1. Beam Test Results for the CMS Forward Pixel Detector
The Telescope
The FPIX Sensor
Pixel Data
150mm x 150mm pixel
thickness 270mm
22x30 pixel array
unirradiated sensor
The pixels on the silicon sensor were bump bonded to a DMILL readout chip (PSI36).
250GeV/c pion beam
Repeater card can be rotated
Triggering on region as small as 1mm2 possible
Semiconductor detectors are “diodes”
By applying a reverse bias voltage to it the depletion zone can be enlarge until it the sensor is fully depleted
If an ionizing particle passes through the bulk it creates electron-hole pairs
Charge carriers move in the E-field and are collected to give the signal
How does a Pixel Detector work ?
Signal to Noise Ratio
Signal height:
Noise:
Signal to noise
ratio of 60
Charge sharing studies
Resolution obtained by Sensors
Resolution in micron between
rows (not rotated)
Resolution in micron between rows (rotated by 20o)
Charge sharing was studied by plotting the sum of the fraction of charge that the center hit pixel shared with its neighbors in a column versus the hit position.
Two cases of beam incidence were investigated.
Charge sharing between rows (not rotated)
Charge sharing between rows (rotated by 20o)
A is a normalization
factor
Comparison of the resolution vs. the hit position for the beam at 20o and 0o incidence.
0o rotation
20o rotation
A function
calculates the difference of the fraction of charge deposited in the neighboring pixels.
Comparison of resolution vs. fraction of charge shared for beam at 20o and 0o incidence.
Position correction curve
Charge sharing can improve the resolution
Highest resolution for large charge sharing
Resolution at 20o rotation mm
Resolution at 0o rotation mm
Resolution is position dependent
Conclusions
Probability function of occurrence of a certain h in an event