Study of the B_c→B_sπ decay with the perturbative QCD approach

The Bc→Bsπ decay is studied with the perturbative QCD approach. Three types of wave functions for Bsmeson are considered.The transition form factor FBc→Bs0(0) and the branching ratio Br(Bc→Bsπ)aresensitivetothemodelofthe Bsmeson wave functions.With appropriate inputs, our estimate on Br(Bc→Bsπ) is comparable with the recent LHCb measurement. A clear signal of Bc→Bsπ decay should be easily observed at the Large Hadron Collider.     

Study of B c → D π in the perturbative QCD approach

We investigate the branching ratios and direct CP-asymmetries of the and decays in the PQCD approach. All the diagrams with emission topology or annihilation topology are calculated strictly. A branching ratio of 10^-6 and 10^-7 for and decay is predicted, respectively. Because of the different weak phase and strong phase from penguin operator and two kinds of tree operator contributions, we predict a possible large direct CP-violation: and when γ = 55°, which can be tested in the coming LHC. PACS: 13.25.Hw, 12.38.Bx     

“Massive” perturbative QCD, Regular in the IR limit

The goal of the research is to devise a modification of the perturbative QCD (pQCD) that should be regular in the low-energy region and could serve as a practical means for the analysis of data below 1 GeV down to the IR limit. Recent observation of the four-loop pQCD series “blow-up” in the region below 1 GeV for the Bjorken Sum Rule gave an impetus to this attempt. The proposed “massive” analytic pQCD has two sources. It can be treated as the common logarithmic pQCD with only one parameter added, the effective “glueball mass” m _gl ? 1 GeV, serving as an IR regulator. At the same time, it looks like a modification of Analytic Perturbation Theory (APT) comprising nonpower perturbative expansion that makes it compatible with linear integral transformations. Figuratively (with minor reservations), the proposed MAPT differs from the minimal APT by simple ansatz Q ² → Q ² + m _g1 ² .     

On the applicability of finite order perturbative QCD calculations of jet rates ine + e − annihilation

We have studied the measurement of α _s using exact second order QCD matrix element calculations of jet rates ine ⁺ e ^?→hadrons. We investigate the dependence of α _s (M _Z ² ), measured by experiments at theZ ⁰ resonance, on the choice of renormalisation scale in terms of the functional form of the three-jet matrix element. We find that only a restricted domain of the jet resolution parametery _c , $\Lambda _{\overline {MS} } $ , and scale gives a perturbation series which is well-behaved to second order, and that this domain is different for the various jet algorithms in current use.     

Anatomy of the ρ resonance from lattice QCD at the physical point

We propose a strategy to access the qq component of the p resonance in lattice QCD. Through a mixed action formalism(overlap valence on domain wall sea), the energy of the qq component is derived at different valence quark masses, and shows a linear dependence on m_π~2. The slope is determined to be c_1 =0.505(3)GeV~(-1), from which the valence πρ sigma term is extracted to be σ_(πρ)~(val)= 9.82(6) MeV using the Feynman-Hellman theorem. At the physical pion mass, the mass of the qq component is interpolated to be m_ρ = 775.9±6.0±1.8 MeV, which is close to the p resonance mass. We also obtain the leptonic decay constant of the qq component to be f_ρ-=208.5±5.5±0.9 MeV, which can be compared with the experimental value f_ρ~(exp)≈221 MeV through the relation f_ρ~(exp)=(1/2)Zf_ρ±, with Z_ρ≈1.13 being the on-shell wavefunction renormalization of p owing to the ρ-π interaction. We emphasize that m_ρand f_ρ of the qq component, which are obtained for the first time from QCD, can be taken as the input parameters of p in effective field theory studies where p acts as a fundamental degree of freedom.     

Analysis of B_c → τν_τ at CEPC

Precise determination of the B_c →τν_τ branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element |V_(cb)|, and probing new physics models. In this paper, we discuss the potential of measuring the process B_c →τν_τ with τ decaying leptonically at the proposed Circular Electron Positron Collider(CEPC). We conclude that during the Z pole operation, the channel signal can achieve five-σ significance with～10~9 Z decays, and the signal strength accuracies for B_c →τν_τ can reach around 1% level at the nominal CEPC Z pole statistics of one trillion Z decays, assuming the total B_c →τν_τ yield is 3.6 × 10~6. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the b → cτν transition. If the total B_c yield can be determined to O(1%)level of accuracy in the future, these results also imply |V_(cb)| could be measured up to O(1%) level of accuracy.     

Analysis of Bc→τvτ at CEPC

Precise determination of the Bc → tvt branching ratio provides an advantageous opportunity for under-standing the electroweak structure of the Standard Model,me...     

Higher order perturbative QCD calculation of jet cross sections ine + e − annihilation

We present in detail the analytic calculation of the Sterman-Weinberg type 3-jet cross section to order α _s ² The fit to recent PLUTO data gives in the \({MS}\) scheme α _s which corresponds to Λ=0.24 GeV in the 1-loop approximation.     

First-principles calculations of the stibnite at the level of modified Becke–Johnson exchange potential

The demand for cheaper, nontoxic and earth-abundant materials as absorbing layer for solar cell is immensely needed to replace scarce, toxic and expensive one. In this regard, chalcogenide materials have considerably attracted the attention of a lot of researchers because of showing a great potential for different applications. Stibnite (Sb₂S₃), a chalcogenide binary material is considerably investigated for exploiting its potential for different energy technologies being a less toxic, abundantly available, stable and efficient, which are the fundamentals for sustainability as well as to realize the dream of green energy. In this study, theoretical calculations of the structural, electronic and optical properties of stibnite (Sb₂S₃) crystal structure are presented using the full potential (FP) linearized augmented plane wave (LAPW) framed within density functional theory (DFT). To incorporate the exchange-correlation part in the total energy functional, besides the local density approximation (LDA), Wu-Cohen parameterized generalized gradient approximation (WC-GGA), Perdew–Burke–Ernzerhof parameterized generalized gradient approximation (PBE-GGA), and Perdew–Burke–Ernzerhof generalized gradient approximation for solids and surfaces (PBEsol-GGA) are used for the calculations of the structural parameters, where the Trans-Blaha approach of the modified Becke–Johnson (TB-mBJ) potential is used to get more reliable results for the fundamental band gap energy value. These calculations are performed by involving spin-orbit coupling (SOC) contribution. Additionally, optical properties, such as imaginary and real parts of the dielectric function, optical conductivity, absorption coefficient, refractive index, reflectivity, and electron energy loss function are analyzed. Our first-principles calculations show that Wu-Cohen GGA (WC-GGA) reproduces results for lattice parameters comparable to the experimental measurements. The obtained results of the band gap energy and optical properties with TB-mBJ potential are also closer to the experimental data and, endorse its potentiality for the photovoltaics applications.     

Pure annihilation type D→PP(V) decays in the perturbative QCD approach

The annihilation type diagrams are di cult to calculate in any kind of model or method. Encouraged by the successful calculation of pure annihilation type B decays in the perturbative QCD factorization approach, we calculate the pure annihilation type D→PP(V) decays in the perturbative QCD approach based on the k_T factorization. Although the expansion parameter 1/m_D is not very small, our leading order numerical results agree with the existing experimental data for most channels. We expect more accurate observation from experiments, which can help us learn about the dynamics of D meson weak decays.     

Measurement of the leptonic branching ratios of the τ lepton

The leptonic branching ratios of the tau lepton have been determined from data collected by the OPAL detector in 1991 and 1992. From a sample of 27196 e⁺e^–+– candidates we find 7322 and 7941 candidates. Using efficiency and background estimates determined from a study of Monte Carlo events and control samples of data, the branching ratios =(18.14±0.20±0.28)% and =(17.48±0.18±0.23)% have been obtained. These new results have been combined with the published results for the 1990 OPAL data to yield the following branching ratios for data taken between 1990 and 1992:

B→(J/ψ,ηc)K decays in the perturbative QCD approach

In this paper, we calculated the B→(J/ψ,ηc)K decays in the perturbative QCD (pQCD) factoriza-tion approach with the inclusion of the partial next-to-leading order (NLO) contributions. With the inclusion of the significant enhancement from the NLO vertex corrections, the NLO pQCD predictions for the branching ra-tios agree with the data within 2σ errors: Br(B0→J/ψK0)=5.2+3.5-2.8×10-4,Br(B+→J/ψK+)=5.6+3.7-2.9×10-4,Br(B0→ηcK0)=5.5+2.3-2.0×10-4,Br(B+→ηcK+)=5.9+2.5-2.1×10-4.     

B→（J/ψ,η_c）K decays in the perturbative QCD approach

In this paper,we calculated the B →（J/ψ,ηc） K decays in the perturbative QCD（pQCD） factorization approach with the inclusion of the partial next-to-leading order（NLO） contributions. With the inclusion of the significant enhancement from the NLO vertex corrections,the NLO pQCD predictions for the branching ratios agree with the data within 2σ errors：Br（B0 → J/ψK0） = 5.2-＋32..58×10-4,Br（B＋ → J/ψK＋） = 5.6-＋32..79×10-4,Br（B0 →ηcK0） = 5.5-＋22..30 × 10-4,Br（B＋ →ηcK＋） = 5.9-＋22..51 × 10-4.