Hard scattering in high-energy QCD

TL;DR

QCD at high energy has matured into a precision phenomenology program, with multiple independent extractions of $\alpha_S(M_Z)$ from event shapes, jet rates, and jet and heavy-quark production across $e^+e^-$, $ep$, and $p\bar p$ data. The work surveys experimental inputs, theory advances (NNLO, NLL resummation), and analytic power corrections, highlighting consistent but not yet ultra-precise determinations of $\alpha_S$ and the still-significant role of hadronisation. Key findings include supportive evidence for colour coherence, flavour universality of $\alpha_S$, and broadly good agreement between data and perturbative QCD across jets, gauge-boson production, and heavy-quark processes, alongside notable tensions in certain high-$x$ or forward regions that point to power corrections and PDF uncertainties. The article emphasizes the need for NNLO cross sections and improved hadronisation modeling to sharpen predictions and facilitate precision tests of the Standard Model.

Abstract

I review the recent results in the field of QCD at high energy presented to this Conference. In particular, I will concentrate on measurements of $\as$ from studies of event structures and jet rates, jet production in hadronic collisions, and heavy quark production.

Figures (24)

• Figure 1: Scaling violations in the fragmentation functions $D(z)$ for quark and gluon jets, from DELPHI.
• Figure 2: H1 fits for $\alpha_{ S}(M_Z)$ and $\alpha_0(2\hbox{GeV})$, from different shape variables.
• Figure 3: Evolution with $\sqrt{S}$ of the 1st moments of various shape variables, from L3. The dashed lines include only the PT contribution, the solid line is a fit including ${\@fontswitch{}{\mathcal{}} O}(1/Q)$ effects.
• Figure 4: Fits for $\alpha_{ S}(M_Z)$ and $\alpha_0(2\hbox{GeV})$, from different shape variables in $e^+e^-$ collisions (Movilla Fernández et al. MovillaFernandez:1999yn).
• Figure 5: Fits for $\alpha_{ S}(M_Z)$ and $\alpha_0(2\hbox{GeV})$, from different shape variables in $e^+e^-$ collisions. The dashed lines correspond to fit 1st moments, the solid lines to fits to distributions. Curves labeled by "old" refer to constant shifts in the broadening variable, while the others are obtained with the $B$-dependent shifts as in eq.( \ref{['eq:bdepshift']}). (Dokshitzer et al. Dokshitzer:1998qp).