In this write-up, we summarize our recent analysis of radiative decays involving light scalar mesons. Our analysis using the vector meson dominance model at tree level indicates that it may be difficult to distinguish $qq\bar{q}\bar{q}$ picture and $q\bar{q}$ picture for the light scalar nonet. Our result on the process of $ϕ\to π^0 ηγ$ shows that the derivative-type $f_0 K\bar{K}$ interaction reproduces experimental data below 950 GeV well, but gives a poor fit above 950 GeV, i.e., in the energy region around the mass of $a_0(980)$, but that the discrepancy can be compensated by the effect of the $K$ loop.
We comment on the implications of the recently measured CP asymmetry in B --> Phi K_S decay. The data disfavor the Standard Model at 2.7 sigma and -if the trend persists in the future with higher statistics - require the existence of CP violation beyond that in the CKM matrix. In particular, the b --> s bar{s} s decay amplitude would require new contributions of comparable size to the Standard Model ones with an order one phase. While not every model can deliver such a large amount of CP and flavor violation, those with substantial FCNC couplings to the Z can reproduce the experimental finding…
Recent data on B->p pbar K, K0 pi pi and K Kbar K hint at a $\sim 2.3$ GeV object recoiling against a kaon. This could be the narrow state observed in J/ψ-> gamma xi. Nonobservation in p pbar annihilation implies ${\cal B}(ξ\to p\bar p) \sim$ few $\times 10^{-3}$, consistent with eta_c and J/ψdecays, but there are actual hints in p pbar -> phi phi and p p-> p pi^+ pi^- pi^+ pi^- p. Simple modeling shows ${\cal B}(B \to ξK){\cal B}(ξ\to p\bar p) \sim 1\times 10^{-6}$, appearing as a spike in the $p\bar p$ spectrum, with $\sim$ 30 events per 100 fb$^{-1}$; modes such as K K_s K_s, K phi phi, K4 …
We report on recent results on the decay of the phi into pi^+ pi^- and phi radiative decays into pi^0 pi^0 gamma and pi^0 eta gamma, which require the consideration of the final state interaction of a pair of mesons in a region inaccessible to Chiral Perturbation Theory. By using nonperturbative chiral unitary methods for the meson meson interaction we can obtain the corresponding decay widths and the results are compared with recent experimental data.
The measured rate for phi to gamma f0(980) appears to be larger than allowed on rather general grounds. We show that mixing between the f0(980) and a0(980), due to their dynamical interaction with the nearby KKbar thresholds, radically affects some existing predictions of their production in phi radiative decay. We predict that Gamma(phi to gamma f0)/Gamma(phi to gamma a_0) approx 3; that sum (b.r.(phi to gamma f0) + b.r. (phi to gamma a_0)) < 5 x 10^-4 with probable individual branching ratios 2 x 10^-4 and 0.7 x 10^-4 respectively.
The photon polarization in radiative decays B -> Y gamma is known to be a subtle probe of the effective Lagrangian structure and possible New Physics effects. We discuss exclusive decay mode B -> phi K gamma where the experimentally distinct final state makes analysis especially promising. The possibility to extract information on the photon polarization out of the data entirely depends on the partial waves interference pattern in the phi K system.
Current predictions for the ratio of phi -> K^+K^-/K_LK_S decay rates exceed the corresponding experimental value in about five standard deviations. By far, the dominant sources of isospin breaking to this ratio are the phase-space (52%) and the electromagnetic radiative (4.3%, computed within scalar QED) corrections. Here we estimate the effects of the electromagnetic structure of kaons and other model-dependent contributions into the radiative corrections.
The light cone QCD sum rules method is used to calculate the transition form factor for the radiative (phi -> f_0 gamma) decay, assuming that the quark content of the (f_0) meson is pure (bar{s}s) state. The branching ratio is estimated to be Br(phi -> f_0 gamma) = 3.5 x (1 pm 0.3) x 10^(-4). A comparison of our prediction on branching ratio with the theoretical results and experimental data existing in literature is presented.
We study how the scalar f_0(980) and a_0(980) states are produced in the two-photon collisions and radiative decays of the phi meson through unitarized Born amplitudes with the charged pion and kaon loops followed by S-wave meson-meson scattering amplitudes. We found in a previous paper that f_0(980) is generated as the bound state resonance, but a_0(980) as the cusp, and find herre that the nature of the generation of both states is consistent with the features of the production processes.
The study of radiative phi decays into scalar mesons, with subsequent decay into pi pi gamma, constitutes an important topic at the electron-positron collider DAPHNE. The interference of the respective amplitude with the one for pi+ pi- gamma production, where the photon originates from initial state radiation, will allow for unambiguous tests of models for the phi -> gamma f0(-> pi pi) amplitude. The forward-backward asymmetry of charged pions, which is a clear signal of such an interference, amounts up to 30 % and is at the same time quite sensitive to the details of the various amplitudes. …
A coupled channel model is used to study the nature of the scalar mesons produced in the decay phi - gamma pi pi. The KKbar molecular picture of f0(980) is found to be in a good agreement with the recent experimental data from SND and CMD-2. The structure of the light scalar mesons is elucidated by investigating the S-matrix poles and the qqbar spectral density.
We have studied the phi(1020)a0(980) S-wave scattering at threshold energies employing chiral Lagrangians coupled to vector mesons by minimal coupling. The interaction is described without new free parameters by considering the scalar isovector a0(980) resonance as dynamically generated in coupled channels, and demanding that the recently measured e+ e- -> phi(1020) f0(980) cross section is reproduced. For some realistic choices of the parameters, the presence of a dynamically generated isovector companion of the Y(2175) is revealed. We have also investigated the corrections to the e+ e- -> ph…
Muon pair production through the radiative return is of importance for a measurement of the hadronic production cross section in two ways: it provides an independent calibration and it may give rise to an important background for a measurement of the pion form factor. With this motivation the Monte Carlo event generator PHOKHARA is extended to include next-to-leading order radiative corrections to the reaction $e^+e^-\to μ^+μ^-γ$. Furthermore, virtual ISR corrections to FSR from pions are introduced, which extends the applicability of the generator into a new kinematical regime. Finally, the e…
Different conclusions about quark nature of f0(980) based on the analysis of data on the reaction phi(1020) -> gamma f0(980) make it necessary to perform detailed comparison of formulae used by various groups for the calculation of partial widths of radiative decays. We carry out a comparative analysis of methods of calculation of radiative decays like phi -> gamma f0 and phi -> gamma eta performed by F.E.Close et al., Phys. Rev. D 65, 092003 (2002), and A.V.Anisovich et al., Eur. Phys. J. A 12, 103 (2001); Yad. Fiz. 65, 523 (2002).
We study the radiative $ϕ$ decay into $π^0 π^0 γ$ and $π^0 ηγ$ taking into account mechanisms in which there are two sequential vector-vector-pseudoscalar or axial-vector--vector--pseudoscalar steps followed by the coupling of a vector meson to the photon, considering the final state interaction of the two mesons. There are other mechanisms in which two kaons are produced through the same sequential mechanisms or from $ϕ$ decay into two kaons and then undergo final state interaction leading to the final pair of pions or $π^0 η$, this latter mechanism being the leading one. The results of the p…
In this article we rederive the Boost operators in Coulomb-Gauge Yang-Mills theory employing the path-integral formalism and write down the complete operators for QCD. We immediately apply them to note that what are usually called the pion square, quartic... charge radii, defined from derivatives of the pion form factor at zero squared momentum transfer, are completely blurred out by relativistic and interaction corrections, so that it is not clear at all how to interpret these quantities in terms of the pion charge distribution. The form factor therefore measures matrix elements of powers of …
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma decays in the framework of a U(3)xU(3) linear sigma model which includes constituent quarks. For the first two decays this approach improves results based on the anomalous Wess-Zumino term, with contributions due to SU(3) symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays are dominated by resonant eta' exchange . Our calculation for the later decays improves and update similar calculations in the -closely related- framework of vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x…
We consider several hints for new physics involving CP-asymmetries in B-decays and interpret them in terms of generic contributions to effective Wilson coefficients. The effects we focus on are: the differences in the fitted value of sin(2 beta) versus the ones directly measured via the time dependent CP asymmetries in B -> J/psi K or via B -> (phi,eta') K; the difference between the direct CP asymmetries in B- -> K- pi0 and B0 -> K- pi+ and the ~2.2 sigma indications for the CP-asymmetry in Bs -> J/psi phi. To alleviate concerns regarding the disagreement between inclusive and exclusive Vub, …
The radiative decays of the phi meson are known to be a good source of information about the a0(980) and f0(980) scalar mesons. We discuss these decays starting from a non-linear model Lagrangian which maintains the (broken) chiral symmetry for the pseudoscalar (P), scalar (S) and vector (V) nonets involved. The characteristic feature is derivative coupling for the SPP interaction. In an initial approximation which models all the scalar nonet radiative processes together with the help of a point like vertex, it is noted that the derivative coupling prevents the a0 and f0 resonance peaks from g…
We employ chaotic (phi^2 and phi^4) inflation to illustrate the important role radiative corrections can play during the inflationary phase. Yukawa interactions of phi, in particular, lead to corrections of the form -kappa phi^4 ln(phi/mu), where kappa>0 and mu is a renormalization scale. For instance, phi^4 chaotic inflation with radiative corrections looks compatible with the most recent WMAP (5 year) analysis, in sharp contrast to the tree level case. We obtain the 95% confidence limits 2.4x10^-14<~kappa<~5.7x10^-14, 0.931<~n_s<~0.958 and 0.038<~r<~0.205, where n_s and r respectively denote…
Recently two hints for new physics have emerged: The B_s mixing phase phi_s and the rate of D_s -> (mu,tau) nu exposing a discrepancy of \sim 3 sigma and 3.8 sigma deviation from the Standard Model respectively. Moreover the difference of the CP asymmetries in B -> K pi between the charged and neutral modes is at the 5.3 sigma level which is somewhat larger than expected. New physics in phi_s or A_CP(B -> K pi) would be in contradiction with the minimal flavour violation hypothesis. The latter has recently attracted attention because of the absence of deviation in CP and flavour violation in t…
Radiative corrections to gauge boson and Higgs production computed recently using soft-collinear effective theory (SCET) require the one-loop high-scale matching coefficients in the standard model. We give explicit expressions for the matching coefficients for the effective field theory (EFT) operators for q qbar -> VV and q qbar -> phi^+ phi for a general gauge theory with an arbitrary number of gauge groups. The group theory factors are given explicitly for the standard model, including both QCD and electroweak corrections.
The phi(1020) radiative decays form a good playground for study of the low-lying a0(980) and f0(980) scalar mesons. The complicated interplay of kaon loop mechanism, isoscalar meson mixing and momentum dependence of the effective couplings manifests itself in the invariant mass distributions in the phi(1020) -> pi0 pi0 gamma and pi eta gamma spectra. These distributions are fitted in framework of Resonance Chiral Theory.
We show on gauge invariance grounds that the fine threshold phenomenon is discovered in the radiative decays phi->gamma a0->gamma pi0 eta and phi->gamma f0->gamma pi0pi0. This enables to conclude that production of the lightest scalar mesons a0(980) and f0(980) in these decays is caused by the four-quark transitions, resulting in strong restrictions on the large NC expansions of the decay amplitudes. The analysis shows that these constraints give new evidences in favor of the four-quark nature of a0(980) and f0(980) mesons.
Strong interactions between pairs of the K+ K- and K0 K0bar mesons can be studied in radiative decays of phi(1020) mesons. We present a theoretical model of the reactions e+ e- --> phi --> K+ K- gamma and e+ e- --> phi --> K0 K0bar gamma. The K+ K- and K0 K0bar effective mass dependence of the differential cross sections is derived. The total cross sections and the branching fractions for the two radiative phi decays are calculated.
We study the rho^0 and phi decays into pi^+ pi^- gamma, pi^0 pi^0 gamma and phi into pi^0 eta gamma using a chiral unitary approach to deal with the final state interaction of the M M system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the rho^0 --> pi^+ pi^- gamma decay. In the case of phi decay the contribution to pi^+ pi^- gamma and pi^0 pi^0 gamma decay proceeds via kaonic loops and gives a distribution of pi pi invariant masses in which the f_0(980) resonance shows up with a very distinct peak. The spectrum found for phi --> pi^0 p…
Cross sections of the e+e- annihilation into one photon plus two vector mesons, such as J/psi rho, J/psi phi, and rho phi at the center of mass energy \sqrt{s}=10.58GeV are calculated. These shed light on the measurement of the e+e- annihilation cross section via radiative return in B-factories. At another center of mass energy \sqrt{s}=3.097GeV, namely the J/psi resonance peak, the processes e+e- --> gamma VV and e+e- --> gamma gamma V (with V being rho, omega, or phi) are calculated with similar method. These calculations give estimation of the background levels in the study of radiative or …
Partial widths of the radiative decays $ϕ(1020)\toγf_0(980)$, $γη$, $γη'$, $γπ^0$ and $f_0(980)\toγγ$ are calculated assuming all mesons under consideration to be $q\bar q$ states: $ϕ(1020)$ is dominantly an $s\bar s$ state ($n\bar n$ component $\lesssim 1%$), $η$, $η'$ and $π^0$ are standard $q\bar q$ states, $η= n\bar n\cosθ- s\bar s\sinθ$ and $η'=n\bar n\sinθ+ s\bar s\cosθ$ with $θ\simeq 37^\circ$, and $f_0(980)$ is the $q\bar q$ meson with the flavour wave function $n\bar n\cosϕ+ s\bar s \sinϕ$. Calculated partial widths for the decays $ϕ\toγη$, $γη'$, $γπ^0$ are in a reasonable agreement …
We study different types of radiative decays involving f0(980) and a0(980) mesons within a unified ChPT-based approach at one-loop level. Light scalar resonances which are seen in pi pi, pi eta, K K-bar channels of phi(1020) radiative decays and in J/psi decays are responsible for key questions of low-energy dynamics in the strong interaction sector, and decays phi(1020) -> gamma a0(980), phi(1020) -> gamma f0(980), a0(980) -> gamma gamma, f0(980) -> gamma gamma are of interest for current experimental programs in Juelich, Frascati and Novosibirsk. From theoretical point of view it is importan…
A consistent description of the pi0 pi0 invariant mass distribution in the phi(1020) -> f0(980) gamma -> pi0 pi0 gamma decay and the pi0 eta in phi(1020) -> a0(980) gamma -> pi0 eta gamma is suggested. A search for the consequences of the flavor SU(3) symmetry for the scalar mesons can be based on such an analysis. In order to accurately treat the pseudoscalar meson dynamics, which is very important for the scalar meson decays, we employ Resonance Chiral Theory.
We study a vector dominance model which predicts a fairly large number of currently interesting decay amplitudes of the types S -> γγ, V -> S γand S -> V γ, where S and V denote scalar and vector mesons, in terms of three parameters. As an application, the model makes it easy to study in detail a recent proposal to boost the ratio Gamma(phi -> f_0 gamma) / Gamma(phi -> a_0 gamma) by including the isospin violating a_0 - f_0 mixing. However we find that this effect is actually small in our model.
Currently there are New Physics hints in mixing-induced CP violation S(phi K0), S(pi0 K0) < S(J/psi K0), unequal direct CP violation A(K+ pi-) differs A(K+ pi0), and maybe even in measured S(J/psi K0) vs prediction from global fit to other data. However, these hints either suffer from experimental uncertainties, or uncertain hadronic corrections, and are not yet unequivocal. Motivated by these hints, however, we point out that a unique probe may be direct CP violation in B to JψK mode. An asymmetry observed at 1% or higher would indicate New Physics.
The radiative return offers the unique possibility for a measurement of the cross section of electron--positron annihilation into hadrons over a wide range of energies. The large luminosity of present phi- and B-factories easily compensates for the additional factor of alpha due to the emission of a hard photon. Final states with photons at large angles can be easily identified. The rate for events with collinear photons, however, is enhanced by a large logarithm and allows, in particular at lower energies, for a complementary measurement. The Monte Carlo generator PHOKHARA, which includes nex…
The measurement of the pion form factor and, more generally, of the cross section for electron--positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the $Φ$- or $B$-meson factories. For detailed understanding and analysis of this reaction, the construction of a Monte Carlo program, PHOKHARA, has been undertaken. Version 2.0 was based on a next-to-leading order (NLO) treatment of the corrections from initial-state radiation (ISR). In the present paper a further extension of PHOKHARA (version 3.0) is described, which i…
A prediction for the contributions of chiral loops and the L$σ$M model to the radiative $ϕ\toπ^0ηγ$ decay mode is presented. The L$σ$M is used as an appropriate framework for describing the pole effects of the $a_0(980)$ scalar resonance. As a result, a better agreement with present available data is achieved for the higher part of the $π^0η$ invariant mass spectrum. For the branching ratio, a value of $B(ϕ\toπ^0ηγ)=(0.75$--$0.95)\times 10^{-4}$ is found.
We study interference patterns in the phi -> gamma a0 + pi0 rho -> gamma pi eta and phi -> gamma f0 + pi0 rho -> gamma pi0 pi0 reactions. Taking into account the interference, we fit the experimental data and show that the background reaction does not distort the pi0eta spectrum in the decay phi -> gamma pi eta everywhere over the energy region and does not distort the pi0 pi0 spectrum in the decay phi -> gamma pi0 pi0 when the invariant mass m_{pi0 pi0} > 670 MeV. We discuss the details of the scalar meson production in the radiative decays and note that there are conclusive arguments in favo…
We study the potential of radiative decays of the Upsilon(1S) and of the phi mesons to search for a light pseudoscalar Higgs boson, proposed as a possible interpretation of Sigma+ --> p mu+mu- events observed by the HyperCP collaboration at Fermilab. We conclude that the detection of this signal should certainly be possible with the current CLEO Upsilon(1S) data, and is within the reach of KLOE in at least part of the range of couplings suggested by the HyperCP findings.
We have measured the radiative decays phi -> eta gamma, phi ->etaprime gamma selecting pi+ pi- gamma gamma gamma final state in a sample of about 5 times 10^7 phi mesons produced at the Frascati phi factory DAFNE. We obtain Gamma(phi -> etaprime gamma)/Gamma(phi -> eta gamma)=(4.70 +- 0.47 +- 0.31) times 10^-3. From this result we derive new accurate values for the branching ratio BR(phi ->etaprime gamma) = (6.10 +- 0.61 +- 0.43) times 10^-5, and the mixing angle of pseudoscalar mesons in the flavour basis phi_P=(41.8 +1.9 -1.6) degrees.
We briefly summarize some searches for Higgs bosons with a mass of m_phi <= 110 GeV at LEP and the LHC. We discuss a possible signal in the diphoton decay mode at m_phi = 96 GeV as reported by CMS, together with a 2 sigma hint in the bb final state at LEP. We briefly review possible interpretation of such a new particle in various BSM models. We focus on possible explanations as reported within the NMSSM and the munuSSM. Conclusions for future collider projects are briefly outlined.
The scalar contributions to the radiative decay $ϕ\to K^0\bar K^0γ$ are studied within the framework of the Linear Sigma Model. Theoretical predictions for the associated subprocesses $ϕ\to f_0γ$ and $ϕ\to a_0γ$ as well as the ratio $ϕ\to f_0γ/a_0γ$ are also given.
The measurement of the pion form factor and, more generally, of the cross section for electron-positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the Phi- or B-meson factories. This quantity is crucial for predictions of the hadronic contributions to the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling. But the radiative return opens the possibility of many other physical applications. The physics potential of this method at high luminosity meson factories is discussed, the …
Main theoretical approaches to weak radiative hyperon decays are briefly reviewed. It is emphasized that only approaches with great predictive power should be seriously considered when seeking a resolution of the puzzle presented by observed large negative asymmetry alpha (Sigma ^+ --> p gamma). In such cases, asymmetry in the Xi ^0 --> Lambda gamma decay is always large while its sign is positive (negative) if Hara's theorem is violated (satisfied). Measuring this asymmetry is therefore crucial for determining whether the large value of alpha (Sigma ^+ --> p gamma) is due to large SU(3) break…
We present an improved calculation of $B\to$ light vector form factors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is typically 10% and can be improved, at least in part, by reducing the uncertainty of hadronic input parameters. We present our results in a way which details the dependence of the form factors on these parameters and facilitates the incorporation of future updates of their values from e.g. lattice calculat…
We analyze the electromagnetic and strong decay properties of the light scalars a0(980) and f0(980) within a hadronic molecule interpretation. Both scalars are discussed within a covariant and gauge invariant model which also allows for finite size effects due to their spatially extended structure in the K Kbar-bound state picture. Allowing for f0-a0 mixing we also study its influence on the radiative decays f0/a0 to gamma gamma, f0/a0 to gamma omega, and f0/a0 to gamma rho as well as the phi production of the f0 and a0. Furthermore, we apply our formalism to describe the strong f0 to pi pi an…
The constraints followed from gauge invariance and analyticity are considered for the amplitudes of radiative transitions of composite systems when composite systems are treated in terms of spectral integrals. We discuss gauge-invariant amplitudes for the transitions S -> gamma S and V -> gamma S with scalar S and vector V mesons being two-particle composite systems of scalar (or pseudoscalar) constituents, and we demonstrate the mechanism of cancellation of false kinematical singularities. Furthermore, we explain how to generalize the performed consideration for quark-antiquark systems, in pa…
Viable explanations of a hinted 750 GeV scalar resonance may be sought within the extensions of the SM Higgs sector aimed at generating neutrino masses at the loop level. We confront a compatibility with the 750 GeV diphoton excess for two recent models which do not need to impose ad hoc symmetry to forbid the tree-level masses: a one-loop mass model providing the H(750) candidate within its real triplet scalar representation and a three-loop mass model providing it within its two Higgs doublets. Besides accounting for the 750 GeV resonance, we demonstrate that these complementary neutrino-mas…
The process of Radiative Emission of Neutrino Pair (RENP) in atoms is sensitive to the absolute neutrino mass scale, the type of spectrum neutrino masses obey and the nature - Dirac or Majorana - of massive neutrinos. We analyse the possibility to test the hypothesis of existence of neutrinos with masses at the eV scale coupled to the electron in the weak charged lepton current in an RENP experiment. The presence of eV scale neutrinos in the neutrino mixing is associated with the existence of sterile neutrinos which mix with the active flavour neutrinos. At present there are a number of hints …
The nature of the light scalar mesons is one of the most intriguing open challenges in hadronic spectroscopy. It is argued that radiative decays involving these scalars can serve as an important decisive tool in establishing their nature. In particular, special emphasis is made on the radiative decays of the scalars themselves (in addition to the radiative decays of the phi-meson with the scalars appearing in the final state), including their two-photon decays. All the above mentioned processes are considered in detail in the (point-like) kaon molecule model of the scalars and explicit predict…
We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R_phi = BR(phi to eta' gamma)/ BR(phi to eta gamma) together with several vector meson radiative decays to pseudoscalars (V to P gamma), pseudoscalar mesons radiative decays to vectors (P to V gamma) and the eta' to gamma gamma, pi^0 to gamma gamma widths. From the fit we extract a gluonium fraction of Z^2_G = 0.12 +- 0.04, the pseudoscalar mixing angle psi_P = (40.4 +- 0.6) degree and the phi-omega mixing angle psi_V = (3.32 +- 0.09) degree. Z^2_G and psi_P are fairly consistent with …
Recently, the CDF and D0 collaborations measured indirect CP violation in Bs -> J/psi phi and found a hint of a signal. If taken at face value, this can be interpreted as a nonzero phase of Bs-Bsbar mixing (beta_s), in disagreement with the standard model, which predicts that beta_s ~= 0. In this paper, we argue that this analysis may be incomplete. In particular, there can be new physics (NP) in the bbar -> sbar c cbar decay. If so, the value of beta_s is different than for the case in which NP is assumed to be present only in the mixing. We have examined several models of NP and found that, …
In the standard model (SM), we re-investigate the rare decay $B\to ϕπ$, which has been viewed as an ideal probe to detect the new physics signals beyond the SM. Contributions in the naive factorization method, the radiative corrections, the long-distance contributions, and the contributions due to the $ω$-$ϕ$ mixing are taken into account. We find that the tiny branching ratio in the naive factorization can be dramatically enhanced by the radiative corrections and the $ω$-$ϕ$ mixing effect, while the long-distance contributions are negligibly small. Assuming the Cabibbo-Kobayashi-Maskawa angle…
Using an improved "analytic K-matrix model", we reconsider the extraction of the sigma/f_0(600) and f_0(980) gamma-gamma widths from gamma-gamma to pi-pi scatterings data of Crystal Ball and Belle. Our main results are summarized in Tables 3 and 4. The averaged sigma "direct width" to gamma-gamma is 0.16(3) keV which confirms a previous result of [1] and which does neither favour a large four-quark (diquark-antidiquark) nor a molecule nor a pure \bar qq component. The "direct width" of the f_0(980) of 0.28(2) keV is much larger than the four-quark expectation but can be compatible with a \bar …
The X(3872) with quantum numbers J(PC) = 1(++) is considered as a composite state containing both molecular hadronic and a c bar(c) component. Based on this structure assumption we first constrain model parameters in order to reproduce the predictions for the radiative decay widths of X(3872) to J/psi gamma and X(3872) to psi(2S) gamma as obtained in c bar(c) potential models. Depending on these predictions we find that further inclusion of the molecular component can in principle lead to an improved description of the radiative X(3872) decays. We also show that strong decay modes of the X(387…
We will describe several pioneering efforts in the study of electromagnetic radiative corrections to semileptonic decay processes, with particular emphasis on the role of lattice QCD. These studies are essential for the precise extraction of the matrix element $V_{ud}$ from beta decays of pion, free neutron and $J^P=0^+$ nuclei, and are crucial to address several recently-emerged anomalies involving $V_{ud}$ and $V_{us}$, which may provide hints for physics beyond the Standard Model.
We present the first complete results for the semileptonic and rare radiative form factors of B-mesons weak decay into a light vector-meson (rho, omega, K*, phi) in the light-cone sum-rule approach. The calculation includes radiative corrections, higher-twist corrections and SU(3)-breaking effects. The theoretical uncertainty is investigated in detail. A simple parametrization of the form factors is given in terms of three parameters each. We find that the form factors observe several relations inspired by heavy-quark symmetry.
We report on further evidence that the Y(3940) and the recently observed Y(4140) are heavy hadron molecule states with quantum numbers J(PC) = 0(++). The Y(3940) state is considered to be a superposition of D*(+)D*(-) and D*(0) barD*(0), while the Y(4140) is a bound state of Ds*(+) and Ds*(-) mesons. For the first time we give predictions for the strong Y(3940) to Jpsi omega, Y(4140) to Jpsi phi and radiative Y(3940)/Y(4140) to gamma gamma decay widths in a phenomenological Lagrangian approach. Results for the strong Jpsi V (V = omega, phi) decays clearly support the molecular interpretation o…
$B$-meson decays involving radiative and electroweak penguin processes are sensitive probes to new physics beyond the standard model. The Belle experiment recently reported measurements of the inclusive radiative decay $B \to X^{}_{s} γ$, and exclusive radiative decays $B \to K^{\ast} γ$ and $B \to K^{0}_{S} ηγ$. A lepton-flavor dependent measurements of angular observables for the decays $B \to K^{\ast} \ell \ell$ by Belle hinted at possible deviation from lepton-flavor-universality. Any departure from lepton flavor universality is essentially accompanied by lepton flavor violation. Recently,…
The following topics are considered. 1) Confinement, chiral dynamics, and light scalar mesons. 2) Chiral shielding of the $σ(600)$. 3) The $ϕ$ meson radiative decays about nature of light scalar resonances. 4) The $J/ψ$ decays about nature of light scalar resonances. 5) The $a_0(980)\toγγ$ and $f_0(980)\toγγ$ decays about nature of light scalar resonances. 6) New round in $γγ\toπ^+π^-$, the Belle data. Arguments in favor of the four-quark model of the $a_0(980)$ and $f_0(980)$ mesons are given.
The form factor of the vector meson V conversion transition into the pseudoscalar meson P and the lepton pair l+l- is presented for V=rho0,omega,phi and P=pi0,eta. Our approach is based on the chiral effective field theory with resonances. The normalized form factor for omega -> pi gamma* transition was fitted to the recent NA 60 data by varying the only free parameter sigma_V. The results are compared to the available data and to the predictions of other models.
