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The Quest for θ 13 with the Double Chooz Detector. Jelena Mari čić Drexel University On behalf of the Double Chooz Collaboration. Outline. Physics motivation for the Double Chooz experiment Repetitio est mater studiorum Challenges of the high precision reactor neutrino experiment

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jelena mari i drexel university on behalf of the double chooz collaboration

The Quest for θ13 with the Double Chooz Detector

Jelena Maričić

Drexel University

On behalf of

the Double Chooz Collaboration

  • Physics motivation for the Double Chooz experiment
    • Repetitio est mater studiorum
  • Challenges of the high precision reactor neutrino experiment
  • Detector overview
  • Future prospects

J. Maricic-Double Chooz

neutrino oscillations
Neutrino oscillations

(ne,nm,nt)T = U (n1,n2,n3)T

U=matrice PMSN : 3 angles,1cp violation phase

(+2 mass differences)

solar n

leptonic CP phase d

atmospheric n

θ23 ~ 45


q13< 13

θ12 ~ 32

*CP violation is responsible

for matter- antimatterasymmetry

Leptons = e, , , e, , 

Leptonic CP violation phase 

completely unknown

Θ13 small  directly affects prospects of measuring

leptonic CP violation phase

The future quest for 13

Accelerators Reactors

J. Maricic-Double Chooz


13& Reactor Experiments

  • <E> ~ a few MeV  only disappearance experiments sin2(213) measurement independent of -CP
  • 1-P(e e) = sin2(213)sin2(m231L/4E) + O(m221/m231)
  •  weak dependence in m221
  • a few MeV e + short baselines  negligible matter effects (O[10-4] )
  •  sin2(213) measurement independent of sign(m213)

13 & Accelerator Experiments

Appearance probability :

 dependences in sin(223), sin(23), sign(m231), -CP phase in [0,2]

J. Maricic-Double Chooz

how well can we measure cp violation
How well can We Measure CP Violation?


without beam


Even with

beam upgrade

chance <15%

If sin22θ13

< 0.025

NOvA and T2K

will not start before


Courtesy of R. Svoboda

It would be great to know ASAP if the value of θ13 is large or small

J. Maricic-Double Chooz

best current constraint chooz

e e (disappearance experiment)

Pth= 8.4 GWth, L = 1.050 km, M = 5 toverburden: 300 mwe

Best current constraint: CHOOZ

R = 1.01  2.8%(stat)2.7%(syst)

World best constraint!

@m2atm = 2 10-3 eV2

sin2(2θ13) < 0.2

(90% C.L)

e  x

M. Apollonio et. al., Eur.Phys.J. C27 (2003) 331-374

J. Maricic-Double Chooz

reactor neutrino detection signature
Reactor Neutrino Detection Signature
  • Reactors are tremendous sources of neutrinos:

P = 8GW  N~1021s-1

Neutrino detection:

+ 



Distinctive two-step signature:

-prompt event

Photons from e+ annihilation

Ee = E+ 0.8 MeV + O(Ee/mn)

-delayed event

Photons from n capture on dedicated

nuclei (Gd)

t ~ 30 s E ~ 8 MeV

J. Maricic-Double Chooz

expected backgrounds in reactor neutrino experiments
Expected Backgrounds in Reactor Neutrino Experiments

Accidental bkg:

  • e+-like signal: radioactivity from materials, PMTs, surrounding rock Rate=Re
  • n signal: n from cosmic  spallation, thermalized in detector and captured on Gd (Rn)

 Accidental coincidence

Rate = Re x Rn x Δt

Correlated bkg:

  • fast n (by cosmic ) recoil on p (low energy) and captured on Gd
  • long-lived (9Li, 8He) -decaying isotopes induced by 

Bkg reduction and knowledge is critical for oscillation measurement !

J. Maricic-Double Chooz




Target volume

5,55 m3

10,2 m3

Target composition

6,77 1028 H/m3

6,82 1028 H/m3

Data taking period

Few months

3-5 years

Event rate


Far: 60 000/3 y

Near: ~3 106/3 y

Statistical error



How Can We Improve Limit on θ13 Based on Experience with CHOOZ ?

CHOOZ : Rosc = 1.01 ± 2.8% (stat) ±2.7% (syst)

  • Statistics
    • More powerful reactor


    • Larger detection volume
    • Longer exposure
  • Experimental error:  flux and cross-section uncertainty
    • Multi-detector
    • Identical detectors to reduce inter-detector systematics

(goal: towards σrelative~0,6%)

  • Background
    • Improve detector design larger S/B
    • Increase overburden
    • Improve bkg knowledge by direct measurement
    • subtraction error<1%

 Luminosity increase L = t x P(GW) x Np

J. Maricic-Double Chooz


13 at Reactors: The Double Chooz a New Experimental Concept

1,050 m

280 m

Far Detector


Near Detector





P(ee) ~

1 - sin2 213 sin2(m213L/4E)+…

J. Maricic-Double Chooz

13 at reactors
13 at Reactors

Two independent sets of information:

Normalisation + Spectrum distortion

m2atm = 2.0 10-3 eV2




Events/200 KeV/3 years

E (MeV)

Far Detector: ~

60 000events/3y

-Reactor efficiency: 80%

-Detector efficiency: 80%

E (MeV)

Near Detector: ~ 3 106 events/3y

-Reactor efficiency: 80%

-Detector efficiency: 80%

-Dead time: 50%

J. Maricic-Double Chooz

detector overview
Detector Overview

J. Maricic-Double Chooz

the chooz site
The Chooz Site

~1000 ev/day

~70 ev/day

80 m.w.e.

300 m.w.e.

Chooz-B reactors

J. Maricic-Double Chooz

reactor induced systematics
Reactor-Induced Systematics

Distance ratio

exactly cancels

reactor thermal

power uncertainty.




Uncertainty due

to solid angle is



J. Maricic-Double Chooz


511 keV

511 keV






 ~ 8 MeV

The detector design

Muon Outer-VETO:

7 m

  • -target: 80% dodecane + 20% PXE + 0.1% Gd

Volume for -interaction

-catcher: 80% dodecane + 20% PXE

Extra-volume for -interaction


Acrylic vessels  «hardware» definition of fiducial volume

Non-scintillating buffer: same liquid (+ quencher?) Isolate PMTs from target area

Muon Inner-VETO: scintillating oil

Shielding: steel 17 cm: >7

 Improved background reduction

PMT support structure: steel tank, optical insulation target/veto

J. Maricic-Double Chooz

the detectors
The detectors

AcrylicTarget vessel

(Inner radius =1,15m

H = 2,474m

t = 8mm)

Acrylic Gamma catcher vessel

(Inner radius= 1,696m

Inner H = 3,55 m

t = 12mm)


LS + 0,1%Gd

Stainless steel Buffer

(Inner radius = 2,758m

Inner H = 5,674m

t = 3mm)

Muons VETO


Inner radius = 3,471m

Thickness = 200mm

J. Maricic-Double Chooz

technological challenges
Technological Challenges

J. Maricic-Double Chooz

what is the state of the art
What is the State of the Art?
  • Chooz had a 1.6% absolute detector systematic uncertainty, the best to date. Total uncertainty 2.7%
  • Bugey is the only experiment that has tried to build identical detectors. Result was 2.0% relative error. 5.0% total.
  • Double Choozgoal is 0.6% relative uncertainty.

J. Maricic-Double Chooz

how will we do this
How will We Do This?
  • We will use a physical tank for the fiducial volume instead of fitted vertex, unlike KamLAND, which has 4.7% uncertainty doing this (before 4p system)
  • We will control detector temperature at Near and Far Detector with active heating.
  • We will remix scintillator when starting Near Detector, or else throwaway first batch.
  • We will control the magnetic field inside detector and have developed a way to demagnetize the steel components. All PMT’s will have individual  metal shields.

J. Maricic-Double Chooz

  • We have developed systems to measure the mass of target poured into each detector (0.2%)
  • We have considered variation of g, effects of finite size core and detector on distance (<0.1%)
  • We have considered effects of different depth for Near and Far (<0.1%)
  • Swapcalibrationsystems, which can be done easily, cheaply, and at the same time

J. Maricic-Double Chooz

scintillator stability studies
Scintillator Stability Studies
  • Solvant: 20% PXE – 80% Dodecane
  • Gd loading: being developed @MPIK & LNGS
    • 0.1% Gd loading
    • Two formulations under study:
    • Gd-CBX Based on Carboxilic acids (+stabilizers)
    • Gd-Acac & Gd-Dmp Beta Dikitonate
    • Long term Stability
      • LY ~7000 ph/MeV: 6 g/l ppo + 50 mg/l Bis-MSB
      • Attenuation length: a few meters at 420 nm


Long term stability is essential for near-far detector comparison

Results on the different formulation now available on 2 years’ tests.

LY~8000 /MeV

L = 5-10 m

Validation through optical

monitoring of the liquids.

J. Maricic-Double Chooz


A 1/5 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

Stable in the detector

  • Inner Target: 120 l : 20%PXE+80%dodecane+0.1%Gd
  • Gamma Catcher: 220 l : 20%PXE+80%dodecane

All teflon filling system

J. Maricic-Double Chooz




μ capture

n from  capture

Recoil p



Recoil p

n capture

on Gd

Spallation fast


Muon simulation

Measured angular distributions

are well reproduced

  • Knowledge of  fluxes at underground  experiments is essential for a precise determination of the induced backgrounds: spallation n’s, radioactive nuclei, bremsstrahlung ’s…
  • A measurement of  distribution was performed at Chooz in 1995. They were correctly parametrized, but no detailed information on the energy spectrum was available.



Detailed simulation with MUSIC +

rock composition + hill profile:


053007,2006 [hep-ph/0604078]

J. Maricic-Double Chooz







Relative Normalization: Analysis

  • @Chooz: 1.5% syst. err.

- 7 analysis cuts

- Efficiency ~70%

  • Goal Double-Chooz: ~0.3% syst. err.

- 2 to 3 analysis cuts

Selection cuts

    • - neutron energy
    • (- distance e+ - n )
    • [level of accidentals]
    • - t (e+ - n)




J. Maricic-Double Chooz

data acquisition system

Level 1 trigger

(analog sum above 0.5 MeV)


Level 2 trigger

(2 coincident Level 1 triggers)

Event builder

(-like -tagged)


Data Acquisition System


dead-time DAQ

~ 400 (target)

+ 100 (veto) PMTs

Flash-ADC CAEN N(V)1726

developed by APC-Paris + CAEN

  • 4 channels
  • Wave-form sampling @ 500MHz
  • 8-bit resolution (few PEs/ch for ν evts)
  • Continuous digitising with zero deadtime (if DAQ sustains trigger rate)
  • 2s waveform data recording

NIM version available, under test @APC

Several components of VME version ready

J. Maricic-Double Chooz

prospects with double chooz
Prospects with Double Chooz

J. Maricic-Double Chooz

double chooz timeline
Double Chooz Timeline

90% C.L.

Double Chooz will improve

the limit on sin2213

significantly and soon!

  • Data Taking
    • mid 2008 Far detector completion
    • > 1 year sin2213 > ~0.07 with far detector alone
    • 2009 Near detector completion
    • > 1 year sin2213 > 0.04 with 2 detectors
    • > 3 year sin2213 > 0.02-0.03 with 2 detectors







2009… …2011






Data taking

and analysis

J. Maricic-Double Chooz

the double chooz collaboration
group of ~120 scientists from 8 countries

France, U.S., Germany, Spain, Russia, Italy, Brazil, U.K., Japan

Very Experienced: Chooz, Bugey, KamLAND, Super-Kamiokande, SNO,Borexino

The Double Chooz Collaboration

Spokesperson: H. de Kerret (APC)

Over 100 members in the collaboration

J. Maricic-Double Chooz

conclusion and summary
Conclusion and Summary
  • Double Chooz is a significant technological challenge.
  • There has been a huge amount of work done to control systematics in order to minimize technological and cost risk. Backgrounds are under control. It is a huge advantage to have data from a previous neutrino experiment at the same site.
  • The collaboration is extremely experienced, with many members having done several previous reactor experiments.
  • The schedule is conservative and realistic.
  • Double Chooz will achieve an unprecedented high precision measurement for a reactor neutrino experiment.
  • Great gain in knowledge that will in prospect help get tighter constraints on geo-neutrino measurements with future detectors.

J. Maricic-Double Chooz


Complementarity with Superbeams

3 discovery potential

3 sensitivity (no signal)

For a fair comparison of Reactor & Beam programs,

both information should always be quoted together!

J. Maricic-Double Chooz



J. Maricic-Double Chooz


On the median

Near detector location

  • Uncorrelated fluctuations included
  • Relative Error : 0.6%
  • Spectral shape uncertainty 2%
  • m2 known at 20%
  • Power flucutation of each core: 3%

Available and suitable area

~250 m


3 years data taking

J. Maricic-Double Chooz


Phototubes baseline

  • 10‘‘ Ultra low background tubes
  • 365 PMTs
  • 13 % coverage
  • Energy resolution goal: 7 % at 1 MeV
  • Current work:
    • PMT selection (radiopurity)
      • ETL 9354KB ?
      • Hamamatsu R5912 ?
      • Photonis: XP1806 ?
    • Angular sensitivity, Concentrators?
    • Tilting tube options
    • Cabling & Tightness
    • B fields shielding

J. Maricic-Double Chooz







Relative Normalization: Analysis

  • @Chooz: 1.5% syst. err.

- 7 analysis cuts

- Efficiency ~70%

  • Goal Double-Chooz: ~0.3% syst. err.

- 2 to 3 analysis cuts

Selection cuts

    • - neutron energy
    • (- distance e+ - n ) [level of accidentals]
    • - t (e+ - n)




J. Maricic-Double Chooz


How well can they resolve the mass ordering problem?

Phase 1

has no

chance of

even 2s

if sin22q13

< 0.025

Billion $


J. Maricic-Double Chooz


Fit Using Extended Spectrum

Fitted flat backround

rate <8 MeV

is 254/114 days

=2.23(0.14) d-1

Consistent with

published paper

Fit Range



J. Maricic-Double Chooz

role of 13 in neutrino oscillations
Role of θ13 in Neutrino Oscillations

(ne,nm,nt)T = U (n1,n2,n3)T

s13 sin θ13

Chooz experiment

R = 1.01  2.8%(stat)2.7%(syst)

U=matrice PMNS : 3 angles,1CP violation phase

(+2 mass differences)

Only the upper limit on the value of angle θ13 has been set!

Value of θ13directly influences prospects of measuring CP violation phase in the weak sector!

World best constraint: CHOOZ experiment!

(e  e disappearance exp)

@m2atm = 2 10-3 eV2

sin2(2θ13) < 0.2

(90% C.L)

e  x

M. Apollonio et. al., Eur.Phys.J. C27 (2003) 331-374


The future quest for θ13


J. Maricic-Double Chooz