[Clascomment] OPT-IN: phi-meson photoproduction on Hydrogen in the neutral decay mode

[JM Laget]

Dear Moskov

So, I understand that the slope that you plotted is the slope of the 
differential cross section dsigma/dt.

The solution of the apparent discrepancy is as follows:

At high energies it turns out that, in the phi production channel, the t 
distribution exhibits a slope of 5.6+/-0.3 Gev^{-2} below -t=0.4 GeV^2 
(Desy data), as in the rho and omega production channels, but a slope of 
4.1+/-0.23 GeV^{-2} above (see figure 108 on page 339 in Rev. Mod. Phys. 
50 April 1979). Some authors tried to fit B(t) with a parabolic form. It 
also turns out that this (continuous) change of slope is accounted for 
by the Pomeron exchange model as well as the two gluon exchange model.

Obviously, the linear dependency in exp(Bt) is local, and the extraction 
of B depend of the t range.

At low energy t_min is significant, and your fit is performed in the 
range -1<t<-0.4 approximatively. Consequently, it is not surprising that 
you get values of B closer to 4, rather to 6. Also, other contributions 
(coupling to the K Lambda* channel, etc...) lead to, a different t 
dependency.

This solves the problem, but I suggest to be more clear concerning the 
meaning and the range of the fit: this will ease the reading for 
researchers more familiar with high energy data.

I cc this message to Curtis, since we had a similar discussion in the 
charged decay mode.

Good luck for the publication,

JM

Le 30/05/2013 02:46, Amaryan, Moskov a écrit :
> Dear Jean-Marc,
>
> The slope \beta on the right panel in Fig.13 is defined in the first 
> paragraph of subsection C. Total cross section of section IV.
> Our results are compared with existing data from other facilities. 
> Similarly, the slope called B_{\phi} in the charged channel paper by CMU,
> presented in Fig.25 is very much compatible with our result being in 
> the range of 3-4 GeV^{-2}, peaking around \sqrt{s}=2.1 GeV.
> Nowhere we have seen the slope of the cross section d\sigma/dt around 
> 6GeV^{-2}, could you be more specific, please?
> One can call the y-axis of the left panel as the amplitude, but the 
> slope (right panel)  is  the slope of the t-dependence of differential
> cross section, why should we call it the slope parameter of the 
> diffractive amplitude?
>
> Best regards,
> Moskov.
>
>
> On May 29, 2013, at 12:37 PM, Jean-Marc Laget wrote:
>
>> Dear Lead Authors,
>>
>> In Figure 13, the slope parameter is certainly meant to be the slope 
>> parameter of the diffractive amplitude and not the slope parameter of 
>> the differential cross section, which according to previous 
>> experiments ranges around 6 GeV^2 (instead of 3).
>>
>> In order to prevent confusion for the reader, I strongly suggest to:
>>
>> 1- Plot the slope parameter of the cross section, as it is usually done;
>>
>> 2- Define the meaning of "beta", even if you decide to stick to the 
>> present format of figure 13.
>>
>> In the comparison with previous data, I do not understand why you do 
>> not include the latest CLAS charged decay mode results (CMU analysis) 
>> which are in the final stage of the review by the collaboration. Both 
>> analysis use the same data set and I guess that the author list will 
>> be quite similar. Also both papers will end up as a CLAS 
>> collaboration publication!!
>>
>> All the best,
>>
>> JM
>
> ---------------------------------------------------------
> Moskov Amaryan
> Professor of Physics
> College of Sciences
> Old Dominion University
> 4600 Elkhorn Avenue
> Norfolk, VA 23529
> 757-623-5579 (phone)
> 757-623-3038 (fax)
> mamaryan at odu.edu <mailto:mamaryan at odu.edu>
> http://www.lions.odu.edu/~mamaryan <http://www.lions.odu.edu/%7Emamaryan>
>
>
>
>
>

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