Changes between Version 3 and Version 4 of perWeight

Timestamp:

Mar 7, 2016, 11:04:16 AM (8 years ago)

Author:

mosel

Comment:

--

perWeight

@@ -5 +5 @@
 (following text is taken - slightly modified - from: O.Buss, PhD thesis, [http://www.uni-giessen.de/cms/fbz/fb07/fachgebiete/physik/einrichtungen/theorie/theorie1/publications/dissertation/buss_diss pdf], Appendix B.1) 
 
-For some calculations, e.g. low-energetic πA or γA collision, it is a good assumption, that the
-target nucleus stays very close to its ground state. Henceforth, one keeps as an approximation
-the target nucleus constant in time. This basically means that the phase space density of
+For reactions which are not violent enough to disrupt the whole target nucleus, e.g. low-energy πA, γA or A collision at not too high energies, the  target nucleus stays very close to its ground state. Henceforth, one keeps as an approximation
+the target nucleus constant in time ('frozen approximation'). This basically means that the phase space density of
 the target is not allowed to change during the run. The test-particles which represent this
 constant target nucleus are called ''real'' test-particles. However, one also wants to consider the
@@ -13 +12 @@
 The ''perturbative'' test-particles are propagated and may collide with ''real'' ones, the products are
 ''perturbative'' particles again. However, ''perturbative'' particles may not scatter among each other.
-Furthermore, they are neglected in the calculation of the actual densities. One can simulate in
-this fashion the effects of the almost constant target on the outgoing nucleons without modifying
+Furthermore, their feedback on the actual densities is neglected. One can simulate in
+this fashion the effects of the almost constant target on the outgoing pparticles without modifying
 the target. E.g. in πA collisions we initialize all initial state pions as ''perturbative'' test-particles.
-Thus the target stays automatically constant and all products of the collisions of pions and
+Thus the target automatically remains frozen and all products of the collisions of pions and
 target nucleons are assigned to the ''perturbative'' regime.
 
-Furthermore, since the ''perturbative'' particles do not react among each other or modify the ''real''
-particles in a reaction, one can also split a ''perturbative'' particle in \(N_{test}\) pieces (several ''perturbative''
+Furthermore, since the ''perturbative'' particles do not react among themselves or modify the ''real''
+particles in a reaction, one can also split a ''perturbative'' particle into \(N_{test}\) pieces (several ''perturbative''
 particles) during a run. Each piece is given a corresponding weight \(1/N_{test}\) and one simulates like
 this \(N_{test}\) possible final state scenarios of the same ''perturbative'' particle during one run.
@@ -28 +27 @@
 == The perturbative weigth 'perWeight' ==
 
-Usually, in the cases mentioned above, where ou use the seperation into ''real'' and ''perturbative'' particles like this, you want to calculate some final quantity like \(d\sigma^A_{tot}=\int_{nucleus}d^3r\int \frac{d^3p}{(2\pi)^3} d\sigma^N_{tot}\,\times\,\dots \). Here we are hiding all medium modifications, as e.g. Pauli blocking, flux corrections or medium modifications of the cross section in the part "\(\,\times\,\dots \)". Now, solving this via the testparticle ansatz (with \(N_{test}\) being the number of test particles), this quantity is calulated as \(d\sigma^A_{tot}=\frac{1}{N_{test}}\sum_{j=1}^{N_{test}\cdot A}d\sigma^j_{tot}\,\times\,\dots \), with \(d\sigma^j_{tot}=d\sigma^N_{tot}(\vec r_j,\vec p_j)\) standing for the cross section of the \(j\)-th test-particle.
+Usually, in the cases mentioned above, where one uses the seperation into ''real'' and ''perturbative'' particles, one wants to calculate some final quantity like \(d\sigma^A_{tot}=\int_{nucleus}d^3r\int \frac{d^3p}{(2\pi)^3} d\sigma^N_{tot}\,\times\,\dots \). Here we are hiding all medium modifications, as e.g. Pauli blocking, flux corrections or medium modifications of the cross section in the part "\(\,\times\,\dots \)". Now, solving this via the testparticle ansatz (with \(N_{test}\) being the number of test particles), this quantity is calulated as \(d\sigma^A_{tot}=\frac{1}{N_{test}}\sum_{j=1}^{N_{test}\cdot A}d\sigma^j_{tot}\,\times\,\dots \), with \(d\sigma^j_{tot}\) standing for the cross section of the \(j\)-th test-particle.
 
 The internal implementation of calculations like this in GiBUU is, that a loop runs over all \(N_{test}\cdot A\) target nucleons and creates some event. Thus all these events have the same probability. But since they should be weighted according \(d\sigma^j_{tot}\), this is corrected by giving all (final state) particles coming out of event \(j\) the weight \(d\sigma^j_{tot}\).