RECENT RESULTS IN K2K EXPERIMENT

1
RECENT RESULTS IN K2K EXPERIMENT

• Shimpei YAMAMOTO (Kyoto Univ.)
• 10th ICEPP Symposium _at_Hakuba
• 16-FEB-2004

2
K2K collaboration

• JAPAN High Energy Accelerator Research
  Organization (KEK)
• Institute for Cosmic Ray Research (ICRR),
  University of Tokyo
• Kobe University / Kyoto University
• Niigata University / Okayama University
• Tokyo University of Science / Tohoku University
• KOREA Chonnam National University
• Dongshin University / Korea University
• Seoul National University
• U.S.A. Boston University / University of
  California, Irvine
• University of Hawaii, Manoa
• Massachusetts Institute of Technology
• State University of New York at Stony Brook
• University of Washington at Seattle
• POLAND Warsaw University / Solton Institute
• Since 2002
• JAPAN Hiroshima University, Osaka University
• CANADA TRIUMF / University of British Columbia
• EUROPE Rome / Saclay / Barcelona / Valencia /
  Geneva

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Outline

• K2K neutrino oscillation
• Recent status results
• nm?nx oscillation analysis
• ne appearance
• New near detector SciBar
• Prospects
• Summary

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K2K LBL n oscillation exp.
Super-Kamiokande(SK)
SciFi
LG(K2K-I) SciBar(K2K-II)
nm
50kt water cherenkov detector (22.5kt fid. vol.)
MRD
1kt
nm
Near Detectors
ltEngt1.3GeV L250km (fixed) 98 nm
12GeV-PS_at_KEK n beamline Beam monitor
KEK
SK
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Neutrino Oscillation in K2K

• oscillation prob.

• Aiming results
• Reduction of n events
• Distortion of nm spectrum
• ne appearance
• ? osci. parameters (sin22?,?m2)
• Near to far extrapolation
• Rate spectrum shape _at_SK

null oscillation
w/ oscillation
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Neutrino Beamline
pAl ? p ? m nm
ene (1.3) nm (0.5)

• Fast extraction every 2.2sec
• Beam spill 1.1us

double horm high eff. of p collection Pion
monitor near/far flux ratio Muon monitor beam
intensity direction
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Near Detectors (ND)

fiducial 1kt Water Cherenkov detector (KT)
25 ton same type as SK Scintillation Fiber
tracker (SciFi) 6 ton detect protons ?
QE/nQE Muon Range Detector (MRD)
700 ton (Fe) n beam monitor Lead Glass
calorimeter (LG) detect
electrons from SciFi
K2K-I Mar,1999 Jul,2001 SKI
(11146PMTs) SK accident
K2K-II Dec,2002 SKII (5200PMTs)
LG removed SciBar (Oct,2003 -)
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Delivered protons on target
9.5x1019 POT (8.4x1019 for analysis)
12/23
99
01
02
03
00
10/7
6/23
12/21
K2K-II
K2K-I
56x1012 (protons per pulse)
9
K2K event selection in SK
GPS
?500msec
HE Trig.
Tspill
TSK
No Decay-e
TSpill Abs. time of spill start TSK Abs. time
of SK event TOF 0.83ms (KEK to Kamioka)
FCFV
Jun.99 Apr.03 6.4 x 1019 proton on target
?5msec
K2K-I part of K2K-II
FC fully contained (No activity in Outer
Detector) FV 22.5kt Fiducial Volume
72 events
Expected atm. n BG 2x10-3 within 1.5ms.
1.5ms
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K2K events in SK
Jun.1999Apr.2003
K2K-I (56 events)
K2K-II (16 events)
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nm?nX oscillation analysis (K2K-I)
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Analysis flow
Near site

• Num. of events Observed (pm,qm) distributions
• ?
• Neutrino Flux
• Fit nm spectrum interaction model
• fnear(En) (8 bins)
• nQE/QE ratio
• Error matrix (to include correlation)

Near to Far extrapolation RFN(En)
Prediction _at_far site

• NSK Number of FCFV events
• SSK(Enrec) Enrec distribution (shape) of 1Rm

Use Maximum Likelihood Fit in (sin22q, Dm2)
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Reconstruction of En
m
pm
nm
qm
proton
E rec. _at_SK

• Use single-ring m-like FCFV (1Rm) events
• Assume QE int. and reconstruct En

( 50 of K2K 1Rm events are CCQE)
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n interaction (1GeV)
Charged current quasi-elastic scat, (CCQE)
? En can be reconstructed from Pm and qm.
m
pm
nm
qm
1kt single ring m-like FCFV SciFi QE-like
2track single track (proton invisible)
proton
pm muon momentum
qm muon angle
pion productions (nonQE)
pm
m
nm
qm
1kt single/multi ring FCFV SciFi nonQE-like
2track
nucleon
p
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Spectrum measurement _at_ND

• 1KT Pmlt1.5GeV/c, 4p acceptance
• 1-ring m-like(1Rm) fully contained
• in Fid.25ton(FC) 22,476ev.
• SciFi Pmgt1GeV/c, qmlt60deg.
• 1-track m-like 5963ev.
• 2-track QE-like (Dqplt25deg.) 764ev.
• 2-track nonQE-like (Dqpgt30deg.) 1288ev.
• PIMON
• p (p,q) distribution
• ? Neutrino Spectrum (gt1GeV)
• Fitting Parameters
• En 8 bins, nonQE/QE ratio

QE-like
nonQE-like
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SciFi pm/qm
qm
Pm
1-track m
2-track QE-like
2-track nQE-like
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1kt pm/qm
pm and qm distributions of 1kt 1ring m-like FCFV
events
qm
Pm
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Allowed region (nm?nX)
Use both Number of events Spectrum shape
(June 99 July 01)
(Nov. 99 July 01)
56obs ?

80.1
6.2 -5.4 exp

• Null oscillation probability less than 1.
• Dm21.53.9 x 10-3 eV2, sin22q1(90CL)

Allowed region
reconstructed En
Normalized by area
Expectation w/o oscillation
Best fit point 2.8x10-3
Best Fit
68
90
99
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Comparison w/ SK result
K2K
SK
90 C.L.
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Search for ne appearance(K2K-I)
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Search for ne appearance
Fully contained Single ring e-like
(ring pattern and opening
angle) Visible energygt100MeV w/o decay electrons
data
nm MC
Ring pattern
ne MC
NC of nm MC
Opening angle
To be submitted for publication
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Data reduction summary
DATA SET June99 July01 (4.81019POT)

electron candidate 1 event (obs.)
2.4 events (exp.)
DATA
nm MC
beam ne MC
signal ne MC (CC) sin22qme1 , Dm22.8x10-3eV2
80
28
FCFV
56
0.82
20
50
Single ring
32
0.48
18
2.9
PID (e-like)
1
0.42
18
2.6
Evisgt100MeV
1
0.41
16
2.0
w/o decay-e
1
0.35
NC87 CC1p7 CCmp4 CCQE2
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Excluded region (nm?ne)
K2K(90CL)
Dm2 (eV2)
SK atm.n allowed (90CL)
CHOOZ(90CL) ne disappearance
sin22qme
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Near Detector Upgrade
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SciBar detector
Upgrade near detector to explore low E
region (after removal of LG)
2003.10.03

• Fine segmented scintillator tracker
• Scintillator target fully active

Working well !!

• Spec. analysis status will be presented by
  following talkers.

nm
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Prospects

• K2K-II is running stably
• n flux in low energy region by SciBar
• SciFI n flux measurement using PID
• Improvement of Near/Far extrapolation (Harp)
• K2K events in SK-II

New results of oscillation analysis come soon !
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Summary

• K2K-I data has been analyzed so far
• nm?nx oscillation analysis
• Null oscillation prob less than 1
• Dm21.53.9 x 10-3 eV2 _at_sin22q1(90CL)
  (consistent w/ atm. n)
• ne appearance search
• 1 ne candidate (consistent with BG)
• K2K-II running stably
• New near detector SciBar
• Low energy neutrino flux _at_ND
• K2K events in SK-II
• New results of oscillation analysis will come soon

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supplements
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Pion monitor
Measure Momentum / Angle Dist. of ps
Just after Horn/Target Well known p Decay
Kinematics Well Defined Decay Volume Geometry
?Predict ?µ Energy Spectrum at Near Site
Far Site
?µ Flux Ratio (Far/Near) as
a Function of Neutrino Energy
Ring Image Gas Cherenkov Detector (Index of
Refraction is Changeable) To Avoid Severe Proton
Beam Background, ?µ Energy Information above 1GeV
is Available (ß of 12GeV Proton ß of 2GeV p)
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Muon monitor
Silicon Pad Detector Array
Segmented Ionization Chamber
Behind beam dump ?sensitive to initially high
energy m (gt5.5GeV) Provide fast (spill-by-spill)
monitoring of Intensity ? targeting/horn
stability Profile ? beam direction
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Stability of n spectrum _at_ND
Neutrino spectrum measurement by the Pion
monitor Energy and angle of muons produced in the
CC interactions by MRD
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ne candidate event
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Method of n flux fitting (ND)
Prepare MC templates
Measured (pm , qm)
neutrino spectrum f (En) and n interaction
model (QE/non-QE ratio).
qm
En QE(MC) non-QE(MC)
qm
0 0.5 GeV
pm
0.5 0.75GeV
pm
Fit the parameters.
f (En) , QE/non-QE ratio
0.75 1.0GeV
c2227 for 197 d.o.f. (90 from 1kt, 137 from
FGD) for fitted (pm , qm) dist. of 1KT and FGD
(124 data points)




7bins
8bins


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Contribution of sys. errors on spectrum
Spec.
nQE/QE
Spec.nQE/QE
Total
F/N
eSK
SK Escale