Results with the RPC system of OPERA and perspectives A. Bertolin (INFN-Padova)

1. Mini-Workshop: "LNGS results on the neutrino velocity topic“ LNGS Seminars March 28th 2011 Results with the RPC system of OPERA and perspectives A. Bertolin (INFN-Padova) On behalf of the OPERA collaboration

2. Time measurements with the OPERA RPC detectors TT RPC1 RPC2 • 22, RPC0, + 22, RPC1, planes of Resistive Plate Chambers • each plane is measuring the x - y coordinates (copper readout strips) and the • time stamp of the first signal (x or y) reaching the readout • goal: evaluate all delays in the detection process

3. Delay due to signal formation in the RPC gas mixture hardware setup: test RPC + PMT in lab. avalanche signal too small “discriminate” only the streamer

4. Delay due to signal formation in the RPC gas mixture (cont.) avalanche @ 7 kV streamer @ 7 kV working point: fully efficient detectors delay due to signal formation: 30 ± 5 ns

5. Delay due to signal propagation in RPC readout strips method: inject a triangular pulse at strip end point, the readout flat is detached from the strip starting point, a reflected pulse is measured at the strip end point digitized scope output injected triangular pulse reflected pulse strip delay: 4.82 ± 0.17 ns/m (taking into account different strips, triangular wave frequency …)

6. Delay due to signal propagation in flat cables distribution of the hor. and ver. flat delays as implemented in the geometry: delay (ns) delay (ns) • send a squared wave through a BNC cable, delay between pulse and reflection: 151.6 ns • attach the same BNC cable to the lowest horizontal flat, flat cable detached from the other side, measure the delay between pulse and reflection: 310 ns • = 310 - 151.6 / 2 ns = 79.2 (± 1) ns • idem for the second horizontal flat from the top • d = 237- 151.6 / 2 ns = 42.7 (± 1) ns

7. Readout electronic delays: schematic layout ctrl board mezzanine: DAQ time stamp CLK fanout extender PPS reset (0.6 sec) + CLK signals default path FEB board PPmS known delay: function generator, used for a fixed delay part, + lemo cables principle: the PPmS signal is sent to the FEB board with a known delay by comparing the DAQ time stamp and the known delay one gets the overall time delay of the default path Master Clock

8. Delay due to signal propagation through the FEB board delay from FEB input flat connector to the mezzanine input pin (where the signal is time stamped) scope value: 124 ns this value has to be corrected for the extra cables used for this measurement delay from the FEB input flat connector to the mezzanine input pin = 102.8 ± 1 ns FEB polarity, FEB channel to channel dependence: variations seen within ± 1 ns

9. Delay due to PPS reset (+ CLK) propagation • cyan: signal sent to the FEB input, KNOWN delay with respect to the OPERA Master Clock • light green: PPS reset signal at the mezzanine input pin • taking into account the extra cables and delays used for this measurement delay due to PPS (+ CLK) propagation = 4207.5 ns • the 5 peaks structure of the light green signal corresponds to the ± 25 ns jitter (-2 -1 0 +1 +2) of the OPERA Master Clock (see G. Sirri’s talk)

10. Delay internal to the mezzanine in the conditions just presented total delay between the (first of the 5) PPS and the trigger signal = 308.0 ns if the internal mezzanine delay was 0 ns the DAQ output should be 308.0 ns in these conditions the DAQ goes from 25 to 26 counts, inflection point of the quantization curve, i.e. 260 ns (first of the 5 pulses) the difference, 48.0 ± 2 ns, should be equal to the time needed to reset the DAQ scale and time stamp the FEB pulse first PPS at 260 ns first PPS at 250 ns

11. Principle of the time measurement: mean time at track start TT take the average time of the RPC muon track hits in successive planes, each one scaled to the leftmost hit RPC plane RPC1 RPC2 • hits are individually corrected for: • propagation in the RPC readout strips and flat cables • processing in the FEB boards • delays due to the OPERA DAQ system (down to the Hall C Master Clock) • drift of the OPERA Master Clock (see G. Sirri’s talk)

12. Cross check on the quality of the (relative) RPC time alignment mean t SM2 mean t SM1 the time difference use the extrapolated time at the A1 reference point (end point of the CERN – LNGS base line, zA1 = -270.226 cm)

13. Independent time stamp system for the RPC goal: RPC time stamp independent from the OPERA Master Clock a VME PPmS receiver designed for Nautilus (LNF electronics workshop: R. Lenci, M. Beretta, A. Balla) is available: 1) PPmS decoding 2) event time stamp 3) PPmS repetition some modifications will be needed to cope with the light yield available underground (about 2 mW) inputs: 9 XPC/RPC planes (per magnet) with Timing Boards, needed to trigger the High Precision Tracker are working hard to have it ready for the next BB

14. Conclusions • presented a summary of all the RPC delays • presented an RPC timing algorithm where all delays are computed on an event by event basis • achieved a 4 ns time resolution • 2011 BB data have been analyzed, the result … will be addressed in M. Sioli’s talk … • an RPC time stamp independent from the OPERA Master Clock is being setup for the next BB run, 1 ns time resolution