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ATLAS Forward Proton Project
The ATLAS Forward Proton Project (AFP project) is a project at the ATLAS experiment at the Large Hadron Collider to detect protons in its forward area. It began with research and development in 2004 and was approved in 2015.
The initial FP420 R&D project was an international collaboration with members from 29 institutes from 10 countries, with aim of assessing the feasibility of installing proton tagging detectors at 420m from the interaction points of the ATLAS and CMS experiments. The main area of interest that motivated the project was the study proton-proton interactions and central exclusive production in the forward area of the machine. The particles involved travel down the forward area of the beam-pipe, where most of the energy emitted from collisions travels, but have smaller momenta than the original proton beams and have trajectories that diverge from it (because they are bent by different amounts by the collider magnets) and eventually hit the beam-pipe walls in places where they can be detected separately from the original beam. So this required installing new proton detectors at various distances along that beam-pipe. The existing ALFA proton detectors at ATLAS were only suitable for low-energy runs, whereas the new detectors were intended for high-energy collision measurements.
The research and development for the AFP project began in 2004. An initial letter of intent was submitted in 2009. The initial goal was to have two sets of proton detectors positioned in groups denoted "220" (at 216m and 224m distance) and "420" (at 416m and 424m), but the project was delayed in 2010 by the United Kingdom cutting funding, resulting in a decision to abandon the 420 detectors and only have the 220 ones. (The 420 detectors would in any case have presented greater technical difficulties over the 220 ones, as they would have involved also altering the liquid helium system already present at that location, and although necessary for Higgs boson studies they were not necessary for other studies.)
This reduced project went through a formal Technical Proposal stage, and was in 2012 approved by the ATLAS Collaboration Executive Board and endorsed by the LHC Experiments Committee. There were technical reviews in 2014, with the project getting ATLAS Upgrade approval in June of that year. An initial test beam that November demonstrated that the various systems were correctly integrated, and after a kick-off meeting on 2015-02-03 the ATLAS Executive Board confirmed its decision on 2015-02-30. At the time, installation of the detectors was aimed to be completed by 2017, for use in LHC Run 2.
The detectors at 216m are known as the "near" detectors, and the ones at 224m the "far" detectors, their separation being 15σ. They first began to collect data from LHC runs in 2016, but only in low-luminosity ones. From 2017 they were collecting data from all LHC runs.
The silicon tracking detectors (SiT) used in the project were modelled on the Insertable B-Layer (IBL) detector at ATLAS, using pixel measurements combined with magnet data to provide momentum spectrometry. In order to provide the ability to remove and re-insert the detectors they are mounted inside Roman pots. Each of the "far" detectors also includes a time-of-flight detector, designed to reduce "pile up" by measuring the differences in particle time-of-flight on both sides of the ATLAS interaction point and comparing it to the reconstructed position of the collision vertex. The time of flight detectors comprise a microchannel-plate photomultiplier (MCP-PMT) reading L-shaped quartz bars. Of particular concern is degradation caused by backscatter of positive ions, to combat which the photomultipliers are coated using atomic layer deposition. They are expected to withstand 3×1015 neq/cm2 per 100 fb−1. Earlier designs for ToF called QUARTIC ("QUARtz TIming Cherenkov") were based on straight quartz bars. Originally, an alternative system named GASTOV was considered, which used a gas rather than quartz to generate the Cherenkov radiation recorded by the photomultiplier.
The silicon pixel sensors are positioned 2mm to 3mm from the beam. The construction of the pixel sensors is complicated by the uneven radiation doses that they receive over the course of their operating lifetimes. To harden them against this radiation their manufacture is more complex than that of a simple planar arrangement.
Their operating temperature also affects performance, and they are operated at a temperature of −20 °C with primary (Vortex Tube) and secondary (a vacuum kept between 5mbar and 30mbar) cooling systems. The vacuum system has a useful side-effect of reducing the mechanical stress caused by atmospheric pressure on the Roman pots, which have thin windows and floors.
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ATLAS Forward Proton Project AI simulator
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ATLAS Forward Proton Project
The ATLAS Forward Proton Project (AFP project) is a project at the ATLAS experiment at the Large Hadron Collider to detect protons in its forward area. It began with research and development in 2004 and was approved in 2015.
The initial FP420 R&D project was an international collaboration with members from 29 institutes from 10 countries, with aim of assessing the feasibility of installing proton tagging detectors at 420m from the interaction points of the ATLAS and CMS experiments. The main area of interest that motivated the project was the study proton-proton interactions and central exclusive production in the forward area of the machine. The particles involved travel down the forward area of the beam-pipe, where most of the energy emitted from collisions travels, but have smaller momenta than the original proton beams and have trajectories that diverge from it (because they are bent by different amounts by the collider magnets) and eventually hit the beam-pipe walls in places where they can be detected separately from the original beam. So this required installing new proton detectors at various distances along that beam-pipe. The existing ALFA proton detectors at ATLAS were only suitable for low-energy runs, whereas the new detectors were intended for high-energy collision measurements.
The research and development for the AFP project began in 2004. An initial letter of intent was submitted in 2009. The initial goal was to have two sets of proton detectors positioned in groups denoted "220" (at 216m and 224m distance) and "420" (at 416m and 424m), but the project was delayed in 2010 by the United Kingdom cutting funding, resulting in a decision to abandon the 420 detectors and only have the 220 ones. (The 420 detectors would in any case have presented greater technical difficulties over the 220 ones, as they would have involved also altering the liquid helium system already present at that location, and although necessary for Higgs boson studies they were not necessary for other studies.)
This reduced project went through a formal Technical Proposal stage, and was in 2012 approved by the ATLAS Collaboration Executive Board and endorsed by the LHC Experiments Committee. There were technical reviews in 2014, with the project getting ATLAS Upgrade approval in June of that year. An initial test beam that November demonstrated that the various systems were correctly integrated, and after a kick-off meeting on 2015-02-03 the ATLAS Executive Board confirmed its decision on 2015-02-30. At the time, installation of the detectors was aimed to be completed by 2017, for use in LHC Run 2.
The detectors at 216m are known as the "near" detectors, and the ones at 224m the "far" detectors, their separation being 15σ. They first began to collect data from LHC runs in 2016, but only in low-luminosity ones. From 2017 they were collecting data from all LHC runs.
The silicon tracking detectors (SiT) used in the project were modelled on the Insertable B-Layer (IBL) detector at ATLAS, using pixel measurements combined with magnet data to provide momentum spectrometry. In order to provide the ability to remove and re-insert the detectors they are mounted inside Roman pots. Each of the "far" detectors also includes a time-of-flight detector, designed to reduce "pile up" by measuring the differences in particle time-of-flight on both sides of the ATLAS interaction point and comparing it to the reconstructed position of the collision vertex. The time of flight detectors comprise a microchannel-plate photomultiplier (MCP-PMT) reading L-shaped quartz bars. Of particular concern is degradation caused by backscatter of positive ions, to combat which the photomultipliers are coated using atomic layer deposition. They are expected to withstand 3×1015 neq/cm2 per 100 fb−1. Earlier designs for ToF called QUARTIC ("QUARtz TIming Cherenkov") were based on straight quartz bars. Originally, an alternative system named GASTOV was considered, which used a gas rather than quartz to generate the Cherenkov radiation recorded by the photomultiplier.
The silicon pixel sensors are positioned 2mm to 3mm from the beam. The construction of the pixel sensors is complicated by the uneven radiation doses that they receive over the course of their operating lifetimes. To harden them against this radiation their manufacture is more complex than that of a simple planar arrangement.
Their operating temperature also affects performance, and they are operated at a temperature of −20 °C with primary (Vortex Tube) and secondary (a vacuum kept between 5mbar and 30mbar) cooling systems. The vacuum system has a useful side-effect of reducing the mechanical stress caused by atmospheric pressure on the Roman pots, which have thin windows and floors.