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The PrimEx experiment

Primex Hycal, the crystal calorimeter

The image shows the crystal calorimeter built for PrimEx.

The Primakoff experiment (PrimEx) has completed the current most precise measurement of the neutral pion lifetime using the small angle coherent photoproduction of the pi-zero in the Coulomb field of a nucleus, i.e. the Primakoff effect. The pi0 to gamma-gamma decay proceeds primarily via the chiral anomaly and represents one of the most definitive tests of low-energy QCD.

The Primex result for the neutral pion
          lifetime The figure shows the result compared with those from previous experiments. The results indicated with a red dot use the same technique. The actual lifetime is about 0.000 000 000 000 000 53 seconds. The Primex collaboration expects to obtain more data, and are working on a new experiment with the 12 GeV CEBAF upgrade to measure the properties of the eta and eta-prime mesons.

More information can be found at the PrimEx experiment website.

Feynman diagram for pion production

The Feynman diagram for the Primakoff effect


The NCA&T group in 2003. Prof. Ashot Gasparian (left) is spokesperson for PrimEx.

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