Nuclear effects in leptoproduction of secondaries
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ELEMENTARY PARTICLES AND FIELDS Theory
Nuclear Effects in Leptoproduction of Secondaries* Ya. A. Berdnikov1), M. M. Ryzhinskiy1)** , and Yu. M. Shabelski2)*** Received March 10, 2006
Abstract—We estimate the energy losses in the case of deep-inelastic scattering on nuclear targets in terms of the effective change of the virtual photon energy. Our phenomenological results are in reasonable agreement with theoretical calculations. The difference in secondary production processes in hard and soft interactions is discussed. PACS numbers: 25.30.-c, 25.75.Dw, 13.87.Fh DOI: 10.1134/S1063778807040151
1. INTRODUCTION The inclusive spectra of secondaries (pions, kaons, p, and p¯) measured in lepton–nucleus (lA) deepinelastic scattering (DIS) [1–3] become ever softer with the increase of atomic weight of the target. In this paper we consider the A dependences of these spectra using the same method as in our previous paper [4]. In the case of DIS only some part of the projectile lepton energy (ν = El − El ) is transfered to the target. Thus, one can consider the virtual photon as a projectile to draw an analogy between the DIS and hadroproduction processes. It is convenient to analyze DIS data in terms of energy fractions of the virtual photon carried by the produced hadron. Therefore in this paper we will use the variable zh =
Eh , ν
(1)
where Eh is the energy of the produced hadron in the lab frame. At high energies in the case of nucleon target the maximum value of zh is close to unity (zh max → 1). In the case of a nuclear target the situation is more complicated because there are many different contributions [5, 6] from the final-state interactions with nuclear matter which decrease the spectra at large zh . On the other hand, the processes which lead to the so-called cumulative effect [7–9] increase the boundaries of the available zh region3) . The modification of ∗
The text was submitted by the authors in English. St. Petersburg State Polytechnic University, Russia. 2) Petersburg Nuclear Physics Institute, RAS, Gatchina. ** E-mail: [email protected] *** E-mail: [email protected] 3) The last processes have rather small cross section.
parton structure function [10] should be accounted for. In all processes on nuclear targets (except coherent ones) some fraction of energy is used for nuclear disintegration. The nuclear target is destroyed and several nucleons, as well as light nuclear fragments (say, α particles), appear in the final state. It can be considered as a phase-space limitation for the produced secondaries. The corresponding fraction of initial energy used on this effect numerically is not as small (it is many times larger than the nuclear binding energy). The energy used for nuclear disintegration is taken from the beam or secondary-particle energy, primarely via some QCD process, discussed in [5, 6]. After several stages this energy transforms (in part, as a minimum) into kinetic energy of the target fragments. So the portion of the last kinetic energy allows us to estimate the primary energy los
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