Studies on monolithic active pixel sensors for the Inner Tracking System upgrade of ALICE experiment

Abstract

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC. It is designed to study the physics of strongly interacting matter, and in particular the properties of the Quark-Gluon Plasma (QGP), using nucleus- nucleus collisions at unprecedented energy densities. One of the major goals of the ALICE physics program is the study of rare probes at low transverse momentum. The reconstruction of the rare probes requires a precise determination of the primary and secondary vertices that is performed in ALICE by the Inner Tracking System (ITS). The present ITS made of 6 layers of three technologies of silicon devices allows, for example, to reconstruct D mesons with the transverse momentum down to ∼ 2 GeV/c. In order to enhance the ALICE physics capabilities, and, in particu- lar, the tracking performance for heavy-flavour detection, an upgrade of the ITS has been planned for the second long shutdown of LHC (LS2) in 2017/18. The upgraded detector will have greatly improved features in terms of impact parameter resolution, standalone tracking efficiency at low p T , momentum resolution and readout capabilities. Monolithic Active Pixel Sensors (MAPS) can offer a granularity 50 times larger than in current ITS and also significantly reduce the ma- terial budget. Therefore, MAPS were chosen to be implemented in all layers of the new ITS. In the present work the characteristics of MAPS prototypes in the ALICE upgrade framework were studied, including noise performances, response to soft X-rays emitted by 55 Fe source, signal to noise ratio, detection efficiency and spatial resolution. Morever a development of a testbeam telescope setup designed to perform a comparative study of the first two full scale MAPS proto- types designed for the ALICE ITS will be discussed