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HALO - a Helium and Lead Observatory

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 - a Helium and Lead Observatory. A “SN detector of opportunity” / An evolution of

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HALO - a Helium and Lead Observatory

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  1. 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 - a Helium and Lead Observatory A “SN detector of opportunity” / An evolution of LAND – the Lead Astronomical Neutrino Dectector, C.K. Hargrove et al., Astropart. Phys. 5 183, 1996.

  2. Galactic supernova are rare / little known Unique opportunity for particle physics, astronomers, SN dynamics SNEWS Lead; high  x-sect., low n cap. x-sect. Motivation / Physics

  3. Neutrinos from supernovae • Neutrinos leaving star are expected to be in a Fermi-Dirac distribution according to escape depth: • Oscillations redistribute neutrino temperatures • SK, Kamland are primarily sensitive to νe • HALO’s sensitivity to νe and NC valuable

  4. Contribute to data recorded from next galactic supernova Confirmation of presence of νe signal Handle on νtemperatures and cooling rate through 1n / 2n ratio Maximize scientific opportunity through participation in SNEWS Physics Objectives

  5. Inter- experiment collaboration to disseminate the news of a galactic SN Coincidence between detectors required in 10 second window SNEWS is “live” – a “GOLD” coincidence would be sent to subscribers; “Individual” non-coincident alerts also possible now > 250 subscribers to e-mail distribution list > 2000 amateur subscribers through Sky & Telescope GCN (Gamma-ray burst Coordinates Network) HALO could bridge a gap between SNO and SNO+ SNEWS – Supernova Early Warning System

  6. Initially use materials on hand 80 tonnes of Pb from decommissioned Deep River Cosmic-ray station (high  x-sect., low n-capture x-sect.) ~285 m 3He proportional counter neutron detectors (NCDs) plus DAQ from SNO Use lead in its current geometry HALO - Phase 1 (80 tonne detector) 88 kg / block 865 blocks

  7. In 80 tonnes of lead for a SN @ 10kpc†, Assuming FD distribution around T=8 MeV for νμ’s, ντ’s. 68 neutrons through νe charged current channels 30 single neutrons 19 double neutrons (38 total) 21 neutrons through νx neutral current channels 9 single neutrons 6 double neutrons (12 total) ~ 89 neutrons liberated; ie. 1.1 n/tonne HALO - SN neutrino signal – Phase 1 †- Engel, McLaughlin, Volpe, Phys. Rev. D 67, 013005 (2003)

  8. HALO - using SNO’s NCD 3He counters NCD removal from SNO occurred in early 2007. Close to 700 m of low background 3He counters are stored underground awaiting HALO deployment. Space in SNOLAB available early 2008.

  9. NCD Energy Spectrum Energy spectrum from one NCD string with an AmBe neutron source. 764-keV peak 191-keV shoulder from proton going into the wall

  10. Other Backgrounds Internal alphas in n-region 3.5x10-4 Hz*Length/200m Cosmic ray induced neutrons 1.3x10-5(ε) Hz Multi-neutron bursts thermalize in ~200μs Gamma Backgrounds < 1x10-5 Hz ie. small for burst detection, but still a need for more detailed simulation of backgrounds with emphasis on external neutrons

  11. Monte Carlo Studies – Phase 1 Choice of moderator D2O versus polypropylene? Twice the volume required; O($700K) in Phase 1 No significant gain in neutron capture efficiency dominated by neutron leakage not competition for neutron capture Stick with plastics! Paint / epoxy coating of lead blocks as moderator? Distribution of moderator various options simulated best efficiency and least material for moderator immediately surrounding 3He counters 1-2 mm of coating on lead blocks doesn’t hurt capture efficiency but doesn’t replace need for moderator

  12. Monte Carlo Studies – Phase 1 Optimize for capture efficiency as function of moderator thickness 42% capture efficiency for 6mm polypropylene moderator Done in a fiducial volume to avoid confusion from edge-effects and to understand maximum efficiency. For single NCD per column. Peaks at 57% for 3 or 4 NCDs Per column.

  13. Monte Carlo Studies – Phase 1 However, with only 80 T the volume-averaged efficiency falls to 17.5% (60% loss relative to “fiducial volume” one) •  Add reflector • 20 cm water adequate • recover to 25% capture efficiency (volume averaged); 40% loss • reduces external neutron background • from 0.1Hz from thermal flux to 0.002Hz • from ~ Hz to 0.04 Hz for fast flux • coverage on 5 sides versus 6 has a < 1% effect on efficiency

  14. Monte Carlo Studies – Phase 1

  15. For the phase 1 detector nearly half of the neutrons escape detection by exiting the detector New thoughts (Stan Yen / TRIUMF) are to boost the detected SN signal by replacing the water reflector with Gd-loaded scintillator Several options being actively investigated Needs to be incorporated into MC studies Early days… Recovering some of the leaked neutrons…

  16. Optimize for Full ~700m of 3He counters and possibly 130 m of 10BF3 counters Increased volume of lead Allow for modification of block geometry HALO – Phase 2 (full NCD array)

  17. HALO - Monte Carlo Studies F. Fleurot

  18. Monte Carlo Studies • Phase 2 Interpretation - More is better; but what is optimum? • # of 2n events detected varies mass * capture efficiency 2 • Optimizing on m*ε2 with fiducial volume efficiency suggests optimum • near 1.5kT, but • - insufficient points done • - needs further MC work to define • Good news • – 1 kT of Pb occupies a cube only 4.5 m on a side; O($1M material) • Detailed costing and design for Phase 2 still to come …

  19. Further Work Continue with refinement of MC work SN modeling; sensitivity of Phase 2 to additional physics update Pb cross-sections, neutron energy distributions Modeling of backgrounds Addition of Gd-loaded scintillator blanket finalize design of Phase 2 detector Collaboration building Engineering work for Phase 1 installation Proceed with Full Proposal, Technical Review, and funding application for Phase 1 and R&D for Phase II

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