Double Chooz

1
Double Chooz

• Optimizing Chooz for a possible Theta 13
  measurement
• Steven Dazeley (Louisiana State University)
• NuFact05 Rome

2
Introduction

• Quark mixing is small (CKM matrix)
• Lepton mixing is mostly large (PMNS matrix) ,
  except for ?13, which is constrained to be small.
  The Chooz upper limit on sin2(2?13) is 0.2
• Why?
• Might help to nail down ?13

3
Introduction (ne oscillations)

• ne survival probability can be written as
  
• P(ne ?ne) ? 1 sin2(2q13) sin2(Dm213L/4E)
• assuming latest measurements of Dm223, Dm212,
  sin2(2q23) and sin2(2q12) from SK, SNO and
  KamLAND.
• A good reactor q13 reactor disappearance
  experiment can achieve a clean measurement of q13

4
Appearance measurement of q13?

• Naively q13 with an appearance experiment seems
  easier. However in practice it is difficult to
  get a clean measurement of q13
• Assuming a normal mass hierarchy (m1ltm2ltm3),
  the ne survival probability can be written as
  
• P(nm ?ne) ? sin2(2q13) sin 2 (2q23)
  sin2(Dm231L/4E)
• asin(2q13) sind sin(2q12)
  sin(2q23)
• (Dm231L/4E) sin
  2(Dm231L/4E)
• asin(2q13) cosd sin(2q12)
  sin(2q23)
• (Dm231L/4E)
  cos(Dm231L/4E) sin(Dm231L/4E)
• a2 cos2q23 sin2(2q12)
  (Dm231L/4E)2
• where the term refers to neutrinos(-) or
  antineutrinos(), and a Dm212/
  Dm223
• A complicated equation that suffers from
  parameter correlations and degeneracies. Cant
  separate the CP violation phase d and q13
• In addition long baseline beam experiments ?
  matter effects

5
Double-Chooz
Type PWR
Cores 2
Power 8.4 GWth
Couplage 1996/1997
(, in to 2000) 66, 57
Constructeur Framatome
Opérateur EDF
Chooz-Near
Chooz-Far
Near site D100-200 m, overburden 50-80 mwe Far
site D1.1 km, overburden 300 mwe
6
The Chooz Site
1100m Baseline 300MWE Overburden
2 x 4200MW Reactors
7
CHOOZ result
nep?en Neutron/positron coincidence 200 days
reactor on 142 days reactor off Stopped due to
systematic error of reactor flux

• Sin22?13 lt 0.19 (at 2.0 x10-3
  eV2)

8
Double Chooz Improvements on Chooz

• Near detector ? exact measurement of reactor
  flux, cancels reactor systematics
• Increase S/N to 100 (Chooz 25)
• Increase Gd loaded target 2x
• 95cm non-scintillating buffer region
• Improved veto
• Non Gd loaded scintillating gamma catcher
  region ? better energy reconstruction of gammas
  produced inside target
• Increase detector running time (want gt 50000
  events, Compare with Chooz 2700)
• Reactor steady operation (Chooz ran during
  reactor commissioning phase)
• Stable scintillator (MPI-Heidelberg RD for LENS)

Allows lower threshold
9
Double-CHOOZ(far) Detector
We will start data-taking in 2007 with the far
detector
7 m
Shielding steel and external vessel (studies,
réalisation, intégration ? IN2P3/ PCC)
Target- Gd loaded scintillator
Gamma catcher scintillator with no Gd
7 m
BUFFER Mineral Oil with no scintillator
Optically separated inner veto to tag muons
7 m
Modular Frame to support photomultipliers
10
Backgrounds (accidentals)

• Accidentals
• U, Th, K in detector, allowed concentrations to
  achieve accidental rate below 1 s-1
• U,Th in scint 10-12 g/g
• K in scint 10-10 g/g
• U,Th in acrylic 10-10 g/g
• K in acrylic 10-8 g/g
• External background (from PMTs mostly). 2 s-1
  due to buffer region (Given estimates from
  Hamamatsu and ETI, measurements from CTF and
  Monte Carlo studies of buffer thickness)
• Intrinsic ns due to U, Th in target
  nint ? 0.4 s-1
  (CU,Th/10-6), i.e. negligible

11
Backgrounds (Correlated)

• 9Li, 8He (? beta-neutron cascades, prompt
  capture signature) due to muon spallation has
  largest uncertainty
• Chooz measured reactor off data ? 9Li, 8He rate
  0.2 /day
• Therefore Double Chooz 9Li 8He rate 0.4/day (2x
  Chooz)
• Uncertainty can be checked by single reactor data
  (30 of the time), better if both reactors off
  (rare but only need 2 weeks)
• External Neutrons (prompt capture) ? 1 /day
  after veto and energy cut (Far detector, MC
  studies are continuing)

12
Systematics

• Goal is systematic uncertainty of 0.6

CHOOZ Double Chooz
Reactor Cross section 1.9 ------
Number of protons 0.8 0.2
Detector efficiency 1.5 0.5
Reactor power 0.7 ------
Energy per fission 0.6 ------
13
Systematics cont.

• Position 10cm (Chooz) ? 0.15 due mainly to near
  detector
• Volume Chooz absolute uncertainty 0.3, Double
  Chooz aims for 0.15 relative uncertainty
• Same mobile tank to fill both targets
• Build both inner acrylic vessels at manufacturer
• Combine weight and flux measurement of liquid
  going in
• Density - single scintillator batch temp
  control ? 0.1 relative uncertainty
• Number H atoms - single batch again

14
Systematics cont.

• n capture eff. 0.2 rel. error (AmBe, Cf
  sources)
• Spill in-out effect cancels for identical
  detectors
• 2nd order effect due to solid angle between
  near and far detectors and correlation between
  prompt and neutron capture angle ? 0.2 error
• 500 keV Prompt e E cut inefficiency 0.1 (MC)
  , therefore rel. uncertainty neg.
• Uncertainty on background 10. S/N100 so rel.
  error small
• Selection cuts reduce number of cuts from 7
  (CHOOZ) to 2 (Energy, time)
• E cut on n capture 6 MeV 100 keV error ? 0.2
  error on number of ns
• Time (prompt to delayed) should be negligible
  rel. error
• Dead time again should be controlled, must be
  measured very accurately

15
Systematics detail
Double Chooz Goal
Solid angle 0.2
Volume 0.2
Density 0.1
Fraction H atoms 0.1
Neutron Efficiency 0.2
Neutron Energy cut 0.2
Time cut 0.1
Dead time 0.2
Acquisition 0.1
Background 0.2
Total 0.6
16
Milestones

• Detector Construction Can Begin In 2006
• Near Laboratory
• Finalize designs in 2005
• Civil construction 2006-7
• Data Taking
• Oct 07 Sin22q13 gt (0.19) with far detector
  alone
• Nov 07 Near Detector Completion
• Dec 08 Sin22q13 gt ( 0.05) sensitivity - 2
  detectors
• Dec 10 Sin22q13 gt ( 0.03)

17
Phototubes

• Baseline 1040 8 PMTs in two detectors
• 12.9 photo-cathode coverage
• 190 pe/ MeV (MC)

• PMT related backgrounds about MC radioassay
  estimates from Hamamatsu, ETI). Also crushed two
  PMTs to check company estimates, OK
• Recent work on
• Cabling schemes
• Sensitivity to B fields
• Angular sensitivity
• Tilting tube options
• Phototube comparisons

18
Outer Veto (Near detector)

• The Outer Veto provides additional tagging of m
  induced background ns.
• Prototype counters designed/tested
• A Fluka simulation of ms aimed at the near
  detector is being used to specify needed coverage

19
Expected Sensitivity 2007-2012

• Far Detector starts in 2007
• Near detector follows 16 months later
• Double Chooz can surpass the original Chooz bound
  in 6 months
• 90 C.L. contour if sin2(2?13)0
• ?m2atm 2.8 10-3 eV2 is supposed to be known at
  20 by MINOS

20
Low q13 not theoretically favored
Region of q13 accessible to Double CHOOZ
2.
1.
21
Summary

• Possibility to measure q13 on a time scale useful
  for an accelerator program.
• Double Chooz is an evolutionary experiment with
  respect to systematic errors.
• Experience from a wide variety of n experiments,
  but particularly Chooz, Palo Verde, KamLAND, LENS
  Borexino.
• RD for larger reactor experiments (scintillator,
  systematic errors, backgrounds.)

22
Extra slides
23
Correlated Neutrons from Missed Stopped Muons

• R (1-e)Rm fm- fc fn
• veto efficiency 0.999
• Rm stopped mu rate 6 and 0.05 Hz
• fm- fraction of m- 0.44
• fc capture fraction 0.079
• fn fraction neutron 0.80

Conservative assumes stopped muon deposits
energy in right range
NEAR 15/day FAR 0.2/day
(signal 4000/day)
(signal 85/day)
24
Prompt neutron production inside DC

• 5000 h-1 (Near) and 540 h-1 (Far) from comparing
  CTF, MACRO, LVD results and scaling via E0.75
  method.
• Chooz measured rate was 45 h-1 for all tagged
  neutron-like events g (2/0.8)(45) 113 h-1 in
  Double Chooz Far.
• 99.9 efficient veto for Far gives 3 d-1 from
  Chooz measurement.
• Using scaling from Chooz for Near gives 1150
  h-1 (gives 30 d-1 after 99.9 veto). 300 ms veto
  gets rid of most.

25

• Using Reactor Off Data g 0.4 9Li event/day at
  most in Double Chooz FAR. 0.5 of expected
  signal.
• Chooz 12 each spend 15 of time off in the
  normal cycle. Almost 1/3 of the time we will have
  50 power. History shows that zero power occurs
  periodically, also.
• 178 ms half-life and low muon rate through Far
  target gives an opportunity to measure this to
  required 10 precision
• extrapolation to Near gives 6/day (0.15 of
  signal). Reduced power/Reactor Off for even 1
  week sufficient.

26
Fast Neutrons
27
First Test Simulation of the original Chooz
detector

• Shielding depth 300 m.w.e
• Muon flux 0.67 /m2s
• Target volume 5.6 m3
• Simulated time 31 hours

28
Simulation of the original Chooz detector
Neutron rates
Target Target (after Veto cut)
Neutron rate /hour 26.3 ? 0.9 0.13 ? 0.06
(four events!)
29
Simulation of the original Chooz detector Result

• The correlated neutron background in the Chooz
  experiment was simulated, with the most likely
  value being 0.8 events/day.
• A background rate higher than 1.6 events/day can
  be excluded at a 90 confidence level.
• Compare to the measured correlated neutron
  background rate 1.0 events/day.
• The MC is reliable!

30
Correlated neutron background in the Double Chooz
detector
31
Visible energy deposition by neutrons no muon
veto
Shielding 100 m.w.e. Time 42.9 h
32
Visible energy deposition by neutrons after
muon veto cut
Shielding 100 m.w.e. Time 42.9 h
33
Visible energy deposition by neutrons after
muon veto cut
Visible energy deposition
Shielding 100 m.w.e. Time 42.9 h
34
Correlated neutron background in the Double Chooz
detector

• 337.729.956 muons tracked (42.92 hours simulated
  time)
• 1985 hours computer time
• 580335 neutrons tracked
• 20642 neutrons thermalized in the target
• 21 neutrons undetected by muon veto
• 1 neutron created a correlated background event

35
Results - 1

• The neutron capture rate in the Gd-loaded target
  is about 480/hour at 100 mwe
• scaling 920/hour (Near) and 90/hour (Far)
• from Chooz 1150/hour (Near) 113/hour (Far)
• Only 0.3 of these neutrons create a signal in
  the scintillator within the energy window of 1MeV
  8MeV
• A total correlated background rate gt 2
  counts/day can be excluded at 98 (for 100 m.w.e.
  shielding)

36
Total Muon Rates

• NEAR 600 Hz (flat) 1100 Hz (hemi) at 60
  mwe (proposal 570 Hz)
• FAR 25 Hz (proposal 24 Hz)
• Stopping 2 Hz (flat) 4 Hz (hemi)

37
Stopping Muon Rate (10 tons)
Stopping ms from White Paper 2 Hz
NEAR

• DC proposal
• 3 Hz (flat)
• 6 Hz for
• hemispherical

38
Good Agreement
White Paper 0.03 Hz DC proposal 0.025
FAR
39
Correlated Neutrons from Missed Stopped Muons

• R (1-e)Rm fm- fc fn
• veto efficiency 0.999
• Rm stopped mu rate 6 and 0.05 Hz
• fm- fraction of m- 0.44
• fc capture fraction 0.079
• fn fraction neutron f.s. 0.80

Conservative assumes stopped muon deposits
energy in right range
(signal 4000/day)
NEAR 15/day FAR 0.2/day
(signal 85/day)
Note can measure using outer veto and energetic
stoppers