26 jan, 20041 meg software status framework for meg mc, unification of largeprototype/beam test,...
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26 Jan, 2004 1
MEG Software Status
Framework for MEG MC,Unification of LargePrototype/beam test,
Scheduleand
DC reconstruction
MEG Software Group
26 Jan, 2004 2
Framework for MEG MC
26 Jan, 2004 3
Framework for MEG MC(1)
• Unified framework with double option:– Tokyo or Pisa code,
• Framework based on:– Fortran 77,– CERNLIB,– ZEBRA,– GEANT3,
• Distributed via CVS.
26 Jan, 2004 4
Framework for MEG MC(2)
• Tree structure & skeleton … ready;
• Materials & tracking medium … merged;
• Event generator … stand alone & built-in;
• DC, TC, Magnet and B field … merged;
• ZEBRA structure … in progress;
• Scintillation photon tracking … in progress.
26 Jan, 2004 5
To be done: MEG MC
• Merge Liq. Xe Geometry;
• Test of reduced number of PMT in Liq. Xe;
• Digitization for all the sub detectors;
• Full reconstruction program;
• Offline database… ODB? Separate database (e.g.PostgreSQL, MySQL, etc.)?
26 Jan, 2004 6
LargePrototype/beam test
26 Jan, 2004 7
LargePrototype/beam test unification(1)
• MC Merge into the new framework… just finished.– Common output format for DATA/MC;– Scintillation photon tracking in Liq. Xe
… Full ray tracing or geometrical tracking;– Reflection on the PMT quartz window
… Fresnel or total reflection;– Scintillation light spectrum
… Monochromatic, Gaussian, Basov et.al, etc.– Rayleigh scattering/absorption in Liq. Xe.
26 Jan, 2004 8
LargePrototype/beam test unification(2)
• Analyzer– NaI calibration/gain correction
… merged;– NaI vertex/energy reconstruction
… stand alone program, merging into analyzer being in progress.
26 Jan, 2004 9
To be done: LargePrototype/beam test
• NaI response simulation;
• LiH target and Vessel simulation;
• phase space simulation for 0;
• Offline database … ODB? Separate database (e.g. PostgreSQL, MySQL, etc.)?
26 Jan, 2004 10
Schedule/man power• Will be discussed in the Software meeting
and reported in the review meeting.
26 Jan, 2004 11
DC reconstruction• Track Dictionary
– Efficiency– Resolution
• L-R ambiguity solution
26 Jan, 2004 12
Several tracks with similar kinematics
producing a single hit pattern
Hit pattern
Single and unique string(i.e. a dictionary key)
Average (over the set) track parameters
The dictionary concept
Several tracks with similar kinematics
producing a single hit pattern
Several tracks with similar kinematics
producing a single hit pattern
Several tracks with similar kinematics
producing a single hit pattern
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The track dictionary is a ordered list of records:
Key (hit pattern) average track parameters + rms
The track dictionary exploits the “digital” response of the spectrometer
NO Tdrift usedNO z measurements used yet
26 Jan, 2004 14
MC sample used to build the dictionary:
• Positrons from Michel decay;
• Unpolarized muons;
• Generator level cuts: 0.08 < |cosθ| < 0.35;-60° < φ < 60° .
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The population of the patterns is not uniform: 40% has 1 entry 43% has 2 ÷ 10 entries 13% has 11 ÷ 50 entries 4% more than 50 entries
Number of events in a dictionary record
250000 generated events 12900 patterns; efficiency = 95%
26 Jan, 2004 16
Momentum componentsfor events in the dictionary
Event by eventdistributions
Average in eachDictionary record
Track first turn has hits in at least three sectors
Px / MeV Px / MeV
Py / MeV Py / MeV
Pz / MeV Pz / MeV
LEFT RIGHT
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The comparison of the distributions of an average parameter in the dictionary with the actual parameter distribution shows:
• Px and Py have similar shapes;• Pz
• a hit pattern in the spectrometer cannot tell the sign of Pz;
• the shape of the distribution of |Pz| is not well reproduced
poor |Pz| resolution of the dictionary.
pMC - < pdict > σ
Generate a sample of independent events
For tracks in the dictionary acceptance (Nsectors > 2)
find the dictionary keycompare;
Px with <Px>(key);normalize to RMS<Px>
vertex X
vertex Y
vertex Z
Px
Py
Pz
What is the dictionary “resolution” for all parameters ?
26 Jan, 2004 19
To be done: dictionary
• Optimize stats. given by 1 – eff. ~ 10-3 - 10-4 and by looking at RMS vs. stats. (intrinsic resolution of method);
• Add noise hits;
• Add inefficiency of Drift Chamber;
• Add drift time;
• Superimpose tracks.
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Starting from digit ID and drift time, in each sector we have 4 possiblesolution (4 tangent segments)
Digitization of the MC hitfrom x,y,z to: number of sector (1-17), number of chamber (1-2) number of wire (1-9) D.C.A(digit) smearing of 200m Tdrift (const Vdrift) Z(digit) smearing of 300m
First reconstruction stepdrift circle
LEFT – RIGHT AMBIGUITY SOLUTION
26 Jan, 2004
P
Q
T
The assumption: track ~ circle with centre in Cif PT and QT are straight segments tangent to C and intersecting in point T, then α = α´
The strategy: select the right tangents in two consecutive sectors by choosing the pair giving the minimum ´
Intrinsic limitations:• non uniform B implies that
tracks are not exactly circles • drift distance resolution
‘
C
’
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The plot shows the distribution of for 1000 tracks
All possible combinations (23097)
Exact combinations (3778)
We need to define a cut on
which allows to keep high efficiency for
correct left-right choices and to reject wrong
combinations
rad rejects57% of the incorrect
solutions
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efficiency
With Δα = 0.24 rad we reach90% of total efficiency in L – R solution.
By definition, the total efficiency comes from two terms:
-Tracks where the L – R ambigurity is solved in each sector (60%);
-Tracks where the L – R ambigurity isn’t solved only in 1 sector (30%) cut
Efficiency vs
26 Jan, 2004 24
To be done: L-R Ambiguity solving
• improve efficiency, evaluate timing;
• study the effect of resolution varying with the impact parameter;
• use the “calibrated” digits, (i.e. x,y.z as estimated after left-right ambiguity resolution) as starting points for F. Cei’s algorithm estimating track parameters.
A long term plan once a fit algorithm is defined
• Get dictionary output – if the hit pattern corresponds to a key – when/if the resolution is appropriate for the fit (save
computing time)
go to the track fit
• Solve left-right ambiguity – if the track is not found in the dictionary – if the hit pattern gives ambiguous track parameters
(high combinatorial calculations only when needed)
go to the track fit
else