FAST: A precision measurement of muon lifetime.

1. FAST: A precision measurement of muon lifetime. Chiara Casella FAST collaboration: A.Barczyk (1) , J. Berdugo (2) , J. Casaus (2) , C. Casella (3,4) , K. Deiters (4), P. Dick (4), A. Dijksman (4), J. Kirkby (1), L. Malgeri (1), C. Mana (2), J. Marin (2), G. Martinez (2), C. Petitjean (4), M. Pohl (3,5), E. Sanchez (2), C. Willmott (2) CERN 1 , CIEMAT 2 , UNIGE 3 , PSI 4 , NIJMEGEN 5 Journée DPNC 2004

2. 9 ppm 0.07 ppm (PDG 2002) 0.5 ppm (Van Ritbergen and Stuart - 1998) ≤12 ppm (PDG 2002) Goal of the experiment • Balandin et al. (1974) • Bardin et al. (1984) • Giovanetti et al. (1984) • the uncertainty on tm is the dominant contribution to the uncertainty on GF: • FAST goal: Journée DPNC 2004

3. Target and optoelectronics readout x 96 x 96 PSPM x 96 Preamp Analogue electronics x 96 Discri LL - data x 16 TDC HL - data • Dual threshold discriminators: • low thr : mip’s • high thr : stopping pcls x 16 LV2 board Digital electronics Description of the experiment 1 pixel=0.4 x 0.4 x 20 cm3 12.8 x 19.2 x 20.0 cm3 32 x 48 pixels = 1536 pixels 8 x 12 = 96 groups of 16 bars p+ DC pion beam p = 170 MeV/c at PSI - pM1 area p+ m+nm tp~ 26 ns m+  e+nmne tm~ 2.2 ms Journée DPNC 2004

4. Sample of 1012 events needed (p+  m+  e+) Suppression of systematic effects at the ppm level Remove time dependent effects that, together with asymmetries in the target, could compromise the measurement High beam rate, because PARALLELISATION is needed! ~ 1 MHz (2-3 months data taking) Very high data rate Constraints on the DAQ FAST DAQ design  80 MB/sec + ONLINE ANALYSIS !!! Ability to disentangle overlapping events Tracking capabilities and high granularity of the target DC beam Isotropic muon source (by the identification of p+  m+ decay) mSR effects suppression 1ppm requirement Journée DPNC 2004

5. LV2 trigger idea: • all the relevant time informations are contained in the “superpixel” (5x5 pixels) centered on the stoppingp • no need to read 16 TDC’s always at the same time – but only the TDC’s containing at least one pixel of the superpixel DATA REDUCTION beam p • LV2 trigger task: • find the stoppingp coordinates • search for the subsequent m • trigger only the interested TDC’s • flag the event if another p is found in the superpixel • (LV2 trigger input = HL data from discriminators) m Level 2 trigger (i.e. data reduction) Max data rate sustainable by DAQ 80 MB/sec (Simulated) Raw data rate from the target 2300 MB/sec Trigger system (level 2 trigger) to reduce data bandwidth: Journée DPNC 2004

6. Level 2 trigger • Level 2 trigger : the only hardware missing element • CIEMAT – Madrid in charge of it • Prototype tests performed: • Single board (1/16) prototype tested - Dec 2003 • Prototype (1/4) tested - June 2004 • Prototype (1/4) test ? - July 2004 (?) • Final level 2 commissioning: end 2004 Journée DPNC 2004

7. 2003 Activities: • Target completed + assembling at PSI • 80/96 tubes available • Complete readout and DAQ chain • No LV2 trigger available • DAQ chain tested • 75 MB/sec • Fine tuning of the detectorand beam (High Voltages, Thresholds, Ranges, Timing properties) • Some problems found • Some improvements needed • Few days of data taking, LV2 trigger prototype tested Beam time: Sept – Dec 2003 Journée DPNC 2004

8. 2003 beam test : fine tuning HV efficiency curves for each tube Preliminary beam tuning (p stopping points distribution) Blind in the vertical (z) direction beam profile ! ! ! beam range of beam p (and m) in the target with variable thickness absorber y x Journée DPNC 2004

9. 2003 beam test : timing properties 20 tubes, 2000 commissioning Afterpulses structure in old commissioned tubes 60 tubes, 2002 commissioning • replaced 20 old tubes • impedance mismatch cured: - preamp modified - replaced preamp / dicrim cables reflection @ 50 ns mismatch prempl/discr Time resolution monitored using straight tracks st~1 ns stable with time Journée DPNC 2004

10. 2003 beam test: Muon lifetime • few days run (‘long run’) • total statistics : 7.4 107 events from online analysis • (10% written to disk for offline studies) • Run conditions: - narrow p trigger - no LV2 trigger ( all 16 TDC’s) - low LV1 (beam) trigger rate • Good background suppression • Good exponential fit: - in agreement with PDG value, within a bigger error: st PDG ~ 40 ps; st 2003 ~ 350 ps Journée DPNC 2004

11. 2003 beam test: Pion lifetime Unexpected result from HL run • Pion lifetime: not primary FAST goal • Short dedicated high threshold run • Good exponential fit, in agreement with PDG value st PDG = 0.005 ns st 2003 = 0.024 ns • Preliminary result… but feasible measurement !!! Journée DPNC 2004

12. What’s going on now • 20 old tubes replaced, 16 new tubes in place • Preamplifiers modified, impedance mismatch cured  Re-tuning of the target • New DAQ version (faster!) • Improvements in the target: • Magnetic field • Z-counter Journée DPNC 2004

13. Permanent magnet ~ 80 G to suppress residual mSR effects: B = 80 G forces m‘s to precess on a known time scale ( ~ 1 ms) z • Suppress beam m’s • Measure vertical beam profile • Measure tm as a function of the z position in the target x y Hodoscope Z-counter Near future improvements Journée DPNC 2004

14. FAST is a small dimension experiment! 2003 testbeam: successful test - Understanding of the detector - Readout and DAQ chain performances - Preliminary (and encouraging) results! 2004 beam time ( 6 August) magnet Z-counter End 2004: Level 2 trigger  First FAST data taking run Conclusions and future plans: Journée DPNC 2004