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Photos of the SELEX Experiment

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SELEX The distribution of the D0 K+ combined mass for all candidates in the data sample including Anti-particle combinations (D0bar K-). There are two clear peaks. The lower, at a mass of 2570 MeV/c2, is the known DsJ(2573) meson, discovered in 1994. This peak's width is more than the detector resolution showing the the "natural width (Gamma)" of this state due to its short lifetime. The value measured for the natural width of 14 MeV/c2 is consistent with previous measurements. The detector resolution is better by a factor of 2 in this D0 K+ decay mode than in the Ds+ eta0 mode making Selex more sensitive to the lifetimes of these state in this decay mode.

The second peak is at a mass of 2632 MeV/c2 - the same mass (within uncertainties) seen in the Ds+ eta0 decay mode. The width of this peak is consistent with the resolution of the detector. This state very likely lives several times longer than the lower mass state. Both peaks have high statistical significance (more than 5 standard deviations).

High Resolution EPS File

SELEX The distribution of the Ds+ eta0 combined mass for all candidates in the data sample including Anti-particle combinations (Ds- eta0). There is a clear peak at a mass of 2635 MeV/2 with a very high statistical significance (more than 7 standard deviations). The width of this peak is completely consistent with what is expected from the resolution of the detector.

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SELEX Peter Cooper (left) and Jim Russ frame the list of SELEX institutions at the experiment hall.

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SELEX SELEX spokesperson Jim Russ of Carnegie Mellon University holds a metaphoric bucket for decays of the newly-observed meson and its unexpected decay pattern. Says Russ: "It's like watching a water bucket with a large hole and small hole in the bottom. For some reason, the water is pouring out the small hole six times faster than it's coming out of the large one. Something unusual must be going on inside the bucket."

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SELEX Anatoly Evdokimov of the Institute of Theoretical and Experimental Physics in Moscow, Russia led the analysis leading to the observation of the new meson, and will present the results in a seminar at Fermilab on Friday, June 18.

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SELEX Experimenter Mark Mattson checked SELEX apparatus in 1999.

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last modified 6/17/2004   email Fermilab