The SLD Detector at the SLC

The SLAC Large Detector (SLD) is a modern high-energy particle physics detector running at the Stanford Linear Collider (SLC). The SLC delivers high-energy e + e – beams which collide in the detector. The Z 0 s are produced in the e + e – collisions at the center of the detector, and quickly decay into many different kinds of particles. The SLD detector consists of a large solenoidal mag-\net surrounded by layers of iron which serve first, as a support frame for internal detector components, second, as a flux return for the magnetic field, and finally, as material to absorb the high-energy particles from the decay of the Z 0 s. Instruments forming the internal components of the detector track the particle trajectories, identify them by particle type, and
measure the momenta and energies.

Since 1992, the SLD detector has accumulated a data set of approximately 500,000 Z 0 s. These data are used for precision studies of the electroweak sector of the Standard Model, for investigations into the physics of heavy quarks which are produced in the Z 0 decays, and to study the physics of strong interactions (QCD) through the quark and gluon effects in the Z 0 decays.

The SLC delivers polarized e – beams to the SLD. Use of the electron polarization is unique to the SLD, and is exploited in all of the studies mentioned above. The SLD detector has the world’s only CCD-pixel silicon particle detector at its center, used for precise tracking. The precision tracking allows the SLD to see the decay vertices of charm and bottom quarks. This capability gives the SLD the purest sample of heavy quarks in
any of the e + e – detectors.

Polarized beams in the SLC provide a unique and sensitive tool for the precision studies of electroweak processes using the SLD. Electrons are produced in a polarized state by photoemission from a 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 0 s. Studies of the polarization effect in Z 0 production and decay lead to precision measurements of certain electroweak parameters. These studies in the SLD detector have led to the most precise measurement of the electroweak mixing parameter.

An example of where polarization plays an important role is in the production of hadrons at the peak of the Z 0 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 the Z 0 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 measure-ments.

Future plans for the SLD involve precision studies at b and anti-b quark final states of the Z 0 decays. With the anticipated large data sets possible, measurements of the quantum mechanical oscillations (B 0 s <-> anti-B 0 s) can be made. These measurements could establish the first observation of such phenomena in mesons made purely of heavy quarks, and the rate of these oscillations provide important information on the nature of the
Standard Model.

SLAC