FP420: FAST TIMING DETECTORS

1. FP420: FAST TIMING DETECTORS James Pinfold University of Alberta For the Fast Timing Group: GASTOF: Louvain QUARTIC: Alberta, FNAL, UTA Forward Physics at the LHC December 2007

2. Rationale for Fast Timing Detectors (1) Section 1.1 -Pile-up & Background Reduction + Subsubsection 1.1 - Timing • Precision timing will be required to reduce pile-up background, enabling FP420 to operate effectively at design luminosity • Backgrounds are: • (a) three interactions, one with a central system, and two with opposite direction single diffractive protons • (b) two interactions, one with a central system, and the second with two opposite direction protons • (c) two interactions, one with a central system and a proton, the second with a proton in the opposite direction. [X][p][p] [Xp][p] [X][pp] Scales with L2 Scales with L2 Scales with L3 James L Pinfold Manchester 2007 1

3. Rationale for Fast Timing Detectors (2) Subsection 1.1 - Pile-up & Background Reduction + Subsubsection 1.1 - Timing • For two protons coming from the same event: • Z-position = ½(Dt=tL - tR)c dZ-position = (c/√2)dt • Aim for dt = 10(20) ps  dZ ~ 2.1(4.2) mm (look for match with ATLAS/CMS main Z) • For dt = 20 ps, we obtain a factor of 24 for the first two cases and 17 for the third. • Case (a) dominates at high luminosity, and in the case of dt = 10 ps, we would expect a factor of nearly 50 rejection, enabling FP420 to operate at the design luminosity. James L Pinfold Manchester 2007 2

4. The Baseline Plan Subsection 1.3 – Timing Detectors • Two types of Cerenkov detector are employed: • GASTOF – a gas Cerenkov detector that makes a single measurement • QUARTIC – two QUARTIC detectors each with 4 rows of 8 15 mm long fused silica bar allowing up to a 4-fold improvement of resolution over that of a single bar • Both detectors employ Micro Channel Plate PMTs (MCP-PMTs) 30 cm James L Pinfold Manchester 2007 3

5. GASTOF - Louvain Subsection 1.3 – Timing Detectors • Presents little material to beam with thin windows, mirror and gas, • It has a gas radiator at atmospheric pressure in a rectangular tube of 30cm length a thin 45o concave mirror at the end of the tube reflects incident light onto the MCP-PMT • The gas radiator is (C4F8O/C4F10) with refractive index n ~ 1.0014 (C4F8O) between 400600 nm – the Cerenkov angle (b =1) is ~3o • Intrinsically rad hard the only sensitive element being the MCP-PMT James L Pinfold Manchester 2007 4

6. QUARTIC – Alberta, FNAL, UTA Subsection 1.3 Timing Detectors • Each QUARTIC detector has 4 rows of 8 15 mm long fused silica bars – Cerenkov light is transmitted to the MCP-PMT by air light guides - used to avoid time dispersion from thel dep. of the refractive index of quartz • The refractive index of fused silica is ~1.5, giving a Cerenkov angle of 50o • An array of bars is mounted at the Cerenkov angle to minimize the # reflections as the light propagates to the MCP-PMT. • The QUARTIC detectors will be positioned after the last silicon tracking station because of the multiple scattering effects in the fused silica. • Again, this arrangement is intrinsically rad hard James L Pinfold Manchester 2007 5

7. Simulation Subsection 1.4 Detector Simulations • A GEANT4 simulation of both detectors follows the Cerenkov radiation and its l dependent propagation & absorption in the radiator, reflection and arrival time at the face of the MCP-PMT Most photons Arrive within 15 ps Rise time ~1ps Photons arrive within an r.m.s Of ~1 ps #P.E.’s ~13 This figure shows the arrival time of photons at the MCP-PMT in GASTOF – time resolution is dominated by the transit time jitter and the electronics The above distribution show the #PE and the distribution of photon arrival times for for a QUARTIC bar, including the QE and collection efficiency of the Burle Tube. James L Pinfold Manchester 2006 6

8. Electronics and Data Acquisition Subsection 1.7 - Electronics and Data Acquisition • The readout electronics must be fast with low noise to attain the best timing resolution – a single channel of electronics is shown below • Amplifier and Constant Fraction Discriminator • Louvain & Alberta have a similar CFD design designed to work with rise times as short as 150 ps and to be insensitive to amp non linearity & sat. • Louvain has a separate amplifier and CFD board. The Alberta group combines the amplifier (Phillips BGA2717) and CFD on one board. • The TDC (for the test beam we used the Phillips 7186 25 ps TDC) • The baseline solution for the final detector is the HPTDC that has a ~20ps resolution – it is radiation hard and LHC compatible (a 40 MHz clock, etc) • We are investigating the CAEN 1290 VME boards (containing HPTDC chips) for use in the summer 2008 test beam at CERN • The Alberta group is designing a rad-hard HPTDC board for ATLAS • For the GASTOF detector a single photon counter (Boston Elec. SPC-134 with 5ps rise time ) can replace the amp+CFD+TDC ($10K/channel) Combined in the ALTA approach James L Pinfold Manchester 2006 7

9. Location of the Electronics Subsection 1.7 - Electronics and Data Acquisition • The amplifier-CFD combination would ideally be placed close to the detector: • We will utilize SMA 18 GHZ cable and may locate these electronics in a shielded compartment in the base of the cryostat support • If the radiation hardness of the CFD is an issue we will keep the amplifier near (~1m) to the detector and have a remote CFD (Louvain solution) located near to the TDC • The TDC board (and possibly the CFD) will be housed in a small radiation shielded crate in the vicinity (5m10m?) of the FP420 detector • Low and High voltage power supplies are standard units will follow the same specification as the silicon detector supplies Combined in the ALTA approach James L Pinfold Manchester 2006 8

10. Test Beam Studies (1) Subsection 1.5 - Performance in Test Beam Measurements • T958 FNAL Test beam using pre-prototype/prototype detectors with NIM/CAMAC readout in Fall 2006, Mar 2007 and July 2007. • Test beam was 120 GeV protons • CERN test beam in October 2007. GHz Tektronix DPO70404 4 GHz Digital Osc.  James L Pinfold Manchester 2006 9

11. FNAL Test Beam Setup Subsection 1.5 - Performance in Test Beam Measurements Test Beam Phase II March 2007 • DAQ system triggered by scintillator tiles of each end of the detector setup • Multiwire chambers provide track position measurement information • Two GASTOFS (G1&G2) and two 8-channel QUARTICS (QA&QB) used • Readout: • G1 (Burle 85011-501 25mm pores), G2 (Hamamatsu R3809U-50 6mm pores) • QA used Burle 85011-501 with 10 and 25 mm pores, respectively James L Pinfold Manchester 2006 10

12. CERN Test Beam Setup Subsection 1.5 - Performance in Test Beam Measurements • ATLAS silicon tracking + FP420 3-D silicon prototype • One GASTOF and two new one row 8-channel QUARTICS used • Readout: • GASTOF use a Hamamatsu R3809U-50 6mm pores • QUARTIC A and B used Burle 85011-501 with 10 and 25 mm pores • CERN run included HPTDC tests using a CAEN board • Test beam results still under consideration Test Beam Layout October 2007 James L Pinfold Manchester 2006 11

13. Test Beam Studies (2) Subsection 1.5 - Performance in Test Beam Measurements • First results (2006 TB) • GASTOF <70 ps/GASTOF , 90% efficiency • QUARTIC 110 ps/bar Efficiency 50-60% • QUARTIC - For events with a few bars on we see the anticipated √N dependent improvement G1-G2 James L Pinfold Manchester 2006 12

14. Extrapolating Results (2007 TB) Subsection 1.5 - Performance in Test Beam Measurements • For the GASTOF detectors alone taking out the effect of the electronics): • 32 ps for GASTOF GI & 13 ps for GASTOF G2 • The efficiencies are: • 98% for G1 & 80% for G2 • The single channel GASTOF will use a photon counter with resolution < 13ps from GASTOF only, with this readout we expect overall GASTOF+electronics resolution between 15-20 ps range. • The overall performance of the QUARTIC bars + electronics was improved from 110 ps/bar (1st run) to 82 ps/bar(2nd run) • Unfolding the resolutions of the QUARTIC bars we find a time resolution of ~60 ps (82ps with the addition of the CFD+TDC) • The efficiency of the quartic bars is ~80% • Thus we expect ~13 measurements for two 8-bar QUARTICs • This implies a resolution of ~23 ps from the QUARTIC detectors alone using the measured resolution of 82 ps. • Assuming 80% efficiency the expected resolution with envisaged improvements in the electronics is 66ps/√13 = 18ps. James L Pinfold Manchester 2006 13

15. Reference Timing System Subsection 1.5 – Reference Timing System • A reference is obtained from the 400 MHz LHC RF converted to an optical pulse which is split and sent along fibres to both L & R detectors for each BC - pulse to pulse jitter between pulse arrival is negligible • To monitor long term drifts (e.g. DTemp between two arms) the optical signal will be split at the detectors and returned to source for comparison • At the detector stations the optical pulses are converted to electrical signals and are recorded in the detector TDCs – this conversion is envisaged to give an r.m.s (L-R) jitter of 4 ps. • Our reference timing system is designed to provide sLR ~ 5 ps James L Pinfold Manchester 2006 14

16. Central Detector Timing Subsection 1.8 – Central Detector Timing • We can also use the central detector to provide timing information for background reduction • One would use the LAr EM calorimeter to provide the timing measurements. • A 70 ps event resolution already would provide an additional factor of two in pile-up rejection (already useful). • If it were possible to reduce the noise term to ~10 ps – in this case there would be an additional factor of 12 rejection. From Test Beam ECAL Noise Term 500 ps/E(GeV) Constant term 70 ps Jet-1 Jet-2 James L Pinfold Manchester 2006 15

17. Central Detector Timing - Suggested in 2001 A “QUARTIC-type” detector was also described in this document James L Pinfold Manchester 2006 16

18. New Developments (QUARTIC -1) • Preliminary test of the Alberta ACFD board by Jerry Va’vra at SLAC using a laser gave a measured resolution of 19 ps • Experience with this test system indicates that the ACFD itself adds less than 15ps to the measurement • Work on the ATLAS HPTDC board has begun at Alberta spearheaded by Shengli Liu (HPTDC board) with Lars Holm (ACFD board) + Scott Kolya & Marc Kelly (FP420/ATLAS interface) • Aim to have 8 channel board (1 HPTDC) ready for summer test beam. • First in a series of regular meetings on CFD+HPTDC development starting at CERN in January. • Fast timing group being set up at FNAL (Mike) – starting 12/07 James L Pinfold Manchester 2006 17

19. New Developments (QUARTIC-2) James L Pinfold Manchester 2006 18

20. New Developments-(QUARTIC-3) • Hardware: • FNAL has built a single row detector for CERN test beam to reduce coherent noise, cross-talk, etc. • We now have a Lecroy Model WAVEMASTER 8620A 4 ch, 6 GHz BW, 20GS/s per channel, 10 Mpts/ch (acquired by AB) • Putting together a laser test stand, using a PLP-10 picosecond laser for bench testing of QUARTIC • Testbeam plans – we will run at CERN in June and September • June 2008 run will take more scope data and use CAEN based HPTDC • September 2008 run integrated test-beam with timing detectors in the readout • People • Andrew will be on sabbatical at CERN from January to August 2008 • We graduated two key people Yao (Alberta - pending PhD exam) and Duarte (UTA - MSc) • Currently on QUARTIC we only have Shane Sivey at UTA - we are looking for new students James L Pinfold Manchester 2006 19

21. New Developments (GASTOF) • Start detailed laser tests to finalize FE electronics and study rate effects • Finalize irradiation studies of PMT-MCP (including online data), start FE irradiations • Complete MC studies for next Gastof prototype, and multicell solution • Prepare full DAQ test setup James L Pinfold Manchester 2006 20

22. Future Plans and Concerns Subsection 1.9 Future Plan and Concerns • We need a simulation of the radiation environment of the detectors for: • Detector background calculations • Radiation testing of electronics and detector components • We need to radiation hardness studies of QUARTIC + electronics • Our goal is 10 ps timing resolution, e.g. • We are investigating a QUARTIC geometries with improved light output • Improve monitoring/understanding of light output, efficiency & correlations between QUARTIC bars • Improving electronics and simulation of the detector+readout • We are also looking into timing more than one proton per event by: • Using multiple GASTOFs • Deploying smaller granularity bars and pixels in QUARTIC • Reference timing is also being looked at, options include interferometrically stabilized fibre-optic links. • We are studying other light detectors such as silicon PMTs • We are also working with other groups in the area of fast timing eg H. Fritsch at Chicago who is developing detectors with ~ps resolution. James L Pinfold Manchester 2006 21

23. Conclusions • We are on track for ~10 ps resolution with no obvious show stoppers • If all works well the jitter on the reference timing will be ~5ps Looking to the future • Cerenkov radiators can provide the necessary fast signal • The reference timing could be interferometrically stabilized fibre-optic links (claim ~10fs resolution) • BUT, the best transit time jitter in a MCP-PMT seems to be ~10ps • In order to get to get ~2ps for high lumi running we face a challenge • We could proceed by following the ideas of H. Frisch who is aiming for 1 ps ToF resolution: • Small pore size MCPs • Precision simulations • Custom made fast electronics • OR - we could use some new technology • We have taken up this challenge James L Pinfold Manchester 2006 22

24. EXTRA SLIDES

25. TIMING DISTRIBUTION IN ACCELERATORS VIA STABILIZED OPTICAL FIBER LINKS* A schematic of the concept for transmission of an RF signal is shown in Fig. 1. The RF modulates the amplitude of an optical carrier of a frequency-stabilized laser with a 2 kHz linewidth (greater than 25 km coherence length.) The fiber stabilization system relies on maintaining constant the relative optical phase between the forward optical carrier and the signal reflected at the far end of the fiber in an unequal arm Michelson interferometer configuration, consisting of the transmission fiber (longarm) and a reference fiber (short arm). At the receiver end of the fiber an acousto-optic frequency shifter doubly shifts the retroreflected optical carrier (and AM sidebands) by 55 MHz. When the long and short arm signals are superimposed on a photodiode, a beat at 110 MHz is seen, which can be compared in phase with a 110 MHz reference oscillator. When these 110 MHz signals are stabilized in relative phase, the optical phase delay of the transmission fiber is constant with respect to the reference. This technique is called optical heterodyning[3].