Diapositive 1

1
Summary of the Reactor/?13 Meeting At College
de France, Paris April 22-23, 2003 Thierry
Lasserre On Behalf the reactor/?13 european
working group CEA/Saclay Low energy Neutrino
Workshop University of Alabama, Tuscaloosa May 1
2003
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European momentum

• Working group
• PCC APC (from CHOOZ), CEA/Saclay
• MPI Heidelberg
• TU Munchen,
• Kurchatov Institute
• INFN/Bologna
• First meeting in December 2002
• Second meeting in April 2003
• Next around the end of the summer ?
• Goal Is it possible to build a set of 2
  detectors to measure/constrain ?13 with a new
  reactor experiment before 2010-11 ? Where ? What
  the optimum detector design ? Preliminary answer
  should come this year

T. Lasserre
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European momentum

• 22-23/04/03 Meeting List of Participants
• H. de Kerret (PCCAPC)
• M. Obolinski (PCCAPC)
• O. Dadoun (PCCAPC)
• D. Vignaud (PCCAPC)
• J. Lamblin (PCCAPC)
• S. Schoenert (MPIK)
• T. Knoepfle (MPIK)
• L. Oberauer (TUM)
• F. Von Feilitzsch (TUM)
• C. Hagner (Virginia Polytechnic Institute)
• T. Schwetz (TUM)
• M. Selvi (INFN, Bologna)
• M. Cribier (SaclayAPC)
• C. Cavata (Saclay)
• T.L (Saclay)

T. Lasserre
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Reactor/?13 meeting, Paris, 22-23/04/03 Tuesday
22 April 14h 14h15 Introduction 14h15
15h15 Reactor Neutrino Experiments compared to
Superbeams (Thomas Schwetz, TUM 4515)
15h15 16h00 The CHOOZ experiment the
Ue32 measurement review of systematic errors.
How and where to improve ? (H. de Kerret
3015) 16h00 16h30 Coffee break 16h30
17h30 Review of the current proposals (Kr2Det,
Kashiwasaki, etc ) Potential experiment sites
in France ? (T. L 4515) 17h30 18h00 
Discussion Wednesday 23 April 9h00 - 9h30
Analysis methods to account for near and far
detectors Systematic error handling (T.
Schwetz, TUM, 30) 09h30 10h15 Discussion
Backgrounds Accidental Correlated In-situ
measurements (chaiperson Stefan
Schoenert) 10h15 10h45 Coffee break 10h45
11h30 Discussion - Detector design
(chairperson Lothar Oberauer) 11h30 12h30
Conclusions
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Parameter degeneracy in LBL experiments

LBL ?? disappearance gives sin2(2?23) ? 2
solutions ?23 ?/2-?23

?m213 ? 2 solutions m1gtm3 or m3gtm1 LBL
appearance probability given by
sin2(2 ?13 )
P(??? ?e) K1 sin2(?23 ) sin2(2 ?13 )
K2 sin(2?23 ) sin(?13 ) sign(?m231)
cos(?) ? K3 sin(2?23 ) sin(?13 )
sin (?)

• K1,K2,K3 known constants (within experimental
  error)
• dependence on sin(2?23), sin(?23) ? 2 solutions
• dependence on sign(?m231) ? 2 solutions
• ?-CP phase can run in 0,2? ? Interval of
  solutions in general

P(??? ?e)
Ue32 measurement with reactors

• Few MeV ?e ? disappearance experiments
• 1-P(?e? ?e) sin2(2?13)sin2(?m231L/4E)
  O(?m221/?m231)
• Few MeV ?e very short baseline ? No matter
  effect contribution (O(10-4) relative effect)
  Ue32 ? measurement independent of sign(?m213)
• Ue32 measurement independent of the ?-CP phase

T. Lasserre
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Achievable constraint on ?13 with a reactor
experiment (hep-ph/0303232, P. Huber et. al.)
T. Schwetz
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Achievable constraint on ?13 with a reactor
experiment (hep-ph/0303232, P. Huber et. al.)
T. Schwetz
8
Complementarity Reactor/Superbeam
(hep-ph/0303232, P. Huber et. al.)

• 30-50 tons detectors

T. Schwetz

• Reactor experiment slightly less sensitive to
  non optimal ?m231
• LBL (JHF) rather sensitive to ?m221 (especially
  if LMA-II)

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Complementarity Reactor/Superbeam
(hep-ph/0303232, P. Huber et. al.)
T. Schwetz
Systematics
Correlations Degeneracies
Reactor dominated by systematics LBL dominated
by correlations and degeneracies
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The past CHOOZ (H.D.K)
Spectre des positrons ?e p ? e n

• Site CHOOZ reactor, Ardennes (France)
• 2 cores 2x4200 MWth
• Depth 300 mwe
• 5 tons of liquid scintillator (gadolinium
  loaded)
• ltLgt 1 km
• Exclusion ?? ? ?e ?m2sol lt 7x10-4 eV2 (90 CL)
• (slightly lower limit obtained at Palo-Verde)
• Best constraint on sin2(2?13) lt 0.14

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CHOOZ Systematics (H.D.K)

• Be carfull It is also possible to increase
  CHOOZ systematics (scintillating buffer for
  exemple)
• Detector design with 2 identical low background
  detectors ? Overall systematics controlled at lt 1

T. Lasserre
12
Positron Detection (H.D.K)

• Energy threshold effect
• If Eth gt Emin ? systematics due to threshold
• Lower threshold ? lower backgrounds
  (accidentalcorrelated)
• Advantage if Eth lt Emin
• No systematics on energy threshold (0.8 in
  CHOOZ, xx in KamLAND)
• Start of the spectrum provides calibration point
  between near and far detctors
• Allow to understand measure background at low
  energy (lt1 MeV)

• Edge effects Interaction of ? close to the
  target volume
• No scintillating buffer One ?s can escape
  without being detected ? Energy calibration !
• Scintillating buffer (CHOOZ case) full energy
  of e always detected within the target
• BUT e efficiency non zero outside the target
  volume ? to control !
• Spill in/out compensation of loss and gain of
  efficiency near the vessel
• Cancel if near and far detector are identical
  
• Identical detector ? No absolute energy scale
  needed
• To check Light propagation around the vessel

T. Lasserre
13
Neutron Detection (H.D.K)

• Gd loaded scintillator To be or not to be ?
• Gd ? 8 MeV ?s
• H2 ? 2.2 MeV ?s
• Edge effect H2 scintillator non-scintillating
  buffer
• spill out ? n-capture with target decrease
  efficiency (?s escape)
• spill in ? n-capture outside target increase
  efficiency (?s come back in target)
• ? partial compensation spill in/out (MC, 1
  error in CHOOZ)
• ? Cancel if near and far detector are identical

• Other reasons to have 2 identical detectors
• Ratio Gd/H2 capture (80 on Gd) Error will
  depend on detector geometry
• Time capture on Gd the tail has no reason to be
  exponential
• Energy window for n capture on Gd/H2

T. Lasserre
14
(e - n) Tag (H.D.K)

• Distance Cut d(e - n)lt100 cm
• Position reconstruction is not a technique at
  the level (tails) !
• Position reconstruction was not in CHOOZ design
• Not mandatory if accidental background very low
• Lower accidental background 1 systematic error
  less !
• Time Cut neutron capture on
• Hydrogen exponential behavior of neutron time
  capture (can be demonstrated)
• Gadolinium exponential behaviour ? Increase
  systematics
• 0.4 systematics in CHOOZ
• ?Lower accidental background no need of Gd ?

T. Lasserre
15
Backgrounds from radioactivity
Accidental background (S.S, L.O, T.L)
Based on estimation done for the HLMA project,
S.Schoenert, T.L, L.Oberauer, Astropart.Phys.
18 (2003) 565-579

• Accidental background rate
• bacc bp x bd x ? x Vcoincx Vdet
• ? Goal rate bacclt 1/year within a 20 tons PXE
  target detector
• Case 1 with position reconstruction
• ? Vdet 1 m3
• ? Constraint bp.bd lt 1.6 10-6 s-2m-6
• ? CHOOZ systematics 0.4
• Case 2 without position reconstruction ? 0
  systematics
• ? Vdet Vdet
• ? Constraint bp.bd lt 8 10-8 s-2m-6
• With Borexino material for estimation bpbd
  6.10-8 s-2m-8 !
• Position reconstruction no required but at the
  limit

bp, bd specific prompt, delayed rate Vdet
detector volume 20m³ ? coincidence time
1ms Vcoinc coincidence volume 1m³ or Vdet
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Detector Design Scintillator

• Unloaded scintillator provide best
• Optical properties (light yield, attenuation
  lenght)
• Radiopurity
• Stability
• ? PSD !!! To fight fast neutron background
• Gd loaded scintillator
• Shorten neutron capture time x3 ? Helps only
  for accidental background
• Increase neutron capture energy release to 8 MeV
  instead of 2.2 MeV on Hydrogen
• Chemical stability (but CHOOZ, Palo-Verde, and
  LENS ? gt 5-8 loading)
• Radiopurity ? More difficult
• Gd/H neutron capture systematics
• If Gd same batch to be used for both detectors
  to avoid effect such as systematics on the Gd
  content of the near and far detectors etc

T. Lasserre
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Detector Design Buffer

• Question scintillating or non-sintillating
  buffer ?
• Scintillating
• Help to get positron energy ? No energy
  threshold ? 0 systematics !
• Help to get neutron 2.2/8 MeV peak
• BUT high activity in buffer due to PMTs 40K
• BUT high activity in buffer due to muons
  crossing the buffer (no shallow depth)
• More expensive ?
• Same fluor / wavelenght shifter? time constants
  ?
• Non-scintillating
• Not the CHOOZ design
• More difficult to understand positron neutron
  spectrum ?
• Increase of systematics cut for energy
  threshold ! Light prop. around vessel !
• ? Solution scintillating buffer encapsulated
  PMTs and deep detector site ?

T. Lasserre
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Detector Design Vessel(s)

• Vessel(s) separation between Target and Buffer
• Target Volume uncertainty
• Near detector Vnear ?Vnear
• Far detector Vfar ?Vfar
• Ideally Vnear Vfar ? systematics cancel but
  relative error O(?Vnear-?Vfar)
• Nylon Vessel (BOREXINO, KamLAND) Should not be
  underestimated
• Volume shape more difficult to control ?
• Compatibility with PC
• Buoyancy problems if slight density differences
  between target and buffer
• Plexigass Vessel
• Volume Shape well under control
• Compatibility problems ?
• Contains protons ? act as a target
• Shape of the vessel Spherical ? CHOOZ like ?

T. Lasserre
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The 3-Volume detector (H.D.K)

• CHOOZ Gd-loaded scintillator H scintillating
  buffer
• BOREXINO H scintillator Non-scintillating
  buffer
• 3V detector H2/Gd loaded scintillator Proton
  free scintillator Non-scintillating buffer
• 3V detector Gd Target H2 sint. Buffer
  Non-scintillating buffer
• A very nice detector, and easier to understand ?
  
• See the start of the positron spectrum
• No threshold effect for positron energy
• n-capture peak very well defined
• Target volume perfectly defined
• No PMT activity seen (non scintillating buffer)
• Technically ?
• Need to construct a 2-volume inner vessel ?
  plexiglass
• Proton free scintillator expensive
• C6F6 Expensive ? d 1.6 (shielding,
  buoyancy problem)

T. Lasserre