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A search for rare $B \to D \mu^+\mu^-$ decays

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Abstract

A search for rare $B \rightarrow D \mu^+ \mu^-$ decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb$^{-1}$. No significant signals are observed in the non-resonant $\mu^+\mu^-$ modes, and upper limits of $\mathcal{B}(B^0 \rightarrow \overline{D}^0 \mu^+ \mu^-) < 5.1 \times 10^{-8}$, $\mathcal{B}(B^+ \rightarrow D_s^+ \mu^+ \mu^-) < 3.2 \times 10^{-8}$, $\mathcal{B}(B_s^0 \rightarrow \overline{D}^0 \mu^+ \mu^-) < 1.6 \times 10^{-7}$ and $f_c/f_u \cdot \mathcal{B}(B_c^+ \rightarrow D_s^+ \mu^+ \mu^-) < 9.6 \times 10^{-8}$ are set at the 95% confidence level, where $f_c$ and $f_u$ are the fragmentation fractions of a $B$ meson with a $c$ and $u$ quark respectively in proton-proton collisions. Each result is either the first such measurement or an improvement by three orders of magnitude on an existing limit. Separate upper limits are calculated when the muon pair originates from a $J/\psi \rightarrow \mu^+ \mu^-$ decay. The branching fraction of $B_c^+ \rightarrow D_s^+ J/\psi$ multiplied by the fragmentation-fraction ratio is measured to be $f_c/f_u \cdot \mathcal{B}(B_c^+ \rightarrow D_s^+ J/\psi ) = (1.63 \pm 0.15 \pm 0.13) \times 10^{-5}$, where the first uncertainty is statistical and the second systematic.

Figures and captions

The leading diagrams for the decays: (a) $ B ^0_{\left( s \right)} \rightarrow \overline{ D } {}^0 \mu ^+\mu ^- $ , (b) $ B^+_{(c)} \rightarrow D ^+_ s \mu ^+\mu ^- $ , (c) $ B _ c ^+ \rightarrow D ^+_ s \mu ^+\mu ^- $ , (d) $ B ^0_{\left( s \right)} \rightarrow \overline{ D } {}^0 { J \mskip -3mu/\mskip -2mu\psi } $ , (e) $ B^+_{(c)} \rightarrow D ^+_ s { J \mskip -3mu/\mskip -2mu\psi } $ and (f) $ B _ c ^+ \rightarrow D ^+_ s { J \mskip -3mu/\mskip -2mu\psi } $ . Dashed lines represent the charged weak current, and a gluon exchange with unconnected quark lines is implied. Where two quark currents are indicated, the quark in parenthesis leads to a CKM-suppressed process.

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Invariant-mass distributions of (left) $ B ^0_{\left( s \right)} \rightarrow \overline{ D } {}^0 \mu ^+\mu ^- $ candidates and (right) {\mbox $ B ^0_{\left( s \right)} \rightarrow \overline{ D } {}^0 { J \mskip -3mu/\mskip -2mu\psi } $ } candidates with the fits superimposed.

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Invariant-mass distributions of (left) $ B ^+ \rightarrow D ^+_ s \mu ^+\mu ^- $ candidates and (right) {\mbox $ B ^+ \rightarrow D ^+_ s { J \mskip -3mu/\mskip -2mu\psi } $ } candidates with the fits superimposed.

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Invariant-mass distributions of (left) $ B _ c ^+ \rightarrow D ^+_ s \mu ^+\mu ^- $ candidates and (right) {\mbox $ B _ c ^+ \rightarrow D ^+_ s { J \mskip -3mu/\mskip -2mu\psi } $ } candidates with the fits superimposed.

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Animated gif made out of all figures.

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Tables and captions

A summary of the branching fractions of the decays (taken from Ref. [39]) and the fragmentation ratio (taken from Ref. [51]) which are used in the calculation of Eq. ???. The value of $\mathcal{B}\left( K ^{*0} \rightarrow K ^+ \pi ^- \right)$ is taken from the ratio of isospin amplitudes.

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Fitted yields and efficiencies for the decays $ B \rightarrow D \mu ^+\mu ^- $ , $ B \rightarrow D { J \mskip -3mu/\mskip -2mu\psi } $ and the normalisation modes (before S-wave subtraction). The quoted uncertainties arise solely from the limited size of the simulation samples.

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Relative systematic uncertainties for the branching-fraction measurements defined in Eq. ???, quoted separately for the different sources. The total is the sum in quadrature along the corresponding row.

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Upper limits at the 90 % and 95 % confidence levels for $ B \rightarrow D \mu ^+\mu ^- $ and $ B \rightarrow D { J \mskip -3mu/\mskip -2mu\psi } $ decays.

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Created on 27 April 2024.