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

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Presentation on theme: "First Results from BOREXINO and Prospects of Low Energy Neutrino Astronomy Oxford University and RAL November 20 th and 21st Lothar Oberauer, Physikdepartment."— Presentation transcript:

1 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

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

3 Neutrino Mixing Flavor eigenstatesMass eigenstates 2 mixing angles are measured:         m 2 3 – m 2 2 ~ 2.6 x eV 2 atmospheric and accelerator  exp. m 2 2 – m 2 1 ~ 8 x eV 2 solar and reactor experiments Open:    CP violating phase  Absolute mass scale (m < 2.2 eV) ? Mass hierarchy ? Mixing matrix=x

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

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

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

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

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

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- prediction lowered by factor ~ 2 !  Impact on age of globular clusters

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

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 ~ 10 2 km => oscillation smeared out and non-coherent Effective e mass (due to forward scattering on electrons) is enhanced by a potential A A ~ G F N e E 2 => for E > 1 MeV matter effect dominates and leads to an enhanced e suppression for those energies… Missing info here before BOREXINO Now additional Improvement on uncertainty on pp- e flux Vaccum regime Matter regime 1 10 MeV

13 This effect is only possible for m 2 > m 1 => Information on mass hierarchy in the m 2 m 1 system

14 BOREXINO Neutrino electron scattering e   e Liquid scintillator technology (~300t): Low energy threshold (~60 keV) Good energy resolution 1 MeV ) Sensitivity on sub-MeV neutrinos Online since May 16th, 2007

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

16 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 Borexino Detector and Plants External Labs

17 BOREXINO Detector layout Water Tank:  and n shield  water Č detector 208 PMTs in water 2100 m 3 Carbon steel plates Scintillator: 270 t PC+PPO in a 150  m thick nylon vessel Stainless Steel Sphere: 2212 PMTs + concentrators 1350 m 3 Nylon vessels: Inner: 4.25 m Outer: 5.50 m Excellent shielding of external background Increasing purity from outside to the central region

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

19 14 C dominates below 200 KeV 210 Po NOT in eq. with 210 Pb Mainly external  s and  s Photoelectrons Statistics of this plot: ~ 1 day Arbitrary units Energy Spectrum (no cuts)

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

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

22 Fiducial volume cut Rejection of external background (mostly gammas) R < 3.3 m (100 t nominal mass) Radial distribution R2R2 gauss z vs R c scatter plot FV

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

24 238 U and 232 Th 212 Bi 212 Po 208 Pb   = ns 2.25 MeV ~800 KeV eq. Only 3 bulk candidates (47.4d) 232 Th Events are mainly in the south vessel surface (probably particulate) 214 Bi- 214 Po 212 Bi- 212 Po 214 Bi 214 Po 210 Pb   = 236  s 3.2 MeV ~700 KeV eq. 238 U: < g/g 232 Th: < g/g

25  /  Separation in BOREXINO  particles  particles pe; near the 210 Po peak 2 gaussians fit Full separation at high energy ns  Gatti parameter

26 7 Be signal: fit without  subtraction Strategy:  Fit the shoulder region only  Area between 14 C end point and 210 Po peak to limit 85 Kr content  pep neutrinos fixed at SSM-LMA value Fit components:  7 Be  85 Kr  CNO+ 210 Bi combined  Light yield left free 7 Be 85 Kr CNO Bi 210 Po peak not included in this fit These bins used to limit 85 Kr content in fit

27 7 Be signal: fit  subtraction of 210 Po peak 210 Po background is subtracted:  For each energy bin, a fit to the  Gatti variable is done with two gaussians  From the fit result, the number of  particles in that bin is determined  This number is subtracted  The resulting spectrum is fitted in the energy range between 270 and 800keV The two analysis yield fully compatible results

28 BOREXINO 1st result (astro-ph v2) Scattering rate of 7 Be solar on electrons 7 Be Rate: 47 ± 7 STAT ± 12 SYS c/d/100 t

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

30 Survival probability P ee for solar e Energy in MeV SNO, SuperKamiokande 0.34 ± ± 0.19 BOREXINO 0.86< 0.44 Gallium experiments: 8 B and 7 Be neutrinos subtracted ! Transition of vacuum to matter dominated  oscillations predicted by MSW-effect It implies m 2 > m 1 P ee

31 Prospects of BOREXINO Improvement of systematical uncertainty up to now it is dominated by uncertainty on fiducial volume => calibrations 7 Be 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 8 B-neutrinos below 5.5 MeV Additional features: Geo neutrinos & reactor neutrinos & Supernova neutrinos (~100 events) for a galactic SN type II

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

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

34 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”)

35 LAGUNA L arge A pparatus for G rand U nification and N eutrino A strophysics 30m 100m MEMPHYS Water Čerenkov 500 kt target in 3 tanks, 3x 81,000 PMs LENA liquid scintillator 13,500 PMs for 50 kt target Wasser Čerenkov muon veto GLACIER liquid-Argon 100 kt target, 20m driftlength, 28,000 PMs foor Čerenkov- und szintillation coordinated F&E “Design Study” European Collaboration, FP7 Proposal APPEC Roadmap

36 LENA: Diffuse SN Background e + 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)

37 Core Collapse emission Flavor conversion Shock wave EARTH OBSERVING SN NEUTRINOS sensitive to SN dynamics -> matter induced oscillation Event rate spectra   : from simulations of SN explosions  P : from oscillations + simulations (density profile)   : (well) known   : under control

38 Supernova neutrino luminosity (rough sketch) 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! T. Janka, MPA

39 Galactic Supernova neutrino burst in LENA

40 Event rates in LENA

41 SN Neutrino predicted rates vary with … - distance and progenitor mass (here: 10 kpc, 8 solar masses) - the used SN neutrino model (mean energies, pinching) - neutrino physics (value of  13, mass hierarchy) variation: x kpc Aims - physics of the core-collapse (neutronisation burst, cooling …) - determine neutrino parameters - look for matter oscillation effects (envelope, shock wave, Earth)

42 Matter effects in the Earth mass hierarchy theta_13 Matter effects in the SN: mass hierarchy and theta_13 time development of the shock wave?

43 Separation of SN models ? Yes, independent from oscillation model ! neutral current reactions in LENA e.g. TBPKRJLL 12 C: p: for 8 solar mass progenitor and 10 kpc distance Garching, Munich Lawrence, Livermore Berkeley,Arizona

44 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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