CERN Program Library Long Writeup W5013 - CERNLIB ...

where:
n number of energy bins
q i momentum of the photon with energy E i of the i th bin
q n upper
( )
limit for the momentum of the scattered photon
α i A qi
2
|F T (q)| 2
f i (q)
A (qn 2)
g i (q) = 1+µ2 rejection function.
2
Therefore, for given values of the random numbers r 1 and r 2 , GRAYL samples the momentum of the scattered
photon and the scattering angle θ via the following steps:
1. sample A ( q 2) = r 1 A ( qn
2 )
2. find the (q i−1 ,q i ] interval which gives A ( qi−1) 2 ( ≤ A q
2 ) ≤ A ( qi
2 )
3. calculate the linear extrapolation:
( (
q = q i−1 + A q 2) ( ))
− A qi−1
2 q i − q i−1
A ( qi
2 ) ( ) (4)
− A qi−1
2
4. calculate µ = cosθ =1− q 2 /(2k 2 )
5. calculate g i (q) =(1+µ 2 )/2
6. if g i (q) >r 2 the event is accepted, otherwise go back to 1.
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