The Geometrical Factor of PAMELA by means of GPAMELA

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The Geometrical Factor of PAMELA by means of
GPAMELA
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AIM OF THE WORK

• Comparison with Analitic Method (AM) by
  
  S.Ricciarini to check GPAMELA reliability
  differences between the 2 setups
• Calculation of the Geometrical Factor with
  GPAMELA complete geometry effect of dead
  volumes

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COMPARISON WITH THE ANALITIC METHOD

• ANALITIC METHOD
• No physics (except the magnetic field)
• Simplified geometry (TOF and tracker planes
  approximated as rectangles)
• Geometrical cuts

• GPAMELA
• Particles interactions with materials (energy
  loss and production of secondaries)
• Complex geometry (dead volumes boxes,
  carbon-fibre rails, glue, aluminium frames,
  etc..)
• Cuts on interaction points (GPAMELA hit
  structure)

NOTE no information is recorded on traversing
insensitive materials (magnet, frames, boxes,
etc..)
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OUTLINES

• As a first attempt, the 2 setups give different
  results.
• It was necessary to modify the GPAMELA code to
  reproduce as close as possible the same ideal
  conditions used in the Analitic Calculation
  

Modifications of the detector sensitive
geometries
Semplification of the physics
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SIMULATION PHYSICS

• Effects of interactions of incident particles
  traversing materials excluded
• NO ENERGY LOSS AND PRODUCTION OF SECONDARIES
  NO INTERACTION WITH THE MAGNET
• PARTICLES AFFECTED ONLY BY THE MAGNETIC FIELD
• Modification of the code in order to save the
  GPAMELA hit structure in absence of ionization.

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SIMULATION GEOMETRY

• in the analitic calculation the tracking and the
  TOF planes are approximated as rectangles
• the real geometry implemented in GPAMELA includes
  boxes, carbon-fibre rails, glue, aluminium
  frames, etc..
• Modification to reproduce the most possible the
  same geometrical conditions
• dimensions of the sensitive area of the silicon
  paddles extended up to the ones of insensitive
  silicon boxes containing them

NO DEAD VOLUMES
increase of the planes sensitive area ( 5)
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THE SIMULATION SETUP

• Only TOF system and spectrometer simulated
• Same rigidity values used in the Analitic Method,
  chosen to cover the interval of interest 0 lt ?
  lt 500 GV/c.
• For each momentum 2x106 muons generated
• Generation surface A60x52 cm2 just above the S1
  scintillator (Z 104.2689 cm)
• Generation uniform in x, y, cos2(?), in a 2? sr
  solid angle
• Geometrical factor G for each value calculated
  according to Sullivan

J. D. Sullivan, Geometrical factor and
directional response of single and multi-element
particle telescopes, Nuclear Instr. and Methods
95, 5 (1971).
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SELECTION CRITERIA

• ANALITIC METHOD
• TOF selectionfor each pair of layers of the
  TOF system the trajectory must cross at least
  one of the two rectangles defining the
  layers((S11 or S12) and (S21 or S22) and (S31
  or S32))
• Spectrometer selection
• the trajectory must traverse the parallelepiped
  defining the magnetic cavity of the spectrometer
  by crossing its upper and lower faces
• check on 3 intermediate planes (to assure the
  particle had not escaped from the lateral walls
  of the cavity)
• the trajectory must cross the detectors T1 and T6.

• GPAMELA
• TOF selectioninteraction (hit) on at least one
  of the two layers for each plane((S11 or S12)
  and (S21 or S22) and (S31 or S32))
• Spectrometer selection
• interaction (hit) on T1 and T6
• interaction on at least 3 of the internal planes
  (T2 to T5) of the tracking system
• MAGNET TREATED AS TRANSPARENT
• cut on the impact position point in the plane
  requiring the crossing of an area as large as the
  magnet hole (cavity)
• additional cut on the impact position on T1 and
  T6 (given by the projection of the solid angle
  viewed by the magnet cavity on these planes).

MODIFICATIONS OF GPAMELA PHYSICS
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SELECTION CRITERIACUTS USED IN THE SIMULATION

• GPAMELA 1
• TOF selection,
• at least 3 tracker internal planes hit

• GPAMELA 3
• TOF selection,
• all tracker planes hit

• GPAMELA 4
• TOF selection
• all tracker planes hit
• cuts on T1 and T6.

• GPAMELA 2
• TOF selection,
• at least 3 tracker internal planes hit,
• cuts on T1 and T6

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GEOMETRICAL FACTORcomparison with the analitic
method
2160
NO DEAD VOLUMES
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GEOMETRICAL FACTORcomparison with the analitic
method
NO DEAD VOLUMES
(GAM - GGPA) / GAM
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RESULTS
2160
Good agreement between GPAMELA 2 selection and
ANALITIC METHODs one
NO DEAD VOLUMES
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RESULTS

• GPAMELA 2 selection similar to ANALITIC METHODs
  one good agreement

GAM 21.6 0.13 cm2 sr GGPA2 21.5 0.32
cm2 sr
(Linear regression on the 10 higher rigidities
1512 GV/c)
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NEW RESULTS !!!
Dead Volumes reintroduced
Only GPAMELA 2 selection considered
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GEOMETRICAL FACTORcalculation with full geometry
DEAD VOLUMES INSERTED
2160
1940
Decrease of the geometrical factor (10 ) !!!
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NEW RESULTS

• Full geometry implemented in GPAMELA without
  modifications

GAnalitic Method 21.6 0.13 cm2 sr GGPAMELA 2
19.4 0.31 cm2 sr
Effect of deadvolumes
Decrease of the geometrical factor (10 ) !!!
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CONCLUSIONS

• A calculation of the PAMELA's geometrical factor
  was done using the GPAMELA program.
• In order to test the validity of the results
  before going further with the full simulation
  with antiprotons and positrons, they were
  compared with the ones obtained by Ricciarini's
  Analitic Method.
• As a first attempt the results from the Monte
  Carlo were different from the Ricciarini's ones.
• After some modications of the detector sensitive
  geometries and semplification of the physics, the
  same results were obtained, showing GPAMELA
  reliability.
• Simulations without approximations indicate that
  the real geometrical factor is about the 10
  smaller (19.4 cm2sr) because of the presence of
  dead volumes!

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NEXT STEP

• Calculation of PAMELAs acceptance with the full
  simulation with antiprotons and positrons!!!

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GEOMETRICAL FACTORcalculation with full geometry
NO GEOMETRY MODIFICATION
Comparison with the AM