1. The HADES timing RPC Inner TOF Wall P.Fonte for the HADES RPC group DIRAC phase1 9th International Workshop on Resistive Plate Chambers and Related Detectors (RPC2007) 13-16 February 2008, Mumbai, India

2. RPC2007P.Fonte The HADES tRPC inner TOF Wall The HADES RPC group GSI - Gesellschaft für Schwerionenforschung mbH, Darmstadt, Germany D.Gonzalez, W.Koenig IFIC – Universidade de Valencia, Spain J.Diaz, A.Gil LABCAF - Universidade de Santiago de Compostela, Spain D.Belver, P.Cabanelas, E.Castro, J.A.Garzón, M.Zapata LIP - Laboratório de Instrumentação e Física Experimental de Partículas, Coimbra, Portugal A.Blanco, N.Carolino, O.Cunha, P.Fonte, L.Lopes, A.Pereira, C.Silva, C.C.Sousa

3. RPC2007P.Fonte The HADES tRPC inner TOF Wall

4. RPC2007P.Fonte The HADES tRPC inner TOF Wall

5. RPC2007P.Fonte The HADES tRPC inner TOF Wall Expanded Inner TOF Wall - TOFINO (to be upgraded by tRPCs) RICH inner MDCs (I-II) outer MDCs (III-IV) magnet TOF(scintillatorbased) SHOWERdetector

6. RPC2007P.Fonte The HADES tRPC inner TOF Wall Quite small: ~6 m diameter

7. RPC2007P.Fonte The HADES tRPC inner TOF Wall 8 m 2

8. RPC2007P.Fonte The HADES tRPC inner TOF Wall Strong dilepton enhancement over hadronic cocktails

9. RPC2007P.Fonte The HADES tRPC inner TOF Wall

10. RPC2007P.Fonte The HADES tRPC inner TOF Wall C+C Au+Au Heavy nuclei colisions Lots of particles (up to 30/sector)Unevenly distributed radially by a factor ~2 over the inner TOF area

11. RPC2007P.Fonte The HADES tRPC inner TOF Wall Operational parameter matched to the HADES overall performance  Multi-hit capability hit-loss probability below 20%  Minimum 150 channels/sector  effective cluster size  resolution100 ps (  ) or better  In principle not difficult for a good detector  Potential problems: mechanics, crosstalk (hard to measure).  rate capability up to 1 kHz/cm 2 in some areas  Not so easy for almost continuous beam  efficiencyabove 95% for single hits  In principle no problem, except for geometric coverage  Area ~8/6 m2/sector  Fast!no long R&D time available RPC design criteria

12. RPC2007P.Fonte The HADES tRPC inner TOF Wall Concept validation, 2003First prototype test, 2005 Partially instrumented Final prototype test, 2007 Fully instrumented Time frame

13. RPC2007P.Fonte The HADES tRPC inner TOF Wall  Accept crosstalk and use an excess of granularity to accommodate the “effective cluster size” (minimum distance between clusters for uncompromised performance) +Simple, large area detector. Just segment the readout. +Excess of granularity has positive side effects, such as better position resolution and possibly slightly better time resolution. -Hard to design (detailed 3D electromagnetic model needed), hard to test (particularly the influence on time resolution) and oversizes all downstream system components (FEE, DAQ, etc).  Minimize crosstalk and cluster size by individually shielding each “cell” +Straightforward multi-hit response. No discussions about “effective cluster size”. Easy to test on the bench: cluster size  1. -Much more difficult detector mechanics. Two layers needed for good geometric coverage. +Two layers provide a useful redundancy on a fraction of the events: +strong suppression of timing tails (very important for PID of rare particles – see poster by A.Mangiarotti), slight improvement of the time resolution. +Detector becomes self-calibrated – isochronous surface may be created without resorting to external devices  Ignore the whole issue Multi-hit capability - basic choices

14. RPC2007P.Fonte The HADES tRPC inner TOF Wall

15. RPC2007P.Fonte The HADES tRPC inner TOF Wall  187 cells/sector distributed in 29 rows and 6 columns, 3 on top and 3 on bottom  1122 cells total  124 different detectors with variable width, length and shape  no attempt at impedance matching All put together: final prototype rows

16. RPC2007P.Fonte The HADES tRPC inner TOF Wall  0.27 mm  4 gaps  minimum for good efficiency  Aluminum and glass 2mm electrods  minimize amount of glass for maximum rate capability  try to keep good mechanics  Heat-tolerant materials GlassAluminium Spring-loaded pressure plate HADES cells Fully shielded HV & readout in the center

17. RPC2007P.Fonte The HADES tRPC inner TOF Wall Assembly in gas box HV distribution PCB 50  signal Feedthrough PCB HV capacitor (~1cm 2 ) Further shielding between feedthrougs Full shielding only on upper 1/3

18. RPC2007P.Fonte The HADES tRPC inner TOF Wall t1t1 t2t2 Readout scheme FEE

19. RPC2007P.Fonte The HADES tRPC inner TOF Wall 4 channel 3GHz amp+timing comparator + QtoWidth conversion Support motherboard (mechanics, services, signal routing) t1t1 t2t2 FEE electronics Details: talk by D.Belver

20. RPC2007P.Fonte The HADES tRPC inner TOF Wall TRB (Time Readout Board) 128 multihit TDC channels (CERN’s HPTDC) TDC and DAQ (by GSI electronics group) Details: talk by D.Belver

21. RPC2007P.Fonte The HADES tRPC inner TOF Wall System in action Results: talk by P.Cabanelas

22. RPC2007P.Fonte The HADES tRPC inner TOF Wall Rate capability Temperature 33º C Volume resistivity 3  10 12  cm ProblemSolution: warm glass Glass has an exponential resistivity temperature coeficient of a factor 10 per 25ºC. [C.Gustavino et al., 2004] This seems to be remarkably constant across glass makers and even glass types Temperature 20º C Volume resistivity 1  10 13  cm

23. RPC2007P.Fonte The HADES tRPC inner TOF Wall Crosstalk How good all this shielding really is? Fully shielded region Linearized cell numbering, roughly preserving geometrical vicinity relations For single good hits (hits with redundancy were rejected)

24. RPC2007P.Fonte The HADES tRPC inner TOF Wall Crosstalk Crosstalk mostly to the opposite plane Fully-shielded region For single good hits (hits with redundancy were rejected) Affects both time and position resolution measurements (next talk)

25. RPC2007P.Fonte The HADES tRPC inner TOF Wall Crosstalk Non-shielded region Crosstalk to all neighbours For single good hits (hits with redundancy were rejected)

26. RPC2007P.Fonte The HADES tRPC inner TOF Wall Crosstalk For single good hits (hits with redundancy were rejected) Fully shielded region There is a clear difference between partial and full shielding. Is there any visible difference in performance?

27. RPC2007P.Fonte The HADES tRPC inner TOF Wall Crosstalk There is a clear difference between partial and full shielding. Is there any visible difference in performance? Yes (see next talk): time measurement is a delicate business! Fully shielded region For single good hits (hits with redundancy were rejected)

28. RPC2007P.Fonte The HADES tRPC inner TOF Wall Conclusion  The HADES spectrometer will be upgraded by an 8m 2 tRPC Inner TOF Wall  The system was designed for robust multihit performance and minimum FEE overhead by individually shielding each of the 1122 RPC “cells”  Built-in measurement redundancy provides tails-free timing measurements on a large fraction of the particles, very important for the PID of rare particles (poster by A.Mangiarotti) and also self-calibration capability  A fully instrumented (talk by D.Belver) prototype sector has been successfully tested in realistic beam conditions with satisfactory performance (talk by P.Cabanelas)  Production is ongoing with installation foreseen for late 2008 and commissioning in 2009