1. M. Misiaszek (Instytut Fizyki UJ, Kraków) Rekonstrukcja oddziaływań neutrin w detektorze BOREXINO Kurchatov Inst. (Russia) Dubna JINR (Russia) Heidelberg (Germany) Munich (Germany) Jagiellonian U. Cracow (Poland) Perugia Genova APC Paris Milano Princeton University Virginia Tech.University Seminarium neutrinowe IFT, Wrocław 16 listopada 2009

2. Borexino aims to measure low energy solar neutrinos in real time by elastic neutrino-electron scattering in a volume of highly purified liquid scintillator Mono-energetic 0.862 MeV 7 Be ν is the main target 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 cant 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

3. 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: Inner: 4.25 m Outer: 5.50 m Design based on the principle of graded shielding

4. CNO 7 Be 11 C 10 C 14 C pp+pep+ 8 B 238 U + 232 Th The expected signal and the irreducible background

5. Borexino is continuously taking data since 13/05/2007

23. Algorytmy do rekonstrukcji pozycji zdarzeń oparte są o metodę największej wiarygodności, którą poszukuje się najbardziej prawdopodobnego miejsca emisji fotonów. x0x0 t4t4 t5t5 t6t6 t1t1 t2t2 t3t3 t i = const + tof i + t ' i tof i = n/c * d i (x i,y i,z i ) Zakładamy próbną pozycję zdarzenia x 0 Obliczamy tof (czas przelotu) dla każdego fotonu Odejmujemy tof od każdego t i Porównujemy otrzymany rozkład t' i z oczekiwanym rozkładem fotonów emitowanych ze scyntylatora Algorytm przeszukuje inne pozycje x 0 dopóki nie znajdzie pozycji dla której dopasowanie jest najlepsze titi t'it'i (x i,y i,z i )

24. Rozkład przestrzenny zdarzeń Odrzucenie zdarzeń tła (głównie pr. gamma) R < 3.3 m (100 t masy scyntylatora) Rozkład radialny R2R2 gauss z vs R c scatter plot FV

25. 238 U and 232 Th 212 Bi 212 Po 208 Pb = 432.8 ns 2.25 MeV ~800 KeV eq. Only 3 bulk candidates (47.4d) 214 Bi- 214 Po 212 Bi- 212 Po 214 Bi 214 Po 210 Pb = 236 s 3.2 MeV ~700 KeV eq. 238 U: < 2. 10 -17 g/g 232 Th: < 1. 10 -17 g/g

26. Kształt impulsu w detektorze BOREXINO [ns]

28. / discrimination particles Small deformation due to average SSS light reflectivity particles 250-260 pe; near the 210 Po peak 200-210 pe; low energy side of the 210 Po peak 2 gaussians fit Full separation at high energy ns Gatti parameter

29. 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)

30. Konwersja liczby zmierzonych fotoelektronów do energii zdarzenia Fit parametrów do kształtu elektronów z 14 C ~ 500 pe /MeV Monitoring stabilności detektora Liczba fotoelektronówDate N

31. 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

32. The measured energy spectrum: May07 - Oct08

33. Records in the radiopurity achieved by Borexino MaterialTypical conc.Borexino level in the scintillator 14 Cscintillator 14 C/ 12 C<10 -12 238 U, 232 Th equiv.- Hall C dust - stainless. steel - nylon ~1 ppm ~1ppb ~1ppt K nat Hall C dust~1 ppm 222 Rn- external air. - air underground ~20 Bq/m 3 ~40-100 Bq/m 3 85 Kr 39 Ar in N 2 for stripping~1.1 Bq/m 3 ~13 mBq/m 3 - 222 Rn - 238 U, 232 Th equiv. LNGS - Hall C water~50 Bq/m 3 ~10 -10 g/g

34. Fit between 100-800 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

35. 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 (192 days of live time)

36. Survival probability of the e

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

38. 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:

39. The low threshold measurement of the 8B solar neutrinos 2.6 MeV s from 208 Tl on PMTs 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

40. 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

41. 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 (0.2-0.8 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, 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 0.9-1.5 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 network SNEWS.

42. Literatura First real time detection of 7Be solar neutrinos by Borexino (Phys. Lett. B 658 (2008) 101-108) New results on solar neutrino fluxes from 192 days of Borexino data (Phys. Rev. Lett. 101 (2008) 091302 ) Measurement of the solar 8 B neutrino flux with 246 live days of Borexino and observation of the MSW vacuum-matter transition (arXiv:0808.2868v1)