Heavy Flavor Physics

PEP-II

In the science of particle physics, the frontier may be probed in several ways. One way is to build a new accelerator having higher beam energy than its predecessors; another is to build a collider having an already-explored energy range but a much higher reaction rate. The latter method facilitates precision measurements and studies of weak signals—measurements and studies that can give access to subtle and profound effects not measurable by any other means.

At SLAC, work is continuing on a program of the latter type: a B factory. The program has as its centerpiece colliding-beam storage rings of unprecedented luminosity. (Luminosity is a measure of the reaction rate; the larger the luminosity, the greater the reaction rate.) The B factory has been designed to be built at SLAC as an improvement called PEP-II, to the existing PEP storage ring. PEP-II will collide asymmetric energy beams (9 GeV e – on 3.1 GeV e + ) at a center-of-mass energy of about 10.5 GeV and will provide a very copious source of heavy-flavor particles (about 10 8 per year), such as bottom quarks, charm quarks, and tau leptons. The primary physics effort is focused around a broad-based program to explore one of nature’s leading mysteries—the source of CP violation.

In the current view CP violation is required to explain the predominence of matter over anti-matter in the observed universe. These studies require very large samples of neutral B mesons. In addition to the CP program, areas of research such as rare B meson decays, charm quark, and tau physics will be pursued with data sets 100 times larger than those currently available.

Experiments at PEP-II will present many unique and exciting challenges that have required innovative approaches to the physics and to detector design over a broad range of activities. A nine-nation team of physicists from North America, Europe and the Far East is constructing the B Factory detector, BABAR. This research offers many opportunities for graduate student involvement. Students have worked on the construction and commissioning of the detector and the two-storage-ring machine, as well as the development and expansion of strategies and algorithms for extracting the physics.

First physics running begins in Spring 1999, when the accumulation of enormous volumes of data will commence. At that time, physics analysis will be the main opportunity for graduate students.

SLAC Participation at Cornell

SLAC physicists are working with the CLEO Collaboration at the CESR 10 GeV electron-positron collider in studies of the rare decay properties of the tau lepton and the eta meson. The driving interest is the possibility of finding new physics effects. The collaboration has a large amount of data and a well-understood detector. In particular, the data includes the largest number of tau lepton decays accumulated to date. This research is suitable for
graduate students who wish to work on an ongoing electron-positron collider experiment while carrying out data analysis and new physics searches as individual research work.

SLAC