MC simulation of a-detector

1
MC simulation of a-detector

• Geometry materials
• Calculation procedure
• Position resolution
• Cross-talk, multiplicities
• Conclusions

Vít Vorobel
ALFA meeting CERN 24.5.2006
2
Geometry materials

• Beam
• section ?1.5 mm, uniform xy-distribution
• no divergence
• direction changing up to 50 mrad with respect to
  z-axis.
• Si-1,2,3 Si, r 2.3g/cm3, 0.3x100x100mm
• PS Polystyrene (C8H8)n , r1.05g/cm3 ,8x16x12mm
• Air 20O2, 80N2, r 1.29mg/cm3
• ALFA detector
• Ceramics Al2O3 , r3.7g/cm3 , 0.17x16x12mm
• Plastic layers material as PS, 0.5x16x12mm,
  logically divided to
• Sensitive cores of fibers ?0.48 mm
• Insensitive everything else simulating cladding,
  glue, and spacers
• Fibers positioned regulary with x and pinch from
  metrology data, slope45
• Fibers are not cutted on the edge.

Si-1
Si-2
Si-3
PS
ALFA
23.17
173
135
270
160
3
Calculation procedure

• Shower simulation
• Tool
• GEANT 4, version 7.0
• Record
• energies deposited in fibers
• coordinates of Si-plates penetration
• Translation of energy deposition to signal
  amplitude

4
Calculation procedure

• XY determination
• ALFA detector
• overlapping algorithm (by Hasko Stenzel)
• Si-telescope

z0 - position of reference plane
2 points Si-2,3
3 poins Si-1,2,3
minimal
5
Resolution vs signal-cut
Safe plato about the used cut 0.9 p.e.
6
Resolution vs reference plane position

• Both,
• strong dependence of the resolution on z0 and
• difference between the used methods
• are consequences of multiple scattering.
• After many scattering, the particle is
  significantly deviated from the original
  direction (explains 1)) and does not remember
  the intersection with the Si-1 detector which
  explains 2) the worse result from Si-1,2,3.
• No difference between methods Si-123, Si-12 and
  Si-23 for 7TeV protons 20.1 mm.

ALFA
Decision use Si-123 for resolution determination
and Si-23 for angle cut.
7
We are approaching !
By Hasko Stenzel
8
Energy scan processes contribution
20mm !!!

• No contribution from bremsstrahlung and
  d-electrons
• Dominant contribution from multiple scattering

9
Resolution vs detector tilt
The beam is rotating in MC instead of the
detector.
10
Cross-talk

• The nearest fibers
• Bremsatrahlung 1
• d-electrons 3

The shower gradually develops
11
Cross-talk details
12
Multiplicities
By Hasko Stenzel
13
Conclusion

• Resolution
• d-electrons bremsstrahlung have negligible
  influence (may be changed in HE)
• Dominant process is multiple scattering (getting
  improve in HE 20mm)
• MC agrees with data for 6GeV, for lower energy MC
  gives worse resolution.
• Cross-talk, multiplicities
• MC bremsstrahlung 1, d-electrons 3 are the same
  order as data.
• Both, cross-talk and multiplicities are more
  frequent in experimental data then in MC by
  factor 2.
• Looking forward the HE test.