Online Data Reduction for the Belle II Experiment using DATCON

TL;DR

The paper presents an FPGA-based online data reduction system for the Belle II experiment that efficiently reduces data volume while maintaining high ROI detection efficiency, enabling better handling of high-luminosity collision data.

Contribution

It introduces DATCON, a novel FPGA-based system for real-time track reconstruction and data reduction in the Belle II experiment, improving data handling at high luminosity.

Findings

Data stream reduced by a factor of ten.

ROI finding efficiency exceeds 90%.

Effective track reconstruction using Hough transformations.

Abstract

The new Belle II experiment at the asymmetric $e^+ e^-$ accelerator SuperKEKB at KEK in Japan is designed to deliver a peak luminosity of $8\times10^{35}\text{cm}^{-2}\text{s}^{-1}$. To perform high-precision track reconstruction, e.g. for measurements of time-dependent CP-violating decays and secondary vertices, the Belle II detector is equipped with a highly segmented pixel detector (PXD). The high instantaneous luminosity and short bunch crossing times result in a large stream of data in the PXD, which needs to be significantly reduced for offline storage. The data reduction is performed using an FPGA-based Data Acquisition Tracking and Concentrator Online Node (DATCON), which uses information from the Belle II silicon strip vertex detector (SVD) surrounding the PXD to carry out online track reconstruction, extrapolation to the PXD, and Region of Interest (ROI) determination on the PXD. The data stream is reduced by a factor of ten with an ROI finding efficiency of >90% for PXD hits inside the ROI down to 50 MeV in $p_\text{T}$ of the stable particles. We will present the current status of the implementation of the track reconstruction using Hough transformations, and the results obtained for simulated \Upsilon(4S) $\rightarrow \, B\bar{B}$ events.