The Totem Experiment at the Lhc

In order to fulfil its physics programme the TOTEM experiment1 has to cope with the challenge of triggering and recording events in the very forward region with a good acceptance for particles produced at very small angles with respect to the beam. The evaluation of the total cross section with an error down to 1÷2% will in particular require the simultaneous measurement of the elastic scattering at low values for the squared four-momentum transfer (|t| ∼ (pθ)) as well as of the inelastic interaction rate with losses reduced to few per-cents. This involves the detection of scattered protons at a location very close to the beam, together with efficient forward particle detection in inelastic events. A flexible trigger provided by its detectors will allow to take data under all LHC running scenarios. The combination of the CMS 2 and TOTEM experiments, representing the largest acceptance detector ever built at a hadron collider, will also allow the study of a wide range of diffractive processes with an unprecedented coverage in rapidity. For this purpose the TOTEM trigger and data acquisition (DAQ) systems are designed to be compatible with the CMS ones, in order to allow common data taking periods foreseen at a later stage 3. In the following, after a general overview of the experimental apparatus, the main features of the TOTEM physics programme will be described.