Peter,
The problem you have seems to be that your "flat" tof-position
distributions are not flat at all !! Ideally they should be flat
(i.e. constant) in the middle with a half-gaussian fall-off of on each
edge.
Also, your position spectra are narrower for the front tof's rather than
the backward tofs. Now: proton momentum correlates much more strongly with
the electron angle. The proton angle changes slowly and for a given rear
tof, you have various ep-elastic combinations for various electron angles
(think extended target of course). But for a given front tof the proton
momentum range is not that much (<5 % at forward angles)
Now the fact that they are smaller in the front may be related to
energy loss. If a proton is very much out-of-plane it traverses more
material and loses more energy. For the very front electrons you
have protons with the smallest energy. So it may be that for those
events our oop acceptance is narrower than what is allowed by the Wch
opening. If course if the vertical acceptance is narrower for the protons
it will show exactly the same way for the electrons (!), since they are
measured in concidence
Note also that if protons are lower in momentum they will also be bent
more which again tend to have them traverse more material and may lower
their "position threshold" on a tof.
Have you checked that this indeed that case ? How many channels do you
span in "vertical position for the front and in the back ? How much is
that in cm ? Is it smaller than the Wch opening ????
BTW, enforce adc cuts to see coplanarity and cleaner events. Your offset
results should not depend on it.
-- ________________________________________________________________________________ Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124 research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^On Sun, 24 Nov 2002, Peter Karpius wrote:
> I have been slightly distracting myself with this but it may prove useful. > Has anyone tried the following? > > I wrote a macro that: > 1) Fills a 3D surface plot of L vs R position > 2) Cuts the 3D plot on the Z-axis (# of events ->coplanar?) > 3) Projects the cut 3D plot into two 1D histograms, one for each axis. > 4) plots 2D histograms of cut and uncut position. > > It seems to extract coplanar events but I am not sure how much I am > missing. I set the Z axis cutoff at 25% of max based on the datasets. > In this case Runs 2765-2769 & 2757-2763. > > > I put a gif on my website (along with another tdc offset drift study I am > doing). Please check it out and tell me what you think? Here is the > direct link (just scroll to the bottom once you get there): > > > http://pubpages.unh.edu/~pkarpius/tdc_offset.htm > > > Please tell me if this can be of any use. I appreciate all > comments. Thanks!! > > Pete > > > PS I will get right on the self timing peak stuff next (sorry for the > delay!) > > ---------------------------------------------- > Pete Karpius > Graduate Research Assistant > Nuclear Physics Group > University of New Hampshire > phone: (603)862-1220 > FAX: (603)862-2998 > email: karpiusp@einstein.unh.edu > http://pubpages.unh.edu/~pkarpius/homepage.htm > ---------------------------------------------- >
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