Measurements of bottom-antibottom azimuthal production correlations in proton-antiproton collisions ats=1.8 TeV

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Abstract

We have measured the azimuthal angular correlation of $b\overline{b}$ production, using $86.5\text{ }\text{ }\mathrm{p}{\mathrm{b}}^{\ensuremath{-}1}$ of data collected by Collider Detector at Fermilab (CDF) in $p\overline{p}$ collisions at $\sqrt{s}=1.8\text{ }\text{ }\mathrm{TeV}$ during 1994--1995. In high-energy $p\overline{p}$ collisions, such as at the Tevatron, $b\overline{b}$ production can be schematically categorized into three mechanisms. The leading-order (LO) process is ``flavor creation,'' where both $b$ and $\overline{b}$ 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 $b\overline{b}$ cross section, while providing very different opening angle distributions from the LO process. An azimuthal opening angle between bottom and antibottom, $\ensuremath{\Delta}\ensuremath{\phi}$, has been used for the correlation measurement to probe the interaction creating $b\overline{b}$ pairs. The $\ensuremath{\Delta}\ensuremath{\phi}$ distribution has been obtained from two different methods. One method measures the $\ensuremath{\Delta}\ensuremath{\phi}$ between bottom hadrons using events with two reconstructed secondary vertex tags. The other method uses $b\overline{b}\ensuremath{\rightarrow}(J/\ensuremath{\psi}X)(\ensuremath{\ell}{X}^{\ensuremath{'}})$ events, where the charged lepton ($\ensuremath{\ell}$) is an electron ($e$) or a muon ($\ensuremath{\mu}$), to measure $\ensuremath{\Delta}\ensuremath{\phi}$ between bottom quarks. The $b\overline{b}$ purity is determined as a function of $\ensuremath{\Delta}\ensuremath{\phi}$ by fitting the decay length of the $J/\ensuremath{\psi}$ and the impact parameter of the $\ensuremath{\ell}$. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the $b\overline{b}$ pairs produced in the same azimuthal hemisphere, ${f}_{\mathrm{toward}}$. The measured ${f}_{\mathrm{toward}}$ values are consistent with both parton shower Monte Carlo and NLO QCD predictions.

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