• vertex detector
• silicon detector
• superkekb
• belle ii
• event time

My thesis work focuses on the estimate of the event time with the Silicon Vertex Detector (SVD), which is a 4-layer device based on double-sided strip detector readout by fast electronics (the APV25 chip developed for the CMS experiment). % whose backward regions modules are developed in Pisa.
It has a high hit detection efficiency ($>$99\% for most sensors) and a time resolution on crossing particles of 2-4ns. Its properties are briefly discussed, starting from the functioning principles of strip detectors, and going through the data acquisition modality, controlled by the APV25 front-end electronics, and the cluster (set of adjacent strips, crossed by a particle, that pass precise selection criteria) reconstruction.

The event time is estimated with an algorithm, that I developed, computing it as the average of times of the SVD clusters that are used in the tracking.
I studied a selection of the tracks and of the clusters associated to tracks in order to improve the event time resolution and avoid biases in the results while keeping a very high efficiency. The performance of the SVD event time estimator can be compared to the estimates provided by other sub-detectors in terms of efficiency and resolution, evaluated both on simulated events with nominal background, and on data, acquired in 2021, for different types of events (hadronic, muonic, bhabha). The performance is very good: $\sim$99.8\% absolute efficiency, higher than the one of other detectors, and 8.6ns standard deviation, compatible with the trigger jitter, on hadronic events. The resolution on the residuals between the event time computed by the Silicon Vertex Detector and by the other sub-detectors is $\mathcal{O}$(1ns); moreover, the execution time in the online reconstruction of the module that computes the event time in the Silicon Vertex Detector is around 2000 times shorter than those of the other sub-detectors: thanks to this excellent result, the algorithm will be implemented in the next release of the Belle II software.
The excellent event time resolution and the high absolute efficiency should allow a better beam background rejection, and should make it easier to retain good physics performance while increasing the luminosity.