Framework for amplitude analysis involving single meson production via quasi-elastic scattering of a real photon on a nucleon target. Focus on expandability and easy interfacing with Monte-Carlo tools and event generators.
Such processes are of interest at many experiments at JLab and the future EIC.
Requires ROOT (tested with version 6.17) with MathMore libraries installed.
To install use:
git clone --recursive https://github.com/dwinney/jpacPhoto.git
cd jpacPhoto
mkdir build && cd build
cmake ..
cmake --build . --target installThis will create a jpacPhoto/lib with libraries that can be linked to other code. The full suite of executables (e.g. to reproduce plots and results in [1] and [2]) will also be built in jpacPhoto/bin.
Note: cloning with the --recursive flag is required to initiate the jpacStyle submodule. Compiling can also be sped up with the optional -jN flag where N is the number of available cores.
The main object of interest is the abstract amplitude class. This allows you to build observables from helicity amplitudes:
- Probability distribution ( Σ_λ | A |^2 )
- Differential cross section ( dσ / dt )
- Integrated total cross section ( σ )
- Polarization asymmetries ( A_LL and K_LL )
- Spin density matrix elements ( ρ^α_λ,λ' )
- Integrated beam asymmetry ( Σ_4pi )
- Beam asymmetry in the y-direction ( Σ_y )
- Parity asymmetry ( P_σ )
Available amplitudes, so far, include:
- Single baryon resonance (s-channel)
- Pomeron exchange (t-channel)
- (fixed-spin and reggeized) Charged pseudo-scalar meson exchange (t-channel)
- (fixed-spin and reggeized) Vector meson exchange (t-channel)
- Primakoff effect off nuclear target (t-channel)
- (fixed-spin) Dirac fermion exchange (u-channel)
- (fixed-spin) Rarita-Schwinger fermion exchange (u-channel)
Incoherent (interfering) sums of amplitudes may be constructed through the amplitude_sum class.
The executables folder includes multiple applications of the above amplitudes to different reactions. See documentation in each respective .cpp file for usage.
Plots are automatically created using the JPAC collaboration style guidelines. For more information see the jpacStyle library.
