This paper is a review of the present status of neutrino mass physics, which grew out of an APS sponsored study of neutrinos in 2004. After a discussion of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, it summarizes what can be learned about neutrino interactions as well as the nature of new physics beyond the Standard Model from the various proposed neutrino experiments. The intriguing possibility that neutrino mass physics may be at the heart of our understanding of a long standing puzzle of cosmology, i.e. the origin of matter?antimatter asymmetry is also discussed.

/pdf/theory-of-neutrinos-a-white-paper-4bwov15tmt.pdf

Theory of neutrinos: a white paper

The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Super-beams, Laboratori Nazionali di Frascati, Rome, 21–26 June 2005) and NuFact06 (Ivine, CA, 24–30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second-generation super-beam experiments, beta-beam facilities and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report.

/pdf/physics-at-a-future-neutrino-factory-and-super-beam-facility-2yrdk225mo.pdf

Physics at a future Neutrino Factory and super-beam facility

Upper limits for charm hadron decays to two muons plus hadrons

New limits on effective Majorana neutrino masses from rare kaon decays

It is certainly fair to say that understanding the nature of the neutrino is one of the most critical issues in particle physics, nowadays. In fact, a lot of experimental and theoretical work is being devoted to this problem. To study the properties of neutrinos there are essentially two different approaches. The first one makes use of neutrino (antineutrino) beams from high-energy accelerators and nuclear reactors, or takes advantage of the scarce neutrinos provided to us by nature (solar or cosmic neutrinos). The other approach consists in searching for processes where neutrinos do not appear: either they annihilate each other or they are replaced by some (more or less exotic) particle. For instance, neutrinoless double beta decay was proposed a long time ago as a probe of the Majorana nature of the neutrino. We now recognize the utmost importance of neutrinoless double beta decay in the context of the modern gauge theories and the quest for physics beyond the Standard Model: some fundamental issues are the problem of neutrino masses, the presence of right-handed charged weak currents, the existence of Goldstone bosons (majorons). Another well-known example is the neutrinoless process μ → eγ, which historically has led to the “two neutrino hypothesis”, and is nowadays considered as one of the most powerful probes to search for physics beyond the Standard Model, as we shall see below.

http://iopscience.iop.org/article/10.1088/0034-4885/58/1/002/pdf

Searches for lepton-flavour violation

Data taken by the Mark II detector at the SLAC {ital e}{sup +}{ital e}{sup {minus}} storage ring PEP was used to search for exclusive decays of {ital D}{sup {plus minus}} and {ital B}{sup {plus minus}} mesons into two charged leptons plus a charged pion or kaon. All possible charge and lepton combinations consistent with charge conservation were considered and no evidence for any signals was found. We obtain upper limits for the various branching ratios ranging from 2.5{times}10{sup {minus}3} to 9.2{times}10{sup {minus}3}, at a 90% confidence level. Some of these limits can be used to constrain leptoquark masses in various models.

https://www.slac.stanford.edu/pubs/slacpubs/4750/slac-pub-4999.pdf

B. W. LeClaire

Papers

Upper limits on D and B decays to two leptons plus or K