<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi,<div class="">yes, will try to exclude gpp from the sim. chain and see if there’s still an error with the photon energy.</div><div class="">MK: I agree that for MC the correction is trivial since you now the generated 4vector. </div><div class=""><br class=""></div><div class="">The kinfit is not used at all for MC. It is used for real data, where you need to derive the “true” photon momentum from data itself. I did so as the missing photon from gamma p -> p pi0 -> p e+ e- gamma, by doing a kinfit to the hypothesis gamma p -> p pi0 -> e+ e- (gamma) and using the missing 4-momentum from kinfit as the “real” photon momentum.</div><div class=""><br class=""></div><div class="">Bests,</div><div class=""><br class=""></div><div class="">Andrea</div><div class=""><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jan 16, 2019, at 14:24, John W. Price <<a href="mailto:jprice@csudh.edu" class="">jprice@csudh.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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Hi Andrea:
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<div class="">Can you do a test *without* including gpp? This might help isolate the cause of the issue.</div>
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<div class="">John<br class="">
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<div class="">John W. Price</div>
<div class="">Professor, CSUDH Department of Physics</div>
<div class="">Coordinator, Science, Mathematics, and Technology Program</div>
<div class="">310-243-3403</div>
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On Jan 16, 2019, at 05:15, Michael Kunkel <<a href="mailto:mkunkel@jlab.org" class="">mkunkel@jlab.org</a>> wrote:<br class="">
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<div dir="ltr" class="">Greetings Andrea,
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<div class="">I believe you just verified what Diane Schott and I had been trying to convince other of for many years. :)</div>
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<div class="">However, the correction for simulation is quite trivial since we already know the generated 4vector. </div>
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<div class="">I don’t believe the kinfit package handles this problem.<br class="">
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<div style="direction: inherit;" class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">BR<br class="">
MK <br class="">
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Michael C. Kunkel, USMC, PhD<br class="">
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On Jan 16, 2019, at 05:59, Andrea Celentano <<a href="mailto:andrea.celentano@ge.infn.it" class="">andrea.celentano@ge.infn.it</a>> wrote:<br class="">
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<div dir="ltr" class=""><span class="">Hi MK,</span><br class="">
<span class="">last meeting before holidays I presented the corrections necessary for photons, for both MC and data. For MC, the reconstructed photon energy is affected by a major shift with respect to the generated one - much larger than what happens for real data.
I remember you pointed out that this may be due to a non correct parametrization of the EC sampling fraction in the MC chain (gsim + gpp + a1c). For data, this effect is not present, since the difference between the measured photon energy and the “real” one
(as obtained from the kin. fit of gamma p -> p pi0 -> p e+ e- (gamma)) is much smaller.</span><br class="">
<span class="">Therefore, I suspect this effect is related to an error in gsim or gpp rather than a1c, or that different reconstruction routines are used in a1c for data and MC.</span><br class="">
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<span class="">Can you comment more on this?</span><br class="">
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<span class="">Thanks</span><br class="">
<span class="">Bests,</span><br class="">
<span class="">Andrea</span></div>
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