ISSN 0253-2778

CN 34-1054/N

2016 Vol. 46, No. 5

Display Method:
Original Paper
Charm studies at Belle experiment
LI Longke (for the Belle Collaboration)
2016, 46(5): 347-357. doi: 10.3969/j.issn.0253-2778.2016.05.001
In this proceeding, a summary is given of the newly published or preliminary experimental results on charm studies at Belle experiment at KEKB. It mainly includes three parts: ① D0-D0 mixing and CP violation. Some decay channels give the new measurement results with better precision; ② search for D0 rare decay with most restrictive upper limit; ③ some new results for charmed baryon studies, such as doubly charmed baryons, charmed strange baryons and so on.
Charm physics at BESIII
MA Hailong (for the BESIII Collaboration)
2016, 46(5): 358-368. doi: 10.3969/j.issn.0253-2778.2016.05.002
Based on 293 and 0567 fb-1 data taken at the center-of-mass energies s=3773 and 4599 GeV with the BESIII detector, we report the precise measurements of the decay constant fD+, the form factors of D semileptonic decays, the Dalitz plot analysis of D+→K0Sπ+π0, the strong phase differences in D→K0S/Lπ+π- and K-π+, the D0D0 mixing parameter yCP, the searches for 2-body hadronic decays D0(+)→ωπ0(+), rare decays of D0→γγ and D+→K(π)±ee+ as well as the significant improved measurements of the absolute branching fractions for Λ+c→Λe+νe and 12 hadronic final states.
Measurement of the D0→π-e+ν branching fraction, form factor and implications for Vub
GRIESSINGER K. (for the BaBar Collaboration)
2016, 46(5): 369-373. doi: 10.3969/j.issn.0253-2778.2016.05.003
The decay D0→π-e+ν is studied at the BaBar experiment using a sample of 500 million c events recorded near the CM energy 106 GeV. Using this data, the branching fraction of the process D0→π-e+ν is extracted, as well as the hadronic form factor fπ+,D and the CKM matrix element Vcd. Applying a relation between the decays D0→π-e+ν and B0→π-e+ν, the matrix element Vub is calculated and its precision will become competitive once new theoretical calculations appear.
A resolution of the puzzle of low Vus values from inclusive flavor-breaking sum rule analyses of hadronic τ decay data
2016, 46(5): 374-382. doi: 10.3969/j.issn.0253-2778.2016.05.004
Continuum and lattice methods are used to investigate systematic issues in the sum rule determination of Vus using inclusive hadronic τ decay data. Results for Vus employing assumptions for D>4 OPE contributions used in previous conventional implementations of this approach are shown to display unphysical dependence on the sum rule weight, w, and choice of upper limit, s0, of the relevant experimental spectral integrals. Continuum and lattice results suggest a new implementation of the sum rule approach with not just |Vus|, but also D>4 effective condensates fit to data. Lattice results are also shown to provide a quantitative assessment of truncation uncertainties for the slowly converging D=2 OPE series. The new sum rule implementation yields |Vus| results free of unphysical s0- and w-dependences and ~0.002 0 higher than that obtained using the conventional implementation. With preliminary new experimental results for the Kπ branching fraction, the resulting |Vus| is in excellent agreement with that based on Kl3, and compatible within errors with expectations from three-family unitarity.
Radiative μ and τ leptonic decays
2016, 46(5): 383-391. doi: 10.3969/j.issn.0253-2778.2016.05.005
Precise data on radiative leptonic τ decays offer the opportunity to probe the electromagnetic properties of the τ and may allow to determine its anomalous magnetic moment which, in spite of its precise Standard Model prediction, has never been measured. Recently, the branching fractions of the radiative leptonic τ decays (τ→lνγ, with l=e,μ) were measured by the Babar Collaboration. These precise measurements, with a relative error of about 3%, must be compared with the branching ratios at the next-to-leading order in QED. Indeed the radiative corrections are expected to be of order 10%, for l=e, and 3%, for l=μ. Here, we present the prediction of the differential decay rates and branching ratios of the radiative μ and τ leptonic decays in the Standard Model at the next-to-leading order and we compare them with the recent Babar measurements. Moreover, we report on a dedicated feasibility study for the measurements of the τ anomalous magnetic moment at Belle and Belle II.
L→ll′l′νlνL in the SM and beyond
2016, 46(5): 392-397. doi: 10.3969/j.issn.0253-2778.2016.05.006
The L→ll′l′νlνL decays (L=τ,μ; l,l′=μ,e) in the Standard Model (SM) and in the effective field theory (EFT) description of the weak charged current are studied at low energy, both for polarized and unpolarized L, keeping for the first time l,l′ mass dependence. The discrepancy is clarified between two previous SM calculations improving their precision. The recent 35σ anomaly found in τ→eγeντ could be checked using our precise prediction for the τ→eee eντ decays, which shall be measured analysing already existing data from the first generation B-factories. It is shown how measurements of the di-l′ mass distribution (with appropriate cuts) and T-asymmetries are able to reveal the corresponding lepton flavor violating (LFV) processes without neutrinos in the final state.
τ→KSπ-ντ and τ→K-ηντ decays: A combined analysis
2016, 46(5): 398-406. doi: 10.3969/j.issn.0253-2778.2016.05.007
The decay spectra of τ-→KSπ-ντ and τ-→K-ηντ decays are studied in a combined analysis using a dispersive representation of the required vector and scalar form factors. The K*(1410) resonance parameters are extracted with improved precision as compared to previous studies, with the findings MK*′=1 304±17 MeV and ΓK*′=171±62 MeV. Isospin violations in the form factor slopes are investigated as the K-π0 vector form factor enters the description of the decay τ-→K-ηντ. In this respect, the spectrum of the transition τ-→K-π0ντ would be extremely useful.
New Physics searches with muons: Theoretical review
2016, 46(5): 407-415. doi: 10.3969/j.issn.0253-2778.2016.05.008
We summarize current issues related to New Physics searches with muons with focuses on the ratio of magnetic moments of the muon and the proton, needed for the muon gμ-2 determination; on using the bound-electron g-2 to help independently check the persisting discrepancy between the measured gμ-2 and the Standard Model; and on the bound-muon decay as a background for the muon-electron conversion.
Overview of the Fermilab muon g-2 experiment
KIM SeungCheon (for the Muon g- Collaboration)
2016, 46(5): 416-423. doi: 10.3969/j.issn.0253-2778.2016.05.009
The measurement of the anomalous magnetic moment of muon provides a precision test of the Standard Model. The Brookhaven muon g-2 experiment (E821) measured the muon magnetic moment anomaly with 0.54 ppm precision, a more than 3σ deviation from the Standard Model predictions, spurring speculation about the possibility of New Physics. The new g-2 experiment at Fermilab (E989) will reduce the combined statistical and systematic error of the BNL experiment by a factor of 4. An overview of the new experiment is described.
Measuring the leading order hadronic contribution to the muon g-2 in the space-like region
2016, 46(5): 424-430. doi: 10.3969/j.issn.0253-2778.2016.05.010
Recently a novel approach to determining the leading hadronic corrections to the muon g-2 has been proposed. It consists in a measurement of the effective electromagnetic coupling in the space-like region extracted from Bhabha scattering data. The new method may become feasible at flavor factories, leading to an alternative determination, possibly competitive with the accuracy of the present evaluations based on the dispersive approach via time-like data.
γγ physics and transition form factor measurements at KLOE\KLOE-2
GAUZZI P. (for the KLOE- Collaboration)
2016, 46(5): 431-438. doi: 10.3969/j.issn.0253-2778.2016.05.011
The KLOE results on the measurement of the transition form factors of the η and π0 mesons in  Dalitz decays are presented, and the determination of the Γ(η→γγ) in γγ collisions is also reported. The prospects for γγ physics of the new data-taking, started in November 2014 with the upgraded detector, are reviewed.
Measurements of π0π0 production and form factors for f0(980) and f2(1270) in single-tag two-photon process
XU Qingnian (for the Belle Collaboration)
2016, 46(5): 439-448. doi: 10.3969/j.issn.0253-2778.2016.05.012
A measurement is reported of differential cross section of π0 pair production in single-tag two-photon collisions. These results are obtained with 759 fb-1 of the data collected with the Belle detector at the KEKB asymmetric energy e+e- collider. The cross section is measured for Q2 up to 30 GeV2, where Q2 is the negative of the invariant mass squared of the tagged virtual photon, in the kinematic range 05<W<21 GeV and |cos θ*|<10 for the total energy and pion scattering angle, respectively. The transition form factor of the f0(980) and that of the f2(1270) with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.