In this short review, the calculation of the next-to-next-to-leading order QCD corrections to the inclusive radiative decay B -> X_s gamma is described. I summarize the salient features of the calculational framework adopted, discuss the results obtained in the last few years, and indicate the technical tools that made the NNLO calculations possible. I conclude by comparing the current NNLO theoretical estimate for the branching ratio with the experimental measurement and by briefly discussing the size and origin of the residual theoretical uncertainty.
Radiative W production at hadron colliders is an important testing ground for the Standard Model. We consider W gamma gamma production which is sensitive to the quartic WW gamma gamma coupling. Furthermore the Standard Model amplitude for this process contains a radiation zero. We present a calculation of the NLO QCD corrections for W gamma gamma production at the LHC.
We have calculated the O(alpha) radiative corrections to the tau decay tau -> pi (K) nu, taking into account both the point meson contribution and the structure dependent radiation. We find for the ratio Gamma(tau -> pi nu (gamma)) / Gamma(pi -> mu nu (gamma)) a radiative correction of + 1.2% and for Gamma(tau -> K nu (gamma)) / Gamma(K -> mu nu (gamma)) one of + 2.0%. We compare our results with an earlier estimation and with experimental data.
Supported by recent lattice results, we consider a scenario in which a U(1)-breaking condensate survives across the chiral transition in QCD. This scenario has important consequences on the pseudoscalar-meson sector, which can be studied using an effective Lagrangian model. In particular, generalizing the results obtained in a previous paper (where the zero-temperature case was considered), we study the effects of this U(1) chiral condensate on the radiative decay eta' --> gamma gamma at finite temperature.
The radiative "B_c -> tau nu_tau gamma" decay is analyzed in the standard model. The branching ratio of this decay is calculated and the contributions of the Bremstrahlung and structure dependent parts are compared. It is shown that this decay can be detected at LHC.
We discuss a model-independent framework for the analysis of the radiative B-meson decays B -> K* gamma and B -> rho gamma based on the heavy-quark limit of QCD. We present a factorization formula for the treatment of B -> V gamma matrix elements involving charm (or up-quark) loops, which contribute at leading power in Lambda_QCD/m_B to the decay amplitude. Annihilation topologies are power suppressed, but still calculable in some cases. The framework of QCD factorization is necessary to compute exclusive b -> s(d) gamma decays systematically beyond the leading logarithmic approximation. Resul…
The role of gauge invariance in calculating B -> V gamma radiative weak decays is clarified. It is shown that the gauge invariance severely restricts the contributions mediated by the usual weak non-leptonic Hamiltonian dominated by u and c quaks with one photon attachment. Such contributions are found to be almost negligible.
The coupling constant of rho --> eta gamma decay is calculated in the framework of light cone QCD sum rules. A comparison of our prediction on the coupling constant with the result obtained from analysis of the experimental data is performed.
The transition form factors responsible for the radiative $Σ_Q \to Λ_Q γ$ and $Ξ_Q^\prime \to Ξγ$ decays of the negative parity baryons are examined within light cone QCD sum rules. The decay widths of the radiative transitions are calculated using the obtained results of the form factors.
The "g_{Delta N gamma}" coupling for the "Delta -> N gamma" decay is calculated in framework of the light cone QCD sum rules and is found to be g_{Delta N gamma} = (1.6 pm 0.2) GeV^(-1). Using this value of g_{Delta N gamma} we estimate the branching ratio of the Delta^+ -> N gamma decay, which is in a very good agreement with the experimental result.
In this work, the radiative Bc -> D*_s gamma decay is investigated in the framework of QCD sum rules. The transition form factors responsible for the decay are calculated. The branching ratio for this decay is estimated to be order of 10^-5 which can be measurable at LHC.
The radiative B -> tau^+ tau^- gamma decay is investigated in the framework of the Standard Model. When only short (short and long together) distance contributions are taken into account, the Branching Ratio is found as 9.54x10^(-9) (1.52x10^(-8)), for the value of the cut delta = 0.01 imposed on the photon energy.
The radiative decays of heavy baryons and lowest three doublets of heavy mesons are studied with the light cone QCD sum rules in the leading order of heavy quark effective theory.
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.
Next-to-leading order electroweak and QCD radiative corrections to the Drell-Yan process with high dimuon masses for experiments CMS LHC at CERN have been studied in fully differential form. The FORTRAN code READY for numerical analysis of Drell-Yan observables has been presented. The radiative corrections are found to become significant for CMS LHC experiment setup.
We investigate a new method to probe the helicity of the photon emitted in the b -> s gamma transition. The method relies on the observation of interference effects between two resonance contributions, B -> K*(K gamma) gamma and B -> eta_c(gamma gamma) K or B -> chi_c0(gamma gamma) K to the same final state K gamma gamma. Decays of the type B -> K_res(K gamma) gamma dominate the B -> K gamma gamma yield throughout most of the phase space, and may be accessible at current B meson facilities already.
We describe several problems related to the studies of the effects of radiative QCD corrections in the phenomenological and theoretical considerations thus summarizing the work of the QCD part of the Symposium on "Radiative Corrections: Status and Outlook".
The O(alpha) electroweak radiative corrections to gamma gamma --> WW --> 4f within the electroweak Standard Model are calculated in double-pole approximation (DPA). Virtual corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for gamma gamma --> 4f + gamma. Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-spac…
We apply a phenomenological Lagrangian approach to the radiative decay Y(4260) -> X(3872) + gamma. The Y(4260) and X(3872) resonances are considered as composite states containing both molecular hadronic and charmonium components. Having a leading molecular component in the X(3872) and a sole molecular configuration for the Y(4260) results in a prediction compatible with present data.
We investigate the radiative B_c -> rho^+ gamma and B_c -> K^{*+} gamma decays in the standard model. The transition form factors are calculated in the framework of the light cone QCD sum rules method. We estimate the branching ratios of the B_c -> rho^+ gamma and B_c -> K^{*+} gamma decays.
We analyze the double radiative B-meson decays B_s -> gamma gamma and B_d -> gamma gamma in QCD factorization based on the heavy-quark limit m_b >> Lambda_QCD. We systematically discuss the various contributions to these exclusive processes. The dominant effect arises from the magnetic-moment type transition b -> s(d) gamma where an additional photon is emitted from the light quark (one-particle reducible diagram). The contributions from one-particle irreducible diagrams are power suppressed. We argue that they are still calculable within QCD factorization. They are used to compute the CP-asym…
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.
The radiative decays $ B^{*} (D^{*})\to B(D) γ$ are investigated in the framework of light cone QCD sum rules. The transition amplitude and decay rates are estimated.It is shown that our results on branching ratios of D meson decays are in good agreement with the existing experimental data.
The radiative decays $ B^{*} (D^{*})\rightarrow B(D) γ$ are investigated in the framework of light cone QCD sum rules. The transition amplitude and decay rates are estimated.It is shown that our results on branching ratios of D meson decays are in good agreement with the existing experimental data.
QCD radiative correction to Higgs $\rightarrow$ two photons decay rate is calculated. Below the threshold we found negligible correction, thus supporting results obtained earlier by Djouadi et all [7]. Above the threshold radiative correction appears to be large for both real and imaginary part of H $γγ$ vertex. This leads to radiative correction for $Γ$(H $\rightarrow γγ$) to be of order 20--100 percents at $m_{t}=150 GeV$. Possible applications of our results for Higgs search at Next Linear Colliders (NLC) are briefly discussed.
We predict observables in radiative B decays to vector mesons using holographic AdS/QCD Distribution Amplitudes for the vector mesons. We find that end-point divergences can be avoided when computing power-suppressed contributions in the heavy quark limit. The results reported here can be found in references [1] and [2].
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 exclusive process e+ e- -> e+ e- rho^0_L rho^0_L allows to study various dynamics and factorization properties of perturbative QCD. At moderate energy, we demonstrate how collinear QCD factorization emerges, involving generalized distribution amplitudes (GDA) and transition distribution amplitudes (TDA). At higher energies, in the Regge limit of QCD, we show that it offers a promising probe of the BFKL resummation effects to be studied at the International Linear Collider (ILC).
The transition magnetic dipole and electric quadrupole moments of the radiative decays of the sextet heavy flavored spin 3/2 to the heavy spin 1/2 baryons are calculated within the light cone QCD sum rules approach. Using the obtained results, the decay rate for these transitions are also computed and compared with the existing predictions of the other approaches.
A substantial enhancement is found of the $b \to c\,{\overline c}\, s$ decay rate due to the QCD interaction within the $\overline c s$ pair, which enhancement may amount to 30\%, or more. Some general features of calculation of the QCD radiative corrections in two first orders are discussed.
The exclusive reaction of rho meson pair electroproduction in gamma*gamma* collisions is a nice place to study various dynamics and factorization properties in the perturbative sector of QCD. At low energy (quarks dominance), this process can be considered as a way to explore QCD factorizations involving generalized distribution amplitudes (GDA) and transition distribution amplitudes (TDA), and, in the Regge limit of QCD (gluons dominance), it seems to offer a promising probe of the BFKL resummation effects which could be studied at the next international linear collider (ILC).
We present analytic results for the one-loop corrections of the helicity amplitudes of the QCD five-parton subprocesses involving four quarks and one gluon obtained with a standard Feynman diagram calculation using dimensional reduction.
Higgs boson radiative decays of the form $H\rightarrow f\bar{f}γ$ are calculated in the Standard Model using the complete one-loop expressions for the decay amplitudes. Contributions to the radiative width from leptons and light quarks are given. We also present $e\bar{e}$ invariant mass distributions for $H\rightarrow e\bar{e}γ$, which illustrate the importance of the photon pole contribution and the effects of the box diagrams.
The decay constants and the radiative decay widths of η_b(nS) and η_c(nS) are computed within a semirelativistic quark model, using a potential found through the AdS/QCD correspondence. For η_c, the results are in agreement with experimental data, while in the case of η'_c a discrepancy is found and the possible reasons are discussed.
The exclusive process e+ e- -> e+ e-rho0_L rho0_L allows to study various dynamics and factorization properties of perturbative QCD. At moderate energy, we demonstrate how collinear QCD factorization emerges, involving either generalized distribution amplitudes (GDA) or transition distribution amplitudes (TDA). At higher energies, in the Regge limit of QCD, we show that it offers a promising probe of the BFKL resummation effects to be studied at ILC.
The transition form factors of the radiative decays of the heavy tensor mesons to heavy pseudoscalar and heavy vector mesons are calculated in the framework of the light cone QCD sum rules method at the point $Q^2=0$. Using the obtained values of the transition form factors at the point $Q^2=0$ the corresponding decay widths are estimated. The results show that the radiative decays of the heavy--light tensor mesons can be measurable in the future planned experiments at LHCb.
Evaluation of anomalous couplings in the $γγ\to W^+W^-$ process needs to calculate the cross section $σ(W^+W^-)$ with a high precision. Therefore one has to consider the main contribution of high order effects. In this paper contributions of anomalous quartic boson interaction given by ${\cal L}_0$, ${\cal L}_c$, $\tilde{\cal L}_0$ are analyzed in high-energy region. Influence of high order effects is studed in dependences of $σ(W^+W^-)$ on anomalous constants and contour plots with statistical error $2δ$.
In this article, we calculate the $B_c^* \to B_c$ electromagnetic form-factor with the three-point QCD sum rules, then study the radiative decays $ B_c^{*\pm} \to B_c^{\pm} γ$. Experimentally, we can study the radiative transitions using the decay cascades $B_c^{*\pm}\to B_c^{\pm} γ\to J/ψ\ell^{\pm}\barν_{\ell} γ\to μ^+ μ^- \ell^{\pm}\barν_{\ell} γ$ in the future at the LHCb.
We have calculated the next-to-leading order perturbative QCD corrections to the photon energy spectrum in radiative Upsilon decays. The higher-order corrections significantly modify the shape of the spectrum, in particular at large photon energies, and thereby reduce the discrepancy between experimental data and previous leading-order predictions. The next-to-leading order calculation of the photon energy spectrum allows a more reliable determination of the strong coupling constant from radiative Upsilon decays by restricting the analysis to the region of the energy spectrum that can be descr…
Motivated by the observation of the decay B to K* gamma by the CLEO collaboration, we have systematically analyzed the weak radiative decay Lambda_b to Lambda gamma, evaluating the confined effects of quarks in the covariant oscillator quark model. This decay process receives both short distance (electromagnetic penguins at the one loop level) the long distance contributions in the quark level. The long distance contributions are analyzed using the vector meson dominance (VMD) method. The estimated branching ratio is found to be 0.23 times 10^-5.
We discuss exclusive radiative decays in QCD factorization within the Standard Model. In particular, we consider the decays B -> V gamma, with a vector meson K* or rho in the final state, and the double radiative modes B_s -> gamma gamma and B_d -> gamma gamma. At quark level, all these decays are governed by the flavour-changing neutral-current b -> s gamma or b -> d gamma transitions, which appear at the one-loop level in the Standard Model. Such processes allow us to study CP violation and the interplay of strong and electroweak interactions, to determine parameters of the CKM matrix, and t…
Using a recent calculation of transition magnetic moments in the 1/N_c expansion and a calculation showing the suppression of E2/M1 by powers of N_c, we compute the widths for the radiative decays Sigma^* --> Sigma gamma, Sigma^* --> Lambda gamma, and Xi^* --> Xi gamma.
We compute the J/psi+gamma invariant-mass distributions from the QCD subprocess g + g --> J/psi+gamma. At large masses, this subprocess is the dominant mechanism for J/psi+gamma production, and data could provide a good test of QCD. The mass distribution peaks at relatively small masses (3.4 - 4.0 GeV) and the subprocess could, therefore, represent a significant QCD background to J/psi+gamma decay of heavier charmonia. We also analyze the J/psi angular distribution in the J/psi+gamma rest frame.
The radiative decays D^0 -> K^0(bar) P^0 gamma with nonresonant K^0(bar) P^0 (P^0 = pi^0, eta, eta') are considered within the framework which combines heavy quark effective theory and the chiral Lagrangian. Due to neutral mesons the amplitudes do not have bremsstrahlung contributions. We assume factorization for the weak matrix elements. Light (virtual) vector mesons are found to give the main contribution to the decay amplitudes. The decay D^0 -> K^0(bar) pi^0 gamma is predicted to have a branching ratio of 3 x 10^(-4), with comparable contributions from parity-conserving and parity-violatin…
The coupling constant g_{rho sigma gamma} is determined from light cone QCD sum rules. A comparison of our result with the ones existing in literature is presented.
The radiative decays of decuplet to octet baryons are analyzed within the light cone QCD sum rules framework.The electromagnetic transition form factors for these decays are calculated up to twist four accuracy for photon wave functions as well as including first order strange quark mass corrections. A comparison of our results with predictions of lattice theory and existing experimental data is presented.
We show that radiatively generated Majorana mass for antiquarks is same as the Cooper-pair gap. We then calculate the electromagnetic corrections to mass of particles in the color-flavor locking phase of QCD at high density. The mass spectrum forms multiplets under $SU(2)_V\times U(1)_V$. The charged pions and kaons get the electromagnetic mass which is proportional to the Cooper-pair gap.
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 …
The coupling constant of a0-->rho-gamma and f0-->rho-gamma decays are calculated using 3-point sum rule. We estimate the coupling constant g_a0-rho-gamma and g_f0-rho-gamma which are an essential ingredient in the analysis of physical processes involving isoscalar f0(980) and isovector a0(980) mesons.
The sensitivity of observables in radiative decays psi(2S) -> gamma chi_{1,2} -> gamma gamma J/psi to quadrupole (M2) admixtures in the dominant electric dipole (E1) transitions is explored. Emphasis is placed on distributions in a single angle, and several examples are given.
This paper is devoted to the calculation of the quark-gluon-Reggeized quark effective vertex in perturbative QCD in the next-to-leading order. The case of QCD with massive quarks is considered. This vertex has a number of applications, in particular, the result can be used for determination of the next-to-leading correction to the massive Reggeized quark trajectory.
We investigate the a0-omega-gamma vertex and estimate the coupling constant in the framework of the light cone QCD sum rules. We compare our result with the value of the coupling constant was calculated in the QCD sum rules.
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…
A QCD analysis of the reactions A B -> gamma^* gamma and gamma^* gamma -> A B in the forward region shows that they can be factorized in a way which is quite similar to the frameword developped for deeply virtual Compton scattering. The generalized parton distributions (GPDs) related to this latter process being replaced by new non perturbative hadronic matrix elements, the transition distribution amplitudes (TDAs).
Exclusive weak radiative B meson decays are studied using the covariant oscillator quark model. The branching ratios for the processes B0 to K*0 gamma and B to K* gamma have been estimated. These are in reasonable agreement with the available experimental data. The calculation has been extended to the CKM-suppressed decay processes B- to rho- gamma and Bs to K*0 gamma .
We present a complete calculation of the Leading Order QCD corrections to the quark level decay amplitude for b -> s gamma gamma and study their relevance for both the inclusive branching ratio BR(B -> X_s gamma gamma) and for the exclusive decay channel B_s -> gamma gamma. In addition to the uncertainties in the short distance calculation, due to the choice of the renormalization scale, an appreciable uncertainty in both B_s -> gamma gamma and B -> X_s gamma gamma is introduced by the matrix element calculation. We also briefly discuss some long distance effects, especially those due to the e…
QCD sum rules are used to calculate the contribution of short-distance single-quark transition $s\rightarrow d γ$, to the amplitudes of the hyperon radiative decay, $Ω^-\rightarrow Ξ^-γ$. We re-evaluate the Wilson coefficient of the effective operator responsible for this transition. We obtain a branching ratio which is comparable to the unitarity limit.
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.
The coupling constant of g_phi-pion-gamma decay is calculated using light cone QCD sum rules. A comparison of our result with the ones existing in the literature is presented.
An analytic formula for the two-loop QCD correction of the decay H --> 2 gamma is presented. To evaluate all master integrals a `Risch-like' algorithm was exploited.
