Solar Neutrino TPC Status (Sep. 2002)

1. Solar Neutrino TPCStatus (Sep. 2002) • 7 institutions, 27 physicists • 1.9 M$ R&D proposal submitted and presented to SAGENAP 2002 • 8 papers presented to NESS02, 2 accepted for publication in NIM, two more ready to be submitted • Sept. 1992 is when a Solar Neutrino TPC (Hellaz) was first proposed

2. Our proposal • Measure directly the solar neutrino energy spectrum from 200 keV to 2 MeV (includes 99.99% of solar neutrinos by species, and 65% by flux) • Unambiguous solar signature via directional measurement • Some neutrino flavor separation (Paper 1) • Measure precisely the LMA mixing angle and test the SSM

3. The TPC as a solar neutrino detector • measures electron angle to 10-15 degrees • Measures, subtracts all backgrounds • Measures neutrino energy to ~20% ( En > 200 keV) • Very low systematics from study of gold-plated, high-statistics, kinematically constrained background events • 1400-2000 events per year (LMA) for 7.6 Tons detector (4000 m3, 10 Atm.)

4. Detector features (Paper 2, to be published in NIM) • Directionality well-measured • 100 keV tracks have 9cm range, well tracked (Paper 3) • Detector planes from MUNU • Need 10-13 g/g purity in the first 20cm material surrounding TPC (ice and old Homestake rails). • Cryogenic gas used (He/CH4) and very cold filling (20K) for radon purification purposes. Purity to be measured during R&D • Long electron drift sought (need 20ppb O2, ICARUS has obtained 0.1 ppb). R&D program will measure attenuation lengths to 400 meters. • Excellent, novel educational opportunities due to imaging properties, strength of existing REU/RET programs (Paper 8).

5. LMA solution is bad for business (Paper 1, to be submitted to PRD)

6. We will work after SNO and KAMLAND – need high precision

7. Physics Reach (Paper I) - 4 parameters fit results, tests SSM and mixing

8. Subpercent systematics (paper 7) • Directional background subtraction is systematics-free • Cosmic rays chamber calibration very accurate (10,000 evts per day) • Measurement of electron energy by range is inherently stable over time • Measurement of fiducial volume by delta ray counting is precise to 0.1% • Three independent electron energy measurements: range, charge, dE/dx slope

9. Subpercent systematics contd. Two types of kin. Constr. Bkg events: cosmic+delta ray and double Comptons T tan2q = 2m and T1tan2q1+ T2tan2q2=4m Tracking efficiency to be measured from QED-expected T distributions

10. Our collaboration • Currently the largest amongst proposed solar neutrino experiments • Very active (8 papers presented at NESS02, including 4 publication level, 1 educational paper) • Has proposed novel methods to obtain 14C-free materials (paper 5, submitted to NIM) and radiopure steel (paper 6) • Very much appreciates the importance of seeking common solutions to technical problems

11. Our collaboration contd. • We have not been active in the Homestake Collaboration, in great part because • NO SITE IS PERFECT FOR US. BUT ALL SITES ARE THOUGHT TO BE WORKABLE • Depth is not a major concern to those experiments which have background rejection methods (paper 4, to be published in NIM)

12. Conclusions • After SNO and KAMLAND success, the issue of subpercent solar neutrino physics has been forced • Even our formerly proposed detector is too small, hundreds of Ton-years exposure and subpercent systematics are needs. We should consider a 70 Tons helium TPC. • Solar neutrinos remain the anchor of the subterranean science program because the opportunity for subpercent physics exists

13. Measured Spectra from TPC (Background subtracted)