A first look at the Gigatracker simulation

NA62 Gigatracker Working Group28 July 2009

Massimiliano FioriniCERN

SoftwareNA62 MonteCarlo

fast simulation of the beam line based on Flyocalled by Geant4 to generate primary particlesbeam particle passed to Geant4 at a given position

along the beam line default: beam track passed just in front of the 1st

Gigatracker station

only Gigatracker enabled: all other detectors excluded

3×106 events generated with two different “range cuts” for electrons in silicon:1st case: 1 mm (corresponds to 541 keV)2nd case: 1 m (corresponds to 990 eV)

numbers and plots refer only to 1st Gigatracker station

Beam Spectrometer Layout

pπpK

pυ

pυ

θπK13.2 m 9.6 m

60 m

m

GTK2

GTK3GTK1

2nd achromat

3 Gigatracker (GTK) stations: 60 mm × 27 mm dimension

300 m × 300 m pixel cells pixel structure and GTK geometry implemented in

MonteCarlo by S. Bifani (see presentation on April 2009 Meeting):Si sensor (200 m thickness), Sn-Pb bump bond (15 m

thickness, 10 m diameter cylinder), Si read-out chip (100 m thickness), carbon fiber support (100 m thickness)

1st case

Number of hits on GTK1

Number of hits on GTK1 (zoom)

Number of hits

Events

Event fraction

[%]

0 11 -

1 2.98 M

99.3

2 363 0.01

3 8.2 k 0.27

4 4.1 k 0.14

5 1.9 k 0.06

> 5 7.2 k 0.24

Fraction of events with more than 1 hit: 0.72 %

New classes added (1)class GigaTrackerPixelgathers all the hits’ energy belonging to the same

pixel sensitive volumemethods implemented:

AddEnergy(Double_t)GetNHit()GetEnergy()GetPixelID()GetPositionX()GetPositionY()SetClusterID(Int_t)GetClusterID()

New classes added (2)class GigaTrackerClustercollection of adjacent pixels (side-side, corner-corner)

in a C++ vectormethods implemented:

AddPixel(GigaTrackerPixel)GetNPixels()GetPixelVector()GetDistance(GigaTrackerCluster)GetEnergy()GetPositionX()GetPositionY()GetWPositionX()GetWPositionY()

Number of pixels GTK1

Number of pixels 0 1 2 3 4 5

Event fraction [%] - 99.7 0.2 0.06 0.03 0.02

Fraction of events with more than 1 pixel: 0.3%

Number of hits per pixel GTK1

Number of hits 0 1 2 3 4 5

Pixel fraction [%] - 99.0 0.09 0.5 0.2 0.09

Fraction of pixels with more than 1 hit: 1.0 %

Number of clusters GTK1

Fraction of events with more than 1 cluster: 0.03 %

Number of clusters

Event fraction

[%]

0 -

1 99.97

2 0.03

3 -

Number of pixels per cluster GTK1

Number of pixels 0 1 2 3 4 5

Cluster fraction [%] - 99.7 0.2 0.06 0.02 0.01

Fraction of clusters with more than 1 pixel: 0.3 %

Energy release GTK1 per event

mean energy: 72.4 keV (~20k e-h)most probable energy: 53.7 keV (~15k e-h)FWHM: ~25 keV (~7k e-h)minimum energy: ~29 keV (~8k e-h)

Hit position (X-Y) inside a pixel

uniform pixel population (average on all pixel of one GTK station)

r.m.s. = 86.8 m for both X and Y [300 m/SQRT(12) = 86.6 m]

Hit position (Z) inside a pixel

in all cases the energy is released just at the entrance of the silicon sensor

only for multiple hits, the energy is deposited also at different depths along the sensor, up to the full thickness (200 µm)

Hit position spread GTK1

hit position spread (with respect to first hit) in GTK1r.m.s. (from un-zoomed plots) ~500 m for both X and Y

Position resolution

single clusterarithmetic pixel position average (no weight)r.m.s. = 86.8 m for both X and Y

Charge sharing among pixels

analyze single cluster formed by 2 pixels only (0.2%)

pixel ordering given by Geant4if both pixels have an energy

below 28.8 keV (8 k e-h) the event is inefficient

found 9 inefficient events over 5595 (0.16 ± 0.05) % inefficiency

2nd case

Number of hits on GTK1

Number of pixels GTK1

Fraction of events with more than 1 pixel: 2.4%

Number of hits per pixel GTK1

Fraction of pixels with more than 1 hit: 97.2 %

Number of clusters GTK1

Fraction of events with more than 1 cluster: 0.06 %

Number of clusters

Event fraction

[%]

0 -

1 99.94

2 0.06

3 -

Number of pixels per cluster GTK1

Fraction of clusters with more than 1 pixel: 2.4 %

Hit position (Z) inside a pixel

in all cases the energy is still released at the entry face of the silicon sensor

now the energy is deposited much more often also at different depths along the sensor, up to the full thickness

Hit position spread GTK1

hit position spread (with respect to first hit) in GTK1r.m.s. (from un-zoomed plots) ~100 m for both X and Y

(before was ~500 m)

Position resolution

single clusterarithmetic pixel position average (no weight)r.m.s. = ~86 m for both X and Y

Charge sharing among pixels

analyze single cluster formed by 2 pixels only

pixel ordering given by Geant4if both pixels have an energy

below 28.8 keV (8 k e-h) the event is inefficient

Found 28 inefficient events over 58498 (0.05 ± 0.01) % inefficiency

Conclusions and To Do List

use of new NA62 MonteCarlo with the aim of studying charge sharing effects among Gigatracker pixelstwo classes implemented for reconstruction purposesvery preliminary results show a low inefficiency for

particle detection in case that charge is distributed among 2 adjacent pixels

To Do listincrease statisticsvariations of other Geant4 parameters from the

PhysicsListmore detailed study of δ-rays production and “tracking”

by Geant4take into account other effects after-generation

(diffusion, drift)