Precision measurements with reactor neutrinos

Transcription

1 Precision measurements with reactor neutrinos Stefan Schönert, MPIK Heidelberg in collaboration with T. Lasserre and L. Oberauer ECT* Trento, June 15-21, 2003

2 Outline Reactor as source of anti-ν e s production, detection, uncertainties 3-flavour survival probability Long baseline: m² sol KamLAND, BOREXINO Medium baseline (High-LMA solutions) : m² sol, Θ sol, m² atm, Θ 13, hierarchy Heilbronn, Boulby or Mt. Ventoux Short baseline: Θ 13 Kr2det, new initiatives

3 Production and detection of reactor ν e s Production: Anti-ν e emitted in beta decays of fission products; E ~ 0-9 MeV Detection via cc: inv-β decay on protons: ν e + p e + + n (E ν >1.8 MeV) Energy Tag NB: energy too low to produce µ,τ leptons disappearance mode! Spectrum: φ(e) σ(e) sigma (10-43 cm 2 per MeV per fission) energy (MeV) MeV different cross section (stand. spec.) - per fission per MeV E-43 cm 2

4 φ(e) σ(e) uncertainties Integral measurement: uncertainty of de φ(e) σ(e) ~ 1.4% (Declais et al.) Differential measurement (Bugey-3): (Achkar et al.) Data/Model

5 3-flavour survival probability atmospheric term solar term interference term P independent of CP phase; matter effects negligible Adjacent oscillation peaks in energy spectrum: = If U e3 not too small atmospheric driven oscillation visible on ~20 km baseline can probe U e3 parameters interference term sensitive to hierarchy (sin²θ cos²θ) (Petcov & Piai) sin 2 (2θ 13 ) = 4 U e3 2 (1 - U e3 2 )

6 Probing the solar term with LBL ( m² sol - Θ sol ) atmospheric term solar term interference term

7 KamLAND 95 % C.L. LMA-II LMA-I NB: LMA-I and II derived from limited statistics- potentially unstable Loss of m² sensitivity >~ ev²

8 maximal mixing, 250 kev bins, NO ENERGY RESOLUTION KamLAND positron spectra for LMA parameters 1x10-4 ev 2 2x10-4 ev 2 3x10-4 ev 2 4x10-4 ev 2 5x10-4 ev 2 for m 2 1.5x10-4 ev 2 limited information on m 2 Dedicated experiment for ~1.5x10-4 ev 2 < m 2 <9x10-4 ev 2 Strumia& Barbieri Schönert Strumia&Vissani Piai&Petcov Lisi

9 KamLAND with 5-fold statistics HLMA area HLMA area If LMA-I true (x5 KL exposure) If LMA-II true (x5 KL exposure) Lisi s (LowNu 2003) Degenerate solutions expected; in particular in high-lma (HLMA) parameter space (baseline too long!)

10 BOREXINO as LBL reactor experiment Located at the LNGS laboratories Main reactors in France, Swizterland, Germany, <L> ~ 800 km 300 tons of pseudocumene (PC), ~30 interactions/year (22 events above 2.6 MeV) Goals: 1) 7 Be solar neutrinos 2) Test MSW-LMA solution with reactors anti-neutrinos KamLAND confirmation Optimum: few 10-6 < m 2 < ~ ev 2 Rate analysis only (no shape distorsion expected) (S.S Taup97)

11 The HLMA Heilbronn, Germany The Heilbronn salt mine New reactor neutrino project to probe the HLMA region m 2 > ev 2 Northern Site (180m, 480 mwe) 77%@ 20 km & 74%@ 20 km If Obrigheim OFF Southern Site (240m, 640 mwe) ~ 2000 caverns 15 x x m T. Lasserre S. Schönert (MPIK), T. L. (CEA/Saclay), L. Oberauer (INFN,TUM), Astrop. Phys. 18, hep-exp/ ,

12 : m 2 sol & sin²2θ sol Simulation of (kochendorf) No background included 250 kev bins - 100% efficiency Exposure: 115 tons / 3 years (2000 events) Sensitivity starts at >~ ev 2 m 2 sol ev2 sin²2θ sol δ( m 2 sol ) 1σ δ(sin²2θ sol ) 1σ >2x < 5 % ~5 % sin²2θ sol = 0.8 sin²2θ sol = 0.8 LMA-II 99% C.L HLMA region LMA-I 5x10-5 ev 2 7x10-5 ev 2 9x10-5 ev 2 LMA-II 12x10-5 ev 2 16x10-5 ev 2 20x10-5 ev 2 T. Lasserre

13 The Boulby site, England T. Lasserre

14 BOULBY: a possible site for HLMA? Motivation: LMA-II m 2 21 ~ ev 2 If LMA-II is the solution precision of KamLAND? HLMA@Heilbronn sensibility starts at 1.5e-4 ev2 The Boulby mine location Existing underground laboratory 25 km away for the Hartlepool nuclear plant (AGR type, yield~40%,3.2 GW th ) Overburden: 1100 m of rocks. Muon flux attenuated by 10 6 Statistics 2000 evts / 500 tons PXE / 3 years Flux(Hartlepool)/Flux(Total) = 81 % 90% of the flux from 5 nuclear plants Reactor Hartlepool Heysham Torness Discimination power between LMA-I and LMA-II Sensitivity starts at m 2 21 ~ 1.2 Graveline % 10-4 ev 2 Discrimination power within the LMA-II solution Paluel % Others L (km) P (GW th ) F/F tot 81 % 4.5 % 1.5 % ~10 % T. Lasserre

15 : m 2 sol & sin²2θ sol No 5% systematic error included Simulation of No background included 250 kev bins - 100% efficiency Exposure: 500 tons / 3 years (2000 events) Sensitivity starts at >~ ev 2 m 2 sol ev2 sin²2θ sol δ( m 2 sol ) 1σ δ(sin²2θ sol ) 1σ >1.5x < 5 % ~5 % sin²2θ sol = 0.8 sin²2θ sol = 0.8 LMA-II 99% C.L LMA-I 5x10-5 ev 2 7x10-5 ev 2 9x10-5 ev 2 LMA-II 12x10-5 ev 2 16x10-5 ev 2 20x10-5 ev 2

16 Preliminary: The Mt Ventoux location Simulation of Ventoux LMA-I 99% C.L LMA-II 99% C.L 2% systematic error included 4 main nuclear power plants included Le Bugey 181 km 2.66 GW th St Alban 145 km 1.92 GW th Tricastin 73 km 2.84 GW th Cruas 59 km 2.59 GW th Reactor experiment close to the first minimum of the «solar» oscillation (LMA-I) Discrimination between LMA-I & LMA-II Accurate determination of the solar mixing parameters if enough statistics > 500 t target volume! C. Bouchiat (ENS) hep-ph/03xxxxx No background included 250 kev bins - 100% efficiency Exposure: 500 tons / 3 years (~2000 events) Sensitivity starts at >~ few 10-5 ev 2

17 Improvement of sin 2 (2θ sol ) determination CP violation observables involve the product sin 2 (2θ 12 ) x m 2 12 Reactor osc. minimum provides the best sin 2 (2θ 12 ) measurement ~70-80km for LMA-I & >20km for LMA-II Theoretical studies (no specific location) A. Bandyopadhyay et al.: LMA-I : km, >20 GWth,3 ktons year precision of sin²θ ~3 % Choubey, Petcov & Piai: (hep-ph/ ) 20 to 30km baseline (HLMA parameter range) precision of sin²θ ~6-7%

18 Probing the atmospheric and interference term with HLMA ( m² 31 - Θ 13 ) atmospheric term solar term interference term If U e3 2 ~O(10-2 ) & m 2 sol lower-similar m2 atm baseline ~ 20km BOTH atmospheric and solar oscillations develop without being averaged 2 by-products of the HLMA: constraint on U e3 2 & ν mass hierarchy? However, exposure of O(10 32 protons.year) needed

19 HLMA: constraint on U e3 2 m 2 sol = 5x10-5 ev 2 m 2 sol = 1x10-4 ev 2 No-oscillation 2ν mixing 3ν mixing & NH 3ν mixing & IH m 2 sol = 2x10-4 ev 2 m 2 sol = 3x10-4 ev 2 HLMA@Heilbronn Visible energy, unbinned spectra No energy resolution m 2 atm = ev 2 sin²2θ sol =0.8 U e3 2 = 0.04 HLMA: ν mass hierarchy? sin 2 (θ sol ) cos 2 (θ sol ) m 2 atm L m 2 sol L m 2 atm L Interference term : Normal Hierarchy (NH) sin 2 (θ sol ) Inverted Hierarchy (IH) cos 2 (θ sol ) (Petcov & Piai, hep-ph/ ) Sensitivivity to the masshierarchy:~2-4 x 10-4 ev² if U e3 ²~O(10-2 ), for m 2 atm = ev 2 (for HLMA@Heilbronn)

20 Ultimate reactor Θ 13 experiment with (1-2 km) baseline experiment atmospheric term solar term interference term Far ~2km Near m Increase statistics (with respect to Chooz) Decrease systematic errors (with respect to Chooz)

21 Kr2Det - Probing U e3 with reactor-ν e Two identical detectors (Borexino design) No-oscillation: ratio of e + spectrum = const. Krasnoyarsk reactor underground site: 600 mwe Det 1 Det 2 reactor ν e 150 m 1100 m Target: 45m³ 50m³ Rate: 2700 / d 50 / d S/B: >> 1 ~10:1

22 Kr2Det - Sensitivity Expected sensitivity: sin 2 2θ 0.012, U e (90 %CL) at m 2 = ev 2

23 Parameter degeneracy in LBL experiments LBL ν µ disappearance gives: sin 2 (2θ 23 ) 2 solutions : θ 23 & π/2-θ 23 m solutions m 1 >m 3 or m 3 >m 1 LBL appearance probability given by: P(ν µ ν e ) ~ K 1 sin 2 (θ 23 ) sin 2 (2 θ 13 ) + K 2 sin(2θ 23 ) sin(θ 13 ) sign( m 2 31 ) cos(δ) K 3 sin(2θ 23 ) sin(θ 13 ) sin (δ) K 1,K 2,K 3 : known constants (within experimental error) dependence on sin(2θ 23 ), sin(θ 23 ) 2 solutions dependence on sign( m 2 31 ) 2 solutions δ-cp phase can run in [0,2π] Interval of solutions in general U e3 2 measurement with reactors Few MeV ν e disappearance experiments 1-P(ν e ν e ) = sin 2 (2θ 13 )sin 2 ( m 2 31 L/4E) + O( m2 21 / m2 31 ) Few MeVν e + very short baseline No matter effect contribution (O(10-4 ) relative effect) U e3 2 measurement independent of sign( m 2 13 ) U e3 2 measurement independent of the δ-cp phase

24 Complementarity of LBL and reactor experiments sin 2 (2 θ 13 ) Reactor LBL P(ν µ ν e )

25 Achievable constraint on θ 13 with a reactor experiment (hep-ph/ , P. Huber et. al.) Reactor I: 10 GW th. 10 tons. 4 years Reactor II: 10 GW th. 200 tons. 4 years Near detector : no-oscillation Far detector : 1.7 km Systematics Correlations & Degeneracies T. Lasser re

26 Many Experiment Sites Under Consideration Reactor Complex Near Detector Far Detector 1, 2 cores ON/OFF Ok 4 7 cores No ON/OFF < 500 m 5-50 tons > 150 mwe km 5-50 tons > 300 mwe Reactor Location N/F Distances Thermal Power Overburden Target mass Chooz France 1100 m 8.5 GW (2) 300 mwe 5 t Krasnoyarsk Russia 115/1000 m 1.6 GW (1) 600 mwe 54 t Wolf Creek US (KS)?/? 3.2 GW (1) 300 mwe? Angra Brazil?/? ~ 4 GW (1)?? Texono Taiwan?/~2 km? 4.1 GW (1)?? Diablo Canyon US (Cal)?/? 6.1 GW (2) mwe t? Penly France <500m/1.8 km 8.5 GW (2) mwe 28 t Flamanville France <500m/1.8 km 8.5 GW (2) 300 mwe 28 t Paluel France <500m/1.8 km 17 GW (4) mwe 14 t Cruas France >500m/1.8 km 11.7 GW (4) >500 mwe 20 t Kashiwasaki Japan?/1.3 km 24.3 GW (7) 500 mwe 5 t

27 The Paluel site Net Power Evts/14 tons/y 17 GW th km Near site: horizontal gallery < 500 m > 100 m.w.e 0.5 km Far site: horizontally gallery from La grande vallee or with a -10% slope to go down to -75 m 300 m.w.e (chalk) h=3 meters h=75 meters T. Lasserre

28 The Diabolo Canyon Site Road in another km from the nuclear core! T. Lasserre

29 The Kashiwasaki site Road in another km from the nuclear core! m m ~1.3 km Reactor power: 24.3 GW th Baseline = 1.3 km (compromise ) 7 cores Add complexity: 2 near detectors 3 identical detectors of 5 tons 3 shafts to dig (10 M$, <1 year) Near meter depth Far meter depth Start data taking ~ T. Lasserre

30 ν e detection free of background Anti-ν e tag: ν e + p e + + n, ~1.8 MeV Threshold Prompt e+, E P =1-8 MeV, visible energy Delayed neutron capture on H, E D =2.2 MeV Time correlation: τ 200µsec Space correlation: < 1m 3 Prompt(β/γ) - Delayed(β/γ) pulse shape discrimination Backgrounds - Geophysical anti-ν e s - Background from radioactivity rocks, detector material, water shielding, scintillator - Background induced by cosmic rays - radioactive nuclei produced in the detector - neutrons induced by muons in detector & rocks Depend on depth (Detailed background study carried out for HLMA project) Goal: error from background << total systematic error

31 Challenge: 1% systematic errors CHOOZ systematic error : 2.8% Goal: Improve by a factor 3 Method: Two identical detectors + Technical improvements? Systematics Reactor Detector Tagging errors Ee+<8 Mev 6<En (MeV)<12 de+-geode<30cm dn-geode<30cm de+-n < 100 cm 2 < n delay < 100 µs n multiplicity = 1 Error origin cross section/fission Power E/Fission Σ Scint. Density Target volume % H Spill in/out Σ e+ energy e+ pos. cut / vessel (30cm) n capture n energy n pos. cut / vessel (30 cm) (e+-n) distance (e+-n) time delay n multiplicity Σ CHOOZ 1.9% 0.7% 0.6% 2.1% 0.1% 0.3% 1.2% 1.0% 2.5% 0.8% 0.1% 1.0% 0.4% 0.1% 0.3% 0.4% 0.5% 1.5% 2 id. detectors + low accidentals << 1% - -(δv) - - << 1% No threshold 0% No Distance cut 0% - - <~ 0.5 %? Overall systematics < 1% should be achievable, but difficult job!

32 The Russian dolls (3 layers) detector Detector to be located at > 300 mwe to control muon induced backgrounds Muon Veto Gd Loaded Scintillator Scintillating Buffer 20 tons Non-scintillating Buffer (Example)

33 Forthcoming U e3 2 constraints Experiment sin 2 (2θ 13 ) U e3 2 θ 13 (deg) U e3 2 constraint CHOOZ <0.14 <0.036 <11 - MINOS <0.06-? <0.015-? <7.1-?? ICARUS 5 years <0.04-? <0.010-? <5.8-? 2011? OPERA 5 years <0.06-? <0.015-? <7.1-? 2011? NUMI-OA 5 years < < <2.3-? 2012? JHF2K 5 years < < <2.3-? 2012? Kr2Det (Russia) <0.016 <0.004 <4.6? US proposals <0.01 < <2? Kashiwasaki (Jp) <0.026 < < ? σ sys = 1% PALUEL/PENLY/ FLAMANVILLE? <0.02 <0.005 <4.1 ~2010? When the C.L. are not given, upper limits correspond to 90% C.L m 2 atm = ev 2 and sin 2 (2θ atm ) = 1 sin 2 (2θ 13 ) = 4 U e3 2 (1 - U e3 2 ) Non exhaustive table T. Lasserre

34 World-wide momentum Working group : PCC & CEA/Saclay & APC, MPI Heidelberg, TU Muenchen, Kurchatov Institute, INFN/Bologna (contact person: T. Lasserre CEA/Saclay) Alabama, Argonne, Berkeley LBL, Caltech, Chicago, Columbia (Hawaii, Livermore, MIT, Standford/SLAC, Univ. Cal., Irvine, Los Alamos ) Tohoku Univ., Tokyo M. Univ. Goal: Is it possible to build a set of 2 detectors to measure/constrain θ 13 with a new reactor experiment to start data taking in ? Which detector site? What the optimum detector design? December 2002: European meeting I, Heidelberg April 2003: European meeting II, Paris May 2003: World-wide meeting I, USA Summer 2003: World-wide meeting II, Europe End of 2003: World-wide meeting III,?

35 Summary Solar Neutrino Mixing Parameters KamLAND: spectral shape analysis required exclude HLMA? high-lma km baseline (θ sol, m sol ²)? low-lma measurement of θ first oscillation minimum Constraint on θ 13 with a new reactor experiment growing interest in the world since one year (White paper in preparation) 2 identical detectors experiment : ~500m & 1.5-2km Challenge: systematic error level Priority: Securing one site (or more ) Very rough cost estimation: ~20 M$ (+ excavation) Time constraint: real impact if the reactor experiment starts data taking ~2008, as the next generation LBL experiments T. Lasserre