Incoherent diffractive J/Psi-production in high energy nuclear DIS

TL;DR

High-energy nuclear DIS in the small-x regime is dominated by nonlinear gluon dynamics and saturation, which must be described with the Color Glass Condensate and the dipole picture. The paper computes incoherent diffractive J/psi production using two CGC-inspired dipole cross sections (IIM and IPsat) extended to nuclei via an independent-scattering, factorized-b profile. It shows that incoherent diffraction is suppressed in large nuclei due to saturation, with a transition from A scaling in the dilute limit to A^(1/3) in the black-disk limit, and that the t-dependence can reveal fluctuations in the gluon density. The results suggest that incoherent diffractive measurements in future nuclear DIS experiments provide a sensitive probe of small-x gluon saturation and the spatial structure of the nuclear wavefunction.

Abstract

We compute cross sections for incoherent diffractive J/Psi production in lepton-nucleus deep inelastic scattering. The cross section is proportional to A in the dilute limit and to A^(1/3) in the black disc limit, with a large nuclear suppression due to saturation effects. The t-dependence of the cross section, if it can be measured accurately enough, is sensitive to the impact parameter profile of the gluons in the nucleus and their fluctuations, a quantity that determines the initial conditions of a relativistic heavy ion collision. The nuclear suppression in incoherent diffraction shows how the transverse spatial distribution of the gluons in the nucleus gradually becomes smoother at high energy. Since the values of the momentum transfer |t| involved are relatively large, this process should be easier to measure in future nuclear DIS experiments than coherent diffraction.

Figures (9)

• Figure 1: The $r$-dependence of the different proton dipole cross sections used, at $x=0.0001$ and $b=0$. As discussed in Sec. \ref{['sec:res']}, the "IPnonsat"-curve is Eq. (\ref{['eq:BEKWfact']}) linearized in $r^2F(x,r)$.
• Figure 2: Comparison of the used dipole cross sections to HERA data Chekanov:2004mw*Aktas:2005xu on diffractive vector meson production.
• Figure 3: The quasielastic and coherent diffractive $J/\Psi$ cross sections in gold nuclei at $Q^2= 0$ and ${x_\mathbb{P}} = 0.001$. Shown are the IPsat and IIM parametrizations. We also show the result for the linearized "IPnonsat" version (used e.g. in Ref. Caldwell:2009ke) where the incoherent cross section is explicitly $A$ times that of the proton. Our approximation (\ref{['eq:amplisq']}) is not valid for small $|t|$; the corresponding part of the distribution has been left out.
• Figure 4: The "nuclear transparency" ratio of cross sections vs. $Q^2$ for IPsat, IIM parametrizations at ${x_\mathbb{P}}= 10^{-2}$ (the upper three curves, blue) and $10^{-4}$ (the lower 3 curves, black). For comparison we also include we also include the result if unitarization effects are included at the nucleus but not at the nucleon level in the IPsat-parametrization. (See text for discussion).
• Figure 5: The "nuclear transparency" ratio of cross sections vs. $Q^2$ using the "Gaus-LC" vector meson wavefunctions. The labeling is the same as in Fig. \ref{['fig:ratiovsq']}.