Abstract
The observation of hydrogenlike πK atoms, consisting of π^{-}K^{+} or π^{+}K^{-} mesons, is presented. The atoms are produced by 24 GeV/c protons from the CERN PS accelerator, interacting with platinum or nickel foil targets. The breakup (ionization) of πK atoms in the same targets yields characteristic πK pairs, called "atomic pairs," with small relative momenta Q in the pair center-of-mass system. The upgraded DIRAC experiment observed 349±62 such atomic πK pairs, corresponding to a signal of 5.6 standard deviations. This is the first statistically significant observation of the strange dimesonic πK atom.
Highlights
The observation of hydrogenlike πK atoms, consisting of π−Kþ or πþK− mesons, is presented
The longitudinal (QL) and transverse ðQT 1⁄4 Q2X þ Q2YÞ components of the vector Q~ are defined with respect to the direction of the total laboratory pair momentum.] In the experiment from 2008 to 2010, DIRAC detected an excess of 178 Æ 49 πK pairs in a Ni target, an effect of only 3.6 σ [3]
The observation and the lifetime measurement of the πK atom involving strangeness provides a direct determination of a difference of basic S-wave πK scattering lengths
Summary
The correction of the setup geometry, the simulation of the detector response, the background suppression, and the admixture evaluation were significantly improved for the whole running period These improvements allow a statistically reliable πK atom observation for the first time. The observation and the lifetime measurement of the πK atom involving strangeness provides a direct determination of a difference of basic S-wave πK scattering lengths [11]. This atom is an electromagnetically bound πK state with a Bohr radius of aB 1⁄4 249 fm and a binding energy (ground state) of EB 1⁄4 2.9 keV. The π∓KÆ Coulomb pair production is described in the pointlike production approximation by d2σC dp~ Kdp~π
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