Real-time Track Reconstruction with FPGAs: an example from MUonE

Abstract

The feasibility of real-time track fitting of straight tracks for online event selection is shown in the context of the MUonE experiment. In order to reach the high throughput and low latency required for real-time track fitting, the tracking algorithm is implemented using High-Level Synthesis for an FPGA, which provides provides a balance between flexibility and performance. Hardware tracking results from a test with high-rate muons at the CERN M2 beam are presented. This test, a joint effort by the MUonE and Compact Muon Solenoid (CMS) experiments, operated with Two-Strip (2S) modules provided by the CMS tracker group. The prototype version of the fitter used in this test achieves 3.75 $μ$s latency and 7.75 % resource use. A comparison of the results with those obtained from a pure software implementation shows agreement well below relevant uncertainty scales. Developments since the test are also presented, with the hardware algorithm now reaching 1.35 $μ$s latency and producing pipelined fitting results above 50 MHz while requiring less resources than the initial version. Doing so required including certain assumptions in the algorithm, but these assumptions hold for linear track fitting in general and algorithm remains useful in contexts other than MUonE.