Workbook

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the third (Level 2) is a software filter implemented on a farm of 48 VAX. Station
4000 computers with full event information available. A supplementary
Level 1.5 trigger refines the Level 1 muon trigger.
Initial running concentrated on commissioning the apparatus and
understanding the effects of the Main Ring beam which passes through the
calorimeter 2m above the Tevatron beam. First collisions were observed on
May 12, 1992 and the data run started after a brief shutdown in August. Over
the whole of Run la, DO accumulated 15pb- 1 of collider data including special
and calibration data runs. The overall ratio of beam data recorded to beam
available was about 70%, with the main loss coming from the veto imposed to
stop triggering during Main Ring injection and transition and while Main
Ring protons pass through the detector. Data were taken at a rate ofabout 2 Hz
and reconstructed at the same rate on a multi-processor UNIX farm.
DO is now taking data in Run lb. The detector has been improved for the
higher luminosities compared with Run la by the addition of a cosmic ray
shield for the muon system and hardware Level 1.5 trigger for electrons
capable of performing both threshold and simple isolation cuts. The
bandwidth to tape was approximately doubled and now is 1.6 MHz which
corresponds to an event rate of 3Hz.
Current la and Ib physics analyses at DO are organized into five groups.
The Top Quark Group was able to set a mass limit of mt > 131 GeV using
Run la data. With the larger statistics available from Run Ib, we reported
observation of the top quark, with a mass of about 200 GeV, in February 1995.
This is a major accomplishment in understanding the Standard Model. We
will refine our measurements of the properties and decays of the top quark as
we continue to take data in Run lb.
The QCD Group has presented cross sections for inclusive jets in the
central and forward regions and differential cross sections for dijet
production. The dijet angular distributions have been measured, and photon
cross sections and angular distributions presented. Many new analyses have
extended the study of QCD at the Tevatron Collider into new regimes: the
observation of rapidity gaps between forward and backward jets is a signal for
colorless exchange, e.g. pomerons; the decorrelation in azimuthal angle
between forward and backward jets allows tests of resummation in mixedscale
problems; measurement of energy flow around jets allows the color
coherence of gluon emission to be probed.
The Electroweak Group focuses on the production and decay of Wand Z
bosons. Results presented from Run Ia data include the W mass, Wand Z
production cross sections, and PT distributions. The production of dibosons
(Wy, Zy, WW, WZ) through trilinear couplings, a test of the Standard Model,
has been studied with Run Ia data. DO is also using vector-boson-plus-jet
events as a QCD laboratory: the strong coupling constant as has been
measured from W+jet events and color coherence effects can be studied here
too.