New theta pentaquark and standard model

[jgraber]

Polemically speaking, if the standard model is so good, and we understand it so well, how come there are so many different explanations for the new theta pentaquark?
What is that guy, anyway?
All the best, Jim Graber

 

[mathman]

Many body (more than 2) problems have always been difficult to handle even thogh the basic physics is well understood. This is probably just another example, made even more complicated by the fact that QCD is a difficult theory.

 

[zack_vt]

Mathman is right. We have a theory that describes quark interactions, but it is fairly complicated. Most often, to do specific calculations for a system, certain assumptions have to be made. This leads to different predictions based on different assumptions. There are some who say that under a certain set of assumptions, one can see the new particle as a 5-quark bound state. Others think it is a 2 or 3 quark bound state. One thing is clear, a lot more data is needed. We haven't measured the spin of this new particle, for one. The physical properties of the particle also need to be more accurately measured. To date, the data we have collected has been from experiments not optimized to measure the new particle. Several experiments have begun and are beginning soon with observation of the new particle in mind. We will have a better idea of what we are dealing with in a year or so. Stay tuned.

-Z

 

[humanino]

Many people are not convinced that pentaquark truly exists. One has to perform many cuts in the data before extracting such a small signal, and this procedure might very well produce a spurious peak. The only really convincing result would be the angular distribution of the pentaquark decay. It should fit a well-known distribution, such as spin 1/2 angular decay e.g.

By the way, how many valence quarks can a hadron be made out ? The experimental data today gives 2, 3 or 5. The physicist might guess here : "OK, this is easy and neat : a hadron can only be composed of a prime number of valence quarks !" Proving this conjecture would doubtlessly be one of the most beautiful result I have ever heard of... (^_^)