The OLD version of this page is linked here.

The Tampa Conference update of this page is linked here.

At the Jefferson Laboratory (Newport News, VA, USA), new results from another high-statistics search for the pentaquark were presented at the Users Group Meeting on June 20, 2005. The new results are for a deuterium target, rather than the hydrogen target results presented at the Tampa APS meeting (see link above). Why are the deuterium result important? For several reasons: (1) most theoretical models predict a much larger probability to produce the pentaquark from a neutron than from a proton (see link below), (2) the CLAS Collaboration published positive results at low-statistics already for the deuterium target, and (3) the only way to check that the previous signal was real or just a statistical fluctuation is to get high-statistics. The main results are: (1) the previous pentaquark signal could not be reproduced at high-statistics, suggesting that it was a statistical fluctuation, (2) if the pentaquark does exist, it either has a very broad energy-spread (also called the energy width) or it has a lower-than-expected probability to be produced under the conditions measured by the CLAS detector. Note that these findings contradict the earlier (low-statistics) result from CLAS, and hence it deals another blow to possible existence of the pentaquark. However, the existence of the pentaquark is still an open question. There are many other experiments with positive evidence for the "Theta" pentaquark. In fact, new positive evidence was just presented by the LEPS Collaboration (from Japan) at the recent Bejing meeting (see the link below). In addition, the STAR Collaboration has also presented new, positive results for the Theta+ (also at the Bejing meeting). The mystery deepens, and can only be solved by looking at data from new experiments which are planned or in progress.

The following links may be useful for more information: News Release from Jefferson Lab . Explanation for the general public. Explanation for the general scientist. Explanation for physicists .

Other useful links: PhysOrg.com article on the new Jefferson Lab results. D. Carman's presentation at the annual Jefferson Lab Users Group Meeting (June, 2005). PDF T. Nakano's presentation for the LEPS Collaboration at the International Conference on QCD and Hadronic Physics (Beijing, China, June 20, 2005). Plenary talks website H. Huang's presentation for the STAR Collaboration at the International Conference on QCD and Hadronic Physics (Beijing, China, June 20, 2005). Parallel talks website

Last modified: April 15, 2005 Kenneth Hicks