The study of B→K()l+l- decays in family non-universal Z' models

In a combined investigation of B→K^(*)l⁺l^- decays, constraints on the related couplings in family non-universal Z' models are derived. We find that within the allowed parameter space, the recently observed forward-backward asymmetry in the B→K^(*)l⁺l^- decay can be explained by flipping the signs of the Wilson coefficients C₉^eff and C₁₀. With the obtained constraints, we also calculate the branching ratio of the B_s→μ⁺μ^- decay. The upper bound of our prediction is nearly an order of magnitude smaller than the upper bound given by the CDF Collaboration recently.     

Lepton number violation in D meson decay

The lepton number violation(LNV) process can be induced by introducing a fourth generation heavy Majorana neutrino,which is coupled to the charged leptons of the Standard Model(SM). There have been many previous studies on the leptonic number violating decay processes with this mechanism. We follow the trend to study the process: D→Kllπ with the same-sign dilepton final states. We restrict ourselves to certain neutrino mass regions,in which the heavy neutrino could be on-shell and the dominant contribution to the branching fraction comes from the resonance enhanced effect. Applying the narrow width approximation(NWA),we found that the upper limit for the branching fractions for D0→ K-l+l+π-are generally at the order of 10-12 to 10-9,if we take the most stringent upper limit bound currently available in the literature for the mixing matrix elements. We also provide the constraints,which is competitive compared to the LNV B decays,on the mixing matrix element |VeN|2 based on the upper limit of D0→ K-e+e+π-estimated from the Monte-Carlo(MC) study at BESⅢ. Although the constraints are worse than the ones from(0νββ) decay in the literature,the future experiment at the charm factory may yield more stringent constraints.     

Constraints on the R-Parity Violating Couplings Using the Newest Measurement of the Decay B_s~0→μ~+μ~-

Recently, the LHCb collaboration reported the first evidence for the decay B0s→μ+μ-. A branching ratio of B(B0s→μ+μ-)=(3.2+1.51.2)×10 9is given. Using the newest data, and together with the most precise predictions of the Standard Model contributions to the decay, we derive the constraints on the combinations of the R-parity violating parameters. Our results are several orders of magnitudes stronger than the constraints in the previous literature. We also update the constraints on the relevant parameters using the upper limit ofB(B0d→μ+μ-).     

Analysis of B → a1（1260）（b1（1235））K decays in the perturbative QCD approach

Within the framework of the perturbative quantum chromodynamics（PQCD） approach, we study the charmless two-body decays B → a₁（1260）K*, b₁（1235）K*. Using the decay constants and the light-cone distribution amplitudes for these mesons derived from the QCD sum rule method, we find the following results.（a） Our predictions for the branching ratios are consistent with the QCD factorization（QCDF） results within errors, but much larger than the naive factorization approach calculation values.（b） We predict that the anomalous polarizations occurring in the decays B→φK*, ρK*also happen in B→a₁ K*decays, while they do not happen in B→b₁ K*decays. Here the contributions from the annihilation diagrams play an important role in explaining the larger transverse polarizations in the B→a₁ K*decays, while they are not sensitive to the polarizations for the B→b₁ K*decays.（c） Our predictions for the direct C P-asymmetries agree well with the QCDF results within errors. The decaysˉB⁰→b₁₊K*-, B-→b₁⁰K*-have larger direct C P-asymmetries, which could be measured by the present LHCb experiment and the forthcoming Super-B experiment.     

The littlest Higgs model with T-parity and some lepton flavor violation decay processes

The new particles predicted by the littlest Higgs model with T-parity (called LHT model) can induce the lepton flavor violation (LFV) couplings at the one-loop level,which can add contributions to some LFV processes.Taking into account the constraints of the experimental data on the relevant free parameters,we calculate the branching ratios of the LFV decay processes Z → l ˉl and τ-→μ-P 1 P 2 with P 1 P 2 = π + π-,K + K-,and K0 ˉK 0 in the context of this new physics model.We find that the LHT model can indeed make significant contributions to some of these LFV decay processes.The Z factory option for the future high energy e + e-collider experiments will give severe constraints on the LHT model.     

b→cτ■ decay in supersymmetry with R-parity violation

In past years,several hints of lepton flavor universality(LFU)violation have emerged from the b→ct■,and b→sl~+l-data.More recently,the Belle Collaboration has reported the first measurement of the D* longitudinal polarization fraction in the B→D*τV decay.Motivated by this intriguing result,along with the recent measurements of RJ/Ψand τ polarization,we present the study of b→ct■ decays in supersymmetry(SUSY)with R-parity violation(RPV).We consider B→D(*)t■,Bc→ηct■,Bc→J/ψt■ and ∧b→∧ct■ modes and focus on the branching ratios,LFU ratios,forward-backward asymmetries,polarizations of daughter hadrons,and the τ lepton.The RPV SUSY was capable of explaining the RD(*) anomalies at the 2σ level,after taking into account various flavor constraints.In the allowed parameter space,the differential branching fractions and LFU ratios are largely enhanced by the SUSY effects,especially in the large dilepton invariant mass region.Moreover,a lower bound B(B~+→K~+vv)7.37×10~(-6) is obtained.These observables could provide testable signatures at the high-luminosity LHC and SuperKEKB,and correlate with direct searches for SUSY.     

Search for new physics in the B→K~((*))l~+l~- decays at BABAR

Based on a data sample of 384 million BB pairs collected with the BABAR detector at the PEP-Ⅱ asymmetric e + e ￣ storage ring,we measure branching fractions,direct CP,isospin and lepton-flavor asymmetries for the rare decays B → K (*) l + l￣ in two di-lepton mass bins above and below the J/ψ resonance.For the B → K* l + l￣ decay,we also measure the K* longitudinal polarization fraction and the di-lepton forwardbackward asymmetry.     

Implications of the RK and R_(K*) anomalies

We discuss the implications of the recently reported R_K and R_(K*) anomalies, the lepton flavor nonuniversality in the B → Kl~+l~-and B → K~*l~+~l- decay channels. Using two sets of hadronic inputs of form factors, we perform a fit of new physics to the R_K and R_(K*) data, and significant new physics contributions are found. We suggest the study of lepton flavor universality in a number of related rare B,Bs,Bc and Λb decay channels, and in particular we give predictions for the μ-to-e ratios of decay widths with different polarizations of the final state particles, and of the b → dl~+l~- processes, which are presumably more sensitive to the structure of the underlying new physics. With the new physics contributions embedded in the Wilson coefficients, we present theoretical predictions for lepton flavor non-universality in these processes.     

Analysis of B → a_1(1260)(b_1(1235))K decays in the perturbative QCD approach

Within the framework of the perturbative quantum chromodynamics(PQCD) approach, we study the charmless two-body decays B → a_1(1260)K*, b_1(1235)K*. Using the decay constants and the light-cone distribution amplitudes for these mesons derived from the QCD sum rule method, we find the following results.(a) Our predictions for the branching ratios are consistent with the QCD factorization(QCDF) results within errors, but much larger than the naive factorization approach calculation values.(b) We predict that the anomalous polarizations occurring in the decays B→φK*, ρK*also happen in B→a_1 K*decays, while they do not happen in B→b_1 K*decays. Here the contributions from the annihilation diagrams play an important role in explaining the larger transverse polarizations in the B→a_1 K*decays, while they are not sensitive to the polarizations for the B→b_1 K*decays.(c) Our predictions for the direct C P-asymmetries agree well with the QCDF results within errors. The decaysˉB~0→b_1_+K*-, B-→b_1~0K*-have larger direct C P-asymmetries, which could be measured by the present LHCb experiment and the forthcoming Super-B experiment.     

B→ X8γ, X8l＋l- Decays and Constraints on Mass Insertion Parameters in MSSM

In this paper, we study the upper bounds on the mass insertion parameters （δAB^q）ij in the minimal super symmetric standard model. We found that the information from the measured branching ratio of B→ X8γ, X8l＋l- decay can help us to improve the upper bounds on the mass insertions parameters （δAB^u,d）3j,i3 Some regions allowed by the data of Br（B→ X8γ） are excluded by the requirement of an SM-like C7γ （rnb） imposedby the data of Br（B→ X8γ, X8l＋l- ）.     

Measuring DO-D-O mixing in D→Fo(980)K* and more

We investigate the DO-D-O mixing through the doubly Cabibbo suppressed (DCS) channel DO→fO(980)K*O and its charge conjugate channel,in which the K*O meson is reconstructed in both K+π- and KsπO final state.Although the decay DO→ fo(980)K* has a small branching ratio,the final state mesons are relatively easy to identify.The fo(980) meson can be replaced by the S-wave π+π- state,or a longitudinally polarized vector meson pO.All mixing parameters,including the mass difference and decay width difference,can be extracted by studying the time-dependent decay width of these channels.We show that the method is valid in all regions for mixing parameters and it does not depend on the strong phase difference.     

Branching fractions and direct C P asymmetries of ■_s →K~0h~+h′~-(h(′)=K,π) decays

Motivated by the recent LHCb collaboration measurements of charmless three-body decays of ■s meson, we calculate the branching fractions of ■ s →K0π+π-, ■s→K0K+K-, ■s→K0π+K- and ■s→K0K+π- decay modes using the factorization approach.Both the resonant and nonresonant contributions are studied in detail. For the decays ■s→K0π+π- and ■s→K0K+K-, our results agree well with experimental data, and the former is dominated by the K*, while the latter one is dominated by the nonresonant contribution. Considering the flavor S U(3) symmetry violation, the sum of branching fractions of ■s→K0π+K- and ■s→K0K+π-could accommodate the data well too. It should be noted that both branching fractions are sensitive to the scalar density Kπ|ˉsq|0.Furthermore, the resonant contributions are dominated by the scalar K*0(1430). We hope that these branching fractions could be measured individually in the experiments so as to test the factorization approach and the flavor S U(3) asymmetry. Moreover, the direct C P asymmetries of these decays are also investigated, which could be measured in the running LHCb experiment and Super-b factory in the future.     

Branching ratio and CP asymmetry of Bs→K0(1430)η(') decays in the PQCD approach

In the two-quark model supposition for K0*(1430), which can be viewed as either the first excited state (ScenarioⅠ) or the lowest lying state (Scenario Ⅱ), the branching ratios and the direct CP-violating asymmetries for decays s0 → K0*0(1430)η (’) are studied by employing the perturbative QCD factorization approach. We find the following results: (a) The CP averaged branching ratios ofs0 → K0*0 (1430)η ands0→ K0*0(1430)η’ are small and both in the order of 10-7 . If one views K0* (1430) as the lowest lying state, B(s0→K0*0(1430)η) ≈ 3.9×10-7 and B(s0→K0*0(1430)η’) ≈ 7.8×10-7.(b) While the direct CP-violating asymmetries of these two decays are not small: if we still take the parameters of K0* (1430) in scenario , ACPdir(s0→K0*0(1430)η) ≈ 56.2% and ACPdir(s0→ K0*0(1430)η’) ≈ 42.4%. (c) The annihilation contributions will play an important role in accounting for future data, because both the branching ratios and the direct CP asymmetries of these two decays are sensitive to the annihilation type contributions.     

Effects of a Family Non-universal Z' Boson in B_d → μ~+μ~-and B~-→ π~-μ~+μ~-,ρ~-μ~+μ~-Decays

Motivated by the recently updated experimental measurement on Bˉd →μ+μ and B →πμ+μ decays by CDF and Belle collaborations,we revisit these decays,as well as B →ρμ+μ decay,within the Standard Model,and evaluate the effects of a family non-universal Z' boson.Under the constraint from B(B →πμ+μ),we find the ranges of the Z' couplings SμLμR 5.2 × 10 2 or DμLμR 8.1 × 10 2 are excluded.Within the allowed Z' parameters spaces,comparing with the SM predictions,we find that B(Bˉd →μ+μ),B(B →πμ+μ),and B(B →ρμ+μ) could be enhanced by a factor about 226%,245%,and 254%,respectively,by Z' contributions.However,they are hardly to be reduced.Furthermore,the zero crossing in the normalized forward-backward asymmetry spectrum of B →ρμ+μ decay at low dimuon mass always exists.     

Pure annihilation type decays B0→Ds- （K2*）+ and Bs →a2 in the perturbative QCD approach

We calculate the branching ratios of pure annihilation type decays B 0 →D_s^- （K₂^*）⁺ and Bs → a₂ using the perturbative QCD approach based on k T factorization. The branching ratios are predicted to be （60.6 +17.3+4.3+3.2 16.5 10.4 2.1 ）× 10^-6 for B⁰ →D_s^- （K₂^*）⁺ , （1.1 +0.4+0.1+0.1-0.4-0.2-0.1 ）×10-6 for Bs → ⁰a₂⁰ and （2.3 +0.8+0.2+0.1-0.8-0.4-0.1 ）×10-6 for Bs→D^-a₂⁺ . They are large enough to be measured in the ongoing experiment. Due to the shortage of contributions from penguin operators, there are no direct CP asymmetries for these decays in the Standard Model. We also derive simple relations among these decay channels to reduce theoretical uncertainties for the experiments, to test the accuracy of theory, and to search for a signal of new physics.     

Double heavy tri-hadron bound state via delocalized π bond

The number of exotic candidates that are beyond the conventional quark model has increased dramatically over recent decades.Some of these can be viewed as analogues of the deuteron.Similarly,the existence of the triton indicates that bound states formed by three hadrons could also exist.To illustrate this possibility,we study the DD~*K and■systems using the Born-Oppenheimer approximation.To leading order,only one-pion exchange potentials are considered.This means that the three constituents share one virtual pion.This is similar to the role of the delocalizedπbond for the formation of benzene in chemistry.After solving the Schr?dinger equation,we find two three-body DD~*K and■ bound states with masses 4317.92~_(-6.55)(+6.13)Me V and11013.65_(-8.84)~(+8.49)Me V,respectively.The masses of their ■and■ analogues are 4317.92~_(-6.55)(+6.13)Me V and11013.65_(-9.02)~(+8.68)Me V,respectively.From the experimental side,the ■bound state could be found by analyzing the current world data on the B→J/ψππKprocess,by focusing on the J/ψπK channel.     

Study of the process e~+e~- →π~+π~-π~0π~0 at energies s～(1/2)<1 GeV

In an experiment with the Spherical Neutral Detector at VEPP-2M collider the cross section of the process e+e-→π+π-π0π0 was measured.At energies s～(1/2)920 MeV this cross section was measured for the first time.The energy dependence of the cross section is well discribed by the vector dominance model with contributions from ρ,ρ,ρ mesons.The decay probability ρ→π+π-π0π0 was found to be Bρ =(1.60±0.74±0.18)×10-5.The upper limit for the decay ω→π+π-π0π0 was improved by two orders of magnitude compared to the previous measurements and is Bω 2×10-4 at 90% confidence level.     

Rare Decay B → Xsvv in the Two-Higgs-Doublet Model of Type-Ⅲ

In this paper, we calculated the new physics contribution to theoretically very clean rare decay B → Xsvvin the general two-Higgs-doublet model (model Ⅲ). Within the considered parameter space, we found that (a) thenew physics contribution can provide one to two orders of enhancement to the branching ratio B(B → Xsvv) and cansaturate the experimental bound on B(B → Xs vv) in some regions of the parameter space; (b) besides the CLEO data ofB → Xsγ, the ALEPH upper limit on B(B → Xsvv) also leads to further constraint on the size of the Yukawa couplingλtt: λtt ＜ 6.4 for λbb = 2.7 and mH+ = 200 GeV.     

Phenomenology of b→cτ■ decays in a scalar leptoquark model

During the past few years,signs of lepton flavor universality(LFU)violation have been observed in b→cτ■ and b→sl+l-transitions.Recently,the D* and τ polarization fractions P_L~D* and P_L~τ in B→D*τ■decay were likewise measured by the Belle collaboration.Motivated by these intriguing results,we revisit the RD(*)and RK(*) anomalies in a scalar leptoquark(LQ)model,where two scalar LQs,one of which is a S U(2)L singlet and the other a S U(2)L triplet,are introduced simultaneously.We consider five b→ cτ■ mediated decays,B→D(*)τ■,B_c→ηcτ■,Bc→J/ψt■,and ∧_b→∧_cτ■,and focus on the LQ effects on the q~2 distributions of the branching fractions,LFU ratios,and various angular observables in these decays.Under the combined constraints of the available data on RD(*),RJ/ψ,P_L~τ(D*),and pLD*,we perform scans for the LQ couplings and make predictions for a number of observables.Numerically it is found that both the differential branching fractions and LFU ratios are largely enhanced by the LQ effects,with the latter expected to provide testable signatures at the SuperKEKB and High-Luminosity LHC experiments.     

B→K0^＊（1430）K Decays in Perturbative QCD Approach

In this article, we calculate the branching ratios of B→K0^＊ （1430）K decays by employing the pertur-bative QCD （pQCD） approach at leading order. We perform the evaluations in the two scenarios for the scalar meson spectrum. We find that （i） The leading order pQCD predictions for the branching ratio Br（B^＋→K^＋K0^＊（1430）^0）are in good agreement with the experimental upper limit in both scenarios, while the pQCD predictions for other considered B→K0^＊（1430）K decay modes are also presented and will be tested by the LHC experiments; （ii） The annihilation contributions play an important role in these considered decays, for B^0→K0^＊（1430）^±K^± decays,for example,which are found to be （1-4）×10^-6.