New detector for studies of cumulative processes in hadron collisions in NA61(SHINE) at the CERN SPS

Abstract

Abstract. The increase of luminosity of the SPS beams expected after 2020 allows considering the investigation of rather rare processes. In particular, so-called cumulative particle production can be studied in hadron collisions by measurements of secondary particle yields in regions kinematically forbidden for reactions with free nucleons. Such processes could be either a result of hard parton collisions with some large-density multi-quark configuration or of the formation of heavy baryonic resonances. Measurements in the backward hemisphere in fixed target experiment should provide the event-by-event data that could be used, along with those from the forward region, for a correlation analysis, thus resulting in new constraints on models. In this report the preliminary design, ideas, technology and the first GEANT simulations of a proposed new detector are presented and discussed. IntroductionProduction of particles from nuclei in a region, kinematically forbidden for reactions with free nucleons is called the cumulative effect.The first clear experimental confirmation of the cumulative effect was obtained by the group of A.M. Baldin and V.S. Stavinsky in Dubna, where in 1971 the first relativistic deuteron beams were produced [1,2]. In these experiments the emission of pions with energy higher than half of the energy of the incident deuterons was observed. The classical explanation of this effect is the presence of nuclear fluctons, droplets of cold dense nuclear matter in nuclei, composed of a few nucleons. Nevertheless, one has to keep in mind that some contribution from rescattering processes at large (nuclear) distances on several free nucleons is possible.From the modern point of view fluctons in nuclei must be interpreted as the presence of multi-quark (6q-, 9q-, 12q-and so on) clusters in nuclear matter, allowing two mechanisms of cumulative fragment production. The first is fragmentation of one fast quark of the flucton into a cumulative hadron [3], and the second proposes cumulative hadron formation due to the coherent coalescence of three fast flucton quarks in the framework of the Coherent Quark Coalescence (CQC) model as formulated in [4]. The latter mechanism is more convenient for the production of cumulative nucleons. The dominant process for the production of light cumulative fragments, e.g. deuterons, is coherent coalescence of weakly virtual nucleons [5]. In contrast to the treatment of fluctons as droplets of cold QGP some theories propose that clusters appear due to the formation and subsequent statistical decay of massive hadron clusters (fireballs) [6][7][8]. The observed particles, i.e. mesons, nucleons, and light nuclei are emitted from the fireball. This approach allows to successfully describe the momentum spectra of protons and light nuclei