2021 Impact factor 4.991
Particles and Fields
Eur. Phys. J. C 8, 619-629
DOI 10.1007/s100529901111

A theoretical reappraisal of branching ratios and CP asymmetries in the decays $B \to (X_d,X_s) \ell^+ \ell^-$and determination of the CKM parameters

A. Ali1 - G. Hiller2

1 Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
2 INFN, Laboratori Nazionali di Frascati, I-00044 Frascati, Italy

Received: 30 December 1998 / Published online: 27 April 1999

We present a theoretical reappraisal of the branching ratios and CP asymmetries for the decays $ B \to X_q \ell^+ \ell^-$, with q=d,s, taking into account current theoretical uncertainties in the description of the inclusive decay amplitudes from the long-distance contributions, an improved treatment of the renormalization scale dependence, and other parametric dependencies. Concentrating on the partial branching ratios $\Delta {\cal B}(B \to X_q
\ell^+ \ell^-)$, integrated over the invariant dilepton mass region $1~\mbox{GeV}^2 \leq s \leq 6~\mbox{GeV}^2$, we calculate theoretical precision on the charge-conjugate averaged partial branching ratios $\langle \Delta{\cal B}_q \rangle=
(\Delta {\cal B}(B \to X_q \ell^+ \ell^-) + \Delta {\cal B}(\bar{B} \to
\bar{X}_q \ell^+ \ell^-))/2$,CP asymmetries in partial decay rates $(a_{CP})_q=(\Delta {\cal B}(B \to X_q
\ell^+ \ell^-) -
\Delta {\cal B}(\bar{B} \to \bar{X}_q \ell^+ \ell^-))/(2 \langle \Delta{\cal
B}_q \rangle)$, and the ratio of the branching ratios $\Delta {\cal R} = \langle \Delta{\cal B}_d \rangle/\langle
\Delta{\cal B}_s \rangle$. For the central values of the CKM parameters, we find $\langle \Delta {\cal B}_s \rangle =(2.22^{+0.29}_{-0.30}) \times 10^{-6}$,$\langle \Delta {\cal B}_d \rangle =(9.61^{+1.32}_{-1.47}) \times 10^{-8}$,$(a_{CP})_s =-(0.19^{+0.17}_{-0.19})\%$, $(a_{CP})_d
=(4.40^{+3.87}_{-4.46})\%$, and $\Delta {\cal R} =(4.32 \pm 0.03)\%$.The dependence of $\langle \Delta{\cal B}_d \rangle$ and $\Delta {\cal R}$ on the CKM parameters is worked out and the resulting constraints on the unitarity triangle from an eventual measurement of $\Delta {\cal R}$ are illustrated.

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