Micromegas TPC Beam Test Micromegas TPC Beam Test ResultResult

H.Kuroiwa (Hiroshima Univ.)

Collaboration with Saclay, Orsay, Carlton, MPI, DESY, MSU, KEK, Tsukuba U, TUAT, Kogakuin U, Kinki U,

Saga U

MotivationMicromegasTPCSetupPreliminary ResultsSummary

The 8th ACFA Workshop on Physics and Detector at the Linear Collider

Jul. 12, 2005, EXCO, Daegu, Korea

MotivationMotivation

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, 2005We try to understand Micromegas TPC performance

Previous talk

MicromegasMicromegas

Micromesh supported by 50-100μm - high insulating pillars

Multiplication takes place between the anode and the mesh

One stage Direct detection of avalanche electr

ons– Small E×B effect– Fast signals– Self-suppression of positive ion feedba

ckthe ions return to the grid

– Better spatial resolution– No wire angular effect

50μm

S1

S2

TPCTPC 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 sensit

ive sampled every 80 ns digitized by 6 TPDs

Mesh SignalsMesh Signals

There is a 55Fe 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 Ampte

k)

55Fe 6keV

Escape 3keV

Ar + 5%isobutane

Experimental SetupExperimental Setup

KEK-PS π2 beam line– 4GeV π-

Super conducting magnet (JACEE)– B = 0, 0.5 and 1T

Gas– Ar + isobutane (95:5)

vd = 4.18cm/μsec at 220V/cm

Preliminary ResultsPreliminary Results

Charge DistributionPad ResponseX ResolutionZ Resolution

•Analysis–Double fit (developed at DESY)

Charge DistributionCharge Distribution Charge distribution (B = 1T)

– For 12 rows

charge distribution at Row6 as a function of Z

We saw no significant attenuation

Edge effect

Edge effect

Pad Response FunctionPad Response Functionis evaluated by a normalized charge (NQi = Qi/∑Q)

on pad i, as a function of (Xpad - Xtrack)

anode Z →

cathode

Charge width for different drift regions (B = 0T)

Distribution becomes wider at longer drift distance

B = 0T

B = 0.5T

B = 1T

Measured CD in good agreement with Mag. Simulation

Width of PRF Width of PRF as a function as a function of Zof Z

Preliminary resultsPreliminary results

X Resolution X Resolution as a function of Z as a function of Z

cmmMagCd /469)(

cmmMagCd /285)(

cmmMagCd /193)(

Cd fixed for each B

12/3.2 mm

Row6 + Row7Cd = Cd(PRF)

Preliminary resultsPreliminary results

X Resolution (How to Fit?)X Resolution (How to Fit?)

σ0 : resolution w/o diffusionCd : diffusion constant Neff : effective number of electrons

effx N

zCd

22

02

Diffusion

Other1- fix Cd from PRF

2- fit σx = f(z) with σ0 and Neff free

3- Plot Magboltz curve with :σ0 obtained from the fit (2)Cd is known Neff from (2)

Z Resolution Z Resolution as a function of Z as a function of Z

σz 500μm at 0.5T⋍

B = 0T

B = 1T

B = 0.5T

Unlike σX, σZ has no significant B-dependence

Preliminary resultsPreliminary results

SummarySummary

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

σx 200μm , σ⋍ z 800μm at 1T⋍

– But these results are still very preliminary