1. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 1 R&D on improved RPCs for phase 2 upgrade M. Abbrescia on behalf of the RPC upgrade group

2. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 2 Introduction New branch of the RPC project recently created, dealing with possible improvements of the systems in LS2 and afterwards. Activities spread all over the world (literally!), on different detectors/methologies trying to find synergies among groups and steer R&D Organizing a meeting every two weeks on Wedsneday Different areas of interests, for instance:  GRPC project at high-eta R&D project submitted  Improved electronics with CMS RPCs  Multi-gap bakelite RPCs  Studies of “general” interest

3. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 3 Basic ideas Let us start with one basic point:  All detectors foreseen for LS2 (phase 1) or LS3 (phase 2) upgrades must stand a rate capability higher then the present From 1 kHz/cm 2  5-10 kHz/cm 2  Rate capability in RPCs is improved essentially in three ways: Reducing the electrode resistivity Changing the operating conditions Changing detector configuration (changing detector)

4. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 4 The role of resistivity CMS/RPCs are characterized by a resistivity around 10 10 Ωcm  Proposed glass-RPC have a resistivity of the same order of magnitude At a first approximation, the improvement observed is not due to the resistivity (confirmed by a few hints)  Previous studies and a (semi) theoretical consideration limit the lowest resistivity usable at 10 7 Ωcm At this point the detector practically looses its self-quenching capabilities (behaves like having metallic plates)  In principle a lot of room (3 orders of magnitude) to exploit: Need studies on (new?) materials Detector less stable

5. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 5 Changing the operating conditions …usually stated (very unprecisely) like “reducing the charge”. While resistivity affects the RPC time constant τ~ρε (and the voltage drop in the bakelite/glass plates) the charge associated to the avalanche is directly proportional to the local voltage drop in the gap. Please note an important concept: given a certain electronics amplification/threshold (and almost any detector configuration): equal efficiency means equal induced charge (and v.v.) It is possible to works at lower operating voltages only if the readout sensitivity is lowered Different electronics Improved signal/noise ratio (of the whole system)

6. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 6 Effects of a new electronics Investigated by the group from Ghent, which reported in the RPC upgrade meeting (N. Zaganidis, S. Vanheule, A. Fagot et al.) New Front-End based on a new BJT transistor developed by ATLAS group  comparison between standard CMS and “new” electronics 30 mV threshold with a HV filter 215-220 mV threshold, effect of the HV filter negligible Data taken with cosmics, important to check a real rate capability improvement at GIF

7. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 7 Set up Ad-hoc shielding Also a HV filter used All details at: N. Zaganidis et al.

8. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 8 Some results Essentially, great care has to be put to reduce the noise/signal ratio at the detector level N. Zaganidis et al.

9. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 9 Changing detector configuration Slides by Kyon Sei Lee et al.  Double RPCs made with 2-gap multigaps Two separated gas volume + a strip plane Each gas envelope = 2 gaps Prototypes made with phenolic laminates 45 x 45 cm 2 (active area) HPL thickness: 2.0 mm Spacers : 1050 ± 20 μm (Polycarbonate) → 900 ± 20 μm later to get HV eff ~ 9.6 kV Strip pitch = 27 mm The idea is to improve the ratio between induced charge and charge inside the gap. It is not straightforward to deduce how much the improvement in rate capability should be; no linearity in this case

10. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 10 Basic ideas 4-gap RPC detector Plastic scintillator Plastic scintillators Slides by Kyon Sei Lee et al.

11. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 11 Some results Efficiency Data measured with 1 ADC + 1 TDC → Current FEBs NOT used A linear amp → linearly ⅹ 10 for raw detector pulses TDC threshold for TDC stops = 9 mV (roughly equivalent to ~ 150 fC) Efficiency and charge Efficiency and time resolution

12. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 12 Tests@high rate 200-mCi 137 Cs (born in Nov. 2001) - 5.3 GBq Mean distances 31.7, 42.4, 52.8 cm Gamma-rates in the test N γ = 418.2 kHz cm -2 at 31.7 cm N γ = 233.8 kHz cm -2 at 42.2 cm N γ = 150.7 kHz cm -2 at 52.8 cm ε γ (GEANT4) = 0.0113 with six 2-mm thick HPLs ~ 800-V difference between muon and gamma plateaus

13. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 13 R&D on glass RPC PCB support (polycarbonate) PCB (1.2mm)+ASICs(1.7 mm) Mylar layer (50μ) Readout ASIC (Hardroc2, 1.6mm) PCB interconnect Readout pads (1cm x 1cm) Mylar (175μ) Glass fiber frame (≈1.2mm) Cathode glass (1.1mm) + resistive coating Anode glass (0.7mm) + resistive coating Ceramic ball spacer Total thickness (detector 3 mm+ readout electronics 3 mm): 6.0mm Gas gap(1.2mm) 30X30 cm 2 Slides by I. Laktineh et al.

14. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 14 GRPC@high rate Comparison between standard GRPC and low-resistivity (10 10 Ωcm) GRPC; Resitivity seems to be comparable to the bakelite… electronics? Slides by I. Laktineh et al.

15. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 15 Multi-gap GRPC@high rate Using a multi-gap structure the performance improves even more, as expected: Rate capability 20-30 kHz/cm 2 (2-3 times single gap) Time resolution better than 100 ps A lot of work going on about the electronics Need to disentangle effects related to material, electronics, and detector configuration

16. Marcello Abbrescia Muon general meeting, Mon 29-Apr-2013- p. 16 Conclusions Many different activities!  Need to coordinate R&D with the requirements of CMS is a 100 ps time resolution of the muon systems useful for CMS? Let hardware and software people speak together Here people is really needed  Understand what will happen in 10 years from now (aging?) and take action What if we should replace the whole RPC (or muon) system? Would we be able to propose a new detector merging the performance of the different detector used now?