Speaker
Description
During the upcoming LHC Long Shutdown 3 the ALICE experiment will upgrade
its 3 Inner Tracking System (ITS2) layers to ITS3. The final design of ITS3 will
have silicon sensors of up to 27 cm × 10 cm, thinned to about 50µm and bent
into a cylindrical shape. The sensor prototypes developed are MOnolithic Stitched
Sensors (MOSS) that are made of 10 Repeated Sensor Units (RSU). A single-RSU,
referred to as a babyMOSS, is manufactured to facilitate in- beam characterization
and irradiation studies. Each babyMOSS has a top and bottom half-unit (HU). The
difference between these half units is the pitch of the pixels, with the top HU having
a pixel pitch of 22.5µm and the bottom HU having a pixel pitch of 18µm.
The design of the pixel features a low-doped, deep n-type implant in the pixel,
which helps to deplete the pixel over its full area. Implants of neighboring pixels
are separated by a gap, which enhances charge collection near pixel edges. For a
subset of sensors, and only for pixels with a 22.5 µm pitch, the pixel-to-pixel gap
width was increased from the baseline 2.5 µm to 5.0 µm.
This presentation provides results from the test beam on babyMOSS chips per-
formed in September 2025 at the CERN PS with a telescope composed of six baby-
MOSS tracking planes. For this testbeam, two babyMOSS sensors representing dif-
ferent pixel variants were tested with negatively charged pions of 7 GeV. A cooling
plate was provided to keep the babyMOSS devices under test at a constant tem-
perature of 27◦C. Time over Threshold (ToT) data were collected in the testbeam,
along with source and pulsing data separately for a ToT analysis. This analysis is
to study charge collection in the babyMOSS prototype for different reverse biases
and for different pixel variants.