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Birth of the Large Scale Imaging Water Cherenkov Detector

This talk discusses the birth and development of the Large Scale Imaging Water Cherenkov Detector, a groundbreaking experiment in physics. It covers the concept, detector characteristics, background rejection methods, and the formation of the IMB Collaboration.

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Birth of the Large Scale Imaging Water Cherenkov Detector

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  1. Birth of the Large Scale Imaging Water Cherenkov Detector Bruce Cortez Sulak Festschrift Boston University Oct 22, 2005 Sulak Festschrift Oct 21, 2005

  2. Agenda and Sulak Timeline Focus of this talk Michigan Location: Harvard Construction Data IMB Collab. Proposal Grad Students B. Cortez G.W. Foster J. Strait W. Kozaneck M.Levi S. Seidel D. Casper Jan ‘78 Jan ‘79 Jan ‘80 Jan ‘81 Jan ’82 Jan ‘83 Sulak Festschrift Oct 21, 2005

  3. The Beginning • September 1978 • Larry’s mission • A. Salaam’s statement that proton decay in the most important experiment in physics • Grand Unified Theories were now predicting lifetimes of < 1031 years. • Key characteristics • Large (lifetimes up to 1033 years) • Underground for background rejection • Sensitive to large numbers of decay modes • Early October • Internal memo on proposed Proton Decay detector • Scale up liquid scintillator detector to 100 T • Visit to NY mine • Quickly abandoned effort due to limited lifetime improvement Sulak Festschrift Oct 21, 2005

  4. October 1978 – The Concept • Visit to U. Chicago / FNAL • Bruce Brown water Cherenkov calorimeter prototype detector • DUMAND idea to use water Cherenkov detector technique in massive undersea volume array • Larry realized we can use this concept and scale to massive detector with track detection and particle identification • 2 month activity to determine • Detector characteristics • Signal • Background rejection • Presentation by Larry at Madison Seminar on Proton Stability December 8, 1978 – the blueprint for proton decay detector Sulak Festschrift Oct 21, 2005

  5. December 8, 1978 Paper • Totally active, underground water Cherenkov detector • Charged particles detected by Cherenkov light • Surface array of photomultiplier tubes (PMT) • 1033 year limit achievable Sulak Festschrift Oct 21, 2005

  6. Detector Overview • Cubic – 20 m on each side • Fiducial volume of 14x14x14 m3 • 1.5 x 1033 nucleons (2.5KT) • Surface array of 5” diameter hemisperical photomultiplier tubes (PMT) • Spacing – 0.7m between PMT • Total 2400 PMT • Energy threshold 30 Mev • Muon decay detection eff. 50% Sulak Festschrift Oct 21, 2005

  7. Cherenkov Geometry Sulak Festschrift Oct 21, 2005

  8. Dec ‘78Track Geometry • Initial simulation showing p → e+π0 event with positron and two photons from π0 decay • (Most showering effects are suppressed) • Vertex reconstruction and track angle reconstruction requires PMT timing resolution of a few ns. Sulak Festschrift Oct 21, 2005

  9. How much light? • Requires transparency ( λ > 30m) at the 300-500 nm wavelengths • High efficiency photocathode material (>50%) • Single photoelectron detection critical • 1 Gev signal (e.g. p → e+π0) requires minimum 200 photoelectrons, for sufficient energy resolution, background rejection, as well as ability to detect decay modes with less light • Phototube coverage of surface ~2%. Sulak Festschrift Oct 21, 2005

  10. Dec ‘78: Background Rejection • Main background is atmospheric neutrinos • Estimate background rejection of factor of 2000 for p → e+π0 • Requires reconstruction of vertex • Requires separation of energy into two hemispheres for each particle • Requires determining angle between two tracks • Requires ~10% energy resolution on each particle • Neutrinos could be used for neutrino oscillations study down to 10-3 ev Sulak Festschrift Oct 21, 2005

  11. Formation of IMB Collaboration • January 1979 letter of intent to William Wallenmeyer, DOE to present proposal • Irvine, Michigan, Brookhaven • Co-spokesman • Fred Reines (Irvine) • Jack Vandervelde (Michigan) Sulak Festschrift Oct 21, 2005

  12. IMB Collaboration ( April 1980) Note: Many members missing from picture Sulak Festschrift Oct 21, 2005

  13. IMB 1987 Sulak Festschrift Oct 21, 2005

  14. IMB Collaboration - Today Sulak Festschrift Oct 21, 2005

  15. Proposal Presented to DOE: 6/79 Sulak Festschrift Oct 21, 2005

  16. Feasibility of the original design was demonstrated by the IMB collaboration in 1H79 • Site selection : Morton Salt Mine outside Cleveland • Realistic plans for construction of underground laboratory and excavation of large cavity • Demonstration of water purification (reverse osmosis system) • Supports > 30 m transparency • Can be scaled to the necessary size • PMT studies – photcathode efficiency, pulse size, timing resolution, dark noise, etc – on specific EMI 5” and 8” PMT • Low cost electronics proof of concept • Waterproof PMT housings • Inclusion of more physical effects (nuclear effects, electromagnetic showers) in simulations • Event reconstruction software shown to be better than smearing due to above physical effects Sulak Festschrift Oct 21, 2005

  17. What Changed from December • Actually – very little – proposed experiment design very similar to original paper • Small difference: • More detailed light collection estimates plus budgetary constraints increased PMT spacing to 1.2m (with 8” PMT) or 1.0m with 5” PMT • Closer to 1% photocathode coverage of surface Sulak Festschrift Oct 21, 2005

  18. Competing Proposal - HPW • Harvard Purdue Wisconsin • Water Cherenkov detector with PMT distributed throughout volume with mirrors at edges to increase light collection • We had rejected this idea • Mirrors will confuse the track/particle detection • Even if the later reflected light can be eliminated, the prompt light has fewer PMTs listed by ~ factor of 2 making track reconstruction difficult Sulak Festschrift Oct 21, 2005

  19. Surface array has twice as many lit PMT as volume array (ignoring mirrors • More PMTs in surface array means better track reconstruction and better background rejection • Reflected light in volume array increases the total amount of light collected, but only confuses the track reconstruction ability Sulak Festschrift Oct 21, 2005

  20. DOE Decision • DOE picked IMB as the primary detector • IMB given sufficient funding to go ahead with construction program • HPW given some funding to continue • “Underground physics” (non-accelerator) given boost by DOE Sulak Festschrift Oct 21, 2005

  21. Kamioka Early Feb 79 Proposal • Initial concept for water Cherenkov detector • Slab design – thin veto on top, followed by iron slab followed by larger detector • Much higher photocathode coverage proposed (> 10%) • Eventual cylindrical design, based on 20” hemispherical PMT. • Timing electronics not in original detector Sulak Festschrift Oct 21, 2005

  22. Kamioka Feb ‘79 • Ref to Sulak paper • Fewer PMTs as proposed by Sulak makes Kamioka proposal more practical Sulak Festschrift Oct 21, 2005

  23. 1979-1982: IMB Detector • Detector excavation constraints - slightly non-cubical detector • 23m x 17m x 18m • 5” PMT chosen: 2048 total • 1 meter spacing • Fall 1981 : Initial fill • Aborted due to leaks due to stretching beyond elastic limit in corners • Summer 1982: Final fill • Lightweight concrete poured into corners behind liner as fill occurred to reduce/eliminate stretching • First good data Aug 1982 Sulak Festschrift Oct 21, 2005

  24. First IMB Results – 6.5x1031 year limit on p → e+π0 • Additional data / analysis extended this limit by about a factor of 5, and also set limits between 1031 and 1032 for many decay modes • The Dec ‘78 assertion by Larry that the detector would detect proton decay events, and reject neutrino background (for e+π0 ) to a factor of 2000 was nearly borne out (including IMB III upgrade) Sulak Festschrift Oct 21, 2005

  25. Mock Up in U. Mich (“Disco Room”) Larry with approx 100 5” PMT Sulak Festschrift Oct 21, 2005

  26. Fully Assembled and filled 2048 PMT with supports Sulak Festschrift Oct 21, 2005

  27. Early (Aug ‘82) 2-track event - Classified as neutrino event with ~130° opening angle Sulak Festschrift Oct 21, 2005

  28. Epilogue I (1986-1988) • Limitations of first generation water Cherenkov detectors became clear • Kamioka II upgrade (1986) (with U.Penn) included timing electronics and led to solar neutrino measurements • IMB III upgrade increased light collection by factor of ~4 with 8” PMT and waveshifter plates • Both experiments detected the neutrinos from SN1987a - Neutrino Astronomy Sulak Festschrift Oct 21, 2005

  29. Epilogue 2 (1995-present) • Based on success of IMB/Kamioka, consensus established to push the water cherenkov technology to the limit to get best physics results on proton decay, solar neutrinos, neutrino oscillations, etc • Joint US / Japanese funding required • SuperK experiment had size (30KT), photocathode coverage (40%), fiducial volume, timing resolution, and depth sufficient for physics objectives • Joint US-Japanese effort that included members from both first generation experiments • Positive neutrino oscillation signal reported for atmospheric neutrinos • SNO experiment used water Cherenkov techniques as well, but with D2O to allow detection of neutral current interactions for more solar model independent measurement of neutrino oscillation from solar neutrino • Nobel prize 2002 awarded to M. Koshiba of Kamioka experiment for “pioneering … detection of cosmic neutrinos” Sulak Festschrift Oct 21, 2005

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