Integrated Branching Ratio Research Articles

Revisiting radiative leptonic B decay * *Y.B.W is Supported in part by the National Natural Science Foundation of China (NSFC) (11675082, 11735010)

In this paper, we summarize the existing methods of solving the evolution equation of the leading-twist B-meson LCDA. Then, in the Mellin space, we derive a factorization formula with next-to-leading-logarithmic (NLL) resummation for the form factors in the decay at leading power in . Furthermore, we investigate the power suppressed local contributions, factorizable non-local contributions (which are suppressed by and ), and soft contributions to the form factors. In the numerical analysis, which employs the two-loop-level hard function and the jet function, we find that both the resummation effect and the power corrections can sizably decrease the form factors. Finally, the integrated branching ratios are also calculated for comparison with future experimental data.

Theoretical analysis of the doubly radiative decays η(′)→π0γγ and η′→ηγγ

The scalar and vector meson exchange contributions to the doubly radiative decays ${\ensuremath{\eta}}^{(\ensuremath{'})}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma}\ensuremath{\gamma}$ are analyzed within the linear sigma model and vector meson dominance frameworks, respectively. Predictions for the diphoton invariant mass spectra and the associated integrated branching ratios are given and compared with current available experimental data. While a satisfactory description of the shape of the $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ decay spectra is obtained, thus supporting the validity of the approach, the corresponding branching ratios cannot be reproduced simultaneously. A first theoretical prediction for the recently measured ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\gamma}\ensuremath{\gamma}$ by the BESIII Collaboration is also presented.

Isovector scalar a0(980) and a0(1450) resonances in the B→ψ(KK¯,πη) decays

We present an analysis of two isovector scalar resonant contributions to the $B$ decays into charmonia plus $K\bar K$ or $\pi\eta$ pair in the perturbative QCD approach. The Flatt\'{e} model for the $a_0(980)$ resonance and the Breit Wigner formula for the $a_0(1450)$ resonance are adopted to parametrize the timelike form factors in the dimeson distribution amplitudes, which capture the important final state interactions in these processes. The predicted distribution in the $K^+K^-$ invariant mass as well as its integrated branching ratio for the $a_0(980)$ resonance in the $B^0\rightarrow J/\psi K^+K^-$ mode agree well with the current available experimental data. The obtained branching ratio of the quasi-two-body decay $B^0\rightarrow J/\psi a_0(980)(\rightarrow \pi^0\eta)$ can reach the order of $10^{-6}$, letting the corresponding measurement appear feasible. For the $a_0(1450)$ component, our results could be tested by further experiments in the LHCb and Belle II. We also discuss some theoretical uncertainties in detail in our calculation.

Subleading power corrections to the B→γlν decay in the perturbative QCD approach

The leptonic radiative decay $B\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\ell}\ensuremath{\nu}$ is of great importance in the determination of $B$-meson wave functions, and evaluating the form factors ${F}_{V,A}$ is the essential problem on the study of this channel. We compute the next-to-leading power corrections to the form factors within the framework of PQCD approach, including the power suppressed hard kernel, the contribution from a complete set of three-particle $B$-meson wave functions up to twist-4 and two-particle off light-cone wave functions, the $1/{m}_{b}$ corrections in heavy quark effective theory (HQET), and the contribution from hadronic structure of photon. In spite of large theoretical uncertainties, the overall power suppressed contributions decreases about 50% of the leading power result. The ${\ensuremath{\lambda}}_{B}$ dependence of the integrated branching ratio is reduced after including the subleading power contributions, thus the power corrections lead to more ambiguity in the determination of ${\ensuremath{\lambda}}_{B}$ from $B\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\ell}\ensuremath{\nu}$ decay.

A data-driven approach to and single and double Dalitz decays**Supported by the FPI scholarship BES-2012-055371 (S.G-S), the Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya under grant 2014 SGR 1450, the Ministerio de Ciencia e Innovación under grant FPA2011-25948, the Ministerio de Economía y Competitividad under grants CICYT-FEDER-FPA 2014-55613-P and SEV-2012-0234, the Spanish Consolider-Ingenio

The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays and (; or ) are predicted by means of a data-driven approach based on the use of rational approximants applied to and transition form factor experimental data in the space-like region.

A study of B→K∗ℓ+ℓ− decay in soft-collinear effective theory

A brief account of the study of rare B decay $B \to K^\ast \ell^+ \ell^-$ using soft-collinear effective theory (SCET) is presented. Theoretical underpinning of this work is a factorization formula, derived to leading power in $1/m_b$ and valid to all orders in $\alpha_s$. Partially integrated branching ratio in the dilepton squared mass range $1 {GeV}^2 \le q^2 \le 7 {GeV}^2$ and the forward-backward (FB) asymmetry of the leptons are calculated. For the zero-point of the FB asymmetry, we get $q_0^2=(4.07^{+0.16}_{-0.13}) {GeV}^2$. The scale-related uncertainty of $q_0^2$ is improved compared to the earlier estimate of the same.

B→K*ℓ+ℓ- decay in soft-collinear effective theory

We study the rare B decay $B \to K^* \ell^+ \ell^-$ using soft-collinear effective theory (SCET). At leading power in $1/m_b$, a factorization formula is obtained valid to all orders in $\alpha_s$. For phenomenological application, we calculate the decay amplitude including order $\alpha_s$ corrections, and resum the logarithms by evolving the matching coefficients from the hard scale ${\cal O}(m_b)$ down to the scale $\sqrt{m_b \Lambda_h}$. The branching ratio for $B \to K^* \ell^+ \ell^-$ is uncertain due to the imprecise knowledge of the soft form factors $\zeta_\perp (q^2)$ and $\zeta_\parallel (q^2)$. Constraining the soft form factor $\zeta_\perp (q^2=0)$ from data on $B \to K^* \gamma$ yields $\zeta_\perp (q^2=0)=0.32 \pm 0.02$. Using this input, together with the light-cone sum rules to determine the $q^2$dependence of $\zeta_\perp (q^2)$ and the other soft form factor $\zeta_\parallel (q^2)$, we eastimate the partially integrated branching ratio in the range $1~{GeV}^2 \le q^2 \le 7~{GeV}^2$ to be $(2.92^{+0.67}_{-0.61}) \times 10^{-7}$. We discuss how to reduce the form factor related uncertainty by combining data on $B \to \rho (\to \pi \pi) \ell \nu_\ell$ and $B\to K^* (\to K\pi) \ell^+\ell^-$. The forward-backward asymmetry is less sensitive to the input parameters. In particular, for the zero-point of the forward backward asymmetry in the standard model, we get $q_0^2=(4.07^{+0.13}_{-0.12})~{GeV}^2$. The scale dependence of $q_0^2$ is discussed in detail.

Electromagnetic logarithms in [formula omitted

The B ¯ → X s ℓ + ℓ − decay rate is known at the next-to-next-to-leading order in QCD. It is proportional to α em ( μ ) 2 and has a ± 4 % scale uncertainty before including the O ( α em ln ( M W 2 / m b 2 ) ) electromagnetic corrections. We evaluate these corrections and confirm the earlier findings of Bobeth et al. Furthermore, we complete the calculation of logarithmically enhanced electromagnetic effects by including also QED corrections to the matrix elements of four-fermion operators. Such corrections contain a collinear logarithm ln ( m b 2 / m ℓ 2 ) that survives integration over the low dilepton invariant mass region 1 GeV 2 < m ℓ ℓ 2 < 6 GeV 2 and enhances the integrated decay rate in this domain. For the low- m ℓ ℓ 2 integrated branching ratio in the muonic case, we find B ( B → X s μ + μ − ) = ( 1.59 ± 0.11 ) × 10 −6 , where the error includes the parametric and perturbative uncertainties only. For B ( B → X s e + e − ) , in the current BaBar and Belle setups, the logarithm of the lepton mass gets replaced by angular cut parameters and the integrated branching ratio for the electrons is expected to be close to that for the muons.

Simple approach to fourth generation effects inB→Xsl+l−decay

In a scenario in which fourth generation fermions exist, we study effects of new physics on the differential decay width, forward-backward asymmetry $A_{\text{FB}}$ and integrated branching ratio for $B\to X_s \ell^+ \ell^-$ decay with $(\ell=e,\mu)$. Prediction of the new physics on the mentioned quantities essentially differs from the Standard Model results, in certain regions of the parameter space, enhancement of new physics on the above mentioned physical quantities can yield values as large as two times of the SM predictions, whence present limits of experimental measurements of branching ratio is spanned, contraints of the new physics can be extracted. For the fourth generation CKM factor $V_{t^\prime b}^\ast V_{t^\prime s}$ we use $\pm 10^{-2}$ and $\pm 10^{-3}$ ranges, take into consideration the possibility of a complex phase where it may bring sizable contributions, obtained no significant dependency on the imaginary part of the new CKM factor. For the above mentioned quantities with a new family, deviations from the SM are promising, can be used as a probe of new physics.

Ab initioground state andL2,3x-ray magnetic circular dichroism of Mn-based Heusler alloys

Relativistic full-potential calculations within the generalized gradient approximation (GGA) for a series of Mn-based Heusler alloys are presented. Calculated equilibrium lattice parameters deviate less than 1.2% from the experimental values. The main features of a half metallic system are present in the density of states for the PtMnSb and NiMnSb. We predict that PdMnSb shows half metallic character under hydrostatic pressure. The substitution of Sb in PtMnSb by Sn or Te destroys the minority spin band gap. Spin and orbital magnetic moments for all the systems are in good agreement with previous calculations and experimental data. ${L}_{2,3}$ x-ray absorption and x-ray magnetic circular dichroism (XMCD) spectra are calculated for all the five compounds. Pt spectra present big deviations from system to system in the PtMnY (Y=Sn,Sb,Te) compounds while Mn spectra show only small deviations. For all these spectra GGA underestimates the ${L}_{3}{/L}_{2}$ integrated branching ratio and produces a much smaller ${L}_{2}$ peak intensity for the Ni site in NiMnSb. The XMCD sum rules are used to compute the spin and orbital magnetic moments and the results are compared to the direct calculations.

A model independent analysis of B → Xsℓ +ℓ − decays in supersymmetry

Recently the semileptonic decays B a ̊ X se +e −, B a ̊ X sμ +μ − in generic supersymmetric extensions of the Standard Model have been studied in ref. [1]. In this talk I review the main points of this analysis. SUSY effects are parameterized using the mass insertion approximation formalism and differences with MSSM results are pointed out. Constraints on SUSY contributions coming from other processes ( e.g. b → sγ) are taken into account. Chargino and gluino contributions to photon and Z-mediated decays are computed and non-perturbative corrections are considered. We find that the integrated branching ratios and the asymmetries can be strongly modified. Moreover, the behavior of the differential Forward-Backward asymmetry remarkably changes with respect to the Standard Model expectation.

Formula omitted]decays in supersymmetry

We study the semileptonic decays B→ X s e + e −, B→ X s μ + μ − in generic supersymmetric extensions of the Standard Model. SUSY effects are parameterized using the mass insertion approximation formalism and differences with the Constrained MSSM results are pointed out. Constraints on SUSY contributions coming from other processes (e.g. b→ sγ) are taken into account. Chargino and gluino contributions to photon and Z-mediated decays are computed and non-perturbative corrections are considered. We find that the integrated branching ratios and the asymmetries can be strongly modified. Moreover, the behavior of the differential forward–backward asymmetry remarkably changes with respect to the Standard Model expectation.

Radiative muon absorption in oxygen.

The photon spectrum from radiative absorption of negative muons in $^{16}\mathrm{O}$ has been measured with a high-resolution pair spectrometer. The integrated branching ratio for photons with energies greater than 57 MeV relative to the total muon absorption rate is (3.8\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$. The data are consistent with nuclear model calculations for a value of the induced pseudoscalar coupling in $^{16}\mathrm{O}$ of ${g}_{P}$/${g}_{A}$=13.5\ifmmode\pm\else\textpm\fi{}1.5.

Charged particle emission following pion capture in nuclei

We have identified the charged particles emitted following pion capture in thin (0.05 g/cm 2) targets of Li, Be, 10B, C, O, Mg, S, Ca, Co and Pb and have measured their energy spectra as well as the integrated branching ratios above threshold energies of 6, 8 and 9 MeV for the proton, deuteron and triton mode, respectively.

Possible violation of the δS=δQ selection rule in leptonic decays of σ+-hyperons

We have found a possible example of the rare decayσ+→nΜ+Ν, which violatesδS=δQ. The positive decay track of theσ+ comes to rest in the hydrogen bubble chamber and decays into ane+. This track has all the characteristics of a stoppingΜ+. The decay neutron fortuitously scatters twice, producing two recoil protons. The only other possible interpretation of the event isσ+→nγ(π+→Μ+Ν), where theπ+→Μ+Ν decay produces no deflection (θ<0.1 rad) and no significant change in curvature. Using thep-wave radiative decay predictions ofBarshay et al. we calculate that the integrated branching ratio for such “accidental” events isγ(σ+→nγ(π+→Μ stop + Ν))/γ(σ+→nπ+)=1.6×10−6.