ATLAS beamline and failure case simulation

1. ATLAS beamline and failure case simulation A. Sbrizzi H.Burkhardt, B.DiGirolamo, A.Sbrizzi Acknowledgements to: L.Chytkha, R.Kwee, T.Sykora

2. Introduction • Tobias Baer (PhD Thesis): “Very Fast Losses of the Circulating LHC Beam, their Mitigation and Machine Protection” • […] (Un)identified falling objects (UFOs) are one of the most relevant surprises after the LHC start-up. They have significantly affected the LHC availability and may become a major performance limitation for future LHC operation. UFOs are most likely micrometer-sized dust particles which lead to very fast beam losses with a duration of a few turns when they interact with the beam. • In 2011/12, the diagnostics for UFO events were significantly improved, dedicated experiments and measurements in the LHC and in the laboratory were made and complemented by MAD-X and FLUKA simulations and theoretical studies. […] A. Sbrizzi

3. Plan • We would like to study the effect in ATLAS of UFOs interacting with the beam in the “proximity” of IP1. • We would like to answer questions like: • How does a proton-UFO shower looks like? Composition, size… • How many particles do we see in the ATLAS inner detector per UFO collision? • What fraction of the beam must collide to reach the limit of 1010 particles? • What is the dependency in the position? • We are investigating the possibility of using Geant4 • Stand-alone Geant4 simulations • ATLAS simulation framework • Advantage: no need to interface different simulations A. Sbrizzi

4. Standalone Geant4 • Shoot a 7 TeV proton against a “UFO-like” target (1 mm Cu) and look at produced particles to estimate shower composition and size > 1 particle Secondary particles A. Sbrizzi Default physics list: FTFP_BERT 1.3 10 cm2 screen at 8 m Secondary particles 20 particles per collision (10 charged, 10 neutral). Shower cone 2.5 mrad (20 mm spot at 8 m).

5. ATLAS Forward Region • The ATLAS collaboration has developed a simulation of the ATLAS Forward Region (19-269m) inside the ATLAS simulation framework (Athena) with the aim of studying ATLAS forward detectors performance (AFP, ALFA, ZDC) • L. Adamczyk at al., https://cds.cern.ch/record/1595009 • L. Chytka, kfe.fjfi.cvut.cz/~chytka/AtlasFWRSim.pdf • https://twiki.cern.ch/twiki/bin/viewauth/Atlas/FullSimulationATLASForwardRegion A. Sbrizzi

6. ATLAS Forward Region Beam screen • Geometry • Extracted from LSS1R.xlsx • Full beam pipe with beam screens • Collimators: TCL4,5,6 • Transition volumes need better description • Magnets • Magnet fields from twiss files • Inner triplets field maps (Q1, Q2, Q3) can also be used (provided by the FLUKA team) • MQXA_NOMINAL.dat, MQXB_NOMINAL.dat (+ bilinear interpolation) • Magnet rotations and shifts being implemented • Magnet dead material not yet implemented • Cross-check with MAD-X • Maximum discrepancy Δx=1mm • Reason: difference in dipole setting • High precision not needed for these studies A. Sbrizzi

7. ATLAS Forward Region hits • Possibility to store Simulation Hits • To do particle back tracking • To count particles through a surface • T. Keck et al., https://cds.cern.ch/record/1594939 A. Sbrizzi Number of particles through a half-plane in front of ALFA in 100 SoftQCD events

8. First attempt • First attempt to shoot a 7 TeV proton from 200m towards the IP A. Sbrizzi • Next • Add “UFO-like” objects in the ATLAS Forward Region • Shoot particles against the UFO towards the IP1 • Look at particles through different xy planes • Look at particles in ATLAS inner detectors

9. Summary • We are investigating the possibility of using Geant4 simulations available in the ATLAS simulation framework to study the effect of UFO collisions in ATLAS. • First results this week • Compare results with FLUKA simulations • Compare results with UFO candidates in data • Look at other tools • BDM: FLUKA -> G4 geometry translation A. Sbrizzi

10. Back-up A. Sbrizzi

11. A. Sbrizzi