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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 2 Introduction Quark mixing is small (CKM matrix) Lepton mixing is mostly large (PMNS matrix), except for θ 13, which is constrained to be small. The Chooz upper limit on sin 2 (2θ 13 ) is 0.2 Why? Might help to nail down θ 13

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 3 Introduction ( e oscillations)  e survival probability can be written as: P( e  e ) ≃ 1 – sin 2 (2  13 ) sin 2 (  m 2 13 L/4E)  assuming latest measurements of  m 2 23,  m 2 12, sin 2 (2  23 ) and sin 2 (2  12 ) from SK, SNO and KamLAND.  A good reactor  13 reactor disappearance experiment can achieve a clean measurement of  13

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 4 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 (m 1 <m 2 <m 3 ), the e survival probability can be written as: P(   e ) ≃ sin 2 (2  13 ) sin 2 (2  23 ) sin 2 (  m 2 31 L/4E) ∓  sin(2  13 ) sin  sin(2  12 ) sin(2  23 ) (  m 2 31 L/4E) sin 2 (  m 2 31 L/4E) –  sin(2  13 ) cos  sin(2  12 ) sin(2  23 ) (  m 2 31 L/4E) cos(  m 2 31 L/4E) sin(  m 2 31 L/4E) +    cos 2  23 sin 2 (2  12 ) (  m 2 31 L/4E) 2 where the ∓ term refers to neutrinos(-) or antineutrinos(+), and  m 2 12 /  m 2 23 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 5 Near site: D~ m, overburden mwe Far site: D~1.1 km, overburden 300 mwe TypePWR Cores2 Power8.4 GW th Couplage1996/199 7 (%, in to 2000)66, 57 ConstructeurFramatom e OpérateurEDF Chooz-Far Chooz-Near Double-Chooz

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 6 Chooz-near Chooz-far The Chooz Site 2 x 4200MW Reactors 1100m Baseline 300MWE Overburden

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 7 CHOOZ result  Sin 2 2θ 13 < 0.19 (at 2.0 x10 -3 eV 2 ) e p→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 sin 2 2 θ 13 (90% CL) sin 2 2 θ 13 ∆m 2

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 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 > 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 9 Double-CHOOZ (far) Detector Gamma catcher: scintillator with no Gd 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 10 Backgrounds (accidentals) Accidentals U, Th, K in detector, allowed concentrations to achieve accidental rate below 1 s -1 :  U,Th in scint ~ g/g  K in scint ~ g/g  U,Th in acrylic ~ g/g  K in acrylic ~ 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 n int ≃ 0.4 s -1 (C U,Th /10 -6 ), i.e. negligible

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 11 Backgrounds (Correlated) 9 Li, 8 He (  beta-neutron cascades, prompt + capture signature) due to muon spallation has largest uncertainty Chooz measured reactor off data  9 Li, 8 He rate 0.2 /day Therefore Double Chooz 9 Li 8 He 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)

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 12 Systematics Goal is systematic uncertainty of 0.6% CHOOZDouble Chooz Reactor Cross section1.9% Number of protons0.8%0.2% Detector efficiency1.5%0.5% Reactor power0.7% Energy per fission0.6%------

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 14 Systematics cont. n capture eff. – 0.2% rel. error (AmBe, Cf sources) Spill in-out effect – cancels for identical detectors  2 nd 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 15 Systematics detail Double Chooz Goal Solid angle0.2% Volume0.2% Density0.1% Fraction H atoms0.1% Neutron Efficiency0.2% Neutron Energy cut0.2% Time cut0.1% Dead time0.2% Acquisition0.1% Background0.2% Total0.6%

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 16 Milestones  Detector Construction Can Begin In 2006  Near Laboratory  Finalize designs in 2005  Civil construction  Data Taking  Oct 07 Sin 2 2  13 > (0.19) with far detector alone  Nov 07 Near Detector Completion  Dec 08 Sin 2 2  13 > ( 0.05) sensitivity - 2 detectors  Dec 10 Sin 2 2  13 > ( 0.03) SiteData takingProposalConstruction ?& design Far detector starts Near detector starts

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 17 Phototubes ₪Baseline – ” 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 18 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 19 Far detector only Far & Near detectors together 05/ /200805/ /2010  sys =2.5%  sys =0.6% Expected Sensitivity  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 sin 2 (2  13 )=0   m 2 atm = eV 2 is supposed to be known at 20% by MINOS

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 20 Low  13 not theoretically favored Region of  13 accessible to Double CHOOZ 1. 2.

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 21 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.)

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 22 Extra slides

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 23 Correlated Neutrons from Missed Stopped Muons R = (1-  )R  f   f c f n  veto efficiency = R  stopped mu rate = 6 and 0.05 Hz f  fraction of    = 0.44 f c capture fraction = f n 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)

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 24 Prompt neutron production inside DC 5000 h -1 (Near) and 540 h -1 (Far) from comparing CTF, MACRO, LVD results and scaling via E 0.75 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.

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 25 Using Reactor Off Data  Li 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.

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 26 Fast Neutrons

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 27 First Test: Simulation of the original Chooz detector Shielding depth: 300 m.w.e Muon flux: 0.67 /m 2 s Target volume: 5.6 m 3 Simulated time: 31 hours

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 28 Simulation of the original Chooz detector: Neutron rates Target (after Veto cut) Neutron rate /hour 26.3   0.06 (four events!)

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 29 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

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 30 Correlated neutron background in the Double Chooz detector

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 31 Visible energy deposition by neutrons – no muon veto Shielding = 100 m.w.e. Time = 42.9 h

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 32 Visible energy deposition by neutrons – after muon veto cut Shielding = 100 m.w.e. Time = 42.9 h

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 33 Visible energy deposition by neutrons – after muon veto cut Shielding = 100 m.w.e. Time = 42.9 h Visible energy deposition

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 34 Correlated neutron background in the Double Chooz detector muons tracked (42.92 hours simulated time) 1985 hours computer time neutrons tracked neutrons thermalized in the target 21 neutrons undetected by muon veto 1 neutron created a correlated background event

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 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 > 2 counts/day can be excluded at 98% (for 100 m.w.e. shielding)

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 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)

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 37 Stopping Muon Rate (10 tons) Stopping  ’s from White Paper: 2 Hz NEAR DC proposal: 3 Hz (flat) ~6 Hz for hemispherical

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 38 Good Agreement FAR White Paper: 0.03 Hz DC proposal: 0.025

NuFact05, RomeSteven Dazeley (Louisiana State Univ.) 39 Correlated Neutrons from Missed Stopped Muons R = (1-  )R  f   f c f n  veto efficiency = R  stopped mu rate = 6 and 0.05 Hz f  fraction of    = 0.44 f c capture fraction = f n 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