Abstract for the Thesis entitled.
"A Search for Supersymmetric Quarks and Gluons in pbar p Collisions at 
sqrt s = 1.8 TeV with the CDF Detector"

by Farhad Keyvan
University of California, Los Angeles, California
Advisor: Professor J. Hauser

Abstract
--------

This thesis reports on a search for Supersymmetric (SUSY) partners of the 
Standard Model (SM) quark (squark q~) and gluon (gluino g~) in 1.8 TeV ppbar
Collisions at CDF. The search uses 19.0 pb-1 of Run 1A (1992-93) data.
According to the Minimal Supesymmetric Standard Model (MSSM) which provides the
context for this search, squarks and gluinos can be created in pairs at the
Tevatron, and subsequently decay into missing transverse energy (MET) and jets.
The data consists of 2.0 million DST events from the Exotic data stream. The MET
plus multijet channel is dominated by several major and minor backgrounds. These
backgrounds can be divided into two distinct groups: 1) non-physics (spoiled
events due to bad runs, detector problems, and cosmic rays), 2) physics (events
due to W, Z, top decays, and QCD).  Cuts on the data are applied to cleanup the
non-physics events, and to remove the physics backgrounds as much as possible
without gross reduction in signal effciency. After all cuts, 23 events are left
containing three or more jets and large MET. There are 6 events containing four
jets and large MET. There are no events with five or more jets in the final
event sample. The W/Z/top background events are simulated using existing Monte
Carlo (MC) programs. The W/Z simulations are normalized to the existing data,
and the latest top decay cross section (sigma) is used to estimate these
contaminations to our final event sample. To estimate the QCD (events with
significantly mismeasured jet energy) contamination, actual data is used.  The
total estimated background to the three or more jet final sample is
33.8+12.5-10.1(stat)+15.1-7.8(sys.) events, and to the four or more jet sample
is 8.4+4.5-3.3(stat)+2.7-2.3(sys) events. Since the final number of sample
events is within the uncertainty of the total background estimate, limits are
set at 95% C.L. for the masses of squarks and gluinos.  Millions of SUSY events
are simulated with different MSSM parameters, varying the squark and gluino
masses.It is shown that for the region where Mq~ > Mg~, higher mass limits can
be set if four or more jets are required.  This is due to improved signal to
noise ratio for such high jet multiplicity sample.  On the other hand in the
region where Mq~ < Mg~ three or more jets are required since the signal
cross-section for higher jet multiplicities drops off much more rapidly than for
the other region.  This search concludes that the limits at 95% C.L. upper limit
in the MSSM are Mg~ > 183 GeV/c^2 (Mg~ independent of Mq~), and Mg~ > 218
GeV/c^2 and Mq~ > 218 GeV/c^2 (Mg~ = Mq~).


Posted to /cdf/pub/thesis/cdf4584_keyvan_thesis.ps
    http://www-cdf.fnal.gov/thesis/cdf4584_keyvan_thesis.ps

Posted by groer@cdfsga