Measurement of the D+ and Ds+ decays into K+K−K+

Abstract We present the first clear observation of the doubly Cabibbo suppressed decay D + → K − K + K + and the first observation of the singly Cabibbo suppressed decay D s + → K − K + K + . These signals have been obtained by analyzing the high statistics sample of photoproduced charm particles of the FOCUS (E831) experiment at Fermilab. We measure the following relative branching ratios: Γ ( D + → K − K + K + )/ Γ ( D + → K − π + π + )=(9.49±2.17±0.22)×10 −4 and Γ(D s + →K − K + K + )/Γ(D s + →K − K + π + )=(8.95±2.12 +2.24 −2.31 )×10 −3 , where the first error is statistical and the second is systematic.