Comment onπ 0 → 2γ decay and the pion wave function

It has been claimed in a recent paper that the result given by the axial anomaly for the process ⁰ 2 can be reproduced with the pion wave function calculated from a QCD sum rule. We examine the method and discover several deficiencies. In particular, the result does not coincide with the correct value given by the anomaly, but has an opposite sign.     

Supersymmetric predictions for the inclusiveb→sγ decay

We present an update study of the penguin induced transitionbs in the minimalN=1 supersymmetric extension of the Standard Model with radiative breaking of the electroweak group. We include the effects of one-loop corrections to the Higgs potential and scalar masses, and perform a detailed analysis of the implications of the recently advocated relation |B|2 for the bilinear SUSY soft breaking parameter in grand unified theories. We show that the present upper and lower experimental limits on the inclusive decay sharply constrain the parameter space of the model for a wide range of tan values.     

Measurement of the decay rate and the parameter αK* of the decay KL → μμγ

The rate of the decay of the neutral K meson into K _L ⁰ → μμγ has been measured with the NA48 detector at the CERN SPS. A total of 59 events has been observed with an estimated background of 14 events. The overall Kaon flux was determined to be 1.2 × 10⁹. This observation corresponds to a branching ratio of (3.4 ± 0.6_stat ± 0.4_sys × 10^-7. Using this branching ratio the parameter α_K* describing the relative strength of the two contributing amplitudes to this decay, through intermediate pseudoscalar or vectorlike mesons, was measured to be α_K* = -0.04+ _-0.21 ^+0.24 .     

A measurement of the branching ratio for the∑ + →pγ decay

We have measured the weak radiative decay branching ratio (∑ ⁺ →pγ)/(∑ ⁺ →pπ⁰). The experiment was carried out at Brookhaven National Laboratory using a low-energy separatedK ^? beam stopping in liquid hydrogen. The∑ ⁺ was tagged by observing the pion fromK ^? K ⁺ p→∑ ⁺π^? in a range telescope, and the gamma was detected in a segmented NaI detector. The result is (2.81±0.39 _?0.43 ^+0.21 )×10^?3, which is consistent with previous measurements. This corresponds to a branching ratio for (∑ ⁺ →pγ)/(∑ ⁺ → all) of (1.45±0.20 _?0.22 ^+0.11 )×10^?3, where the quoted errors are statistical and systematic, respectively. A total of 408 signal events were observed, doubling the previous world total.     

Calculation of the axial form factor of the decay π → evγ by means of QCD sum rules

The axial form factor of the decay π → evγ is calculated by means of QCD sum rules, using the experimental value for the mean- squared charge radius of the pion. The ratio of the axial to vector form factor is predicted to be γ = 0.42±0.2.     

New measurement of the π → μνγ decay

We have measured the branching ratio of the radiative decay π → μνγ. The energies of the gamma-ray and of the muon were both measured and the Dalitz-plot distribution of the decay was obtained. The data agree well with the theoretical prediction (QED internal bremsstrahlung) down to a γ-ray energy of 1 MeV. The discrepancy reported in a previous experiment is not confirmed.     

Measurement of the relative probability of the decay φ → η′γ in the channel η′ → ηπ0π0, η → γγ

The process e ⁺ e ^? → η′γ, η′ → η π⁰π⁰, η → γγ is investigated by an SND detector in experiment on a VEPP-2M equipment with colliding electron-positron beams. The analysis of experimental data yields a value of B(? → η′γ)=(6.7 _?4.2 ^+5.0 ±1.5)×10^?5 for the decay probability. Taking into account a previous measurement of this quantity by an SND detector in the decay channel η′ → π⁺π^?η, one finally obtains B(?→η ′γ)=(6.7 _?2.4 ^+2.8 ±0.8)×10^?5.     

Upper limit for the Ξ0→Σ0γ radiative decay

We report here a new measurement of the upper limit for the branching ratio of the radiative weak decay Ξ⁰→Σ⁰γ of < 8.0×10⁻³ at the 90% confidence level. This is more than an order of magnitude less than previous limits and consistent with rates from similar decays.     

Radiative leptonic decay Bc^-→τ^vτ^-γ in the standard model and the two-Higgs-doublet model

We analyze the radiative leptonic Bc decay Bc^-→τ^vτ^-γ in the Standard Model and the two- Higgs-doublet model using the non-relativistic constituent quark model. The results confirm that this channel is experimentally promising in view of the large number of Bc mesons which are expected to be produced at future hadron facilities. We also find that this decay is sensitive to the parameters of the two-Higgs-doublet model, and it can be tested in future experiments.     

Tau leptons and the decay H → ττ at CMS

The tau lepton and its reconstruction at CMS are briefly described. This is followed by a summary of the searches for a standard model Higgs boson and neutral Higgs bosons from the minimal supersymmetric extension of the standard model decaying into pairs of tau leptons performed by the CMS Collaboration. The data samples used in these searches were collected during the first running period of the LHC and contain 4.9 fb^?1 at \(\sqrt {s}=7\,\text {TeV}\) and 19.7 fb^?1 at \(\sqrt {s}=8\,\text {TeV}\).     

On the contribution of interference of electromagnetic and chromomagnetic dipole operators in the $$ \bar B $$ → Xsγ decay at O(αs2)

The contribution of c-quark loops into the interference of the electromagnetic and chromomagnetic dipole operators in the \(\bar B\) → X _s γ decay is calculated to O(α _s ² ) within the framework of the Standard Model (SM). Several new calculation techniques, such as Laporta’s automated algorithm, the second order decomposition method, and Mellin-Barnes representation, have been used.     

To the problem of KL→π0γγ decay

It is shown that the contribution of diagrams with intermediate state vector mesons to the K_L ⁰ amplitude, intensively discussed in literature in recent years, is close to zero provided that theSU(3) group breaking is taken into account. At the same time, the contribution of scalar mesons in the intermediate state is essential. The obtained estimates for Br(K_L ⁰) conform with the recent experimental data Br(K_L ⁰ )=(2·1 ± 0·6)×10^–6.Dedicated to the memory of our friend Prof. M. Gmitro.We wish to thank S. B. Gerasimov and A. B. Govorkov for useful discussions.     

First observation of the KS→π0γγ decay

Using the NA48 detector at the CERN SPS, 31 K_S→π⁰γγ candidates with an estimated background of 13.7±3.2 events have been observed. This first observation leads to a branching ratio of BR(K_S→π⁰γγ)_z>0.2=(4.9±1.6_stat±0.9_syst)×10⁻⁸ in agreement with Chiral Perturbation Theory predictions.     

Properties of the decay H→γγ using the approximate α_s~4 corrections and the principle of maximum conformality

The decay channel H→γγ is an important channel for probing the properties of the Higgs boson.In this paper,we analyze its decay width by using the perturbative QCD corrections up to the α_s~4 order with the help of the principle of maximum conformality(PMC).PMC has been suggested in literature for eliminating the conventional renormalization scheme-and-scale ambiguities.After applying PMC,we observe that an accurate renormalization scale independent decay width Γ(H→γγ) up to the N~4 LO level can be achieved.Taking the Higgs mass,M_H = 125.09±0.21 ±0.11 GeV,given by the ATLAS and CMS collaborations,we obtain Γ(H→γγ)|LHC = 9.364_(0.075)~(0.076) KeV.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Probing magnetic moment operators in H_γ production and H→τ~+τ~-γ rare decay

The magnetic moment(a_γ) and weak magnetic moment(a_W) of charged leptons and quarks are sensitive to quantum effects of new physics heavy resonances.In effective field theory,a_γ and a_W are induced by two independent operators.Therefore,one has to measure both ay and aw to shed light on new physics.The aw's of the SM fermions are measured at the LEP.In this work,we analyze the contributions from magnetic and weak magnetic moment operators in the processes of pp→H_γ and gg→H→τ~+τ~-γ at the High-Luminosity Large Hadron Collider.We demonstrate that the two processes can cover most of the parameter space that cannot be probed at the LEP.     

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.