Dazeley WG1

Double Chooz: 

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

Introduction: 

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

Introduction (ne oscillations): 

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

Appearance measurement of q13?: 

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 (m1<m2<m3), 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. Can’t separate the CP violation phase d and q13 In addition long baseline beam experiments  matter effects

Slide5: 

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

The Chooz Site: 

The Chooz Site 2 x 4200MW Reactors 1100m Baseline 300MWE Overburden

CHOOZ result: 

CHOOZ result nep→e+n; Neutron/positron coincidence 200 days reactor on; 142 days reactor off Stopped due to systematic error of reactor flux

Double Chooz Improvements on Chooz: 

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

Slide9: 

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 2007 with the far detector Optically separated inner veto to tag muons

Backgrounds (accidentals): 

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

Backgrounds (Correlated): 

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)

Systematics: 

Systematics Goal is systematic uncertainty of 0.6%

Systematics cont.: 

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

Systematics cont.: 

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

Systematics detail: 

Systematics detail

Milestones: 

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

Phototubes: 

Phototubes

Outer Veto (Near detector): 

Outer Veto (Near detector) The Outer Veto provides additional tagging of m induced background n’s. Prototype counters designed/tested A Fluka simulation of m’s aimed at the near detector is being used to specify needed coverage

Expected Sensitivity 2007-2012: 

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

Low q13 not theoretically favored : 

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

Summary: 

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

Extra slides: 

Extra slides

Correlated Neutrons from Missed Stopped Muons: 

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 NEAR: ~15/day FAR: ~0.2/day Conservative: assumes stopped muon deposits energy in right range (signal ~4000/day) (signal ~85/day)

Prompt neutron production inside DC: 

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.

Slide25: 

Using Reactor Off Data g 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.

Fast Neutrons: 

Fast Neutrons

First Test: Simulation of the original Chooz detector: 

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

Simulation of the original Chooz detector: Neutron rates: 

Simulation of the original Chooz detector: Neutron rates (four events!)

Slide29: 

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

Correlated neutron background in the Double Chooz detector: 

Correlated neutron background in the Double Chooz detector

Visible energy deposition by neutrons – no muon veto: 

Visible energy deposition by neutrons – no muon veto Shielding = 100 m.w.e. Time = 42.9 h

Visible energy deposition by neutrons – after muon veto cut: 

Visible energy deposition by neutrons – after muon veto cut Shielding = 100 m.w.e. Time = 42.9 h

Visible energy deposition by neutrons – after muon veto cut: 

Visible energy deposition by neutrons – after muon veto cut Shielding = 100 m.w.e. Time = 42.9 h Visible energy deposition

Correlated neutron background in the Double Chooz detector: 

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

Results - 1: 

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)

Total Muon Rates: 

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)

Stopping Muon Rate (10 tons): 

Stopping Muon Rate (10 tons) Stopping m’s from White Paper: 2 Hz NEAR DC proposal: 3 Hz (flat) ~6 Hz for hemispherical

Good Agreement : 

Good Agreement FAR White Paper: 0.03 Hz DC proposal: 0.025

Correlated Neutrons from Missed Stopped Muons: 

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