Craig Bookwalter (Florida State University)
In addition to ordinary qqbar pairs, the meson spectrum of quantum chromodynamics (QCD) permits many other bound states, such as gluonic hybrids, glueballs, and tetraquarks. Experimental discovery and study of these exotic states provides insight on the nonperturbative regime of QCD.Previous experiments have performed partial-wave analyses on pion-production data and claim observation of a J^{PC} = 1^{-+} state decaying via rho pi. This state is now known as the pi_1(1600) and its mass seems to be consistent with lattice calculations of the lowest-lying gluonic hybrid. However, recent theoretical work has suggested that photon beams may produce gluonic hybrids at enhanced levels compared to pion production. To that end, the E004-05 experiment at Jefferson Lab's CEBAF Large Acceptance Spectrometer (CLAS) has recently acquired the world's largest photoproduction dataset. A partial-wave analysis of a sample of gamma p-> pi+pi+pi- n events has been performed, and preliminary results indicate that not only is the \pi_1(1600) not produced at enhanced levels--it is not produced at all.
Details of this analysis and the ramifications of its results will be presented.
Oct 31 at 4pm in Geo/Phys Room 407