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Geoneutrinos in Borexino

Geoneutrinos in Borexino. Introduction to Borexino Radiopurity in Borexino Physics Test results Borexino and Geoneutrinos. Marco G. Giammarchi & Lino Miramonti Dip. di Fisica dell’Universita’ and Infn Milano. Laboratori Nazionali del Gran Sasso. 3700 mwe overburden. Borexino.

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Geoneutrinos in Borexino

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  1. Geoneutrinos in Borexino • Introduction to Borexino • Radiopurity in Borexino • Physics Test results • Borexino and Geoneutrinos Marco G. Giammarchi & Lino Miramonti Dip. di Fisica dell’Universita’ and Infn Milano Marco G. Giammarchi, Infn Milano

  2. Laboratori Nazionali del Gran Sasso 3700 mwe overburden Marco G. Giammarchi, Infn Milano

  3. Borexino • Borexino is located under the Gran sasso mountain which provides a shield against cosmic rays (residual flux = 1 m /m2 hour); • The core of the detector is shielded by successive layers of increasingly pure materials Core of the detector: 300 tons of liquid scintillator contained in a nylon vessel of 4.25 m radius (PC+PPO); 1st shield: 1000 tons of ultra-pure buffer liquid (pure PC) contained in a stainless steel sphere of 7 m radius; 2214 photomultiplier tubes pointing towards the center to view the light emitted by the scintillator; 2nd shield: 2400 tons of ultra-pure water contained in a cylindrical dome; 200 PMTs mounted on the SSS pointing outwards to detect light emitted in the water by muons Marco G. Giammarchi, Infn Milano

  4. Nylon vessels installation Marco G. Giammarchi, Infn Milano

  5. Nylon vessels installed and inflated (May 2004) Marco G. Giammarchi, Infn Milano

  6. Experimental Hall In Gran Sasso (Hall C) Stainless Steel Sphere (SSS) Optical fiber istallation PMTs ready to be mounted Marco G. Giammarchi, Infn Milano

  7. Final closure of the Inner detector (2004) Marco G. Giammarchi, Infn Milano

  8. Monocromatic ! En=862 keV FSSM=4.8x109n/sec/cm2 s=10-44 cm2 “n window” (0.25-0.8 MeV) expected rate (LMA hypothesis) is 35 counts/day in the neutrino window Marco G. Giammarchi, Infn Milano

  9. Radiopurity constraints • This translates into the following requirements on the most critical contaminants (238U , 232Th , 40K, 210Po, 210Pb, 39Ar, 85Kr) : • To lower the threshold down to 250 keV, it is mandatory to reach very high radiopurity levels in the active part of the detector ; Intrinsic contamination of the scintillator for what concerns isotopes belonging to the U and Th chain < 10-16 g/g; 14C /12C <10-18 in the scintillator Intrinsic contamination of the scintillator for what concerns 40K < 10-14 g/g; Contamination of the nylon vessel for what concerns the U and Th chain < 10-12 g/g; Constraints on N2 used to sparge scintillator: <0.14 ppt of Kr in N2 (0.2 mBq 85Kr/m3 N2) Constraints on N2 used to sparge scintillator: <0.36 ppm of Ar in N2 (0.5 mBq 39Ar/m3 N2) Contamination of the buffer liquid in U and Th chain < 10-14 g/g; Contamination of the external water in U and Th chain < 10-10 g/g; Each of these points required careful selection and clean handling of materials, + implementation of purification techniques Marco G. Giammarchi, Infn Milano

  10. Counting Test Facility (CTF) • CTF is a prototype of BX. Its main goal was to verify the capability to reach the very low-levels of contamination needed for Borexino • CTF campaigns • CTF1: 95-97 • CTF2: 2000 (pxe) • CTF3: 2001 still ongoing • 100 PMTs • 4 tons of scintillator • 4.5m thickness of water shield • Muon-veto detector CTF high mass and very low levels of background contamination make it a unique detector to search for rare or forbidden processes with high sensitivity Marco G. Giammarchi, Infn Milano

  11. Physics results of the Counting Test Facility of Borexino (CTF) Marco G. Giammarchi, Infn Milano

  12. Neutrino magnetic moment [Physics Letters B 563 (2003) 35 - a non-zero mnwould increase the en scattering cross-section by the term; - this effect becomes dominant at low energy - mn < 5.5 x 10-10mB (90% C.L.) - it is the best limit with low energy neutrino • e-n scattering • 14C spectrum • Residual radioactive bkg Limits on electron stability [Phys. Lett. B 525 (2002) 29] - Non-conservation of electric charge would lead to electron decay via two processes: e  g + n , e  n + n + n - search for the decay eg+n (256keV line) - t > 4.6 x 1026 y (90% C.L.) - currently world best limit (quoted on the PdG) Marco G. Giammarchi, Infn Milano

  13. Limits on Pauli Esclusion Principle [Europ. Physical Journal C37 (2004) 421] - we look for non-Paulian transitions in 12C and 16O nuclei from 1P shell to a filled 1S1/2 shell; - the obtained limits significantly improves (up to three order of magnitude) previous limits Limits on nucleon decay into invisible channels [Physics Letters B 563 (2003) 23] - different channels were considered in which a single nucleon or a pair of nucleons bounded in C or O nuclei decay with the emission of invisible particles (neutrinos, majorons…) - the obtained limits are comparable or improve previous limits; Limits on Heavy neutrino mixing in 8B decay [JETP Lett. Vol. 78 No 5 (2003)261] - If heavy neutrinos nH with m > 2 me are emitted in 8B reaction in the sun then the decay nH nL + e+ + e- should be observed; - CTF significantly improves limits on (mnH - ׀UeH׀2) parameter space; Other papers are under preparation: “Constraints on the solar anti-neutrino flux obtained with the BX prototype” F < 3x105 cm-2 s-1 (90% C.L.) first limit at low energy Marco G. Giammarchi, Infn Milano

  14. Geoneutrinos detection in Borexino Earth emits a tiny heat flux with an average value of ΦH~ 60 mW/m2 Integrating over the Earth surface: HE ~ 30 TW Detecting antineutrino emitted by the decay of radioactive isotopes It is possible to study the radiochemical composition of the Earth Giving constrain on the heat generation within the Earth. Marco G. Giammarchi, Infn Milano

  15. 238U and 232Th chains have 4 βwith E > 1.8 MeV : The terrestrial antineutrino spectrum above 1.8 MeV has a “2-component” shape. high energy component coming solely from U chain and low energy component coming with contributions from U + Th chains This signature allows individual assay of U and Th abundance in the Earth Anti-neutrino from 40K are under threshold Marco G. Giammarchi, Infn Milano

  16. Background from nuclear Reactors Borexino is located in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E Earth data from F. Mantovani et al., Phys. Rev. D 69 (2004) 013001 Data from the International Nuclear Safety Center(http://www.insc.anl.gov) Marco G. Giammarchi, Infn Milano

  17. Background from Po-210 Pb concentration measured in the Counting Test Facility Alpha particles reacting on C-13: • Pb-210 related background negligible • Only significant source of background are nuclear reactors • Accidental rate also negligible (< 10% of reactors background) Marco G. Giammarchi, Infn Milano

  18. Positron energy spectrum from antineutrino events in Borexino The number expected events in Borexino are: The background will be: U+Th European Reactors Predicted accuracy of about 30% in 5 years of data taking Marco G. Giammarchi, Infn Milano

  19. Conclusion and outlook Borexino is a low background high sensitivity underground detector which is located on continental crust and can give important information on geoneutrino fluxes. • Following August 2002 accident, Borexino activity has suffered from severe restrictions especially for what concerns fluid handling operations; • In spite of this, the detector installation has continued and was completed in 2004; • Following this, it was possible to start the re-commissioning of all ancillary plants which had been stopped three years ago; the re-commissioning is currently taking place; • We expect to start filling the detector with scintillator in June 2006; • We expect to start data-taking with the filled detector in november 2006 Marco G. Giammarchi, Infn Milano

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