Probing GPDs in exclusive electroproduction of dijets

Abstract

We summarize the formalism for calculating the exclusive dijet production in $e p \to e^{\prime} jj p$ in collinear QCD factorization, using generalized parton distributions (GPDs) as the soft hadronic input modeled in the double distribution (DD) approach. We include all leading-order contributions coming from light sea and valence quark exchanges, and gluon exchanges for both light quark-antiquark ($q\bar{q}$) production and also the heavy $c\bar{c}$ final state. We present results for several differential distributions for the cross section evaluated over a broad region of phase space, covering a wide range of inelasticity and photon virtuality. The gluon and sea contributions exhibit similar shapes, whereas the valence contribution, though relatively small, shows a markedly different behavior. The latter becomes particularly noticeable at large $x_{\mathbb{P}}$, a kinematic region not explored at HERA, but potentially accessible in future measurements at the Electron Ion Collider (EIC). This requires further feasibility studies. We also present the azimuthal angle modulation between the leptonic and the outgoing dijet planes for the general case, as well as for the ZEUS kinematic region where we see reasonable agreement with the data for diffractive deep inelastic scattering (DIS) parameter $β\gtrsim 0.4$.

Figures (14)

• Figure 1: The hard and exclusive diffractive dijet (jj) production in deep inelastic electron-proton scattering in the two-gluon exchange model.
• Figure 2: Feynman diagrams contributing to the exclusive dijet production in the $\gamma^{\ast}p\xrightarrow{}q\bar{q}p$ subprocess. The left panel presents the gluon exchange contribution whereas the right panel shows the quark exchange contribution.
• Figure 3: GPDs used in this work as a function of the momentum fraction $x$. The top-left panel shows the forward gluon GPD vs $x$ for $\xi=0.1$ as a solid blue line and its derivative with respect to $x$ as a dash-dotted red line, the top-right panel shows the forward u-valence quark GPDs vs $x$ at $\xi=0.2,0.1$ and $0.05$ with red, blue and black curves respectively, and the bottom panel shows the forward s-sea quark $x\cdot$GPD vs $x$ at $\xi=0.1,0.01$ and $0.001$ with red, blue and black curves, respectively.
• Figure 4: The left panel shows the $Q^2$ distribution of the cross section whereas the right panel shows the distribution in the Mandelstam variable $t$. The solid black curve represents the total contribution from sea and valence light $u,d,s$ quark exchanges as well as gluon exchanges, including both light quark--antiquark production and the heavy $c\bar{c}$ final state. The solid magenta curve shows the gluon contribution, the red dash--dotted curve corresponds to the valence quark contribution, the blue long--dashed curve to the sea quark contribution, and the green short--dashed curve to the gluon-induced contribution to the $c\bar{c}$ final state.
• Figure 5: The left panel shows the dependence of the cross section on the invariant centre of mass energy of the $\gamma^{\ast}p$ subprocess $W$ whereas the right panel shows the distribution in inelasticity variable $y$. Identification of the curves is the same as in Fig. \ref{['fig:Qt']}.