Exclusive channels in semi-inclusive production of pions and kaons

TL;DR

This paper quantifies the impact of exclusive meson production channels on semi-inclusive electroproduction of pions and kaons within a leading-twist QCD factorization framework. By modeling generalized parton distributions with a double-distribution approach and incorporating meson distribution amplitudes, it evaluates cross sections for exclusive pseudoscalar and vector mesons and compares them to fragmentation-based semi-inclusive predictions. The analysis finds that ρ^0 production can significantly contribute to semi-inclusive π production at large z, while other exclusive channels are comparatively smaller, especially for kaons, and highlights substantial power corrections at moderate Q^2. The results demonstrate the importance of exclusive channels in certain kinematic regimes, constrain GPD inputs, and point to the need for higher-order calculations and power-correction treatments to accurately interpret semi-inclusive data.

Abstract

We investigate the role of exclusive channels in semi-inclusive electroproduction of pions and kaons. Using the QCD factorization theorem for hard exclusive processes we evaluate the cross sections for exclusive pseudoscalar and vector meson production in terms of generalized parton distributions and meson distribution amplitudes. We investigate the uncertainties arising from the modeling of the nonperturbative input quantities. Combining these results with available experimental data, we compare the cross sections for exclusive channels to that obtained from quark fragmentation in semi-inclusive deep inelastic scattering. We find that rho^0 production is the only exclusive channel with significant contributions to semi-inclusive pion production at large z and moderate Q^2. The corresponding contribution to kaon production from the decay of exclusively produced phi and K^* is rather small.

Figures (18)

• Figure 1: Example graphs for exclusive meson production in the generalized Bjorken limit. The large blob denotes the $p\to B$ transition GPD and the small one the meson distribution amplitude.
• Figure 2: Leading-twist cross sections for $\gamma^*_L\, p\to \pi^+ n$ (left) and $\gamma^*_L\, p\to K^+ \Lambda$ (right) for $Q^2 =2.5 \,\hbox{GeV}^2$. An upper cut on $-t$ of $1\,\hbox{GeV}^2$ has been applied here and in all further plots of this paper. Shown are the individual contributions from $|\tilde{\mathcal{}}{H}|^2$ and $|\tilde{\mathcal{}}{E}|^2$, and their coherent sum according to (\ref{['H-tilde-combinations']}).
• Figure 3: Leading-twist cross section for $\gamma^*_L\, p\to \pi^+ n$ (left) and $\gamma^*_L\, p\to K^+ \Lambda$ (right) at $Q^2=2.5 \,\hbox{GeV}^2$ obtained with different values of the parameter $\Lambda$ in the form factor multiplying the pion or kaon pole contribution in (\ref{['meson-pole']}).
• Figure 4: Left: Leading-twist cross section for $\gamma^*_L\, p\to K^+ \Lambda$ at $Q^2 = 2.5 \,\hbox{GeV}^2$ calculated with the asymptotic kaon distribution amplitude and with the one from Khodjamirian, Mannel and Melcher (KMM) Khodjamirian:2004ga. Right: The same cross section calculated with different parton distributions in the model for $\tilde{H}$. The distributions from Leader, Sidorov and Stamenov (LSS) Leader:1998qv and from Blümlein and Böttcher (BB) Blumlein:2002be are taken at a scale $\mu = 1\,\hbox{GeV}$.
• Figure 5: Leading-twist cross section for $\gamma^*_L\, p\to \rho^0 p$ at $Q^2 =2.5\,\hbox{GeV}^2$. Shown are the individual contributions from quark and gluon distributions and their coherent sum. The parton densities in the double distribution model are taken at scale $\mu^2 = 1.2\,\hbox{GeV}^2$ for the upper and at $\mu^2 = 2.5 \,\hbox{GeV}^2$ for the lower plots.