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Status of BBSIM PEPII geometry: gnbpip
Terry Geld
Simulation Parallel Meeting
28 Oct 1998
Presented by Bill Lockman

Contributors: C.Cheng, S.Devmal, G.DeDomenico, S.Emery, T.L.Geld, D.Kirkby, B.Meadows


The Background Commissioning group has upgraded the beamline geometry. The motivation for this comes from trying to get MC background predictions to agree with measured background rates in the commissioning runs. We found from the January HER run, that if we include enough of the beamline, impose a reasonable pressure profile and include far distant Coulomb scatters (full ring TURTLE simulation), we can get data and MC to agree to within a factor of ~1-2.

Now we have upgraded to the final beamline (B1, Q1, Q2, Q4, Q5) in preparation for the upcoming HER+LER commissioning runs. The TURTLE decks have also been upgraded to the final beamline configuration.

These upgrades can be used by BaBar detectors also to reevaluate the effects of background in their detector.


  • Many small updates to improve geometry.
  • BPMO and SSVD have both been fixed to solve overlap problems.
  • Determined part of the MCPF (forward IFR) overlap due to double creation of the endcap door plate. Removed that piece from gnbpip. Margaret Haire solved other gnmuon overlap problems.
  • HER & LER TURTLE decks finished, initial set of lost particle background rays available (see BkgCom HN).
  • Major magnetic field improvements. These changes result in reasonable, but not perfect agreement between the nominal orbits in GEANT and MAGBENDS.
    • Updated B1.
    • Added Q2, Q4, Q5.
    • Updated Q1, including x', y' tilt to Support Tube.
    • Modify TMAXFD, max field deflection allowed per step, in magnet vacuum volumes to force small step size.
  • Implemented a flag for cosmic ray run so the endplugs only can be turned on (only part of gnbpip in place for cosmics).

To Do

  • Add far upstream beamline components to try to reproduce HER background into SOB.
  • Finish LER beampipes (in progress).
  • Add final Q2 septum chamber (temporary Al one is currently modelled). Still waiting for final design and drawings.
  • Add additional steel pieces for support tube support system.

Last modified: Mon Oct 26 08:46:09 PST 1998