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# Double Chooz

Double Chooz. Optimizing Chooz for a possible Theta 13 measurement Steven Dazeley (Louisiana State University) NuFact05 Rome. Introduction. Quark mixing is small (CKM matrix)

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## Double Chooz

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

2. 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 Steven Dazeley (Louisiana State Univ.)

3. 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 Steven Dazeley (Louisiana State Univ.)

4. 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) + a2cos2q23 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 Steven Dazeley (Louisiana State Univ.)

5. Double-Chooz Chooz-Near Chooz-Far Near site: D~100-200 m, overburden 50-80 mwe Far site: D~1.1 km, overburden 300 mwe Steven Dazeley (Louisiana State Univ.)

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

7. ∆m2 Palo Verde SK allowed sin22θ13 (90% CL) Chooz sin22θ13 CHOOZ result nep→e+n; Neutron/positron coincidence 200 days reactor on; 142 days reactor off Stopped due to systematic error of reactor flux • Sin22θ13 < 0.19 (at 2.0 x10-3 eV2) Steven 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 > 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 Steven Dazeley (Louisiana State Univ.)

9. Double-CHOOZ(far) Detector We will start data-taking in 2007 with the far detector 7 m Shielding steel and external vessel (studies, réalisation, intégration  IN2P3/ PCC) Target- Gd loaded scintillator Gamma catcher: scintillator with no Gd 7 m BUFFER Mineral Oil with no scintillator Optically separated inner veto to tag muons 7 m Modular Frame to support photomultipliers Steven 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 ~ 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 Steven Dazeley (Louisiana State Univ.)

11. 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 9Li8He 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) Steven Dazeley (Louisiana State Univ.)

12. Systematics • Goal is systematic uncertainty of 0.6% Steven 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 Steven 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 • 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 Steven Dazeley (Louisiana State Univ.)

15. Systematics detail Steven Dazeley (Louisiana State Univ.)

16. Far detector starts Near detector starts 2004 2005 2006 2007 2008 2009 2003 Site Proposal & design Construction ? Data taking 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) Steven Dazeley (Louisiana State Univ.)

17. 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 Steven Dazeley (Louisiana State Univ.)

18. 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 Steven Dazeley (Louisiana State Univ.)

19. 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 sys=2.5% sys=0.6% Far detector only Far & Near detectors together 05/2007 05/2008 05/2009 05/2010 Expected Sensitivity 2007-2012 Steven Dazeley (Louisiana State Univ.)

20. Low q13 not theoretically favored Region of q13 accessible to Double CHOOZ 2. 1. Steven Dazeley (Louisiana State Univ.)

21. 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.) Steven Dazeley (Louisiana State Univ.)

22. Extra slides Steven Dazeley (Louisiana State Univ.)

23. 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 Conservative: assumes stopped muon deposits energy in right range NEAR: ~15/day FAR: ~0.2/day (signal ~4000/day) (signal ~85/day) Steven 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 E0.75 method. • Chooz measured rate was 45h-1 for all tagged neutron-like events g (2/0.8)(45)= 113h-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 ~1150h-1 (gives ~30 d-1 after 99.9% veto). 300 ms veto gets rid of most. Steven Dazeley (Louisiana State Univ.)

25. Using Reactor Off Data g0.49Li event/day atmost 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. Steven Dazeley (Louisiana State Univ.)

26. Fast Neutrons Steven Dazeley (Louisiana State Univ.)

27. 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: 31hours Steven Dazeley (Louisiana State Univ.)

28. Simulation of the original Chooz detector: Neutron rates (four events!) Steven Dazeley (Louisiana State Univ.)

29. Simulation of the original Chooz detector: Result • 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! Steven Dazeley (Louisiana State Univ.)

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

31. Visible energy deposition by neutrons –nomuonveto Steven Dazeley (Louisiana State Univ.) Shielding = 100 m.w.e. Time = 42.9 h

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

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

34. 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 Steven 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) Steven 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) Steven Dazeley (Louisiana State Univ.)

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

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

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

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