Abstract
We report evidence for πK atoms production, using 24 GeV/ c proton beam from CERN PS interacting with a thin Ni target. We have identified (178 ± 49) πK pairs, which were produced in a bound state — πK atom, which was subsequently broken-up (ionized) in the Ni target. Our analysis yields a first measurement of the πK atom lifetime (2.5 −1.8 +3.0 ) fs [1]. This lifetime is connected in a model-independent way to the S-wave isospin-odd πK scattering length | a 0 − | = 1/3| a 1/2 − a 3/2 | = (0.11 −0.04 +0.09 ) M π −1 ( a I for isospin I ).
Highlights
Low-energy QCD and Chiral Perturbation Theory (ChPT) [2] predict ππ and πK scattering lengths with high precision [3, 4]
Lifetime of πK atoms is limited by strong interaction through the decay into a pair of neutral pion and kaon, π0 K 0 or π0 K 0, other decay channels contribution is of the order 10−3
The DIRAC apparatus with its secondary channel is inclined by 5.7◦ with respect to the primary proton beam
Summary
Low-energy QCD and Chiral Perturbation Theory (ChPT) [2] predict ππ and πK scattering lengths with high precision [3, 4]. For processes involving u- and d-quarks theoretical predictions have been experimentally checked by π+ π− atom lifetime measurement [5] and by analysis of Kdecays [6, 7]. Detection and lifetime measurement of πK atom cast a look into processes which involve s-quark as well. Its ground state binding energy is 2.9 keV, Bohr radius aB = 249 fm and Bohr momentum is. The AπK decay width ΓπK in the ground state (1S) is directly related to the S-wave isospin-odd πK scattering length a−0 = 13 (a1/2 − a3/2 )[8, 9]:
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