INTRODUCTION

The example simulates the channeling of 400 GeV/c protons in bent Si crystal. Channeling occurs when particles enter a crystal aligned with atomic planes or axes. In bent crystals, the particles are trapped between atomic planes and follow the crystal curvature being deflected. If the particle direction is tangent to a bent crystal plane is reflected to the opposite direction with respect to channeling, i.e., it suffer ‘volume reflection’. The example provides the physical model for planar channeling and volume reflection in bent crystals.

GEOMETRY

The geometry is a bent Si crystal with three Si detectors placed at -9.998 m, -0.320 m and 10.756 m with respect to bent crystal position. The Si detectors allows to measure incoming and outgoing angle after the interaction with the Si bent crystal. The geometry is all under vacuum.

PRIMARY EVENT

The primary events are 400 GeV/c protons at -1.05 m from the crystal with 13.36 microrad x 11.25 microrad divergence.

PHYSICS

In the example the physics of channeling and volume reflection has been added to the standard Geant4 physics. The description of the used model can be found in the paper ‘A model for the interaction of high-energy particles in straight and bent crystals implemented in Geant4’ by E. Bagli et al., available online at http://arxiv.org/abs/1403.5819

EXECUTION & OUTPUT

The executable must be run from within the source directory of the example to ensure that it can find the path for crystal data files.

Data files for Si crystal interplanar potential, nuclei and electron density are stored in a named subdirectory’data’

Upon execution, the macro

2009_PLB680_129.mac

will automatically run the example with 1000 protons.

Use

/xtal/setBR XXX 0. 0. m

To change crystal bending to XXX meters

Use

/xtal/setSize 1.0 70. XXX mm

To change crystal length to XXX millimeter

Use

/xtal/setEC data/Si220

To select the (110) Si crystal plane of channeling

GPS commands are used for the primary generator.

ExExhCh.root

The output is the ExExhCh.root file with the TTree ExExChTree has the leaves:

angXin : incoming particle X angle at the crystal
angYin : incoming particle Y angle at the crystal
posXin : hitting X position of the particle at the crystal
posYin : hitting Y position of the particle at the crystal
angXout: outgoing particle X angle out of the the crystal
angYout: outgoing particle Y angle out of the the crystal