1. Borexino results and future Davide Franco CNRS-APC GdR Neutrino 2012 October 30-31, 2012

2. Davide Franco – APC CNRS – GdR Neutrino 2012 Neutrino Production In The Sun pp chain: pp, pep, 7 Be, hep,and 8 B CNO cycle: 13 N, 15 O, and 17 F

3. Davide Franco – APC CNRS – GdR Neutrino 2012 Solar Neutrino Spectra SNO SuperK (real time) HomestakeGallex GNO Sage Borexino (real time)

4. Davide Franco – APC CNRS – GdR Neutrino 2012 The Standard Solar Model before 2004 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)), was in agreement within 0.5 in % with the solar sound speed measured by helioseismology.

5. Davide Franco – APC CNRS – GdR Neutrino 2012 The Standard Solar Model after 2004 Latest work by Asplund, Grevesse and Sauval (Nucl. Phys. A 777, 1 (2006)) indicates a lower metallicity by a factor ~2. This result destroys the agreement with helioseismology [cm -2 s -1 ] pp (10 10 ) pep (10 10 ) hep (10 3 ) 7 Be (10 9 ) 8 B (10 6 ) 13 N (10 8 ) 15 O (10 8 ) 17 F (10 6 ) GS 985.971.417.915.085.882.822.095.65 AGS 096.031.448.184.644.852.071.473.48  -1%-2%-3%-9%-18%-27%-30%-38% Solar neutrino measurements could solve the problem!

6. Davide Franco – APC CNRS – GdR Neutrino 2012 Borexino goals First ever observations of sub-MeV neutrinos in real time Check the balance between photon luminosity and neutrino luminosity of the Sun CNO neutrinos (direct indication of metallicity in the Sun’s core) pep neutrinos (indirect constraint on pp neutrino flux) Low energy (3-5 MeV) 8 B neutrinos Tail end of pp neutrino spectrum? Test of the matter-vacuum oscillation transition with 7 Be, pep, and low energy 8 B neutrinos SNEWS network for supernovae First evidence (>3  ) of geoneutrinos Neutrino speed of light Limit on the neutrino magnetic moment by analyzing the 7 Be energy spectrum and with Cr source Sterile neutrinos with sources

7. Davide Franco – APC CNRS – GdR Neutrino 2012 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

8. Davide Franco – APC CNRS – GdR Neutrino 2012 Davide Franco – Università di Milano & INFN APC – January 26, 2009 Abruzzo 120 Km da Roma Laboratori Nazionali del Gran Sasso Assergi (AQ) Italy ~3500 m.w.e Borexino – Rivelatore e impianti Laboratori esterni

9. Davide Franco – APC CNRS – GdR Neutrino 2012 Detector layout and radiopurity 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 1350 m 3 Nylon vessels: Inner: 4.25 m Outer: 5.50 m

10. Davide Franco – APC CNRS – GdR Neutrino 2012 Detection principles and signature Borexino detects solar via their elastic scattering off electrons in a volume of highly purified liquid scintillator Mono-energetic 0.862 MeV 7 Be are the main target, and the only considered so far Mono-energetic pep, CNO and possibly pp will be studied in the future Detection via scintillation light: Very low energy threshold Good position reconstruction Good energy resolution BUT… No direction measurement The induced events can’t be distinguished from other  events due to natural radioactivity Extreme radiopurity of the scintillator is a must! Typical rate (SSM+LMA+Borexino)

11. Davide Franco – APC CNRS – GdR Neutrino 2012 Borexino background RadioIsotopeConcentration or FluxStrategy for Reduction NameSourceTypicalRequiredHardwareSoftwareAchieved  cosmic~200 s -1 m -2 ~ 10 -10 UndergroundCherenkov signal <10 -10 at sea level Cherenkov detectorPS analysis(overall) Ext.  rock Water Tank shieldingFiducial Volumenegligible Int.  PMTs, SSS Material SelectionFiducial Volumenegligible Water, Vessels Clean constr. and handling 14 CIntrinsic PC/PPO~ 10 -12 ~ 10 -18 Old Oil, check in CTFThreshold cut ~ 10 -18 238 UDust~ 10 -5 -10 -6 g/g < 10 -16 g/g Distillation, Water Extraction ~ 2 10 -17 232 ThOrganometallic (?)(dust)(in scintillator)Filtration, cleanliness ~ 7 10 -18 7 BeCosmogenic ( 12 C)~ 3 10 -2 Bq/t< 10 -6 Bq/tonFast procurement, distillationNot yet measurable? 40 KDust,~ 2 10 -6 g/g< 10 -14 g/g scin.Water ExtractionNot yet measurable? PPO(dust)< 10 -11 g/g PPODistillation 210 PbSurface contam. Cleanliness, distillationNot yet measurable? from 222 Rn decay (NOT in eq. with 210 Po) 210 Po Surface contam. Cleanliness, distillationSpectral analysis ~ 14 from 222 Rn decay  stat. subtraction ~ 0.01 c/d/t 222 Rnair, emanation from~ 10 Bq/l (air)< 1 c/d/100 tWater and PC N 2 stripping,Delayed coincidence< 0.02 c/d/t materials, vessels~100 Bq/l (water)(scintillator)cleanliness, material selection 39 ArAir (nitrogen)~17 mBq/m 3 (air)< 1 c/d/100 tSelect vendor, leak tightnessNot yet measurable? 85 Kr Air (nitrogen)~ 1 Bq/m 3 in air< 1 c/d/100 tSelect vendor, leak tightnessSpectral fit = 25±3 (learn how to measure it)fast coincidence = 29±14

12. Davide Franco – APC CNRS – GdR Neutrino 2012 Detector Calibration May 2007 Detector response vs position: 100 Hz 14 C+ 222 Rn in scintillator in >100 positions Quenching and energy scale: Beta: 14 C, 222 Rn in scintillator Alpha: 222 Rn in scintillator Gamma: 139 Ce, 57 Co, 60 Co, 203 Hg, 65 Zn, 40 K, 85 Sr, 54 Mn Neutron: AmBe MC-G4Bx Data Pulse shape of 14 C events LY ~ 500 p.e./MeV Ph.Y. ~ 12000 photons/MeV Data - MC

13. Davide Franco – APC CNRS – GdR Neutrino 2012 7 Be neutrino (862 keV) rate @ 4.6% Phys. Rev. Lett. 107, (2011) 141302 740 live days MC Fit Analytical Fit Systematics

14. Davide Franco – APC CNRS – GdR Neutrino 2012 Implication of the 7 Be measurement No oscillation excluded @ 5.0  Assuming MSW-LMA: f 7Be = 0.97± 0.09 f pp = 1.013 +0.003 -0.010 f CNO < 1.7% (95 % C.L.) Pee = 0.51 ± 0.07 @ 867 keV no power to resolve low/high metallicity problem  < 5.4 10 -11  b Neutrino magnetic moment limit:

15. Davide Franco – APC CNRS – GdR Neutrino 2012 The Day-Night Asymmetry A dn = 0.001 ± 0.012 (stat) ± 0.007 (syst) LOW ruled out at 8.5  A neutrino “regeneration” is expected only in the LOW solution

16. Davide Franco – APC CNRS – GdR Neutrino 2012 8 B neutrinos with the lowest threshold: 3 MeV 2.6 MeV  ’s from 208 Tl on PMT’s and in the buffer All volume R < 3 m (100 tons) Energy spectrum in Borexino (after  subtraction) Expected 8 B rate in 100 tons of liquid scintillator above 2.8 MeV: 0.26±0.03 c/d/100 tons > 5  distant from the 2.6 MeV  peak S/B ratio < 1/6000!!! live-time: 246 days

17. Davide Franco – APC CNRS – GdR Neutrino 2012 8 B neutrino rate measurement raw spectrum  cut FV cut cosmogenic, neutron, 214 Bi and 10 C cuts 208 Tl 3.0-16.3 MeV5.0-16.3 MeV Rate [c/d/100 tons]0.22±0.04±0.0 1 0.13±0.02± 0.01  ES exp [10 6 cm −2 s −1 ] 2.4±0.4±0.12.7±0.4±0.2  ES exp /  ES th 0.88±0.191.08±0.23

18. Davide Franco – APC CNRS – GdR Neutrino 2012 First observation of pep neutrinos  + 12 C →  + 11 C + n + p → d +  → 11 B + e + + e Three Fold Coincidence (TFC): space-time veto removes 90% of 11 C paid with 50% loss of exposure 11 C  ~ 30 min

19. Davide Franco – APC CNRS – GdR Neutrino 2012 o-Ps in scintillators Measurements of the o-Ps mean-life and formation probability in scintillators with the PALS technique D. Franco, G. Consolati, D. Trezzi, Phys. Rev. C83 (2011) 015504 Pulse shape induced distortion MC  ~ 3 ns p ~ 50% ANR JCJC: NuToPs

20. Davide Franco – APC CNRS – GdR Neutrino 2012 Multivariate maximum likelihood fit Energy spectral fit Radial fit Pulse shape fit Pulse shape test

21. Davide Franco – APC CNRS – GdR Neutrino 2012 pep neutrinos: results pep neutrinos: Rate: 3.1 ± 0.6 (stat) ± 0.3 (sys) cpd/100 t Assuming MSW-LMA: Φ pep = 1.6 ± 0.3 10 8 cm -2 s -1 No oscillations excluded at 97% C.L. Absence of pep solar ν excluded at 98% CNO neutrinos: only limits, correlation with 210 Bi; CNO limit obtained assuming pep @ SSM CNO rate < 7.1 cpd/100 t (95% c.l.) Assuming MSW-LMA: Φ CNO < 7.7 10 8 cm -2 s -1 (95% C.L.) the strongest limit to date not sufficient to resolve metallicity problem Δχ 2 profile for fixed pep and CNO rates Borexino limit

22. Davide Franco – APC CNRS – GdR Neutrino 2012 The Borexino Solar neutrino spectroscopy

23. Davide Franco – APC CNRS – GdR Neutrino 2012 Status and future perspectives Since July 2010, purification campaigns: Nitrogen stripping successful in 85 Kr removal: 85 Kr < 8.8 cpd / 100 t (2007-2010: 31.2 ± 5) moderate success in 210 Bi removal by water extraction: 210 Bi : (16 + 4) cpd / 100 t (2007-2010: 41.0 ± 2.8) unprecedented 238 U and 232 Th radio-purity: 238 U < 9.7 10 -19 g/g and 232 Th < 2.9 10 -18 g/g 210 Po natural decreasing: ~5 cpd / t Borexino phase II started: Solar neutrino program: - Improve 7 Be, 8 B → test of MSW - Confirm pep at more than 3 σ - CNO neutrino measurement → probe metallicity - Attempt direct pp measurement more statistics for an update of geo-neutrino measurement; sterile neutrinos with sources

24. Davide Franco – APC CNRS – GdR Neutrino 2012 CNO Neutrino Measurement Main background: 210 Bi Criticality: similar spectral shapes Strategy suggested by Villante et al. (Phys.Lett.B701:336-341,2011): Constraining 210 Bi rate looking at 210 Po decay Energy Energy + Decay Time 210 Po R(t=0) = 2000 cpd/100 ton M = 100 ton  t = 1 year

25. Davide Franco – APC CNRS – GdR Neutrino 2012 SOX ERC Advanced Granted: ~3.5 MEuro Goal Borexino sterile neutrino oscillation measurement with a 51 Cr ( 144 Ce) source 5.Activity: several 1000 evts within 1 year 6. E >250 keV ( 14 C background) 7. Half-life ≥1 month 1. Limited heat 2. Efficient shielding 3. Low impurities level 4. Compactness Requirements

26. Davide Franco – APC CNRS – GdR Neutrino 2012 Sterile Neutrinos in Borexino A B C A: underneath WT D=825 cm No change to present configuration C: center Major change Remove inner vessels At the end of Solar Neutrino physics B: inside WT D = 700 cm Need to remove shielding water

27. Davide Franco – APC CNRS – GdR Neutrino 2012 The external 51 Cr signature Multivariate fit: energy radius decay time

28. Davide Franco – APC CNRS – GdR Neutrino 2012 The Sensitivity External source activity=10MCi Error on activity=1% Error on FV=1% External source activity=10MCi Error on activity=1% Error on FV=1% FV error better than 1% already achieved in BX (calibration) Error of 1% on the source intensity is agressive – important effort to achieve it

29. Davide Franco – APC CNRS – GdR Neutrino 2012 Conclusions Phys. Lett. B658:101-108, 2008 Phys. Rev. Lett. 101, 091302, 2008 Nucl. Instr. & Meth A600:568-593, 2009 Nucl. Instr. & Meth A609:58-78, 2009 Phys. Lett. B687:299-304, 2010 Phys. Rev. D82, 033006, 2010 Phys. Rev. C81, 034317, 2010 Phys. Rev. Lett. 107, 141302, 2011 JINST 6 P05005, 2011 Phys. Lett. B707:22–26, 2012 Phys. Rev. Lett. 108, 051302, 2012 Phys. Rev. D85, 092003, 2012 The Phase 1 of the Borexino experiment is over First detection and 5% measurement of 7 Be line 8 B at low energy, 7 Be day-night, geo-nu at 99.997% C.L. First detection of pep solar neutrinos New limits on Pauli Principle Violation and Solar Axions Purification was successful, and phase 2 is starting A rich program on solar neutrino physics to be completed Probe MSW through 8 B at low energy, pep and more precise 7 Be Attempt to detect pp in real time and possible interesting upper limit on CNO SOX: Sterile Neutrino Search with neutrino and/or anti-neutrino source