Neutrino Facilities Assessment Committee

Board on Physics and Astronomy

Division on Engineering and Physical Sciences

THE NATIONAL ACADEMIES PRESSWashington, D.C.www.nap.edu

THE NATIONAL ACADEMIES PRESS • 500 Fifth Street, N.W. • Washington, DC 20001

NOTICE: The project that is the subject of this report was approved by the Governing Board of theNational Research Council, whose members are drawn from the councils of the National Academy ofSciences, the National Academy of Engineering, and the Institute of Medicine. The members of thecommittee responsible for the report were chosen for their special competences and with regard forappropriate balance.

This project was supported by Grant No. PHY-0223181 between the National Academy of Sciencesand the National Science Foundation. Any opinions, findings, conclusions or recommendationsexpressed in this publication are those of the author(s) and do not necessarily reflect the views of theorganizations or agencies that provided support for the project.

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Cover: The Super-Kamiokande Detector. Courtesy of the Kamioka Observatory, Institute for Cos-mic Ray Research (ICRR), University of Tokyo.

Copyright 2003 by the National Academy of Sciences. All rights reserved.

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EXECUTIVE SUMMARY 1

1 INTRODUCTION 7

2 SCIENCE OVERVIEW: NEUTRINOS AND BEYOND 9The Neutrino: From Backstage to Center Stage, 9Beyond Neutrinos, 15Special Opportunities, 18

3 SCIENCE POTENTIAL OF ICECUBE 22Introduction, 22The Sources of High-Energy Neutrinos, 25IceCube in an International Context, 31

4 SCIENCE POTENTIAL OF A DEEP UNDERGROUND 32LABORATORYNeutrino Properties, 33Dark Matter, 44Proton Decay, 47Neutrinos, Solar Energy, and the Formation of the Elements, 49

Contents

C O N T E N T Sxiv

Other Science at an Underground Laboratory, 52Underground Science in an International Context, 52

5 CONCLUSIONS 58IceCube, 59A New Deep Underground Laboratory, 61Redundancy and Complementarity, 63

APPENDIXESA Formation of the Committee 67B Charge to the Neutrino Facilities Assessment Committee 70C Biographies of Committee Members and Key NRC Staff 71D Meeting Agendas 79E Glossary and Acronyms 85

S C I E N C E O V E R V I E W : N E U T R I N O S A N D B E Y O N D 11

FIGURE 2.1.1 The Standard Model of particle physics describes the basic building blocks of theuniverse and the rules governing their interactions. This chart displays the basic quarks and leptonsthat make up matter and the four force-carrying boson particles. For each so-called family (columnsin the chart), there are two quarks (an up type and a down type) and two leptons (a neutrino and anassociated partner lepton). The neutrinos have been the most elusive part of the Standard Modelbecause of their minimalist character—they were posited to interact only very weakly, to be mass-less, and to be independent of one another. Recent experiments have shown that neutrinos do infact have mass, and that they can transform into one another. Figure courtesy of Paul Nienaber andAndrew Finn, BooNE Collaboration.

continues

N E U T R I N O S A N D B E Y O N D12

electron

neu

trino

pro

bab

ility

mu

on

neu

trino

pro

bab

ility

arrives atdetector asa mixtureof muon &electronneutrino

SIDEBAR 2.1 CONTINUED

FIGURE 2.1.2 As described in the text,neutrinos have been shown to oscillate—an observation that shows, in effect, thatthey have mass. Understanding neutrinooscillations requires a trip into the worldof quantum mechanics; this figure uses amusical analogy to represent the behaviorof a simplified model. Imagine only twoneutrinos that can oscillate into one an-other, and imagine representing each neu-trino as a musical pitch. Further assumethat only one pitch at a time can be de-tected. Let the muon-neutrino be repre-sented by a G-note and the electron-neu-trino by, say, a B-note. In the absence ofneutrino oscillations, one could assumethat a G-note originated as a G and wouldremain forever a G, and likewise for a B.However, with the possibility of neutrinooscillations, a muon-neutrino G-note can“de-tune” into a B-note as time passes,and vice versa. Since only one pitch at atime can be detected, the neutrino willsometimes “sound” like a G and some-times like a B; the rate of de-tuning is re-lated to the neutrino mixing parameters.The probability of observing the muon-neutrino as an electron-neutrino varies asa function of time (or distance if the neu-trino is traveling), as shown by the sinuso-idal curves alongside the scales. The de-tailed properties of neutrino oscillationsare important to understanding how theStandard Model particles interact and howgalaxies and the universe work. Figurecourtesy of Paul Nienaber and AndrewFinn, BooNE Collaboration.

S C I E N C E P O T E N T I A L O F A D E E P U N D E R G R O U N D L A B O R A T O R Y 39

FIGURE 4.3 Shown here isone depiction of a long-base-line neutrino oscillation exper-iment. The neutrino beam isproduced by focusing an in-tense beam of high-energyprotons on a proton-rich tar-get such as beryllium. Theparticle debris is cleaned andfocused by a powerful electro-magnetic system called a mag-netic horn. The resultingbeam consists of almost en-tirely pions, which will decayin flight into muons andmuon-neutrinos. A steel ab-sorber is used to stop the re-maining pions and newly bornmuons. In the long-baselineexperiment, the berm of earthin the figure is actually formedby Earth itself; a neutrinobeam would travel thousandsof kilometers before arriving atthe target, where the neutrinosare detected and identified bytheir interactions with the de-tector. Figure inspired by il-lustrations from Prof. PaulNienaber and undergraduateAndrew Finn, BooNE Collabo-ration.

Protonsynchrotron

Protons

Decayregion

NearDetector

800-1000 kmthrough Earth

Steel absorber

Magnetic“horn”

Berylliumtarget

Shielding tofilter out

undecayedpions

and left-overmuons

Focuses positive pions

Defocuses negative pions

Muonneutrino beam

Positive pioncan decay to…

Anti-muon Muonneutrino

FarDetector