# Presentation: 469936

##  “miniTPC” plus Double GEM Detector response simulation.                      Hit reconstruction precision.

-  12/04/02  01/22/03  ....
-   R&D PHENIX “Wednesday’s meeting”                                  ( status report )
- N.Smirnov

## Simulation approach (steps)

- Number of ionization interactions / track in a gas    ( F(βɣ)), and position in a space, or “photon absorption position” with “the width of ionization”.
- Number of e- / interaction
- Rectangle and chevron(s) shape of the pad
- “history” of each e-:
-      diffusion – hole – gas amplification – diffusion - hole – gas amplification –diffusion – pad row – pad
-          FEE response ( t-shaping, noise)

## Simulation conditions

- Particle (track) propagation in a gas – GEANT
- Track position: more-less uniform distribution in drift direction;  ~+/-16. deg slope both in xy and zy, picked to zero values.
- Diffusion and Drift velocity is a Function (Gas, E, B).        ( B=0.)
- “Some model” - to calculate/simulate a GEM transparency.
- Gas amplification – Polya distribution, and a function of “r-position” inside of the GEM hole
- “Arriving” time on the pad for each e-   +
-        FEE    t-shaping
- Noise, “(F)ADC” response, pedestal, threshold to select “active” pads.

## Most probable pulse height from three anode strips (0.04 cm); measurement and simulation

-  Double GEM Detector from CERN; 10x10 cm2, 0.04 cm strips.
-   –  measurements were done with X-ray tube; 5.4 keV, 0.01 cm collimator, Ar+CO2(20%)
-  B.Yu at al, IEEE, Nov ,2002
-     – Simulation

## Experimental data for TPC with double GEMs readout (small prototypes) are available (CERN, Canada, Munich, ....)

|  | CERN | Canada |
| --- | --- | --- |
|  Drift distance |      25 cm |      15 cm |
| Transfer Gap |      2.0 mm |      2.2 mm |
|  Induction Gap |      3.0 mm |      5.4 mm |
|  Pad size | 1.27x12.5 mm2 | 2.x6. and 3.x5. mm2 |
| Number of Pad rows |        8 |        5 |
| Working Gas |   P10 |  P10, Ar/CO2(10%) |
| FEE | STAR, modified |  ALEPH + FADC      (200 MHZ,  8 b.) |
|  Gas amplification |   ~ 4400 |   ~5000 |
|  Noise |  ~ 1000 e- |  ~2000 e- |

## “Canada Variant” FEE time response simulation

- FADC response  for fixed pad row and “active” pads
-  ( no noise).

-   t_bins, 5ns/bin

-  ADC channel

## Hit position reconstruction

-  If number of active pads (in pad row) > 1.
-  --   x_w = ∑(qi x x_pad) / ∑qi
-  -- If number of active pads < 5 :
-    gauss fit of a histogram (q – n of pad) was done with “special approach” for 2 active pads variant: ( “x_gf” ). Then line fit was done and hit residuals were calculated
-       ---- all hits are in a fit: (“dx_ln”)
-       ---- except the hit that was used to get a residuals:      (“dx_ln_1”)
-  -- “nonlinearity” correction was done for x_w values:
-    ( “x_corr”)

## Hit position reconstruction; nonlinearity correction

- Pad size: 2x6 mm2, P10, Ar+CO2

- Pad size: 3x5 mm2

-  (x_w – x_simul), cm

-  x_w in “pad coordinate system”, cm

-  hit position (reconstructed-simulated) before and after correction

-  - (x_corr – x_simul)

-  - (x_w – x_simul)

- - (x_gf – x_simul)

-   2 x 6 mm2             3 x 5 mm2

-  P10

-  Ar+CO2

-  Different variants of hit position reconstruction

## Sigma of gauss fit (reconstructed-simulated), mm.Drift: 0-15 cm,  Slope: +/- 16 deg

|  |  dx_w |  dx_gf |  dx_cor |  dx_ln | dx_ln_1 |
| --- | --- | --- | --- | --- | --- |
| P10
2x6 mm2 | 0.252 | 0.268 | 0.253 | 0.207 | 0.359 |
| P10 
 3x5 mm2 | 0.344 | 0.357 | 0.323 | 0.274 | 0.475 |
| Ar+CO2
2x6 mm2 | 0.193 | 0.222 | 0.153 | 0.178 | 0.314 |
| Ar+CO2
3x5 mm2 | 0.370 | 0.310 | 0.270 | 0.252 | 0.44 |

## Simulation – Data comparison, P10, “Canada”

- Pad size 2.x6. mm2

- Pad size 3.x5. mm2

- Resolution in X, mm

- Drift distance, cm

- Experimental data

- “gauss fit”

- “nonlinearity correction”

## Simulation – Data comparison, Ar+CO2(10%), “Canada”.

- Drift distance, cm

- Resolution in X, mm

- Pad size 2x6 mm2

- Pad size 3x5 mm2

- Experimental data

-  nonlinearity correction

- Gauss fit

-  factor ~2 smaller transfer diffusion and
- factor ~3 smaller drift speed compare with P10

## Number of active pads and Q per cluster for different variants.

- P10

- Ar+CO2

-   2x6 mm2                 3x5 mm2

-   2x6 mm2                 3x5 mm2

## Hit resolution as a function of a slope ( in xy )

- P10,  pad size  2x6 mm2                                       3x5 mm2

## Hit reconstruction resolution in a drift direction.

- P10

- Ar+CO2

- Pad size 2x6 mm2          3x5 mm2

## Space resolution as a function of a pad size (in RΦ direction) for 40. cm max drift distance, “custom” FEE and 20.ns time-bin

| 0.1 cm |  0.0092 cm
 (0.0041) |
| --- | --- |
| 0.2  |  0.0234
 (0.0088) |
| 0.25  |  0.0364
 (0.0099) |
| 0.3  |  0.0479
 (0.0155) |

- Sigma, cm, gauss fit (x_simul – x_reco)

- Pad size, cm

- Sigma of gauss fit, cm.
- hit position in RPhi (simulated-reconstructed)

- HIJING, CH4

- One track/event
-  CF4(10%)+Ar

- ( in brackets: x-y line fit using 5 pad rows,  gaussian fit (x0-x0 simulated))

-  CERN TPC+GEMs:
-  measurement – 0.0178
-  simulation –
-   0.0169

- Comparison of the hit reconstruction precision for rectangle and chevron
-  pad shapes. Pad size: 1.0x0.2 cm2, 10 saws in a case of chevron shape

- Xsimul – Xreco, cm

- Xsimul – Xreco, cm

- Hit position (along pad-row), cm,
-  simulated

- Track slope, deg

-  rectangle pads

-  chevron pads

## Space resolution, one pad-row, Chevron Pad structure: 1.0x0.2 cm – 10 saws.

- After slope correction

- Before

-  dX, cm

-  dX, cm

- Slope, deg.

- Slope, deg.

- Sigma, gauss fit: 0.032 cm

-  0.006 cm