Hindawi Publishing Corporation Advances in High Energy Physics Volume 2012, Article ID 203692, 19 pages doi:10.1155/2012/203692 Research Article Final State Interaction Effects on the B  → J/ψρ  Decay Behnam Mohammadi and Hossein Mehraban Physics Department, Semnan University, P.O. Box 35195-363, Semnan, Iran Correspondence should be addressed to Behnam Mohammadi, b mohammadi@sun.semnan.ac.ir Received 1 January 2012; Accepted 14 April 2012 Academic Editor: Ira Rothstein Copyright q 2012 B. Mohammadi and H. Mehraban. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The exclusive decay of B  → J/ψρ  is studied in the framework of the QCD factorization QCDF method and final state interaction FSI. A direct B  → J/ψρ  decay is only occurred via a tree and a penguin based on the quark diagram analysis. The result that is found by using the QCDF method is less than the experimental result, so, the role of FSI is considered. The intermediate states D  D 0 , D ∗ D 0∗ , D ∗ D 0 , and D  D 0∗ via the exchange of D - and D -∗ are contributed to the B  → J/ψρ  decay. The above intermediate states is calculated by using the QCDF method. In the FSI effects the results of our calculations depend on ”η” as the phenomenological parameter. The range of this parameter are selected from 1 to 2. For the exchanged particles D - and D -∗ , it is found that if η  1.58 ∼ 1.83 is selected the numbers of the branching ratio are placed in the experimental range. The experimental branching ratio of B  → J/ψρ  decay is 5 ± 0.8 × 10 -5 , and our prediction number is 1.42 ± 0.36 × 10 -5 in the absence of FSI effects, and it becomes 4.2 ∼ 5.8 × 10 -5 when FSI contributions are taken into account. 1. Introduction The importance of FSI in weak nonleptonic B meson decays is investigated by using a relativistic chiral unitary approach based on coupled channels 1–3. The chiral Lagrangian approach is proved to be reliable for evaluating hadronic processes, but there are too many free parameters which are determined by fitting data, so that its applications are much constrained. Therefore, we have tried to look for some simplified models which can give rise to reasonable estimation of FSI 4, 5. The FSI can be considered as a rescattering process of some intermediate two-body states with one particle exchange in the t-channel and computed via the absorptive part of the hadronic loop level HLL diagrams. The calculation with the single-meson-exchange scenario is obviously much simpler and straightforward. Moreover, some theoretical uncertainties are included in an off-shell form factor which