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Simulations of MICE

Simulations of MICE. 16-19 March 2005 BENE Week Rikard Sandström Geneva University. Outline. What we do & how G4MICE Features Geant4 in MICE Example of G4 simulations Detector response, reconstruction, analysis Example of Digitization Other tools G4BeamLine TURTLE ICOOL others

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Simulations of MICE

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  1. Simulations of MICE 16-19 March 2005 BENE Week Rikard Sandström Geneva University

  2. Outline • What we do & how • G4MICE • Features • Geant4 in MICE • Example of G4 simulations • Detector response, reconstruction, analysis • Example of Digitization • Other tools • G4BeamLine • TURTLE • ICOOL • others • Present status of G4MICE

  3. What we do, how we do it • Using software to simulate • Beamline • Particle physics • Detectors • Reconstruction of events • Analysis of (simulated) reconstructed events • Problems, such as • RF background • Misalignment • Main path: Geant4 based simulations • G4MICE • 1.0 released a few weeks ago • Geant-4.6.2.p02 • Will move to Geant-4.7.0.p01 soon

  4. Features of G4MICE 40 mm • Detailed simulations of the full MICE cooling channel • RF cavities • absorbers • all detectors (TOF’s, CKOV’s, SciFi tracker, • TPG tracker, EM-calorimeter) • iron shields, etc • beam contamination • RF background • User specified number of cooling cells -> NuFact! • All parameters can be given as input • Tweakability & user friendly • Turn on/off detectors, processes, RF field etc • Digitization, reconstruction & analysis of most detectors • Built in unit test for most subsystems

  5. Geant4 in MICE • Great care taken to confirm results with • Theory • PDG data • Independent simulations (ICOOL, EGSnrc) • Fair agreement, gets better with every G4 release Energy loss in absorber (Chris) Energy deposition in EMCal fibers (Rikard) Red = ICOOL Blue = G4MICE

  6. Edep fiber/lead is constant for muons, and different for e and µ. Fibers sees electrons, photons convert in lead, fiber/lead dep decreases with z. Example: Energy deposition in EMCal

  7. Example: Dark current simulations • Scenario: • Electrons are ripped off RF cavities at high E field. • They are accelerated through the cavities, losing energy in Be windows. • Can turn around if E-field flips. • Hit vacuum and absorber windows, and 35 cm liquid H2. • Conversion to brems-strahlung photons. • Photons convert to electrons in trackers.

  8. How I did it • Measurements at Fermilab gave dark current per area. • Agrees with F ~ j x B • What area should we consider? • Assumed emission rate: • Given the 40 kHz/cm2 of emitted electrons off a cavity at 8 MV/m, 201.25 MHz frequency, and a conservative assumption of area to be considered, we have 7.92 e- hitting the absorber per energy peak (and period). • 8 energy peaks * 2 linacs * 7.92 = 126.72 e- per period in total. • Tungsten coated windows lowers emission. • Studies using 201 MHz cavity and atom probe tomography right now. • Calculated propagation in Matlab, using energy loss from STAR. • More on next slide. • Matlab results are started at cavity exits in G4MICE (Geant4). Windows are modelled as torispherical. • Starting time and energy as calculated in Matlab. • Effect of background is digitized & reconstructed together with real muon, and analyzed. • SciFi trackers are OK with this rate of background.

  9. RF phase calculations in Matlab • The phases for the background electrons assumes phases optimized for a mu+ at 200 MeV/c on axis. • This causes a symmetry breaking in z! • Assumes phase difference between neighboring cavities is constant. • Phase diff = 2.0498 rad = 1.621 ns. • This gives the muon an energy gain of 10.8 MeV per set of four RF-cavities, including energy loss in Be windows. • Energy loss is calculated using STAR data for ionization and bremsstrahlung.

  10. Accelerating e- in the RF, intro • The electrons are assumed to have zero kinetic energy when emitted from beryllium windows. • The electrons emitted at the peak values of the E-field only (+ and - respectively). • They are accelerated using the same Matlab model as used for the muon. • This results in • energy when leaving the RF-system • travel time for leaving the RF-system

  11. Accelerating e- in the RF, 4 cavs Downstream direction Upstream direction

  12. Detector response, recon & analysis • Simulated hits in detectors are transformed to ADC counts etc (Digitization). • As close to real life as possible. • ex. use light yield and dead channel in tracker from test data • Reconstruction should see no formal difference between simulated signal and experimental signal. • Reconstruction package reconstructs the events, given digits from detector response. • The Analysis package calculates emittance along z (among other things). • User can add his own analysis. • Tools exist to convert all output files to ROOT files. • ”Analysis does everything for you, but perhaps not coffee” - Malcolm Ellis

  13. Example: Digitization of TPG • Objective: Find out whether 100 cm He or 18 cm Ne tracker is better. • Simulation stores hundreds of points along a track. • Digitization: • Poisson distributes clusters along the track. • Garfield determines how many drift electrons for a given cluster. • Driftelectrons drift to GEMs. • GEMs amplify signal, and gives further spread. • Readout strips picks up charge, converts into time dependent amplitude. • At given intervals, amplitudes are collected. • If there is more than one digit on a strip at a given sampling their amplitudes are summed up. • Noise is added. • The resulting digits are written to file, ready for Reconstruction. • Digits know about all their ancestors.

  14. ISIS Beam G4BeamLine Iron Shield TOF0 TOF1 Diffuser Iron Shield TOF2 Ckov2Cal Proton Absorber Ckov1 Other tools than G4MICE • Acceptance, field matching, emittance is often calculated outside G4MICE • ICOOL (Ulisse Bravar) • Less detailed than G4MICE, but well used, well known.Allows iterative optical matching. • TURTLE (Kevin Tilley) • Used for optimizing beam line (rates & acceptance) • G4BeamLine (Tom Roberts) • Useful tool here used in a similar manner as TURTLE. • Lahet, Mars, standalone Geant4 (Kenny Walaron) • Target studies • FLUKA (Lara Howlett) • Target studies • Matlab (Rikard Sandström) • RF background transportation in time dependent fields • Garfield (Edda Gschwendtner) • Low energy ionization in gas • Output from ICOOL, TURTLE and G4BeamLine can be used as input beams for G4MICE! • G4MICE can also reuse its own output as input beam.

  15. Present status of G4MICE • Beam line, cooling cell and detectors described. • Detector response • Some detectors have functional reconstruction. • Work in progress. • StartedPID • Expect results later (autumn?). • Many questions of simulation physics solved. • bug fixes in Geant-4.6. • RF background will be measured this spring at FNAL. • G4MICE is already used for production. • Analysis tools -> listen to Chris.

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