Precise measurement of the e^＋e^- →π^＋π^-（γ） cross section with the initial state radiation method at BABAR

We present a precise BABAR measurement on the cross section of the process e^＋e^- →π^＋π^-（γ） from threshold to an energy of 3 GeV with the initial state radiation （ISR） technique, using 232 fb^-1 of data collected with the BABAR detector at e^＋e^- center-of-mass energies near 10.58 GeV. The ISR luminosity is determined from a study of the leptonic process e^＋e^- →μ^＋μ^-γ（γ）. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the ππ cross section measured from threshold to 1.8 GeV is （514.1± 2.2（stat） ± 3.1（syst）） × 10^-10.     

Study of the process e~+e~- →π~+π~-π~0π~0 at energies s～(1/2)<1 GeV

In an experiment with the Spherical Neutral Detector at VEPP-2M collider the cross section of the process e+e-→π+π-π0π0 was measured.At energies s～(1/2)920 MeV this cross section was measured for the first time.The energy dependence of the cross section is well discribed by the vector dominance model with contributions from ρ,ρ,ρ mesons.The decay probability ρ→π+π-π0π0 was found to be Bρ =(1.60±0.74±0.18)×10-5.The upper limit for the decay ω→π+π-π0π0 was improved by two orders of magnitude compared to the previous measurements and is Bω 2×10-4 at 90% confidence level.     

Combined fit to BABAR and Belle Data on e~+e~- →φπ~+π~- and φf_0(980)

A combined fit is performed to the BABAR and Belle measurements of the e+e- →φπ+π- and φf0(980) cross sections for center-of-mass energy between threshold and 3.0 GeV. The resonance parameters of the φ(1680) and Y(2175) are determined. The mass is (1681+-1102) MeV/c2 and the width is (221-+3244) MeV/c2 for the φ(1680), and the mass is (2117+-5499) MeV/c2 and the width is (164+-6890) MeV/c2 for the Y(2175). This information will shed light on the understanding of the nature of the excited φ and Y states observed in e+e- annihilation.     

A discussion on vacuum polarization correction to the cross-section of e~+e~-→γ~*/ψ →μ~+μ~-

Vacuum polarization is a part of the initial-state radiative correction for the cross-section of e~+e~- annihilation processes. In the energy region in the vicinity of narrow resonances J/ψ and ψ(3686), the vacuum polarization contribution from the resonant component has a significant effect on the line-shape of the lepton pair production cross-section. This paper discusses some basic concepts and describes an analytical calculation of the cross-section of e~+e~-→γ*/ψ→μ+μ-considering the single and double vacuum polarization effect of the virtual photon propagator. Moreover, it presents some numerical comparisons with the traditional treatments.     

Evidence for resonant structures in e~+e~-→π~+π~-h_c

The cross sections of e+e-→π+π-hc at center-of-mass energies from 3.90 to 4.42 GeV were measured by the BES and the CLEO-c experiments. Resonant structures are evident in the e+e-→π+π-hc line shape. The fit to the line shape results in a narrow structure at a mass of(4216±18) MeV/c2and a width of(39±32) MeV, and a possible wide structure of mass(4293±9) MeV/c2and width(222±67) MeV. Here, the errors are combined statistical and systematic errors. This may indicate that the Y(4260) state observed in e+e-→π+π-J/ψ has a fine structure in it.     

Z′particles and e~+ e~- → τ~+ μ~-

We analyze the cross section of e + e-→τ + μ-within the frameworks of SM and its Z extension.The theoretical prediction of the SM on the total cross section is suppressed by the tiny neutrino masses.On the other hand,the contributions from Z to the cross section are enhanced drastically because of the tree level FCNC couplings among Z and leptons.     

Helicity Amplitude Analysis of Z_c(3900)~± in e~+e~- →π~+π~-J/ψ

It is crucial to determine the spin and parity(J~P) of Z_c(3900)~± for understanding its structure.We perform a helicity amplitude analysis on Z_c(3900)~± in the process e~+e~-→π~+π~-J/φ with the hypotheses J~P= 0~-,1~+,1~-,2~+ and 2~-.To estimate the significance of J~P = 1~+ over other hypotheses,we perform a Monte Carlo simulation study,and we also discuss the prospect of measuring the spin parity in the future experiment with a large data sample.     

Effects of the littlest Higgs model on the process e~+ e~- → μ~+ μ~- at a Z~0-factory

We investigate the possibilities of finding the effects of the littlest Higgs (LH) model on the process e + e - →μ + μ - at the leadingorder at a possible Z 0-factory.We study the impacts of the LH model on the observables,such as,the total cross section,the distribution of the transverse momentum of μ-,and the forward-backward charge asymmetry of μin polarized and unpolarized electron-positron collision modes.Besides,we analyze the relations between the observables and the LH model parameters,and discuss the observables of process e + e→μ + μ-in different incoming electron-positron polarization modes.We conclude that one could observe the effects contributed by the LH model on the process e + e-→μ + μin a reasonable parameter space,or might put more stringent constraints on the LH parameters in the future experiments at the possible Z 0-factory.     

Measurement of e~+e~-→D■ cross sections at the ψ(3770) resonance

We report new measurements of the cross sections for the production of DD final states at theψ(3770)resonance.Our data sample consists of an integrated luminosity of 2.93 fb~(-1)of e~+e~-annihilation data produced by the BEPCⅡ collider and collected and analyzed with the BESⅢ detector.We exclusively reconstruct three D~0and six D~+hadronic decay modes and use the ratio of the yield of fully reconstructed DD events(double tags)to the yield of all reconstructed D or D mesons(single tags)to determine the number of D~0 D~0and D~+D~-events,benefiting from the cancellation of many systematic uncertainties.Combining these yields with an independent determination of the integrated luminosity of the data sample,we find the cross sections to beσ(e~+e~-→D~0D~0)=(3.615±0.010±0.038)nb andσ(e~+e~-→D~+D~-)=(2.830±0.011±0.026)nb,where the uncertainties are statistical and systematic,respectively.     

Interference effects on Higgs mass measurement in e~+e~-→H(γγ)Z at CEPC

A high luminosity Circular Electron Positron Collider(CEPC) as a Higgs Factory will be helpful for precision measurements of the Higgs mass. The signal-background interference effect is carefully studied for the Higgs diphoton decay mode in associated Z boson production at future e~+e~-colliders at energy 246 GeV. The mass shifts go up from about 20 MeV to 50 MeV for the experimental mass resolution ranging from 0.8 GeV to 2 GeV.     

Exclusive measurement of the pp → nnπ+π+ reaction at 1.1 GeV

First exclusive data for the $\ensuremath{pp \to nn\pi^+\pi^+}$ reaction have been obtained at CELSIUS with the WASA detector setup at a beam energy of T_p = 1.1 GeV. Total and differential cross-sections disagree with theoretical calculations, which predict the $ \Delta$ $ \Delta$ excitation to be the dominant process at this beam energy. Instead, the data require the excitation of one of the nucleons to a higher-lying $ \Delta$ state, preferably the $\ensuremath{\Delta(1600)P_{33}}$ , to be the leading process.     

Mixed electroweak-QCD corrections to e~+e~-→μ~+μ~-H at CEPC with finite-width effect

The associated production of Higgs boson with a muon pair, e~+e~-→μ+μ-H, is one of the golden channels to pin down the properties of the Higgs boson in the prospective Higgs factories exemplified by CEPC.The projected accuracy of the corresponding cross section measurement is about per cent level at CEPC. In this work, we investigate both O(α) weak correction and the O(ααs) mixed electroweak-QCD corrections for this channel,appropriately taking into account the effect of finite Z~0 width. The μ~+μ~-invariant mass spectrum is also predicted.The mixed electroweak-QCD correction turns out to reach 1.5% of the Born-order result, and thereby must be included in future confrontation with the data. We also observe that, after including higher-order corrections, the simplified prediction for the integrated cross section employing the narrow-width-approximation may deviate from our full result by a few per cents.     

Event generators for η/η’ rare decays into π~+π~-1~+1~- 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 BES 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 BES Monte Carlo simulation package. In the BES 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.     

Measurements of decay branching fractions of H→b■/c■/gg in associated (e~+e~-/μ~+μ~-)H production at the CEPC

The high-precision measurement of Higgs boson properties is one of the primary goals of the Circular Electron Positron Collider(CEPC).The measurements ofH→b■/c■/gg decay branching fraction in the CEPC experiment is presented,considering a scenario of analysing 5000 fb-1 e~+e~-collision data with the center-of-mass energy of 250 Ge V.In this study the Higgs bosons are produced in association with a pair of leptons,dominantly mediated by the ZH production process.The statistical uncertainty of the signal cross section is estimated to be about 1%in theH→b■ final state,and approximately 5%-10%in theH→c■/gg final states.In addition,the main sources of the systematic uncertainties and their impacts to the measurements of branching fractions are discussed.This study demonstrates the potential of precise measurement of the hadronic final states of the Higgs boson decay at the CEPC,and will provide key information to understand the Yukawa couplings between the Higgs boson and quarks,which are predicted to be the origin of quarks’masses in the standard model.     

Perturbative QCD for J/ψ inclusive production via initial state radiation in e~+e~- collisions

The process e+e-→J/ψ+X with the center-of-mass(CM)energy in the range from 3.7 to 10.6 GeV is calculated up to the next-to-leading order(NLO)in quantum chromodynamics(QCD).At 10.6 GeV,the result is consistent with the experimental result from Belle.However,the predictions are much smaller than the background in the measurements at BESIII in the low CM energy range from 3.7 to 4.6 GeV.This indicates that the convergence of the QCD perturbative expansion becomes worse as the CM energy is closer to the inclusive J/ψ production threshold.For a further study of the QCD mechanism of J/ψ production in e~+e~-collisions with different CM energies,the initial state radiation effect of e~+e~-→J/ψ +gg and e~+e~-→J/ψ+cc are calculated in QCD NLO.The results are plotted and the number of events for different CM energy bins are provided for SuperKEKB.This provides a method to precisely test the validity of perturbative predictions for J/ψ production in future measurements.     

J/ψ→π~03(π~+π~-)分支比的测定

用BESⅠ的 7.8× 1 0 6 J/ ψ数据更为精确地测定了J/ ψ→π0 3 (π+π- )和J/ ψ→ω2 (π+π- )的分支比 (Br(J/ ψ→π0 3 (π+π- ) ) =( 2 .52± 0 .0 6± 0 .4 3 ) % ,Br(J/ ψ→ω2 (π+π- ) ) =( 1 .3 1± 0 .0 9± 0 .2 1 ) % .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 .     

Phenomenological studies on B~0 → [K~-π~+]_(S/V)[π~+π~-]_(V/S) → K~-π~+π~+π~- decay

Within the quasi-two-body decay model,we study the localized CP violation and branching fraction of the four-body decay B~0→[K~-π~+]_(s/V)[π~+π~-]_(V/)S→K-π~+π~-π~+ when the K~-π~+and π~-π~+ pair invariant masses are0.35 m(K~-π~+)2.04 GeV and 0 mπ~-π~+1.06 GeV,with the pairs being dominated by the K_0~*(700)~0,K~*(892)~0,K~*(1410)~0,K_0~*(1430) and K~*(1680)~0,and fo(500),ρ~0(770),ω(782) and fo(980) resonances,respectively.When dealing with the dynamical functions of these resonances,fo(500),ρ~0(770),fo(980) and K_0~*(1430) are modeled with the Bugg model,Gounaris-Sakurai function,Flatte formalism and LASS lineshape,respectively,while the others are described by the relativistic Breit-Wigner function.Adopting the end point divergence parameters ρA ∈[0,0.5] andΦ_A∈[0,2π],our predicted results are F_(CP)(B~0→K~-π~+π~+π~-)∈[-0.365,0.447] and B(B~0→K-π~+π~+π~-)∈[6.11,185.32] x 10~(-8),based on the hypothetical qq structures for the scalar mesons in the QCD factorization approach.Meanwhile,we calculate the CP violating asymmetries and branching fractions of the two-body decays B~0→SV(VS) and all the individual four-body decays B~0→SV(VS)→K~-π~+π~-π~+,respectively.Our theoretical results for the two-body decays B~0→K~*(892)~0 fo(980),B~0→K_0~*(1430)~0ω(782),B~0→K~*(892)~0 f~0(980),B~0→K_0~*(1430)~0ρ,and B~0→(1430)~0ω are consistent with the available experimental data,with the remaining predictions await testing in future high precision experiments.     

Categorization of two-loop Feynman diagrams in the O(α~2) correction to e~+e~-→ ZH

The e~+e~-→ZH process is the dominant process for the Higgs boson production at the future Higgs factory.In order to match the analysis on the Higgs properties with highly precise experiment data,it will be crucial to include the theoretical prediction to the full next-to-next-to-leading order electroweak effect in the production rateσ(e~+e~-→ZH).In this inspiring work,we categorize the two-loop Feynman diagrams of the O(α~2) correction to e~+e~-ZH into 6 categories according to relevant topological structures.Although 25377 diagrams contribute to the O(a~2) correction in total,the number of the most challenging diagrams with seven denominators is 2250,which contain only 3 12 non-planar diagrams with 155 independent types.This categorization could be a valuable reference for the complete calculation in future.     

Detection of Charged Higgs Bosons in e~+e~-(γγ)→tφ~- Production at the ILC

In the context of the left-right twin Higgs (LRTH) model,we have studied the charged Higgs bosons production processes e~+e~-(γγ)→tφ~at the International Linear Collider (ILC).It is found that the cross sections of these two processes could reach a few fb with reasonable parameter values.With the yearly integrated luminosity of L=500 fb-1 expected at the ILC,one could collect hundreds up to thousands of charged Higgs events via these two processes.Therefore,our researches in this paper can help us search for charged Higgs bosons,and furthermore,to test the LRTH model.     

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.