FJPPLFCPPLLCTPC Analysis meeting Gain fluctuations and Neff Analysis

FJPPL-FCPPL-LCTPC Analysis meeting Gain fluctuations and Neff Analysis of March 2010 data Neff measurement Gain fluctuation measurements with Time. Pix Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 1

B=0 data : Drift velocity measurements (200 ns shaping) Tmax (μs) 10 9 8 7 6 5 4 3 2 Module 4 Module 5 1 0 0 10 20 30 40 50 60 Z (cm) Vdrift = 7. 698 +- 0. 040 cm/µs at E=230 V/cm (Magboltz : 7. 583+-0. 025(gas comp. )) The difference is 1. 5+-0. 6 % Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 2

B=0 data : Drift velocity measurements Drift Velocity in T 2 K gas and compared to Magboltz simulations for P=1035 h. Pa, T=19°C and 35 ppm H 20 Vd (cm/μs) 9 8 7 6 5 4 Simulations (Magboltz) 3 2 1 0 0 100 200 300 400 Ed (V/cm) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 3

B=1 T data : comparison of resistive ink and Carbon-loaded polyimide Pad Response Functions, z ~ 5 cm Resistive ink Beijing, 30/03/2010 CLP P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 4

Bias Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 5

Residuals Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 6

MEAN RESIDUAL vs ROW number Z=5 cm Z-independent distortions Distortions up to 50 microns for resistive paint Rms 7 micron for CLP film Z=35 cm Z=50 cm Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 7

Resolution vs Drift Distance CLP module c 2 /NDOF = 15. 4 / 11 Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting Fits for Z>30 and z<30 give consistent results 8

Reject multiple tracks Relaxed cuts : less than 5 hits (>30 ADC) outside 10 central pad lines Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 9

Stability with cuts Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 10

Stability of Neff with gain Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 11

Neff is the same for resistive ink Resistive ink module Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 12

RESULTS • s 0 = 53 µm : confirms previous results. 1/57 times the pad size. No hodoscope effect down to 3 cm drift. • Neff = 42. 5 ± 0. 5 (stat) ± 1. 5 (CD) at P=1035 h. Pa, with CD = 95. 5± 1. 6 µm/√cm(B=0. 98 T). – To be compared to • <1/N>-1 from Heed (H. Schindler) : 47. 1 (in these conditions) • Thus <G 2>/<G>2 = 1. 11 ± 0. 04 (qpolya ~8± 2. 3 !) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 13

Expectation from Heed (H. Schindler) 5 Ge. V electrons Pad length 6. 84 mm 1/N Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 14

Discussion • Neff is close to the maximum value allowed by ionization statistics. • Penning effect in the drift volume could increase Neff • Difficult to imagine un-controlled systematics that lead to overestimate Neff • Maybe CD is overestimated but unlikely. Usually measurements agree within few % Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 15

Expectations for 1/<1/N> P=1035 h. Pa T=19°C T 2 K gas Pitch 6. 84 mm (m. M@DESY) Pitch 5. 4 mm (GEM@DESY) 5 Ge. V e- 47. 1 34. 9 320 Me. V µ 32. 1 23. 8 Caveat : does not scale with pad length! (would be false by 7% between 5. 4 and 7 mm) So it makes no sense to give it by unit length! Expectations for Ntot Beijing, 30/03/2010 Pitch 6. 84 mm (m. M@DESY) Pitch 5. 4 mm (GEM@DESY) 5 Ge. V e- 61. 9 49. 0 320 Me. V µ 46. 0 36. 5 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 16

ult s re d he s i l Ar: CO 2 / 90: 10 ub p n U CD = 223 µ/√cm Neff ~ 26 (cosmics, 6 mm pads) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 17

4 Ge. V/c + beam, B=1 T (KEK) Effect of diffusion: should become negligible at high magnetic field for a high t gas Beijing, Feb. 6, 2007 P. Colas - Micromegas TPC 18

KEK B=1 T 4 Ge. V π+ beam - resolution comparison Old algorithm vs new fixed window PRF algorithm Transverse spatial resolution Ar+5%i. C 4 H 10 E=70 V/cm DTr = 124 µ/ cm (Magboltz) @ B= 1 T Preliminary σ0=(50± 2)μm Neff=21. 1± 1. 1 σ0=(27± 2)μm Neff=35. 9± 1. 3 2 mm x 6 mm pads Madhu Dixit LCWS 10, Beijing 19

ACFA LCWS 2007, Cosmics (COSMO) • B=0. 5 T • Resolution at 0 distance ~50 µ even at low gain Gain = 2300 Gain = 4700 Neff=28. 8± 2. 2 Neff=25. 2± 2. 1 At 4 T with this gas, the point resol° is better than 80 µm at z=2 m Beijing, Feb. 6, 2007 P. Colas - Micromegas TPC 20

Dependence of resolution with data taking conditions Relaxed fiducial cuts Z=5 cm Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 21

Same, with hard fiducial cuts 140 CLP module Resolution (µm) 120 100 80 60 40 20 0 1000 Peaking time (ns) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 22

Dependence of resolution with data taking conditions Resolution at z=5 cm (µm) 90 80 70 60 50 40 30 20 10 0 350 370 390 410 Vmesh (V) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 23

Avalanche statistics K. Fujii Polya : not the exact solution, but provides a simple parametrization of the avalanche size G. Z = G / <G> q = 0 : exponential distribution Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 24

Micromegas + Time. Pix Fe 55 source DRIFT Chamber operated with an Ar+5% isobutane mixture DRIFT SPACE ED ~ 0. 7 k. V/cm MICROMESH EA ~ 80 k. V/cm READOUT 2. 5 cm 50 µm Time. Pix In. Grid (Nikhef-Twente) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 25

1) Measure Time Over Threshold (linear with charge above 5 ke-) for single isolated pixels : direct access to avalanche charge distribution. 2) See electrons from an X-ray conversion one by one (55 Fe) and count them. Efficiency vs gain sensitive to q parameter threshold Beijing, 30/03/2010 3) (not repeated here, see RD 51 in Crete) Measure fluctuations of primary ionization and derive gain fluctuations from energy resolution. P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 26

Gain fluctuations from Time Over Threshold This gives a direct access to avalanche size. Number of electrons 10000 20000 30000 TOT (in 28 ns time bins) Select isolated clusters with only 1 pixel. These are single electron avalanches (~10 µ rms radius). TOT is linear with number of electrons seen by the amplifier above 5 ke- : Ne = 167 TOT – 6700 (red curve, corresponding to the threshold setting of our data taking) Valid up to 30 000 electrons. U in (Volts) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 27

Z from Time Over Threshold distributions Z = G/<G> = (167*TOT-6700)/G(V) from a measurement using a source. Unfortunately, the tails are dominated by TOT resolution effects. Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 28

Avalanche size distribution from TOT Polya fits above Zmin = 5000/<G> (region of linearity of TOT) are good However theta values are not reliable (very correlated with the gain measurement and the TOT scale. There is a discrepancy between the average number of electrons and the gain: this is a possible effect from the protection layer and from the shaping by electronics. HV mesh Gain fitted q 310 V 2900 5. 3± 1. 3 330 V 6000 3. 4± 0. 1 350 V 12600 4. 2 We do not regard these fitted values as measurements of theta. They point to a value of ~4 but with very large systematic errors (factor of 2? ) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 29

Monte Carlo simulation ELECTRON COUNTING Gas : Ar+5% isobutane Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 30

In our setup, we use the Chromium K-edge to cut the Kb line (Center for X-Ray Optics) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 31

Monte Carlo simulation. Shows that we need enough drift distance to separate the clusters. Also shows that the escape peak is better contained than the photopeak. Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 32

Drift distance (z) cut performed using the diffusion : sqrt(rmsx 2 + rmsy 2 ) > 28 pixels (cluster separation) Cloud center within a window around the chip center (containment) Data Vmesh = 350 V Gas : Ar+5% isobutane NUMBER OF CLUSTERS Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 33

Use escape peak (only one line, better contained) Then correct for collection efficiency (96. 5 +- 1 % from MC, in this range of field ratios : 80 -90) Convert U_grid into gain/threshold (threshold = 1150 e-) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 34

Collection efficiency from simulation : 96. 5± 1 % Gain measurements (from a 80 x 80 mm 2 copper mesh with the same gap 50 µm, gas : Ar+5% isobutane) 1µ thickness 2µ thickness Prediction from R. Veenhof et al. , Data (in red) from D. Attié et al. (see also D. Arrogancia et al. 2009) Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 35

q~1 at moderate gain (few 1000). Maybe higher at gains above 5000 Exponential behaviour (q=0) strongly excluded, as well as q>2 Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 36

Determination of W and F The background is totally negligible (time cut taking 30 time buckets around the electron cloud among 11000) The probability for merging two clusters is small, with the rms cuts. The probability for loosing electrons by the containment cuts is small. Attachment also is negligible. The main inefficiency comes from collection : 96. 5+-1 % from simulation. Using the escape peak: W= 2897 e. V / 120. 4 = 24. 06 +- 0. 25 e. V Gas : Ar+5% isobutane This translates to 245+-3 electrons for the 5. 9 ke. V line, larger than what is usually admitted for pure Ar (227). Photoelectric effect on the mesh is not excluded. This could also be a Penning effect in the conversion region. The Fano factor could be derived from the rms of the escape line (6. 8 e- ) but needs large corrections from inefficiencies. Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 37

Next steps • Measure space resolution for a given length of charged track with Time. Pix or Octopuce data, and cross-check Ntot from Heed with data Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 38

CONCLUSIONS In. Grid, Microbulk, and Time. Pix are new detectors which allow to study the conversion and avalanche processes with unprecedented accuracy. Time Over Threshold measurements give access to direct measurement of the fluctuations, provided absolute gain and TOT calibration can be better controlled. The onset of single electron efficiency with Micromegas gain allows the exponential fluctuations to be excluded and favours Polya fluctuations with q close to 1 at moderate gain and reaching a few units at gains of 10 000. To measure Fano fluctuations will require an improved setup with a longer drift and better controled field. Special thanks to R. Veenhof, J. Timmermans and Y. Bilevych Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 39

Thanks to D. ATTIÉ1), M. CAMPBELL 2 ), M. CHEFDEVILLE 3) , E. DELAGNES 1) , K. FUJII 4) , I. GIOMATARIS 1) , H. VAN DER GRAAF 5) , X. LLOPART 2) , M. LUPBERGER 1) , H. SCHINDLER 2) , J. SCHMITZ 6), M. TITOV 1) 1) CEA/Irfu Saclay, 2) CERN, 3)LAPP Annecy, 4)KEK, 5)Nikhef, 6)Twente U. Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 40