H elium A nd L ead O bservatory

1. H elium And L ead Observatory A lead detector for supernova neutrinos in SNOLAB

2. The end of a massive star's life: no nuclear energy from iron core → core collapse

3. Gravitational energy lowered by nuclear protons absorbing orbital electrons and emitting νe .The iron core shrinks to only ~ 1/25,000 of its former diameter, and becomes a dense sphere of mostly neutrons of nuclear density νe νe “football stadium” -------> “cherry”

4. e- e+ e e+ e- e e+ e- ν ν ν ν e e Z0 Z0 Z0 Z0 e Gravitational pot energy -> kinetic energy of infalling material. In this hot environment bremsstrahlung and e+-e- annihilation _ produces e+-e- pairs as well as ν ν pairs of all flavours. _ _ e+ e-

5. The shockwave takes several hours to reach the surface and blow away the outer layers of the star. That is when the optical radiation is produced, and even that constitutes only ~1% of the energy emitted. 99% of energy is emitted as prompt ν’s. Observing a supernova explosion in optical wavelengths is like sweeping up the confetti hours after the parade went by. The real action has long passed! Neutrinos give us a window to view the core collapse as it happens – one of the motivations for a supernova neutrino detector.

6. In normal matter (e.g. lead), the mean free path of a 1 MeV neutrino is ~4x1020 cm (400 light years). But in the collapsed core of a supernova, which is of nuclear matter density, the mean free path of a neutrino is only ≤ 1 km The neutrinos cannot freely escape – they are trapped, thermalize to a Fermi-Dirac energy distribution, and gradually diffuse out the surface.

7. Because they interact less strongly with matter, the νμ and ντ are more penetrating, and come from regions closer to the core, and therefore have a hotter spectrum than do the νe. . If we can measure the temperature of the different flavours of neutrinos as a function of time, we could verify this picture of the basic physical processes of the core collapse

8. Measuring the neutrino temperature, in each neutrino flavour, as the neutron star cools down, would be the astrophysicist's dream! However The pristine picture is complicated by flavour changes. These are of three types: 1. vacuum neutrino oscillations 2. matter induced (MSW) neutrino oscillations 3. neutrino-neutrino interactions

9. 3. Neutrino induced oscillations In the collapsed core, the neutrino density is so large that the neutrinos exert a significant potential on each other, and a MSW-like flavour transition due to ν-ν interactions (rather than ν-e interactions) can occur. This leads to spectacular flavour swapping and spectral splitting for the νe, but only if we have inverted mass hierarchy and if θ13 ≠ 0. Fogli et al. hep-ph/07071998 NEW!

10. Initial flux at r~10 km from E. Lisi, TAUP'07, Sendai 2007 Final flux at r~200 km after collective ν-ν interactions most dramatic for νe anti-neutrinos undergo flavor swap high energy neutrinos undergo flavor swap, but low energy neutrinos don't (spectral split)‏

11. Comparison of rate in HALO (νe) with prediction based on measured anti-νe spectrum in SNO+ or Super-K could be a signature for flavour-swapping. Very New ! Without flavour swapping, νe spectrum is softer than anti-νe, so using measured anti-νe as a proxy for νe overpredicts νe interaction rate in HALO

12. With flavour-swapping, the high energy νe and anti-νe spectra are identical. Using the measured anti-νe spectrum from SNO+ as a proxy for νe yields a good prediction of the rate in HALO. A robust signature of flavour-swapping independent of supernova size, temperature, distance.

13. Water Cerenkov and Liquid Scintillator mostly sensitive to ‗ νe + p → e+ + n Pb mostly sensitive to νe νe + n (nuclear) → e - + p because the large neutron excess Pauli blocks the anti-νe + p reaction Pb

14. Why observe supernova neutrinos? For the astrophysicist: - early warning of a SN for optical observations - observe signals directly from the core collapse - observe formation of a Black Hole - measure effective temperature of matter at different stages, as the proto-neutron star forms and cools For the particle physicist: - observe ν's from the only situation in the universe where ν's are trapped and thermalize - observe ν-ν interactions and collective behaviour of a large density of neutrinos—not possible elsewhere! - resolve normal versus inverted ν mass hierarchy—even a crude measurement of νe energy can do this if θ13≠0. - a Pb detector offers unique sensitivity to the interesting νe channel

16. Design Overview Areas of progress Funding Physics motivation (S. Yen) Active Personnel Preparation for moving Pb Mechanical studies Simulation work Summary budget and timetable HALO - a Helium and Lead ObservatoryProgress Report

17. Philosophy - to produce a Very low cost Low maintenance Low impact in terms of lab resources (space) Long-term, high livetime dedicated supernova detector HALO - Design Overview “Helium” – because of the availability of the 3He neutron detectors from SNO + “Lead” – because of high -Pb cross-sections, low n-capture cross-sections, sensitivity to e (dominantly) and x complementing water Cerenkov and liquid scintillator detectors

18. Lead Array 32 three meter long columns of annular Lead blocks 76 tonnes total lead mass (864 blocks) Neutron detectors Four 3 meter 3He detectors per column 384 meters total length Moderator 250mm Schedule 40 PP tubing Reflector 20 cm thick graphite blocks HALO-I - Design Overview

19. In 76 tonnes of lead for a SN @ 10kpc†, Assuming FD distribution around T=8 MeV for νμ’s, ντ’s. 65 neutrons through νe charged current channels 29 single neutrons 18 double neutrons (36 total) 20 neutrons through νx neutral current channels 8 single neutrons 6 double neutrons (12 total) ~ 85 neutrons liberated; ie. 1.1 n/tonne HALO - SN neutrino signal – Phase 1 †- Engel, McLaughlin, Volpe, Phys. Rev. D 67, 013005 (2003)

20. Funding Two years support from NSERC ($50K + $40K) necessitates a reduced scope  budget / timetable at end of talk Active Personnel C. Virtue (50%) S. Yen (25%) T. Shantz (100%) HALO MSc student – HALO design / construction S. Korte (10%) SNO+ MSc student – SN simulation J. Farine (10% **) Backgrounds and Calibration F. Duncan (10% **) A. Habig (10% **) Slow Controls ** soon to be harnessed, declared interests Areas of Progress

21. Preparation for moving Pb underground – inspection August 2008 Areas of Progress

22. Presence of lead carbonate (white powder) on many blocks Lead Blocks in Storage

23. Re-affirms need to paint blocks to halt deteriorization and to immobilize residual lead carbonate Paint Selection Criteria: great adhesion due to the handling requirements ability to bond on surfaces with abrasion resistant thin layers of lead carbonate Short curing time Minimal paint-paint welding together in stacked geometry long-lasting tough finish; a paint that physically deteriorates in the SNOLAB clean environment is to be avoided minimal U and Th content of paint;  we would assay prior to application; a clear coat without pigments likely avoids these concerns Paint Selection – Taylor Shantz

24. Following discussions with Industrial Hygenists at SLAC and PPPL, and EXO engineers, seven candidate paints were considered and three selected for standardized testing ASTM D 3359-08 – “Measuring Adhesion by Tape Test” is currently being used to compare the adhesion of the three candidate paints We are also assessing the paint to paint welding issue in the same tests Paint Selection

25. Select an appropriate paint Complete design of lifting jig (Oleg Li) and fabricate Finish developing the production painting plan Labour intensive / costly (handling ~900 88kg pieces) Requires lead handling precautions / procedures Will collect statistics on block dimensions during handling for painting input into lead array structural support Short term Paint plan

26. Options considered Mechanical Studies Default stacking Oleg Li Narrow Stacking On-edge stacking Vertical Stacking

27. Preliminary Stress analysis (1200 lbs) Stress, Deformation, Safety Factor Mechanical Studies Safety Factor (Min = 4.10)

28. Long-term creep tests Mechanical Studies 1 tonne load

29. program is to measure creep rate as function of load and then leave under maximum load as a long term test hope is to use creep data to “calibrate” a structural mechanics simulation package modelling the compression test geometry and then to model long term creep in real HALO geometry still considering whether an accelerated test to rupture in a 5 tonne press would give useful information at lower creep rates Characterization of Creep in Lead Tertiary Creep Secondary Creep Primary Creep Generic Creep-Rupture curve with exaggerated times to properly display the three stages.

30. GEANT code that follows neutrons produced uniformly in volume of lead, with initial energies selected from expected SN -induced n energy distribution exists / was used to optimize HALO design has been previously reported at other workshops this code is not well-suited to physics sensitivity studies that we would like to perform, so Stephen is adding HALO specific cross-sections to SNGEN (J. Heise) he will also add the spectral splitting and flavour swapping phenomenology to permit such physics sensitivity studies SNGEN will be the physics generator that passes particle lists to the GEANT code to complete the simulation. Simulation Work – Stephen Korte

31. Budget

32. savings achieved by reducing / deferring # of electronics channels (daisy-chaining) deferring graphite reflector or using water Stan Yen’s travel supported by TRIUMF outside of grant short-fall is of order $60K to complete detector we will submit a request for SNOLAB infrastructure support (cranes, lifting jigs, shielding, assembly labour, etc. for discussion) a further NSERC grant will likely be required to complete the detector Budget

33. “First Pass” ScheduleHALO Construction