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First Results from the Borexino Solar Neutrino Experiment

First Results from the Borexino Solar Neutrino Experiment. Celebrating F.Avignone, E.Fiorini & P. Rosen University of South Carolina May 16, 2008 Frank Calaprice. First Contact with Frank Avignone. 65 Zn source given by Ray Davis. Axion Searches Summary of Texono Coll. 2006. 65 Zn.

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First Results from the Borexino Solar Neutrino Experiment

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  1. First Results from the Borexino Solar Neutrino Experiment Celebrating F.Avignone, E.Fiorini & P. Rosen University of South Carolina May 16, 2008 Frank Calaprice

  2. First Contact with Frank Avignone 65Zn source given by Ray Davis

  3. Axion Searches Summary of Texono Coll. 2006 65Zn

  4. Science with Borexino • The Neutrino • The Sun • The Earth • Supernovae

  5. Basic Neutrino Facts • Postulated in 1931 by Pauli to preserve energy conservation in -decay. • First Observed by Cowan and Reines in 1950’s by inverse beta decay: e+p->n+e+. • Electric charge: 0; Spin: 1/2; Mass: very small • Like other fermions, comes in 3 flavors: • e, ,  • Interactions: only via the weak force (and gravity)

  6. Solar Neutrino Production • Occurs in two cycles: • pp and CNO (mostly pp) • In each pp cycle: • 26.7 MeV released • 2 neutrinos created • 4 protons are converted to 4He • Total Flux constrained by luminosity: •  =( 2’s/26.7MeV) (L/4r2) ~ 6.6x1010/cm2/s.

  7. Solar Neutrino Energy Spectrum

  8. Birth of Solar Neutrino Experiments • 1965-67: Davis builds 615 ton chlorine (C2Cl4) detector • Deep underground to suppress cosmic ray backgrounds. • Homestake Mine (4800 mwe depth) • Low background proportional detector for 37Ar decay. • 37Cl + e -> 37Ar +e- • Detect 37Ar +e- -> 37Cl + e (t 1/2 ~ 37 d) • Detected ~1/3 of expected rate.

  9. Chlorine Data 1970-1994

  10. Neutrino Oscillations • The Solar Neutrino Problem was explained by neutrino oscillations, the possibility of which was first suggested by Pontecorvo in 1967. • An electron neutrino that oscillates into a muon neutrino would not be detected in the chlorine reaction. • Experimental proof of oscillations came decades later from experiments on atmospheric neutrinos (SuperK), solar neutrinos (SNO), and reactor anti-neutrinos (Kamland).

  11. Neutrino Vacuum Oscillations • In 1967 Pontecorvo showed that non-conservation of lepton charge number would lead to oscillations in vacuum between various neutrino states. • In 1968 Gribov and Pontecorvo suggested this could explain the low result of Davis. • The neutrino rate is 2 times smaller if the oscillation length is smaller than the region where neutrinos are formed. • The vacuum oscillation length is smaller than the sun’s core for the observed mass value. • Matter enhancement was needed to get the full deficit

  12. Matter Enhanced Oscillations • 1978 Wolfenstein shows that neutrino oscillations are modified when neutrinos interact with matter. • 1985 Mikhaev and Smirnow show that neutrinos may undergo a resonant flavor conversion if the density of matter varies, as in the sun. • The MSW theory describes the enhanced oscillation in matter.

  13. The Sudbury Neutrino Observatory (SNO) • SNO is water Cherenkov detector with heavy (deuterated) water. • Detects 8B neutrinos • Two reactions enable charged and neutral currents to be observed • e+ d -> p + p +e- (only e detected) • x+ d -> p + n + x (all ’s; x = e, ) • Observed that e oscillated to x • Total rate of neutrinos agrees with predictions • Oscillations proven to be cause of deficit!

  14. SNO Results Clinch Neutrino Oscillations SNO First Results: 2001 Neutral current interactions(sensitive to all neutrinos equally) Elastic scattering interactions(sensitive to all neutrinos, enhanced sensitivity for electron neutrinos) Charged current interactions(sensitive only to electron neutrinos)

  15. The SNO Mixing Parameters

  16. The Kamland Detector

  17. Kamland Results 2003

  18. KamLAND Results 2005 Neutrinos from 53 Reactors

  19. The Vacuum-Matter Transition • Above about 2 MeV solar neutrino oscillations are influenced by interactions with matter, the MSW effect. • Below ~ 2 MeV neutrino oscillations are vacuum-like. • The 0.86 MeV 7Be neutrino provides a data point in the vacuum region • The Predicted Vacuum-Matter transition is being tested by Borexino. p-p, 7Be, pep 8B

  20. Non-Standard Neutrino-MatterInteractions? Friedland, Lundardini & Peña-Garay Exploring the vacuum-matter transition is sensitive to new physics. New neutrino-matter couplings (either flavor-changing or lepton flavor violating) can be parametrized by a new MSW-equivalent term ε Where is the relative effect of new physics the largest? At resonance! Blue: Standard  oscillations Red: Non-standard interactions tuned to agree with experiments.

  21. Borexino Historical Highlights • 1989-92: Prototype CTF Detector started • 1995-96: Low background in CTF achieved • 1996-98: Funding INFN,NSF, BMBF, DFG • 1998-2002: Borexino construction • August 16 2002: Accidental release of ~50 liter of liquid scintillator shuts down Borexino and LNGS • 2002-2005: Legal and political actions: Princeton • 2005 Borexino Restarts Fluid Operations • August 16, 2007 First Borexino Results on Web.

  22. John Bahcall-Martin Deutsch • Borexino Mishap August 16 2002 • Martin Deutsch January 29, 1917 August 16, 2002. • John Bahcall December 30, 1934 August 17, 2005 • Borexino First Results Paper August 16 2007

  23. The Borexino Detector

  24. Detection Principles • Detect -e scattering via scintillation light • Features: • Low energy threshold (> 250 keV to avoid 14C) • Good position recostruction by time of flight • Good energy resolution (500 pe/MeV) • Drawbacks: • No directional measurements • ν induced events can’t be distinguished from other β/γ due to natural radioactivity • Experiment requires extreme ssuppression of all radioactive contaminants

  25. Solar Neutrino Science Goals • Test MSW vacuum solution of neutrino oscillations at low energy. • Look for non-standard interactions. • Measure CNO neutrinos- metallicity problem. • Compare neutrino and photon luminosities

  26. Neutrinos and Solar Metallicity • A direct measurement of the CNO neutrinos rate could help solve the latest controversy surrounding the Standard Solar Model. • One fundamental input of the Standard Solar Model is the metallicity of the Sun - abundance of all elements above Helium • The Standard Solar Model, based on the old metallicity derived by Grevesse and Sauval (Space Sci. Rev. 85, 161 (1998)), is in agreement within 0.5% with the solar sound speed measured by helioseismology. • Latest work by Asplund, Grevesse and Sauval (Nucl. Phys. A 777, 1 (2006)) indicates a metallicity lower by a factor ~2. This result destroys the agreement with helioseismology • Can use solar neutrino measurements to help resolve! 7Be (12% difference) and CNO (50-60% difference)

  27. Low Energy Neutrino Spectrum pep Mono-energetic 7Be and pep neutrinos produce a Box-like electron recoil energy spectrum

  28. The Underground Halls of the Gran Sasso Laboratory • Halls in tunnel off A24 autostrada with horizontal drive-in access • Under 1400 m rock shielding (~3800 mwe) • Muon flux reduced by factor of ~106 to ~1 muon/m2/hr • BX in Hall C ~20mx20mx100m To Rome ~ 100 km

  29. Special Methods Developed • Low background nylon vessel fabricated in hermetically sealed low radon clean room (~1 yr) • Rapid transport of scintillator solvent (PC) from production plant to underground lab to avoid cosmogenic production of radioactivity (7Be) • Underground purification plant to distill scintillator components. • Gas stripping of scintlllator with special nitrogen, free of radioactive 85Kr and 39Ar from air. • All materials electropolished SS or teflon, precision cleaned with a dedicated cleaning module • Vacuum tightness standard: 10-8 atm-cc/s

  30. Purification of Scintillator

  31. Assembly of Distillation Column in Princeton Cleanroom 100

  32. Assembly of Columns Installing sieve trays in distillation column Installing structured packing in stripping column

  33. Fabrication of Nylon Vessel John Bahcall

  34. Raw Spectrum- No cuts

  35. Expected Spectrum

  36. Data with Fiducial Cut (100 tons)Kills gamma background from PMTs

  37. Data: α/β Statistical Subtraction

  38. Data with Expected pep & CNO

  39. Published Data on 7Be Rate Phys Lett B 658 (2008) 101 Expected interaction rate in absence of oscillations: 75±4 cpd/100 tons for LMA-MSW oscillations: 49±4 cpd/100 tons Measured: 47± 7± 12 cpd/100ton

  40. Matter-VacuumBefore Borexino

  41. After Borexino

  42. Future Possibilities? Borexino could possibly measure pep, 8B, and pp

  43. t = 432.8 ns b a 212Bi 212Po 208Pb ~800 KeV eq. 2.25 MeV Specs: 232Th: 1. 10-16 g/g 0.035 cpd/ton Background: 232Th Assuming secular equilibrium, 232Th is measured with the delayed coincidence: 212Bi-212Po =423±42 ns Time (ns) Events are mainly in the south vessel surface (probably particulate) z (m) Only few bulk candidates R (m) R(m) From 212Bi-212Po correlated eventsin the scintillator: 232Th: < 6 ×10-18 g(Th)/g (90% C.L.)

  44. t = 236 ms b a 214Bi 214Po 210Pb ~700 KeV eq. 3.2 MeV Specs: 238U: 1. 10-16 g/g Background: 238U Assuming secular equilibrium, 238U is measured with the delayed coincidence: 214Bi-214Po =240±8s Time s Setp - Oct 2007 214Bi-214Po z (m) < 2 cpd/100 tons 238U: = 6.6 ± 1.7×10-18 g(U)/g R(m)

  45. Big background! 60 cpd/1ton Background: 210Po • Not in equilibrium with 210Pb and 210Bi. But how??? • 210Po decays as expected. • Where it comes from is not understood at all! • It is also a serious problem for other experiments- dark matter, double beta decay

  46. b g 85Kr 85mRb 85Rb 514 keV 173 keV • = 1.46 ms - BR: 0.43% b 85Kr 85Rb 687 keV = 10.76 y - BR: 99.56% 85Kr  decay : (b decay has an energy spectrum similar to the 7Be recoil electron ) Background: 85Kr 85Kr is studied through : 85Kr came from a small leak during a short part of filling. Important background to be removed in future purification.

  47. Removal of 11C • Produced by muons: 25 cpd/100ton • Obscures pep (2 cpd/100ton) • Muon rate too high and half-life too long to veto all events after each muon. • Strategy suggested by Martin Dentsch • Look for muon-neutron coincidence and veto events near where the neutron is detected.

  48. μ Track n Capture 11C

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