[d2n-analysis-talk] H2 update report

[Brad Sawatzky]

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