M. Misiaszek (Institute of Physics, Jagellonian U., Krakow) on behalf of the Borexino Collaboration Results from the Borexino experiment Kurchatov Inst. (Russia) Dubna JINR (Russia) Heidelberg (Germany) Munich (Germany) Jagellonian U. Cracow (Poland) Perugia Genova APC Paris Milano Princeton University Virginia Tech.University Cracow Epiphany Conference 5-8 January, 2010 Krakow, Poland

Since May 2007 BOREXINO measures low energy solar neutrinos in real time by elastic neutrino-electron scattering in a volume of highly purified liquid scintillator Mono-energetic MeV 7 Be 8 B, pep, CNO and possibly pp ν Geoneutrinos Supernova ν Detection via scintillation light Very low energy threshold Good position reconstruction Good energy resolution Drawbacks: No direction measurements ν induced events can’t be distinguished from β-decay due to natural radioactivity Extreme radiopurity of the scintillator Typical rate (SSM+LMA+Borexino) The physics goals and detection principles of Borexino

Detector design and layout Water Tank:  and n shield  water Ch detector 208 PMTs in water 2100 m 3 20 legs Carbon steel plates Scintillator: 270 t PC+PPO in a 125  m thick nylon vessel Stainless Steel Sphere: 2212 photomultipliers 1350 m 3 Nylon vessels: Outer: 5.50 m Inner: 4.25 m Design based on the principle of graded shielding

Borexino is continuously taking data since 13/05/2007

Final spectrum after all cuts  Kr+  Be  shoulder 14 C 210 Po (only, not in eq. with 210 Pb!) 11 C Understanding the final spectrum: main components Last cut: 214 Bi- 214 Po and Rn daughters removal No  s After fiducial volume cut (“100 tons”)

The measured energy spectrum: May07 - Oct08

Records in the radiopurity achieved by Borexino MaterialTypical conc.Borexino level in the scintillator 14 Cscintillator 14 C/ 12 C< U, 232 Th equiv.- Hall C dust - stainless. steel - nylon ~1 ppm ~1 ppb ~1 ppt~10 -5 ppt K nat Hall C dust~1 ppm 222 Rn- external air. - air underground ~20 Bq/m 3 ~ Bq/m 3 85 Kr 39 Ar in N 2 for stripping~1.1 Bq/m 3 ~13 mBq/m Rn U, 232 Th equiv. LNGS - Hall C water~50 Bq/m 3 ~ g/g

Fit between p.e.; Light yield: a free fit parameter; Ionization quenching included (Birks’ parametrization); 210 Bi, 11 C and 85 Kr free fit parameters; Others v fixed Fit to the spectrum without and with  subtraction is performed giving consistent results R 7Be = 49 ± 3 stat ± 4 sys cpd/100 tons The measurement of the 7 Be flux (192 days of live time) Borexino Collaboration Phys. Lett. B 658 (2008) : after 2 months of data taking Borexino Collaboration PRL 101 (2008) : 192 days of live time

Expected rate (cpd/100 t) No oscillation75 ± 4 BPS07(GS98) HighZ48 ± 4 BPS07(AGS05) LowZ44 ± 4 No-oscillation hypothesis rejected at 4  level 7 Be: (49 ± 3 stat ±4 sys ) cpd/100 tons (192 days) The analysis of the calibration data is in progress The measurement of the 7 Be flux

Before Borexino After Borexino Survival probability of the e First measurement of the ratio between the survival probabilities in vacuum and in matter

Results already achieved in Borexino 1.First direct experimental evidence of the vacuum regime and of the transition region in the neutrino oscillation at very low energy: measurement of the 7 Be flux ( MeV) and strong limit on the pp flux. 2.First determination of the ratio between the e survival probability in vacuum and in matter: 1.6 ± 0.33 (from the 7 Be flux and the 8 B flux, measured with a threshold down to 2.8 MeV). 3.Measurements of the day/night effect for at very low energy: 4.First validation of the MSW-LMA model in the vacuum regime and in the transition region within the error (10% for the 7 Be flux measurement: stat.+ syst.). 5.Best limits for CNO flux, magnetic moment ( μ eff <5.4· μB ), Pauli principle violation. What next A.Measurement of the 7 Be flux with a total error  final validation of the MSW-LMA model; important insight for the Standard Solar Model metallicity puzzle and stronger limits on the pp flux. B.Determination of the survival probability ratio, day/night effect, etc. with strongly reduced errors. C.Study of the pep and CNO region (energy spectrum in the range MeV) with the suppression of the 11 C muon produced. D.Measurements of the geoneutrinos (the Gran Sasso region is especially favoured due to the absence of the main background: reactor ). Observatory Borexino is a Supernova observatory in the SNEWS network.

Additional slides

Survival probability of the e

Limits obtained by Borexino after 200 days of data taking - the best in the literature 1- Limits on pp e CNO solar fluxes; with the Luminosity constraint: 2- Limit on the neutrino magnetic moment: 3- Limits on the Pauli principle from 12 C transitions: relative strenghts

The low threshold measurement of the 8B solar neutrinos 2.6 MeV  ’s from 208 Tl on PMT’s and in the buffer Borexino threshold: 2.8 MeV Expected (MSW-LMA) count rate due to 8B neutrinos above 2.8 MeV: 0.26±0.03 c/d/100 tons Borexino energy spectrum after muon subtraction: 246 days of live time

The low threshold measurement of the 8B solar neutrinos Major background sources: 1) Muons; 2) Gammas from neutron capture; 3) Radon emanation from the nylon vessel; 4) Short lived (t < 2 s) cosmogenic isotopes; 5) Long lived (t > 2 s) cosmogenic isotopes ( 10 C); 6) Bulk 232 Th contamination ( 208 Tl); The Borexino 8 B spectrum  7Be and 8B flux measured with the same detector  Borexino 8B flux above 5 MeV agrees with existing data  Neutrino oscillation is confirmed by the 8B of Borexino at 4.2 sigma

100 Hz 14 C+ 222 Rn source diluted in PC: 115 points inside the sphere b : 14 C, 222 Rn diluted in scintillator a : 222 Rn diluted in scintillator g : 54 Mn, 85 Sr, 222 Rn in air N : AmBe  Source localization within 2 cm through red laser light and CCD camera  Accurate handling and manipulation of the source and of the materials inserted in the scintillator The Borexino calibration A first calibration campaign with on axis and off axis radioactive sources has been performed (Oct 08 on axis, Jan-Feb09 off axis)  accurate position reconstruction  precise energy calibration  detector response vs scintillation position

 /  discrimination  particles Small deformation due to average SSS light reflectivity  particles pe; near the 210 Po peak pe; low energy side of the 210 Po peak 2 gaussians fit Full separation at high energy ns  Gatti parameter