1. Module-0 of AFP ToF Detector Libor Nozka on behalf of ATLAS Forward Proton Group Palacky University 1

2. AFP Project  required resolution: 10  m (x-axis), 30  m (y-axis),  Si pixel sensors (designed for IBL), readout: FE-I4 336x80 pixels, pixel size 50x250  m 2 (total 1.68x2.00  m 2 ) Tracking System  ATLAS Forward Proton (AFP), measurement of scattered protons under very small angle in ATLAS Forward Region  required resolution ~10 ps  2x ToF „front-to-front“  Each ToF with L-shaped Cherenkov-radiationg Quartz bars (LQBar) forming a matrix 4x2,  Fast MCP-PMT XPM85112: 4x4 pixels, TTS<35 ps Time of Flight (ToF) system Both systems: High rate capability 5 MHz, and radiation hardness 2

3. Components of AFP fast timing 3

4. AFP TestBeam, November 2014 CERN  CERN-SPS, Blg. 887, BeamLine H6B, Beam: pions+, 120 GeV  Tracker prototype: 4 layers (3.75 mm pitch) in front of timing system, one extry layer 13.5 mm behind  ToF prototype: matrix 4x2 LQBars, 48° tilted from beam 4

5. Design of LQBars Details in L. Nozka, A. Brandt, M. Rijssenbeek, T. Sykora et al. Optics Express 2014 reference possible combinations Quartz/Air guide  Several geometry combinations of Quartz and Air guide (prompt light guide vs. extra optical boundary),  Main criteria: maximum of hit count on sensor in first 250 ps of light pulse development,  Geometry optimization: taper to mimic a parabolic collimator in the knee Initialy we started with QUARTIC by M. Albrow suited to AFP design with Hamburg Beampipe but it does not fit into final Roman Pot design => we needed to bend bars 5

6. Design of LQBars Distribution of generated vertices reaching sensor = acceptance profile due to geometry constrains we call them wings 6

7. Design of LQBars Geometry optimization – effort to compress the signal into first 250-300 ps => make side wing faster Adding a taper 7

8. Design of LQBars Hit count on sensor during pulse development 8

9. Construction of prototype – optical part  matrix 4x2 = 4 trains, each with two bars,  first train: radiator 3x6 mm cross-section, taper 18 degs radiator arm light-guide arm 9

10. Construction of prototype – optical part  Construction done in our optical workshop (cutting, grinding, polishing, PVD deposition, gluing),  Material: Suprasil, knee coded by layers Al 120 nm + SiO2 140 nm (protective layer)  Arms glued by Epotek 305 Basic setup measurements in our lab, results in DUV soon 10

11. Construction of prototype – holder Michael Rijssenbeek There was no optical grease between bars and PMT 11

12. Photomultiplier 12

13. TestBeam Setup 13

14. Measurements - integration  Main aim: Tracker+ToF integration Integration results related to ToF Correlation between Tracker and bars ToF efficiency w.r.t. Tracker Plots by Joern Lange, Emanuele Cavallaro, Ivan Lopez Paz based on AFP TestBeam 2014 14

15. Measurements –ToF resolution Train 1Train 2 Correlation between bars 0.5 => high cross-talk Combined resolution dropped by approx. 5 ps w.r.t. average bar resolution, still high (optical cross-talk, optical arrangement ?) Integration with tracker was preferred and ToF performance measurements had lower priority => measurement scenarios were not optimized for ToF performance measurements Train 2A2B HV [V]  (1A)  (1B)  comb Corr. factor* 1750?? 18004842 0.59 18503631290.44 19003934310.51 Train 1A1B HV [V]  (1A)  (1B)  comb Corr. factor* 17506375640.76 18004451440.64 18503536310.53 19003130250.52 *Correlation factor measures the amount of linear association between signals of both bars 15

16. Summary  New prototype of AFP ToF was designed and tested,  New design is based on LQBars of „L“ shape analyzed and optimized with MC studies in Geant4  TestBeam showed promising results but integration with tracker was preferred and ToF performance measurements had lower priority  Reduction of optical cross-talk is our next step, there are several possible options including surface treatment Next AFP TestBeam  Geometry updates of LQBars including surface treatment (suppression of optical cross-talk, rejection of side wings)  More attention to ToF performance 16