Asymmetries for and production are usually discussed in terms of parton fusion models which rely on bound-state phenomenology[38] for identifying various possible production mechanisms. Two paths which are likely to contribute to () production are,
and
One expects the resonance to be produced primarily via the second path, since its mass lies above the region. The parton-level asymmetry for indirect production via the state is maximally large and independent of kinematics, . Theoretical evidence[36,38] and experimental data from hadron production of [39] suggest that of the cross section is via this path at fixed-target energies. Unfortunately the asymmetry for the three-gluon mechanism has the opposite sign to the production path, resulting in cancellation[36]. In the dominant kinematic region, , one finds[36] . Nevertheless, using a model which includes both direct and indirect production of the and resonances, Doncheski and Robinett[36] predict sizable values, , near .
Production of the , , and resonances produces substantial yield in the dimuon channel in the RHIC energy range as is evident in Table 2.
Table 2: Numbers of pairs accepted into the upgraded PHENIX
spectrometer for an integrated luminosity of
.
Lower limit errors (neglecting background subtraction and systematic errors) may be calculated as , where is the proton beam polarization.
In order to get a qualitative picture of asymmetries in quarkonium production, Fig. 11 shows for several published structure functions[31,32,33,34]. Equation 13 has been used with , approximating the cancellation between the two production mechanisms as calculated by Doncheski and Robinett[36]. The polarized structure functions of Refs.[31,32,33] have the property over much of the x range. Equation 13 then becomes,
Thus there is no dependence on , and polarization effects increase linearly with . The points in Fig. 11 are plotted on the curve of Ref.[32] with errors determined by the numbers of Table 2. Both and data would be most significant in constraining the current models at the lowest collision energy.
Figure 11: Asymmetries using the polarized structure functions of
Ref.[34] (solid), Ref.[33]
(medium dash), Ref.[32] (long dash), and Ref.
[31] (short dash). A parton-level asymmetry,
has been assumed. The points show error
estimates for (squares) and (circles)
production described in the text.