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LCWS 2005 SLAC, March 19 Low Angle Bhabha Events and Electron Veto.

LCWS 2005 SLAC, March 19 Low Angle Bhabha Events and Electron Veto. Comparison Between Different Crossing Angle Designs. Vladimir Drugakov NC PHEP, Minsk/DESY Andrey Elagin JINR, Dubna. Motivation. Bhabha scattering: - e + + e - → e + + e - + (n γ )

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LCWS 2005 SLAC, March 19 Low Angle Bhabha Events and Electron Veto.

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  1. LCWS 2005SLAC, March 19Low Angle Bhabha Events and Electron Veto. Comparison Between Different Crossing Angle Designs Vladimir Drugakov NC PHEP, Minsk/DESY Andrey Elagin JINR, Dubna

  2. Motivation Bhabha scattering: -e+ + e-→ e+ + e- + (nγ) -∂σ/∂θ ~ 1/θ3 → high probability at very small angles ≡ BeamCal is the most hit sub-detector Veto rate: - incomplete reconstructed events will be vetoed Incomplete reconstruction: - kinematics, i.e.γ-radiation deflects particles - reconstruction problem on top of the beamstrahlung remnants Study: - Impact of Bhabha events on the veto rate for different crossing angles

  3. Motivation Bhabha scattering: -e+ + e-→e+ + e- + (nγ) -∂σ/∂θ ~ 1/θ3 → high probability at very small angles ≡ BeamCal is the most hit sub-detector Veto rate: - incomplete reconstructed events will be vetoed Incomplete reconstruction: - kinematics, i.e.γ-radiation deflects particles - reconstruction problem on top of the beamstrahlung remnants Study: - Impact of bhabha events on veto rate for different crossing angles

  4. μ- e- ~ μ- χ0 μ+ Z0 ~ μ+ e+ χ0 e- e- γ* μ- μ+ γ* e+ e+ New Particle Searches The Physics: smuon pair production Signature: μ+ μ-+ missing energy σ ~ 102 fb (SPS1a) The Background: two-photon events Signature: μ+ μ- + missing energy (if electrons are not tagged) σ ~ 106 fb e+ + e-→ e++ e- + (nγ) e+ + e-→μ+ + μ-→ μ++ μ- + χ0 + χ0 = e+ + e-→ e++ e-+μ++ μ- ~ ~ i.e. mimic two-photon event → to be vetoed

  5. Motivation Bhabha scattering: -e+ + e-→ e+ + e- + (nγ) -∂σ/∂θ ~ 1/θ3 → high probability at very small angles ≡ BeamCal is the most hit sub-detector Veto rate: - incomplete reconstructed events will be vetoed Incomplete reconstruction: - kinematics, i.e.γ-radiation deflects particles - reconstruction problem on top of the beamstrahlung remnants Study: - Impact of bhabha events on veto rate for different crossing angles

  6. Beamstrahlung remnants. Pairs BeamCal will be hit by beamstrahlung remnants carrying about 20 TeV of energy per bunch crossing. the distribution of this energy per bunch crossing at √s = 500GeV 100GeV electron on top of beamstrahlung Severe background for electron recognition

  7. Motivation Bhabha scattering: -e+ + e-→ e+ + e- + (nγ) -∂σ/∂θ ~ 1/θ3 → high probability at very small angles ≡ BeamCal is the most hit sub-detector Veto rate: - incomplete reconstructed events will be vetoed Incomplete reconstruction: - kinematics, i.e.γ-radiation deflects particles - reconstruction problem on top of the beamstrahlung remnants Study: - impact of bhabha events on veto rate for different crossing angles

  8. Simulation Procedure Geometry: -3 designs Generation: -BHLUMI + TEEGG 4-momenta recalculation: -Lorentz boost for finite X-angle designs Tracking in magnetic field: - GEANT4 Detection efficiency for each particle: - parametrization routines Calculation of probabilities: - lost - incomplete reconstruction ≡ veto - full reconstruction

  9. IP out out Z in in → B Geometry “blind area”

  10. Simulation Procedure Benchmark geometry: -3 designs Generation: -BHLUMI + TEEGG 4-momenta recalculation: -Lorentz boost for finite X-angle designs Tracking in magnetic field: - GEANT4 Detection efficiency for each particle: - parametrization routines Calculation of probabilities: - lost - incomplete reconstruction ≡ veto - full reconstruction

  11. Bhabha generation BHLUMI: + all topologies - minimal angle > 0 TEEGG: + 1 particle in BCal + minimal angle ≈ 0 compensate Selection BHLUMI: - both particles above BCal TEEGG: -1 particle in BCal

  12. Simulation Procedure Benchmark geometry: -3 designs Generation: -BHLUMI + TEEGG 4-momenta recalculation: -Lorentz boost for finite X-angle designs Tracking in magnetic field: - GEANT4 Detection efficiency for each particle: - parametrization routines Calculation of probabilities: - lost - incomplete reconstruction ≡ veto - full reconstruction

  13. Simulation Procedure Benchmark geometry: -3 designs Generation: -BHLUMI + TEEGG 4-momenta recalculation: -Lorentz boost for finite X-angle designs Tracking in magnetic field: - GEANT4 Detection efficiency for each particle: - parametrization routines Calculation of probabilities: - lost - incomplete reconstruction ≡ veto - full reconstruction

  14. Simulation Procedure Benchmark geometry: -3 designs Generation: -BHLUMI + TEEGG 4-momenta recalculation: -Lorentz boost for finite X-angle designs Tracking in magnetic field: - GEANT4 Detection efficiency for each particle: - parametrization routines Calculation of probabilities: - lost - incomplete reconstruction ≡ veto - full reconstruction

  15. Electron Recognition Efficiency -- √s = 500GeV Fake rate is less then 1% cells are colored when the efficiency is less then 90% chain of towers at φ = 90° (the most affected) Recognition efficiency are parametrized as function of: - electron energy - pairs energy density

  16. Simulation Procedure Geometry: -3 designs Generation: -BHLUMI + TEEGG 4-momenta recalculation: -Lorentz boost for finite X-angle designs Tracking in magnetic field: - GEANT4 Detection efficiency for each particle: - parametrization routines Calculation of probabilities: - lost - incomplete reconstruction ≡ veto - full reconstruction

  17. Results Note: - Energy cut = 150GeV - energy resolution is not included Conclusions: - appreciable contribution to veto rate - 2 mrad scheme: insignificant rise - 20 mrad scheme: rise by a factor of 2

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