A new generation of RPCs to be tested for the super- LHC CERN GIF workshop 20/06/2011 G. Aielli

What we learned about rate capability&ageing A fundamental experience on 2 mm gap RPCs with plastic laminate semiconductive electrodes has been accumulated in the framework of the LHC These RPCs were successfully tested at the GIF at rates as high as 1 kHz/cm/2 However the test has also shown that this very high rate could hardly be maintained for 10 years due to observed ageing effects Two main effects were identified and studied - Increase of the electrode resistivity - Possible increase of the current in case of low gas flow or high temperatures… xx

ATLAS barrel background map Range from 4 to 30 Hz/cm^2 at L=10^34 Good agreement with MC Sum of deltaI Row Labels Grand Total 1.DP DP DP DP DP DP DP DP DP DP DP DP DP DP DP DP Grand Total

T. Kawamoto4 Radiation and cavern background CSC EI EM EO BI BM BO FLUGG/RBTF MDT hits/tube (kHz) from FLUGG x kHz/tube at 7 TeV  ~ 200kHz/tube at 14 TeV 5x x x10 34 EI EM EO BI BM BO

Present ATLAS background scenario In the ATLAS barrel expected 10 Hz/cm^2 –  0.3C in 10 ATLAS years (safety factor 5) – 30 pC per count at standard w.p. ATLAS mixture – GIF ageing test certified – Background measured  in agreement with MC – The safety factor includes the sLHC upgrade In the forward region we expect 10 kHz/cm^2. If we want to propose RPCs for the unmatched space-time resolution and low cost – Either we have to certify an RPC ageing for 30 C/cm^2 !!!!! – Or we manage to work with a total charge per count 100 times lower (0.3 pC)… – Or something in between In the ATLAS barrel expected 10 Hz/cm^2 –  0.3C in 10 ATLAS years (safety factor 5) – 30 pC per count at standard w.p. ATLAS mixture – GIF ageing test certified – Background measured  in agreement with MC – The safety factor includes the sLHC upgrade In the forward region we expect 10 kHz/cm^2. If we want to propose RPCs for the unmatched space-time resolution and low cost – Either we have to certify an RPC ageing for 30 C/cm^2 !!!!! – Or we manage to work with a total charge per count 100 times lower (0.3 pC)… – Or something in between

The purpose The main purpose is to propose a new generation of RPCs fully adequate to operate in presence of a very high radiation background like the one expected at the super LHC This goal should be achieved without increasing the operating current which determines the detector ageing and power dissipation Two parameters have to be focused for this purpose: - the gas gap width which determines the amount of delivered charge per avalanche - the sensitivity of front end electronics which determines the minimum charge that can be discriminated from the noise Moreover another factor can be gained by increasing the prompt/total signal fraction essentially given by the gas gap layout and working mode The main purpose is to propose a new generation of RPCs fully adequate to operate in presence of a very high radiation background like the one expected at the super LHC This goal should be achieved without increasing the operating current which determines the detector ageing and power dissipation Two parameters have to be focused for this purpose: - the gas gap width which determines the amount of delivered charge per avalanche - the sensitivity of front end electronics which determines the minimum charge that can be discriminated from the noise Moreover another factor can be gained by increasing the prompt/total signal fraction essentially given by the gas gap layout and working mode

Systematic study of the gas gap size It was carried out on small size (8x50 cm2) gas gaps of 2.0, 1.0 and 0.5 mm irradiated with cosmic rays The analysis of these signals is crucial to understand the RPC working features. It is also a good starting point to understand complex devices like multigap RPCs, that proven to be ideal instruments to get time resolutions as good as 70 ps Our final purpose is to study the possibility to replace the present single gap of 2 mm with 2 (or 3) thinner gaps It was carried out on small size (8x50 cm2) gas gaps of 2.0, 1.0 and 0.5 mm irradiated with cosmic rays The analysis of these signals is crucial to understand the RPC working features. It is also a good starting point to understand complex devices like multigap RPCs, that proven to be ideal instruments to get time resolutions as good as 70 ps Our final purpose is to study the possibility to replace the present single gap of 2 mm with 2 (or 3) thinner gaps

Prompt and current signal for 2 mm gap time (ns) time (μs) amplitude (mV)

Prompt and current signal for 1 mm gap time (ns) time (μs) amplitude (mV)

Prompt and current signal for 0.5 mm gap time (ns) time (μs) amplitude (mV)

Currents of 2/1/0.5 mm gaps irradiated with a 60 Co source 18 X slope factor 6 X slope factor

Total charge vs electric field

Detection efficiency vs electric field (1.5 mV threshold) 5% inefficiency due to spacers

RPC performance vs. Front End electronics We are producing a new series of front end circuits of better sensitivity, which can discriminate extremely small signals from the noise The purpose is to operate RPCs at lower gas gain, i.e. at lower operating voltage, in order to reach larger rate capabilities The first experimental results show that the rate capability can be increased by one order of magnitude We are producing a new series of front end circuits of better sensitivity, which can discriminate extremely small signals from the noise The purpose is to operate RPCs at lower gas gain, i.e. at lower operating voltage, in order to reach larger rate capabilities The first experimental results show that the rate capability can be increased by one order of magnitude

The higher sensitivity of the new front end circuit allows to lower the operating voltage by about 600 V thus reducing the gas gain by about a factor of 7

Test at the GIF (cern) of a Atlas standard 2 mm gap equipped with a new di FE circuit (see Cardarelli’s talk)

Trigger concepts vs detector features Fast detectors are crucial to reject low energy uncorrelated background So far the time resolution was considered to be relevant only for an efficient bunch crossing identification  At rates as high as 10 kHz/cm2 an excellent time resolution allows to make very short time coincidences between contiguous detectors which is crucial to cope with the uncorrelated background Time propagation along the strips is automatically corrected for contiguous detector layers

AND 2ns Strip delay correction Using the doublet 2 ns coincidence (2/3 majority) Maximum geometrical delay:  x*tan  v  negligible Equivalent to ~40 cm segmentation in Phi Overall virtual PAD of 40x1 cm^2 xx  2ns * v

Precision tracking trigger with RPCs The method of the charge centroid applied to the RPCs allows to obtain a space resolution of the order of 0.1 mm on both coordinates The time required for the DAQ and the centroid calculation would be however too long for a 1 st level trigger A precision tracking suitable for trigger purposes can be obtained using narrow strips, typically 2 mm pitch, coupled to a very fast maximum selector circuit

RPC for the Small Wheel upgrade Baseline: Hybrid RPC-sMDT detector – Integration of mechanical structure – Sharing of LV and Readout RPC is designed to provide: – 1 mrad angular resolution on bending coordinate – 1 mm resolution second coordinate – Sub ns timing and TOF capability – Full coverage and tracking efficiency > 97% Baseline: Hybrid RPC-sMDT detector – Integration of mechanical structure – Sharing of LV and Readout RPC is designed to provide: – 1 mrad angular resolution on bending coordinate – 1 mm resolution second coordinate – Sub ns timing and TOF capability – Full coverage and tracking efficiency > 97% 1 st layer2 nd layer cm θ The trigger function is provided by an electronic chain measuring the azimuth angle from digital local coordinates. – The zero suppression is applied on chamber – The angle calculation requires about 50 ns on top of the signal delivery time to USA15 The trigger function is provided by an electronic chain measuring the azimuth angle from digital local coordinates. – The zero suppression is applied on chamber – The angle calculation requires about 50 ns on top of the signal delivery time to USA15 sMDT

Overall CS=2 result Tracking residuals

RPC based fast trigger scheme for the SW The New RPC Front End allowed a new working mode with a factor 10 less of charge per count  10 KHz/cm^2 as tested Tracking trigger: a new type of – low-cost – low-consumption – Fast – compact electronic readout circuit (by R. Cardarelli) allows fast precision tracking for local trigger generation on the Eta. It works finding the maximum of the RPC charge distribution CERN, 9 March, 2011ACES

Amp and Maximum Selector Amp and Maximum Selector Maximum selector (next GIF test) CERN, 9 March, 2011ACES ns - N strips are processed at the same time (N in the range of ~10) - The Maximum selector amplifies the inputs and outputs a negative signal only in correspondence of the strip above a settable fractional threshold chosen to have one or two strips firing (cluster size 1 or 2) - The decoder transforms the simple digital pattern in to a number representing the hit coordinate on the chamber - The processing time is 7-10 ns

A new scheme of fast tracking trigger 2 mm pitch micro strips grouped by 8 Maximum selector 2 transistor 20 mW per channel decoder Output : binary number giving the position of the maximum; 8x4 strips =5 bits +1 for CS=2 Strip pitch 2 mm σ = 2/3 mm / √12 = 190 µm (CS=2) Single RPC plane spatial resolution It will be tested in the summer H8 test beam Stripped readout plane N1 N2 TRIGGER DECISION: N2-N1 <X 40 ns delay for processing RPC2 RPC1

2/3 2ns Trigger layout for a muon station Narrow coincidence performed locally on facing Eta strip groups Broader (10 ns) global coincidence RPC1 AND RPC2 The same scheme can be repeated for Phi view if a further rejection factor is needed 2/3 2ns RPC1 AND RPC2 10 ns coincidence 40 cm

GIF test plans The most wanted position is as close as possible to the gif for testing small dimension prototypes: from 20x20 cm^2 to 50x 100 cm^2 July: combined test MDT+RPC in front of the source to test the Maximum selector circuit August test of an RPC doublet for trigger purposes In parallel try to restart the tower (leaks?) to integrate as much as possible in terms of charge (present limit 0.3 C/cm^2)  combined ATLAS CMS effort to save man power?