[Clas_cascades] Minutes Thu Jul 29 posted

[Zhiwen Zhao]

On 8/5/2010 12:52 AM, Hovanes Egiyan wrote:
> Hi Zhiwen,
>
> Thanks for your comments and questions. See my answers below.
>
> Hovanes.
>
>
> Zhiwen Zhao wrote:
>> Some of my comments on the July 29, 2010 version Phi--(1862) analysis note
>> Many of them are certainly my problem of understanding.
>>
>> 1. p10. It might be good to mention that momentum cut of p and pip are
>> determined by comparison with simulation ( at least this is what I remember
>> how it's done?)
> The cut off for momenta of protons of pions were set so that the kinematics does
> not get distorted
> by particles who have very large uncertainty in their momentum determination.
>  From data and simulations
> we see that there are not that many protons with P<300 MeV and pion under 100
> MeV. The cut values
> were not selected from any special study, I just picked them such that there
> would not be "very large"
> energy losses or under uncertainties for their momenta.
>> 2. p13. the second last paragraph, should it be "as a function of phi". Also
>> has the momentum correction be applied? I notice it improves the resolution a
>> little bit in Lambda1520 study
> The p-dependent and phi dependent corrections in the paragraphs above. Since
> Paul wrote this I am not
> absolutely sure, but I think it is correct.
I am referring to the sentence "Finally, the θ dependent drift chamber 
misalignments were studied as a function of θ." I didn't check Paul's note on 
this, but just feel it may be "a function of phi" or "a function of momentum" etc.
>> 3. p15. \tau is the life time in particle rest frame, the actual decay length
>> in lab frame is c\tau\gamma\beta or c\tau*p/m, I see the equation 5 missing
>> the \beta ?
> p/m is not really equal (gamma beta), it is (gamma beta c). I think Eq. 5 is
> correct.
I had a typo there, decay length = c\tau\gamma\beta or \tau*p/m
In the formula you used, Is beta missing?
>> 4. p21. The difference between event start time and tagger hit time is 3.2ns.
>> How is it determined? For E,T-counter matching, I remember it's 1-187 Ecounter
>> to 1-19 Tcounter. Tagger cut is not present for both liberal and conservative
>> selection, right?
> I picked a shorter range for the tagger E-counters to avoid the lowest energy
> E-counters, which is safer.
> In the energy this matches 4.55 to 5.5 GeV. The 3.2 ns was determined by
> studying the effects of this cut.
> http://clasweb.jlab.org/rungroups/eg3/wiki/index.php/Study_of_the_tagger_timing_cuts
>
>> 5. p26. In the right plot of fig 15, why those sideband in simulation? Why
>> many beta > 1 particles?
> I am not sure what the origin of beta>1 particles is. But I think there aren't
> so many of them.
They are weird, I have those in my lambda1520 sim.
>> 6. p29. If we can determine the ST effect in every mass bin, why can we use
>> the the "actual acceptance with ST requirement" instead of using the "nominal
>> acceptance with a 15+-5% correction?
> I could do that, but did not. To do this I have to reprocess all the MC files to
> include the ST hits
> in the cooked BOS files and the ROOT files. This would take a long time and very
> likely would
> result in ~15% chenge in acceptance. We would still need to quote some
> uncertainty ~5%. So,
> it would be more proper to do acceptance corrections the way you are suggesting,
> and it is
> doable, but would take longer time.
>> 7. p37. what are the three independent parallel analysis?
> I know that Joern, Paul and myself for Phi(1860)-- and did not see it.
I mean the reader won't know if you don't mention it or give a reference.
>> 8. p43. I am not very clear about why the "unknown" background is as it is?
> The polynomial mass is just seemed to be enough to describe the mass dependence
> of the background.
> The ctau dependence would be purely Gaussian if there were no detached vertices
> involved in the
> background events (events without Xi-). A possibility of detached vertices in
> the background events
> would translate is some sort of exponential dependence in the distance between
> the vertices which
> would look like and exponential dependence in ctau (of course convoluted with
> Gaussian because of
> the vertex resolution). This seemed to work best.
>
I think the physics is clear, but I was just a little confused by the 
description in the note, you may want to double check it.
>> 9. p51. The final upper limit plots show no sign of Phi--, but with all the
>> fluctuation (particularly those peaking structures), can we conclude that we
>> can detect the Phi-- if it is actually there?
> If Phi-- was produced with large enough cross sections we would be able to see
> it. You should remember that the
> number is the cross sections which is at 90% confidence is larger than the cross
> section at that mass point. The variation
> of that number is representative of the statistical variation of the number of
> events from one bin to another. We quote
> an average value from 1.80 to 1.92 to have a single number, but our sensitivity
> estimate is mass dependent.
Indeed, it's strong mass dependence bothers me. Suppose the Phi-- is there with 
a cross section as large as 2nb appearing on the same plot. I won't be able to 
tell if it's a resonance or just some statistical fluctuation.
>
>> 10. p60. For the last sentence of the statement, the 700pb upper limit safely
>> exclude the models without form factor in Fig 2, but can it really exclude the
>> the model with form factor and coupling g>0, which is almost at or below 1nb.
> I think we can exclude g=+1.27, but probably not g=0, and certainly not g=-1.27.
> This needs to be carefully
> discussed in the actual paper.
>> Thanks
>>
>> Zhiwen
>>
>>
>> On 7/29/2010 2:33 PM, Elton Smith wrote:
>>> Present: Elton, Stepan, Hovanes, Kijun
>>> On the phone: Lewis, Zhiwen<br>
>>> Notes by Elton.
>>>
>>> == Announcements==
>>>
>>> == Normalization ==
>>> # No changes, latest version posted on wiki
>>> # All tex and figures will be added to the cvs repository for save
>>> keeping.
>>>
>>> == Comments on PHi-- Note ==
>>> # Correction for decays outside of target estimated to be 15+/-5%.
>>> # This correction has been included into the upper limits
>>> # All documentation has been updated to reflect latest results
>>> # Upper limit has increased to 700 pb, with the addition of the 15% loss
>>> for decays with 5% uncertainty, as well as updated number number of
>>> 10->15% uncertainty in normalization.
>>> # Figure 20? in normalization note has been included into the response to
>>> the committee. Lewis will send Hovanes the .eps file for best
>>>
>>> == Draft of Phi-- Paper ==
>>> # Hovanes will start a draft of the paper.
>>> # The draft will be provided to committee as soon as appropriate, but
>>> response will not be delayed.
>>> # We discussed how to include comparison of g11/eg3 Delta production.
>>> Elton suggests to mention comparison in text but no figure so that CLAS
>>> may allow publication to proceed without formal review of that data. In
>>> any case the final results depend on it only indirectly as input to the
>>> systematic error on the normalization.
>>>
>>> == Theses ==
>>> # Zhiwen and Haiyun should provide final pdf versions of their theses to
>>> Reinhard for posting on CLAS thesis page.
>>>
>>>
>>> == Next Meeting Aug 5, 9:00 am ==
>>> # Everyone read and comment on Phi-- analysis note and response to
>>> committee. Any suggestions should be incorporated before next week.
>>>
>>>
>>> Elton Smith
>>> Jefferson Lab MS 12H5
>>> 12000 Jefferson Ave
>>> Suite # 16
>>> Newport News, VA 23606
>>> elton at jlab.org
>>> (757) 269-7625
>>> (757) 269-6331 fax
>>> _______________________________________________
>>> Clas_cascades mailing list
>>> Clas_cascades at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/clas_cascades
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