We have measured the azimuthal angular correlation of bb-bar
production, using 86.5 pb-1 of data collected by Collider Detector at
Fermilab (CDF) in p anti-p collisions at s**(1/2) = 1.8 TeV during 1994-1995. In
high-energy p anti-p collisions, such as at the Tevatron, bb-bar production can
be schematically categorized into three mechanisms. The leading-order (LO)
process is "flavor creation," where both b and b-bar quarks substantially
participate in the hard scattering and result in a distinct back-to-back
signal in final state. The "flavor excitation" and the "gluon splitting"
processes, which appear at next-leading-order (NLO), are known to make a
comparable contribution to total bb-bar cross section, while providing very
different opening angle distributions from the LO process. An azimuthal
opening angle between bottom and anti-bottom, Delta phi, has been used for
the correlation measurements to probe the interaction creating bb-bar pairs.
The Delta phi distribution has been obtained from two different methods.
One method measures the Delta phi between bottom hadrons using events with
two reconstructed secondary vertex tags. The other method uses bb-bar -->
(J/psi X)(l X') events, where the charged lepton (l) is an electron (e) or a
muon (mu), to measure Delta phi between bottom quarks. The bb-bar purity is
determined as a function of Delta phi by fitting the decay length of the
J/psi and the impact parameter of the l. Both methods quantify the
contribution from higher-order production mechanisms by the fraction of the
bb-bar pairs produced in the same azimuthal hemisphere, f_toward. The
measured f_toward values are consistent with both parton shower Monte Carlo
and NLO QCD predictions.
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Updated: Monday, 2005 May 23 08:59:27 CDT automatically from input from Carol Picciolo