Single spin asymmetries in inclusive hadron production from SIDIS to hadronic collisions: universality and phenomenology

Abstract

In a perturbative QCD approach, with inclusion of spin and transverse momentum effects, experimental data on azimuthal asymmetries observed in polarized semi-inclusive deeply inelastic scattering and e+ e- annihilations can be used to determine the Sivers, transversity and Collins soft functions. By using these functions, within the same scheme, we predict p(transv. polarized) p -> h + X single spin asymmetries in remarkable agreement with RHIC experimental data.

Figures (3)

• Figure 1: Panel (a): Invariant differential cross section for $pp \to \pi^0 +X$ at $\sqrt{s}= 200$ GeV and two pseudorapidity values, $\eta=3.3$ and $\eta=3.8$, vs. $E_\pi$. Data are from STAR Adams:2006uz. Curves are obtained adopting the unpolarized $k_\perp$-dependent PDFs and FFs of Ref. Anselmino:2005nn. Panels (b), (c) and (d): $A_N$ for $pp \to \pi^0 +X$ at $\sqrt{s}= 200$ GeV and two pseudorapidity values, $\eta=3.3$ and $\eta=3.7$, vs. $x_F$ (b), and at different $x_F$ values vs. $p_T$, (c) and (d). Data are from STAR Nogach:2006gm. Curves are obtained using the Sivers functions as determined in Ref. Anselmino:2005ea by fitting SIDIS data.
• Figure 2: Panels (a) and (b): Invariant differential cross section for $pp \to \pi^\pm +X$ at $\sqrt{s}= 200$ GeV and two pseudorapidity values, $y=2.95$ and $y=3.3$, vs. $p_T$. Data are from BRAHMS Arsene:2007jd. Curves are obtained adopting the same choices as in Fig. 1(a). Panels (c) and (d): $A_N$ for $pp \to \pi^\pm +X$ at $\sqrt{s}= 200$ GeV and two different scattering angles, $\theta=2.3^\circ$ and $\theta=4^\circ$, vs. $x_F$. Data are from BRAHMS Lee:2007zzh. Thick curves are obtained adding the Sivers effect, as extracted from SIDIS data in Ref. Anselmino:2005ea, and the Collins effect coupled with the transversity function, as extracted from a global fit of SIDIS and $e^+e^-$ data in Ref. Anselmino:2007fs. The thin lines show the Collins effect: notice that its sign is opposite w.r.t. the Sivers contribution.
• Figure 3: Panels (a) and (b): Invariant differential cross section for $pp \to K^\pm +X$ at $\sqrt{s}= 200$ GeV and two pseudorapidity values, $y=2.95$ and $y=3.3$, vs. $p_T$. Data are from BRAHMS Arsene:2007jd. Curves are obtained adopting the same choices as in Fig. 1(a). Panel (c): $A_N$ for $pp \to K^\pm +X$ at $\sqrt{s}= 200$ GeV and fixed scattering angle, $\theta=2.3^\circ$, vs. $x_F$. Data are from BRAHMS Lee:2007zzh. Curves are obtained with the Sivers function as determined in Ref. Anselmino:2005ea by fitting SIDIS data.