Low energy protons as probes of hadronization dynamics

Energetic quarks liberated from hadrons in nuclear deep-inelastic scattering propagate through the nuclear
medium, interacting with it via several processes. These include quark energy loss and nuclear interactions
of forming hadrons. One manifestation of these interactions is the enhanced emission of low-energy charged
particles, referred to as grey tracks. We use the theoretical components of the BeAGLE event generator to
interpret grey track signatures of parton transport and hadron formation by comparing its predictions to E665
data. We extend the base version of BeAGLE by adding four different options for describing parton energy
loss. The E665 data we used consists of multiplicity ratios for fixed-target scattering of 490 GeV muons on
xenon normalized to deuterium as a function of the number of grey tracks. We compare multiplicity ratios for
E665 grey tracks to the predictions of BeAGLE, varying the options and parameters to determine which physics
phenomena can be identified by these data. We find that grey tracks are unaffected by modifications of the
forward production. Thus their production must be dominated by interactions with hadrons in the backward
region. This offers the advantage that selecting certain particles in the forward region is unlikely to bias a
centrality selection. We see a strong correlation between the number of grey tracks and the in-medium path
length. Our energy loss model does not reproduce the suppression observed in the projectile region. We see
an underprediction of the proton production rate in backward kinematics, suggesting that a stronger source of
interaction with the nuclear medium is needed for accurate modeling. These results lay an important foundation
for future spectator tagging studies at both Jefferson Laboratory and at the Electron-Ion Collider, where neutron
and proton grey track studies will be feasible down to very small momenta.