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

[Jonathan Zarling]

Hi all,

I appreciate the deep thinking on this, I too had been wondering about implications of the various strategies. I guess I'd like to ask/clarify two things:

  *   Is the tagged flux is universal, if you adopt the typical accidental subtraction scheme?
I.e. if properly calibrated, it should incorporate any rate dependence, tagger inefficiency, dependence on final state, etc. Assuming this strategy fits well with the downstream analysis. Then on the other hand, if you do something else, say picking our "pick the best in-time chi^2 photon" cut, the tagged flux doesn't have any easy correspondence.
  *   Do we gain meaningful statistical precision by doing something that sidesteps accidental subtraction?
If the tagger efficiency becomes large enough in a stats. limited analysis, this "pick the best in-time chi^2 photon" would also pick up events where the true photon is lost, but some accidental comes along with similar-ish energy. This feels hacky to me. Could we just go whole-hog and not skip using beam photons altogether? At least in principle. I'm wondering about the b1 pi cross sections and charmonia measurements. Just curious if the charge to the beamline group becomes the same here.

I hope I'm not retreading anything above, there was a lot to go through here. I guess I'm particularly interested to make sure the eta p cross section results (which DON'T do any of this best combo picking, typical accidental subtraction only) shouldn't be affected by the discussion in this chain.

Cheers,
Jon
________________________________
From: Halld-tagger <halld-tagger-bounces at jlab.org> on behalf of Richard Jones via Halld-tagger <halld-tagger at jlab.org>
Sent: Tuesday, February 21, 2023 9:49 AM
To: Shepherd, Matthew <mashephe at indiana.edu>
Cc: Hall D beam working group <halld-tagger at jlab.org>
Subject: Re: [Halld-tagger] [EXTERNAL] Fwd: Accidental subtraction

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<mailto:mashephe at indiana.edu>> wrote:
*Message sent from a system outside of UConn.*




---------- Forwarded message ----------
From: "Shepherd, Matthew" <mashephe at indiana.edu<mailto:mashephe at indiana.edu>>
To: Richard Jones <richard.t.jones at uconn.edu<mailto:richard.t.jones at uconn.edu>>
Cc: Hall D beam working group <halld-tagger at jlab.org<mailto:halld-tagger at jlab.org>>
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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<mailto: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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