T2K 2km water Cherenkov detector

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T2K 2km water Cherenkov detector

• Kimihiro Okumura (ICRR)
• 27-Sep-2005
• NuInt05 _at_ Okayama Univ.

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T2K 2km working group
Boston Univ. (USA) E.Keran, M.Litos, J.Raaf,
J.Stone, L.R.Sulak CEA Saclay (France)
J.Bouchez, C.Cavata, M. Fechner, L.Mosca,
F.Perre, M.Zito CIEMAT (Spain) I. Gil-Botella,
P.Ladron de Guevara, L. Romero Columbia
University (USA) E.Aprile, K.Giboni, K.Ni, M.
Yamashita Duke University (USA) K.Scholberg, N.
Tanimoto, C.W. Walter ETH Zurich (Switzerland)
W.Bachmann, A.Badertcher, M.Baer, Y. Ge, M.
Laffanchi, A.Meregaglia, M.Messina, G.Natterer,
A.Rubbia ICRR Univ. of Tokyo (Japan) I.Higuchi,
Y. Itow, T. Kajita, K. Kaneyuki, Y. Koshio, M.
Miura, S. Moriyama, N. Nakahata, S. Nakayama, T.
Namba, K. Okumura, Y. Obayashi, C. Saji, M.
Shiozawa, Y. Suzuki, T. Takeuchi INFN Sezione di
Napoli (Italy) A. Ereditato Institute of
Experimental Physics, Warsaw Univ. (Poland) D.
Keilczewska H.Niewodniczanski Institute of
Nuclear Physics, Krakow (Poland) A. Szelc, A.
Zalewska Institute for Nuclear Research RAS
(Russia) A. Butkevich, S.P. Mikheyev A.Soltan
Institute for Nuclear Studies, Warsawa (Poland)
P. Przewlocki, E. Rondio Institute of Physics,
University of Silesia, Katowice (Poland) J.
Holeczek, J. Kisiel Laboratori Nazionali di
Franscati (LNF) (Italy) G. Mannocchi Laboratori
Nazionali di Gran Sasso (Italy) O.
Palamara Louisiana State University (USA) S.
Dazeley, S. Hatakeyama, R. McNeil, W. Metcalf,
R.Svoboda Universita dellAquila (Italy) F.
Cavanna, G. Piano Mortari University of
California Irvine (USA) D. Casper, J. Dumore,
S. Mine, H.W. Sobel, W.R. Kropp, M.B. Smy, M.R.
Vagins University of California, Los Angeles
(USA) D. Cline, M. Felcini, B. Lisowski, C.
Matthey, S. Otwinowski Universite Claude Berard
Lyon-1 (France) D. Autiero, Y. Declais, J.
Marteaux Universidad de Granada (Spain) A.
Bueno, S. Navas-Concha University of Sheffield
(UK) P.K. Lightfoot, N. Spooner Universita di
Torino (Italy) P. Picchi University of Valencia
(Spain) J.J. Cadenas University of Washington,
Seattle (USA) H. Berns, R. Gran, J.
Wilkes Wroclaw University, Wroclaw (Poland) J.
Sobczyk Yale University (USA) A. Curioni, B.T.
Fleming
27 institutions, 90 people
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T2K
J-PARC
SK
n

• baseline Tokai to Kamioka 295km
• J-PARC 40GeV PS 1.35MW

• 2.5º off-axis beam
• Peak neutrino energy 700MeV
• first beam expected in 2009

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Physics of T2K

• ?e appearance determine ?13

sin22q130.1
Optimistic!
d(Dm2) lt 10-4eV2 d(sin22q23) 0.01
Sensitivity
sin22q13gt0.01
Sensitivity
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Motivation of 2KM detector

• Good Near/Far flux ratio
• measure neutrino spectrum before oscillation
  without correction
• Water Cherenkov detector available
• not too much event rate at 2KM avoid event
  overlap per spill
• same analysis method available with far detector
  (SK)
• Fine-grain liquid Argon (LAr) detector will
  provide independent measurements such as
  non-QE/QE, NC p0 interactions with excellent
  track imaging and low-energy particle detection

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Near/Far flux ratio vs detector distance
?
2.5º
p
2 km
295 km
0m
280m
F280m/FSK
F2km/FSK
1.5km
295km(SK)
280m
2km away from the neutrino source F/N ratio
spread lt 5 over all energies.
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2KM detector configuration
The 2KM detector is made of three sub-systems.
Muon Ranger Measure high energy tail of neutrino
spectrum.
? Direction
Liquid Argon Detector
Water Cherenkov Detector Same detector
technology as SK
see A. Meregaglias talk
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2KM water Cherenkov detector geometry

• detector size
• most muons contain inside detector
• low interaction rate
• 1interaction/spill/1kton

2m
Fid. Mass 100tons
F4.5m
F9.3m
F8.5m
4m
6.3m
2m
2m
12.3m
13.8m
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Muon Range Detector
Measure high energy tail of the neutrino spectrum
which is source of NC BG and sensitive to the
electron neutrino BG.
Constrain the kaon produced neutrino flux which
also produces a large fraction of the intrinsic
electron neutrino background.
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Why Water Cherenkov
Minimize systematics in prediction at far
detector.
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Same Target as Far Detector
Maximum Oscillation Effect
High event rate for studies 120,000
QE events/yr/100 tons
70,000 non-QE
events/yr/100 tons
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Expected sensitivity w/ and w/o 2KM measurement

• Included systematics
• Flux
• 20 on each true energy bin
• Cross-sections
• CC quasi-elastic 15 ? 5
• CC 1p 30 ? 15
• other CC 30 ? 15
• NC p0 30 ? 15
• other NC 30 ? 15
• Fiducial Volume
• SK 2.5
• 2km 5
• Energy Resolution
• SK and 2km 3

correlated between 2KM and SK
?? disappearance sin2?23 and ?m223
uncorrelated

• 2KM WC detector will provide ultimate sensitivity
  using cancellation mechanism

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WC simulation study

• GEANT4 simulation developed by 2KM group.
• MC tuning done using K2K 1KT
• PMT size 20 or 8 ?
• 8 conf. seems to match SK

similar to K2K 1kton
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Study on WC detector granularity
nm QE events PID
nm non-QE/QE separation
m-like
e-like
8 PMT
20 PMT
20 PMT
QE
8 PMT
non-QE

• Reconstruction performance of both configurations
  were compared by simulation study
• Concluded that 8 PMT configuration has better
  performance and matches SK Performance
• better non-QE/QE separation and PID performance
• muon acceptance same as SK within 1

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2KM WC measurement for ne appearance search

• Goal predict ne appearance background _at_ SK using
  same analysis method owing to similar detector
  response
• Analysis strategy
• simulate T2K beam events for SK and 2KM
• Apply reconstruction and standard analysis cut
  for both detectors
• Extrapolate measured background from 2KM to SK
  with simple scaling method

NSK N2KM?(MSK/M2KM)?(LSK/L2KM)2?(eSK/e2KM)
this time assume 1
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Backgrounds in ne appearance search
BG
NC ?0
Electrons
Signal

• NC p0 is the largest contribution
• Other BG intrinsic beam ne, CC nm mis-ID
• ne appearance sensitivity depends on BG
  systematic error

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Expected sensitivity of ne appearance search
In 5yrs SK exposure total BG error should be
lt10
T2K phase-II neutrino beam upgrade and
Hyper-K megaton detector
we should control errors to 5 level in order
to maximize potential
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e/p0 separation variables
SK
2KM

• e/p0 separation special cut to reduce NC p0
  background
• Response of 2KM and SK are very similar

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Measured events at 2KM
Simulate 5yrs 2KM dataApply same analysis
cutsas at SK2000 events total
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Extrapolate 2KM BG to SK
2KM and SK overlaid
Total background from SK MC 24.4 Extrapolated
background from 2KM 25.6 1.8 (7.0)
Preliminary estimate simple extrapolation gives
uncertainty in BG of 7 - better than goal of
10
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Strategy for detector-related systematics

• As we have seen, 2KM water Cherenkov detector has
  a merit that systematic errors related to
  neutrino flux and target almost canceled between
  2KM and SK.
• However, systematics related to detector response
  does not canceled. In order to achieve 5 error,
  reducing detector-related systematic error is
  important.
• From K2K 1kton experience, we know that energy
  scale, fiducial error and ring separation
  (including e/p0 separation) are the largest
  contributions
• In this preliminary analysis, systematic errors
  are estimated conservatively
• It is important to develop calibration system to
  reduce these systematics
• fiducial error ? fiducial grid PMTs
• e/p0 separation ? cone generator

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Option for reducing fiducial systematics
grid PMTs for fiducial volume

• Add grid of small (2-inch) PMTs near the edge of
  fiducial volume
• provide more accurate vertex information for
  fiducial-edge events
• simulation study shows that vertex shift can be
  constrained less than 5cm (corresponding a few
  in fiducial volume error)
• test data at K2K 1kton taken in this summer and
  analysis is going

n
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Option for reducing e/p0 separation systematics
Cone generator
p0-like two cone DATA

• Generate artificial Cherenkov rings similar to
  p0-2g/electron charge profile by laser ball
  enclosed in derlin vessel
• Provide same control sample for e/p0 separation
  between 2km detector and SK

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Summary

• 2KM water Cherenkov detector can measure accurate
  neutrino flux before oscillation
• systermatics due to target and flux are canceled
• very similar response between 2KM and SK by
  simulation study
• 2km detector is essential for ultimate
  sensitivity for ne appearance search
• background at SK can be predicted less than 10
  uncertainties

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Prediction of nm spectrum _at_ SK

• Expected SK nm spectrum (w/o oscillation) and
  extrapolated 2KM spectrum by baseline and
  detector mass are compared
• Spectrum difference becomes reasonably flat
  within 5 in all energy