Marcello Abbrescia RPCs for CMS during Phase II RPC rate capability M. Abbrescia, The dynamic behaviour of Resistive Plate Chambers, NIM A 533 (2004) 7–10 RPCs are considered to be installed in the RE3/1 and RE4/1 stations of CMS during LS3 Main concern for their installation during CMS construction was their rate capability Preliminary results show that the expected rate in RE3/1 and RE4/1 should be < 600 Hz/cm 2 Request on rate capability ≈ 2 kHz/cm 2

Marcello Abbrescia Improving rate capability of RPCs: Possible options  Reducing the electrode resistivity (to be < Ωcm) Reduces the electrode recovery time constant τ ≈ ρε Lowest resistivity usable ≈ 10 7 Ωcm At this point the detector practically looses its self-quenching capabilities In principle a lot of room (3 orders of magnitude) to exploit Needs important R&D on electrodes materials (glass or bakelite)  Changing the operating conditions reducing the charge/avalanche, i.e. transferring part of the needed amplification from gas to FE electronics (already done in 1990s!) needs careful study on signal to noise ratio (adequate shielding)  Changing detector configuration Improves the ratio (induced signal)/(charge in the gap) i.e., pass from single to double-gap, or from double to multi-gap Just some of these possibilities are being explored in present R&D, sometimes in combination Rate capability in RPCs can be improved in many ways:

Marcello Abbrescia Additional features  In addition we could decide to improve also: Spatial resolution – from O(1 cm)  O(1-0.1 mm) Might be very useful in case of trigger requirements Time resolution – from O(1 ns)  O(100 ps) Time resolution is inversely related to the gap width and the number of gaps Might be very useful for background rejection, Pile Up mitigation (and else) Given requirement on rate capability, choice of the technology will be driven by the physics case: plus robustness, cost, ease of construction, etc. For instance, if the advantage of a 100 ps time resolution would be demonstrated, this would push us toward a multigap solution

Marcello Abbrescia Baseline solution  Standard CMS RPC were certified for 1 kHz/cm 2 The improvement needed (a factor of 2) is not so much  Could be achieved with the very same CMS RPCs with a slightly lower resistivity bakelite Acceptance range of CMS RPC bakelite resistivity: 2-6 × Ωcm It would be enough to choose the one with lowest resistivity Activity is going on to produce (or locate already existing) bakelite samples  Could be achieved with the very same CMS RPCs and a slightly improved electronics ATLAS electronics would be fine (even an overkill) Test are going on (in Bari and previously at Ghent) on ATLAS electronics with CMS RPCs

Marcello Abbrescia Present R&D in CMS  Develop an improved detector for the present system gas, cooling, mechanics and services  Develop a high rate capability bakelite RPC for the high η region  Develop a high rate capability and time resolution glass RPC for the high η region (alternative solution to bakelite RPCs)  GIF++ tests to study the performance and stability of the chambers at high rate and up to 3000 fb test at GIF: Goals: resistivity and current measurements. Then move all at GIF++ to get the fb -1 Equipment: 2 CMS chambers equipped with CMS electronics + 13 gaps + 6 glass RPCs Bakelite RPC bakelite ( ) : Low resistivity Bakelite (10 9 – Ωcm) test smaller gap ( < 2 mm) to reduce HV working point Improved gas distribution and components New FE electronics with ATLAS chip

Marcello Abbrescia CMS RPCs with ATLAS electronics Test at GIF++ necessary ( ) SEU study New Front-End based on a new BJT transistor developed by the ATLAS group comparison between standard CMS and “new” electronics Data taken with cosmics, important to check a real rate capability improvement at GIF 30 mV threshold with a HV filter mV threshold, effect of the HV filter negligible Preliminary results Preliminary results First tests already started in 2013 with a limited number of channels

Marcello Abbrescia R&D on glass RPCs New “low” resisitivity (10 10 Ωcm) glass used for high rate RPC RPC rate capability depends linearly on electrode resistivity Smoother electrode surfaces  reduces the intrinsic noise Improved electronics characterized by lower thresholds and higher amplification 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 Ceramic ball spacer Gas gap(1.2mm) Single gap option Multigap option: a variation of the double-gap configuration used for CMS: “double triple-gaps” High rate + high time resolution “Array” of small-size glass tiles to cover large surfaces CMS R&D #12.01

Marcello Abbrescia GRPCs for CMS: performance Effect of reduced resistivity on rate capability Caveat: localized irradiation different from an uniform irradiation At the moment low resistivity GRPCs at GIF for a series of high rate and aging tests Very promising performance at localized beam tests even at high rate Rate capability ~ 30 kHz/cm 2 Time resolution ps Multigap configuration Single- gap configuration “Low” resistivity “High” resistivity

Marcello Abbrescia “Synergetic” tests at GIF Common efforts already started between:  RPC bakelite and glass  CMS and ATLAS and ALICE “Standard” tests: 1.Measure and monitor bakelite resistivity 2.Current monitoring stability 3.RPC sensitivity 4.RPC rate capability Plans: Comparison among CMS electronic and new electronics (ATLAS and Lyon) Set-up for HF measurements on Bakelite and Glass RPC to study the HF production as a function of chambers parameter, irradiation and gas mixture composition RPC consolidation (improved chambers for the existing system)