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Re: Overview Talk
Hall D PID Mail List:
Geoffrey
Thank you for your comments and your points are well worth considering.
Nevertheless, the a2/a4 measurement is a real measurement and
seeing a smaller signal that is 3% of the larger signal is a not
insignificant point to make to an audience of reviewers who are
likely to be somewhat skeptical of the effectiveness of amplitude
analyses. Nobody has shown that PWA must fail but that doesn't
mean it will actually produce results. Statistics are surely important,
something that was lacking in the past, but so is a more robust
control of systematics, now made possible by better acceptance,
resolution and particle ID. And has also been pointed out time and
again, by exploring a regime that has not been accessible earlier
for technical reasons.
It was good to hear from you and thanks
Alex
At 7:55 PM -0400 3/25/08, Geoffrey Fox wrote:
>As a skeptical voice from the past, I would note that a2/a4 are not
>good examples as they have "unusually" high spin and strong
>couplings (to exchanged rho?); I believe you are looking for lower
>spin (at given mass) signals which are much much harder. Your
>strongest answer to skeptics is statistics plus reasonable
>expectation that interesting states will be produced albeit in a
>crowded world where a difficult PWA needed. Certainly nobody has
>shown PWA must fail.
>
>Alex Dzierba wrote:
>>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/
>>
>>
>
>--
>:
>: Geoffrey Fox gcf@indiana.edu FAX 8128567972 http://www.infomall.org
>: Phones Cell 812-219-4643 Home 8123239196 Lab 8128567977
>: SkypeIn 812-669-0772 with voicemail, International cell 8123910207
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~