R-functions for the HRS
Update 8/3/05:
Error found and corrected in description of the dipole exit used to generate
the with-septum files.
Update 3/11/04:
Data files added for the Right and Left arms as used in the Hypernuclear
(E94-107) experiment
Update
Update 4/29/02:
Data files changed to reflect a new, improved spectrometer model.
(A
way to make cuts on data and optimally use the full acceptance)
John
J. LeRose 8/03/05
There now exists a
subroutine/function package that can be used to generate cuts in HRS data.
These routines use a so-called r-function to evaluate where a given trajectory
(characterized by y0, d, theta0, and phi0) lies with respect
to the boundaries of the acceptance of the spectrometer. As such, the
r-function value can be used as a parameter for placing a systematic cut on
data or simulations without artificially excluding too much acceptance.
The entire r-function package (source code and both new and old data files, both arms with septum too!) is included in a single tar file, which you can get HERE
tar file
contents:
Fortran Source files: see http://www.jlab.org/~lerose/r-functions/r-function.f & http://www.jlab.org/~lerose/r-functions/test-r-function.f
In the CUE the files can also be found in: home/lerose/public_html/r-functions/r-function.f and
test-r-function.f. Comments regarding usage can be
found in the source files. The first file, r-function.f,
contains the source code for the routines needed to use the r-functions. They
are:
Data files: see :
http://www.jlab.org/~lerose/r-functions/New-Left/collimator/ for left arm with collimator
http://www.jlab.org/~lerose/r-functions/New-Left/no-collimator/ for left arm without collimator
http://www.jlab.org/~lerose/r-functions/New-Right/collimator/ for right arm with collimator
http://www.jlab.org/~lerose/r-functions/New-Right/no-collimator/ for right arm without collimator
http://www.jlab.org/~lerose/r-functions/Right_6degree/collimator/ for right arm at 6 degrees (septum) with collimation
for GDH
http://www.jlab.org/~lerose/r-functions/left_septum_hypernuclear/ for left arm at 6 degrees (septum) with collimation for
Hypernuclear (E94-107)
http://www.jlab.org/~lerose/r-functions/right_septum_hypernuclear/ for right arm at 6 degrees (septum) with collimation
for Hypernuclear (E94-107)
old data files with older spectrometer
models can still be found at:
http://www.jlab.org/~lerose/r-functions/leftarm/collimator/ for left arm with collimator
http://www.jlab.org/~lerose/r-functions/leftarm/no-collimator/ for left arm without collimator
http://www.jlab.org/~lerose/r-functions/rightarm/collimator/ for right arm with collimator
http://www.jlab.org/~lerose/r-functions/rightarm/no-collimator/ for right arm without collimator
At each of these locations there are 15
files entitled:
Information.dat (general information about the files)
dy-dd.dat (parameters of the lookup table)
min-max.dat (rfunnction parameters)
linei.dat (i = 1,12) (more rfunction parameters)
Re choice of data files: In general the differences between left and right
are very small, except of course for left and right with septum. As a practical
matter, for a generic HRS (no septum) one could use the left or right
r-function equally well with either arm. With and without collimator, however,
are significantly different.
General Discussion:
The solid angle acceptance of the HRS is a
complicated function of y0 and d (DW = F(y,d)). The r-function tells you,
for the solid angle acceptance appropriate for a given value of y0
and d, where in relation to the boundary of that solid angle acceptance, a
given value of q0 and f0 lie. The r-function provided above uses a lookup
table approach to determine the boundaries of the solid angle at (y0,
d).
These boundaries take the form of 16 straight lines, whose parameters are
contained in the files linei.dat and min-max.dat. The r-function then evaluates the distance between
a given point (q0, f0) and each of those lines. The minimum of those
distances is then returned as the r-function value.
The 16 straight lines are shown in the
figure below along with the actual points that are the edges of the acceptance
at y0 = d = 0.
A contour plots of a sample r-functions appear below:
Enjoy!
Please send comments or questions to John LeRose: lerose@jlab.org