Alan Chodos - Ghost Particle: In Search of the Elusive and Mysterious Neutrino

Alan Chodos and James Riordon

Foreword by Don Lincoln

The MIT Press

Cambridge, Massachusetts | London, England

2023 Massachusetts Institute of Technology

All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher.

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Library of Congress Cataloging-in-Publication Data

Names: Chodos, Alan, author. | Riordon, James R., author.

Title: Ghost particle : in search of the elusive and mysterious neutrino / Alan Chodos and James Riordon ; foreword by Don Lincoln

Description: Cambridge, Massachusetts : The MIT Press, [2023] | Includes bibliographical references and index.

Identifiers: LCCN 2022017646 (print) | LCCN 2022017647 (ebook) | ISBN 9780262047876 (hardcover) | ISBN 9780262373555 (epub) | ISBN 9780262373562 (pdf)

Subjects: LCSH: Neutrinos. | Neutrino astrophysics.

Classification: LCC QC793.5.N42 C45 2023 (print) | LCC QC793.5.N42 (ebook) | DDC 539.7/215dc23/eng20220927

LC record available at https://lccn.loc.gov/2022017646

LC ebook record available at https://lccn.loc.gov/2022017647

10987654321

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To Louie and Abraham, in hope for the future.A.C.

In memory of grandfather Clyde Lorrain Cowan Jr. With love for Mom, J.P., M.M., N.J., and little A.J.J.R.

Don Lincoln

I have something very important to tell you.

Now, I dont want you to be alarmed, but you are under a constant barrage by an insidious form of highly penetrating radiation. A powerful and uncontrolled nuclear reactor, generating an alarming 400 trillion trillion (4 1026) watts of power, is spewing these subatomic particles in every direction and they are sleeting through you at the staggering rate of 500 trillion (5 1014) every single second.

Id tell you to seek shelter, but this form of exotic radiation is implacable; it can pass through the entire Earth with ease. You can run, but you cannot hide from this steady and relentless assault. After all, if the radiation can pass through the Earth, there is no way to shield yourself.

Frightened? Thats understandable. What youve read sounds frightening. But you shouldnt be. The form of radiation Im talking about is the benign neutrino, emitted when two protons in the Sun fuse together, ensuring among other things that your day at the beach will be pleasant. Despite the neutrinos nuclear origin, they pose no danger at all. And you already kind of know that. If neutrinos pass through the Earth essentially never interacting, they certainly can pass through you. In fact, of the approximately trillion trillion (1024) neutrinos that pass through you during a 70-year lifetime, perhaps a single one will interact in your body. It is for this reason that they are often called the ghosts of the subatomic world.

Because the neutrino interacts so little with ordinary matter, you should be forgiven if you asked yourself why you should be interested in it, but that would be a hasty question. In fact, the neutrino is one of the most fascinating of the denizens of the subatomic world. It has surprised researchers again and again, and it remains one of the least understood, with many outstanding questions.

Neutrinos were postulated in 1930, as a solution to a pressing mystery at the time. A form of radiation, called beta radiation, didnt seem to make sense. It seemed that energy was disappearing in the nuclear decay and that would have upended one of the cornerstone laws of physicsthe law of conservation of energy. The neutrino was proposed to be lightperhaps masslessand to interact very weaklyweaker than any other subatomic particle.

The weakness with which neutrinos interact with matter means they are very difficult to detect; indeed, it took a quarter century and the taming of nuclear power for scientists to devise a clever enough method to produce and detect them. However, the validation of the existence of neutrinos was just the beginning. Just a year or two after neutrinos were observed, another team of researchers discovered that they were unique in the subatomic realm. While all denizens of the microcosm act as if they spin like a top, neutrinos and their antimatter counterparts were discovered to spin differently. It seems that neutrino interactions can distinguish between matter and antimatter.

And the surprises kept coming. A few years later, scientists found that there was not a single kind of neutrino but rather two, followed by the discovery of a third variant a quarter century later. The next puzzle was that measurements of the neutrinos emitted by the sun came up short, leading researchers to wonder if perhaps we didnt understand how the sun burned. Another option was that the three distinct types of neutrinos could morph into one another in a dizzying form of subatomic switcheroo, called neutrino oscillation. Neutrino oscillation was a crazy idea, until it was shown to be true near the start of the twenty-first century.

Even now, neutrinos have not revealed all of their secrets. While neutrino oscillation proved that neutrinos have a very small mass, scientists still dont know what the mass of a neutrino is. Indeedand this is a true weirdnessthe three types of neutrinos dont have a distinct and single mass, but rather a mix of three different values. This behavior is another property unique to neutrinos. Although researchers know something about the difference between the three different mass values, the absolute number still eludes us.

While scientists found that nuclear interactions involving neutrinos seemed to treat matter and antimatter neutrinos differently, the question of whether neutrinos and antimatter neutrinos are different or the same is still an open question. And researchers are building new facilities to study whether neutrinos and antimatter neutrinos oscillate in the same way or differently. If they differ, neutrinos may prove to be the reason why all of the matter of the universe exists. Its truly an exciting time to be studying neutrinos.

To be up to date in the field of particle physics means knowing about the past and future of neutrino research, and thats why Ghost Particle by Alan Chodos and James Riordon is such a timely and fascinating book. They delve deeply into the history of neutrino research, telling a series of gripping tales of scientific investigation. Chodos and Riordon tell of the letter that started it all. They regale us with plans to use an atomic bomb to search for neutrinos, followed by the less dramatic, but no less exciting, effort by researchers to use classified nuclear reactors to finish the job. They tell of Cold War defections and a missing-person case worthy of the best mystery writer. They divulge the details of an experiment searching for a handful of atoms of argon in an Olympic-size swimming pool of dry-cleaning fluid. And they tell of a future experiment, which involves firing a beam of neutrinos through the Earth to a detector about 1,300 kilometers (800 miles) awaya device built a mile underground in an abandoned gold mine and so huge that it will require the excavation of nearly a million tons of rock to build.