Slicing Pomerons in ultraperipheral collisions using forward neutrons from nuclear breakup

We argue that measurements of forward neutrons from nuclear breakup in inclusive high energy photon-nucleus (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>γ</a:mi><a:mi>A</a:mi></a:mrow></a:math>) scattering provide a novel way to study small-<b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>x</b:mi></b:math> dynamics of QCD in heavy-ion ultraperipheral collisions (UPCs). Using models for hadronic fluctuations of the real photon and neutron emission in nuclear fragmentation, we calculate the distribution over the number of evaporation neutrons produced in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>γ</c:mi><c:mtext>Pb</c:mtext></c:mrow></c:math> collisions at the Large Hadron Collider. We show that it is correlated with the number of wounded nucleons (inelastic collisions) and, hence, can constrain the mechanism of nuclear shadowing and its <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>x</d:mi></d:math> dependence.