Solar Neutrinos in Large Liquid Scintillator Detectors

Transcription

1 Solar Neutrinos in Large Liquid Scintillator Detectors M. Chen Queen s University DOANOW March 24, 2007

2 Low Energy Solar Neutrinos complete our understanding of neutrinos from the Sun pep, CNO, 7 Be, pp p-p Solar Fusion Chain p + p 2 H + e + + ν e p + e + p 2 H + ν e 2 H + p 3 He + γ 3 He + 3 He 4 He + 2 p 3 He + p 4 He + e + + ν e 3 He + 4 He 7 Be + γ 7 Be + e 7 Li + γ + ν e 7 Be + p 8 B + γ CNO Cycle 12 C + p 13 N + γ 13 N 13 C + e + + ν e 13 C + p 14 N + γ 14 N + p 15 O + γ 15 O 15 N + e + + ν e 7 Li + p α+ α 8 B 2 α + e + + ν e 15 N + p 12 C + α

3 Ga, Cl and SNO Data Distilled deduce the survival probability high energy: directly from SNO medium energy: Cl minus high low energy: Ga minus high, medium θ x is θ 13 we observe that the survival probability for solar neutrinos versus energy is not yet accurately determined from existing experiments transition between vacuum and matter oscillations in the Sun has not been accurately determined Barger, Marfatia, Whisnant, hep-ph/ there is even some tension in existing low and medium data

4 Things You Could Learn with precision data from low energy solar neutrinos fix Δm 2 with KamLAND data, vary θ 13 (with θ 12 fixed or varying) low energy solar neutrino data helps constrain θ 13 extract Δm 2 from solar data, strongly affected by the position of the transition low energy solar neutrino data are key compare with Δm 2 from KamLAND neutrinos versus antineutrinos, tests CPT invariance compare position/shape of the transition at lower energy with the prediction from LMA MSW oscillations might reveal deviations from Standard Model couplings (due to non-standard interactions or coupling to a sterile neutrino admixture) and many of these studies have been done, all pointing to the fact that at the transition (between 1-2 MeV) there is sensitivity to new neutrino physics! (e.g. Balantekin or Friedland, Peña-Garay, Lunardini, or Barger and colleagues )

5 Neutrino-Matter Interaction best-fit oscillation parameters suggest MSW occurs but we have no direct evidence of MSW day-night effect not observed no spectral distortion for 8 B ν s from Peña-Garay testing the vacuum-matter transition is sensitive to new physics for Δm 2 = ev 2, θ = 34 N e at the centre of the Sun E is 1-2 MeV Hamiltonian for neutrino propagation in the Sun

6 New Physics MSW is linear in G F and limits from ν-scattering experiments ( g 2 ) aren t that restrictive oscillation solutions with NSI can fit existing solar and atmospheric neutrino data NSI not currently constrained new pep solar ν data would reveal NSI good fit with NSI pep solar neutrinos are at the sweet spot to test for new physics Friedland, Lunardini, Peña-Garay, hep-ph/

7 Mass-Varying Neutrinos cosmological connection: mass scale of neutrinos and the mass scale of dark energy are similar postulating a scalar field and neutrino coupling results in neutrinos whose mass varies with the background field (e.g. of other neutrinos) Fardon, Nelson, Weiner, hep-ph/ solar neutrinos affected? pep ν: a sensitive probe pep Barger, Huber, Marfatia, hep-ph/

8 Why pep Solar Neutrinos? SSM pep flux: uncertainty ±1.5% known source known cross section (ν-e scattering) measuring the rate gives the survival probability precision test for neutrino physics with low energy solar neutrinos, have to achieve precision similar to SNO or better it s no longer sufficient to just detect the neutrinos pep solar neutrinos: E ν = 1.44 MeV are at the right energy to search for new physics P ee Solar Neutrino Survival Probability E ν [MeV] Sat Mar 19 17:13: pep ν stat + syst + SSM errors estimated Δm 2 = ev 2 tan 2 θ = 0.45 SNO CC/NC observing the rise confirms MSW and our understanding of solar neutrinos

9 Event Rates (Oscillated) 7 Be, pep and CNO Recoil Electron Spectrum events/kton/yr/bin Be solar neutrinos resolution with 450 photoelectrons/mev 3600 pep/year/kton >0.8 MeV 400 using BS05(OP) and best-fit LMA CNO/year/kton >0.8 MeV T e [MeV] Sat Mar 19 18:33:32 18:34:40 18:35:

10 Real KamLAND Backgrounds external pep window

11 pep Solar ν Backgrounds radiopurity requirements 40 K, 210 Bi (Rn daughter) 85 Kr, 210 Po (seen in KamLAND) not a problem since pep signal is at higher energy than 7 Be U, Thnot a problem if one can repeat KamLAND scintillator purity 14 C not a problem since pep signal is at higher energy

12 11 C Cosmogenic Background these plots from the KamLAND proposal muon rate in KamLAND: 26,000 d 1 compared with SNO: 70 d 1

13 Requirements for a Liquid Scintillator pep Solar ν Detector depth to reduce/eliminate 11 C background good light output from the scintillator studied the effect of varying the energy resolution; found not a steep dependence radiopurity control of Rn exposure because of 210 Bi eliminate 40 K internal contamination

14 Depth Matters! Depth Matters!

15 11 C Rate versus Depth P is the rate of 11 C produced per day in 100 tons does not depend all that much on E μ SNO tons has signal: 3600 pep/year 11 C background: 550 events/year Hanohano 10 kton has signal: 36,000 pep/year 11 C background: <550,000 events/year from Galbiati et al. approximately same depth (slightly greater) as Gran Sasso horizontal overburden is superior

16 11 C Tagging Galbiati et al. looked at the efficiency of tagging the 11 C cosmogenic events cannot tag based on just the muon and a delayed cosmogenic event too many muons and 11 C half-life is 20 minutes require a muon and a neutron to tag a delayed cosmogenic event even still, there s a tagging inefficiency of 5-10% 11 C production without detectable neutron muon-induced neutron rate determines the dead time at 4000 m.w.e.: ~40 per day in 100 tons if for each tag you re dead for 2 hours you want each volume firing the veto only 4 times per day or less to successfully tag 11 C events in Hanohano requires muon track determination of a volume of 10 tons out of 10,000 tons

17 Sudbury Neutrino Observatory 1000 tonnes D 2 O 12 m diameter Acrylic Vessel 18 m diameter support structure; 9500 PMTs (~60% photocathode coverage) 1700 tonnes inner shielding H 2 O 5300 tonnes outer shielding H 2 O Urylon liner radon seal depth: 2092 m (~6010 m.w.e.) ~70 muons/day

18 SNO+ we plan to fill the SNO detector with liquid scintillator after the heavy water is removed SNO+ will be: deep (and large) enough to make a precision measurement of the pep solar ν survival probability capable of detecting geoneutrinos with a smaller background from reactor neutrinos (compared to KamLAND) dominant source of neutrinos is the Archean continental crust in the Canadian Shield, surrounding Sudbury

19 Requirements for a Liquid Scintillator pep Solar ν Detector depth to reduce/eliminate 11 C background good light output from the scintillator studied and not a steep dependence radiopurity control of Rn exposure because of 210 Bi eliminate 40 K internal contamination

20 SNO+ Liquid Scintillator new liquid scintillator identified linear alkylbenzene compatible with acrylic, undiluted high light yield pure (light attenuation length, in excess of 20 m at 420 nm) low cost high flash point safe low toxicity safe smallest scattering of all scintillating solvents investigated density ρ = 0.86 g/cm 3 SNO+ light output (photoelectrons/mev) will be approximately 3-4 that of KamLAND ~900 p.e./mev for 54% PMT area coverage

21 LAB Scintillator Optimization safe scintillators LAB has 50-75% greater light yield than KamLAND scintillator

22 SNO+ Signals and Backgrounds resolution with 450 photoelectrons/mev 7 Be solar neutrinos

23 Requirements for a Liquid Scintillator pep Solar ν Detector depth to reduce/eliminate 11 C background good light output from the scintillator studied and not a steep dependence radiopurity control of Rn exposure because of 210 Bi eliminate 40 K internal contamination

24 SNO+ Solar Neutrino Prospects with backgrounds at KamLAND levels U, Th achieved 210 Pb and 40 K post-purification KamLAND targets external γ backgrounds use SNO external activities define fiducial volume we already know there is a reasonable-sized fiducial volume that can be defined

25 Solar Signals with Backgrounds

26 Solar Signals with Backgrounds

27 pep Sensitivity Study 210 Pb at equilibrium with U levels KamLAND post-purification purification targets for 40 K U and Th at current KamLAND levels 3 years livetime 3.4% pep uncertainty, 5.1% CNO uncertainty with 210 Bi constrained

28 SNO+ Summary diverse and exciting physics goals solar neutrinos, precision test of neutrino interactions and MSW, reactor oscillation confirmation, geo-neutrinos in a geologicallyinteresting location, supernova neutrino watch, possibility of a competitive double beta decay experiment relatively low-cost continuation of an existing detector we are planning to make the transition from SNO to SNO+ this year and next new collaborators needed and welcome