[Triumf-seminars] TRIUMF Seminar today at 14:00

[postmaster@admin.triumf.ca]

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Date/Time: Fri 2004-11-12 at 14:00

Location:  Auditorium          

Speaker:   Harry Lipkin (Weizmann Institute, Israel and Argonne Nat. Lab)

Title:     Why pentaquarks are seen in some experiments and not in others

Abstract: People keep asking whether the pentaquark really exists. This is the wrong question. They recall the a2 splitting and the zeta particle which went away. But I am now haunted by a different memory. In the summer of 1964 Jim Smith told me about evidence of their kaon experiment at Brookhaven for a 2pi decay of the long-lived kaon. He asked me whether this could be explained without CP violation. I didn't see how and stupidly believed that there must be something wrong with their data. But their data were right and appeared as the second published evidence for CP violation.

My response to the wrong question about pentaquark existence is what I should have told Jim Smith in 1964. Nature is providing us with new data that theorists do not understand. The right question is how can we understand the meaning of these data and how can we point experimentalists in the right direction to clarify the physics which may be very interesting.

The Theta+ pentaquark is a very narrow (Gamma~1MeV) KN resonance. Why do some experiments see it and others do not? The lowest quark configuration that can describe it is exotic: uudd(sbar). Why have no exotics been seen before? Is this the beginning of a new spectroscpy? Can it teach us about how QCD makes hadrons from quarks and gluons?

Stimulants available 15 minutes before the talk.

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