Transcript ppt - Infn
SNO Liquid Scintillator Project NOW 2004 17 September 2004 Mark Chen Queen’s University & The Canadian Institute for Advanced Research Introduction • Fall 04 to Dec 06: SNO Phase III – 3He proportional counter array now in place • dedicated Neutral Current Detectors (NCD’s) – nominal end date: 31 Dec 2006 • bring total uncertainty on 8B solar n NC signal below 5% – physics with heavy water will be complete what should be done with the detector after? Fill with Liquid Scintillator • SNO plus liquid scintillator → physics program – pep and CNO solar neutrinos – geo-neutrinos – 240 km baseline reactor oscillation confirmation – supernova neutrinos • working name: SNO+ Low Energy Solar Neutrinos • test solar models: 7Be, pep, CNO • precision survival probability measurement: pep • observe rise in survival probability at lower energies: lower energy 8B, 7Be, pep from Peña-Garay Survival Probability Rise SSM pep flux: predicted to ±1-2% allows precision test Dm2 = 7.9 × 10−5 eV2 tan2q = 0.4 SNO CC/NC pep n Event Rates (Oscillated) 7Be solar neutrinos 3000 pep/year/600 tons >0.8 MeV using BPB2001 and best-fit LMA 3900 CNO/year/600 tons >0.8 MeV 11C Cosmogenic Background these plots from KamLAND proposal muon rate in KamLAND: 26,000 d−1 compared with SNO: 70 d−1 Real KamLAND Backgrounds external pep window pep Solar n Backgrounds • 11C cosmogenic production – t1/2 = 20 min makes this difficult to veto at shallower depths – positron decay guarantees >1 MeV energy deposited, right in the pep n-e− recoil window – but at SNO depths, muon rate is small enough to allow easy tagging (or even tolerate this background without veto) • CNO neutrinos are a “background” – good energy resolution desired to see clear “recoil edge” for monoenergetic pep n – clearly interesting, for astrophysics, first observation of CNO n • radiopurity requirements challenging – – 40K, 210Bi (Rn daughter) 85Kr, 210Po (seen in KamLAND) not a problem since pep signal is at higher energy than 7Be – U, Th not a problem if can achieve KamLAND-level purity More on pep Solar Neutrinos from J. Bahcall and C. Peña-Garay “Our global analyses show that a measurement of the n-e scattering rate by pep solar neutrinos would yield essentially equivalent information about neutrino oscillation parameters and solar neutrino fluxes as a measurement of the n-e scattering rate by pp solar neutrinos.” • which is to say that a pep solar neutrino experiment would be an alternative to a pp solar neutrino experiment, in some regards… Antineutrino Geophysics • • can we detect antineutrinos from b- decay of U and Th in the Earth’s mantle and crust? knowing Earth’s total radioactivity would be very important for geophysics – – – • understanding thermal history of the Earth thought to account for ~40% total heat generation dominant heat source driving mantle convection how much in the mantle and the crust? More on Geo-Neutrinos • detecting geo-neutrinos from natural radioactivity in the Earth (U, Th) helps to determine the radiogenic portion of Earth’s total heat flow • by doing so, it also tests theories of Earth’s origin based upon the “Bulk Silicate Earth”…e.g. see Rothschild, Chen, Calaprice, Geophys. Res. Lett., 25, 1083 (1998) • e.g. see NOW 2004 talk by G. Fiorentini… Geo-Neutrino Signal terrestrial antineutrino event rates: • Borexino: 10 events per year (280 tons of C9H12) / 29 events reactor • KamLAND: 29 events per year (1000 tons CH2) • Sudbury: 64 events per year (1000 tons CH2) / 87 events reactor Rothschild, Chen, Calaprice (1998) above plot for Borexino…geo/reactor ratio at Sudbury would be twice as high KamLAND will soon make first detection… SNO+ Geo-Neutrinos from G. Fiorentini “SNO is considering move to liquid scintillator after physics with heavy water is completed. With very low reactor background, well in the middle of Canadian shield (an “easy” geological situation) it will have have excellent opportunities.” • which is to say that fundamental models are tested by experimental values…if those model calculations and measurements (for Sudbury) have smaller uncertainties (than for Kamioka), what we learn from the experimental measurements (at Sudbury) has potentially greater value Reactor Antineutrinos • SNO+ can try to confirm reactor neutrino oscillations • move KamLAND’s spectral distortion to higher energies by going to a longer baseline • this moves KamLAND spectral distortion features away from the geo-neutrinos – improves geo-neutrino detection – spectral shape confirmation Top Ten List • table from Suekane’s NOON2003 talk Location, Location, Location Bruce Bruce-SNO+ • 240 km baseline – places 2nd oscillation maximum in the middle of the reactor neutrino positron spectrum • 51 events per year (no oscillation expectation) from 6 reactors at full power 14 GWth • there are 2 more reactors at Bruce that may be restarted • not a precision test, will not further constrain oscillation parameters…just a confirmation, with statistics like K2K (e.g. in 3 years, expectation of ~150 events, observation of ~100 events…) KamLAND Spectral Distortion T. Araki et al., hep-ex/0406035 (2004) SNO+ Spectral Distortion 3 Measurements for Low Cost • for relatively little cost, there is an opportunity to use existing equipment (i.e. most of the SNO detector) to enable new measurements • costs are: – liquid scintillator procurement – mechanics of new configuration – fluid handling and safety systems – scintillator purification Supernova Neutrinos • 1 kton organic liquid scintillator would maintain excellent supernova neutrino capability – – – – – ne + p ne + 12C (CC) ne + 12C (CC) nx NC excitation of 12C (NC) nx + p elastic scattering (NC) [large rate] [large rate] see Beacom et al., PRD 66, 033001(2002) SNOLAB LOI • letter of interest submitted on 12 April 2004 • SNO+ option “study group” M. Chen*, A. Hallin, C. Kraus, J.R. Leslie, J. Maneira, R. MacLellan, A.B. McDonald, A. Wright Queen’s M. Boulay Los Alamos D. Hahn, M. Yeh Brookhaven X. Dai Carleton B. Cleveland, R. Ford SNOLAB D. Hallman, C. Virtue Laurentian R.G.H. Robertson U of Washington • potential collaborators from outside SNO have indicated some interest • fully funded expansion of SNO underground site into an international facility for underground experiments – – – – double beta decay dark matter solar neutrinos supernova neutrinos • excavation expected to begin late 2004, completed by 2006 • space ready for experiments in 2007 Technical Aspects of R&D • liquid scintillator cocktail design – optimize optical properties (attenuation length, light yield, pulseshape discrimination, scattering) – chemical compatibility with acrylic – high density preferred (r = 1 g/cm3) to use with existing H2O buffer outside the acrylic vessel • • • • • mechanical “hold-down” system cover gas improvements (lower radon) safety, fluid handling underground scintillator purification SNO detector state (surviving PMT’s, acrylic vessel certification) • calibrations and operations Schedule • SNO+ R&D: one year – – – – complete technical description full cost estimates completed feasibility studies fully-developed science goals • if above okay, full proposal(s) to be submitted 11/2005 • call for new collaborators in parallel with above • when above approved, 2 years to first fill (04/2008) Double Beta Decay: SNO++ • SNO plus liquid scintillator plus double beta isotopes: SNO++ • add bb isotopes to liquid scintillator – dissolved Xe gas (2%) – chemical loading (Nd, Se, Te) – dispersion of nanoparticles (Nd2O3, TeO2) • enormous quantities (high statistics) and low backgrounds trade off for poor energy resolution of liquid scintillator Candidate Selection 2n bb Background Test <mn> = 0.150 eV • 0n: 1057 events per year with 1% Ndloaded liquid scintillator (natural Nd) • S/B: 0n/2n (upper half peak) = 2.3 • crude illustration below: statistical test of the shape to extract 0n and 2n components! Summary • R&D to develop SNO+ underway • staged approach envisioned: – deployment of pure scintillator for antineutrinos – next stage: go for purification to try for low energy solar neutrinos – next stage: deploy double beta (e.g. nanoparticles), would jump to this stage ASAP – long-term program provides steady and “early” science output for SNOLAB • new collaborators are welcome