A precision measurement of direct CP violation in the decay of neutral kaons into two pions

The direct CP violation parameter Re(ϵ′/ϵ) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997–1999). The new data yield the result: Re(ϵ′/ϵ)=(13.7±3.1)×10−4. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(ϵ′/ϵ)=(14.7±2.2)×10−4 is obtained from the NA48 experiment.