[Clas12_verystrange] Xi(1820)

[Lei Guo]

On Apr 13, 2012, at 11:47 AM, Michael Dugger wrote:

>
> Hi,
>
> There was some concern regarding Johann's number for the detection  
> efficiency of gamma p -> K+ K+ Xi(1820) when K+ K+ K- pi- are  
> detected. The concern was that the reaction requires four charged  
> particles but is much lower than gamma p -> K+ K+ K0 Omega- when K+ K 
> + pi+ pi- are detected. Both reactions have four charged particles  
> detected but the Omega- reaction has a reported efficiency of about  
> 3.85 % and the Xi(1820) reaction has a reported efficiency of about  
> 0.3%.
>
> I think I know what the problem is.
>
> For the K+ K+ K0 Omega- reaction, when we see: K+ K+ pi+ pi- there  
> are three positive charged particles and one negative. For the K+ K+  
> Xi-(1820) reaction, when we detect K+ K+ K- pi- there are two  
> positive charged particles and two negative particles.
>
> The negative particle detection efficiency for CLAS12 is not very  
> good. You can see a plot of efficiencies (in percent) versus  
> momentum for pions, kaons, and protons at
> http://www.jlab.org/Hall-B/secure/clas12/omegaMinus/ASU/efficiencyPlots.gif
>
> When I create gamma p -> K+ K+ Xi-(1820) events (phase space), where  
> Xi-(1820) -> Lambda K- (phase space again), and have Pythia decay  
> the Lambda, I get an efficiency of 0.2% when K+ K+ K- pi- are seen.


What about detecting K+K+K-proton?

Lei

>
> The efficiency I get is actually lower than what Johann sees (0.3%).  
> I think that the difference is probably due to the differences in  
> the assumed distribution. Since Johann uses a model and I just have  
> a simplistic phase space generation, Johann's numbers are probably  
> more realistic.
>
> Take care,
> Michael,