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Summary: Pentaquark discussion session

Summary: Pentaquark discussion session. K. Cho, K. Daum, V. Kubarovsky, H. Park, A. Sbrizzi, N. Solomey* * Outside observer not involved with Pentaquark search. Comparison of observation and non-observations:. There are pentaquark signal observations 13 independent experiments

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Summary: Pentaquark discussion session

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  1. Summary: Pentaquark discussion session K. Cho, K. Daum, V. Kubarovsky, H. Park, A. Sbrizzi, N. Solomey* * Outside observer not involved with Pentaquark search

  2. Comparison of observation and non-observations: • There are pentaquark signal observations • 13 independent experiments • photon-production, diffraction production. • There are pentaquark non-observations • Just as many experiments show spectra with no observation of pentaquark peaks, mostly e+e- and pp colliders • How do we compare these two?

  3. Non-observations: • Experiments should refrain from making plots of non-observations without taking sufficient care. A spectrum with no peak can be misleading: • acceptance of experiment may be very small. • Without a model of production/decay it is hard to know if an experiment should be seeing it. • A cross section limit is needed to compare to observation; without that it is meaningless.

  4. Non-observations • If the pentaquark exists then why not the • di-baryon (qqq qqq) • di-meson (qq qq) • This could be explained by many reasons, but there are color-neutral combinations of these states that also should be allowed.

  5. Observations: • Observations are all low statistics. • In KTeV there was a di-baryon signal of 60 events that vanished with more data. • The sample yielding 40 events at JLab needs to be expanded upon to see if the signal remains. A ten-fold increase would add confidence. • Need to start to measure cross sections to compare with non-observations limits. • All other observations have comparable statistics except for Zeus which has 200, but with a large background.

  6. Observation: • Possible errors in analysis should be avoided. • As pointed out by HyperCP the use of a track twice (a ghost track due to background accidentals or electronics ringing) usually results in a peak at 1530 MeV/c2. These ghost tracks even exist in bubble chamber data. • Blind analyses are of the utmost necessity (if we knew the physics) for any future claims of a signal observation. Experiments should use MC-generated events with well-understood models before looking at the real data.

  7. Conclusion: • It is our opinion that it is too early to determine definitively if the pentaquark truly exists. • More results needed: • Higher Statistics • More experiments • Explain mass discrepancies • Compare cross sections • Measure lifetimes

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