Speaker
Description
To provide precicely bunch-to-bunch luminosity measurement of SuperKEKB, the fast luminosity detector should have less than 4 ns signal width and be radiaitonharded. At SuperKEKB, this has been demonstrated using CVD diamond detectors at 4m from the IP. LGADs (Low Gain Avalanche Diode) have recently been installed at SuperKEKB and tested as a potential alternative with the Lumibelle2 collaboration. This sensor has a much faster rise time and shorter signal width on the order of a nanosecond, which is more suitable for the fast bunch-to-bunch luminosity measurement. The areas of the LGAD detector is 3.9mm x 7.5mm and 7.5 mm x 7.5mm are operated in a single-channel parallel-readout scheme.The detector was characterized on the bench with a 90Sr 𝛽source under different bias voltages, and front-end coupling/shaping capacitance settings. The signal amplitude, baseline noise, pulse width,
and timing-related waveform properties were evaluated. Laboratory tests show that the LGAD
readout chain provides clearly distinguishable signal amplitudes, low baseline noise, and pulse
widths below the nominal 4 ns bunch spacing of SuperKEKB. After installation in the LER
and HER regions of SuperKEKB, beam data recorded during operation show that the precision of the LGAD
could be ~2% and provide much higher counting rates than the current diamond channels.These results indicate that the LGAD-based detector can provide a stronger and statistically more precise signal for fast luminosity monitoring.