thank you for the clarification. Extracting a rho, theta is a
refininement. I think nobody ever bothered with that at AmPS or IUCF,
to first order you should not worry either. However, please be aware that
the beam diamter - for all practical purposes - is << cell diameter. YOu
can assume it to be a pencil beam. The actual radius may be 1-2 mm, but
actually does not matter since our spectrometer is only sensitive to
the z component. Doesn't it make sense ? We are only trying to save MC
efficiency and cpu time here, so maybe this whole discussion is not
crucial.
now, beam haloes is another thing. Bu they are not really ameble to a
simple parametrization. These were my 2 cents. I was only confused by the
previous email. - tb
-- ________________________________________________________________________________ Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124 research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^On Wed, 11 Sep 2002, Aaron Joseph Maschinot wrote:
> > I should clarify what I said about the default (triangular) vertex > distribution. The triangular distribution works in two steps: > > 1) Two random numbers, z and rho, are picked. z lies (randomly) within > -20cm < z < +20cm. rho lies (randomly) within 0 < rho < 1. After > picking such (random) z and rho values, the following value is computed: > value = ((1.0 - abs(z)/20.0) > rho) > If value == 1 (i.e. if (1.0 - abs(z)/20.0) is indeed greater than > rho), then program execution goes on to step 2); otherwise, step 1) is > repeated over again. > > 2) A random value for rho between 0 < rho < 0.5mm is picked. Also a > random value for theta between 0 < theta < 2*pi is picked. Then the > (cylindrical) vertex point (rho, theta, z) is assigned, where the z > value comes from 1). > > Thus, 1) incorporates the triangular probability distribution portion; 2) > incorporates choosing the actual vertex point. > > Aaron > > > > On Wed, 11 Sep 2002, Tancredi Botto wrote: > > > > > > > The most realistic vertex method that the Monte Carlo currently has is > > > vertex style 0. This style has an extended target of total length 40cm > > > and has a triangular distribution in (cylindrical) rho about this length, > > > out to a maximum of 0.5mm, centered in the middle of the target. > > > > > > > I am not sure I understand what you mean. The triangular distribution is > > only a function of z, the cell length > > > > rho(x) = rho(0) * ( 1 - |z|/L) > > > > where 2L is the cell lenght (40 cm). rho(0) can be found from the total > > (atomic) flow divided by the total cell conductance (you have to add > > the equal contributions from the two hlves, each of length L, diameter d) > > There is no radial dependence. > > > > Cheers, > > tancredi > > > > > > >
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