Rare Decay B_c → D_s *μ~+ μ~- in a Family Non-Universal Z′ Model

Using the form factors calculated in the three-point QCD sum rules, we calculate the new physics contributions to the physical observables of B c → Ds* μ+ μ decay in a family non-universal Z′ model. Under the consideration of three cases of the new physics parameters, we find that: (a) the Z′ boson can provide large contributions to the differential decay rates; (b) the forward-backward asymmetry (FBA) can be increased by about 47%, 38%, and 110% at most in S1, S2, and extreme limit values (ELV), respectively. In addition, the zero crossing can be shifted in all the cases; (c) when s 0.08, the value of P L can be changed from 1 in the Standard Model (SM) to 0.5 in S1, 0.6 in S2, and 0 in extreme limit values, respectively; (d) the new physics corrections to P T will decrease the SM prediction about 25% for the cases of S1     

NMSSM neutralino dark matter for CDFⅡW-boson mass and muon g-2 and the promising prospect of direct detection

Two experiments from the Fermilab, E989 and CDF II, have reported two anomalies for muon g-2 and W-boson mass that may indicate the new physics at the low energy scale. Here we examine the possibility of a common origin of these two anomalies in the Next-to-Minimal Supersymmetric Standard Model. Considering various experimental and astrophysical constraints such as the Higgs mass, collider data, flavor physics, dark matter relic density, and direct detection experiments, we find that lighter ele...     

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.     

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.     

Probing the scale of new physics in the ZZγ coupling at e~+e~- colliders

The Z Zγtriple neutral gauge couplings are absent in the Standard Model(SM)at the tree level.They receive no contributions from dimension-6 effective operators,but can arise from effective operators of dimension-8.We study the scale of new physics associated with such dimension-8 operators that can be probed by measuring the reaction e~+e~-→Zγ followed by ■ decays,at future e~+e~- colliders including the CEPC,FCC-ee,ILC and CLIC.We demonstrate how angular distributions of the final-state mono-photon and leptons can play a key r?le in suppressing SM backgrounds.We further demonstrate that using electron/positron beam polarizations can significantly improve the signal sensitivities.We find that the dimension-8 new physics scale can be probed up to the multiTeV region at such lepton colliders.     

Rare semileptonic decays of heavy mesons in the heavy quark limit

We study the branching ratios of D^＋ → D^0e^＋ν, Ds^＋ → D^0e^＋ν, Bs^0→B^＋e^-^-ν, Ds^＋→D^＋e^-e^＋ and Bs^0→B^0e^-e^＋ rare semileptonic decay processes, which are induced by decays of light quarks, the heavy quarks remain unchanged. The branching ratios of these decay processes are estimated in the heavy quark limit and with SU（3） flavor symmetry. We find that the decay rates are very tiny in the framework of the Standard Model. We also estimate the sensitivities of the measurements of these rare decays at the future experiments, such as BES-Ⅲ, super-B and LHC-b. Observations of these decays may shed some light on new physics beyond the standard model.     

Study of the s → dv■ rare hyperon decays in the Standard Model and new physics

FCNC processes offer important tools to test the Standard Model(SM)and to search for possible new physics.In this work,we investigate the s→dvv rare hyperon decays in SM and beyond.We find that in SM the branching ratios for these rare hyperon decays range from 10~(-14) to 10~(-11).When all the errors in the form factors are included,we find that the final branching ratios for most decay modes have an uncertainty of about 5% to 10%.After taking into account the contribution from new physics,the generalized SUSY extension of SM and the minimal 331 model,the decay widths for these channels can be enhanced by a factor of 2～7.     

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.     

Pure annihilation type B → K_0~(*±)(1430)K~((*)■) decays in the family non-universal Z’ model

By assuming that the scalar meson K_0~*(1430) belongs to the first excited states or the lowest lying ground states of qq',we study the pure annihilation-type decays B→K_0~*(1430)K~((*)■) in the QCD factorization approach.Within the Standard Model,the branching fractions are of the order of 10~(-8) 10~(-7),which is possible to measure in the ongoing LHCb experiment or forthcoming Belle-II experiment.We also study these decays in the family non-universal Z' model.The results show that if m_Z≈600 GeV(ζ=0.02),both the branching fractions and CP asymmetries of B~0→K_0~+(1430)K~- could be changed remarkably,which provides us with a place for probing the effect of new physics.These results could be used to constrain the parameters of the Z' model.     

Rare semileptonic decays of heavy mesons in the heavy quark limit

We study the branching ratios of D+→D0e+ν,DS+→D0e+ν,BS0→B+e-ν,DS+→D+e-e+ and BS0→B0e-e+ rare semileptonic decay processes,which are induced by decays of light quarks,the heavy quarks remain unchanged.The branching ratios of these decay processes are estimated in the heavy quark limit and with SU(3) flavor symmetry.We find that the decay rates are very tiny in the framework of the Standard Model.We also estimate the sensitivities of the measurements of these rare decays at the future experiments,such as BES-Ⅲ,super-B and LHC-b.Observations of these decays may shed some light on new physics beyond the standard model.     

Influence of the time-step on the production of free nucleons and pions from heavy-ion collisions around 1 GeV/nucleon

By considering different values of the time-step for the potential updates in the ultra-relativistic quantum molecular dynamics(UrQMD) model, we examine its influence on observables, such as the yield and collective flow of nucleons and pions from heavyion collisions around 1 GeV/nucleon. It is found that these observables are affected to some extent by the choice of the time-step,and the impact of the time-step on the pion-related observables is more visible than that on the nucleon-related ones. However,its effect on the π-/π+yield ratio and elliptic flow difference between neutrons and protons, which have been taken as sensitive observables for probing the density-dependent nuclear symmetry energy at high densities, is fairly weak.     

Investigation of rare semileptonic B_c→(D_(s,d)~((*))μ~+μ~- decays with non-universal Z' effect

We analyze different decay observables of semileptonic decays B_c→(D_(s,d)~((*)))μ~+μ~-,such as the branching ratio,forward-backward asymmetry,polarization fraction,and lepton polarization asymmetry in the non-universal Z'model.We further study the dependence of the branching fraction to the new model parameters and find that the values of different decay parameters increase in the Z' model,which indicates a possible approach for the search of new physics as well as for the unknown phenomena of the charm B meson.     

Hadro- and photo-production of η′ in quasi-free proton and neutron processes

The η′ photoproduction process on quasi-free proton and neutron and the reaction NN→ η′NN are investigated within a relativistic effective Lagrangian approach to hadronic interactions. Resonances with spins 1/2 and 3/2 are considered together with the nucleonic and t-channel meson-exchange current contributions. In photoproduction processes, the S11 resonance is found to be responsible for the sharp rise of the cross sections near threshold. In pp → η′pp, it is found that the S11 resonance dominates the total cross section over the entire energy region considered. The spin observables, in particular the beam and target asymmetries, are shown to be very sensitive to the reaction mechanism and will help impose more stringent constraints on the model parameters.     

New Physics Effects on Rare Decays Bu^＋ → π^＋e^＋e^-, ρ^＋e^＋e^- in a Top Quark Two-Higgs-Doublet Model

Using the form factors from light-cone sum rules, we study the branching ratios and forward-backward asymmetries （FBAs） of the exclusive decays Bu^＋→π^＋e^＋e^- and Bu^＋ →ρ^＋e^＋e^- （e= e,μ） in the standard model （SM） and the top quark two-Higgs-doublet model （T2HDM）. From the numerical results, we find that the new physics contributions cannot provide very large enhancement to the branching ratios and the theoretical predictions are in good agreement with the SM ones. The T2HDM effects on FBAs of these decays are small. Precision measurements of the dilepton invariant mass distributions, especially in the lower dilepton mass region, and the FBAs in the decays Bu^＋ → π^＋ （ρ^＋ ）e^＋ e^- will greatly help in discriminating among the SM and the new physics models.     

B → X_sγ in BLMSSM

Applying the effective Lagrangian method,we study the flavor changing neutral current process b→ sγwithin the minimal supersymmetric extension of the Standard Model,where baryon and lepton numbers are local gauge symmetries.Constraints on the parameters are investigated numerically with the experimental data for the branching ratio of B→ X_sγ.Additionally,we present the corrections to direct CP-violation in B→ X_sγ and time-dependent CP-asymmetry in B→K~*γ.With appropriate assumptions on the parameters,we find the direct CP-violation Acp is very small,while one-loop contributions to S_(K~*_γ) can be significant.     

General scan in flavor parameter space in models with vector quark doublets and an enhancement in the B→X_sγ process

In models with vector-like quark doublets, the mass matrices of up and down type quarks are related.Precise diagonalization of the mass matrices has become an obstacle in numerical studies. In this work we first propose a diagonalization method. As its application, in the Standard Model with one vector-like quark doublet we present the quark mass spectrum and Feynman rules for the calculation of B → X_sγ. We find that i) under the constraints of the CKM matrix measurements, the mass parameters in the bilinear term are constrained to a small value by the small deviation from unitarity; ii) compared with the fourth generation extension of the Standard Model, there is an enhancement to the B → X_sγ process in the contribution of vector-like quarks, resulting in a non-decoupling effect in such models.     

Searching for Electrical Dipole and Chromodipole Moments of a Charm Quark in J／ψ→γφφ Decay

We propose a scheme to search for the electrical dipole moments (EDMs) and chromodipole moments (CDMs) of a charm quark in the decay J/ψ→γφφ based on J/ψ data samples accumulated on the Beijing Electron Positron Collider (BEPC). The EDM and CDM interactions are introduced in this decay and then we relate them to some CP asymmetrical observables, which are predicted in the valence quark model. We propose a method to hunt for these values by measuring associated CP asymmetrical observables, and we also discuss the prospect of such measurement on the BEPC.     

■Study of the Standard Model and Majorana neutrino contributions to

Lepton number violation processes can be induced by the Majorana neutrino exchange, which provide evidence for the Majorana nature of neutrinos. In addition to the natural explanation of the small neutrino masses,Type-I seesaw mechanism predicts the existence of Majorana neutrinos. The aim of this work is to study the B meson rare decays B~+→K~((*))+μ~+μ~-in the Standard Model and its extensions, and then to investigate the same-sign decay process B~+→K~((*)-)μ~+μ~+. The corresponding dilepton invariant mass distributions are calculated. It is found that the dilepton angular distributions could shed light on the properties of new interactions induced by Majorana neutrinos.     

Z→l_i~±l_j~■ jprocesses in the BLMSSM

In a supersymmetric extension of the Standard Model(SM) where baryon and lepton numbers are local gauge symmetries(BLMSSM), we investigate the charged lepton flavor violating(CLFV) processes Z→l_i~±l_j~■ jafter introducing new gauginos and right-handed neutrinos. In this model, the branching ratios of Z→l_i~±l_j~■ jare around(10~(-8)–10~(-10)), which approach the present experimental upper bounds. We hope that the branching ratios for these CLFV processes can be detected in the near future.     

B_(s,d)→μ~+μ_- decays in a flavor changing Z′ model

We study the pure leptonic decays Bs,d →μ+μ- in a Flavor Changing Z′ Model.From the recent measurements of the branching ratios B(Bs,d →μ+μ-),we have derived the bounds on the effective μ-μ-Z′ lepton coupling BμLμ.We find that,(i) if neglecting the contribution from the right-handed lepton coupling BμRμ,we obtain 1.32 < BμLμ < 3.32;(ii) if considering the contribution from the right-handed lepton coupling BμRμ and setting BμLμ =BμRμ,we obtain 0.99相似文献