Upgraded Cherenkov time-of-flight detector for the AFP project.

We present the results of our performance studies of the upgraded Cherenkov time-of-flight (ToF) detector for the AFP (ATLAS Forward Proton) project. The latest version consists of solid L-shaped fused silica bars, new customized ALD-coated micro-channel plate photomultipliers (MCP-PMTs) miniPlanacon XPM85112-S-R2D2 with an extended lifetime which operate at low gains (order of 103), and an updated construction. The improvements were aimed to increase the efficiency, the lifetime as well as the radiation hardness of the detector which has been designed to operate in high radiation areas (above 400 kGy/year). The detector was finally tested at the CERN-SPS test-beam facility (120 GeV π+ particles) in August 2021 prior to its installation at the Large Hadron Collider (LHC) at CERN. Measurements proved the detector kept its inner timing resolution of 20 ps despite the rather low gain of its photodetector and reduced optical throughput caused by inevitable changes in the detector geometry.

Performance studies of new optics for the time-of-flight detector of the AFP project.

We present the results of performance studies of the upgraded optical part of the time-of-flight subdetector prototype for the AFP (ATLAS Forward Proton) detector obtained during the test campaign in a synchrotron test-beam facility with 5 GeV electrons at the DESY laboratory (Hamburg, Germany) in June 2019. The detection of the particle arrival time is based on generation of Cherenkov light in an L-shaped fused silica bar. In the previous version of the ToF, all bars were made of two pieces (radiator and light guide) glued together with a dedicated glue (Epotek 305). This solution suffers from additional radiation damage of glue. We adopted a new technique of bar production without the need of glue. The new bars have a higher optical throughput by a factor of 1.6, reduced fragility, and better geometrical precision.

BRDF profile of Tyvek and its implementation in the Geant4 simulation toolkit.

Diffuse and specular characteristics of the Tyvek 1025-BL material are reported with respect to their implementation in the Geant4 Monte Carlo simulation toolkit. This toolkit incorporates the UNIFIED model. Coefficients defined by the UNIFIED model were calculated from the bidirectional reflectance distribution function (BRDF) profiles measured with a scatterometer for several angles of incidence. Results were amended with profile measurements made by a profilometer.