Forward shower counters for diffractive physics at the LHC

The LHC detectors have incomplete angular coverage in the forward direction, for example in the region 6 less than or similar to vertical bar eta vertical bar less than or similar to 8, which can be improved with the addition of simple scintillation counters around the beam pipes about 50 m to 120 m from the intersection point. These counters detect showers created by particles hitting the beam pipes and nearby material. The absence of signals in these counters in low pileup conditions is an indication of a forward rapidity gap as a signature of diffraction. In addition, they can be used to detect hadrons from low mass diffractive excitations of the proton, not accompanied by a leading proton but adjacent to a rapidity gap over (e. g.) 3 less than or similar to vertical bar eta vertical bar less than or similar to 6. Such a set of forward shower counters, originally used at CDF, was used in CMS (FSC) for high-beta* running with TOTEM during LHC Run-1. During LS1 the CMS FSC system is being upgraded for future low pileup runs. A similar system, called HERSCHEL is being installed in LHCb. ALICE is implementing scintillation counters, ADA and ADC, with 4.5 less than or similar to vertical bar eta vertical bar less than or similar to 6.4.