Abstract
We propose a new method to determine the spatially or impact-parameter dependent nuclear parton distribution functions (nPDFs) using the double parton scattering (DPS) processes in high-energy heavy-ion (proton-nucleus and nucleus-nucleus) collisions. We derive a simple generic DPS formula in nuclear collisions by accommodating both the nuclear collision geometry and the spatially dependent nuclear modification effect, under the assumption that the impact-parameter dependence of nPDFs is only related to the nuclear thickness function. While the geometric effect is widely adopted, the impact of the spatially dependent nuclear modification on DPS cross sections has been overlooked so far, which can, however, be significant when the initial nuclear modification is large. In turn, the DPS cross sections in heavy-ion collisions can provide useful information on the spatial dependence of nPDFs. They can be, in general, obtained in minimum-bias nuclear collisions, featuring the virtue of independence of Glauber modeling.
Highlights
Multiple particle production at high-energy hadron colliders, such as at the LHC, is dominated by simultaneous multiple interactions between partons from the initial hadrons
For the first time, we have considered both the nuclear collision geometry and the impact-parameter dependent nuclear modification in the nuclear parton distribution functions (nPDFs) for double parton scattering (DPS) processes in heavy-ion collisions
A simple generic equation (18) has been derived for evaluating the DPS cross sections in nucleus-nucleus collisions, while its pA counterpart is given in Eq (22)
Summary
Multiple particle production at high-energy hadron colliders, such as at the LHC, is dominated by simultaneous multiple interactions between partons from the initial hadrons. Given the modest amount of available nuclear hard-reaction-process data available in the global fits, almost all considered nPDFs [105,106,107,108,109,110,111,112,113,114,115,116,117] nowadays are only spatially averaged They can only be directly used in minimum-bias nuclear collisions. The primary goal of the paper is to derive the generic expression for the DPS cross section in heavy-ion collisions by accommodating both the nuclear collision geometry and the spatially dependent nuclear modification effect. Appendix A discusses the transverse parton profile and the overlap function, and Appendix B considers the case when the transverse position dependencies of protons and neutrons are different in a nucleus
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