1. Micromegas TPC Beam Test Result H.Kuroiwa (Hiroshima Univ.) Collaboration with Saclay, Orsay, Carlton, MPI, DESY, MSU, KEK, Tsukuba U, TUAT, Kogakuin U, Kinki U, Saga U Motivation Micromegas TPC Setup Preliminary Results Summary The 8 th ACFA Workshop on Physics and Detector at the Linear Collider Jul. 12, 2005, EXCO, Daegu, Korea

2. Motivation Comparison of several sensors using same Field Cage, Electronics, analysis – MWPC : Beam test in Jun, 2004 – GEM : Beam test in Apr, 2005 – Micromegas Beam test in Jun. 22 ～ Jul. 1, 2005 We try to understand Micromegas TPC performance Previous talk

3. Micromegas Micromesh supported by 50-100μm - high insulating pillars Multiplication takes place between the anode and the mesh One stage Direct detection of avalanche electrons – Small E×B effect – Fast signals – Self-suppression of positive ion feedback the ions return to the grid – Better spatial resolution – No wire angular effect 50μm S1 S2 

4. TPC Length of FC : 26 cm Pad – 2×6 mm, 0.3mm gap – 32 pads×12 pad rows ⇒ 384 readout channels – Non-staggered – Pad plane : 10×10cm Readout –ALEPH TPC electronics 24 amplifiers, 16 channels each 500ns shaping time, charge sensitive sampled every 80 ns digitized by 6 TPDs

5. Mesh Signals There is a 55 Fe source attached on the back of the cathode plane to monitor Micromegas stability by looking at mesh signals (Readout by a multi channel analyzer MCA 8000 from Amptek) 55 Fe 6keV Escape 3keV Ar + 5%isobutane

6. Experimental Setup KEK-PS π2 beam line – 4GeV π - Super conducting magnet (JACEE) – B = 0, 0.5 and 1T Gas – Ar + isobutane (95:5) v d = 4.18cm/μsec at 220V/cm

7. Preliminary Results Charge Distribution Pad Response X Resolution Z Resolution Analysis –Double fit (developed at DESY)

8. Charge Distribution Charge distribution (B = 1T) – For 12 rows charge distribution at Row6 as a function of Z We saw no significant attenuation Edge effect

9. Pad Response Function is evaluated by a normalized charge (NQ i = Q i /∑Q) on pad i, as a function of (X pad - X track ) anodeZ → cathode Charge width for different drift regions (B = 0T) Distribution becomes wider at longer drift distance

10. B = 0T B = 0.5T B = 1T Measured C D in good agreement with Mag. Simulation Width of PRF as a function of Z Preliminary results

11. X Resolution as a function of Z C d fixed for each B Row6 + Row7 C d = C d (PRF) Preliminary results

12. X Resolution (How to Fit?) σ 0 : resolution w/o diffusion C d : diffusion constant N eff : effective number of electrons DiffusionOther 1- fix C d from PRF 2- fit σ x = f(z) with σ 0 and N eff free 3- Plot Magboltz curve with : σ 0 obtained from the fit (2) C d is known N eff from (2)

13. Z Resolution as a function of Z σ z ⋍ 500μm at 0.5T B = 0T B = 1T B = 0.5T Unlike σ X, σ Z has no significant B-dependence Preliminary results

14. Summary To measure Micromegas TPC performance – We did the beam test at KEK-PS π2 beam line using 4GeV neg. pions in magnetic field – Micromegas in TPC worked stably Measured diffusion constants are consistent with Mag. simulation σ x ⋍ 200μm, σ z ⋍ 800μm at 1T – But these results are still very preliminary