Abstract
The ATLAS Roman Pot system is designed to determine the total proton-proton cross section as well as the luminosity at the Large Hadron Collider (LHC) by measuring elastic proton scattering at very small angles. The system is made of four Roman Pot stations, located in the LHC tunnel in a distance of about 240 m at both sides of the ATLAS interaction point. Each station is equipped with tracking detectors, inserted in Roman Pots which approach the LHC beams vertically. The tracking detectors consist of multi-layer scintillating fibre structures read out by Multi-Anode-Photo-Multipliers.
Highlights
This article describes all aspects of the ALFA detector which is part of the ATLAS [1] experiment at the LHC
In October 2016, data were taken with an ultra-high β∗ ≈ 2500 m
This opens the possibility to measure the luminosity solely based on elastic scattering
Summary
This article describes all aspects of the ALFA detector which is part of the ATLAS [1] experiment at the LHC. Elastic scattering in the very forward direction can be used to measure the total cross section, σtot, and the luminosity, L, at a collider. The optical theorem connects the total cross section, σtot, to the elastic scattering amplitude, fel, and states: σtot = 4π Im [ fel (t = 0)]. Roman Pots [6] have been used at all pp or pp colliders to position detectors very close to the circulating beam. ATLAS has chosen to equip the Roman Pots with tracking detectors based on scintillating fibres This option has two advantages: the fibres are sensitive up to their physical edge, and they cannot interact with induced electro-magnetic noise from the circulating beams.
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