ρ-ω mixing in J/ψ→VP decays

The study of ρ-ω mixing has mainly focused on vector meson decays with isospin I = 1, namely theρ(ω)→π+π- process. In this paper, we present a study of ρ-ω mixing in ρ(ω)→π+π-π0(I = 0) using a flavor parameterization model for the J/ψ→VP process. By fitting a theoretical framework to PDG data, we obtain the SU(3)-breaking effect parameters sV = 0.03±0.12, sP = 0.17±0.17 and the ρ-ω mixing polarization operatorΠρω =(0.006±0.011) GeV2. New values are found for the branching ratios when the mixing effect is incorporated:Br(J/ψ→ωπ0)=(3.64±0.37)×10-4, Br(J/ψ→ωη)=(1.48±0.17)×10-3, Br(J/ψ→ωη)=(1.55±0.56)×10-4, these are different from the corresponding PDG2012 values by 19%, 15% and 15%, respectively.     

Phenomenological studies on B~0 → [K~-π~+]_(S/V)[π~+π~-]_(V/S) → K~-π~+π~+π~- decay

Within the quasi-two-body decay model,we study the localized CP violation and branching fraction of the four-body decay B~0→[K~-π~+]_(s/V)[π~+π~-]_(V/)S→K-π~+π~-π~+ when the K~-π~+and π~-π~+ pair invariant masses are0.35 m(K~-π~+)2.04 GeV and 0 mπ~-π~+1.06 GeV,with the pairs being dominated by the K_0~*(700)~0,K~*(892)~0,K~*(1410)~0,K_0~*(1430) and K~*(1680)~0,and fo(500),ρ~0(770),ω(782) and fo(980) resonances,respectively.When dealing with the dynamical functions of these resonances,fo(500),ρ~0(770),fo(980) and K_0~*(1430) are modeled with the Bugg model,Gounaris-Sakurai function,Flatte formalism and LASS lineshape,respectively,while the others are described by the relativistic Breit-Wigner function.Adopting the end point divergence parameters ρA ∈[0,0.5] andΦ_A∈[0,2π],our predicted results are F_(CP)(B~0→K~-π~+π~+π~-)∈[-0.365,0.447] and B(B~0→K-π~+π~+π~-)∈[6.11,185.32] x 10~(-8),based on the hypothetical qq structures for the scalar mesons in the QCD factorization approach.Meanwhile,we calculate the CP violating asymmetries and branching fractions of the two-body decays B~0→SV(VS) and all the individual four-body decays B~0→SV(VS)→K~-π~+π~-π~+,respectively.Our theoretical results for the two-body decays B~0→K~*(892)~0 fo(980),B~0→K_0~*(1430)~0ω(782),B~0→K~*(892)~0 f~0(980),B~0→K_0~*(1430)~0ρ,and B~0→(1430)~0ω are consistent with the available experimental data,with the remaining predictions await testing in future high precision experiments.     

Quasi Three-Body Decay of D Meson

The aim of this work is to provide a phenomenological analysis of the contribution of D~0 meson to K*(892)~0π~+π~-(K*(892)~0-→π~+K~-), K~-π~+ω(ω-→π~+π~-π~0) and K~-π~+?(?(1020)-→ K~+K~-) quasi-three-body decays. The analysis of mentioned multi-body decays is such as to factorize into the three-body decay and several channels observed. Hadronic three-body decays receive both resonant and non-resonant contribution. Based on the factorization method, there are tree and emission annihilation diagrams for these decay modes. In the case of D~0 to vector pseudoscalar states appeared in factored terms, the matrix elements of the vector and axial vector currents between the D~0 and PV mesons can be computed by using D~(*+)pole. Considering the non-resonant and resonant amplitude in our computation,the theoretical values of the branching ratio are(9.78 ± 0.46) × 10~(-3),(2.74 ± 0.17) × 10~(-2), and(3.53 ± 0.23) × 10~(-5), while the experimental results of them are(9.9 ±2.3) × 10~(-3),(2.7 ± 0.5) × 10~(-2), and(4 ± 1.7) × 10~(-5) respectively. Comparing computational analysis values with experimental values show that our results are in approximately agreement with them.     

Feasibility study of CP violation in τ~-→ K_Sπ~-ν_τ decays at the Super Tau Charm Facility

We report a feasibility study for violation in τ~-→K_Sπ~-v_τ decays at a Super Tau Charm Facility(STCF).With an expected luminosity of 1 ab~(-1) collected by STCF per year at a center-of-mass energy of 4.26 GeV,the statistical sensitivity for CP violation is determined to be of order 9.7×10~(-4) by measuring the decay-rate difference between τ~+→K_Sπ~+v_τ and τ~-→K_Sπ~-v_τ.The analysis is performed using a reliable fast simulation software package,which can describe the detector responses properly and vary the responses flexibly for further optimization.Moreover,the energy-dependent efficiencies for reconstructing τ~-→K_Sπ~-v_τ are presented.The expected CP sensitivity is proportional to 1/~(1/2)L in the energy region from 4.0 to 5.0 GeV.The sensitivity of CP violation is of order3.1 × 10~(-4) with 10 ab~(-1) integrated luminosity,which is equivalent to ten years' data taking in this energy region at STCF.     

Revisiting the Kπ puzzle in the pQCD factorization approach

In this paper,we calculated the branching ratios and direct CP violation of the four B→Kπ decays with the inclusion of all currently known next-to-leading order(NLO) contributions by employing the perturbative QCD(pQCD) factorization approach.We found that(a) Besides the 10%enhancement from the NLO vertex corrections,the quark-loops and magnetic penguins,the NLO contributions to the form factors can provide an additional~15%enhancement to the branching ratios,and lead to a very good agreement with the data;(b) The NLO pQCD predictions are A_(CP)~(dir)(B~0→K~+π~0)=(-6.5±3.1)%and A_(CP)~(dir)(B~+→K~+π~0)=(2.2±2.0)%,become well consistent with the data due to the inclusion of the NLO contributions.     

S-wave resonance contributions to B_((s))~0→η_c(2S)π~+π~- in the perturbative QCD factorization approach

By employing the perturbative QCD(PQCD) factorization approach, we study the quasi-two-body B_((s))~0→η_c(2S)π~+π~- decays, where the pion pair comes from the S-wave resonance f_0(X). The Breit-Wigner formula for the f_0(500) and f_0(1500) resonances and the Flatt′e model for the f_0(980) resonance are adopted to parameterize the time-like scalar form factors in the two-pion distribution amplitudes. As a comparison, Bugg's model is also used for the wide f_0(500) in this work. For decay rates, we found the following PQCD predictions:(a)-B(B_s~0 →ηc(2S)f_0(X)[π~+π~-]s)= 2.67_(-1.08)~(+1.78) ×10~(-5) when the contributions from f_0(980) and f_0(1500) are all taken into account;(b)B(B~0→η-c(2S)f_0(500)[π~+π~-]s) = 1.40_(-0.56)~(+0.92) ×10~(-6) in the Breit-Wigner model and 1.53_(-0.61)~(+0.97) ×10~(-6) in Bugg's model.     

Study of the production of Λ_b~0 band ~0 hadrons in pp collisions and first measurement of the Λ_b~0→J/ψpK~- branching fraction

The product of the A_b~0(B~0) differential production cross-section and the branching fraction of the decay A_b~0→J/ψpK~-(B~0→J/ψK~*(892)~0) is measured as a function of the beauty hadron transverse momentum,p_T,and rapidity,y.The kinematic region of the measurements is p_T 20 GeV/c and 2.0y4.5.The measurements use a data sample corresponding to an integrated luminosity of 3fb~(-1) collected by the LHCb detector in pp collisions at centre-of-mass energies s~(1/2)=7 TeV in 2011 and s~(1/2)= 8TeV in 2012.Based on previous LHCb results of the fragmentation fraction ratio,f_∧_b~0/f_d,the branching fraction of the decay ∧_b~0→J/ψpK~- is measured to be B(∧_b~0→J/ψpK~-)=(3.17±0.04±0.07±0.34_(-0.28)~(+0.45)×10~(-4)where the first uncertainty is statistical,the second is systematic,the third is due to the uncertainty on the branching fraction of the decay B~0→J/ψK~*(892)~0,and the fourth is due to the knowledge of f_∧_b~0/f_d.The sum of the asymmetries in the production and decay between A_b and A_b~0 is also measured as a function of p_T and y.The previously published branching fraction of A_b~0→J/φpπ~-,relative to that of A_b~0→J/ψpK~-,is updated.The branching fractions of∧_b~0→P_c~+(→J/ψp)K~- are determined.     

Constraining the UT angle γ by CP violation parameters in B~0→π~+π~-

We calculate the tree and penguin amplitudes in the B~0→π~+π~-decay channel employing the perturbative QCD factorization approach. Using the amplitudes as input with the theoretical uncertainties sufficiently considered, we constrain the UT angle γ to 53°γ 70°, from the measurements of the CP violation parameters C_(π~+π~-) and S_(π~+π~-)in B~0→π~+π~-. The U-spin breaking effect between B~0→π~+π~-and B~0 s →K~+K~-is estimated to be around 30%.     

Search for ψ(4S) → ηJ/ψ in B~±→ ηJ/ψK~± and e~+e~-→ ηJ/ψ processes

We search for the ψ(4S) state in the B~±→ηJ/ψK~± and e~+e~-→ηJ/ψ processes based on the Belle measurements with the assumed mass M =(4230±8) MeV/c~2 and width Γ =(38±12) MeV. No significant signal is observed in the ηJ/ψ mass spectra. The 90% confidence level upper limit on the product branching fraction B(B~±→ψ(4S)K~±)B(ψ(4S)→ηJ/ψ) 6.8×10~(-6) is obtained in the B~±→ηJ/ψK~± decays. By assuming the partial width of ψ(4S)→e~+e~-to be 0.63 ke V, a branching fraction limitB(ψ(4S)→ηJ/ψ) 1.3% is obtained at the 90%confidence level in e~+e~-→ηJ/ψ, which is consistent with the theoretical prediction.     

Observation of e~+e~-→D_s~+■~((*)0)K~- and study of the P-wave D_s mesons

Studies of e~+e~→D_s~+■~((*)0)K~-and the P-wave charmed-strange mesons are performed based on an e~+e~-collision data sample corresponding to an integrated luminosity of 567 pb~(-1) collected with the BESIII detector at s~(1/2)=4.600 GeV. The processes of e~+e~-→D_s~+■~(*0)K~- and D_s~+■~0K~- are observed for the first time and are found to be dominated by the modes D_s~+D_(s1)(2536)~-and D_s~+D_(s2)~*(2573)~-, respectively. The Born cross sections are measured to be σ~B(e~+e~-→D_s~+■~(*0)K~-) =(10.1±2.3±0.8) pb and σ~B(e~+e~-→D_s~+■~0K~-) =(19.4±2.3± 1.6) pb, and the products of Born cross section and the decay branching fraction are measured to be σ~B(e~+e~-→D_s~+D_(s1)(2536)~-+c.c.)·B(D_(s1)(2536)~-→■~(*0)K~-)=(7.5±1.8±0.7) pb and σ~B(e~+e~-→D_s~+D_(s2)~*(2573)~-+ c.c.)·B(D_(s2)~*(2573)~-→■~0 K~-)=(19.7 ± 2.9 ±2.0) pb. For the D_(s1)(2536)~-and D_(s2)~*(2573)~-mesons, the masses and widths are measured to be M(D_(s1)(2536)~-)=(2537.7±0.5 ±3.1) MeV/c2, Γ(D_(s1)(2536)~-) =(1.7 ±1.2 ±0.6)MeV, and M(D_(s2)~*(2573)~-)=(2570.7±2.0 ±1.7) MeV/c~2, Γ(D_(s2)~*(2573)~-)=(17.2 ±3.6 ±1.1) MeV. The spin-parity of the D_(s2)~*(2573)~-meson is determined to be J~p= 2~+. In addition, the processes e~+e~-→D_s~+■~((*)0)K~-are searched for using the data samples taken at four(two) center-of-mass energies between 4.416(4.527) and 4.575 GeV, and upper limits at the 90% confidence level on the cross sections are determined.     

Looking for new physics via semi-leptonic and leptonic rare decays of D and D_s

It is well recognized that looking for new physics at lower energy colliders is a path which is complementary to high energy machines such as the LHC.Using the large volume of data collected by BESIII,we may have a unique opportunity to tackle this.In this paper we calculate the branching ratios of the semi-leptonic processes D_s~+ →K~+e~-e~+ and D_s~+ →K~+e~-μ~+,and the leptonic processes D~0→ e~-e~+ and D~0→ e~-μ~+,in the frameworks of the U(1) model,2HDM and unparticle model.It is found that both the U(1) model and 2HDM may influence the semi-leptonic decay rates,but only the U(1) model offers substantial contributions to the pure leptonic decays,and the resultant branching ratio of D~0→e~-μ~+ can be as large as 10~(-7)~10~(-8).This might be observed at the future super τ-charm factory.     

S-wave contributions to ■→(D~0,■)π~+π~- in the perturbative QCD framework

■→(D~0,■)π+π-is induced by the b→c■s/b→u■s transitions,which can interfere if a CP-eigenstate DCP is formed.The interference contribution is sensitive to the CKM angle y.In this work,we study the S-wave π+π-contributions to the process in the perturbative QCD factorization.In the factorization framework,we adopt twomeson light-cone distribution amplitudes,whose normalization is parametrized by the S-wave time-like two-pion form factor with resonance contributions from f_0(500),f_0(980),f_0(1500),f_0(1790).We find that the branching ratio of ■→(D~0,■)(π~+π~-)S is of the order of 10~(-6),and that significant interference exists in ■→D_(CP)(π+π-)S.Future measurement could not only provide useful constraints on the CKM angle y,but would also be helpful for exploring the multi-body decay mechanism of heavy mesons.     

Study of the a_1(1260) resonance in the γp→π~+π~+π~-n reaction

Within an effective Lagrangian approach and resonance model, we study the γp→a_1(1260)~+n andγp→π~+π~+π~-n reactions via the π-exchange mechanism. For the γp→π~+π~+π~-n reaction, we perform a calculation of the differential and total cross-sections by considering the contributions of the a1(1260) intermediate resonance decaying into per and then into π~+π~+π~-. Besides,the non-resonance process is also considered. With a lower mass of a1(1260), the experimental data for the invariant π~+π~+π~-mass distributions can be fairly well reproduced. For theγp→a_1(1260)~+n reaction, with the model parameters, the total cross-section is of the order of 10 μb at the photon beam energy Eγ~2.5 GeV. It is expected that the model calculations in this work could be tested by future experiments.     

Search for the doubly heavy baryons Ω_(bc)~0 and Ξ_(bc)~0 decaying to Λ_c~+π~- and Ξ_c~+π~-

The first search for the doubly heavy Ω_(bc)~0 baryon and a search for the Ξ_(bc)~0 baryon are performed using pp collision data collected via the LHCb experiment from 2016 to 2018 at a centre-of-mass energy of 13 TeV,corresponding to an integrated luminosity of 5.2 fb~(-1).The baryons are reconstructed via their decays to ∧_c~+π~-andΞ_c~+π~-.No significant excess is found for invariant masses between 6700 and 7300 MeV/c2,in a rapidity range from2.0 to 4.5 and a transverse momentum range from 2 to 20 MeV/c.Upper limits are set on the ratio of the Ω_(bc)~0 andΞ_(bc)~0 production cross-section times the branching fraction to ∧_c~+π~-(Ξ_c~+π~-) relative to that of the ∧_b~0(Ξ_b~0) baryon,for different lifetime hypotheses,at 95% confidence level.The upper limits range from 0.5×10~(-4) to 2.5×10~(-4) for theΩ_(bc)~0→∧_c~+π~-(Ξ_(bc)~0→∧_c~+π~-) decay,and from 1.4×10~(-3) to 6.9×10~(-3) for the Ω_(bc)~0→Ξ_c~+π~-(Ξ_(bc)~0→Ξ_c~+π~-) decay,depending on the considered mass and lifetime of the Ω_(bc)~0(Ξ_(bc)~0) baryon.     

The radiative decay D~0→K~(*0)γ with vector meson dominance

Motivated by the experimental measurements of D~0 radiative decay modes, we have proposed a model to study the D~0→K~(*0)γ decay, by establishing a link with D~0→K~(*0) V(V = ρ~0, ω) decays through the vector meson dominance hypothesis. In order to do this properly, we have used the Lagrangians from the local hidden gauge symmetry approach to account for V γ conversion. As a result, we have found the branching ratio B[D~0→K~(*0)γ]=(1.55-3.44)×10~(-4), which is in fair agreement with the experimental values reported by the Belle and Ba Bar collaborations.     

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.     

Helicity Amplitude Analysis of Z_c(3900)~± in e~+e~- →π~+π~-J/ψ

It is crucial to determine the spin and parity(J~P) of Z_c(3900)~± for understanding its structure.We perform a helicity amplitude analysis on Z_c(3900)~± in the process e~+e~-→π~+π~-J/φ with the hypotheses J~P= 0~-,1~+,1~-,2~+ and 2~-.To estimate the significance of J~P = 1~+ over other hypotheses,we perform a Monte Carlo simulation study,and we also discuss the prospect of measuring the spin parity in the future experiment with a large data sample.     

The Three-Pion Decays of the a_1(1260)

We investigate the decay of a_1~+(1260) →π~+π~+π~-with the assumption that the a_1(1260) is dynamically generated from the coupled channel ρπ and KK~*interactions. In addition to the tree level diagrams that proceed via a_1~+(1260) →ρ~0π~+→π~+π~+π~-, we take into account also the final state interactions of ππ→ππ and KK →ππ. We calculate the invariant π~+π~-mass distribution and also the total decay width of a_1~+(1260) →π~+π~+π~-as a function of the mass of a_1(1260). The calculated total decay width of a_1(1260) is significantly different from other model calculations and tied to the dynamical nature of the a_1(1260) resonance. The future experimental observations could test of model calculations and would provide vary valuable information on the relevance of the ρπ component in the a_1(1260) wave function.     

A family of double-beauty tetraquarks: Axial-vector state ■

The spectroscopic parameters and decay channels of the axial-vector tetraquark ■(in what follows,■ are explored using the quantum chromodynamics(QCD) sum rule method.The mass and coupling of this state are calculated using two-point sum rules by taking into account various vacuum condensates,up to 10 dimensions.Our prediction for the mass of this state m=(10215±250) MeV confirms that it is stable with respect to strong and electromagnetic decays and can dissociate to conventional mesons only via weak transformations.We investigate the dominant semileptonic ■ and nonleptonic ■ decays of ■.In these processes,■ is a scalar tetraquark ■ built of a color-triplet diquark and an antidiquark,whereas M is one of the vector mesons ρ~-,K~*(892),D~*(2010)~-,and D_s~(*-).To calculate the partial widths of these decays,we use the QCD three-point sum rule approach and evaluate the weak transition form factors G_i(i=0,1,2,3),which govern these processes.The full width Γ_(full)=(12.9±2.1) × 10~(-8) MeV and the mean lifetime τ=5.1+_(-0.71) ~(+0.99) fs of the tetraquark ■ are computed using the aforementioned weak decays.The obtained information about the parameters of ■ and ■ is useful for experimental investigations of these double-heavy exotic mesons.     

The B→πlv_l semileptonic decay within the LCSR approach under heavy quark effective field theory

The heavy quark effective field theory(HQEFT) provides an effective way to deal with heavy meson decays.In this paper,we adopt two different correlators to derive the light-cone sum rules(LCSR) for the B→π transition form factors(TFFs) in the framework of HQEFT.We label the two LCSR results as LCSR-u and LCSR-R,which stand for the conventional correlator and the right-handed correlator.We observe that the correlation parameter |ρRU| for the branching ratio B(B→πlv_l) is～0.85,implying a consistency of LCSRs with the other correlators.Furthermore,we obtain |V_(ub)|_(LCSR-u)=(3.45_(-0.20)~(+0.28)±0.13_(exp))×10~(-3) and |V_(ub)|_(LCSR-R)=(3.38_(-0.16)~(+0.22)±0.12_(exp))×10~(-3).We also obtain R_π|_(LCSR-u)=0.68_(-0.09)~(+0.10) and R_π|_(LCSR-R)=0.65_(-0.11)~(+0.13),both of which agree with the lattice QCD predictions.Thus,HQEFT provides a useful framework for studying B meson decays.Moreover,by using the right-handed correlator,the twist-2 terms are dominant in TFF f~+(q~2),as their contribution is over～97% in the whole q~2 region,while the large twist-3 uncertainty of the conventional correlator is greatly suppressed.Hence,the LCSR-R predictions can be used to test the properties of the various models for the pion twist-2 distribution amplitudes.