Slide 1

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

Slide 2

Sulak Festschrift Oct 21, 20052 Agenda and Sulak Timeline Jan 78 Jan 79Jan 80Jan 81Jan 82Jan 83 Grad Students J. Strait W. Kozaneck M.Levi B. Cortez G.W. Foster Location:Harvard Michigan IMB Collab. Proposal ConstructionData Focus of this talk S. Seidel D. Casper

Slide 3

Sulak Festschrift Oct 21, 20053 The Beginning September 1978 Larrys mission A. Salaams statement that proton decay in the most important experiment in physics Grand Unified Theories were now predicting lifetimes of < 10 31 years. Key characteristics Large (lifetimes up to 10 33 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

Slide 4

Sulak Festschrift Oct 21, 20054 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

Slide 5

Sulak Festschrift Oct 21, 20055 December 8, 1978 Paper Totally active, underground water Cherenkov detector Charged particles detected by Cherenkov light Surface array of photomultiplier tubes (PMT) 10 33 year limit achievable

Slide 6

Sulak Festschrift Oct 21, 20056 Detector Overview Cubic 20 m on each side Fiducial volume of 14x14x14 m 3 1.5 x 10 33 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%

Slide 7

Sulak Festschrift Oct 21, 20057 Cherenkov Geometry

Slide 8

Sulak Festschrift Oct 21, 20058 Dec 78 Track Geometry Initial simulation showing p e+ 0 event with positron and two photons from 0 decay (Most showering effects are suppressed) Vertex reconstruction and track angle reconstruction requires PMT timing resolution of a few ns.

Slide 9

Sulak Festschrift Oct 21, 20059 How much light? Requires transparency ( > 30m) at the 300-500 nm wavelengths High efficiency photocathode material (>50%) Single photoelectron detection critical 1 Gev signal (e.g. p e + 0 ) 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%.

Slide 10

Sulak Festschrift Oct 21, 200510 Dec 78: Background Rejection Main background is atmospheric neutrinos Estimate background rejection of factor of 2000 for p e + 0 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

Slide 11

Sulak Festschrift Oct 21, 200511 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)

Slide 12

Sulak Festschrift Oct 21, 200512 IMB Collaboration ( April 1980) Note: Many members missing from picture

Slide 13

Sulak Festschrift Oct 21, 200513 IMB 1987

Slide 14

Sulak Festschrift Oct 21, 200514 IMB Collaboration - Today

Slide 15

Sulak Festschrift Oct 21, 200515 Proposal Presented to DOE: 6/79

Slide 16

Sulak Festschrift Oct 21, 200516 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

Slide 17

Sulak Festschrift Oct 21, 200517 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

Slide 18

Sulak Festschrift Oct 21, 200518 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

Slide 19

Sulak Festschrift Oct 21, 200519 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

Slide 20

Sulak Festschrift Oct 21, 200520 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

Slide 21

Sulak Festschrift Oct 21, 200521 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

Slide 22

Sulak Festschrift Oct 21, 200522 Kamioka Feb 79 Ref to Sulak paper Fewer PMTs as proposed by Sulak makes Kamioka proposal more practical

Slide 23

Sulak Festschrift Oct 21, 200523 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

Slide 24

Sulak Festschrift Oct 21, 200524 First IMB Results 6.5x10 31 year limit on p e + 0 Additional data / analysis extended this limit by about a factor of 5, and also set limits between 10 31 and 10 32 for many decay modes The Dec 78 assertion by Larry that the detector would detect proton decay events, and reject neutrino background (for e + 0 ) to a factor of 2000 was nearly borne out (including IMB III upgrade)

Slide 25

Sulak Festschrift Oct 21, 200525 Mock Up in U. Mich (Disco Room) Larry with approx 100 5 PMT

Slide 26

Sulak Festschrift Oct 21, 200526 Fully Assembled and filled 2048 PMT with supports

Slide 27

Sulak Festschrift Oct 21, 200527 Early (Aug 82) 2-track event - Classified as neutrino event with ~130 opening angle

Slide 28

Sulak Festschrift Oct 21, 200528 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

Slide 29

Sulak Festschrift Oct 21, 200529 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 D 2 O 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