Hard Processes with Spin–Dependent Parton Distributions

To test a possible color–octet contribution of heavy quarkonium productions, we propose ψ’–productions for small–pT regions, where the color–singlet ψ’ state cannot be produced by the gluon–gluon fusion owing to charge conjugation. We also point out that these processes are very useful to deduce informations of spin–dependent gluon distributions ∆g. PACS numbers: 13.85.Ni, 13.88.+e, 14.20.Dh, 14.40.Lb, 14.70.Dj Recently, it has been reported that the cross sections of heavy quarkonium productions measured in unpolarized pp̄ collisions by the CDF collaboration are inconsistent with the calculation with the lowest order processes alone[1]. Several groups have proposed new mechanisms: the production proceeds with not only color–singlet but also color–octet quarkonim states and this new mechanism dominates over the lowest order processes for large–pT quarkonium productions[2]. But it does not seem to work for γ+p→ J/ψ+X[3]. The discussion on the color–octet contribution is still controversial. Thus, it is important to test this mechanism in other experiments. On the other hand, measurements of the spin–dependent structure functions of a nucleon g1(x,Q 2) for polarized deep inelastic scatterings (PDIS) imply a surprizing result that the amount of the proton spin carried by quarks, (∼ 30%), is much smaller than expected E–mail: [email protected] , Phone: +81–6–879–8940 , Fax: +81–6–879–8899 .