1. Stockholm, May 2-6, 2006 SNOW 20061 Sub-MeV solar neutrinos: experimental techniques and backgrounds Aldo Ianni Gran Sasso Laboratory, INFN

2. Stockholm, May 2-6, 2006 SNOW 20062  Why do we need to measure sub-MeV solar neutrinos?  Neutrino physics  Astrophysics  How can they be observed?  Upcoming:  100-ton scale ultra-pure organic Liquid Scintillator (high photon yield below 1 MeV)  Elastic Scattering  Future:  liquid noble gases, metal loaded LS, TPC  ES + Inverse Electron Capture

3. Stockholm, May 2-6, 2006 SNOW 20063 Why?

4. Stockholm, May 2-6, 2006 SNOW 20064 Only 0.01% of solar neutrino spectrum measured in real time

5. Stockholm, May 2-6, 2006 SNOW 20065 Measurements vs unknowns

6. Stockholm, May 2-6, 2006 SNOW 20066 MSW-LMA to explain observations Transition of P ee Obtained with SSM constraints!

7. Stockholm, May 2-6, 2006 SNOW 20067 What do we want to measure and why do it? astrophysicsNeutrino physics

8. Stockholm, May 2-6, 2006 SNOW 20068 How difficult is it going to be?

9. Stockholm, May 2-6, 2006 SNOW 20069 What detection channel –ES: not a specific signature, better with Be and pep + asks for a ultra-pure Fiducial Mass –CC: strong signature via inverse electron capture. Internal background may become less important

10. Stockholm, May 2-6, 2006 SNOW 200610 Signatures and requirements for the ES channel 10 -16 g/g With U,Th at 10 -16 g/g and 40 K at 10 -14 g/g internal backg. ~ 20 cpd/100 tons in [0.25,0.8]MeV

11. Stockholm, May 2-6, 2006 SNOW 200611 ES + Ultra-pure liquid scintillators –First thoughts/tests ~1988 to address radiopurity issues High photon yield (10 4 /MeV) allows to perform spectroscopic measurements SSM predicts ~ 0.5 cpd/ton for Be with ES => 100t FM –Borexino a pioneer experiment with a 4-ton prototype showed (1997): that 238 U and 232 Th can be below or on the order of 10 -16 g/g (~10 -6 Bq/ton) that 14 C/ 12 C ~ 10 -18 allows to set a thereshold at 250 keV for ES that self-shielding design works with organic scintillator (  ~ 1 g/cm 3 ) to reduce external background –KamLAND (2002) with a 500 ton-scale mass has measured 238 U and 232 Th at the level of 10 -17 -10 -18 g/g => pep meas. opportunity

12. Stockholm, May 2-6, 2006 SNOW 200612 Beyond U and Th Asking for 1cpd/100tons [0.1  Bq/m 3 PC] it implies: 1.System sealed against 222 Rn ~10 -5 Bq/ton 2.0.4 ppm 39 Ar in N 2 3.0.2 ppt 85 Kr in N 2 210 Pb and 210 Po are often found not in equlibrium due to a different chemistry All spectra normalized to 1

13. Stockholm, May 2-6, 2006 SNOW 200613 Removing/Reducing 210 Bi, 210 Po, 85 Kr, 39 Ar High level of cleanliness Purification of scintillator –Distillation (thought to be the best method on the basis of small set-up tests) –Water extraction –High level nitrogen sparging Beyond U and Th Check radioisotope impurities before filling!

14. Stockholm, May 2-6, 2006 SNOW 200614 What about pep neutrinos? Cosmogenic background: 11 C Possible 11 C background reduction by tagging the sequence (in Borexino and KamLAND): muon + neutron capture + 11 C decay [see Galbiati et al, PRC, 71, 055805 (2005)] Method already tested with Borexino prototype [see hep- ex/0601035 ] SNO+ main goal due to SNOlab depth

15. Stockholm, May 2-6, 2006 SNOW 200615 Reduction of background for pep neutrinos Cylindrical cut Around muon-track Spherical cut around neutron capture vertex to reject 11 C event correlated in time and space Neutron production vertex Muon going through In 95% of cases a neutron is produced together with a 11 C Signal/Noise as large as 2 with only 3% of data rejected @ Gran Sasso

16. Stockholm, May 2-6, 2006 SNOW 200616 11 C tagged with the Borexino prototype Taken from Borexino coll. hep-ex/0601035 11 C decays  + with Q  ~1MeV and  min Measured production rate ~0.14 events/day/ton at Gran Sasso depth

17. Stockholm, May 2-6, 2006 SNOW 200617 Backgrounds for pep besides U,Th, 11 C

18. Stockholm, May 2-6, 2006 SNOW 200618 Next generation projects Goals real-time observation of pp (CC/ES) real-time observation of Be with a CC channel Projects XMASS : LXe, ES CLEAN : LNe, ES (see D. McKinsey this workshop) MOON : 100 Mo CC LENS : 115 In CC

19. Stockholm, May 2-6, 2006 SNOW 200619 Liquid Xe [XMASS] Multi-purpose detector Channel: ES No 14 C! Target: 23t [10t FV] of LXe Design: use of 30cm self- shielding (  = 3.06 g/cm 3 ) Backgrounds (main tasks): – 85 Kr: to be reduced to 4x10 -15 g/g from 10ppm (by distillation) – 136 Xe 0  : isotope separation (<1/100 of natural) 100kg(NOW)->1E3->1E4 2.5 m

20. Stockholm, May 2-6, 2006 SNOW 200620 LENS 115 In abundance = 95.7% Threshold of capture = 0.114 MeV B(GT) = 0.17 [precise measurement with neutrino source in TF] LS stability tested : > 2yr Backgrounds:   decay of 115 In + following Bremsstrahlung  Multiple In  decay Desing: high segmentation with 125t on LS [10t of In] ~4% pp meas. in 5yr

21. Stockholm, May 2-6, 2006 SNOW 200621 MOON Multi-purpose detector [0 , supernova ’s] Channel: inverse e- capture (prompt) + delayed b decay Threshold of capture = 0.168 MeV (g A /g V ) 2 B(GT) = 0.52±0.06 Backgrounds: U,Th at 10 -3 Bq/ton 214 Pb-> 214 Bi-> 214 Po 2  Surface contamination Design: 3.3ton 100 Mo module 6m x 6m x 5m Mo foils 0.05 g/cm 2 x, y reading with scintillators ~10 -9 spatial resolution required Signal: pp: ~337 events/yr/3.3tons Be: ~167 events/yr/3.3tons Test Facility in operation since April 2005 @ Oto underground lab.

22. Stockholm, May 2-6, 2006 SNOW 200622 Conclusions It is great opportunity to measure low energy solar neutrinos First thoughts: 1988! When: Borexino and KamLAND->2007 10% Be meas. [5%] gives 10%Be,1%pp [5%Be,0.5%pp] New goal: pep neutrinos. Precise meas. @ SNO+ Complementary projects under-way >=2010(?)

23. Stockholm, May 2-6, 2006 SNOW 200623

24. Stockholm, May 2-6, 2006 SNOW 200624

25. Stockholm, May 2-6, 2006 SNOW 200625 From Galbiati et al, PRC, 71, 055805 (2005)

26. Stockholm, May 2-6, 2006 SNOW 200626 From Galbiati et al, PRC, 71, 055805 (2005)

27. Stockholm, May 2-6, 2006 SNOW 200627 From Galbiati et al, PRC, 71, 055805 (2005)

28. Stockholm, May 2-6, 2006 SNOW 200628 From Galbiati et al, PRC, 71, 055805 (2005)

29. Stockholm, May 2-6, 2006 SNOW 200629 HeNeArKrXe A210183654 Ion. Potent. (eV) 24.621.615.71412.1 Boiling point (K) 4.22787119.8165 p.e./MeV4E4 4.3E4 long lived isotopes 39 Ar, 42 Ar 85 Kr Density (g/cm 3 ) 0.1251.21.42.63.06 Rad. Length (cm) 75624142.4 From hep-ph/0008296

30. Stockholm, May 2-6, 2006 SNOW 200630 800kg detector 10 ton detector ～ 30cm ～ 80cm ～ 2.5m R&D Dark Matter Search Multipurpose Detector (DM, Solar Neutrino,  ) With light guide XMASS Program with LXe 100kg Prototype M. Nakahata

31. Stockholm, May 2-6, 2006 SNOW 200631 General Properties   x  + e - → x  + e - in 22 tonnes Helium  Ultra-pure (superfluid self-cleaning)  Scintillation + rotons or e-bubbles Event discrimination Position & energy reconstruction R. Lanou Coded Aperture Wafer Array Progress   Frozen N 2 + acrylic to replace graphite moderator  Successful extraction of electrons from drifted e-bubbles … more powerful than rotons Prospects   Technique & physics potential established … Requires large scale prototyping