First πK atom lifetime and πK scattering length measurements

The results of a search for hydrogen-like atoms consisting of <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msup><mrow><mi>π</mi></mrow><mrow><mo>∓</mo></mrow></msup><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup></math> mesons are presented. Evidence for πK atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic πK pairs from their breakup in the same target ( <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>178</mn><mo>±</mo><mn>49</mn></math> ) as well as in terms of produced πK atoms ( <math altimg="si3.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>653</mn><mo>±</mo><mn>42</mn></math> ). Using these results, the analysis yields a first value for the πK atom lifetime of <math altimg="si4.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>τ</mi><mo>=</mo><mo stretchy="false">(</mo><msubsup><mrow><mn>2.5</mn></mrow><mrow><mo>−</mo><mn>1.8</mn></mrow><mrow><mo>+</mo><mn>3.0</mn></mrow></msubsup><mo stretchy="false">)</mo><mtext> fs</mtext></math> and a first measurement of the S-wave isospin-odd πK scattering length <math altimg="si5.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mo stretchy="false">|</mo><msubsup><mrow><mi>a</mi></mrow><mrow><mn>0</mn></mrow><mrow><mo>−</mo></mrow></msubsup><mo stretchy="false">|</mo><mo>=</mo><mfrac><mn>1</mn><mn>3</mn></mfrac><mo stretchy="false">|</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn><mo stretchy="false">/</mo><mn>2</mn></mrow></msub><mo>−</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>3</mn><mo stretchy="false">/</mo><mn>2</mn></mrow></msub><mo stretchy="false">|</mo><mo>=</mo><mo stretchy="false">(</mo><msubsup><mrow><mn>0.11</mn></mrow><mrow><mo>−</mo><mn>0.04</mn></mrow><mrow><mo>+</mo><mn>0.09</mn></mrow></msubsup><mo stretchy="false">)</mo><msubsup><mrow><mi>M</mi></mrow><mrow><mi>π</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msubsup></math> ( <math altimg="si6.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>a</mi></mrow><mrow><mi>I</mi></mrow></msub></math> for isospin I )