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The Detector and Interaction Region for a Photon Collider at TESLA

The Detector and Interaction Region for a Photon Collider at TESLA. Aura Rosca DESY Zeuthen Aachen, Germany, 17-23 July 2003. Higgs Physics Measure two-photon partial width and search for heavy Higgs states in extended Higgs models Electroweak Physics

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The Detector and Interaction Region for a Photon Collider at TESLA

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  1. The Detector and Interaction Region for a Photon Collider at TESLA Aura Rosca DESY Zeuthen Aachen, Germany, 17-23 July 2003

  2. Higgs Physics Measure two-photon partial width and search for heavy Higgs states in extended Higgs models Electroweak Physics Excellent W factory allowing precision study of anomalous gauge boson interactions Physics beyond SM Search for new charged particles, such as supersymetric particles, leptoquarks, excited states of electrons, etc. Motivation Aura Rosca DESY-Zeuthen

  3. Principle of a Photon Collider Crab Crossing Angle 2 deg. 2 mm 2 mm • Run in mode • Convert electrons in high energy photons via Compton backscattering of laser photons • High energy photons follow electron direction Aura Rosca DESY-Zeuthen

  4. Layout of the Beams Electrons Out Electrons Out IP Laser in Laser Out Electrons In Electrons in • Disruption angle is larger then in because of beam-laser interaction • Outgoing beam no longer fits through final quadrupole • need crossing angle to have separate beam pipe for in- and outgoing beam • Four beam pipes will enter the detector from each side. Aura Rosca DESY-Zeuthen

  5. Laser wavelength: Laser energy: Pulse duration: Rayleigh length: Repetition rate: TESLA collision rate Average power: Pulsed laser with correct time structure and relaxed power requirements feed a resonant cavity with quality factor Q ~ 100 Laser Requirements Aura Rosca DESY-Zeuthen

  6. Proposed Ring Cavity • Cavity mounted around detector • Round trip time = repetition rate of the electron bunches • Stabilization of the cavity length within about 0.5 nm Detector focusing mirror e e focusing mirror 12 m laser Aura Rosca DESY-Zeuthen

  7. Laser-Electron Crossing Angle • Need crossing angle electron beam-laser • opening angle laser • distance to e-beam Laser crossing angle • Laser collision angle reduces conversion • Compensated by higher laser energy Aura Rosca DESY-Zeuthen

  8. Electron-Photon Conversion Probability Aura Rosca DESY-Zeuthen

  9. Luminosity ] GeV / 1 - unpolarized s 2 - cm 32 10 [ γγ s d / dL helicity -- Aura Rosca DESY-Zeuthen

  10. Energy distribution on calorimeter face from one BX at z=3.8 m Disrupted beam larger than in case and additionally widened by crab crossing Beam-beam interactions: Incoherent pair production (ICP) Coherent pair production (CP) Neutrons from beam dump Background from physics processes, ex. Background Background can be a factor 10 higher than in LC 14 mrad 2 Units: GeV/mm Aura Rosca DESY-Zeuthen

  11. Design of the Mask ECAL HCAL • Redesign of TESLA detector in forward region to minimize background in TPC and VTX • Two masks • Longer outer mask • Tungsten parts TPC outer mask (tungsten) tungsten parts IP inner mask (tungsten) 183 cm 100 cm Aura Rosca DESY-Zeuthen

  12. Hits per layer for ICP With Mask Incoherent pairs ~ 368 hits Coherent pairs ~ 1 hit in the first layer and 3 hits in three last layers, from one event each 0.03 hits/mm in L1 Background in VTX 1 layer 2 layer 2 no change necessary wrt design 3 layer 4 layer 5 layer Aura Rosca DESY-Zeuthen

  13. < 1% occupancy factor 2.4 higher than in OK for TPC No mask: Incoherent pairs ~ 12900 photons / bunch Coherent pairs ~ 400000 photons / bunch With Mask Incoherent pairs ~ 927 photons / bunch Coherent pairs ~ 2440 photons / bunch Reduction by a factor ~ 125 Background in TPC Aura Rosca DESY-Zeuthen

  14. Beam Steering • Feedback e-e IP: 88 nm x 4.3 nm • Feedback Compton IP: Work in progress.. Aura Rosca DESY-Zeuthen

  15. Beam Steering 1 • Electron beams are stabilized by fast feedback system measuring beam deflection at IP • BPMs need large aperture because disrupted beam is larger • Solution: undisrupted Pilot bunches for beam steering • Electron bunches stable over one train • Photon beams follow electron direction • Separate electrons and photons on dump 2 Dump IP Aura Rosca DESY-Zeuthen

  16. Beam Dump • Photons cannot be deflected electrically or magnetically • Direct line of sight from IP to dump • High neutron flux at vertex detector • Narrow photon beam cannot be spread out and will always hit same window • High thermal load on window • High radiation damage to window WIP… Aura Rosca DESY-Zeuthen

  17. Conclusion • Tesla offers the possibility to work as a Photon Collider • The expected luminosity might be ~20% of the luminosity at the LC • Beam-beam backgrounds are larger but can be reduced redesigning the forward region • Some more items need to be studied for a realistic design of a Photon Collider Aura Rosca DESY-Zeuthen

  18. Acknowledgements • Many thanks to all my colleagues for providing me with their results. Aura Rosca DESY-Zeuthen

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