Upgrade of the ALICE inner tracking system

摘要

The Inner Tracking System (ITS) is the key ALICE detector for the study of heavy flavor production at LHC. Heavy flavor can be studied via the identification of short-lived hadrons containing heavy quarks which have a mean proper decay length in the order of 100-300 μm. To accomplish this task, the ITS is composed of six cylindrical layers of silicon detectors (two pixel, two drift and two strip) with a radial coverage from 3.9 to 43 cm and an average material budget of 1.1% XO per layer. In order to enhance the ALICE physics capabilities, and, in particular, the tracking performance for heavy-flavor detection, the possibility of an ITS upgrade has been studied in great detail. It will make use of the spectacular progress made in the field of imaging sensors over the last 10 years as well as the possibility to install a smaller radius beampipe. The upgraded detector will have greatly improved features in terms of the impact parameter resolution, standalone tracking efficiency at low p_t, momentum resolution and readout capabilities. The usage of the most recent monolithic and/or hybrid pixel detector technologies allows the improvement of the detector material budget and the intrinsic spatial resolution both by a factor of three with respect to the present ITS. The installation of a smaller beam-pipe reduces the distance between the first detector layer and the interaction vertex. Under these assumptions, simulations show that an overall improvement of the impact parameter resolution by a factor of three is possible. The Conceptual Design Report for the Upgrade of the ALICE ITS, which covers the design and performance requirements, the upgrade options, as well as the necessary R&D efforts, was made public in September 2012. An intensive R&D program has been launched to review the different technological options under consideration. The new detector should be ready to be installed during the long LHC shutdown period scheduled in 2017-2018.