Aldo Ianni for the Borexino collaboration 12th International Workshop on Next Generation Nucleon Decay and Neutrino Detectors Zurich, 7 th Nov 2011

Solar neutrino detection in real time above 250 keV with a high purity LS – MAIN GOAL Geo-neutrino detection Supernova neutrino detection in particular neutrino-proton ES scattering Rare processes search: neutrino magnetic moment, Pauli violation process through “forbidden” nucleon transitions … Short baseline sterile neutrino search with a neutrino artificial source

Solar Neutrino Spectrum probed by Borexino 8 B(14%) pp(0.6%) 15 O(15%) 17 F(17%) 13 N(14 %) 7 Be(7%) pep(1.1%)

Borexino Expected Solar e Spectrum Spectrum with irreducible backgrounds pp sensitivity 11 C subtraction 7 Be Compton edge Predicted rates 7 Be: 50 cpd/100tons pep: 2.8 cpd/100tons CNO: 5 cpd/100tons 8 B: 0.5 cpd/100tons 14 C

No event-by-event signature Any process which produces an electron is a source of background Natural radioactivity from intrinsic impurities ( 238 U, 232 Th, 210 Pb, 40 K …) The reduction of background events is a key issue

Borexino filled and operational in May 2007 after 16 years of work

U and Th radiopurity at the level of g/g 7 Be solar neutrino measurement at the level of ~5% Day-night asymmetry for 7 Be solar neutrinos 8 B solar neutrino measurement at ~17% geoneutrinos observation at 4  (not discussed see G. Fiorentini this meeting)  Measurement of pep solar neutrinos (98% C.L.) Strongest bound on CNO neutrinos Search for cosmogenic radioactive isotopes in liquid scintillators Search for rare processes neutrino magnetic moment electron antineutrinos from the sun Muon seasonal variations and cosmogenic backgrounds

BOREXINO Filling Strategy

Calibration system  sources  sources  neutrons 57 Co 139 Ce 203 Hg 85 Sr 54 Mn 65 Zn 60 Co 40 K 14 C 214 Bi 214 PonpnC Energy [MeV] , ALSO: 228 Th external source SSS

Data reduction No muons + no 2ms correlated events FV (<3m) FV(|z|<1.7m) Pulse shape Detector threshold is 25 p.e. Total detector counting rate above threshold is 30 Hz

PRL 107, (2011) Exposure: livedays; ton×yr 46±1.5(stat) (syst) cpd/100t  Be = (3.10±0.15)×10 9 cm -2 s -1 No oscillation hy. disfavoured at 5   pp = × cm -2 s -1 indirect meas. PRL 107, (2011) Exposure: livedays; ton×yr 46±1.5(stat) (syst) cpd/100t  Be = (3.10±0.15)×10 9 cm -2 s -1 No oscillation hy. disfavoured at 5   pp = × cm -2 s -1 indirect meas. 7 Be solar e measurement  subtracted spectrum

Day-Night regeneration LMA Negligible effect expected for Borexino for best-fit LMA LOW

Paper accepted by Phys. Lett. B A dn =2(R n -R d )/(R n +R d ) = ± 0.012(stat) ± 0.007(syst) A dn measured by fitting the day and night spectra exposure: days livetime night livetime

Predicted rate: 2.8 cpd/100tons Visible energy range of interest: 0.8 – 1.2 MeV Main background: cosmogenic 11 C e + emitter ~ 28 cpd/100tons Strategy: apply the so-called Three-Fold-Coincidence (TFC) and a pulse shape discrimination between e + and e - paper on archive and submitted to PRL

Three-Fold-Coincidence Cylindrical cut Around muon-track Spherical cut around neutron Capture to reject 11 C event Neutron production Muon track Borexino coll: CNO and pep neutrino spectroscopy in Borexino: measurement of the deep-underground production of cosmogenic 11 C in an organic liquid scintillator, Phys. Rev. C 74, (2006). Muons crossing the LS produce at least one neutron in 95% of cases Goal: reduce 11 C background 11 C

Exploit pulse shape differences between e + and e - in the LS arising from annihilation of  ’s and ortho-positronium formation 50% of  + decays give ortho-positronum (t 1/2 ~3ns) Tuning of PS parameter with known sources: 214 Bi, 11 C, 10 C Data selected in the FV R< 2.8 m

Fit of 11 C subtracted spectrum CNO spectrum is at 95% CL upper bound 210 Bi main background strongly correlated with CNO Residual spectrum after subtracting all contributions at the best-fit rates R pep = 3.1±0.6 stat ±0.3 sys cpd/100t  pep = (1.6±0.3)×10 8 cm -2 s -1  CNO < 7.7×10 8 cm -2 s -1 95% C.L.  CNO BX /  CNO SSM < 1.5

PRD 82 (2010) Exposure: 345 days in 100 tons FV: Jul 2007 – Aug 2009  B ES = (2.4 ± 0.4 stat ± 0.1 sys )×10 6 cm -2 s -1 no oscillation hy. excluded at 4.2 

Global analysis in particular with the day-night asymmetry measurement (see C. Pena-Garay this meeting) Survival probability: MSW matter-vacuum transition Solar metallicity controvery by means of CNO

BX day-night excluded All solar neutrino data

Since 2005 a new recalculation of the sun’s metallicity has raised a “strong” tension between helioseismology and the SSM HZ LZ data HZ LZ SNO + Borexino 1,3  contours 1,2,3  contours

Only a direct CNO measurement could address this problem In BX this means reduce 210 Bi/ 210 Pb background which is the goal of the ongoing purification Taken from Haxton, Serenelli and Pena-Garay, 2011

A neutrino source experiment in Borexino Sourcedecayt [days] Energy [ MeV] Kg/MCiW/kCi 51 Cre-capture (E g =0.32 MeV 10%) % Sr- 90 YFission product b <2.28 MeV 100% Ce- 144 PrFission product  - 411< MeV 97.9%

Source locations in Borexino A: underneath WT D=825 cm No change to present configuration B: inside WT D = 700 cm Need to remove shielding water C: center Major change Can be done at the end of solar neutrino physics A B C

External 51 Cr source

Tackle down CNO neutrinos by reducing 210 Bi contamination – Water Extraction purification in progress Nitrogen stripping has already removed 85 Kr and this will improve 7 Be measurement and might allow to probe pp neutrinos Improve statistics for geoneutrinos: already doubled previous statistical sample Put forward a program to use a neutrino artificial source ( 51 Cr) in Borexino for sterile neutrino search neutrino-electron interaction at 1 MeV scale

After 16 years of work Borexino is in data taking since 2007 Borexino has performed the first measurement of 7 Be solar neutrino flux at ~5% level in 2011 Borexino has performed the first measurement of 8 B solar neutrinos in a liquid scintillator at 16% level in 2010 Borexino has performed the first observation of geoneutrinos at 4  in 2010 Borexino has provided the first indication of pep solar neutrinos at 98% CL Borexino is performing a purification campaing and entering in a second phase where we hope to tackle down the CNO and pp solar neutrino fluxes Borexino aims to search for sterile neutrinos with an artificial source at 10 PBq level

References on BOREXINO results Technical papers Detector: NIM A 600 (2009) Purification and fluid handling: NIM A 587, (2008) Physics results 7 Be evidence: PL B (2008) 7 Be at 10% + f pp /f CNO : PRL 101, (2008) 8 B neutrinos: PRD 82 (2010) Limits on violation of Pauli forbidden transitions on 12C: PR C 81 (2010) Electron antineutrinos from the sun: PLB 696 (2011) 7 Be at 5%: PRL 107, (2011) Day-night asymmetry: arXiv: , accepted by PL B Seasonal modulation of cosmic muons: arXiv: Technical papers Detector: NIM A 600 (2009) Purification and fluid handling: NIM A 587, (2008) Physics results 7 Be evidence: PL B (2008) 7 Be at 10% + f pp /f CNO : PRL 101, (2008) 8 B neutrinos: PRD 82 (2010) Limits on violation of Pauli forbidden transitions on 12C: PR C 81 (2010) Electron antineutrinos from the sun: PLB 696 (2011) 7 Be at 5%: PRL 107, (2011) Day-night asymmetry: arXiv: , accepted by PL B Seasonal modulation of cosmic muons: arXiv:

Raju Raghavan a mentor for Borexino and a personal friend

solar neutrino signal in 100tons FM corresponds to ~ 6×10 -9 Bq/kg U[Th] at the level of g/g corresponds to 1.2× [4× ] Bq/kg U/Th in soil ~ 12/4 Bq/kg Rn in Borexino FM ~ 1× Bq/kg Rn in air ~ 10 Bq/kg at STD

e+e+  anti-  R prompt-delayed < 1m  t prompt-delayed ~ 256  s  R prompt-delayed < 1m  t prompt-delayed ~ 256  s target LS ~ p p n

Reactors in the World: main source of background Borexino KamLAND

Best-fit parameters from likelihood analysis BSE Max radiogenic Min radiogenic 68%, 90% and 99.73% C.L. 1 

With 238 U and 232 Th at the level of g/g and exploiting offline background reduction one expects ~ 24 cpd – soil has ~ ppm level Other background ( 85 Kr, 39 Ar, 210 Pb, 40 K) sources must also be reduced: goal is ~ 1 cpd/100tons In 1991 best sensitivity with ICP-MS which could be achieved for U and Th was at the level of g/g A prototype for Borexino, the Counting Test Facility, was built and operational in 1994 to prove the feasibility of the experiment

Counting Test Facility