why monte-carlo ?

Jean Favier LAPP CERN Physics and soft meeting 23/04/04

Why Monte-Carlo ?• To understand and separate influences of

parameters (ex: fog d, distorsions,m.i.p grain density) on efficiency

• To guide the optimization of reconstruction programs

• To evaluate track efficiency and systematics errors for different topological conditions

• ECC is the basic OPERA detector , but it is the only one escaping Monte-Carlo !


• THEN:The lack of data for various conditions ( particle type, angles, energies, fog densities, ambiant radioactivity integration times, etc) and poor statistics make difficult the reconstruction programs optimization.

• The large feed-back time between beam tests and scanning

• It was attracting to reproduce emulsions data by Monte-Carlo, as for the other detectors


• Genima GEN : GEANT3 generation of - single track (1 single field 200x200 2 , double layer emulsion set-up) - or neutrino, showers events in a complete brick set-up. - The correct grain density is set by randomly eliminating some

GEANT track hits to obtain the m.i.p density at : 32IMA: single “classico” FORTRAN program: - read GEANT hits - add background fog - constructs the 32 images of grains, fog,etc present in the 2 emulsion

layers NOW 128x128 pixels instead of 1024x1024 : factor 64 in computing time !!!

-Artificial increase of depth of field to approximate reality - clusterises the images pixels NOW Digital Filter - finds micro-track NOW cut >= 8 hits to accept - finds base-track


ccd plane

Focused

plane

Grain plane

d=3.254 mm d=200 mm

r=6mm

The systeme objective-ccd (in red) can move along the optical axis: we keep 16

tomographic planes ; is defined by objective characteristics

The virtual microscope

objective


IMA : makes pictures

• For each “grain” x,y,z we calculate the intercepted surface by a conical prolongation , isolating the surface S of pixels to “dark”. The cone aperture is determined by the lense N.A (numerical aperture):

= arcsin(N.A/nrefr )

• Pixels are filled with grey in each of the 16 picture planes; grey density varies with 1 / S and e-d/ ( is an effective emulsion attenuation lenghth)


Fog and background

• Fog is randomly generated as single grain with a density of 8 grains/ (10 )3

• Album of real emulsions can be used also (radioactivity fossiles tracks)


Emulsion simulation

• 16 images


Emulsion simulation


Emulsion simulation

• 16 images


Performances of the European Scanning SystemPerformances of the European Scanning System

Efficiency

Efficiency is being estimated by European laboratories by using plates from a common test exposure

8 plates in contact were exposed to a beam

The brick was rotated in 14 different positions in order to test the angular dependency of efficiency



Purity

Purity is being estimated by European laboratories measuring plates from a common reference batch with the same parameters used to measure efficiency

Tracks found by the scanning system in a few cm2 are manually checkedin order to evaluate the density of fake tracks

Density of fake tracks is less than 1/cm2



Sy = 0

Sy = -0.180

Base-track

Microtrack

6/7 plates4 averages

cutBkgnd = 1 fake/cm2

Efficiency

Salerno


Offline cut: < -6.667 + 0.4167PH

Efficiency

Napoli


R&D Meeting, LNGS, 4th October 2004

Base-track efficiency Jun. 04 reference brick with leadsheets 18 – 25

= N6

N5 + N6

volume 1: sheets 20 – 25volume 2: sheets 19 – 24volume 3: sheets 18 – 23

6 samples of tracks( external sheets only )

Bari


Efficiency

Neuchatel


Volume tracks Base tracks efficiency vs peaks (averaged over 7 plates)

Error bars = 1 spread of 7 plate efficiencies

Red: y 0 mrad

Black: y 200 mrad

Bologna


Scanning performanceBasetracks MIC1 (SmartTracker6)

Dry objective

Bern


Scanning performanceBasetracks MIC2 (SmartTracker7)

Dry objective

Bern


• How fog can influence efficiency ?- Fog effects will be higher at large angle where the

sensible volume around the track is higher- infection of a good cluster: the resulting barycentre

becomes out of association: the hits number can go down from 6 to 5

- Deformations of good clusters by a fog one can produce a deterioration of qui2

- Oppositely, on a 5 hits track, one fog cluster can, by luck, occupy the sixth rank, so the track will be accepted


Base-track efficiency

Fog effect


Grain

density

Fog=0 (preliminary)

Nhit 6

Nhit 5


• Boliden Lead + Ca (NGL washed by Goslar)• CERN refreshed emulsion (FD (6.3 + 0.5)g/(m)• Spider packing• Delrin cover and side protection• 35°C in the oven (1 year)

FD (6.8 + 0.5)g/(10m)3

Long term test using PbCa (11/2004 11/2005)

20 30 40 50 600

50

100

150

200

Track grains/100 m

Emulsion sensitivity


• Distortion

It is simulated by random rotation (0 to max) of the

microtracks ,leaving fixed the intercept with the basis; we varied max from 0 to 40 mrad

Emulsion layer 1 basis

why monte-carlo ?

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