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First Results from BOREXINO and Prospects of Low Energy Neutrino Astronomy

First Results from BOREXINO and Prospects of Low Energy Neutrino Astronomy. Oxford University and RAL November 20 th and 21st Lothar Oberauer, Physikdepartment E15, TU München. Neutrinos as probes ?. Interactions w w,e w,e,s. Charge 0 -1 +2/3 -1/3.

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First Results from BOREXINO and Prospects of Low Energy Neutrino Astronomy

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  1. First Results from BOREXINO and Prospects of Low Energy Neutrino Astronomy Oxford University and RAL November 20th and 21st Lothar Oberauer, Physikdepartment E15, TU München

  2. Neutrinos as probes ? Interactions w w,e w,e,s Charge 0 -1 +2/3 -1/3 Neutrinos undergo only weak interactions: No deflection in electric or magnetic fields, extremely penetrating => n‘s areperfect carriers of information from the centers of astrophysical objects

  3. Neutrino Mixing Flavor eigenstates = Mixing matrix x Mass eigenstates 2 mixing angles are measured: Q12 ~ 340 Q23 ~ 450 m23 – m22 ~ 2.6 x 10-3 eV2atmospheric n and accelerator n exp. m22 – m21 ~ 8 x 10-5 eV2 solar and reactor n experiments Open: Q13 ? CP violating phase d ? Absolute mass scale (mn < 2.2 eV) ? Mass hierarchy ?

  4. Intrinsic n parameters (particle physics) Low energy n astronomy • Neutrino oscillations (i.e. flavor transitions) and matter depending effects • May complicate interpretation of astrophysical processes • Access to n intrinsic properties not available in laboratory experiments !

  5. Natural Neutrino Sources (experimentally verified) Sun (since 1970) Atmosphere (since ~1990) Earth (since 2005) Supernovae (1987)

  6. Natural Neutrino Sources (not yet verified) Big Bang Active galactic nuclei ? Supernovae remnants ?, Gamma ray bursts ?, Supernovae relic neutrinos ?...

  7. Thermal sources Non-thermalsources Energy Spectra of Astrophysical Neutrinos low energy ~ 1 GeV ? high energy

  8. The dominating solar pp - cycle H. Bethe W. Fowler pp - 1 pp -2 pp -3

  9. The sub-dominant solar CNO - cycle • …dominates in stars with more mass as our sun… • =>Large astrophysical relevance • “bottle-neck” reaction slower than expected (LUNA result) • Solar CNO-n prediction lowered by factor ~ 2 ! • Impact on age of globular clusters

  10. Neutrino Energy in MeV Solar Neutrinos GALLEX GNO SAGE Integral whole spectrum no spectral information BOREXINO Since august 2007 7-Be neutrinos SuperK, SNO Directional information

  11. History of solar neutrino experiments at 2007 • All experiments were successful • Discovery of neutrino • oscillations • Probing thermal • fusion reactions

  12. Oscillations and matter effects Oscillation length ~ 102 km => oscillation smeared out and non-coherent Effective ne mass (due to forward scattering on electrons) is enhanced by a potential A A ~ GFNeE2 => for E > 1 MeV matter effect dominates and leads to an enhanced ne suppression for those energies… Missing info here before BOREXINO Now additional Improvement on uncertainty on pp-ne flux 1 10 MeV Vaccum regime Matter regime

  13. BOREXINO Neutrino electron scattering n e ->n e Liquid scintillator technology (~300t): Low energy threshold (~60 keV) Good energy resolution (~4.5% @ 1 MeV) Sensitivity on sub-MeV neutrinos Online since May 16th, 2007

  14. Milano Perugia Borexino Collaboration Genova Princeton University APC Paris Virginia Tech. University Munich (Germany) Dubna JINR (Russia) Kurchatov Institute (Russia) Jagiellonian U. Cracow (Poland) Heidelberg (Germany)

  15. BOREXINO in the Italian Gran Sasso Underground Laboratory in the mountains of Abruzzo, Italy, ~120 km from Rome Laboratori Nazionali del Gran Sasso LNGS Shielding ~3500 m.w.e External Labs Borexino Detector and Plants

  16. BOREXINO Detector layout Stainless Steel Sphere: 2212 PMTs + concentrators 1350 m3 Scintillator: 270 t PC+PPO in a 150 mm thick nylon vessel Water Tank: g and n shield m water Č detector 208 PMTs in water 2100 m3 Nylon vessels: Inner: 4.25 m Outer: 5.50 m Excellent shielding of external background Increasing purity from outside to the central region Carbon steel plates

  17. The ideal electron recoil spectrum due to solar neutrino scattering pp 7-Be CNO, pep 8B

  18. Energy Spectrum (no cuts) 14C dominates below 200 KeV 210Po NOT in eq. with 210Pb Arbitrary units Mainly external gs and ms Photoelectrons Statistics of this plot: ~ 1 day

  19. Muon cuts Problem: muons going through the buffer may create pulses in the neutrino energy window via Cherenkov light 350 PMS without light concentrators Npe (no-cone) / Npe (all) is higher for muons Sensitive cut (“Deutsch-cut”) on muons using the Inner Detector Additional cuts on pulse shape applicable Neutrino candidates muons

  20. Outer Detector efficiency OD-efficiency ~ 99% Total muon rejection power (incl. cuts ID) ~ 99.99% Preliminary, exact numbers require more detailed studies muons Distribution of events without OD-muon flag

  21. Fiducial volume cut Rejection of external background (mostly gammas) R < 3.3 m (100 t nominal mass) Radial distribution z vs Rc scatter plot Preliminary R2 gauss FV

  22. Spectrum after muon and fiducial volume cuts 210Po (only, not in eq. with 210Pb!) 14C 85Kr+7Be n 11C Last cut: 214Bi-214Po and Rn daughters removal

  23. t = 236 ms t = 432.8 ns b b a a 212Bi 214Bi 212Po 214Po 210Pb 208Pb ~700 KeV eq. ~800 KeV eq. 3.2 MeV 2.25 MeV 238U and 232Th 212Bi-212Po 232Th Events are mainly in the south vessel surface (probably particulate) 212Bi-212Po 214Bi-214Po Only 3 bulk candidates (47.4d) 238U: < 2. 10-17 g/g 232Th: < 1. 10-17 g/g

  24. a/b Separationin BOREXINO a particles Full separation at high energy b particles ns 250-260 pe; near the 210Po peak 2 gaussians fit a/b Gatti parameter

  25. 7Be signal: fit without a/b subtraction 210Po peak not included in this fit • Strategy: • Fit the shoulder region only • Area between 14C end point and 210Po peak to limit 85Kr content • pep neutrinos fixed at SSM-LMA value • Fit components: • 7Be n • 85Kr • CNO+210Bi combined • Light yield left free 7Be n CNO + 210Bi 85Kr These bins used to limit 85Kr content in fit

  26. 210Po background is subtracted: For each energy bin, a fit to the a/b Gatti variable is done with two gaussians From the fit result, the number of a particles in that bin is determined This number is subtracted The resulting spectrum is fitted in the energy range between 270 and 800keV 7Be signal: fit a/b subtraction of 210Po peak The two analysis yield fully compatible results

  27. BOREXINO 1st result (astro-ph 0708.2251v2) • Scattering rate of 7Be solar non electrons 7Be n Rate: 47 ± 7STAT ± 12SYS c/d/100 t

  28. BOREXINO and n-Oscillations • No oscillation hypothesis 75 ± 4 c/100t/d • Oscillation (so-called Large Mixing Solution) 49 ± 4 c/100t/d • BOREXINO experimental result 47 ± 7stat ± 12sys c/100t/d

  29. Survival probability Pee for solar ne Transition of vacuum to matter dominated n - oscillations predicted by MSW-effect It implies m2 > m1 Pee Gallium experiments: 8B and 7Be neutrinos subtracted ! 1.0 0.8 0.63 ± 0.19 BOREXINO 0.6 0.4 0.34 ± 0.04 SNO, SuperKamiokande 0.2 < 0.44 0.86 5.5 - 15 Energy in MeV

  30. Prospects of BOREXINO • Improvement of systematical uncertainty up to now it is dominated by uncertainty on fiducial volume => calibrations • 7Be flux measurement with 10% uncertainty => 1% accuracy for pp-neutrinos ! (BOREXINO + LMA parameters + solar luminosity) • Theoretical uncertainty on pp-neutrino flux ~ 1% => high precision test of thermal fusion processes • Aim to measure CNO and pep-neutrinos, perhaps pp-neutrinos and 8B-neutrinos below 5.5 MeV • Additional features: Geo neutrinos & reactor neutrinos & Supernova neutrinos (~100 events) for a galactic SN type II

  31. CNO and pep Neutrinos • Problem: muon induced 11C nuclei 11C ->11B e+ne (Q = 1.0 MeV, T1/2=20.4min) • Aim: tag via 3-fold delayed coincidence m, n (~ms) reconstruct position of n-capture veto region around this position for ~ 1 hour. Required rejection factor ~ 10 m track reconstruction

  32. LAGUNA • Large Apparatus for Grand Unification and Neutrino Astronomy • Future Observatory for n-Astronomy at low energies • Search for proton decay (GUT) • Detector for “long-baseline” experiments

  33. Astrophysics • Details of a gravitational collapse (Supernova Neutrinos) • Studies of star formation in former epochs of the universe („Diffuse Supernovae Neutrinos Background“ DSNB) • High precision studies of thermo-nuclear fusion processes(Solar Neutrinos) • Test of geophysical models(“Geo-neutrinos”)

  34. LAGUNALarge Apparatus for Grand Unificationand Neutrino Astrophysics 100m 30m coordinated F&E “Design Study”European Collaboration,FP7 Proposal APPEC Roadmap LENAliquid scintillator13,500 PMs for 50 kt targetWasser Čerenkov muon veto MEMPHYSWater Čerenkov500 kt target in 3 tanks,3x 81,000 PMs GLACIERliquid-Argon100 kt target, 20m driftlength,28,000 PMs foor Čerenkov- und szintillation

  35. LENA: Diffuse SN Background • ne + p -> e+ + n • Delayed coincidence • Spectral information • Event rate depends on • Supernova type II rates • Supernova model • Range: 20 to 220 / 10 y • Background: ~ 1 per year M. Wurm et al., Phys. Rev D 75 (2007) 023007

  36. Supernova neutrino luminosity (rough sketch) T. Janka, MPA Relative size of the different luminosities is not well known: it depends on uncertainties of the explosion mechanism and the equation of state of hot neutron star matter. Info on all neutrino flavors and energies desired!

  37. Galactic Supernova neutrino burst in LENA

  38. Event rates in LENA

  39. SN Neutrino predicted ratesvary with …- distance and progenitor mass (here: 10 kpc, 8 solar masses)- the used SN neutrino model (mean energies, pinching)- neutrino physics (value of q13, mass hierarchy) variation: 10-19 x103 ev @ 10kpcAims- physics of the core-collapse (neutronisation burst, n cooling …)- determine neutrino parameters- look for matter oscillation effects (envelope, shock wave, Earth)

  40. Matter effectsin the Earth • mass hierarchy • theta_13 • Matter effects in the SN: • mass hierarchy and theta_13 • time development of the shock wave?

  41. Separation of SN models ? • Yes, independent from oscillation model ! neutral current reactions in LENA e.g. TBP KRJ LL 12C: 700 950 2100 n p: 1500 2150 5750 Lawrence, Livermore Berkeley,Arizona Garching, Munich for 8 solar mass progenitor and 10 kpc distance

  42. Conclusions • Low Energy Neutrino Astronomy is very successful (Borexino direct observation of sub-MeV neutrinos) • Strong impact on questions in particle- and astrophysics • New technologies (photo-sensors, extremely low level background…) • Strong European groups

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