The SLD Detector at the SLC

The SLAC Large Detector (SLD) is a state-of the art device designed to exploit the capabilities of the SLC in order to study physics at the Z peak. Construction of the primary components of the SLD is now completed. It was moved onto the SLC beam line in November 1990 for final checkout. During 1992, 11,000 Z's were collected in the SLD with a 22% polarized e- beam colliding with an unpolarized e+ beam. A second data run began in February 1993, with polarization greater than 60%. After the installation of machine improvements in the winter of 1993, it is anticipated that the SLD will collect an additional 60,000 Z's during the remainder of 1993 (update). The SLD experiment is expected to continue its run for several more years.

For precision studies of electroweak physics with the Z, the SLD is the only e+e- detector to have access to a highly polarized electron beam, thereby allowing certain electroweak measurements at SLC to surpass those being made at LEP, the European e+e- collider, using unpolarized beams. In order to study beauty quark production and decay and charm physics, the SLD will combine the unique features of the SLC (micron spot sizes and a polarized beam) with its unsurpassed 3D silicon CCD vertexing system, its high-precision tracking and fine-grained calorimetry, and its excellent particle identification (using the Cherenkov Ring Imaging technique).

Polarized beams in the SLC provide a unique and sensitive tool for precision studies of electroweak processes using the SLD. Electrons are produced in a polarized state by photoemission from gallium arsenide cathode, using polarized laser light.

These electrons are captured and accelerated through the SLC complex. Longitudinally polarized electrons interacting with unpolarized positrons at high energies produce polarized Z's. Studies of polarization effects in Z production and decay lead to precision measurements of certain electroweak parameters.

An example of where polarization plays an important role is in the production of hadrons at the peak of the Z resonance. The asymmetry in the hadron production rate is sensitive to the masses of the top quark and Higgs boson. This measurement will be important to understand the top quark and the Higgs mechanism. Production of the b quark in Z decay is influenced by the polarization of the incoming electron beam. With polarization, the b or anti-b quarks can be tagged, significantly enhancing the experimental sensitivities in these measurements.

The SLD provides an excellent opportunity for students to do unique physics with the Z. In addition to graduate work in fundamental particle physics, research opportunities exist for students in the areas of detector electronics, detector hardware, online and offline software, and data analysis. SLD physicists are also involved in the development of advanced polarized sources and new cathodes, and in the instrumentation for precision measurement of the beam

polarization. This close coupling between the SLC and the SLD provides a unique opportunity for students to be involved in machine physics and develop ment.

Extracted from the SLAC Graduate Student Handbook by Summer Science Program students Tehani Finch and Evelyn Aviles-Hernandez, June 1994.