Semileptonic decays Bc→(ηc,J/Ψ)lv in the perturbative QCD approach

In this paper we study the semileptonic decays of B_c^-→(η_c,J/Ψ)l^-v_l. We first evaluate the B_c→(η_c,J/Ψ) transition form factors F₀(q²), F₊(q²), V(q²) and A_0,1,2(q²) by employing the pQCD factorization approach, and then we calculate the branching ratios for all considered semileptonic decays. Based on the numerical results and the phenomenological analysis, we find that: (a) the pQCD predictions for the values of the B_c→η_c and B_c→J/Ψ transition form factors agree well with those obtained by using other methods; (b) the pQCD predictions for the branching ratios of the considered decays are Br(B_c^-→η_c e^-v_e(μ^-v_μ)=(4.41_-1.09^+1.22)×10^-3, Br(B_c^-→η_cτ^-v_τ) =(1.37_-0.34^+0.37)×10^-3, Br(B_c^-→J/Ψ e^-v_e(μ^-v_μ)) =(10.03_-1.18^+1.33)×10^-3, and Br(B_c^-→J/Ψτ^-v_τ) =(2.92_-0.34^+0.40)×10^-3; and (c) we also define and calculate two ratios of the branching ratios R_ηc and R_J/Ψ, which will be tested by LHCb and the forthcoming Super-B experiments.     

J/ψ Inclusive Photon Spectrum at BESIII

With a 15M J/ψ inclusive Monte Carlo sample, the absolute branching fraction of J/ψ→γ\η' from the J/ψ inclusive photon spectrum is measured to be Br(J/ψ→γ\η')=(4.68±0.08±0.27)×10^-3, which is in good agreement with the input value. The J/ψ→γf_J(2220) is also searched for using the same sample. Under our assumptions, the statistical significances of J/ψ→γf_J(2220) are larger than 7\σ.     

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.     

Determination of J/φ Event Number via J/φ→μ+μ- and J/φ→ e+e- at BESIII

The decays of J/φ→μ⁺μ^- and J/φ→ e⁺e^- are studied by Monte-Carlo simulation, based on the Beijing Spectrometer (BES)Ⅲ offline software system. The methods of determination of the J/φ event number via J/φ→μ⁺μ^- and J/φ→ e⁺e^- are presented, respectively. These methods can be used to determine the J/φevent number for the coming BESⅢ J/φ data sample.     

由ψ(2S)→π+π－J/ψ道测量J/ψ轻子道衰变分支比

利用北京谱仪(BES)上取得的ψ(2S)数据,对ψ(2S)→π⁺π^－J/ψ,J/ψ→1⁺1^－和J/ψ→任意末态两个过程进行了细致的研究,得到J/ψ的轻子道衰变分支比为B(J/ψ→e⁺e^－)=(5.90±0.07±0.16)%和B(J/ψ→μ⁺μ^－)=(5.96±0.08±0.16)%,由此给出Be/Bμ的值为0.990±0.018±0.024.假定Be=Bμ,J/ψ的轻子道衰变分支比为B(J/ψ→1⁺1^－)=(5.93±0.05±0.16)%.上述结果可用来估计强相互作用耦合常数αs和QCD减除参数∧.     

J/ψ衰变中的ΛΛ,ΛΛγ和ΛΛπ0产生

利用北京正负电子对撞机(BEPC)上的北京谱仪(BES)收集的7.8×10⁶个J/ψ事例,测量得到J/ψ→ΛΛ,ΛΛγ和ΛΛπ⁰三个衰变道的分支比分别为Br(J/ψ→ΛΛ)=(l.08±0.06±0.24)×10^－3,Br(J/ψ→ΛΛγ)－4(90% CL),和Br(J/ψ→ΛΛπ⁰)=(2.3±0.7±0.8)×l0^－4; 第一个衰变道的角分布为dN dcosθ=N₀(1+αcos²0),α=0.52±0.33±0.13.     

北京谱仪上J/ψ→γπ0、γη、γη'→3γ衰变道的分支比测量

分析J/ψ衰变终态为三个光子的衰变道,测量得到了衰变道J/ψ→γπ⁰和J/ψ→γη’的分支比分别为Br(J/ψ→γπ⁰)=(4.6±1.1)×10^－5和Br(J/ψ→、η＇)=(4.12±0.82)×10^－3;相对分支比F(J/ψ→γη’)/F(J/ψ→γη)=4.79±0.85,在实验误差范围内与两个理论模型的预言都能一致.     

First evidence of ψ(2S)→Ω-Ω+

The decay ψ(2S)→Ω^-Ω⁺ is analyzed using 14×10⁶ ψ(2S) events recorded by the Beijing Spectrometer Ⅱ (BESⅡ) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ(2S)→Ω^-Ω⁺ to be 1.5×10⁴ at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω⁺ signal with a statistical signi cance of 3.1|σ. The branching fraction of ψ(2S)Ω⁺ is determined to be (4.80±1.56(stat)±1.30(sys))10⁵.     

J/ψ→π03(π+π－)分支比的测定

用BESⅠ的7.8×10⁶J/ψ数据更为精确地测定了J/ψ→π⁰3(π⁺π^－)和J/ψ→ω²(π⁺π^－)的分支比(Br(J/ψ→π⁰3(π⁺π^－))=(2.52±0.06±0.43)%,Br(J/ψ→π⁰3(π⁺π^－))=(1.31±0.09±0.21)%.同时对4π不变质量谱和ωππ不变质量谱进行研究分析,试图观察是否存在有兴趣的信号.     

Study of charmonium(-like) states via ISR at Belle

The cross sections for e⁺e－→π⁺π^－J/ψ, π⁺π^－ψ(2S), K⁺K^－J/ψ, DD, D⁰D^－+π⁺+c.c., D^*D+c.c., and D^*D^* are measured using data sample collected on or near the Υ(4S) resonance with the Belle detector at KEKB. A peak near 4.25GeV/c², corresponding to the so called Y(4260), is observed in π⁺π^－J/ψ final state. In addition, there is another cluster of events at around 4.05GeV/c². Two resonant structures are observed in the π⁺π^－ψ(2S) invariant mass distribution, one at 4361±9±9MeV/c² with a width of 74±15±10MeV/c², and another at 4664±11±5MeV/c² with a width of 48±15± 3MeV/c². The rich structures observed in all these final states indicate that our understanding of the vector charmonium states above the open charm threshold is still poor, let alone the other possible dynamics such as charmonium hybrids or final state re-scattering and so on.     

ψ(3770)→J/ψπ+π—强跃迁过程的首次观测

观测到ψ(3770)衰变到J/ψπ⁺π^—非DD末态迹象.利用工作在北京正负电子对撞机上的北京谱仪探测器在质心系能量3.773GeV附近获取的8.0±0.5pb^-1数据样本,共观测到6.8±3.0个ψ(3770)→J/ψπ⁺π^—事例.由此得到的分支比为BF(ψ(3770)→J/ψπ⁺π^—)=(0.59±0.26±0.16)%,其对应的分宽度为Γ(ψ(3770)→J/ψπ⁺π^—)=(139±61±41)keV.     

J/ψ→γγV(ρ,φ)衰变的实验研究

利用北京谱仪(BES)收集的7.8×10⁶ J/ψ事例,对J/ψ→γγV(ρ,φ)衰变道中的η(1430)共振态进行了分析.从J/ψ→γγρ衰变模式得到其质量及衰变宽度分别为1431±17MeV和88±28MeV,衰变分支比Br(J/ψ→γη(1430))Br(η(1430)→γρ)=(1.1±0.5±0.3)×10^－4;而从J/ψ→γγφ衰变模式得到其质量及衰变宽度分别为1424±15MeV和73±58MeV,衰变分支比Br(J/ψ→γη(1430))Br(η(1430)→γφ)=(2.0±1.0±0.6)×10^－4.     

Event generators for η/η' rare decays into π+π-l+l- and e+e-μ+μ-

Study of the rare and forbidden decays of η/η' offers a sensitive probe to test fundamental symmetries of quantum chromodynamics and search for new physics beyond the Standard Model. To study the rare decays of η/η' to π⁺π^-e⁺e^-, π⁺π^-μ⁺μ^- and e⁺e^-μ⁺μ^- at the BESⅢ detector, we developed several event generators based on the vector meson dominant model with finite-width corrections and the pseudoscalar mesons mixing theory. The various distributions from event generators are in good agreement with the theoretical predictions, which indicates that the event generators work very well after implemention in the BESⅢ Monte Carlo simulation package. In the BESⅢ physics analysis, the performance of the event generators will be improved in accordance with the distributions of different variables of η/η' from data and the improvement on the theoretical calculations.     

Fourth generation effects in Bs→π^-K^＋ decay

We study the effects of the fourth quark generation model in B_s → π^-K⁺ decay. Combining with the up-to-date experimental measurement for B(B_s → π^-K⁺) and A_cp^dir(B_s → π^-K⁺) by the CDF Collaboration, we derive the new bound of weak phase ø_bd, which are 0°< ø_bd <44°, 321°< ø_bd < 360° and 0°< ø_bd < 26°, 342°< ø_bd < 360° for m_t'=400 and 600 GeV respectively. In these regions, B(B_s → π^-K⁺) and A_cp^dir(B_s → π^-K⁺) consist with the current experimental data within errors.     

不等质量(1/2—1/2)或(1/2-1/2)电磁束缚系统的近似B.S.波函数

本文求解了不等质量(1/2—1/2)电磁束缚系统的Bethe-Salpeter方程. 给出了这类系统的近似B.S.波函数. 利用复合粒子量子场论的微扰展开, 在精确到O(α)的量级下, 计算了Ξ⁰→(Σ⁺μ^－)+ν_μ的衰变率和分支比, 结果是wΞ⁰→(Σ⁺μ^－)+ν_μ=1.12(1/秒)R=[wΞ⁰→(Σ⁺μ^－)+ν_μ]/[wΞ⁰→(Σ⁺μ^－)+ν_μ]≥4.7×10^－7. 类似地, 还讨论了Λ→(pμ^－)+ν_μ过程.     

Production of charmonium(like) states in e+e－ interactions

We present a search for new charmonium like states in e⁺e^－ annihilation using the initial-state radiation and the process e⁺e^－J/ψD^(*)D^(*). The analyses are based on a huge data sample recorded near the Υ(4s) resonance with the Belle detector at the KEKB e⁺e^－ asymmetric-energy collider.     

Analysis of Bs→φμ+μ- decay within supersymmetry

Motivated by the rst measurement on B(B_s→φμ⁺μ^-) by the CDF Collaboration, we study the supersymmetric e ects in semi-leptonic B_s→φμ⁺μ^- decay. In our evaluations, we analyze the dependences of the dimuon invariant mass spectrum and the forward-backward asymmetry on relevant supersymmetric couplings in the MSSM with and without R-parity. The analyses show that the new experimental upper limits of B(B_s→φμ⁺μ^-)from the LHCb Collaboration could further improve the bounds on sneutrino exchange couplings and (δ_LL^u)₂₃ as well as (δ_LL,RR^u)₂₃ mass insertion couplings. In addition, within the allowed ranges of relevant couplings under the constraints from B(B_s→φμ⁺μ^-), B(B→K^(*)μ⁺μ^-) and (B_s→φμ⁺μ^-), the dimuon forward-backward asymmetry and the di erential dimuon forward-backward asymmetry of B_s→φμ⁺μ^-are highly sensitive to the squark exchange contribution and the (δ_LL^u)₂₃ mass insertion contribution. The results obtained in this work will be very useful in searching for supersymmetric signals at the LHC.     

Pure annihilation type decays B0→Ds- K2+ and Bs→Da2 in perturbative QCD approach

We calculate the branching ratios of pure annihilation type decays B⁰→D_s^- K₂^*+ and B_s→Da₂ using the perturbative QCD approach based on k_T factorization. The branching ratios are predicted to be (60.6_{-16.5-10.4-2.1}^{+17.3+4.3+3.2} )× 10^-6 for B⁰→D_s^- K₂^*+, (1.1_-0.4-0.2-0.1^+0.4+0.1+0.1)×10^-6 for B_s→D⁰a₂⁰ and (2.3_-0.8-0.4-0.1^+0.8+0.2+0.1)×10^-6 for B_s→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 search of new physics signal.     

Evidence for e+e-→γχc1,2 at center-of-mass energies from 4.009 to 4.360 GeV

Using data samples collected at center-of-mass energies of √s=4.009, 4.230, 4.260, and 4.360 GeV with the BES0 detector operating at the BEPC/ collider, we perform a search for the process e⁺e^-→γχ_c,j (J =0, 1, 2) and find evidence for e⁺e^-→γχ_c1 and e⁺e^-→γχ_c2 with statistical significances of 3.0σ and 3.4σ, respectively. The Born cross sections σ^B(e⁺e^-→γχ_c,j), as well as their upper limits at the 90% con dence level (C.L.) are determined at each center-of-mass energy.     

Uncertainty study of DS-(D-)→γlν (l=e,μ) decays determined by wave function

Wave function is important for determining decay constants f_DS^- and f_D^-. Using the 5 types of D meson wave functions in the heavy quark limit, we studied the uncertainties of radiative pure-leptonic decays of D_S^-(D^-) mesons. The branching ratios are (1.025390—1.706812) × 10^-5 and (0.953498—1.576725) × 10^-6 for D_S^- and D^- decays, respectively, which are sensitive to the type of wave function.