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

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Sulak Festschrift Oct 21, 2005 1

Birth of the Large Scale Imaging Water Cherenkov Detector

Bruce CortezSulak FestschriftBoston University

Oct 22, 2005

Agenda and Sulak Timeline

Jan ‘78 Jan ‘79 Jan ‘80 Jan ‘81 Jan ’82 Jan ‘83

GradStudents

J. StraitW. KozaneckM.Levi

B. CortezG.W. Foster

Location: Harvard Michigan

IMB Collab. Proposal Construction Data

Focus of this talk

S. SeidelD. Casper

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

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

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

Detector Overview

Cubic – 20 m on each side Fiducial volume of 14x14x14

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%

Cherenkov Geometry

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.

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%.

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

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)

IMB Collaboration ( April 1980)

Note: Many members missing from picture

IMB 1987

IMB Collaboration - Today

Proposal Presented to DOE: 6/79

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

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

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

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

DOE Decision

DOE picked IMB as the primary detector IMB given sufficient funding to go ahead with

construction programHPW given some funding to continue

“Underground physics” (non-accelerator) given boost by DOE

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

Kamioka Feb ‘79

Ref to Sulak paperFewer PMTs as

proposed by Sulak makes Kamioka proposal more practical

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

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)

Mock Up in U. Mich (“Disco Room”)

Larry with approx 100 5” PMT

Fully Assembled and filled

2048 PMT with supports

Early (Aug ‘82) 2-track event - Classified as neutrino event with ~130° opening angle

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

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 1 Birth of the Large Scale Imaging Water Cherenkov Detector Bruce...

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