
///\file "exoticphysics/channeling/.README.txt"
///\brief Example channeling README page

/*! \page Examplechanneling Example channeling

\author Enrico Bagli - INFN and University Ferrara (Italy) \n
 bagli@fe.infn.it

This example shows how channeling in bent crystal can be simulated
in Geant4

\section channeling_s1 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.

\section channeling_s2 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.

\section channeling_s3 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.

\section channeling_s4 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

\section channeling_s5 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
\verbatim
2009_PLB680_129.mac
\endverbatim
will automatically run the
example with 1000 protons.

Use
\verbatim
/xtal/setBR XXX 0. 0. m
\endverbatim
To change crystal bending to XXX meters

Use
\verbatim
/xtal/setSize 1.0 70. XXX mm
\endverbatim
To change crystal length to XXX millimeter

Use
\verbatim
/xtal/setEC data/Si220
\endverbatim
To select the (110) Si crystal plane of channeling

GPS commands are used for the primary generator.

\subsection channeling_s5_sub1 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
*/
