Speaker
Lia Lavezzi
(高能所)
Description
The CGEM-IT (Cylindrical GEM - Inner Tracker) is the upgrade of the
internal tracking system of the BESIII experiment, running at BEPCII in
Beijing, China. The subdetector is currently under construction and its
installation in the spectrometer is foreseen in 2018, after a final
verification that its performance matches the BESIII requirements.
The layout consists of three layers of cylindrically-shaped triple GEMs,
with some important innovations with respect to the existing GEM
detectors, in order to achieve the best performance with the lowest
material budget.
It will be the first cylindrical GEM running with analog readout inside a
1T magnetic field. The analog readout provides the simultaneous
measurement of both the deposited charge and the signal time. Thanks to
this, the CGEM-IT reconstruction will use a combination of two algorithms
to evaluate the spatial position of the charged tracks inside its volume:
the charge centroid and the micro time projection chamber. The two modes
are complementary and can cope with the asymmetry of the electron
avalanche when running in magnetic field and with non-orthogonal incident
tracks.
Both planar chambers and the first cylindrical layer prototype have been
tested during various test beams on the H4 line of SPS (CERN) with muons
and pions of momentum = 150 GeV/c, to evaluate their behaviour under
different working settings.
The efficiencies and resolutions obtained with the two modes will be shown
as well as a comparison between the planar and cylindrical chambers.
