MRST partons generated in a fixed-flavour scheme

Abstract

We generate fixed three- and four-light-flavour sets of partons using MRST2004 partons as input. We show that it is important to set n_f=3 in the strong coupling, as well as in the splitting and coefficient functions, in order to obtain a consistent set of fixed-flavour partons. We compare the description of data using partons in both variable- and fixed-flavour-number-schemes.

Figures (5)

• Figure 1: The effect on the gluon distribution of, using in the 3-flavour FF evolution, a different number of active quark flavours in the coupling and the structure functions. The wrong $\alpha_S$ corresponds to increasing $n_f$ in the coupling at each heavy quark threshold.
• Figure 2: The comparison of the gluon distributions (and the total singlet-quark distributions) in the 3-flavour FFNS and the VFNS.
• Figure 3: The evolution of the gluon distribution in the 3-flavour FFNS and the VFNS, for typical low and high values of $x$.
• Figure 4: The effect on the luminosity distribution for $gg \to X$ of using FFNS or VFNS partons.
• Figure 5: The evolution of $F_2^c(x,Q^2)$ in the 3-flavour FFNS and VFNS (left). The evolution of $F_2^b(x,Q^2)$ in the 3-flavour FFNS and VFNS (right).