The NA48/1 Experiment - Measurement of Rare KS and Hyperon Decays



In 2002, the successor experiment NA48/1 studied rare KS and neutral hyperon decays. For that, the beam line was changed: the KL beam was blocked whereas the KS beam was ~200 times more intensive than in NA48. About 35 billion KS decays were recorded during a three months data taking period, representing the largest sample of KS decays worldwide.

The main goal of the experiment was the measurement of the very rare decays KS -> π0 e+ e- und KS -> π0 μ+ μ-. The physics interest of these decays is that they measure the indirect CP violating contribution of the corresponding KL decays, thereby allowing the direct CP violating component of the KL decay to be extracted. Seven KS -> π0 e+ e- and six KS -> π0 μ+ μ- decays were found with negligible background, and branching ratios of a few 10-9 were measured.

Besides other rare KS decays, decays of neutral hyperons, in particular the Ξ0, can be studied with the NA48/1 data. The quark content of the Ξ0 is (uss), thus being the strangeness carrying partner of the neutron. The integrated flux of Ξ0 hyperons in NA48/1 within the accepted decay region was greater than 2 billion. Like for the KS data, this is the largest sample of Ξ0 decays worldwide, allowing for extremely precise measurements of the properties and the decay channels of the Ξ0 hyperon.

Results obtained with Mainz contribution

  • Measurement of the rare decay KS -> π+ π- π0
  • Measurement of the rate and the form factor of the Ξ0 beta decay Ξ0 -> Σ+ e- ν
  • First precision measurement of the decay Ξ0 -> Σ+ μ- ν
  • Measurement of the rates and the decay asymmetries of the radiative decaysΞ0 -> Λ γ and Ξ0 -> Σ0 γ
  • Measurement of the Ξ0 lifetime
  • Measurement of the ratio of anti-Ξ0 over Ξ0 production in proton nucleon interactions