Gigatracker simulation

A first look at the Gigatracker simulationNA62 Gigatracker Working Group28 July 2009Massimiliano FioriniCERN

SoftwareNA62 MonteCarlofast 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 linedefault: beam track passed just in front of the 1st Gigatracker stationonly Gigatracker enabled: all other detectors excluded3106 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 LayoutppKppK13.2 m9.6 m60 mmGTK2GTK3GTK12nd achromat3 Gigatracker (GTK) stations: 60 mm 27 mm dimension300 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 caseNumber of hits on GTK1

Number of hits on GTK1 (zoom)

Number of hitsEventsEvent fraction[%]011-12.98 M99.323630.0138.2 k0.2744.1 k0.1451.9 k0.06> 57.2 k0.24Fraction 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 pixels012345Event fraction [%]-99.70.20.060.030.02Fraction of events with more than 1 pixel: 0.3%Number of hits per pixel GTK1

Number of hits012345Pixel fraction [%]-99.00.090.50.20.09Fraction of pixels with more than 1 hit: 1.0 %Number of clusters GTK1Fraction of events with more than 1 cluster: 0.03 %

Number of clustersEvent fraction[%]0-199.9720.033-Number of pixels per cluster GTK1

Number of pixels012345Cluster fraction [%]-99.70.20.060.020.01Fraction 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 sensoronly for multiple hits, the energy is deposited also at different depths along the sensor, up to the full thickness (200 m)

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 pixelsanalyze 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 inefficientfound 9 inefficient events over 5595 (0.16 0.05) % inefficiency

2nd caseNumber 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 GTK1Fraction of events with more than 1 cluster: 0.06 %

Number of clustersEvent fraction[%]0-199.9420.063-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 sensornow 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 pixelsanalyze single cluster formed by 2 pixels onlypixel ordering given by Geant4if both pixels have an energy below 28.8 keV (8 k e-h) the event is inefficientFound 28 inefficient events over 58498 (0.05 0.01) % inefficiency

Conclusions and To Do Listuse 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 pixelsTo Do listincrease statisticsvariations of other Geant4 parameters from the PhysicsListmore detailed study of -rays production and tracking by Geant4take into account other effects after-generation (diffusion, drift)