Charge Mapping in SCT_Digitisation

SCT Digitisation Task Force Meeting

24th August 2010

Richard Batley (Cambridge)

-- compare different grid spacings

-- compare with pulse map

-- use toy line charges and “real” GEANT events

First look at charge maps provided by Taka :

(Charge maps would be more straightforward to implement in SCT_Digi and would maintain factorisation of induced charge and electronics models)

Maps available (so far) from Taka :

[5] : strips -2, -1, 0, +1, +2[17] : 0, 5, 10, ..., 80 µm[57] : 2.5, 7.5, ..., 282.5 µm

[50] : 0, 1, 2, ..., 49 ns

1) Pulse map -- 5mm grid, Dt = 1ns

2) Charge maps -- 7.5, 5.0, 2.5, 1.0mm grids, Dt = 0.5ns

map induced charge vs time for point charges

Pulse[5][17][57][50]

Charge[5][11][38][50], ... , Charge[5][81][285][50]

Induced Charge Model (ICM) maps

Use linear interpolation between nearest grid points

map electronics response vs time for point charges(including crosstalk as in current SCT_Digitisation)

Strip 0Strip -1 Strip +1

x

Geometry :

0

0

m285

m80

20,5, yx

250,40, yx

All maps for Vbias = 150 V, Vdep = 65 V, T = 0oC

Map = piecewise linear interpolation with Dt = 0.5 ns(too coarse ?)

Induced charge profiles for point charges (examples) :

(x,y) = (5,20)

(x,y) = (40,250)

strip -2 strip -1 strip 0 strip +1 strip +2

strip -2 strip -1 strip 0 strip +1 strip +2(x,y) = (5,20)

(x,y) = (40,250)

solid curves :

dashed curves :

from charge map + electronics model

directly from pulse map

Corresponding pulseheight profiles :

(1-MIP = 108 eh / mm)

Strip 0Strip -1 Strip +1

0 m80localx

Response to toy tracks

Step length along each toy track = 0.1mm

Uniform 1-MIP line charges :

strip +2

Response to uniform line charges (examples) :

f = 0, x = 0

f = 0, x = 40

strip -2 strip -1 strip 0 strip +1

blue :

red :

1mm charge mapcurrent SCT_Digitisation model

f = 0, x = 40

strip -2 strip -1 strip 0 strip +1 strip +2

blue :

red : current SCT_Digitisation model

f = 0, x = 0

1mm charge map

(dashed = 5mm pulse map)

Corresponding pulseheight profiles :

Cluster size versus angle

2.5mm looks like a reasonable compromise ?

something strange about the 7.5mm charge map

what is the real answer (from the induced charge model) ?

7.5mm5.0mm2.5mm1.0mm

5.0mm grid probably too coarse --

But :

Charge map (5.0mm)Pulse map (5.0mm)SCT_Digi

Comparison with current SCT_Digitisation model :

trackclus xxx Average , integrated over local x of track :

Cluster position bias

7.5mm5.0mm2.5mm1.0mm

( Apply Lorentz correction : )m21.9clusclus xx

Implementation in SCT_Digitisation

Hacked SCT_Digitisation-00-11-41-01 in 15.6.8 to install the 5mm charge map as an option

Processed 100 ZZ4l events using both the charge map and standard digitisations

(charge map digitisation runs very slowly)

standard charge map

standard charge map

Reconstructed tracks :

Summary

... and for “real” GEANT events using hacked version of SCT_Digitisation ...

it works !

gives results consistent with pulse map

(easier to implement than pulse maps, though CPU time may be an issue)

next: study GEANT single muons (need to get single particle generator working again)

suggests using a 2.5mm grid size ?

how does map compare with full ICM ?

Looked at Taka’s charge maps for toy line charges ...

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