production target Al 66cm3cmf

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K2K Near Detector

• Measure nm flux, spectrum, profile
• Measure ne contamination
• Study n 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

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Reconstructed Neutrino Energy Spectra with 1020
POT
The neutrino energy is reconstructed by assuming
quasi-elastic (QE) scattering.
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Oscillated/Non-oscillated with 1020 POT
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Expected Sensitivity
1020 protons on target in 45 years
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Profile and Spectrum at the Near Detector
Neutrino spectrum averaged within a given R
Neutrino profile at 300 m
MRD (Muon Range Detector)
R ? 100cm
R ? 200cm
MRD fiducial vol. for monitor-ing the rate.
R ? 300cm
Number of neutrinos/cm2/1020 POT
Number of neutrinos/cm2/1020 POT
E? (GeV)
R (cm)
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Profile and Spectrum at the Far Detector
Number of neutrinos/cm2/1020 POT
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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)
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Pion Monitor

• Pion monitor is a gas-Cherenkov counter which
  measures the pion p?-?? distribution just after
  the magnetic horn.
• Sensitive to pp gt2 GeV (En gt 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

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Pion Monitor Results and Fitting
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Pion Monitor Unfolded Result
Relative Pion Population in pp-qp plane
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Spectra from Pion Monitor Measurement
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Flux Ratio from Pion Monitor Measurement
R(En)FSK(En)/FFD(En)

• 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

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Muon Monitor

• Sensitive to initially high energy m (gt5.5 GeV)
• Spill-by-spill monitoring of
• Beam intensity
• Targetting
• Horn stability
• Profile
• Beam direction

Segmented ionization chamber
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K2K Experiment Schematic
Near Detector
Confirm above 1 GeV
Uncertainties in the absolute flux normalization
and cross section cancel out between 1kton and SK

Far/near flux ratio
Super-Kamiokande
Consistency check
Comparison This talk Number of events
Future Spectrum
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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 Qtotgt1000p.e.
• 2events/100 spill

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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

8m
Beam
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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.
  sinelastic/selastic

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Protons Delivered onto the Target
Accumulated POT
Protons / pulse
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Beam Direction
SK
SK
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Stability of the Profile Center

• Measured with the Muon Range Detector
• Stable to within
• ? 1 mrad
• Well within the required 3 mrad

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Stability of the Muon Profile Center

• Spill-by-spill measurement with the muon monitor
• Stable within ? 1 mrad

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Stability of the MRD Event Rate

• Measured with the MRD
• Good stability

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Stability of Muon Energy and Angle

• Measured with MRD
• Stable within
• statistical error

• Arbitrary Units

qm (deg)
Em (GeV)
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Expected Number of SK Events
from 1 kton events
These results are consistent with each other.
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Systematic Error
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SK Event

• K2K event selection at SK
• No pre-activity in 30msec
• p.e. in 300ns window gt 200
• OD Nhit in largetst clusterlt10
• Deposite Energy gt 30MeV
• Fiducial cut (distance from wallgt2m)

Detection efficiency e79 for
CC93, for NCinel68
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SK Event Category
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Events vs POT

• FC events in 22.5 kton fiducial volume

All events (FC OD)
KS prob. 12
KS prob. 7
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Arrival Time Distribution
No pre. act
gt 200 p.e.
TSpill, TSK Abs. time of spill start, SK event
measured with GPS TOF 0.83ms(Time of flight from
KEK to Kamioka)
Exped Atm n BG lt10-3 in 1.5ms win.
28 observed.
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Observed vs Expected at SK
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cos qKEK Distribution
1-ring m-like
Need to estimate syst. err. in MC expect.
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Reconstructed m Momentum
Need to estimate syst. err. in MC expect.
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Reconstructed En
Need to estimate syst. err. in MC expect.
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Visible Energy
need to estimate syst. err. in MC expect.
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K2K Run in 2001
Until July 12
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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 _at_ SK
• Observed 28
• Expected 37.8 3.5-3.8 (w/o osc.)
• Deficit of 1GeV nm after 250km flight at 90
  significance
• Statistics doubled this summer

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Future

• Spectrum analysis
• ne appearance
• Study of nm interactions at 1GeV region
• Upgrade of the near detector in summer, 2003

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• Upgrade of the near detector

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Upgrade of the Near Detector(Segmented Liquid
Scintillator with WLS Fiber Readout)
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Upgraded Near Detector
Liquid Scintillator
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Event Simulation
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Neutrino Energy spectrum and the ratio w/ and
w/o oscillation
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JHF-to-SK Neutrino Project http//neutrino.kek.jp
/jhfnu/ Letter of Intent hep-ex/0106019
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Overview
1GeV n beam
Kamioka
Super-K 50 kton Water Cherenkov
JAERI (Tokaimura)
1 MW 50 GeV PS
( conventional n beam)

• nm? nx disappearance ?(?m232)10-4 eV2,
  ?(sin22?23)0.01
• nm? ne appearance sin22?13)0.01
• NC measurement nm ? nt / nm ? ns

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JHK Accelerator Complex
Construction of neutrino beam lines is not yet
approved.
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Comparison of Three Beams
Target Cu. 1cmf, 30cm rod SK size 500m
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Number of CC Events with Various Beams
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MNS Matrix and Parameters

• MNS mixing matrix

• three mixing parameters
• a cp violating phase
• mass-squared differences

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nm Disappearance
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Precision of the Parameters
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ne Appearance Expected Signal and Background

• Reconstruct En as Quasi-Elastic
• interaction
• Apply Energy Cut
• 0.4GeVlt E lt1.2GeV (OAB2o)

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ne Appearance Sensitivities
In the SK allowed region 1.5?10-3ltDm2lt5?10-3
eV2 sin22qme0.005 or sin22q130.01
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NC Measurement
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JHF-to-SK n Second Phase

• Hyper-Kamiokande 1 Mton water Cherenkov detector
  
• JHF beam power upgrade 4MW
• ?200 statistics
• Goal of the 2nd phase
• sin22q13 sensitivity below 10-3 (if q13 not
  discovered in the 1st phase)
• CP phase d to 10 20 degrees (if the solution to
  the solar neutrino problem is MSW-LMA)

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Hyper-Kamiokande A Next-Generation Nucleon Decay
Detector at Kamioka
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CP Violation
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CP Sensitivity