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The TOTEM experiment, small in size compared to the others at the LHC, is dedicated to the
measurement of the total proton-proton cross-sections with a luminosity-independent method and
to study elastic and diffractive scattering at the LHC. Hence the TOTEM collaboration focuses on
physics complementary to the programs of the general-purpose experiments at the LHC, and therefore
had to invest heavily in the design of detectors that will be capable of meeting the challenge of triggering
and recording events in the very forward region. To achieve optimum forward coverage for charged
particles emitted by the pp collisions in the IP5 interaction point, two tracking telescopes, T1 and
T2, will be installed on each side in the pseudo-rapidity region between 3.1 and 6.5, and RomanPot (RP) stations will be placed at distances of 147m and 220m from IP5 .
The telescope closest to the interaction point (T1, centered at z = 9 m) consists of Cathode Strip
Chambers (CSC), while the second one (T2, centered at 13.5 m) makes use of Gas Electron
Multipliers (GEM).
To have a lever arm for local track reconstruction and trigger selections by track angle, each RP
station is composed of two units separated by a few meters distance limited by integration
constraints with the other beam elements. Each RP unit consists of 3 pots, two approaching the
beam vertically and one horizontally . A total of 8 identical RP units or 24 individual pots
are installed in the LHC. The proton detectors in the Roman Pots are silicon devices designed by
TOTEM with the specific objective of reducing down to a few tens of microns the insensitive
area at the edge. High efficiency as close as possible to the physical detector boundary is an
essential feature in view of maximizing the experimental acceptance for protons scattered
elastically or diffractively at polar angles down to a few micro-radians at IP5. To measure
protons at the lowest possible emission angles, special beam optics has been conceived to
optimize proton detection in terms of acceptance and resolution. The read-out of all TOTEM
subsystems is based on the custom-developed digital VFAT chip with trigger capability. The
data acquisition system is designed to be compatible with the CMS DAQ to make common data
taking possible at a later stage.
