The strong decays of K1 resonances

We investigate the K1--> K pi pi strong interaction decays. Using the 3P0 quark-pair-creation model to derive the basic parametrization, we discuss in detail how to obtain the various partial wave amplitudes into the possible quasi-two-body decay channels as well as their relative phases from the currently available experimental data. We obtain the K1 mixing angle to be thetaK1= 60 deg, in agreement with previous works. Our study can be applied to extract the information needed for the photon polarization determination of the radiative B--> K1 gamma decay.Comment: 57 pages, 10 figure

Bˉ→Dτνˉτ\bar B\to D\tau\bar \nu_\tau vs. Bˉ→Dμνˉμ\bar B\to D\mu\bar \nu_\mu

Recent experimental results for the ratio of the branching fractions of $\bar B\to D^{(*)}\tau\bar \nu_\tau$ and $\bar B\to D^{(*)}\mu\bar \nu_\mu$ decays came as a surprise and lead to a discussion of possibility to constraining New Physics through these modes. Here we focus on ${\cal B}(\bar B\to D\tau\bar \nu_\tau)/{\cal B}(\bar B\to D\mu\bar \nu_\mu)$ and argue that the result is consistent with the Standard Model within $2\sigma$, and that the test of compatibility of this ratio with the Standard Model can be done experimentally with a minimal theory input. We also show that these two decay channels can provide us with quite good constraints of the New Physics couplings.Comment: 10 pages (published version

Preparing a commercial quantum key distribution system for certification against implementation loopholes

A commercial quantum key distribution (QKD) system needs to be formally certified to enable its wide deployment. The certification should include the system's robustness against known implementation loopholes and attacks that exploit them. Here we ready a fiber-optic QKD system for this procedure. The system has a prepare-and-measure scheme with decoy-state BB84 protocol, polarisation encoding, qubit source rate of 312.5 MHz, and is manufactured by QRate in Russia. We detail its hardware and post-processing. We analyse the hardware for any possible implementation loopholes and discuss countermeasures. We then amend the system design to address the highest-risk loopholes identified. We also work out technical requirements on the certification lab and outline its possible structure.Comment: 33 pages, 11 figures, 2 table

Impact of B→K0∗ℓ+ℓ−B\to K^\ast_0 \ell^+\ell^- on the New Physics search in B→K∗ℓ+ℓ−B\to K^\ast \ell^+\ell^- decay

We discuss the uncertainty related to the amount of unwanted $B\to K_0^\ast (K\pi)\ell^+\ell^-$ events in the sample of $B\to K^\ast (K\pi)\ell^+\ell^-$. Those events can increase the measured differential decay rate by up to 10% in the low $q^2$ region, and can be a source of non-negligible uncertainty in the full angular distribution of the $B\to K^\ast (K\pi)\ell^+\ell^-$ decay. Although the transverse asymmetries should be unaffected by the presence of the $S$-wave $K\pi$ pairs, coming from the scalar $K_0^\ast$ meson, we show that in practice their normalization might be sensitive to those events and could entail a sizable uncertainty in transverse asymmetries around $q^2=2 GeV^2$. For other $q^2$'s that error is under about 10%.Comment: 16 pages [as published in NPB