Study of the B- --> J/psi K- pi+ pi- Decay and Measurement of the B- --> X(3872) K- Branching Fraction

We study the decay B- --> J/psi K- pi+ pi- using 117 million BBbar events collected at the Y(4S) resonance with the BaBar detector at the PEP-II e+ e- asymmetric-energy storage ring. We measure the branching fractions Br(B- --> J/psi K- pi+ pi-) = (116 +- 7 (stat.) +- 9(syst.))* 10-5 and Br(B- --> X(3872)K-)* Br (X(3872) --> J/psi pi+ pi-) =(1.28+- 0.41)* 10-5 and find the mass of the X(3872) to be 3873.4 +- 1.4 MeV/c2. We search for the h_c narrow state in the decay B- --> h_c K-, h_c --> J/psi pi+ pi- and for the decay B- --> J/psi D0 pi-, with D0 --> K- pi+. We set the 90% C.L. limits Br(B- --> h_c K-)* Br (h_c --> J/psi pi+ pi-) <3.4 * 10-6 and Br(B- --> J/psi D0 pi-) <5.2 * 10-5.