Direct Lifetime Measurement Of The Heavy Hypernuclear

The lifetime for a free A hyperon is about263ps. When the A hyperon was embeded in a nucleus, thus forming a hypernucleus, its’lifetime will decrease from that of free A hyperon decay because of the opening of the non-mesonic decay channel. Many experiments have been devoted to measure the lifetime for the A hypernuclei from light to medium heavy mass region. Generally, the result indicate that the lifetime of the hypernuclei in this mass region decreases from that of free A hyperon and reaches a constant value, about210ps. Due to short range nature of the AN interaction, it’s generally believed that the lifetime of the hypernuclei from medium to heavy mass region satuates at a constant value. It has been difficult to verify this hypothesis. The only exsiting data in the heavy mass region came from COSY-13collaboration, which claimed the lifetime of the hypernuclei in the mass region180<A<225is bout145ps. This is quite controversial to the conclusion obtained from light to medium hypernuclei. Aimed to provide more data in the heavy mass region, the experiment E02-017which is the direct lifetime measurement of the heavy hypernuclei was carried out in the experimental Hall C in Jefferson lab. Fe, Cu, Ag and Bi were employed as the target materials. The fission fragment were measured by a special developed detector FFD. This work will give a brief introduction about this experiment and show the data ananlysis procedure, finally the result will be shown.