Double Chooz

Double Chooz

Optimizing Chooz for a possible Theta 13 measurement

Steven Dazeley (Louisiana State University)NuFact05 Rome

NuFact05, Rome Steven Dazeley (Louisiana State Univ.)

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Introduction

• Quark mixing is small (CKM matrix)

• Lepton mixing is mostly large (PMNS matrix) , except for θ13, which is constrained to be small. The Chooz upper limit on sin2(2θ13) is 0.2

• Why?

• Might help to nail down θ13


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Introduction (e oscillations)

e survival probability can be written as:

P(e e) ≃ 1 – sin2(213) sin2(m213L/4E)

assuming latest measurements of m223,

m212, sin2(223) and sin2(212) from SK, SNO

and KamLAND.

A good reactor 13 reactor disappearance experiment can achieve a clean measurement of 13


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Appearance measurement of 13?

• Naively 13 with an appearance experiment seems easier. However in practice it is difficult to get a “clean” measurement of 13

• Assuming a “normal” mass hierarchy (m1<m2<m3), the e survival probability can be written as:

P( e) ≃ sin2(213) sin 2 (223) sin2(m231L/4E)

∓ sin(213) sinsin(212) sin(223) (m2

31L/4E) sin 2(m231L/4E)

– sin(213) cossin(212) sin(223) (m2

31L/4E) cos(m231L/4E) sin(m2

31L/4E) + cos223 sin2(212) (m2

31L/4E)2

where the ∓ term refers to neutrinos(-) or antineutrinos(+), and m2

12/ m223

• A complicated equation that suffers from parameter correlations and degeneracies. Can’t separate the CP violation phase and 13

• In addition long baseline beam experiments matter effects


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Near site: D~100-200 m, overburden 50-80 mweFar site: D~1.1 km, overburden 300 mwe

Type PWR

Cores 2

Power 8.4 GWth

Couplage 1996/1997

(%, in to 2000) 66, 57

Constructeur Framatome

Opérateur EDF

Chooz-Far

Chooz-Near

Double-Chooz


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Chooz-near

Chooz-far

The Chooz Site

2 x 4200MW Reactors

1100m Baseline300MWE Overburden


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CHOOZ result

Sin22θ13 < 0.19 (at 2.0 x10-3 eV2)

ep→e+n; Neutron/positron coincidence

200 days reactor on; 142 days reactor off

Stopped due to systematic error of reactor flux

Palo Verde

Chooz

SK allowed sin22θ13 (90% CL)

sin22θ13

∆m

2

Adam Bernstein

bars over nu symbols look odd on my PC . There is a bar ovr the C in CHooz in the title.


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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 > 50000 events, Compare with Chooz ~2700)

• Reactor steady operation (Chooz ran during reactor commissioning phase)

• Stable scintillator (MPI-Heidelberg R+D for LENS)

} Allows lower threshold


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Double-CHOOZ(far) Detector

Gamma catcher: scintillator with no Gd

7 m

7 m

BUFFER Mineral Oil with no scintillator

7 m

Shielding steel and external vessel(studies, réalisation, intégration IN2P3/ PCC)

Target- Gd loaded scintillator

Modular Frame to support photomultipliers

We will start data-taking in 2007with the far detector

Optically separated inner veto to tag muons

Adam Bernstein

slight rephrasing of first sentence


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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/gK in scint ~ 10-10 g/gU,Th in acrylic ~ 10-10 g/gK 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 n’s due to U, Th in target nint ≃ 0.4 s-1 (CU,Th/10-6), i.e. negligible


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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)


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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% ------


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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


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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/N~100 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

n’s Time (prompt to delayed) – should be negligible rel. error Dead time – again should be controlled, must be measured very

accurately


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Systematics detailDouble 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%


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Milestones

Detector Construction Can Begin In 2006 Near Laboratory

Finalize designs in 2005Civil construction 2006-7

Data TakingOct 07 Sin2213 > (0.19) with far detector aloneNov 07 Near Detector CompletionDec 08 Sin2213 > ( 0.05) sensitivity - 2 detectorsDec 10 Sin2213 > ( 0.03)

2003 2004 2005 2006 2007 2008 2009Site Data takingProposal Construction ?& design

Far detector starts Near detector starts

Adam Bernstein

first bullet all info on one lineDetector Construction Can Begin in 2006( I know this seems mundane but it helps with clarity)


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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

Adam Bernstein

emphasize that this slide and the next two is all US work - it is not obvious.


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Outer Veto (Near detector) The Outer Veto provides additional tagging of induced background n’s.

Prototype counters designed/tested

A Fluka simulation of ’s aimed at the near detector is being used to specify needed coverage


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Far detector only

Far & Near detectorstogether

05/2007 05/2008 05/2009 05/2010

sys=2.5%

sys=0.6%

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(213)=0

m2atm = 2.8 10-3 eV2 is

supposed to be known at 20% by MINOS


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Low 13 not theoretically favored

Region of 13 accessibleto Double CHOOZ

1.2.

Adam Bernstein

The list of values on the right is hard to read and doesn't add much information


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Summary• Possibility to measure 13 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 experiments,

but particularly Chooz, Palo Verde, KamLAND, LENS & Borexino.

• R&D for larger reactor experiments (scintillator, systematic errors, backgrounds.)


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Extra slides


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Correlated Neutrons from Missed Stopped Muons

R = (1-)R ffc fn

veto efficiency = 0.999R stopped mu rate = 6 and 0.05 Hzf fraction of = 0.44fc capture fraction = 0.079fn fraction neutron = 0.80NEAR: ~15/day

FAR: ~0.2/day

Conservative: assumes stopped muondeposits energy in right range

(signal ~4000/day)

(signal ~85/day)


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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 (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 s veto gets rid of most.


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• Using Reactor Off Data 0.4 9Li event/day at most in Double Chooz FAR. 0.5% of expected signal.

• Chooz 1&2 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.


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Fast Neutrons


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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


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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!)


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• 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!

Simulation of the original Chooz detector: Result


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Correlated neutron background in the Double Chooz detector


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Visible energy deposition by neutrons – no muon veto

Shielding = 100 m.w.e. Time = 42.9 h


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Visible energy deposition by neutrons – after muon veto cut



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Visible energy deposition by neutrons – after muon veto cut


Visible energy deposition


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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


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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 > 2 counts/day can be excluded at 98% (for 100 m.w.e. shielding)


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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)


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Stopping Muon Rate (10 tons)

Stopping ’s fromWhite Paper: 2 Hz NEAR

DC proposal:3 Hz (flat)

~6 Hz forhemispherical


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Good Agreement

FARWhite Paper:0.03 Hz

DC proposal:0.025


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Correlated Neutrons from Missed Stopped Muons

R = (1-)R ffc fn

veto efficiency = 0.999R stopped mu rate = 6 and 0.05 Hzf fraction of = 0.44fc capture fraction = 0.079fn fraction neutron f.s. = 0.80NEAR: ~15/day

FAR: ~0.2/day

Conservative: assumes stopped muondeposits energy in right range

(signal ~4000/day)

(signal ~85/day)Note: can measure using outer veto and energetic stoppers

Double Chooz

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