Micromegas TPC Berkeley-Orsay-Saclay Progress Report

1. Micromegas TPCBerkeley-Orsay-Saclay Progress Report Durham ECFA LC WORKSHOP F. Bieser1, R. Cizeron3,M. Chefdeville4, P. Colas4, C. Coquelet4, E. Delagnes4, A. Giganon4, I. Giomataris4, G. Guilhem3, V. Lepeltier3, J. Pouthas 2, Ph. Rebourgeard4, J.-P Robert4, M. Ronan1, T. Zergueras2 (and many others, not mentionned) 1) LBNL Berkeley, 2) IPN Orsay, 3) LAL Orsay, 4) DAPNIA Saclay • Reminder: the Berkeley-Orsay-Saclay cosmic setup • News since the Paris LCWS : cosmic ray data taking • First preliminary results • Future plans P. Colas - Micromegas TPC

2. The setup Berkeley Saclay Orsay Chamber diameter 50 cm length 50 cm Readout anode pad plane 1024 pads 2x10 mm2 pads 1x10 mm2 pads Copper mesh 50 m pitch 50 m gap P. Colas - Micromegas TPC

3. Online event display (software from D. Karlen, adapted by M.Ronan) Rows 4 & 5 P. Colas - Micromegas TPC

4. History and news Preparatory experiments in a magnetic field (March 2002, June 2002 and January 2003 data takings) showed that Micromegas keeps its good properties in a magnetic field. Pilot run (2 weeks) in November 2003 showed that the whole chain worked well, but DAQ needed to be speeded up. New run (3 weeks) was taken in April-May 2004, with: - new PC - speeded-up DAQ program - optimized triggering Good event rate (was improved by a factor of 20). P. Colas - Micromegas TPC

5. Data 150 000 cosmic tracks recorded at magnetic fields of 0.1, 0.3, 0.5, 0.7, 1, 1.5 & 2 tesla with Ar-CF4:3%, Ar-CH4:10%(P10), Ar-Isobutane:5% and some TDR gas data. Trigger simulation shows good understanding of angular distribution. P. Colas - Micromegas TPC

6. The vessel remained filled with Ar+CF4 for 5 months : no loss of efficiency (However a sudden current increase lead us to remove one card after 10 days. Investigate this month) Aging issues New results obtained at high statistics Measurements of drift velocities: very good agreement with Magboltz, percent level Measurements of diffusion constants : systematics under study Measurement of resolution: very promissing Hope some final results for the Rome IEEE conference. B = 1 T P. Colas - Micromegas TPC

7. Micromegas operation The chamber seems to have very uniform gain response, and the electronic noise is quite low. Plots are shown of the number of pads forming each cluster and of the summed amplitude signals for both 2X10 mm2 pad rows (#0,#1,#8 & #9) and the 1X10 mm2 pad rows (#4 & #5). 2mm pads 2mm pads 1mm pads 1mm pads P. Colas - Micromegas TPC

8. New Ar+3% CF4 results The transverse diffusion is clearly seen in the plot of track width vs. drift distance. We have developed ntuple analysis software to look into the following performance characteristics of our Micromegas TPC operating with ArCF4: - Drift velocity - Transverse diffusion - Gas attenuation - Position resolution - dE/dx resolution - Timing resolution P. Colas - Micromegas TPC

9. Drift velocity measurement We measure the drift velocity from the drift time distribution as shown. The trigger delay to the readout system and pedestal stabilization results in a loss of information for short drift times. The far end of the chamber at roughly 50 cm begins to cut off the distribution at about 100 clock ticks depending on track dip angle. We take the max. drift time from the distribution to be 105 +- 2 ticks. We also determine the drift velocity from individual tracks which are found to exit the far end of the chamber. P. Colas - Micromegas TPC

10. Transverse diffusion measurement We determine the transverse diffusion from max. likelihood fits to individual anode pad signals on 6 pad rows (4 w/ 2mm pitch and 2 rows w/ 1mm pitch). The fitted track spread is used to measure the transverse diffusion. We find no evidence of any track angle dependence in the measurement as shown below. For Ar-CF4:3% at B = 1 Tesla, we measure trans. diff. = 68±0.9 (stat only) microns / cm This implies an expected transverse spread of about 360 microns after 2.5 m drift in a 3 Tesla magnetic field, and a diffusion limited point resolution of 60 microns for 2 mm pads. P. Colas - Micromegas TPC

11. Gas attenuation measurement We have not studied dE/dx information very carefully but have made a truncated mean calculation using the lowest 4 out of 6 pad rows. Using the calculated TrMean we can check the attenuation length in ArCF4 with our relatively long drift length. We find that the attenutation length in ArCF4 is larger than 440 cm at 90% confidence. P. Colas - Micromegas TPC

12. Transverse position resolution We determine the resolution by comparing the position measurements of the two center 1mm pad rows, correcting for track angles and for track fitting errors. The resolution measurements are binned in drift distance and fit with a linear dependence. We take the zero drift intercept as the intrinsic position measurement resolution. We obtain position resolutions as small as 80 microns for vertical tracks using our 1X10 mm2 pads. P. Colas - Micromegas TPC

13. Timing measurement To obtain a first measure of track timing capabilities of a Micro-Pattern Gas Detector (MPGD) TPC, we can compare the time measured in rows 4 and 5. Evt #20 row #4 pad 487 row #5 pad 615 Z position measurement and track timing measurement currently limited by pulse shape analysis software (170 mm). P. Colas - Micromegas TPC

14. Surprise B=1 tesla We observe a strong dependence of the total amplitude on the magnetic field. Not explained by relativistic rise of dE/dx Electronics? Mechanical effect on mesh? Apparent contradiction with previous measurements with a 55Fe source! Cosmic ray data Average amplitude sum To be investigated… (harmless anyway) Magnetic field (T) P. Colas - Micromegas TPC

15. Conclusions The Berkeley-Orsay Saclay Micromegas TPC has taken good data and will get a harvest of interesting measurements. Future plans include: Test charge spreading with a resistive anode with our canadian colleagues Perform beam tests in the MPI setup at KEK Intensify electronics R&D P. Colas - Micromegas TPC