<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Lei,<div><br></div><div>If this has been done in multiple dimensions for each particle, then this is fine for the efficiency map. I was under the impression that it was done for a whole event topology (in comparison with Monte Carlo). Michael did a wonderful job with the efficiency map, no question about it. He deserves all the credit in the world. We also see that the Monte Carlo describes the data very well.</div><div><br></div><div>However, it does not solve the acceptance problem when it comes to reconstructing a meson from its decay products. The best efficiency map does not know the physics in zero-acceptance regions.</div><div><br></div><div>- Volker</div><div><br></div><div><br><div><div>On Jul 12, 2016, at 1:51 PM, Lei Guo <<a href="mailto:lguo@jlab.org">lguo@jlab.org</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><meta http-equiv="Content-Type" content="text/html charset=utf-8"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">The efficiency map is binned in multiple dimensions: z, p, theta and phi, for each particle (proton, pi+ pi-). I think this is applicable.<div class=""><br class=""><div apple-content-edited="true" class="">
<div class=""><div class=""><div class="">Lei Guo</div><div class="">Assistant Professor</div><div class="">Physics Department</div><div class="">Florida International University</div><div class="">Miami, FL</div></div><div class=""><br class=""></div><div class="">email: <a href="mailto:leguo@fiu.edu" class="">leguo@fiu.edu</a> or <a href="mailto:lguo@jlab.org" class="">lguo@jlab.org</a></div><div class="">Office:305-348-0234</div></div>
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<br class=""><div><blockquote type="cite" class=""><div class="">On Jul 12, 2016, at 1:38 PM, Volker Crede <<a href="mailto:crede@fsu.edu" class="">crede@fsu.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; " class=""><div class="">Lei,</div><div class=""><br class=""></div><div class="">Bad TOF paddles were knocked out. The z-dependence cannot be properly taken care of by MK's efficiency map since it depends on the kinematics of the final-state particles. It can provide an average correction which we have been using but it comes with a large systematic uncertainty.</div><div class=""><br class=""></div><div class="">- Volker</div><div class=""><br class=""></div><br class=""><div class=""><div class="">On Jul 12, 2016, at 1:34 PM, Lei Guo <<a href="mailto:lguo@jlab.org" class="">lguo@jlab.org</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">We should expect that the acceptance is z-dependent since it’s such a long target. MK’s efficiency map also is z-dependent. Has the map been applied, and the photon multiplicity been dealt with correctly? Was the bad TOF paddles knocked out?<div class=""><br class=""></div><div class=""><br class=""><div apple-content-edited="true" class="">
<div class=""><div class=""><div class="">Lei Guo</div><div class="">Assistant Professor</div><div class="">Physics Department</div><div class="">Florida International University</div><div class="">Miami, FL</div></div><div class=""><br class=""></div><div class="">email: <a href="mailto:leguo@fiu.edu" class="">leguo@fiu.edu</a> or <a href="mailto:lguo@jlab.org" class="">lguo@jlab.org</a></div><div class="">Office:305-348-0234</div></div>
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<br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jul 12, 2016, at 1:04 PM, Volker Crede <<a href="mailto:crede@fsu.edu" class="">crede@fsu.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; " class="">Hi Carlos and Michael,<div class=""><br class=""></div><div class="">We perform a proper acceptance correction of the g p --> p ω reaction, but we do what almost everybody else does in the earlier meson reconstruction. We look at the invariant 3π mass distributions for each (energy & angle) ω bin, subtract the background either event-based or with side bins, and then we do the same thing with ω --> 3π MC events to determine the acceptance for each kinematic bin. However, if the c.m. angular distribution of one of the decay-π has holes, there will be a mistake from integrating over unknown territory. Each pion is associated with three experimental parameters, so in principle (the neutral pion missing), it will require a six-dimensional acceptance correction. This is of course not very practical and sometimes, with actual holes in the acceptance, even impossible. You cannot correct for something that is unknown. This could be a problem for many analyses that study meson decays and try to determine branching fractions.</div><div class=""><br class=""></div><div class="">We looked at the double-pion channel for the lower energies < 2 GeV to study baryon resonances. We do see Δ's (by simply taking the lab four-vectors) but not as pronounced as in g11a. You see the effect in the mass distributions when you distinguish between the forward and backward half of the target.</div><div class=""><br class=""></div><div class="">- Volker</div><div class=""><br class=""></div><div class=""><br class=""><div class=""><div class="">On Jul 12, 2016, at 12:24 PM, Carlos Salgado <<a href="mailto:salgado@jlab.org" class="">salgado@jlab.org</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; " class="">Hello Volker<div class=""><br class=""></div><div class="">This an interest phenomena. Angular acceptance will be very different in g12/g11 as the target was moved.</div><div class="">But , this different should be taken care of by acceptance corrections? Is that discrepancy remains in cross section, is this showing that the acceptance correction is not right?</div><div class=""><br class=""></div><div class="">Also for PWA, which frame are you using? how the Gottfried-Jackson or Adair distributions look like respect to z_vert?</div><div class="">At higher energies (>3.6GeV) the Δ-peaks are very noticeable in the data I have seen?</div><div class="">Will be great to see Zulkaida's slides next week. See you.</div><div class="">-Carlos</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">On Jul 12, 2016, at 10:44 AM, Volker Crede wrote:<div class=""><br class="Apple-interchange-newline"><blockquote type="cite" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; " class=""><div apple-content-edited="true" class=""><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-style: normal; font-variant: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-stroke-width: 0px; font-size: inherit;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; " class=""><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-style: normal; font-variant: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-stroke-width: 0px; font-size: inherit;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; " class=""><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class="">Good Morning Everyone,</div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class=""><br class=""></div><div style="-webkit-text-decorations-in-effect: none; " class="">I would like to raise another challenging aspect of the g12 experiment that we are currently dealing with at FSU and that may possibly affect other people. For a long time, we have considered the double-pion channel a by-product of Zulkaida's ω analysis. It is the same measured final state and given the good agreement of the g12-ω cross section with the published g11a-ω cross section, we did not expect any serious problems. Note that Zulkaida's g12-ω cross section is however about 7-8% larger on average. The ratio distribution of corresponding g12 / g11a (cross section) data points shows an almost perfect Gaussian; it is shifted by 7-8%, though.</div><div style="-webkit-text-decorations-in-effect: none; " class=""><br class=""></div><div class="">We have accepted that we may not be able to understand this remaining discrepancy. While working with the Bonn-Gatchina group on the PWA of the double-pion channel, we noticed that we are loosing the (usually) dominant Δ-peaks in the invariant pπ mass distributions. This was puzzling since the Δ's show up as pronounced features in the g11a data. Upon investigating this, Zulkaida discovered that the target position plays a crucial role. The center-of-mass angular distributions of our final-state particles (in the ω and ππ channels) depend strongly on the z-vertex; we see huge holes when we plot c.m. angles versus the z-vertex. Cutting out these holes when analyzing final states with more than two particles is not an option (since it does not remove the effect of integrating in higher dimensions and will require a higher-dimensional acceptance correction). I think this was briefly discussed yesterday (but I had to leave the meeting early).</div><div style="-webkit-text-decorations-in-effect: none; " class=""><br class=""></div><div style="-webkit-text-decorations-in-effect: none; " class="">We looked back at the ω channel and compared the cross sections from the forward half of the target with the cross section of the backward half. The angular distributions are in good agreement (the ratio distribution looks Gaussian) but unfortunately, we observe a 10-15% normalization effect. It appears that this could be the missing piece in understanding the discrepancy in the g11a / g12 ω comparison.</div><div style="-webkit-text-decorations-in-effect: none; " class=""><br class=""></div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class="">Zulkaida will prepare some slides for next week's g12 meeting. I am afraid we will have to substantially increase the systematic uncertainty of the ω cross section (unless we apply an event-based acceptance correction using some kind of PWA). It also remains to be seen if and how the two-pion channel can be partial-wave analyzed. This is an issue that could affect all multi-particle final states, e.g. η, η', ω, …</div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class=""><br class=""></div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class="">Has anybody else noticed the problem?</div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class=""><br class=""></div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class="">Best wishes,</div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class=""><br class=""></div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Volker</div><div style="-webkit-text-decorations-in-effect: none; font-weight: normal; " class=""><br class=""></div></div></span></div></span><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline">
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