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BaBar Interaction Region and Backgrounds

[ Beampipe Package | Machine Backgrounds | IR Commissioning ]

BBSIM Beampipe Package

The gnbpip package of BBSIM describes the PEP-II IR geometry and materials and provides support for simulating some machine-related background processes within the framework of GEANT.

The primary archive for the gnbpip package is a CVS repository (click here to review the log of recent changes). Stable debugged versions are also available through the BaBar Software Release Tools (SRT) and become included in coordinated releases of the entire BaBar software base (click here to browse the contents of recent versions of the gnbpip package available through SRT). If you really want the latest features and bugs directly from CVS you can use the SRT addpkg command with the -h flag.

The following material describes aspects of the BBSIM beampipe package in more detail:

As of July 98, the beamline simulation is in the process of being updated. This includes Q4/Q5 simulation done by Sandrine Emery for the HER commissioning; Q2 and endplugs done by Shiral Devmal; inside the support tube done by Chih-hsiang Cheng. Some information concerning that update can be found at this site.

Machine Backgrounds

The unique design of PEP-II required to achieve high luminosity and assymetric energies results in high levels of machine-related backgrounds near the IR. These backgrounds can lead to high detector occupancy and radiation exposure and are an important consideration in the designs of both PEP-II and BaBar. The expected sources of detector backgrounds are:
  • synchrotron-radiation photons produced in the PEP-II magnets,
  • lost beam particles due to bremsstrahlung and Coulomb scattering from residual gas molecules,
  • luminosity-related backgrounds such as elastic and radiative Bhabha scattering, and
  • miscellaneous other sources including inelastic beam-gas interactions, and muons from cosmic rays and interactions in upstream collimators.

The most comprehensive review of detector backgrounds can be found in Chapter 12 of the BaBar Technical Design Report. The results of more recent calculations of expected backgrounds are described in the following material:

  • Generic estimates (ie, ignoring detailed detector geometry) of background rates due to lost-particle and synchrotron radiation are described in the "Background Simulations" section of the Commissioning Proposal,
  • SVT radiation doses expected from lost-particles are described in Section 2.1 of BaBar Note #302 (SVT Monitoring Requirements),
  • B1 and Q1 magnet doses expected from lost-particles and radiative Bhabhas are described in a talk given at an IR meeting (more detailed info is also available here).

IR Commissioning

PEP-II will begin commissioning of the high-energy ring in the spring of 1997, and of the low-energy ring about one year later. We plan to instrument the IR during commissioning with simple detectors optimized for studying machine-related backgrounds.

Other web sites with material relevant to commissioning:

Go to the BaBar Home Page or the PEP-II Near-IR Home Page

This page is maintained by David Kirkby