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Sterile Neutrinos at Borexino SOX

Sterile Neutrinos at Borexino SOX. G. Ranucci – INFN Milano On behalf of the Borexino Collaboration European Strategy for Neutrino Oscillation Physics - II CERN 15 May 2012. Borexino at Gran Sasso : real time detection of low energy neutrinos. Stainless Steel Sphere:

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Sterile Neutrinos at Borexino SOX

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  1. Sterile Neutrinos at BorexinoSOX G. Ranucci – INFN Milano On behalfof the Borexino Collaboration European Strategy for Neutrino Oscillation Physics - II CERN 15 May 2012

  2. Borexino at Gran Sasso: real time detection of low energy neutrinos Stainless Steel Sphere: 2212 photomultipliers 1350 m3 Scintillator: 270 t PC+PPO in a 150 mm thick nylon vessel Design based on the principle of graded shielding Nylon vessels: Inner: 4.25 m Outer: 5.50 m Water Tank: g and n shield m water Č detector 208 PMTs in water 2100 m3 Neutrino electron scattering n e ->n e 20 legs Carbon steel plates

  3. The idea touse a neutrino source in Borexino and in other underground experimentsdates back to at least 20 years • N.G.Basov,V.B.Rozanov, JETP 42 (1985) • Borexino proposal, 1991 (Sr90) Bx • J.N.Bahcall,P.I.Krastev,E.Lisi, Phys.Lett.B348:121-123,1995 • N.Ferrari,G.Fiorentini,B.Ricci, Phys. Lett B 387, 1996 (Cr51) Bx • I.R.Barabanovet al., Astrop. Phys. 8 (1997) • Gallex coll. PL B 420 (1998) 114 Done (Cr51) • A.Ianni,D.Montanino, Astrop. Phys. 10, 1999 (Cr51 and Sr90) Bx • A.Ianni,D.Montanino,G.Scioscia, Eur. Phys. J C8, 1999 (Cr51 and Sr90) Bx • SAGE coll. PRC 59 (1999) 2246 Done(Cr51 and Ar37) • SAGE coll. PRC 73 (2006) 045805 • C.Grieb,J.Link,R.S.Raghavan, Phys.Rev.D75:093006,2007 • V.N.Gravrin et al., arXiv: nucl-ex:1006.2103 • C.Giunti,M.Laveder, Phys.Rev.D82:113009,2010 • C.Giunti,M.Laveder, arXiv:1012.4356

  4. Source Experiment: Physics Case • Probing Short BaselineFlavorOscillations in disappearance • Searchfor Neutrino Magnetic moment • Probe neutrino-electron scattering at 1 MeV scale • Weinberg’s angle • gV and gAcoupling (NSI)

  5. Source location in Borexino • A: underneath WT • D=825 cm • No changetopresent configuration • B: inside WT • D = 700 cm • Needtoremove shielding water • C: center • Majorchange • Removeinnervessels • To bedone at the end ofsolar Neutrinophysics B C A

  6. Source position A

  7. Sources • Activity: several 1000 nevts within 1 year • E >250 keV (14C background) • Half-life ≥1 month • Compact • Limited heat • Efficient shielding • Low impurities level

  8. Neutrino source Anti-Neutrino sources A similar option, but less viable, is106 Ru– 106Rh

  9. Originally proposed by Raju Raghavan 51Cr ~36 kg of Cr 38% enriched in 50Cr 190 W/MCi from 320 keVg’s 7mSv/h (mustbe < 200) DonetwotimesforGallex at 35 MW reactor witheffectivethermalneutronsfluxof ~5.4E13 cm-2s-1 ~1.8 MCi SAGE coll., PRC 59 (1999) 2246 Gallex coll., PL B 420 (1998)

  10. 51Cr source in Gallex shielding size dictated by g-emitting impurities

  11. The case ofne 51Cr source in Borexino The uncorrelated nature of the measure forces the external deployement of the source: too much backg. from the shield for internal deployment Bismuth210 CNO Be7 Source events Window 0.250-0.700 MeV Background perfectly known : solar neutrinos + Bismuth210 Detection as 7Be solar neutrinos

  12. 90Sr-90Y source tSr= 28.79 years tY= 3.8 days 90Sr Inverse beta decay <E>=2±0.2MeV <s>=7.2×10-45cm2 90Y 7.25 kg/MCi ~6700 W/MCi including Bremsstrahlung Product of nuclear fission Used in thermoelectric generators Known technology for 0.2 MCi sources

  13. 106Ru-106Rh source 106Ru tRu= 539 days tRh=29.8 s Inverse beta decay <E>=2.5±0.2 MeV <s>=89.2×10-45cm2 106Rh Productofnuclearfission Advantage w.r.t. 90Sr: lower activity affordable Similar option: 144Ce– 144Pr

  14. Anti-nu Advantages Background free measure (delayed coincidence) -Higher counting rate due to the possibility to exploit the full volume, in this case the FV error can be ignored – the coincidence technique enables to fight efficiently the extra background added from the shield and makes it suited to be located in the center -> more events and less intensity required - Higher energy -> more events because of the quadratic dependence of the cross section from the energy - Same as geo-antinmeasure in Borexino – bckg. totally negligible - Future scalability: in a post solar phase of the experiment the entire sphere can be filled with scintillator - Issues to be considered : heat dissipation, high energy gammas and bremmstralungbackground – shielding and “shadowing” around the center Th= 1.8 MeV

  15. Staged two –phase approach • 51Cr external • Cannot be deployed internally because of background consideration – the test has zero impact on the apparatus and on the «solar» data taking - feasible within a couple of years • Anti-nusource internal • Internal deployment possible thanks to the coincidence measurement – but huge (and very pure) shield • Require a major refurbishment of the detector for the support of the source • Nylon vessel removed and the whole sphere converted into active volume • Done by 2017

  16. 51Cr Source under the detector

  17. At high Dm2the fast wiggles are washed out when the resolution is included

  18. Example of a simulation of the 51Cr source externally positioned Oscillometry analysis: total rate + waveshape of the profile of the detected events The fit allows also to determine precisely the oscillation parameters

  19. Reach of the sterile neutrino search with the 51Cr source Rate + shape + additional handle: time decay of the source event rate to better discriminate against the background Sensitivity to the rate + waveshape 2 analysis of the 51Cr source outside BX • activity=10MCi; • Error on activity=1%; • Error on FV=1%; Reactor anomaly Exclusion contours Sensitivity to the rate only FV error better than 1% already achieved in BX (calibration) Error of 1% on the source intensity is agressive – important effort to achieve it Green region 90% CL excluded from Solar+KamLANDconstraints accounting for the 13  0 value A. Palazzo - Phys. Rev. D 85, 077301 (2012)

  20. Reach of the sterile neutrino search with the 51Cr source 2 analysis of the 51Cr source outside BX • activity=10MCi; • Error on activity=2%; • Error on FV=1%; Reactor anomaly Exclusion curves Error of 2% on the source intensity as achieved in the framework of the Gallex calibration

  21. Weinberg’s Angle @ 1MeV 10 MCi source d(sin2qW) = 2.6% 5MCi source

  22. Neutrino Magnetic Moment Reactoranti-neutrinos: ~6×10-11mB (90% CL) From Borexino (solar): ~5×10-11mB (90% CL)

  23. 144Ce Source at the center of the detector

  24. Waves from a source in the center Enhanced sensitivity due both to the pattern and the increased number of events Oscillation waves

  25. Other simulations – 90Sr at the center Good agreement with the analytical oscillation curves

  26. Reach of the sterile neutrino search with the 144Ce source Adequate coverage of the region of interest of the oscillation parameter plane Error of 1% on the source intensity is agressive – but the FV error could be omitted – included as safety margin

  27. EW couplings • Standard Model • gV = -1/2+2sin2qW = -0.038 • gA = -0.5 • Use three-level cross-section • Use 51Cr and 144Ce source 90 % C.L. 51Cr 144Pr CHARM II withnme ES

  28. Status of the investigation 51Cr • Enriched Cr used for Gallex still available at CEA Saclay • Research reactor • A) High thermal neutron flux throughout the entire target ideally 1E15 n/cm2/sec • B) Enough space to accommodate the material • C) Flexible enough to allow the reconfiguration of the core • The Siloe’ reactor at Grenoble met this requirements, but it is no longer available, no other suitable reactors available in France • Alternatives • Pettenreactor (Netherland) - promising, complete feasibility evaluation to be started soon • Possibility in USA - the “Advanced Test Reactor” at Idaho National Laboratory, featuring neutron fluxes at the required level • Opportunities in Russia are being investigated as well, a couple of reactors could be suited to do the irradiation

  29. Status of the investigation Anti-n More investigations required for the anti-n sources: 90Sr can be available from the Companies who separate it from the other fissions products- Experience in Russia (heating equipments upto 1993) The same consideration apply to the 144Cesource Joint (with potential supplier) feasibility study of the source preparation and delivery to be done

  30. Conclusions Borexino is well suited for a possible source based short baseline ne disappearance test - performances and background perfectly known In a first step a totally non invasive measurement can be performed by deploying externally a 51Cr nsource in the Tunnel underneath the Water Tank specifically prepared for this purpose during the construction of the detector, affording already an interesting sensitivity limit capable to address a sizable portion of the joint reactor and Gallium In the post solar phase scenario an anti-n source can be deployed in the center and the target volume increased achieving the ultimate sensitivity capable to cover a wide region of the oscillation parameter plane, thus fully addressing the reactor anomaly indication Investigations for the sources preparation and procurement in progress Opportunity for LNGS to maintain and strengthen the leadership role gained in the context of neutrino oscillation through the Gallex—GNO and Borexino results in the solar neutrino sector

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