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Background issues for the ATLAS Roman Pot Detectors

Background issues for the ATLAS Roman Pot Detectors. Ilias Efthymiopoulos & P. Grafstrom - CERN 2 nd Meeting of the LHC Machine-Induced Background Working Group CERN - June 24, 2004. Introduction. Layout & Running conditions Forward detectors in Roman Pots at 240 m from IP1

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Background issues for the ATLAS Roman Pot Detectors

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  1. Background issues for the ATLAS Roman Pot Detectors Ilias Efthymiopoulos & P. Grafstrom - CERN 2nd Meeting of the LHC Machine-Induced Background Working Group CERN - June 24, 2004

  2. Introduction Layout & Running conditions • Forward detectors in Roman Pots at 240 m from IP1 • Probe the elastic scattering in the Coulomb interference region • Absolute determination of LHC luminosity, tot and other physics parameters • Special high-beta optics: * = 2650 m • Very small distances to the beam • Detector : scintillating fiber tracker readout with multi-anode PMTs • Sensitive to radiation – limited to luminosities  1031 cm-2 s-1 Background issues to consider • Proton halo  cleaning efficiency of collimators • Beam-gas scattering - short & long range contributions • IP related background not really an issue due to low luminosities

  3. ATLAS RP Layout Roman Pots @ 240 m from IP1

  4. ATLAS RP Layout Roman Pot Locations One Roman Pot Station per side on left and right from IP1 Each RP station consists of two Roman Pot Units separated by 3.4 m, centered at 240.0 m from IP1

  5. Proton beam halo • Beam halo is a serious concern for the Roman Pot operation • it determines the distance of closest approach dmin of the sensitive part of the detector: nσ = dmin/σbeam • Working scenario: 43 bunches, 1010ppb, εN = 1.0 μm rad, at nσ=10 • Assuming 40 h beam lifetime: • With a cleaning efficiency of 210-3 (for 10 )  6kHz beam halo rate on the detectors. (RA LHC MAC 13/3/03) Working point

  6. Background simulations • Based on simulations by N.Mokhov et. al. (Fermilab-conf 03/086) • Study for TOTEM/IP5, “all sources included” • Long range -elastic scattering anywhere in the ring and tails form the collimator (collimator inefficiency) in combination with full shower simulation for losses on LHC limiting apertures • Short range- inelastic beam-gas interactions (few hundred meters) @ 1033 cm-2 s-1 RP at 220 m Origin of radiation: • 0.1  1 % beam related – scale as the beam current • Rest is from IP – scale as the luminosity

  7. Background estimate – extrapolation! • Rate estimates comparable to simple beam halo from collimator cleaning efficiency

  8. Summary • Background estimates for the RP detector indicate a rate of few kHZ for the proposed (low luminosity) running scenario • Largest contribution from the beam halo, estimate based on present knowledge of collimator cleaning efficiency • Extrapolation from IP5 studies including “all sources” of background (beam-gas and accelerator apertures) • Would be interesting to have dedicated studies for the ATLAS/IP1 RP layout • Different RP location wrt TOTEM/IP5 • Different optics • Update with the present knowledge of collimators • Layout at LSS1 and cleaning efficiency

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