Physical Gluons and High $E_T$ Jets

Abstract

We propose a more physical parameterization of the gluon distribution for global parton analyses of deep inelastic and related hard scattering data. In the new parameterization the gluon distribution at large x in the MSbar-scheme is driven by the valence quarks, which naturally produces a shoulder-like form at high x, and hence produces a better description of the Tevatron inclusive jet data. We perform the new analysis at both NLO and NNLO. The improvement is found to be even better at NNLO than at NLO. We make available the new sets of NLO and NNLO partons, which we denote by MRST2004.

Figures (5)

• Figure 1: The $x$ behaviour of CTEQ6.1M parton distributions, $xf(x,Q^2)$, at $Q^2=5~{\rm GeV}^2$.
• Figure 2: The $x$ behaviour of the CTEQ6.1M and CTEQ6D gluon distributions, $xg(x,Q^2)$, at $Q^2=5~{\rm GeV}^2$, obtained from global fits using the $\overline{\rm MS}$ and DIS factorization schemes respectively.
• Figure 3: The previous (default) MRST NLO $\overline{\rm MS}$-scheme gluon compared to that obtained when the high $x$ behaviour of the gluon is determined by the quark transformation between $\overline{\rm MS}$ and DIS schemes, as in (\ref{['eq:gms']}). The two gluons are shown, respectively, by continuous and dashed curves. Also shown by dot-dashed curves is this latter gluon when transformed to the DIS scheme. Exactly the same data sets are used in the two fits.
• Figure 4: The description of the D0 inclusive jet $E_T$ distributions in different rapidity intervals D0 obtained in our standard default NNLO analysis compared to the improvement obtained using the new gluon parameterization of (\ref{['eq:ginput']}). The bands indicate the allowed shifts from the central value for each data point obtained by adding the correlated errors in quadrature. The 'valence-quark driven' parametrization of the gluon improves $\chi^2$ for the description of the D0 data from 88 to 64.
• Figure 5: The previous default MRST NNLO $\overline{\rm MS}$-scheme gluon compared to that obtained when the high $x$ behaviour is determined by the quark transformation between $\overline{\rm MS}$ and DIS schemes. Also shown is this latter gluon when transformed to the DIS scheme.