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.     

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.     

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.     

Analysis of the coupling constants g_(a_0ηπ~0 )and g_(a_0η'π~0) with light-cone QCD sum rules

Abstract In this article, we take the point of view that the light scalar meson a_0(980) is a conventional qq state, and calculate the coupling constants g_(a_0ηπ~0) and g_(a_0η'π~0) with the light-cone QCD sum rules. The central value of the coupling constant g_(a_0ηπ~0) is consistent with that extracted from the radiative decay φ(1020) → a_0(980)γ→ηπ~oγ. The central value and lower bound of the decay width Γ_(α_0→ηπ~0) = 127_(-48)~(+84) MeV are compatible with the experimental data of the total decay width Γ_(α_0(980))= (50-100) MeV from the Particle Data Group with a very model dependent estimation (the decay width can be much larger), while the upper bound is too large. We give a possible explanation for the discrepancy between the theoretical calculation and experimental data.     

Study of the rare decay J/ψ→e~+e~-φ

We study the decay process of J/ψ→e~+e~-φ where the relatively clean electromagnetic(EM) transitions appear at leading order at tree level while the hadronic contributions only emerge via hadronic loop transitions. We include the low-lying scalar f_0(980) and pseudoscalar η/η as the dominant contributions in the evaluation of the hadronic loop contributions. It is found that the hadronic effects are negligible compared with the EM contributions.The decay width of J/ψ→e~+e~-φ is determined to be about 2.12 × 10~(-6) ke V if there is no other leading mechanism contributing. This result will be tested by the BESIII experiment with a large J/ψ data sample.     

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.     

Study ao（980）-f0（980） mixing in charmonium decays

In this proceeding, we propose to directly measure the a0^0（980）-f0 （980） mixing in J/ψ→φf0（980）→φa0^0（980） and Xc1→π^0a0^0（980） →π^0f0（980） with the upgraded Beijing Electron Positron Collider（BEPCII） with BESIII detector. We show that a narrow peak of about 8 MeV will be produced by the a0^0（980）-f0（980） mixing, and the predominant feature makes it standing out from the background contributions. The predicted branching ratios for these two reactions are both expected to be about O（10^-6）, which is unambiguously accessible with 10^9 J/ψ and 3 × 10^8 Xc1 at BESⅢ.     

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.     

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.     

KLOE results on light mesons

The KLOE collaboration has recently published new results concerning scalar and pseudoscalar mesons.Here the φ → a 0 （980）γ → ηπ 0 γ decay analysis and the search for the φ → K 0 K 0 γ decay are discussed,together with the η → π ＋ π-e ＋ edecay measurements annd the new results for the pseudoscalar mixing angle and gluonium content of the η’ meson.     

KLOE results on light mesons

The KLOE collaboration has recently published new results concerning scalar and pseudoscalar mesons.Here the φ→ a 0 (980)γ→ηπ 0 γ decay analysis and the search for the φ→ K 0 K 0 γ decay are discussed,together with the η→π + π-e + edecay measurements annd the new results for the pseudoscalar mixing angle and gluonium content of the η’ meson.     

Study a0(980)-f0(980)mixing in charmonium decays

In this proceeding,we propose to directly measure the a00(980)-f0(980)mixing in J/ψ→φ f0(980)φa00(980)and χc1 →π0a00(980)→π0f0(980)with the upgraded Beijing Electron Positron Collider(BEPCII)with BESⅢ detector.We show that a narrow peak of about 8 MeV will be produced by the a00(980)-f0(980)mixing,and the predominant feature makes it standing out from the background contributions.The predicted branching ratios for these two reactions are both expected to be about O(10-6),which is unambiguously accessible with109 J/ψ and 3 × 108 χc1 at BESⅢ.     

Further insights into the “ρπ puzzle”

Based on a systematic investigation of J/ψ(ψ) → VP,where V and P stand for light vector and pseudoscalar mesons,we identify the role played by the electromagnetic(EM) transitions and intermediate meson loop transitions,which are essential ingredients for understanding the J/ψ and ψ couplings to VP.We show that on the one hand,the EM transitions have relatively larger interferences in ψ→ρπ and K*K+c.c.as explicitly shown by vector meson dominance(VMD).On the other hand,the strong decay of ψ receives relatively larger destructive interferences from the intermediate meson loop transitions.By identifying these mechanisms in an overall study of J/ψ(ψ)→VP,we provide a coherent understanding of the so-called "ρπ puzzle".     

Probing new physics in B → J/ψπ~0 decay

We calculate the branching ratio of B → J/ψπ0 with a mixed formalism that combines the QCDimproved factorization and the perturbative QCD approaches.The result is consistent with experimental data.The quite small penguin contribution in B → J/ψπ0 decay can be calculated with this method.We suggest two methods to extract the weak phase β.One is through the dependence of the mixing induced CP asymmetry SJ/ψπ0 on the weak phase β,the other is from the relation of the total asymmetry ACP with the weak phase β.Our results show that the deviation ΔSJ/ψπ0 of the mixing induced CP asymmetry from sin（-2β） is of O（10-3） and has much less uncertainty.The above O（10-3） deviation can provide a good reference for identifying new physics.     

Cross sections for inelastic 2-to-2 meson-meson scattering in hadronic matter

With quark-antiquark annihilation and creation in the first Born approximation, we study the reactions:K■→K■~*,K■→K~*■, πK→πK~*, πK→ρK, ππ→ K■~*, ππ→K~*■,ππ→K~*■~*,πρ→K■, πρ→K~*■~*,ρρ→K~*■~*, K■~*→ρρ, and K~*■→pp. Unpolarized cross sections for the reactions are obtained from transition amplitudes that are composed of mesonic quark-antiquark relative-motion wave functions and the transition potential for quark-antiquark annihilation and creation. Using a quark-antiquark potential that is equivalent to the transition potential, we prove that the total spin of the two final mesons may not be equal to the total spin of the two initial mesons. Based on flavor matrix elements, cross sections for some isospin channels of reactions can be obtained from other isospin channels of the reactions. Remarkable temperature dependence of the cross sections was observed.     

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.     

Recent results on light hadron spectroscopy from BES Ⅱ

We reported the observation of Y(2175) in φf0(980) mass spectrum in J/ψ→ηφf0(980) with f0(980)→π+π- and the observation of a broad 1-- resonance of K+K-mass in J/ψ→K+K-π0. The results from the partial wave analyses of Jψ→γπ+π- and γπ0π0, as well as J/ψ→pK-∧. are also presented.     

Study on the Effects of the Light CP-odd Higgs via the Leptonic Decays of Pseudoscalar Mesons

To explain the anomalously large decay rate of Σ+→ p+μ+μ- , it was proposed that a new mechanism where a light CP-odd pseudoscalar boson of mA10 = 214.3 MeV makes a crucial contribution. Later, some authors have studied the transition π0→e+e- and Υ→γA10 in terms of the same mechanism and their result indicates that with the suggested mass one cannot fit the data. This discrepancy might be caused by experimental error of Σ+→p+μ+μ- because there were only a few events. Whether the mechanism is a reasonable one motivates us to investigate the transitions π0→e+e-; η(η′) →μ+μ- ; ηc→μ+μ- ;ηb→τ+τ- within the same framework. It is noted that for π0→e+e-, the standard model (SM) prediction is smaller than the data, whereas the experimental central value of η→μ+μ- is also above the SM prediction. It means that there should be extra contributions from other mechanisms and the contribution of A10 may be a possible one. Theoretically calculating the branching ratios of the concerned modes, we would check if we can obtain a universal mass for A10 which reconcile the theoretical predictions and data for all the modes. Unfortunately, we find that it is impossible to have such a mass with the same coupling |ge|. Therefore we conclude that the phenomenology does not favor such a light A10 , even though a small window is still open.     

Helicity Amplitude Analysis of ηc Decays into Hyperon-Antihyperon Pairst

The helicity amplitudes for the processes of e^＋e^- →J/ψ→γηc→γYY（Y： hyperon） are presented, together with the joint angular distributions for ηc decays into ∧∧,∑^0 ∑^0, and [1]-[1]＋. The sensitivities to measure the hyperon decay parameters in these decays are evaluated based on the helicity amplitudes. The prospects to test the Bell inequality in experiment using the decay of ηc→∧∧ are discussed.     

Revisiting the determining fraction of glueball component in f_0 mesons via radiative decays of J/ψ

QCD theory predicts the existence of glueballs,but so far all experimental endeavors have failed to identify any such states.To remedy this discrepancy between QCD,which has proven to be a successful theory for strong interactions,and the failure of experimental searches for glueballs,one is tempted to accept the promising interpretation that the glueballs mix with regular qq states of the same quantum numbers.The lattice estimate of the masses of pure 0~(++) glueballs ranges from 1 to 2 GeV,which is the region of the f_0 family.Thus many authors suggest that the f_0 mesonic series is an ideal place to study possible mixtures of glueballs and qq.In this paper,following the strategy proposed by Close,Farrar and Li,we try to determine the fraction of glueball components in f_0 mesons using the measured mass spectra and the branching ratios of J/ψ radiative decays into f_0 mesons.Since the pioneering papers by Close et al.,more than 20 years have elapsed and more accurate measurements have been done by several experimental collaborations,so it is time to revisit this interesting topic using new data.We suppose f_0(500) and f_0(980) to be pure quark states,while for f_0(1370),f_0(1500) and f_0(1710),to fit both the experimental data of J/ψ radiative decay and their mass spectra,glueball components are needed.Moreover,the mass of the pure 0~(++) glueball is phenomenologically determined.