na62 gigatracker working group 28 july 2009 massimiliano fiorini cern
TRANSCRIPT
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)