QUARTIC a Precise ToF Counter for the ATLAS Forward Physics Project (AFP)

1. QUARTIC a Precise ToF Counter for the ATLAS Forward Physics Project (AFP) 11 ICATPP Conference James L Pinfold University of Alberta

2. Groups Involved University of Alberta, University of Texas at Arlington, University College London. Prague, Saclay, Stoneybrook, Giessen, Manchester, Fermilab, Louvain, Kansas INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

3. The ATLAS Forward Detectors AFP INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

4. The AFP Project ATLAS • AFP is designed to tag forward protons • Selection rules mean that central system is (to a good approx) 0++ • If you see a new particle produced exclusively with proton tags you know its QN • CP violation in the Higgs sector shows up directly as azimuthal asymmetries • Proton tagging may be the discovery channel in certain regions of the MSSM • Tagging the protons means excellent central mass resolution (~ GeV) • Tracking detector requirements • Close to beam => edgeless detectors • High Luminosity => radiation hard • Few micron resolution • We need to suppress pile-up (keep the rapidity gaps open) • This is done by ultra-fast ToF detectors (to determine vertex) INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

5. Rationale for Fast Timing Detectors (1) • Precision timing will be required to reduce pile-up background, enabling AFP to operate at design luminosity • Backgrounds are: • Three interactions, one with a central system, and two with opposite direction single diffractive protons • Two interactions, one with a central system, and the second with two opposite direction protons • Two interactions, one with a central system and a proton, the second with a proton in the opposite direction. [X][pp] [Xp][p] [X][p][p] Scales with L3 Scales with L2 Scales with L2 INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions James L Pinfold Manchester 2007 1

6. Rationale for Fast Timing Detectors (2) • For two protons coming from the same event: • Z-position = ½(Dt=tL - tR)c dZ-position = (c/√2)dt • Aim for dt = 10(20) ps  dZ ~ 2.1(4.2) mm (look for match with ATLAS/CMS main Z) • Fordt = 20 ps, we obtain a factor of 24 for the first two cases and 17 for the third. • Case (a) dominates at high luminosity, and in the case of dt = 10 ps, we would expect a factor of nearly 50 rejection, enabling FP420 to operate at the design lumi. INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions James L Pinfold Manchester 2007 2

7. Baseline Plan 30 cm • Two types of Cerenkov detector are employed: • GASTOF – a gas Cerenkov detector that makes a single measurement • QUARTIC – two QUARTIC detectors each with 4 rows of 8 < ~90 mm long fused silica bar allowing up to a 4-fold improvement of resolution over that of a single bar • Both detectors employ Micro Channel Plate PMTs (MCP-PMTs) James L Pinfold Manchester 2007 3 INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

8. Micro-channel Plate PMT (MCP-PMT) We are working with 10 micron Burle tubes at present INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

9. QUARTIC- Alberta, FNAL, UTA • Each QUARTIC detector has 4 rows of 8 6mm x 6mm x ≤ ~10 cm long fused silica bars • The refractive index of fused silica is ~1.5 ( Cerenkov angle of 50o) • An array of bars is mounted at the Cerenkov angle to minimize the # reflections as the light propagates to the MCP-PMT. • The QUARTIC detectors will be positioned after the last 3D-Si tracking station because of the multiple scattering effects in the fused silica. • This arrangement is intrinsically rad hard INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions James L Pinfold Manchester 2007 5

10. A QUARTIC Prototype OR 2) Use longer bars as the light guide PRO: more light CON: more time disp. • Use short bars and • reflective light guide • PRO: Less time dispersion • CON: less light INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

11. QUARTIC FE-Electronics • The readout electronics must be fast with low noise to attain the best timing resolution – a single electronics channel : • Amplifier and Constant Fraction Discriminator • Louvain & Alberta have a similar CFD design designed to work with rise times as short as 150 ps and to be insensitive to amp non linearity & sat. • The TDC (for the test beam we used the Phillips 7186 25 ps TDC) • The baseline solution for the final detector is the HPTDC that has a ~20ps resolution – it is radiation hard and LHC compatible (a 40 MHz clock, etc) • The Alberta group has designed & built an 8 ch. HPTDC prototype board • For the GASTOF detector a single photon counter (Boston Elec. SPC-134-5ps rise time ) can replace the amp+CFD+TDC ($10K/ch.) Combined in the ALTA approach INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions James L Pinfold Manchester 2006 7

12. QUARTIC Electronics – the CFD ZX60 3 GHz amp • Mini-module approach tuned LCFD mini-module to Burle and Hamamatsu rise times; • 12 channel NIM unit good performance : <10 ps resolution for ≥ 4 PE’s • Remote control for threshold INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

13. QUARTIC Electronics – the HPTDC • 12 ps resolution with pulser; • Successfully tested at UTA laser test stand with laser / 10 m tube/ZX60 amp/LCFD • 13.7 ps with split CFD signal INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

14. The Reference Timing System \ • A reference is obtained from the 400 MHz LHC RF converted to an optical pulse which is split and sent along fibres to both L & R detectors for each BC - pulse to pulse jitter between pulse arrival is negligible • To monitor long term drifts (e.g. DT between 2 arms) the optical signal will be split at the detectors & returned to source for comparison • At the detector stations the optical pulses are converted to electrical signals and are recorded in the detector TDCs – this conversion is envisaged to give an r.m.s (L-R) jitter of 4 ps. • Our reference timing system is designed to provide sLR~5 ps INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions James L Pinfold Manchester 2006 14

15. Testing QUARTIC • Fermilab Test beam T958 experiment to study fast timing counters for FP420 • Used prototype detector to test concept • Test beam at Fermilab Sep. 2006, Mar.+Jul. 2007 • CERN October 2007, June 2008 • LASER Test set up in 2009 (including 6GHz Scope) INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

16. Timing – CERN Test-Beam 2008 Npe=(area/rms)2 56.6/1.4=40 ps/ Bar including CFD! Dt • Time difference between two 9 cm quartz bars after constant fraction discrimination is 56 ps, • implies a single bar resolution of 40 ps for about 10 PE’s (expected 10 PE’s from simulations). • Need to show improvement of resolution with # independent measurement (N) INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

17. The √N Effect 15.7 ps 16.4 ps 16.6 ps • Correct for T0 offset, average and take new time difference wrt reference tube (expect ~9.5 get 10.3 ps ) • Measure time difference of 3 separate fibers (100 pe’s) wrt reference tube 10.3 ps INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

18. MCP-PMT Rate & Current Limits • We need to establish if the MCP-PMT’s are capable of coping with the large expected rates at the LHC: up to 15 MHz in a 6mm x 6mm pixel of the MCP-PMT • The limiting factor is the current in the tube given by: I = f(p frequency) x NPE x e x G(gain) • Using 1 MHz for low lumi conditions and 15 MHz for hi-lumi, with a gain of 5x104 (!) and 10 PE’s expected for our detector, we obtain current limits of 0.24 & 3.5 mA/cm2 • When the tube current is too high the gain falls - saturation • Laser test stand test at UTA show that saturation starts around 0.4 mA/cm2 for the 10 mm pore size Burle MCP-PMT • Luckily, we now have access to a Burle Planicon tube with 10X higher current capability – but we still need to test it INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

19. The Lifetime Challenge • Lifetime due to photocathode damage from positive ions is proportional to extracted charge: Q/year = I*107 sec/year • Using the current limits mentioned previously we get to 35 C/ cm2 /yr (assuming 5x104 gain) at the highest lumi • This is a factor of ~50 more than the expected tube lifetime! • We are pursuing the development of a tube with a ~50 times longer lifetime, the avenues of improvement are: • Including an ion barrier – giving a factor of 5  6 • Electron scrubbing gives a factor of 5  6 (Photonis tests) • Z stack design gives a factor of ~10 improvement (NIM A598,160,09) • Arradiance coating gives a factor of ~10 improvement (under study) INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

20. Conclusion • We are on track to reach the 10 micron time resolution required • More work has to determine final parameters of the detector and electronics design • We have a R&D project to solve the lifetime problem for MCPs at the highest luminosities • We are working with three major manufacturers in this area: PHOTONIS, PHOTEK and ARRADIANCE • The way forward seems well determined! INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

21. Last Words Photo-production Photon-photon Proton Proton Pomeron-Pomeron (or g-g) INTRO QUARTIC Detector Readout Testing QUARTIC Challenges Conclusions

22. EXTRA SLIDES