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Advances in High Energy Physics
Volume 2013 (2013), Article ID 989843, 4 pages
Measurement of the Quasi-Two-Body B Decays
Physics Department, Semnan University, P.O. Box 35195-363, Semnan, Iran
Received 13 December 2012; Revised 14 April 2013; Accepted 28 April 2013
Academic Editor: Alexey Petrov
Copyright © 2013 Hossein Mehraban and Behnam Mohammadi. 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.
We study the contributions of the , , and , , , , , and quasi-two-body decays. There are no existing previous measurements of the three-body branching fractions for three final states of the , , and , but several quasi-two-body modes that can decay to this final state have been seen.
The three-body mesondecays are generally dominated by intermediate vector and scalar resonances; this means that there are a resonance state and a pseudoscalar meson which they proceed by quasi-two-body decays [1–4]. In fact, analysis of three-body decays using the Dalitz plot technique leads us to the many quasi-two decays . The study of the , , and via quasi-two-body decays was considered. These include and , observed in the channel and also seen in ; , seen in ; and , seen in , and channel . The decays and have also been observed with , , and . In this paper, we do not perform a Dalitz plot analysis but instead use information on intermediate modes including narrow resonances by studying the two-body invariant mass distributions, because there are no existing previous measurement branching fractions for some of the three-body decays such as , , and , but quasi-two-body modes that can decay to these final states have been seen. Hence, we present the results of a search for the three-body decay including short-lived intermediate two-body modes that can decay to these final states.
In general factorization approach, to obtain the amplitudes of the two-body decays, the Feynman quark diagrams should be plotted, and quasi-two-body decays of the heavy mesons can be also expressed in terms of some quark-graph amplitudes. For example we take as an illustration. Under the factorization approach, its decay amplitude consists of three distinct factorizable terms: (i) the current-current process through the tree transition, (ii) the transition process induced by penguins, and (iii) the annihilation process. Note that weak-annihilation contributions are too small, so we ignore them in our calculations.
2. Quasi-Two-Body Decay Amplitudes
It is known that in the narrow width approximation, in the models we use to obtain the amplitudes of the decays, the 3-body decay rate obeys the factorization relation  with being a vector meson resonance and , , and are pseudoscalar and vector final state mesons. The intermediate vector meson contributions to three-body decays are identified through the vector current, and their effects are described in terms of the Breit-Wigner formalism. The Breit-Wigner resonant term associated to quasi-two-body state which seems to play an important role as indicated by experiments. We have to calculate the branching ratios of the by using the Feynman quark diagrams and using the experimental information for the decays as follows : We calculate the branching ratios of the intermediate states two-body decays. Feynman diagrams related to these decays are shown in Figures 1 and 2.
A detailed discussion of the QCD factorization (QCDF) approach can be found in [6–9]. Factorization is a property of the heavy-quark limit, in which we assume that the quark mass is parametrically large. The QCDF formalism allows us to compute systematically the matrix elements of the effective weak Hamiltonian in the heavy-quark limit for certain two-body final states , , and . In this section, we obtain the amplitude of , , and decays by using the QCDF method. We adopt leading order Wilson coefficients at the scale for QCDF approach. According to the QCDF, the amplitudes of the , , and decays are given by where where is the absolute value of the 3-momentum of the vector meson in the rest frame.
3. Numerical Results
To proceed with the numerical calculations, we need to specify the input parameters. For the CKM matrix elements, we use , , , and . For and form factors, a good parametrization for the dependence can be given in terms of three parameters (see (6)). We fix for transition , ,  and for transition , , , namely, , , and . The meson masses and decay constants needed in our calculations are (in units of Mev) , , , ; ; . The Wilson coefficients have been calculated in different schemes. In this paper we will use consistently the naive dimensional regularization (NDR) scheme. The values of at the scale at the leading order (LO) and next to leading order (NLO) are shown in Table 1 [9, 14]. Numerical values of effective coefficients for transition at are shown in Table 2. According to Table 2, it is not much difference between effective coefficients at the LO and NLO; therefore, we use them at the LO: , , , and [9, 14].
Now we are able to calculate the branching ratios of the , and decays by using (3)–(5) as follows The experimental result for which turns out to be  is in very good agreement with our prediction. As we know the branching ratio of decay has already been estimated: (a) in  they have used QCD sum rules to calculate the branching ratio and predicted , (b) in  they have analyzed the decay and the decays of into and near the threshold for the charm mesons by separating the decay amplitudes into short-distance factors and long-distance factors, and they have predicted for branching ratio , while the experimental result of this decay is . By using (1), (2), and (7) the branching ratios of quasi-two-body decays are summarized in Table 3. Note that the experimental BRs for decay modes (see (2)) only have lower bounds, so the theory predictions involving these modes in Table 3 only have lower bounds.
In this research we have calculated the branching ratios of the , , and , , , , and decays in the framework of the quasi-two-body method. We have also measured the branching ratios of two-body decays including the short-lived intermediate mesons by using the QCDF method. Our calculation results are shown in Table 3. There are no existing previous measurement branching fractions for some of the three-body decays such as , , and , but quasi-two-body modes that can decay to these final states have been seen.
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