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

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 2x108 - ~4 events per crossing, ~8 background particles with q>5mrad

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 (http://www.fluka.org) Main goal is to estimate background particle fluxes at the region of Inner Tracker, to get occupancy values for different options of IT

Basis for geometry description

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

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

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

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

Photons 1/cm2s R, cm Z, cm

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

Absorbed dose G/y R, cm Z, cm

Spectra in Inner Tracker volume

v09 v10 R, cm R, cm Comparison with v08

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

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

TPC, rates e+e- 105- 103 particles/cm2

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

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

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

Si-strip detectors Rate 105 – 103 cm-2s-1 Channel size 0.02x30 cm2 Time – 10 ns Occupancy = Rate x 0.6x10-8 10-3 - 10-5

CGEM detector Rate 105 – 103 cm-2s-1 Channel size 0.04x30 cm2 Time – 100 ns Occupancy = Rate x 1.2x10-7 10-2 - 10-4

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)