1. in c-tau factory detector
Simulations of physics background
in c-tau factory detector
L.Shekhtman
Budker INP, Novosibirsk State University

2. Main physical background sources:
Two-photon processes e+e-  g*g*e+e-e+e-
6 mb (at 3.5 GeV per beam)
Radiative Bha-Bha e+e- e+e-g(ng) (q>5mrad,
Eg>3MeV) 1.7 mb (at 3.5 GeV per beam)
With 1035 cm-2s-1 - ~8x108 background events per second
If frequency of bunch crossings is 2x ~4 events per
crossing, ~8 background particles with q>5mrad

3. Generated:
1 mln. events with two-photon e+e- production,
generator diag36, cross-section ~6 mb
(F.Ignatov)
105 e+e-ng, generator BHWIDE (LEP/SLC),
cечение 1.7 mb (q>5mrad, Eg>3MeV)
(help of V.Tayurskij)
Simulation of background particles fluxes is performed
with FLUKA package (
Main goal is to estimate background particle fluxes at the
region of Inner Tracker, to get occupancy values for
different options of IT

4. Basis for geometry description

5. CTD geometry in FLUKA R, cm Concrete Iron Aluminum CsI Aerogel Air VP
He+40%C3H8
Air Ar VP
Z, cm

6. Magnetic field
B, T
R, cm
100
100
100
200
Z, cm
R, cm
100
260
Z, cm

7. Electrons & positrons (TPC)
1/cm2s
R, cm
Z, cm

8. Electrons & positrons
1/cm2s
Y, cm
X, cm

9. Photons
1/cm2s
R, cm
Z, cm

10. 1-MeV neutron equivalent flux for Si
1/cm2s
R, cm
Z, cm

11. Absorbed dose
G/y
R, cm
Z, cm

12. Spectra in Inner Tracker volume

13. v09
v10
R, cm
R, cm
Comparison with v08

14. Thickness of end-cap TPC wall affects the flux
v026
Thickness of end-cap TPC wall
affects the flux
v026
v06
R, cm

15. Options of Inner Tracker
Channel size
Time of the measurement
TPC
1x1 mm2
100 ns
Si-strip detector
300x0.2 mm2
10 ns
CGEM detector
300x0.4 mm2
Straw tubes
~600x10 mm2
Compact drift chamber
~600x5 mm2

16. TPC, rates e+e-
particles/cm2

17. TPC, occupancy (fraction of time when system is busy)
Time slice 100 ns – factor 10-7
Readout pads 1x1 mm2 – factor 0.01
Occupancy = rate x 10-9
10-4 – 10-6
Ion space charge
Rate 105 – 3x1011 ions in region 1x1x30cm3
(10% ion backflow)
Field of space charge
Esc~ Q/e0 = 50 V/cm
External field – 500 V/cm

18. Straw tubes, rate
Rates 105 (!) – 103 particles/cm2s

19. 1 – 0.01 Straw tubes, occupancy Length – 60 cm, factor 60
Drift time 100 ns – factor 10-7
Occupancy = rate x 6x10-6
1 – 0.01
Charge flow
105 tracks per cm per s ->
107 primary electrons
Gas ampl. 105 –> 1012 e =
1.6x10-7C/sxcm = 1.6 C/cm per year

20. Si-strip detectors
Rate 105 – 103 cm-2s-1
Channel size 0.02x30 cm2
Time – 10 ns
Occupancy = Rate x 0.6x10-8

21. CGEM detector
Rate 105 – 103 cm-2s-1
Channel size 0.04x30 cm2
Time – 100 ns
Occupancy = Rate x 1.2x10-7

22. Conclusions
Charge particles rate in the region of Inner Tracker 105 – 103 cm-2s-1
Occupancies are too high for straw tube option (and for compact
drift chamber)
Occupancies for other options of IT are acceptable
1 MeV n-equivalent flux for Si is below 1011 n/cm2y
Absorbed dose is below 100 Gy/y (rad-tolerant electronics needed)