Gain fluctuations and Neff Analysis of March 2010 data Neff measurement Gain fluctuation measurements with TimePix Beijing, 30/03/20101 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting FJPPL-FCPPL-LCTPC Analysis meeting

B=0 data : Drift velocity measurements Vdrift = cm/µs at E=230 V/cm (Magboltz : (gas comp.)) The difference is % Beijing, 30/03/20102P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

B=0 data : Drift velocity measurements Drift Velocity in T2K gas and compared to Magboltz simulations for P=1035 hPa, T=19°C and 35 ppm H 2 0 Beijing, 30/03/20103P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

Beijing, 30/03/2010P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting4 Pad Response Functions, z ~ 5 cm CLPResistive ink B=1T data : comparison of resistive ink and Carbon-loaded polyimide

Bias Beijing, 30/03/2010P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting5

Residuals Beijing, 30/03/2010P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting6

Z=5cm Z=35cm Z=50cm MEAN RESIDUAL vs ROW number Z-independent distortions Distortions up to 50 microns for resistive paint Rms 7 micron for CLP film Beijing, 30/03/20107P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

Resolution vs Drift Distance  2 /NDOF = 15.4 / 11 CLP module Beijing, 30/03/20108P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting Fits for Z>30 and z<30 give consistent results

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

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

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

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

RESULTS  0 = 53 µm : confirms previous results. 1/57 times the pad size. No hodoscope effect down to 3cm drift. N eff = 42.5 ± 0.5 (stat) ± 1.5 (C D ) at P=1035 hPa, with C D = 95.5±1.6 µm/√cm(B=0.98 T). – To be compared to -1 from Heed (H. Schindler) : 47.1 (in these conditions) Thus / 2 = 1.11 ± 0.04 (  polya ~8±2.3 !) Beijing, 30/03/201013P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

Expectation from Heed (H.Schindler) Beijing, 30/03/201014P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 1/N 5 GeV electrons Pad length 6.84 mm

Discussion N eff is close to the maximum value allowed by ionization statistics. Penning effect in the drift volume could increase N eff Difficult to imagine un-controlled systematics that lead to overestimate N eff Maybe C D is overestimated but unlikely. Usually measurements agree within few % Beijing, 30/03/201015P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

Expectations for 1/ Pitch 6.84 mm Pitch 5.4 mm 5 GeV e MeV µ Beijing, 30/03/2010P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting16 Caveat : does not scale with pad length! (would be false by 7% between 5.4 and 7mm) So it makes no sense to give it by unit length! P=1035 hPa T=19°C T2K gas Pitch 6.84 mm Pitch 5.4 mm 5 GeV e MeV µ Expectations for N tot

Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 17 Ar:CO2 / 90:10 C D = 223 µ/√cm Neff ~ 26 (cosmics, 6mm pads) Unpublished result

Beijing, Feb.6, 2007P. Colas - Micromegas TPC18 4 GeV/c  + beam, B=1T (KEK) Effect of diffusion: should become negligible at high magnetic field for a high  gas

Madhu Dixit LCWS10, Beijing 19 Transverse spatial resolution Ar+5%iC4H10 E=70V/cm D Tr = 124 µ/  cm B= 1T 2 mm x 6 mm pads σ 0 =(27±2)μm N eff =35.9±1.3 σ 0 =(50±2)μm N eff =21.1±1.1 KEK B=1T 4 GeV π+ beam - resolution comparison Old algorithm vs new fixed window PRF algorithm Preliminary

Beijing, Feb.6, 2007P. Colas - Micromegas TPC20 Gain = 4700 Gain = 2300 Neff=25.2±2.1 Neff=28.8±2.2 At 4 T with this gas, the point resol° is better than 80 µm at z=2m B=0.5 T Resolution at 0 distance ~50 µ even at low gain ACFA LCWS 2007, Cosmics (COSMO)

Dependence of resolution with data taking conditions Beijing, 30/03/201021P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting Relaxed fiducial cuts Z=5cm

Same, with hard fiducial cuts Beijing, 30/03/2010P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting22 Peaking time (ns) Resolution (µm) CLP module

Dependence of resolution with data taking conditions Resolution at z=5cm (µm) V mesh (V) Beijing, 30/03/201023P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

Avalanche statistics Polya : not the exact solution, but provides a simple parametrization of the avalanche size G. Z = G / Beijing, 30/03/201024P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting  = 0 : exponential distribution K. Fujii

Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 25 Micromegas + TimePix TimePix READOUT MICROMESH DRIFT DRIFTSPACE E D ~ 0.7 kV/cm E D ~ 0.7 kV/cm E A ~ 80 kV/cm InGrid (Nikhef-Twente) 2.5 cm 50 µm Fe 55 source Chamber operated with an Ar+5% isobutane mixture

Beijing, 30/03/ ) 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  parameter P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting threshold 3) (not repeated here, see RD51 in Crete) Measure fluctuations of primary ionization and derive gain fluctuations from energy resolution.

Gain fluctuations from Time Over Threshold 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 electrons. This gives a direct access to avalanche size. Number of electrons Beijing, 30/03/ P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting TOT (in 28 ns time bins) U in (Volts)

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

Avalanche size distribution from TOT Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 29 Polya fits above Zmin = 5000/ (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 meshGain fitted  310 V ± V ± V 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?)

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

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

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/ P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting

Data V mesh = 350 V NUMBER OF CLUSTERS Beijing, 30/03/ P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 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) Gas : Ar+5% isobutane

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

Collection efficiency from simulation : 96.5±1 % Gain measurements (from a 80x80 mm2 copper mesh with the same gap 50 µm, gas : Ar+5% isobutane) Beijing, 30/03/ P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting Prediction from R. Veenhof et al., Data (in red) from D. Attié et al. (see also D. Arrogancia et al. 2009) 2µ thickness 1µ thickness

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

Determination of W and F Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 37 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 : % from simulation. Using the escape peak: W= 2897 eV / = eV This translates to electrons for the 5.9 keV 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. Gas : Ar+5% isobutane

Next steps Measure space resolution for a given length of charged track with TimePix or Octopuce data, and cross-check Ntot from Heed with data Beijing, 30/03/2010P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting38

CONCLUSIONS Beijing, 30/03/2010 P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting 39 InGrid, Microbulk, and TimePix 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  close to 1 at moderate gain and reaching a few units at gains of 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

Thanks to D. ATTIÉ 1), 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/ P. Colas - FJPPL-FCPPL-LCTPC Analysis meeting