Orateur
Description
An upgraded vertex detector (or VTX) is in development for the Belle II
experiment. A central concept of the VTX is the usage of a new CMOS
monolithic pixel sensor, OBELIX. The design of this sensor offers new
possibilities for specific read-out modes, such as a fast output for
track-triggering purpose with degraded spatial granularity.
That means the nearly 400 000 pixels of OBELIX are reduced to only 8
macro-pixels, shaped as strips.
This contribution reports the first study investigating the tracking
performance with such macro-pixels and simulations reproducing the VTX
geometry.
A track reconstruction algorithm is developped based on a large look-up
table containing simulated single track hit pattern over three VTX outer
layers. The algorithm is then applied to various simulated data sets as
test samples to evaluate figures of merit.
The reconstruction efficiency exceeds 98 % in average but features a clear
decrease at low momentum below 500 MeV/c. The sensitivity to tracks drops
very rapidly with the distance along the beam axis between the track
origin and the collission point. After a few centimers, no more tracks can
be reconstructed.
These early results show that the low granularity mode is a promising
solution for building a trigger decision based on tracks reconstructed
with the OBELIX sensor.
