[Halld-tagger] [EXTERNAL] Fwd: Accidental subtraction

[Richard Jones]

Matt,

You cannot use the tagged flux unless you use an accidentals subtraction
algorithm. Here are the rules I am claiming.

   1. if you do accidentals subtraction then you have complicated PWA fits,
   but at least you know what your flux should be.
   2. if you do hybrid tagging without full accidentals subtraction then
   you have simple PWA fits, but then you have problems knowing what your flux
   should be.

This is something of a no free lunch theorem that applies here. See my
first response to Peter for more details on how the flux is problematic in
a hybrid tagging scheme.
-Richard

On Tue, Feb 21, 2023 at 9:02 AM Shepherd, Matthew <mashephe at indiana.edu>
wrote:

> *Message sent from a system outside of UConn.*
>
>
>
>
> ---------- Forwarded message ----------
> From: "Shepherd, Matthew" <mashephe at indiana.edu>
> To: Richard Jones <richard.t.jones at uconn.edu>
> Cc: Hall D beam working group <halld-tagger at jlab.org>
> Bcc:
> Date: Tue, 21 Feb 2023 14:01:31 +0000
> Subject: Re: [Halld-tagger] [EXTERNAL] Fwd: Accidental subtraction
>
> Hi Richard,
>
> > On Feb 20, 2023, at 11:08 AM, Richard Jones <richard.t.jones at uconn.edu>
> wrote:
>
> >  Likewise with trying to measure an absolute differential cross section
> for the a2 over a continuum of rho,pi using amplitude analysis to extract
> the a2 part. The problem I am pointing to here is this: what to use for the
> flux is no longer model-independent if you are not doing proper accidentals
> subtraction.
>
> Not sure I understand the details here... "model-independent"?
>
> When doing amplitude analysis the output of the analysis is a tagged,
> acceptance-corrected yield over a range of beam energy.  We then used a
> tagged flux to turn this number into a cross section.  When obtaining the
> tagged acceptance corrected yield, we can use two methods of handling
> pileup of beam photons in the signal RF bin and they produce the same
> result.
>
> Matt
>
>
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