Abstract
Correlations among hadrons with the same electric charge produced in Z 0 decays are studied using the high statistics data collected from 1991 through 1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth order are used to measure genuine particle correlations as a function of the size of phase space domains in rapidity, azimuthal angle and transverse momentum. Both all-charge and like-sign particle combinations show strong positive genuine correlations. One-dimensional cumulants initially increase rapidly with decreasing size of the phase space cells but saturate quickly. In contrast, cumulants in two- and three-dimensional domains continue to increase. The strong rise of the cumulants for all-charge multiplets is increasingly driven by that of like-sign multiplets. This points to the likely influence of Bose–Einstein correlations. Some of the recently proposed algorithms to simulate Bose–Einstein effects, implemented in the Monte Carlo model Pythia , are found to reproduce reasonably well the measured second- and higher-order correlations between particles with the same charge as well as those in all-charge particle multiplets.
Highlights
Correlations in momentum space between hadrons produced in high energy interactions have been extensively studied over many decades in different contexts [1]
Proceeding beyond the usual analyses of two-particle correlations, we show that, at least within the framework of this model, a good description can be achieved of the factorial cumulants up to fourth order in one, two- and three-dimensional phase space domains
The cumulants have been computed changing in turn the following selection criteria: the first measured point was required to be closer than 40 cm to the beam, the requirement of the transverse momentum with respect to the beam axis was removed, the momentum was required to be less than 40 GeV/c, the track polar angle acceptance was changed to | cos θ| < 0.7, and the requirement on the mean energy loss was removed
Summary
Correlations in momentum space between hadrons produced in high energy interactions have been extensively studied over many decades in different contexts [1]. The cumulants for like-sign and all-charge multiplets, measured as a function of M, have been corrected for geometrical acceptance, kinematic cuts, initial-state radiation, resolution, secondary interactions and decays in the detector, using correction factors, Uq(M), calculated for all-charge particle combinations and evaluated as in [22] using the Jetset/Pythia Monte Carlo without BEC. The cumulants have been computed changing in turn the following selection criteria: the first measured point was required to be closer than 40 cm to the beam, the requirement of the transverse momentum with respect to the beam axis was removed, the momentum was required to be less than 40 GeV/c, the track polar angle acceptance was changed to | cos θ| < 0.7, and the requirement on the mean energy loss was removed These changes modify the results by no more than a few percent in the smallest cells, and do not affect the conclusions. It was further verified that our conclusions remain unchanged when events taken at energies off the Z0 peak are excluded from the analysis
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