[Frost] Fwd: FROST follow-up

[Stuart Fegan]

-------- Original Message --------
Subject: 	FROST follow-up
Date: 	Thu, 06 Jun 2013 19:06:14 +0200
From: 	Stuart Fegan <Stuart.Fegan at ge.infn.it>
To: 	Ken Livingston <Kenneth.Livingston at glasgow.ac.uk>
CC: 	Dave Ireland <David.Ireland at glasgow.ac.uk>, 
bryan.mckinnon at glasgow.ac.uk



Hi everyone,

Just some follow up to Monday's meeting and the pesky issue of the sharp
hyperon peaks seen on the kaon missing mass distribution from the carbon
target.  I've played with the vertex cuts to try to see if this was
'free' proton events bleeding through from butanol, ice build-up on the
downstream end of the carbon, or something else.  I've attached a few
plots showing the distributions for two halves of the carbon target (5-6
cm and 6-7cm), and a narrow central region of the carbon foil (5.5-6cm),
contained within the first half.

The half nearest the butanol cell seems to show the lowest proportion of
these events, suggesting contamination from the butanol target is not a
huge issue, with the other half suggesting ice on the end of the carbon
may be present.  That said, the slight enhancement in the proportion of
possible free proton hyperons in the central region (supposedly distant
both from any ice build-up and butanol bleed-through) suggests something
unexpected, but with so little data it's difficult to draw any conclusions.

Going forward, I'm inclined to define a carbon background function by
removing these peaks before fitting a function to the remaining bins,
using hyperon peak positions from butanol (or g8, where there is no
carbon background, if I can find an argument around potential systematic
effects), then using this function to characterise the amount of carbon
present.  This is similar to what Derek developed for Jo's analysis on
the pions, but she has one less peak in her missing mass distribution,
and includes a Gaussian in the fit to account for the sharp peak, rather
than removing it (section 9.6 of her thesis).

With just a couple of weeks until the CLAS meeting, I doubt I'll have
much more on this by then, but I'll keep you informed of any breakthroughs.

Cheers,
Stuart

-- 
Stuart Fegan
INFN-Genova
Via Dodecaneso, 33 - 16146, Genova
Italia

E-mail: Stuart.Fegan at ge.infn.it

"perdona il mio italiano - ancora imparando"



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