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Re: Overview Talk
Hall D PID Mail List:
I agree with Matt's concerns. I think a good approach is to
undersell the prospects with suitable caveats. But they don't
have to be put in the slides explicitly - just talk about them.
I do think it is valuable to show the E852 a2/a4 signals because
it does show that a partial wave analysis can pull out signals at
a 3% (of high cross section signals). There is an underlying
skepticism about the effective of the technique - somewhat
based on anecdotes. And of course there have been faulty
claims. Comparing the results of our expected resolution with
E852 is also useful - we should be able to do just as well for
or better w.r.t. resolutions. After that I would suggest talking about
prospects for photoproduction - on the one hand LQCD
and models suggest favorable production - on the other hand
photoproduction backgrounds are unknown (that's why we're
doing the experiment) and keep in mind the points Matt
brought up. Undersell - don't make specific claims - but
we are aware of possible pitfalls and are gearing up to study
all this. You won't get pushback with this approach.
Alex
At 5:45 PM -0400 3/25/08, Matthew Shepherd wrote:
>Hall D PID Mail List:
>
>
>Hi Curtis,
>
>I'm reading through your talk. There are still several
>typographical errors and such that I'll send in a separate email.
>However, I have one or two "big" concerns that I would like to pick
>out for discussion.
>
>On slides 14 and 15 --
>
>slide 14:
>
>the a4 is 3% of the a2 as observed in E852
>the a2 has a 0.5 mub cross section in photoproduction
>therefore GlueX should detect 3% * 0.5 mub or 15 nb things with E852 stats
>
>I think this is faulty logic.
>
>First of all there is no guarantee that the background in photo
>production and pion production are the same.
>
>More importantly, if a2 is suppressed in photoproduction this
>artificially pushes your claimed sensitivity down. I think to make
>any claim you would have say that a4 production in 3 pi in E852 is X
>% of the total hadronic cross section. Then one might roughly
>estimate X * 120 mu-b for sensitivity in GlueX.
>
>The E852 example also is in a relatively background free channel. A
>high multiplicity final state that is fighting off background from
>other broken events will certainly be more of a challenge. Recall
>in the all of the recent calorimetry work we were comfortable making
>a loose statement about being able to isolate from background a
>state produced at the level of a hundred nb and decaying into the
>"key" channels. This included an analysis of leakage from other
>inclusively produced but mis-reconstructed events.
>
>slide 15:
>
>"GlueX will find exotic hybrids if they exist at a few % of normal mesons."
>
>This statement is not justified anywhere that I can see. It may be
>true under certain qualifying assumptions (hybrids are narrow, they
>have some considerable 3 pi partial width, etc.). Since this is the
>key point for GlueX physics I would avoid making such a statement
>that cannot be defended. In my opinion I would categorize this as a
>sound bite that is very effective in selling the experiment, but we
>now we are at the final design and need to be serious with ourselves
>and also with reviewers. This is the opening talk -- if one of them
>would latch onto that statement and really press you to defend it,
>I'm afraid it could start things off on the wrong foot. I also
>think the panel will be on the lookout for what appears to be
>essential concrete statements like this and attempting to verify
>their validity. We don't want to give them any that can't be backed
>up.
>
>Don't get me wrong; I'm not throwing a wet blanket on GlueX physics.
>I think you should emphasize the potential for discovery -- that's
>what gives me goosebumps -- but I would back off from making strong
>quantitative statements about sensitivity that we cannot clearly
>defend. (If you can rehash your argument for 15 nb using E852
>comparisons that would be great, but as is, I don't quite see the
>logic.)
>
>I'll make other notes on the slides and send them to you in the next hour.
>
>-Matt
>
>
>
>On Mar 24, 2008, at 9:42 PM, Curtis A. Meyer wrote:
>
>>I have reposted the slides to the overview talk to the GlueX
>>portal. It is now consistent with Elton's talk on PID, but I
>>will need to make another pass after Eugene posts his
>>talk.
>>
>>I tried to get all the sensible changes that were recomended
>>today. The reordering of things required a bit more rearranging than
>>I had expected, but I think it is roughly right now. I will be going
>>through it again carefully in the morning.
>>
>> Cheers - Curtis
>>--
>>Professor Curtis A. Meyer Department of Physics
>>Phone: (412) 268-2745 Carnegie Mellon University
>>Fax: (412) 681-0648 Pittsburgh PA 15213-3890
>>cmeyer@ernest.phys.cmu.edu http://www.curtismeyer.com/
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Alex R. Dzierba
Chancellor's Professor of Physics (Emeritus)
Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
JLab Visiting Fellow
Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 / 757-269-7577
Home Phone: 812-825-4063 Cell: 812-327-1881 Fax: 866-541-1263
http://www.dzre.com/alex
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