*Article* **Color Transparency and Hadron Formation Effects in High-Energy Reactions on Nuclei**

**Alexei Larionov 1,2,\* and Mark Strikman 3**


Received: 15 December 2019; Accepted: 13 January 2020; Published: 17 January 2020

**Abstract:** An incoming or outgoing hadron in a hard collision with large momentum transfer gets squeezed in the transverse direction to its momentum. In the case of nuclear targets, this leads to the reduced interaction of such hadrons with surrounding nucleons which is known as color transparency (CT). The identification of CT in exclusive processes on nuclear targets is of significant interest not only by itself but also due to the fact that CT is a necessary condition for the applicability of factorization for the description of the corresponding elementary process. In this paper we discuss the semiexclusive processes *<sup>A</sup>*(*<sup>e</sup>*,*eπ*+), *<sup>A</sup>*(*π*<sup>−</sup>, *<sup>l</sup>*−*<sup>l</sup>*+) and *<sup>A</sup>*(*<sup>γ</sup>*, *π*<sup>−</sup> *p*). Since CT is closely related to hadron formation mechanism, the reduced interaction of 'pre-hadrons' with nucleons is a common feature of generic high-energy inclusive processes on nuclear targets, such as hadron attenuation in deep inelastic scattering (DIS). We will discuss the novel way to study hadron formation via slow neutron production induced by a hard photon interaction with a nucleus. Finally, the opportunity to study hadron formation effects in heavy-ion collisions in the NICA regime will be considered.

**Keywords:** Glauber and Giessen Boltzmann–Uehling–Uhlenbeck (GiBUU) models; formation length; semiexclusive processes; ultraperipheral and central heavy ion collisions; *n*, *p*, *π* and Λ + Σ<sup>0</sup> production
