Neutrino Physics Kai Zuber IOP, Philadelphia, 2004. $125.00 (438 pp.). ISBN 0-7503-0750-1
In the past few years, neutrino physics has blossomed as a subfield of particle physics and astrophysics. Physicists now realize the role neutrinos play in astrophysics and cosmology, from the generation of the excess of matter over antimatter to the evolution of stars and the production of the heavy elements therein.
This blossoming has set the stage for Kai Zuber’s Neutrino Physics, a timely and nearly encyclopedic volume for the emerging subdiscipline. Zuber got his start in the field by studying double-beta decay and has broadened his activities to investigating accelerator energies and the highest-energy cosmic rays. Zuber exhibits an unusually wide range of understanding: The book’s topics range from the obligatory historical recap to a compact theoretical summary and discussions on direct mass searches, the double-beta decay industry, neutrino oscillation phenomenology, atmospheric neutrinos, solar neutrinos, neutrinos from supernovae, ultra high-energy neutrinos, and neutrinos in cosmology.
Neutrinos entered the spotlight in 1987 when researchers observed a great impulse of neutrinos originating from the collapse of a distant star 150 000 light years away in the Large Magellanic Clouds. The event resulted in a huge number of publications. My own computer search reveals 7464 journal articles, all from the observation of handfuls of neutrino interactions in underground detectors at the Kamioka Observatory in Japan, at observatories run by the Irvine-Michigan-Brookhaven (IMB) group in the US, and at the Baksan Observatory in Russia.
What was once a sleepy area of study has become the subject of national review committees and hot competition for new resources. Why all the fuss? For starters, neutrino physicists are still amazed at just being able to detect significant numbers of these ghostly particles. Seventy years ago, physicists were saying it would probably always be impossible to detect neutrinos. But in the mid-1950s, Frederick Reines and Clyde Cowan Jr did detect neutrinos from reactors. A number of accelerator experiments then followed, and, to almost everyone’s surprise, not one but two kinds of neutrinos were found, and later, in the mid-1970s, a third. Researchers at CERN and Fermilab soon found the peculiar neutral coupling of neutrinos that led to the electroweak theory, which unifies both the electromagnetic force and the weak nuclear force.
Beginning in the early 1980s, the IMB group, followed by the Kamioka group, found an unexpected ratio of muon neutrinos to electron neutrinos in the GeV-energy neutrino fluxes produced by cosmic rays penetrating the atmosphere. For at least a decade, physicists did not know the cause of the problem because there were several possible explanations. Researchers at Japan’s Super-Kamiokande detector started taking data in 1996. A year later, experimenters were able to claim evidence for muon-neutrino oscillations and hence nonzero neutrino mass.
Until the Super-Kamiokande results came out in 1998, most of my colleagues (in my informal poll) said that neutrinos had zero mass because there was no reason for them to have any. And almost all theoreticians, when asked, thought that if neutrinos oscillated, they only oscillated with small mixing. What the Super-Kamiokande detector shockingly revealed was that the mixing was not only present but as big as it could be between muon and (probably) tau neutrinos.
Since 2002, beautiful results from the Sudbury Neutrino Observatory (SNO) collaboration have settled the 30-year-old solar neutrino problem in favor of the solar modelers (who got it right) and the theory that electron neutrinos do indeed morph into other flavors. The conclusion was then reinforced by the results of the KamLAND collaboration in 2003, and those results were later updated in 2004. The presence of neutrino oscillations implies that neutrinos have mass, which in turn would force a modification of the 1970s standard model.
But in addition to the largely accepted results obtained by the KamLAND group, researchers also encountered a conundrum. The results from the Liquid Scintillator Neutrino Detector (LSND), which began gathering data in the early 1990s in Los Alamos, New Mexico, point toward a low-level production of neutrinos not compatible with three CPT (charge conjugation, parity, and time reversal) conserving flavors of neutrinos. The LSND results, which should not be easily dismissed, have physicists worried that some important crack remains in their picture of neutrino oscillations.
A simple three-neutrino mixing scheme describes most neutrino interactions. Yet plenty of room exists for other possibilities. It could be that the model requires some admixture of sterile neutrinos or CP violations. Perhaps neutrinos are not Dirac particles but Majorana particles, which are their own antiparticles. And who knows, maybe the CPT symmetry will no longer be etched in stone if the LSND results are confirmed by the MiniBooNE experiment.
I find Zuber’s explanations of these recent developments compact, well written, and up to date. I have consulted the book in the past several months to rapidly inform students about the neutrino business, and they, after looking through it themselves, have found the book comprehensive and understandable. The only text comparable to Zuber’s that I know of is Current Aspects of Neutrino Physics (Springer-Verlag, 2001), edited by David O. Caldwell; however, Caldwell’s book is more for experts and not as smoothly didactic as Zuber’s.
Zuber establishes much of the initial discovery of the neutrino, weak interactions, and number of flavors in chapter 1, and throughout the text he continues to cover some historical background. In chapter 8, his explanation of the results from the LSND is brief and to the point. The MiniBooNE experiment is hardly mentioned because it was just getting started while he was writing his book. With results expected this summer, Zuber’s text will unavoidably need updating.
Zuber does a fine job presenting the above exciting revelations, and much more, in detail that is accessible to graduate students; he gives the facts and lets the reader make the grand conclusions. Yet despite the wealth of information in Neutrino Physics, I must complain about the poor quality of some of the figures, a small fraction of which are unreadable, a failing on the part of the editors. The book has relatively few typos, none of which is important, and the coverage is reasonably uniform if perhaps tilted a bit toward Zuber’s first interest in double-beta decay. Nevertheless, if you want to know what is going on with neutrinos, buy this book!