Measurements of Bottom Anti-Bottom Azimuthal Production Correlations in   Proton-Antiproton Collisions at s**(1/2)= 1.8 TeV
  We have measured the azimuthal angular correlation of bottom anti-bottom production, using 86.5 pb-1 of data collected by Collider Detector at Fermilab (CDF) in proton anti-proton collisions at sqrt{s}=1.8 TeV during 1994-1995. In high-energy p-pbar collisions, such as at the Tevatron, bottom anti-bottom production can be schematically categorized into three mechanisms. The leading-order (LO) process is ``flavor creation,'' where both the bottom and anti-bottom 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 bottom anti-bottom 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 measurement to probe the interaction creating bottom anti-bottom 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 b-bbar --> (J/psi X)(l X') events, where the charged lepton (l) is an electron or a muon, to measure Delta phi between bottom quarks. The bottom anti-bottom purity is determined as a function of Delta phi by fitting the decay length of the J/psi and the impact parameter of the lepton. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the b-bbar 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. 
CDF Collaboration