Simulation of the background in GMC

1
Simulation of the background in GMC

• Background rates in tracking detector and ECAL
• Background hits data structure

2
Geometry setup modifications

• Collimator in the middle part of transport
  solenoid -19cm 3cm
• Last collimator is 12.8cm in radius and has 8
  copper foils 60µ in thickness and Rmin8cm,Rmax
  12.8cm
• Stopping target first disk has radius 10cm
• Space between outer proton absorber and 5cm CH2
  cylinder layer filled with CH2

From GEANT without corrections
Number of muons, electrons
0.00446 µstopped/p 0.00872 µall/p _at_entrance of
DET.SOL.
0.0813e-/p 0.0050e/p
51.1
Conversion electrons acceptance
Background rates from energetic (Egt55MeV) DIO
electrons are negligible
3
Background rates in the tr. Detector as a
function of time
25000 kHz/wire
? from muon capture in tgt

• vane

500 kHz/wire
Beam electrons
Protons from muon capture in tgt (0.1p/µcapture)
25000 kHz/wire
600 kHz/wire
Beam positrons

• cylinder

Beam µ-
Beam µ
4
Proton background
Protons with kinetic energy below 15MeV do not
hit tracking detector !
5
Normalization of proton spectrum
Probability for protons to have hits in tracking
detector
X10-3
Protons per muon capture
15MeV
deuteron
protons
tritium
We use for Al 8x10-3 for protons (Egt15MeV) per
muon capture
Less than 8kHz/wire
Si
Less than 7kHz/wire
Al
Budyashov,Sov.Phys.JETP,33,1971
6
µ- background
Contribution into the detector rates
Configuration I
Iron
Lead
CH2
Brem. ? from tgt
Decay in flight
7
Energy load in electron calorimeter
Less than 100MeV/cell/µbunch
Beam electrons
Beam µ--
Less than 50 keV/cell/100ns in measurement period
neutrons from the target
? from the target
Beam µ
Beam positrons
8
µ- background
Contribution into the detector rates
Configuration II
Iron
CH2
Brem. ? from tgt
µ decay in flight
µ decay in prot abs.
9
Number of muon capture and decays in beam stop in
measurement period
10
Neutron background from beam stop
1000 neutron tracks from beam stop
Beam Stop Configuration I
1000 neutron tracks from beam stop
Beam Stop Configuration II
11
Background rates in the tr. Detector as a
function of time
25000 kHz/wire
? from muon capture in tgt

• vane

500 kHz/wire
Beam electrons
Protons from muon capture in tgt (0.1p/µcapture)
25000 kHz/wire
600 kHz/wire
Beam positrons

• cylinder

Beam µ-
Beam µ
12
Energy load in electron calorimeter
Less than 80MeV/cell/µbunch
Beam electrons
Beam µ--
Less than 60 keV/cell/100ns in measurement period
n from beam stop
? from the target
? from beam stop
Beam µ
Beam positrons
n from target
13
MECO GEANT3 software development

• MECO software is now performs as a multitask
  system, task version is
  stored in database, any task is reproducible by
  any user.
• If different tasks need different big arrays,
  Fortran requires the initial declaration and
  memory allocation for all of them.
  
  The program became really
  large!
• The problem solved by the implementation of C
  routines which dynamically allocates the memory
  only for necessary arrays after the job started.
  The method is implemented for

• Magnetic field map arrays
• Background hits arrays

Allocated memory size depends on number of
magnetic regions or number of the background
files used in a simulation.
14
Background hits array structure

• Dynamically allocated array gmcbcgarray

N words
Nth background

• Dense packed background hits information in the
  array

Nth background array
1st event
nth event record
2nd event
nth event address array
1st
2nd
nth
15
Background hits event record structure
Nhit1 Nhit1 Nhitntrk hit records
nth event record
1tst hit record
nth hit record
2nd hit record
ntrk
Nhit1
Nhit2
Nhitntrk
Volume name Volume copy number X Y Z Time Px Py Pz
E Energy deposition
1 2 3 4 5 6
7 8 9 10 11
nth hit record
16
Background hits simulation
Example of the conversion electron simulation
mixed with background hits from a proton,
neutron,proton, beam muon background. Background
events uniformly distributed in 75ns time window.
Program is ready for cluster reconstruction !
Used background event rates

• Protons 84 MHz ( 6.4 ev/75ns)
• Neutrons 110 MHz ( 8.3 ev/75ns)
• Photons - 192 MHz (14.4 ev/75ns)
• Beam muons 204 MHz (15.2ev/75ns)

- hits in the tr detector from the conv electron
- hits in the ECAL from the conversion electron
- background hits in the tracking detector
- background hits in electron calorimeter
17
Conclusion

• Rates both in tracking detector and electron
  calorimeter are acceptable.
• We can use Iron instead Lead in beam stop.
• Inner surface of the beam stop can be Iron.

• Useful tool to allocate array with variable size
  in Fortran program has been developed.

• Program is ready for cluster reconstruction study