Bs→ϕl+l−B_s \to \phi l^+ l^- decays in the topcolor-assisted technicolor model

Using the updated form factors within the light-cone QCD sum rule approach, we calculate the new physics contributions to rare semileptonic $\bar{B}_s \to \phi\mu^+\mu^-, \phi \tau^+\tau^-$ decays from the new particles appearing in the topcolor-assisted technicolor (TC2) model. In our evaluations, we find that: (i) the branching ratio, normalized forward-backward asymmetry and lepton polarization show highly sensitivity to charged top-pions contributions and little sensitivity to $Z'$ contributions. The TC2 enhancements to the branching ratios of these decays can reach a factor of $2 \sim 4$; (ii) the NP enhancement to the forward-backward asymmetry of the decay $B_s\to \phi \mu^+\mu^-$ is in the range -9% to 22%, but -10% to 0% for decay $B_s\to \phi \tau^+\tau^-$ compared to the SM predictions; (iii) the TC2 model provide an enhancement of more than 30% to the longitudinal polarization asymmetry $P_L$ for decay $B_s\to \phi \mu^+\mu^-$, but a decrease of about 20% to the transverse polarization asymmetry $P_T$ for the decay $B_s\to \phi \tau^+\tau^-$.Comment: 19 pages, 6 figures, figures changed, two references adde

Ultra-low noise magnetic field for quantum gases

Ultra-low noise magnetic field is essential for many branches of scientific research. Examplesinclude experiments conducted on ultra-cold atoms, quantum simulations, as well as precisionmeasurements. In ultra-cold atom experiments specifically, a bias magnetic field will be oftenserved as a quantization axis and be applied for Zeeman splitting. As atomic states areusually sensitive to magnetic fields, a magnetic field characterized by ultra-low noise as wellas high stability is typically required for experimentation. For this study, a bias magneticfield is successfully stabilized at 14.5G, with the root mean square (RMS) value of the noisereduced to 18.5{\mu}G (1.28ppm) by placing{\mu}-metal magnetic shields together with a dynamicalfeedback circuit. Long-time instability is also regulated consistently below 7{\mu}G. The level ofnoise exhibited in the bias magnetic field is further confirmed by evaluating the coherencetime of a Bose-Einstein condensate characterized by Rabi oscillation. It is concluded thatthis approach can be applied to other physical systems as well.Comment: 7 pages, 5 figure

Semileptonic Decays of BcB_c Meson to a P-Wave Charmonium State χc\chi_c or hch_c

The semileptonic decays of meson $B_c$ to a P-wave charmonium state $\chi_c(^3P_J)$ or $h_c(^1P_1)$ are computed. The results show that the decays are sizable so they are accessible in Tevatron and in LHC, especially, with the detectors LHCB and BTeV in the foreseeable future, and of them, the one to the $^1P_1$ charmonium state potentially offers us a novel window to see the unconfirmed $h_c$ particle. In addition, it is pointed out that since the two charmonium radiative decays $\chi_c(^3P_{1,2}) \to J/\psi+\gamma$ have sizable branching ratios, the cascade decays of the concerned decays and the charmonium radiative decays may affect the result of the observing the $B_c$ meson through the semileptonic decays $B_{c}\to {J/\psi}+{l}+\nu_{l}$ substantially.Comment: 8 pages, 2 figure

The Pure Leptonic Decays of B_c Meson and Their Radiative Corrections

The radiative corrections to the pure leptonic decay $B_c \to \ell\nu_{\ell}$ up-to one-loop order is presented. How to cancel the infrared divergences appearing in the loop calculations, and the radiative decay $B_c \to \ell\nu_{\ell}\gamma$ is shown precisely. It is emphasized that the radiative decay may be separated properly and may compare with measurements directly as long as the theoretical `softness' of the photon corresponds to the experimental resolutions. Furthermore with a kind of non-relativistic constituent quark model, a kind of typical long distance contributions to the radiative decays is estimated, and it is shown that the contributions are negligible in comparison with the accuracy of one-loop corrections and the expected experimental measurements.Comment: 20 pages including 6 figures, REVTe