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Published: 2004

Total Pages: 38

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The authors have measured the azimuthal angular correlation of b{bar b} production, using 86.5 pb−1 of data collected by Collider Detector at Fermilab (CDF) in p{bar p} collisions at √s = 1.8 TeV during 1994-1995. In high-energy p{bar p} collisions, such as at the Tevatron, b{bar b} production can be schematically categorized into three mechanisms. The leading-order (LO) process is ''flavor creation'', where both b and {bar b} 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 b{bar b} 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 b{bar b} 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{bar b} → (J/[psi]X)(lX') events, where the charged lepton (l) is an electron (e) or a muon ([mu]), to measure [Delta][phi] between bottom quarks. The b{bar b} 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 b{bar b} pairs produced in the same azimuthal hemisphere, f{sub toward}. The measured f{sub toward} values are consistent with both parton shower Monte Carlo and NLO QCD predictions.