[Frost] Updated my analysis page

[Michael Dugger]

Eugene,

Your talking about the t-channel exchange where the photon directly 
couples to the omega. The question then becomes how spin information is 
passed from the photon-omega-propagator vertex to the 
nucleon-nucleon-propagator vertex. For the case where the propagator is a 
pseudoscalar, I can not see how spin information can be passed from one 
vertex to the other, however, for a pomeron it looks like there can be 
spin information passed from one vertex to the other. Without spin 
information exchange between the vertices, there should be no helicity 
asymmetry (helicity asymmetry is a double polarization observable).

This means that for a pion propagator, it looks like the helicity 
asymmetry should be zero, but for a pomeron it looks like the helicity 
asymmetry can be different from zero.

The big problem is then that at low E_gamma, the pion propagator is 
supposed to dominate. It is this dominance at low E_gamma that Williams 
argues for neglecting the pomeron exchange in his PWA.

So, for now, Patrick assumes that the t-channel will give a helicity 
asymmetry = 0 due to the pion exchange dominance and assumes that the 
nonzero helicity asymmetry in the forward direction must be due to 
s-channel.

-Michael


On Fri, 10 Jun 2011, Eugene Pasyuk wrote:

> My be it it is not so surprising after all. May be it has to do with the 
> helicity conservation and vector dominance. For the circularly polarized 
> photon its spin is parallel or antiprallel to its momentum. Omega has spin 1 
> and VDM tells us that omega and photon is the same thing and what we see is 
> helicity transfer from the photon to omega.
>
> -Eugene
>
>
>
> On 6/10/11 16:11 , Patrick Collins wrote:
>> Hello all,
>> To demonstrate what I was talking about yesterday about t-channel in omega 
>> I've added a couple of plots of beam asymmetry for omega from g8b with 
>> similar W values at the bottom of my page. You can see that the forward 
>> angles are close to zero asymmetry. I took a look at Williams PWA and he 
>> does say that there are two strong resonances in omega production near 
>> threshold the F_15 (1680) and D_13 (1700), so these could be producing the 
>> large helicity asymmtries. I just don't understand why they would be so 
>> strong here and so weak in beam asymmetry, especially in the forward 
>> direction which normally where t-channel is very strong.
>> 
>> http://clasweb.jlab.org/rungroups/g9/wiki/index.php/Patrick%27s_analysis_page#Examples_of_.CE.A3_from_g8b_for_similar_W
>> 
>> Cheers,
>> Patrick
>> 
>> 
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>