This paper discusses the criteria that have been adopted to optimize the signal processing in a shower detector to be employed as LHC beam luminosity monitor. The original aspect ofthis instrument is its ablility to operate on a bunch-by-bunch basis. This means that it must perform accurate charge measurements at a repetition rate of 40 MHz. The detector must withstand an integrated dose of 100 Grad, that is, two to three orders of magnitude beyond those expected in the experiments. To meet the above requirements, an ionization chamber consisting of several gaps of thickness 0.5 mm, filled with a gas that is expected to be radiation resistant, has been designed. Crucial in the development of the system is the signal processing, as the electronic noise may set the dominant limitation to the accuracy of the measurement. This is related to two aspects. One is the short time available for the charge measurement. The second one is the presence of a few meter cable between the detector and the preamplifier, as this must be located out of the region of highest radiation field. Therefore the optimization of the signal-to-noise ratio requires that the best configuration of the chamber gaps be determined under the constraint of the presence of a cable of non-negligible length between detector and preamplifier. The remote placement of the amplifying electronics will require that the front-end electronics be radiation hard although to a lesser extent than the detector.

This paper discusses the criteria that have been adopted to optimize the signal processing in a shower detector to be employed as LHC beam luminosity monitor. The original aspect ofthis instrument is its ablility to operate on a bunch-by-bunch basis. This means that it must perform accurate charge measurements at a repetition rate of 40 MHz. The detector must withstand an integrated dose of 100 Grad, that is, two to three orders of magnitude beyond those expected in the experiments. To meet the above requirements, an ionization chamber consisting of several gaps of thickness 0.5 mm, filled with a gas that is expected to be radiation resistant, has been designed. Crucial in the development of the system is the signal processing, as the electronic noise may set the dominant limitation to the accuracy of the measurement. This is related to two aspects. One is the short time available for the charge measurement. The second one is the presence of a few meter cable between the detector and the preamplifier, as this must be located out of the region of highest radiation field. Therefore the optimization of the signal-to-noise ratio requires that the best configuration of the chamber gaps be determined under the constraint of the presence of a cable of non-negligible length between detector and preamplifier. The remote placement of the amplifying electronics will require that the front-end electronics be radiation hard although to a lesser extent than the detector.

The LHC beam luminosity monitor is based on the following principle. The neutrals that originate in LHC at every PP interaction create showers in the absorbers placed in front of the cryogenic separation dipoles. The shower energy, as it can be measured by suitable detectors in the absorbers is proportional to the number of neutral particles and, therefore, to the luminosity. This principle lends itself to a luminosity measurement on a bunch-by-bunch basis. However, detector and front-end electronics must comply with extremely stringent requirements. To make the bunch-by-bunch measurement feasible, their speed of operation must match the 40 MHz bunch repetition rate of LHC. Besides, in the actual operation the detector must stand extremely high radiation doses. The front-end electronics, to survive, must be located at some distance from the region of high radiation field, which means that a properly terminated, low-noise, cable connection is needed between detector and front-end electronics. After briefly reviewing the solutions that have been adopted for the detector and the front-end electronics and the results that have been obtained so far in tests on the beam, the latest version of the instrument in describe in detail. It will be shown how a clever detector design, a suitable front-end conception based on the use of a "cold resistance" cable termination and a careful low-noise design, along with the use of an effective deconvolution algorithm, make the luminosity measurement possible on a bunch-by-bunch basis at the LHC bunch repetition rates.