Quantitative study of the violation of kt-factorization in hadroproduction of quarks at collider energies

TL;DR

It is shown that violations of kperpendicular factorization are relatively weaker at very small x, where leading twist shadowing is large, and at x values where parton densities are large but leading twistshadowing effects are still small.

Abstract

We demonstrate the violation of kT-factorization for quark production in high energy hadronic collisions. This violation is quantified in the Color Glass Condensate framework and studied as a function of the quark mass, the quark transverse momentum, and the saturation scale Qsat, which is a measure of large parton densities. At x values where parton densities are large but leading twist shadowing effects are still small, violations of kT-factorization can be significant - especially for lighter quarks. At very small x, where leading twist shadowing is large, we show that violations of kT-factorization are relatively weaker.

Figures (4)

• Figure 1: The ratio $\phi_{_A}^{q\bar{q},g}({\boldsymbol l}_\perp;{\boldsymbol k}_\perp)/ \phi_{_A}^{g,g}({\boldsymbol l}_\perp)$ as a function of ${\boldsymbol k}_\perp$ (along a line parallel to ${\boldsymbol l}_\perp$ in the ${\boldsymbol k}_\perp$ plane) for various values of ${\boldsymbol l}_\perp$ and $Q_s^2 = 2~{\rm GeV}^2$. The thin lines represent the same ratio evaluated with the large $N$ approximation for the 3-point correlator in the numerator.
• Figure 2: Comparison of the cross sections obtained with the exact 3-point function and with the large $N$ approximation, for $Q_s^2=2~{\rm GeV}^2$, $m=1.5$ GeV and $m=4.5$ GeV.
• Figure 3: Breaking of $k_\perp$-factorization in the MV model, respectively for strange, charm and bottom quark production.
• Figure 4: Breaking of $k_\perp$-factorization for charm quarks in the non-local Gaussian effective model of IancuIM2. The dashed line shows the result (for $Q_s^2 =15$ GeV$^2$) in the MV model for comparison.