KLOE-2 Inner Tracker: the First Cylindrical GEM Detector

Abstract

KLOE-2 at the DA$\Phi$NE $e^+ e^- $ collider is the main experiment of the INFN Laboratori Nazionali di Frascati (LNF) and is the first high-energy experiment using GEM technology with a cylindrical geometry, a novel detector developed at LNF exploiting kapton properties. Four concentric cylindrical triple-GEM detectors compose the Inner Tracker, inserted around the interaction region and before the inner wall of the pre-existing KLOE Drift Chamber, to improve the resolution on decay vertices close to the interaction point and reconstructed from low-momentum charged secondaries. State-of-the-art solutions have been expressly developed or tuned for this project: single-mask GEM etching, now used also for several LHC experiments upgrades, multi-layer XV patterned readout circuit, PEEK spacer grid, GASTONE front-end board a custom 64-channel ASIC with digital output, and the Global Interface Board for data collection, with a configurable FPGA architecture and Gigabit Ethernet. Alignment and calibration of a cylindrical GEM detector was never done before and represented one of the experiment's challenging activities. The first set of alignment and calibration parameters obtained with cosmic-ray muon data has been used to validate the integrated tracking and vertexing using both Inner Tracker and Drift Chamber information, exploiting the Kalman filter technique. Results obtained with $\phi\to \pi^+ \pi^- \pi^0$ and $K_S \to \pi^+ \pi^- $ samples will be reported. KLOE-2 is presently taking data with the aim of collecting more than 5 fb$^{-1}$ by March 2018. The success of the cylindrical GEM technology developed by the KLOE-2 collaboration paved the way to its usage in other high-energy physics experiments, among these is the BES III experiment at BEPC II.