Simulation of weak decays

Rootfile

A) A file with electron momentum (px,py,pz) as a function of (x,y,z) in bins of size (deltax, deltay, deltaz)

B) A file with photons from external bremsstrahlung with momentum (0,0,pz) as a function of (x,y,z) in same bin sizes.

As a first and maybe good enough approximation the photon momenta in px and py can be neglected since the photon spectrum
is forward peaked. A refinement would be to include px and py but that would be a second calculation.

A first approximation would be bins of 1cm x 1cm x 1cm.

With such distributions of electron and photon momenta in the target one could subsequently start vertices anywhere
in the target for pions, hyperons, etc. and follow their paths or decay products through the magnets.

Adding a generator?

A c++ code (decay.cpp) exists on

/u/home/aniol/moller/src

at JLab.

At present the code does the Lorentz transformation for parallel axes but arbitrary relative velocity between the lab frame and the hyperon rest frame. The 4 momenta and 4 spin are transformed according to the prescriptions in Jackson's book and the Goldstein, Poole & Safko book. There is diagnostic output included which I used to check the code. This can be easily commented out.

It is the first step in a simulation. The code needs the lab 4 momenta and lab 4 spin of the hyperon. As it stands it reads in a file, decay.inp, to get the input values. It converts to the rest frame and gives the rest frame 4 spin. The rest frame momenta of the decay products are then converted back into lab frame values.

I haven't included the angular distribution in the rest frame for the decay to pion + nucleon yet. This should be straight forward. Once this is included I will need to have a way of choosing the lab polarization of the hyperon. There is a new thesis from hall C by Gabrielyan which is in the same directory which will be useful.

I felt it was better to have the beginning of the simulation available now rather than wait for the full treatment. I assume we will be able to start the hyperon anywhere in the target for both electroproduction and photoproduction.

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