[Eg6_analysis] .....

[Eric Voutier]

  Dear Stepan,

  Thanks for this demonstration that looks pretty consistent to me. I
  am still a bit puzzled. In fact, in all the reactions quoted and 
especially
  for incoherent DVCS,  I would expect a t-dependent position of Mx2.
  Beyond this, I dont understand the difference between  3) and 4),
  kinematically speaking 4)-events should be part of 3)-events, it is just
  that 4)-events have some additionnal correlation between the proton and
  the photon.

  I really dont "feel" the origin of the shift, unless there is some hidden
  t  difference between all the events.  Would if be possible to have a 2D
  spectra of the same events you show there  with Mx2 in y an t in  x,
  with t defined from the real photon.
  If I understand something to this puzzle, the peak at about the helium
  mass squared should be associated to small t. For the one at 20 Gev2,
  and just considering kinematics and also the experimental spectra we
  got, I still dont get  how a 28 MeV binding energy  leads to a 5 GeV2
  difference in the missing mass, I should do maths...

   Regards & thanks, Eric

Stepan Stepanyan wrote:
> Hi Eric,
>
> Sorry for responding to your question about the form of the Mx2 that 
> Yohann
> has this late. I finally found some time and made some simulations, 
> just the
> kinematics, of real photon electroproduction reaction with different 
> hadronic
> final states. So the reaction I simulated is, e 4^He -> e' \gamma X, 
> where X was -
> 1) ppnn (breakup to four nucleons)
> 2) pnd (breakup to two nucleons and deuterium)
> 3) p3H (breakup to a proton and triton)
> 4) p3H-spectator (scattering on a proton and the triton is a spectator)
>
> Attached plot shows superposition of missing mass squared of the final 
> state
> electron and the photon from all these reactions, assuming that the 
> target is 4He,
> basically mass square of system X. I required that the electron and 
> the photon
> have momentum and \theta in the CLAS acceptance region, and also required
> that none of hadrons had kinematics in the CLAS detection region (very 
> simple
> but should be Ok for this studies).
> In the graph, the forward peak at Mx2~15 GeV2 is from (4), little bump 
> at ~20 GeV2
> is from (3). (1) peaks at very large Mx2 and  (2) is distributed in 
> the middle. As you
> can see there is a "peak" from two body breakup and looks to me that 
> is what Yohann
> sees. I do not have relative weights of these reactions, but I am sure 
> one can work
> this out and match experimentally observed spectrum with simulations 
> (one should
> include also pi0 production).
>  
> Regards, Stepan
>
> On 3/22/11 10:31 AM, Eric Voutier wrote:
>> It seems I lost phone connection while I was talking.... It does not 
>> work at all by now
>>
>> My main question was about the position of tyhe small bump we are 
>> seeing in Mx2,
>> any idea about the origin of this ??
>>
>> Thanks, eric
>>
>>
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