Search for the rare decays W^(+)→D_(s)^(+)γ and Z→D^(0)γ at LHCb

A search for the rare decays W^(+)→D_(s)^(+)γ and Z→D0γis performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13TeV,corresponding to an integrated luminosity of 2.0fb−1.No significant signal is observed for either decay mode and upper limits on their branching fractions are set using W^(+)→D_(s)^(+)γ and Z→μ+μ−decays as normalization channels.The upper limits are 6.5×10^(−4) and 2.1×10^(−3) at 95% confidence level for the W^(+)→D_(s)^(+)γ and Z→D^(0)γ decay modes,respectively.This is the first reported search for the Z→D^(0)γ decay,while the upper limit on the W+→D+sγbranching fraction improves upon the previous best limit.

Prospects for searching the η→e^+e^- rare decay at the CSR

We study the possibility of searching the η→e＋e- rare decay on the Cooling Storage Ring （CSR） at Lanzhou. The main features of the proposed Internal Target Experiment （ITE） and External Target Facility （ETF） are included in the Monte Carlo simulation. Both the beam condition at the CSR and the major physics backgrounds are carefully taken into account. We conclude that the ITE is more suitable for such a study due to better detector acceptance and higher beam density. At the maximum designed luminosity （1034cm-2s-1 ）, η→e＋e- events can be collected every～400 seconds at the CSR. With a mass resolution of 1 MeV, the expected signal-to-background （S/B） ratio is around 1.

Rare decays B_(s,d)~0→e+e^- in a top quark two-Higgs-doublet model

In the framework of T2HDM, we calculated the new physics contributions involving neutral Higgs bosons to the branching ratios of ^-Bs,d^0→e^＋e^-（e= e,μ） decays. Comparing the theoretical predictions with the experimental upper-limits, we found that （a） The data of Br（^-Bs,d^0→e^＋e^-） give the upper bound on tanβ： tanβ≤22, while Br（^-Bs^0→e^＋e^-） give tanβ≤12 for fixed δ = 0^0, mH＋ = 350 CeV, mH^0 = 160 GeV, mh^0 = 115 GeV and mA^0 = 120 GeV; （b） A light neutral Higgs boson mass mho （mA^0） less than 50 GeV （120 GeV） is excluded by the data of branching ratios for ^-Bs,d^0→e^＋e^-（e = μ） decays with tanβ= 10; （c） The bounds on mh^0 and tanβ, or mA^0 and tanβ are strongly correlated： a smaller （larger） tanβ means a lighter （heavier） neutral Higgs boson.

Search for the rare decay B^(0)→J/ψФ

A search for the rare decay B^(0)→J/ψФis performed using Pp collision data collected with the LHCb dete-ctor at centre-of-mass energies of 7,8 and 13 TeV,corresponding to an integrated luminosity of9 fb.No significant signal of the decay is observed and an upper limitof 1.1x 10^(-7)at 90%confidence level is set on the branching fraction.

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 f0（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-φis determined to be about 2.12 × 10^-6 keV if there is no other leading mechanism contributing. This result will be tested by the BESIII experiment with a large J/ψ data sample.

Improved analysis of the rare decay processes of Λ_(b)

It is noted that in the new Particle Data Group(PDG) version the rare decays of the Λ_(b) baryon have been revised with more accuracy. The new results show that most of the existing theoretical results on the process Λ_(b)→Λ_(γ) Lgbare larger than those of experiments. With the improved higher-order light-cone distribution amplitudes of the Λ baryon, we reanalyze the process in the framework of light-cone quantum chromodynamics sum rules and the branching ratio is estimated to be Br (Λ_(b)→Λ_(γ))=(7.38-0.39+0.40)×10^(16), which is consistent with the new experimental result. Furthermore, another process Λ_(b)→Λl+l- is also analyzed in the same frame. The final branching ratio is calculated to be Br (Λ_(b)→Λl+l-)=1.20×10^(-6), which is in good accordance with the data from the PDG and other theoretical predictions.

Study of the rare decay J/ψ→2γ+hadrons at the BESIII

The two-photon radiative decay process J/ψ→2γ+hadrons was studied,and the main contribution processes,J/ψ→2γ+ggg and J/ψ→2γ+qˉq,were calculated.With the specific conditions at the BESIII,this rare decay process and the main background process e+e?→γγ+hadrons(qˉq)were investigated.The results show that the ratio of signal to background can reach 1.24 with optimized selection criteria at the BESIII.In addition,distributions of the signal and background are presented.All the results show that the signal is large enough to be experimentally measured.

Prospects for rare and forbidden hyperon decays at BESⅢ

The study of hyperon decays at the Beijing Electron Spectrometer Ⅲ （BESⅢ） is proposed to investigate the events of J/φ decay into hyperon pairs, which provide a pristine experimental environment at the Beijing Electron-Positron Collider Ⅱ. About 10^6-10^8 hyperons, i.e., ∧, ∑, ∈, and Ω, will be produced in the J/φ and φ（2S） decays with the proposed data samples at BESⅢ. Based on these samples, the measurement sensitivity of the branching fractions of the hyperon decays is in the range of 10^-5-10^-8. In addition, with the known center-of-mass energy and ＂tag technique＂, rare decays and decays with invisible final states can be probed.

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

It is well recognized that looking for new physics at lower energy colliders is a path wnmn is complemen- tary 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＋ → K＋e-e＋ and D＋ → K＋e-P-＋, and the leptonic processes D0→ e-e＋ and D0→ 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 DO → e- μ＋ can be as large as 10-7 - 10-8. This might be observed at the future super τ-charm factory.

Rare Higgs three body decay induced by top-Higgs FCNC coupling in the littlest Higgs model with T-parity

Motivated by the search for flavor-changing neutral current（FCNC） top quark decays at the LHC,we calculate the rare Higgs three body decay H→Wbc induced by top-Higgs FCNC coupling in the littlest Higgs model with T-parity（LHT）.We find that the branching ratio of H→Wbc in the LHT model can reach O（10^-7） in the allowed parameter space.

Investigation of rare semileptonic Bc→(Ds,d(*)μ+μ- decays with non-universal Z’ effect

We analyze different decay observables of semileptonic decays Bc→(Ds,d(*))μ+μ-,such as the branching ratio,forward-backward asymmetry,polarization fraction,and lepton polarization asymmetry in the non-universal Z’model.We further study the dependence of the branching fraction to the new model parameters and find that the values of different decay parameters increase in the Z’model,which indicates a possible approach for the search of new physics as well as for the unknown phenomena of the charm B meson.

Search for new physics in the B→K^((*))l^+l^- decays at BABAR

Based on a data sample of 384 million BB pairs collected with the BABAR detector at the PEP-Ⅱ asymmetric e ＋ e ￣ storage ring,we measure branching fractions,direct CP,isospin and lepton-flavor asymmetries for the rare decays B → K （＊） l ＋ l￣ in two di-lepton mass bins above and below the J/ψ resonance.For the B → K＊ l ＋ l￣ decay,we also measure the K＊ longitudinal polarization fraction and the di-lepton forwardbackward asymmetry.

Searching for new physics in D^0→μ^+ μ^-,e^+e^-,μ~±e~■ at BES and/or the super charm-tau factory

In contrast with B0-ˉB0, Bs-ˉBs mixing where the standard model（SM） contributions overwhelm that of the new physics beyond standard model（BSM）, a measured relatively large D0-ˉD0mixing where the SM contribution is negligible, definitely implies the existence of the new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the decay mode D0→μ＋μ-could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of the new physics BSM in the leptonic decays of D0. Concretely we discuss the contributions of unparticle or an extra gauge boson Z while imposing the constraints set by fitting the D0-ˉD0mixing data. We find that the long-distance SM effects for D0→lˉl still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as D0→μ±e, the new physics contribution would be significant.

D^0 -~0 mixing and CP violation at BES-Ⅲ

Recently, both BaBar and Belle experiments found evidences of neutral D mixing. In this paper, we discuss the sensitivities of the measurements of D mixing parameters at BES-Ⅲ. With CP tag technique at ψ（3770） peak, the extraction of the strong phase difference in D^0 → Kπ decay at BES-Ⅲ are discussed. We also make an estimate on the measurements of the mixing rate RM by using the coherent data at ψ（3770） peak. The CP violation in D system is predicted with an unobserved level in the Standard Model. Any significant CP violation in the D system indicates the existence of new physics. The sensitivity of the measurements of CP violation in the D system is estimated in the coherent D decays. Finally, the search for the rare D decays are discussed, in which some of the forbidden decays are smoking gun of new physics.

Probing HZγ and Hγγ anomalous couplings in the process e^+e^-→ Hγ

We propose to measure the HZγ and Hγγ anomalous couplings in the process e^＋e^-→Hγ with the sequential decay of H→bb^ˉ. The discovery potential of observing the anomalous couplings are explored in detail.Our study shows that future electron–positron colliders have great potential to test the HZγ and Hγγ couplings.Conservative bounds on the two anomalous couplings are also derived when no new physics signal is detected on top of the SM backgrounds.

Constraint on the warped space from → X_s γ

We analyze the theoretical prediction on the branching ratio of B→Xsγ to order ∧^2EW/∧^2KK in extension of the standard model with a warped extra dimension and the custodial symmetry SU（3）c×SU（2）L×SU（2）R×U（1）××PLR, where AKK denotes the energy scale of low-lying Kaluze-Klein excitations and AEW denotes the electroweak energy scale. Contributions from the infinite series of Kaluze-Klein excitations are summed over through the residue theorem. The numerical result indicates that the present experimental data constrain the parameter space of the concerned model strongly.

Forward-backward asymmetries inΛ_(b)→Λl^(+)l^(-)in the Bethe-Salpeter equation approach

Using the Bethe-Salpeter equation(BSE),we investigate the forward-backward asymmetries(AFB)inΛb→Λl^(+)l^(-)(l=e,μ,τ)in the quark-diquark model.This approach provides precise form factors that are different from those of quantum chromodynamics(QCD)sum rules.We calculate the rare decay form factors forΛb→Λl^(+)l^(-)b and investigate the(integrated)forward-backward asymmetries in these decay channels.We observe the integrated A l FB,ˉA l FB(Λb→Λe^(+)e^(-)=-0.1371,ˉA l FB(Λb→Λμ^(+)μ^(-))=-0.1376,andˉA l FB(Λb→Λτ^(+)τ^(-))=-0.1053;the hadron side asymmetriesˉA h FB(Λb→Λμ^(+)μ^(-))=-0.2315;the lepton-hadron side asymmetriesˉA lh FB(Λb→Λμ^(+)μ^(-))^(-)0.0827;and the longitudinal polarization fractionsˉF L(Λb→Λμ^(+)μ^(-))^(-)0.5681.

Kinetics of fluorescence properties of Eu^(3+) ion in strontium-aluminiumbismuth-borate glasses

Eu3＋ doped strontium-aluminium-bismuth-borate glasses with the chemical composition（50–x）B2O3＋20Bi2O3＋7Al F3＋ 8Sr O＋15Sr F2＋x Eu2O3（where x=0.1 mol.%, 0.5 mol.%, 1.0 mol.% and 1.5 mol.%） were prepared by the conventional melt quenching technique.Structural properties of the prepared glasses were analysed through X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and Raman spectral techniques.Thermal stability of glass was analysed by differential thermal analysis（DTA） curve.Photoluminescence characteristics were studied using excitation, emission spectra and decay curves of Eu3＋ doped strontium-aluminium-bismuth-borate glasses.The Judd-Ofelt（J-O） intensity parameters, Ωλ（λ=2, 4 and 6） were obtained using emission spectra and was used to identify the nature of Eu3＋ ions with their surrounding ligands.Using J-O parameters the transition probabilities（A）, stimulated emission cross-sections σE p, branching ratios（βR） and radiative lifetimes（τmeas and τcal） were evaluated for the 5D0→7F J（J=0, 1, 2, 3 and 4） transition of Eu3＋ ions in the present glasses.The decay profiles were found to be non exponential for all the concentrations and the measured lifetimes（τmeas） were obtained from the decay profiles.The higher values of A, σE p, βR and quantum efficiency（η） for 5D0→7F2 emission transition at 617 nm confirmed the present glass was as active medium for red laser emission applications.

Implications of the RK and R_(K*) anomalies

We discuss the implications of the recently reported R_K and R_（K＊） anomalies, the lepton flavor nonuniversality in the B → Kl~＋l^-and B → K~＊l~＋~l- decay channels. Using two sets of hadronic inputs of form factors, we perform a fit of new physics to the R_K and R_（K＊） data, and significant new physics contributions are found. We suggest the study of lepton flavor universality in a number of related rare B,Bs,Bc and Λb decay channels, and in particular we give predictions for the μ-to-e ratios of decay widths with different polarizations of the final state particles, and of the b → dl~＋l^- processes, which are presumably more sensitive to the structure of the underlying new physics. With the new physics contributions embedded in the Wilson coefficients, we present theoretical predictions for lepton flavor non-universality in these processes.