Real time tracker based upon local hit correlation circuit for silicon strip sensors

For the planned high luminosity upgrade of the Large Hadron Collider (LHC), a significant performance improvement of the detectors is required, including new tracker and trigger systems that makes use of charged track information early on. In this note we explore the principle of real time track reconstruction integrated in the readout electronics. A prototype was built using the silicon strip sensor for the ATLAS phase-II upgrade. The real time tracker is not the baseline for ATLAS but is nevertheless of interest, as the upgraded trigger design has not yet been finalized. For this, a new readout scheme in parallel with conventional readout, called the Fast Cluster Finder (FCF), was included in the latest prototype of the ATLAS strip detector readout chip (ABC130). The FCF is capable of finding hits within 6 ns and transmitting the found hit information synchronously every 25 ns. Using the FCF together with external correlation logic makes it possible to look for pairs of hits consistent with tracks from the interaction point above a transverse momentum threshold. A correlator logic finds correlations between two closely spaced parallel sensors, a “doublet”, and can generate information used as input to a lowest level trigger decision. Such a correlator logic was developed as part of a demonstrator and was successfully tested in an electron beam. The results of this test beam experiment proved the concept of the real time track vector processor with FCF.