[Frost] Followup on today's meeting

[Igor Senderovich]

Dear Steffen, Colleagues,

It's good to hear that our mass distributions agree now. Let me list my cuts for the pi+(X) channel (including the trivial ones) just to make sure we are comparing "apples to apples", top understand any other inconsistencies we may find later.

Note: GPID bank is used primarily.

- Number of GPID particles (GPID_NH) > 0. If one particle, it must be positive
- track accepted if good mass calc. and clear tag: mass_ref==0 && ngrf==1
- pion accepted if in GPID |betam - beta|< 0.08
- event ID as pi+(X) if
  - exactly one pi+ accepted &&
  - no other particles in GPID accepted* &&
  - non-zero helicity value from TGBI

*One may argue that a clear sample may result if no other particles are recorded in GPID bank period.

The rest of the cuts are given explicitly in the talk. MVRT vertex position relative to the beam center from database was used in all cases. I would appreciate any advice you have on selecting this data.


Regarding the final plot in the talk, mass_ref dependence on vertex position - the plot was fresh off the presses and has the opposite sense: it is the fraction of events that does NOT have mass_ref==0. You were right, Franz, that the fraction was too low to be good events. I uploaded the corrected and full statistics version here:
http://clasweb.jlab.org/rungroups/g9/wiki/index.php/Image:Mass_ref_frac_vs_Vz.png
The message is still clear that, for some reason, the polluted downstream edge of C target corresponds to a higher value shoulder in this mass_ref vs z distribution, so that suspending the mass_ref cut introduces more contamination.

All the best and have a good weekend,
-Igor



----- Original Message -----
From: "Steffen Strauch" <strauch at sc.edu>
To: "FROST" <frost at jlab.org>
Sent: Thursday, January 24, 2013 2:24:59 PM
Subject: [Frost] Followup on today's meeting

Dear Colleagues,

In today's meeting Igor Senderovich has presented his nice study of the hydrogen contamination of the 12C target in g9a.  His missing-mass distributions did not agree with the ones I have shown earlier.  Looking through my analysis of the hydrogen contamination I found that I made an additional cut on the data.  I have selected only events where the pion momentum is larger than 0.4 GeV/c.  For this particular study I did not want to worry about additional complications through energy loss corrections, particularly for the contaminated 12C target.  The corrections were made, but only the large momentum particles used.  Relaxing this cut brings the missing-mass distributions into nice agreement.

All the best,
Steffen Strauch



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