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Register a new userStudy of B+- --> D_CP K+- and D^*_CP K+- decays
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We report a study of the modes D_CP K+- and D^*_CP K+- where D^(*) decays to CP eigenstates. The data sample used contains 275 x 10^6 BB events at the Upsilon(4S) resonance collected by the Belle detector at the KEKB energy-asymmetric e^+ e^- collider. The CP asymmetries obtained for D_CP K are: A_1 = 0.06 +- 0.14 (stat) +- 0.05 (sys), A_2 = -0.12 +- 0.14 (stat) +- 0.05 (sys) and for D^*_CP K : A_1^* = -0.20 +- 0.22 (stat) +- 0.04 (sys), A_2^* = 0.13 +- 0.30 (stat) +- 0.08 (sys).
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The B -> D^{(*)} K^- K^{(*)0} decays have been observed for the first time. The branching fractions of the B -> D^{(*)} K^- K^{(*)0} decay modes are measured. Significant signals are found for the B -> D^{(*)} K^- K^{*0} and B^- -> D^0 K^- K^0_S decay modes. The invariant mass and polarization distributions for the K^-K^{*0} and K^-K^0_S subsystems have been studied. For the K^-K^{*0} sybsystem these distributions agree well with those expected for two-body B -> D^{(*)} a_1^-(1260) decays, with a_1^-(1260) -> K^- K^{*0}. The analysis was done using 29.4 fb^{-1} of data collected with the Belle detector at the e^+ e^- asymmetric collider KEKB.
The only anticipated resonant contributions to $B^+to D^+D^-K^+$ decays are charmonium states in the $D^+D^-$ channel. A model-independent analysis, using LHCb proton-proton collision data taken at centre-of-mass energies of $sqrt{s}=7,8,$ and $13$ TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$, is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the $D^+D^-$ pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the $D^-K^+$ channel with masses around 2.9 GeV$/c^2$.
With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavour physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavour physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-pT and flavour data.
A measurement of four branching-fraction ratios for three-body decays of $B$ mesons involving two open-charm hadrons in the final state is presented. Run 1 and Run 2 $pp$ collision data are used, recorded by the LHCb experiment at centre-of-mass energies $7$, $8$, and $13$ TeV and corresponding to an integrated luminosity of $9$ fb$^{-1}$. The measured branching-fraction ratios are [ begin{eqnarray} frac{mathcal{B} (B^+to D^{*+}D^-K^+)}{mathcal{B} (B^+to kern 0.2emoverline{kern -0.2em D}{}^0 D^0 K^+)} &=& 0.517 pm 0.015 pm 0.013 pm 0.011 , frac{mathcal{B} (B^+to D^{*-}D^+K^+)}{mathcal{B} (B^+to kern 0.2emoverline{kern -0.2em D}{}^0 D^0 K^+)} &=& 0.577 pm 0.016 pm 0.013 pm 0.013 , frac{mathcal{B} (B^0to D^{*-}D^0K^+)}{mathcal{B} (B^0to D^- D^0 K^+)} &=& 1.754 pm 0.028 pm 0.016 pm 0.035 , frac{mathcal{B} (B^+to D^{*+}D^-K^+)}{mathcal{B} (B^+to D^{*-}D^+K^+)} &=& 0.907 pm 0.033 pm 0.014 ,end{eqnarray} ] where the first of the uncertainties is statistical, the second systematic, and the third is due to the uncertainties on the $D$-meson branching fractions. These are the most accurate measurements of these ratios to date.
The first observation of the $B^0_stobar{D}^0 K^0_S$ decay mode and evidence for the $B^0_stobar{D}^{*0} K^0_S$ decay mode are reported. The data sample corresponds to an integrated luminosity of 3.0 $text{fb}^{-1}$ collected in $pp$ collisions by LHCb at center-of-mass energies of 7 and 8 TeV. The branching fractions are measured to be begin{align*} mathcal{B}(B^0_stobar{D}^0 bar{K}^0) &= (4.3pm0.5(text{stat})pm0.3(text{syst})pm0.3(text{frag})pm0.6(text{norm}))times10^{-4}, mathcal{B}(B^0_stobar{D}^{*0} bar{K}^0) &= (2.8pm1.0(text{stat})pm0.3(text{syst})pm0.2(text{frag})pm0.4(text{norm}))times10^{-4}, end{align*} where the uncertainties are due to contributions coming from statistical precision, systematic effects, and the precision of two external inputs, the ratio $f_s/f_d$ and the branching fraction of $B^0tobar{D}^0 K^0_S$, which is used as a calibration channel.
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