[Halld-physics] Friday Journal Club

[Volker Crede]

Hi All,

We published an even higher-statistics paper on "p pi0 eta" at ELSA last year (2014):  
	http://dx.doi.org/10.1140/epja/i2014-14074-1

The a0(980) is a dominant isobar and actually nicely observed (even visible in the "pi0 eta" mass distributions); but surprisingly, it is not produced dominantly in the forward direction as expected from t-channel exchange. A significant fraction is produced in the decay of high-mass N* / Delta resonances.

An ELSA paper on "p pi0 pi0" including polarization observables (linear beam; unpolarized target) was published this summer:
	http://dx.doi.org/10.1140/epja/i2015-15095-x

The f0(980) contributes to "pi0 pi0" but not as strong as the a0(980) to "pi0 eta" if I recall correctly. The energy for the ELSA measurements was less than 2.5 GeV.

CLAS has a few data on "p pi0 eta" but with low statistics and poor angular coverage.

- Volker


On Sep 1, 2015, at 11:06 PM, Justin Stevens <jrsteven at jlab.org> wrote:

> Hi All,
> 
> On Aug 31, 2015, at 8:18 AM, Elton Smith wrote:
> 
>> 1) Are there examples of C=+ neutral states produced in photoproduction (i.e. is there evidence for rho-exchange)
> 
> Following up on this, here are a few examples if people are interested:
> 
> 1) f0(980) -> pi+ pi- (CLAS):  http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.102.102001
> 	-Observed in a moment analysis of the unpolarized pi+ pi- angular distributions
> 	-There is also a signal for f2(1270) (JPC=2++) in the same analysis 
> 
> 2) a0(980) -> pi0 eta (CB-ELSA): http://link.springer.com/article/10.1140%2Fepja%2Fi2008-10657-7
> 	-This is lower energy so not ideal for meson spectroscopy, but they did see the a0(980) in the PWA
> 
> 3) pi0 photoproduction (SLAC): http://journals.aps.org/prd/abstract/10.1103/PhysRevD.4.1937
> 	-Similar beam energy to GlueX, measured dsigma/dt and Sigma beam asymmetry
> 
> The a0 and f0 papers are referenced in a recent theory paper by Donnachie and Kalashnikova (http://arxiv.org/abs/1507.07408) which has a Regge model for the vector and axial-vector (ie. rho/omega and b1/h1) exchanges that could produce such states in photoproduction and compares their model to the results from CLAS and CB-ELSA.  The pi0 channel is used to develop the model for f0/a0 production in the paper by Donnachie.  The pi0 channel was also looked at recently by our JPAC colleagues (Mathieu et. al. http://arxiv.org/abs/1505.02321) and they provided code for amplitudes that are incorporated in one of our event generators.
> 
> I think there may also be some analyses of CLAS data in the "pi0 eta p" and "Ks Ks p" final states which are neutral and have C=+.  I've seen these in some talks, but I haven't seen any papers to reference.
> 
> -Justin 
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