Extraction of the CKM phase γ from the charmless two-body B meson decays

Using all experimentally measured charmless B → PP, PV decay modes, where P(V) denotes a light pseudoscalar(vector) meson, we extract the CKM angle γ by a global fit. All hadronic parameters are determined from the experimental data, such that the approach is least model dependent. The contributions of the various decay modes are classified by the topological weak Feynman diagram amplitudes, which are determined by the global fit.To improve the precision of the approach, we consider the flavor SU(3) breaking effects of the topological diagram amplitudes of the decay modes by including the form factors and decay constants. The fit result for the CKM angle γ is( 69.8 ± 2.1 ± 0.9)°. It is consistent with the current world average values but has a smaller uncertainty.     

Measuring D~0-~0mixing in D→f_0(980)K~* and more

We investigate the D0-0 mixing through the doubly Cabibbo suppressed (DCS) channel D0 →f0(980)K0 and its charge conjugate channel, in which the K0 meson is reconstructed in both K π- and KSπ0 final state. Although the decay D0 →f0(980)K* has a small branching ratio, the final state mesons are relatively easy to identify. The f0(980) meson can be replaced by the S-wave π π- state, or a longitudinally polarized vector meson ρ0. 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.     

B_s → f_0 (980) Transition Form Factors Within the k_T Factorization Approach

In the paper, we apply the kT factorization approach to deal with the Bs → f0 (980) transition form factors in the large recoil regions, i.e. the small q 2 regions. For the purpose, we adopt the B-meson wave-functions ΨB , ΨB and δ that include the three-Fock states contributions to do our discussion. Although the scalar meson f0 (980) is widely perceived as the 4-quark bound state (scenario 2), but the distribution amplitudes of 4-quark states are still unknown to us, so we adopt 2-quark model (scenario 1) for scalar meson f0 (980) in our discussion. By varying the B-meson wave-function parameters within their reasonable regions, we obtain F0(0) = F+(0) = 0.20 ± 0.02, FT(0) = 0.24 ± 0.02. Our present results for these form factors are consistent with the light-cone sum rule results obtained in the literature.     

Axion-Like Particles and the Higgs Decays h→PZ and h→Pe~+e~-

Axion-like particles(ALPs)are often defined as relatively light pseudoscalar particles and appear in many extensions of the Standard Model.Taking into account constraints on the free parameters from existing searches and explaining the g-2 deviation,we consider the contributions of ALPs with mass in the range of 1.5GeVm_am_h-m_Z to the exclusive Higgs decays h→PZ and h→Pe~+e~-with P being the pseudoscalar mesonsπ~0,η,η',η_c andη_b in a model-independent approach.We find that,in most of the parameter space range,the contributions of ALP to these decay-processes are ver.y small,while in the case of the ALP mass ma approximatel.y equaling the meson mass m_P,the contributions are significantly large.     

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.     

Pure annihilation decays of B_s~0→a_0~+a_0~- and B_d~0→K_0~(*+)K_0~(*-) in the PQCD approach

We study the CP-averaged branching fractions and the CP-violating asymmetries in the pure annihilation decays ofB _s~0→a_0~+a _0~-andB _d~0→K_0~(*+)K_0~(*-),where a_0[K_0~*]denotes the scalar a_0(980) and a_0(1450)[K_0~*(800)(ork)and K_0~*(1430)],with the perturbative QCD factorization approach under the assumption of two-quark structure for the a_0and K_0~*states.The numerical results show that the branching ratios of theB _d~0→K_0~(*+)K_0~(*-)decays are in the order of 10~(-6),while the decay rates of theB_s~0→a_0~+a _0~-modes are in the order of 10~(-5).In light of the measured modes with the same quark components in the pseudoscalar sector,namely,B _d~0→K~+K~-and B_s~0→p p~(+-),the predictions for the considered decay modes in this work are expected to be measured at the Large Hadron Collider beauty and/or Belle-Ⅱ experiments in the (near) future.Meanwhile,it is of great interest to find that the twist-3 distribution amplitudes φ~S and φ~T with inclusion of the Gegenbauer polynomials for the scalar a_0(1450) and K_0~*(1430)states in scenario2 contribute slightly to the branching ratios while significantly to the CP violations in the B_d~0→K_0~*(14 30)~+K_0*(14 30)~-and B_s~0→a_0(1450)~+a_0(1450)~-decays,which indicates that,compared to the asymptotic φ~Sand φ~T,these Gegenbauer polynomials could change the strong phases evidently in these pure annihilation decay channels.These predictions await for the future confirmation experimentally,which could further provide useful information to help explore the inner structure of the scalars and shed light on the annihilation decay mechanism.     

Study of the CKM angle γ sensitivity using flavor untagged B_s~0→D~((*)0)φ decays

A sensitivity study on the measurement of the CKM angle y from B_S~0→D~((*)0)φ decays is conducted using the D-meson reconstructed in the quasi flavour-specific modes Kπ,K3π,and Kππ~0,as well as CP-eigenstate modes KK and ππ,where the notation D~0 corresponds to a D~0 or D~0 meson.The LHCb experiment is presented as a use case.A statistical uncertainty of approximately 8°-19°can be achieved with the pp collision data collected in the LHCb experiment from 2011 to 2018.The sensitivity to y should be of the order 3°-8° after accumulating 23 fb~(-1) of pp collision data by 2025,whereas it is expected to improve further by 300 fb~(-1) by the second half of the 2030 decade.The accuracy is dependent on the strong parameters r_B~((*)) and δ_B~((*)),which together with γdescribe the interference between the leading amplitudes of the B_S~0→D~((*)0)φ decays.     

Study of ■ decay parameter in J/ψ→Λ■ decay

The helicity amplitudes for J/ψ→Λ■ and the relevant background decays are presented for measuring the ■ decay parameter α (■→π ) in J/ψ→Λ■. The Monte Carlo (MC) simulations based on the helicity amplitudes information are carried out. The likelihood fit method to determine the ■ decay parameter is presented. Based on the MC generated sample, the sensitivity of the measurement for α has been estimated, which shows that the J/ψ→Λ■ channel can be used to measure the ■ decay parameter α (■→π ) well.     

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.     

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.     

D~0-~0 mixing sensitivity estimation at Belle II in wrong-sign decays D~0→K~+π~-π~0 via time-dependent amplitude analysis

The sensitivity of the D~0-~0 mixing parameters x and y is estimated in the wrong-sign decay D~0→K~+π~-π~0 by time-dependent amplitude analysis. The resolution of the D~0 lifetime is essential in time-dependent Dalitz analyses. The Belle II detector, which aims to collect a total integrated luminosity of 50 ab~(-1) of data, has σ = 140 fs in Monte Carlo studies, a factor of two improvement over that of Belle and Ba Bar, so the produced Dalitz signal Monte Carlo samples are smeared with this resolution. Then a time-dependent Dalitz plot fitting is performed on these smeared samples, and the sensitivity of D~0-~0mixing parameters are σ_x = 0.057% and σ_y = 0.049%. These are about an order of magnitude improvement on current experimental results, without considering background effects.     

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.     

Vector meson rescattering effect in understanding the threshold enhancement observed in J/ψ→γp

We propose one possible mechanism,i.e.,the vector meson （VV） rescattering effects,to interpret the near threshold narrow enhancement observed in J/ψ → γpp.The estimate indicates that these effects can give sizeable contributions to this channel,and a destructive interference between different rescattering amplitudes is required to reproduce the line shape of the data.     

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.     

The Role of α_1(1260) in π~-p→α_1~-(1260)p and π~-p → π~-ρ~0p Reactions Near Threshold

We report on a theoretical study of the π~-ρ→α1(1260)p and π~-ρ→π~-ρ~0p reactions near threshold within an effective Lagrangian approach.The production process is described by t-channel ρ~0 meson exchange.For the π~-ρ→π~- ρ~0p reaction,the final π~-ρ~0 results from the decay of the α1(1260) resonance,which is assumed as a dynamically generated state from the K* K and ρπ coupled channel interactions.We calculate the total cross section of the π~-ρ→α1(1260)p reaction.It is shown that,with the coupling constant of the α1(1260) to ρπ channel obtained from the chiral unitary theory and a cut off parameter Δρ~1.5 GeV in the form factors,the experimental measurement can be reproduced.Furthermore,the total and differential cross sections of π~p→α1(1260)p→π~ρ~0p reaction are evaluated,and it is expected that our model calculations can be tested by future experiments.These reactions are important for the study of the α1(1260) resonance and would provide further constraints on the properties of the α1(1260) state.     

On the Mixed Propagator Approach to ρ-ω Mixing

The mixed propagator (MP) approach to ρ-ω mixing is discussed. It is found that under the pole-approximation assumption the results of MP approach is not compatible both with the effective Lagrangian theory andwith the experiment measurement criterion. To overcome these inconsistent, we propose a new MP approach in whichthe physical states of ρ and ω are determined by the requirement of experimental measurement to meson resonance. Interms of this new MP approach, the EM pion form factor Fπ and form factors of ρo →π0γ and of ω→πo γ are derived.The results of Fπ are in good agreement with data. The form factor of ρo →π0γ exhibits a hidden charge-asymmetryenhancement effect which agrees with the prediction of the effective Lagrangian theory.     

Covariant Helicity Amplitude Analysis for J／ψ→γPP

Covariant helicity amplitude analysis for the process of J/ψ→γPP is discussed starting from the Smatrix elements of decay process,we deduce the formulae of helicity coupling amplitudes for two-body decay process,These formulae are used to analyze intermediate resonance states in the process of J/ψ decay to γππ,γKK,γηη′     

Study of Λ decay parameter in J/ψ→ΛΛ decay

The helicity amplitudes for J/ψ→ΛΛ and the relevant background decays are presented for measuring the Λ decay parameter α₊(Λ→pπ⁺) in J/ψ→ΛΛ . The Monte Carlo (MC) simulations based on the helicity amplitudes information are carried out. The likelihood fit method to determine the Λ decay parameter is presented. Based on the MC generated sample, the sensitivity of the measurement for α₊ has been estimated, which shows that the J/ψ→ΛΛ channel can be used to measure the Λ decay parameter α₊(Λ→pπ⁺) well.     

Constraints on the First Generation Scalar Leptoquarks

Inspired by the CMS excess in eejj and evjj channels and possible interpretation using the first generation scalar leptoquarks(SLQs),we consider their contributions to non-standard neutrino interaction and the pion meson Ieptonic decay π→lv.Compared with the relevant experimental data,the constraints on the Brst generation SLQs are obtained.Their corrections to the anomalous magnetic moment a_μ are further calculated and the numerical results show that it is possible to explain the deviation from its standard model prediction.     

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.