Double Chooz - GDR neutrino

Transcription

Double Chooz
Alessandra Tonazzo - APC Paris, Université Paris 7
on behalf of the Double Chooz Collaboration
400 m
• A reminder on the
experimental concept
• Current status
• Ongoing activity
• Expectations
GDR neutrino, CEA Saclay 11/04/08
0
θ13: what we know, why we need more
Measurement at reactors:
The CHOOZ
Experiment
• P(νe→νe) independent of δ-CP, weak
dependence on Δm221
• O(MeV) + small distances ⇒ Matter
effects negligible ⇒ measurement
independent of sign(Δm213)
“Clean” θ13 measurement,
complementary to beams
Experiments can be carried out on a
short time scale and for relatively low
cost ⇒ input on roadmap for future
beams
(cfr talk by T.Schwetz yesterday)
M.Apollonio et. al., Eur.Phys.J. C27 (2003) 331-374
sin 2 2"13 < 0.12 (90%CL)
dominating the present combined limit
1
Reactor θ13 projects «today»
Double Chooz
RENO
Daya Bay
Angra
2
ν detection at reactor experiments
N" ( s#1 ) = 6N Fiss ( s#1 ) $ 2 %1011 P ( s#1 )
P=8GW ⇒Nν~1021s-1 on all solid angle
!
Detection by “inverse beta”
νe + p → e + + n
in scintillator
Prompt photons from e+ annihilation
Ee = Eν + 1.8 MeV + O(Ee/mn)
Delayed photons from n capture on H
or dedicated nuclei (Gd)
Δt ~ 30 µs E ~ 2 MeV [H], 8 MeV [Gd]
3
θ13 at reactors : Backgrounds
µ
Accidental bkg:
• e+-like signal: radioactivity from
materials, PMTs, surrounding rock
(208Tl). (Rate=Re)
• n signal: n from cosmic µ spallation,
thermalised in detector and captured
on Gd (Rn);
γ mimicking n
 Accidental coincidence
Rate = Re x Rn x Δt
µ capture
µ
9Li->e+ n
µ
Gd
Recoil p
n from µ
capture
µ
Gd
Gd
Gd
n capture Recoil p
on Gd
Spallation fast
neutron
Spallation
neutron
Correlated bkg:
 fast n (by cosmic µ) recoil on p (low
energy) and captured on Gd
 long-lived (9Li, 8He) β+n-decaying
isotopes induced by µ
Expect Signal/Bkg > 50
4
How can we improve on CHOOZ ?
CHOOZ : Rosc = 1.01 ± 2.8% (stat) ± 2.7% (syst)
•
Statistics
– Larger detection volume
– Longer exposure
•
Experimental error: ν flux and cross-section uncertainty
– Multi-detector
– Improve detector design
– Identical detectors to reduce inter-detector systematics
(normalisation, calibration …)
•
Background
– Improve detector design
larger S/B
– Increase overburden
– Improve bkg knowledge by direct measurement
5
The "new" experimental concept
Bugey data vs
α θ13
NEW
Imperfect knowledge of
physical processes in
reactors: error ~2%
Use Near Detector
Reactor
Far Detector
Near Detector
νe
νe?
2
6
The Double Chooz Collaboration
 France: CEA/IRFU Saclay, APC Paris,
Subatech Nantes, Strasbourg
 Germany: MPIK Heidelberg, TU München, EKU
Tübingen, Universität Hamburg, Aachen
 Japan: Tohoku, Tokyo, Niigata, …
 Russia: RAS, Kurchatov Institute (Moscow)
 Spain: CIEMAT (Madrid)
 UK: Sussex
 USA: Alabama, ANL, Chicago, Columbia,
Drexel, Kansas State, LSU, LLNL, Notre Dame,
Tennessee, IIT, U.C.Davis
Spokesperson: H. de Kerret (APC)
Project Manager: F. Ardellier (Saclay)
Proposal: hep/ex 0606025
Press release
CEA+CNRS
(France)
19/09/06
7
The Chooz site in the Ardennes
@ 400m
115m.e.w.
Chooz-B Reactors
@ 1050m
300m.e.w.
Meuse
River
8
Neutrino labs
Far site:
Existing experimental hall+pit of
the Chooz experiment will be used
• d = 1050 m
• overburden ~ 300 m.w.e. hill
• ~70 neutrino events/day
Near site:Location defined:
NEW
under a small natural hill
• <d> = 400 m
• overburden >114m.w.e., nearly flat
• ~500 neutrino events/day
9
The detector(s)
OTHER SYSTEMS
-Outer Muon Veto System
-Calibration Systems
-Glove Boxes
Active nu target +
Active shielding +
Passive shielding
TARGET : (th=2,3m)
-Acrylic vessel (th=8mm)
- 10,3 m3 LS doped with 0,1% Gd
Acrylic vessels  «hardware»
definition of fiducial volume
GAMMA CATCHER : (th. = 0,55m)
-Acrylic vessel (th= 8mm)
- 22,6 m3 LS (identical to target)
7m
SHIELDING
@ far site: 15cm Steel
~300t
Buffer : (th.=1,05m)
-Stainless steel vessel (th = 3 mm)
-114,2 m3 mineral oil
-392 PMTs (10 inches)
7m
Inner VETO: (th = 0,5 m)
-Steel vessel (th = 10 mm)
-~80 m3 LS
78 PMTs
10
The detector(s)
Electronics racks
OTHER SYSTEMS
Outer Muon Veto:
Plastic scintillator strips
with X/Y meas
OTHER SYSTEMS
-Calibration Systems
-Glove Boxes
11
R&D + Testing
Gd-doped
scintillator
Acrylic vessels
DAQ
fADCs
Gd-dpm3
PMTs in B-field
CAEN
V1721
L1 trigger board
Material
compatibility
Outer Veto
cosmics
test
Precise
mass meas.
500 MHz - 8bit
under test
@APC
Scintillator
response simulation
12
R&D + Testing
Gd-doped
scintillator
Gd-dpm3
Requirements:
20%PXE + 80%Dodecane
+ 0.1% Gd beta-diketonate
- light transmission in PMT
sensitivity window
- attenuation length >~10m
- Stability over experiment's
lifetime (remember Chooz-1
problem...) :
checked over ~3yrs @T=20o
and T=40o (accelerated)
- Radiopurity
13
Prototyping
1) Scale 1/5 Double Chooz detector
2) Detection of neutrino at JoJo reactor (Japan)
with Kaska prototype
Last stage for the validation of the technical choices for
vessels construction, material compatibility, filling,
and the integration of the detector at the Chooz site
Total of 2000 l of oil
Filling 13/12/2005
Operation ~4 months
Results on scintillator
stability in realisic operation
conditions, although on
short term, are encouraging
- Inner Target: 120 l :
20%PXE+80%dodecane+
0.1%Gd
- Gamma Catcher: 220 l :
20%PXE+80%dodecane
- All Teflon filling system
14
Current activity: Far lab integration
Cleanliness +
radiopurity
measurements
ongoing
Pit refurbished
Access
adapted
15
Current activity : Far detector shield
Steel shielding bars
(~300t, low radioactivity)
demagnetization in progress
8m
16
Current activity : Near lab
Near neutrino lab:
Neutrino Lab
Geological survey
Finalization of access tunnel
+ lab excavation design
>45 m rock
overburden
85 m open air ramp (14%)
155 m of gallery (12%)
y
~12 m
P
ar
n
i
relim
Liquid Handling and
Storage Building
24 m
17
Current activity : Production
Scintillator production:
main components needed for
both detectors have been
delivered & checked
[Heidelberg]
Gd salt:
100 kg
PXE:
8 tons
Mixing to be done in one batch
then transported to site for each detector
Tool for acrylics
handling
PMT support+shield
Target liquid tanks
Iso-tank for GC liquid
18
Current activity : Measurements
Material radioactivity measurements
@LNGS, Modane,Oroville, Saclay
Saclay Ge detector + clean room
PMT response
measurement
19
sin2(2θ13)
DC timescale
2009
20
Systematic uncertainties
 Oscillation parameters
 Δm231 = 2.5 10-3 eV2
 Pull diagram assumptions: computations for 3 y data taking
21
Other potentials
The Double Chooz concept can do more than just measure
neutrino oscillations. Studies for :
 Measurement of reactor thermal power (cfr A.Porta's talk)
Independent of methods used by electric companies
 Non proliferation (cfr A.Porta's talk)
Neutrinos as a new safeguard tool:
Monitor isotopic composition to ensure that civilian nuclear
facilities are not used for military purposes (239Pu etc.)
 Geo-neutrinos
Neutrinos as “probes of the Earth’s interior”
cfr Kamland, Nature 436, 499-503 (28 July 2005)
22
Summary and outlook
•
A new experimental concept to measure θ13:
one reactor and two (or more…) detectors
– Double Chooz will be the first of a new generation of neutrino
experiments based on this concept
•
Ongoing activity
– We are in the construction phase
•
It’s coming soon !
–
–
–
–
2008: start installation of far detector
2009: start data taking with far detector
2010: near detector installation
2012: reach sensitivity sin22θ13~0.03 (for Δm231=2.5x10-3 eV2)
23
Backup: Systematic uncertainties
Chooz
Reactorinduced
Detector
- induced
ν flux and σ
1.9 %
<0.1 %
Reactor power
0.7 %
<0.1 %
Energy per fission
0.6 %
<0.1 %
Solid angle
0.3 %
<0.1 %
Volume
0.3 %
0.2 %
Precise target mass measurement
Density
0.3 %
<0.1 %
Accurate T control (near/far)
H/C ratio &
Gd concentration
1.2 %
<0.1 %
Same scintillator batch + Stability
Spatial effects
1.0 %
<0.1 %
Spill in/out compensate to ~1%
?
0.25 %
Difference near/far is relevant !
1.5 %
0.2 - 0.3 %
(see previous slide)
2.7 %
< 0.6 %
Live time
Analysis
Double-Chooz
From 7 to 3 cuts
Total
Two ‘’identical’’ detectors,
Low bkg
24
The "new" experimental concept
Far vs Near :
two independent sets of information
Normalisation / Spectrum distortion
Dominating at intermediate / high statistics
Ethr
1.0
sin2(2θ13)=0.04
sin2(2θ13)=0.1
sin2(2θ13)=0.2
Ratio Obs/Th
0.9
1.0
0.9
hep-ex/0402041
hep-ex/0606112
0.8
25
Background studies
Accidentals
• radioactivity (dominated by PMTs) +
neutrons induced by cosmic muons
• request singles rate ~5Bq (above 0.7
MeV)
Radiopurity constraints on
detector materials single rate
<0.1 Hz from each contribution
Less stringent than KamLAND and
Borexino, but needs care
Correlated
old Chooz reactor-off data = ~1.5d-1
~50%fast-n/~50%9Li
• validate simulation (Geant-4, Fluka)
• extrapolate to Far and Near detector
Measurements in correlation with
muon signal in the Outer Veto will
provide important information
µ
26
Background studies
Bkg/Signal >50
hep-ex/0606025
estimates with "old" near detector location
= conservative
(with new location: Nnu/2 , Nµ/3)
27
Systematic uncertainties
•
Backgrounds
B/S reduced by larger buffers + outer veto +overburden
Double acrylics vessel ⇒ no need for fiducial volume cut
•
e+
Analysis
n
*
*
*
Δt
* Easier to control near vs far
than absolute
28

Double Chooz - GDR neutrino

Transcription

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