Final-state interaction in semi-inclusive DIS off nuclei

Abstract

The final state interaction (FSI) in Deep Inelastic Scattering (DIS) of leptons off a nucleus A, due to the propagation of the struck nucleon debris and its hadronization in the nuclear environment is considered. The effective cross section of such a partonic system with the nucleons of the medium and its time dependence are estimated, for different values of the Bjorken scaling variable, on the basis of a model which takes into account both the production of hadrons due to the breaking of the color string, which is formed after a quark is knocked out off a bound nucleon, as well as the production of hadrons originating from gluon radiation. It is shown that the interaction, the evolution and the hadronization of the partonic system in the nuclear environment can be thoroughly investigated by a new type of semi-inclusive process, denoted A(e, e ′ (A − 1))X, in which the scattered lepton is detected in coincidence with a heavy nuclear fragment, namely a nucleus A − 1 in low energy and momentum states. As a matter of fact, if FSI is disregarded, the momentum distribution of A − 1 is directly related to the momentum distribution of the nucleon before γ * absorption, i.e. the same quantity which appears in the conventional A(e, e ′ N )X process, where N denotes a nucleon. The rescattering of the struck nucleon debris with the medium damps and distorts the momentum distributions of A − 1 in a way which is very sensitive to the details of effective cross section of the debris with the nucleons of the medium. The total cross section of the process A(e, e ′ (A − 1))X on 4 He, 16 O, and 40 Ca, related to the probability that after a target nucleon experiences a DIS process, the recoiling A − 1 nucleus remains intact in spite of the strong FSI, is evaluated, and the distorted momentum distribution of the recoiling A − 1 system is obtained. It is shown that both quantities are very sensitive to the details of the early stage of hadronization of the nucleon debris in the nuclear medium.2

Time evolution of hadronization and grey tracks in DIS off nuclei

“…[10] it has been proposed as a possible candidate the DIS exclusive process A(e, e ′ B)X, where B is a detected recoil nucleus with a less number of nucleons than the target one [11], and X, as usual, denotes the unobserved jets of hadrons resulting from hadronization. It has indeed been shown [10] that the survival probability of the recoil nucleus B in such a process is rather sensitive to the time evolution of hadronization and, particularly, to its Q 2 dependence. This quantity, which is quite difficult to access experimentally in case of heavy nuclei, could be investigate using few-body nuclei.…”

“…It was found in [10] that the multiplicity of the produced hadrons, or better to say the pre-hadrons which are colorless dipoles, rises with time as…”

“…The string contribution to n h (t) has been found in [10] employing the standard dynamics of string decay [19,20]. The pre-hadron multiplicity as function of time, n M (t), was found in the following form [10],…”

“…were radiated over time interval t after the DIS interaction. The time dependence of the gluon radiation was found in [10] to be controlled by the parameter t 0 = (m N x Bj ) −1 = 0.2 fm/x Bj , and the number of perturbatively radiated gluons was evaluated in the following form…”

“…Note that this expression is different from the one used in [10]. Firstly, we excluded the term σ N N tot corresponding to interaction of the nucleon originated from the first DIS event, since we treat this nucleon as a participant giving rise to the last term in (2).…”