Abstract
Deep Inelastic Scattering (DIS) experiments at the planned Electron-Ion Collider will be affected by details of the hadron formation inside the nuclear volume. Besides semi-inclusive particle production experiments decays of the target nucleus via emission of neutrons provide an additional opportunity to probe this domain. This paper reports on the hybrid dynamical+statistical calculations of low-energy neutron production in muon- and virtual photon-induced collisions with nuclei. We confirm the conclusion that the E665 data on neutron production in $\mu^-$ + Pb DIS at 470 GeV indicate a strong suppression of the final state interaction for hadrons with momenta above $\sim 1$ GeV/c. Ultraperipheral heavy-ion collisions at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC) can be used to test this suppression. The calculations of the neutron multiplicity distributions and $p_t$-spectra in photon - nucleus collisions at the energies accessible at the LHC and RHIC are presented for several models of hadron formation. We argue that studies of neutron production in ultraperipheral heavy ion collisions open a new window on the small-$x$ dynamics and hadron component of the photon wave function.
Highlights
The planned Electron-Ion Collider (EIC) will give us access to the quark and gluon substructure of bound nucleons in energy regimes that extend the earlier experiments at the Hadron-Electron Ring Accelerator (HERA) and Thomas Jefferson National Accelerator Facility (JLab) into a new domain [1]
Largely guided by experience gained from previous studies of the particle- and nucleus-nucleus interactions [13,17,19,20,21], we rely on the hybrid description combining three steps: (1) hard interaction of the incoming γ ∗ with a bound nucleon, (2) propagation of produced particles in the target nucleus, and (3) statistical evaporation of slow neutrons from a nuclear residue
We analyze the E665 data on slow neutron production in inclusive μ− + 208Pb and μ− + 40Ca Deep inelastic scattering (DIS) processes at the beam energy of 470 GeV [12]
Summary
The planned Electron-Ion Collider (EIC) will give us access to the quark and gluon substructure of bound nucleons in energy regimes that extend the earlier experiments at the Hadron-Electron Ring Accelerator (HERA) and Thomas Jefferson National Accelerator Facility (JLab) into a new domain [1]. Experiments at the EIC will use the nucleus both as a target and a laboratory for quantum chromodynamics (QCD) where, e.g., the quark hadronization can be studied In all these experiments, one tacitly assumes an approximate factorization of the initial DIS process and the final-state interactions (FSI) of the particles produced. Neutron multiplicity of about five neutrons per event, it was necessary to assume that only nucleons produced in DIS with momenta 1 GeV/c could interact This surprisingly low value is well below the momentum range where the formation time and color transparency effects become important. This hints at a new dynamics for the hadron formation in the nucleus fragmentation region In another E665 experiment [14] on μ− + Xe DIS at 490 GeV, the multiplicities of so-called gray tracks, ascribed to protons in the momentum range 200–600 MeV/c, have been measured. The neutron yields below 10 MeV are governed by statistical evaporation and agree very well with experiment
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