[d2n-analysis-talk] H2 update report

Wed Apr 28 15:39:01 EDT 2010

Hi Brad,

I had talked to Zein-Eddine and he had a few suggestions. The first thought
that he had was that with a traget length of ~40cm there could be a large
energy loss from events that scatter near the front of the target as
compared to those that scatter at the end of the target. I took a look in
the particle book at the energy loss (MeV cm^2/g)  through liquid H2 for
protons <=1Gev and we do sit right on the slope.

Another thought that he had was that the HRS was set to an angle of 46.2
degrees, not 45 and had a cetral momentum of 0.87 GeV. He was wondering if
maybe we are not centered on the acceptance of the H2 elastic scattering
with 1.12GeV beam.

The trigger prescale for the T5 on these events is 1 and the rate is ~82Hz
In addition to the T5 trigger cut I also cut out the eldtp

The beam cut is just a cut on the beam current. It is a cut around the
average 14.75uA with a +/-1 spead. So all events within +/-1 of 14.75uA are
counted. I took a look at the beam current for all the elastic runs and with
the exception of 1259 they all looked stable. I did check and it is the T5
cut that is responsible for killing 90% of the events.

 I just want to clarify that the no cut events, realy have no cuts, They
were replayed using the analyzer with an empty cdef file, (where most that I
have seen have an automatic trigger cuts in the cdef, requiring a T1 || T2
|| T5 ect. )

And in the past when comparing how many reconstructed tracks I find in
bigbite I would compare to these no cut events, which I now think does not
make any sense. I should be comparing how many reconstructed tracks there
are with respect to some events that staisfy the hardware trigger (ie t2, t5
ect)

On Wed, Apr 28, 2010 at 1:06 PM, Brad Sawatzky <brads at jlab.org> wrote:

> On Tue, 27 Apr 2010, MATTHEW R POSIK wrote:
>
> > I have put together some kinematic plots for H2 elastic run 1258:
> >
> > H2_L_BB.png shows the invariant mass sqrt(w2) (left), scattering angle
> > in degrees, and momentum in GeV . The red Hist is the HRS and the blue
> > histo is the BB. All plots here have T5 coin cut.
> >
> > I then selected events in a tight cut on the BB elastic peak
> > "PriKineBB.W2>0.86&&PriKineBB.W2<0.96 && T5_coin_trigger" and plotted
> > the LHRS theta L.tr.tg_th this is plot lables el_th.png. As you can
> > see there are now 3 resolved peaks in the theta variable.
>
> It smoothed out your previous theta plot a little, but the same
> structure is there...  What are Zein-Eddine's thoughts on where that
> structure is coming from?
>
> > I also looked into the cuts that I was using for selecting good
> > protons in the LHRS. It seems that a lot of events are lost when I
> > make the LHRS acceptence cuts. Here is a run down of how the cuts
> > affect the events, the %diff is how many events are lost compared to
> > the trigger+beam cut, and the cut to cut % is how many events are lost
> > from the previous cut. The tg_xx are the acceptence cuts:
> >
> > *********************************************************************
> >     Cut
> > Events             %diff    from cut to cut
> > *********************************************************************
> > - no cut
> > 4009380              -
> > - triggers+beam
> >  216022             -
>
> It looks like 90% of the data disappear with the triggers+beam cut.
> What were the prescales and individual trigger rates?  What are the
> beam cut(s)?
>
> > - triggers+beam+track
> >  214883              0.50          0.50
> > - triggers+beam+track+tg_y
> >  142087             34.20         33.88
>
> This seems odd to me since at 45 degrees the HRS can not see the target
> windows.  This cut says that 1/3 of the data reconstructs 'outside' the
> valid target region...  I had assumed the HRS was cleaner than that. Can
> Zein-Eddine or Gregg comment on whether it is typical to loose 1/3 of
> the data for elastic data at this stage?
>
> > -triggers+beam+track+tg_y+tg_ph
> >  112676             47.84         20.69
> > -triggers+beam+track+tg_y+tg_ph+tg_th
> >   65533             69.66         41.84
>
> That's a big loss on the tg_th cut (also seen in your earlier slides).
> Given that the structure doesn't go away when you apply LHRS and BB
> kinematic cuts, it seems like those are real eP events...  (Still need
> to understand the structure though.)
>
> > -above +ex_tg_p
> >   65309             69.77          0.30
> > -above +ex_tg_p+energy
> >   53235             75.36         18.49
> > -above +ex_tg_p+energy+cer
> >   50852             76.46          4.47
> > -above +ex_tg_p+energy+cer+vdc
> >   47832             77.85          0.594
> > -above +ex_tg_p+energy+cer+vdc+prl
> >   11339                      **Don't think this one is correct.
> >                                It requires prl1 and prl2 to fire.***
> >
> > -without acceptance cuts
> > 152197
> >
> > I also realized my prl cut is probaly not good, I required both prl1
> > and prl2 to fire. But if the proton deposits all it's energy in prl1
> > than it will not count. So I am going to take that cut out.
>
> That is correct.
>
> -- Brad
>
> --
> Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
> Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
> The most exciting phrase to hear in science, the one that heralds new
>  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov
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-- 
Matthew Posik
Email: posik at temple.edu
Temple University Physics Dept.
Office: BA-319
Office #:  215-204-1331
WebSites:
Temple:
http://quarks.temple.edu/
d2n:
http://hallaweb.jlab.org/experiment/E06-014/
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