PHYSICAL REVIEW D, PARTICLES, FIELDS, GRAVITATION, AND COSMOLOGY
Abstract
We have measured the azimuthal angular correlation of bb⎯⎯ production, using 86.5 pb−1 of data collected by Collider Detector at Fermilab (CDF) in pp⎯⎯ collisions at s√=1.8 TeV during 1994–1995. In high-energy pp⎯⎯ collisions, such as at the Tevatron, bb⎯⎯ production can be schematically categorized into three mechanisms. The leading-order (LO) process is “flavor creation,” where both b and 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 bb⎯⎯ cross section, while providing very different opening angle distributions from the LO process. An azimuthal opening angle between bottom and antibottom, Δφ, has been used for the correlation measurement to probe the interaction creating bb⎯⎯ pairs. The Δφ distribution has been obtained from two different methods. One method measures the Δφ between bottom hadrons using events with two reconstructed secondary vertex tags. The other method uses bb⎯⎯→(J/ψX)(lX′) events, where the charged lepton (l) is an electron (e) or a muon (μ), to measure Δφ between bottom quarks. The bb⎯⎯ purity is determined as a function of Δφ by fitting the decay length of the J/ψ and the impact parameter of the l. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the bb⎯⎯ pairs produced in the same azimuthal hemisphere, ftoward. The measured ftoward values are consistent with both parton shower Monte Carlo and NLO QCD predictions.
