A luminosity monitor for LHC

The Large Hadron Collider (LHC) under construction at CERN will give high luminosities to experiments covering six orders of magnitude from of 1028 cm-2s-1 to 1034 cm-2s-1. A new approach is needed to measure the LHC luminosity. This work reports the study of a LHC luminosity monitor based on the concept of Secondary Emission Chamber (SEC). The main request for such a detector is to cover the six orders of magnitude of the LHC luminosity range. Its precision is expected to be of the order of 2 %. The TOTEM collaboration proposes to calibrate the monitor at low luminosity. The construction of the detector based on the previous SECs developed years ago at CERN is presented. The performances of the new prototype are determined for incident currents between ~10-12 A and 10-13 A. The tests lead to conclude that at the LHC the SEC will be able to measure luminosity with a precision of 3 % within 1 s for luminosity above 1031 cm-2s-1. A conversion of the SEC into an Ionisation Chamber (IC) is proposed to cover the LHC low luminosity region. It is achieved by filling the SEC with argon at atmospheric pressure. The IC response is found to be linear with the foreseen precision over the full experimental range of intensity corresponding to currents between 10-15 A and 10-12 A. The linear continuity between the responses of the monitor in the SEC and the IC modes is observed. We propose to use, at the LHC, the detector in the IC mode at low luminosity and in the SEC mode at high luminosity with a switch in mode at a luminosity of ~ 1031 cm-2s-1.