Search results for "FACTORIZATION"
showing 10 items of 221 documents
Wide Angle Compton Scattering within the SCET factorization Framework
2016
Existing data for the electromagnetic proton form factors and for the cross section of the wide angle Compton scattering (WACS) show that the hard two-gluon exchange mechanism (collinear factorization) is still not applicable in the kinematical region where Mandelstam variables s ~ −t ~ −u are about few GeV2 . On the other hand these observables can be described in phenomenological models where spectator quarks are soft which assumes a large contribution due to the soft-overlap mechanism. It turns out that the simple QCD factorization picture is not complete and must also include the soft-overlap contribution which can be described as a certain matrix element in the soft collinear effective…
Evolution of the $B$-Meson Light-Cone Distribution Amplitude in Laplace Space
2020
The $B$-meson light-cone distribution amplitude is a central quantity governing non-perturbative hadronic dynamics in exclusive $B$ decays. We show that the information needed to describe such processes at leading power in $\Lambda_{\rm QCD}/m_b$ is most directly contained in its Laplace transform $\tilde\phi_+(\eta)$. We derive the renormalization-group (RG) equation satisfied by this function and present its exact solution. We express the RG-improved QCD factorization theorem for the decay $B^-\to\gamma\ell^-\bar\nu$ in terms of $\tilde\phi_+(\eta)$ and show that it is explicitly independent of the factorization scale. We propose an unbiased parameterization of $\tilde\phi_+(\eta)$ in ter…
Factorization and N3LLp+NNLO predictions for the Higgs cross section with a jet veto
2013
We have recently derived a factorization formula for the Higgs-boson production cross section in the presence of a jet veto, which allows for a systematic resummation of large Sudakov logarithms of the form alpha_s^n ln^m(p_T^veto/m_H), along with the large virtual corrections known to affect also the total cross section. Here we determine the ingredients entering this formula at two-loop accuracy. Specifically, we compute the dependence on the jet-radius parameter R, which is encoded in the two-loop coefficient of the collinear anomaly, by means of a direct, fully analytic calculation in the framework of soft-collinear effective theory. We confirm the result obtained by Banfi et al. from a…
Brodsky-Lepage-Mackenzie scale for the pion transition form factor
2002
The next-to-leading order (NLO) Brodsky-Lepage-Mackenzie (BLM) scale for the pion transition form factor is determined. To achieve that, a consistent calculation up to ${n}_{f}$-proportional next-to-next-to-leading order contributions to both the hard-scattering amplitude and the perturbatively calculable part of the pion distribution amplitude is performed. By combining and matching the results obtained for these two amplitudes, a proper cancellation of collinear singularities is established and the ${\ensuremath{\gamma}}_{5}$ ambiguity problem (related to the use of the dimensional regularization method) is resolved by using the naive-${\ensuremath{\gamma}}_{5}$ as well as the 't Hooft--V…
Novel nonperturbative approach for radiativeB¯0(B¯s0)→J/ψγdecays
2016
Radiative ${\overline{B}}^{0}({\overline{B}}_{s}^{0})\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\gamma}$ decays provide an interesting case to test our understanding of (non)perturbative QCD and eventually to probe physics beyond the standard model. Recently, the LHCb Collaboration reported an upper bound, updating the results of the BABAR Collaboration. Previous theoretical predictions based on QCD factorization or perturbative QCD have shown large variations due to different treatment of nonfactorizable contributions and meson-photon transitions. In this paper, we report on a novel approach to estimate the decay rates, which is based on a recently proposed model for $B$ decays…
Symmetries in the angular distribution of exclusive semileptonic B decays
2010
We discuss a method to construct observables protected against QCD uncertainties based on the angular distribution of the exclusive Bd -> K(*0}(-> Kpi) l+ l- decay. We focus on the identification and the interpretation of all the symmetries of the distribution. They constitute a key ingredient to construct a set of so-called transverse observables. We work in the framework of QCD factorization at NLO supplemented by an estimate of power-suppressed Lambda/mb corrections. A discussion of the new physics properties of two of the transverse asymmetries, AT^{(2)} and AT^{(5)}, is presented. A comparison between the transverse asymmetry AT^{(2)} and the forward-backward asymmetry shows that…
Two-loop divergences of scattering amplitudes with massive partons
2009
We complete the study of two-loop infrared singularities of scattering amplitudes with an arbitrary number of massive and massless partons in non-abelian gauge theories. To this end, we calculate the universal functions F_1 and f_2, which completely specify the structure of three-parton correlations in the soft anomalous-dimension matrix, at two-loop order in closed analytic form. Both functions are found to be suppressed like O(m^4/s^2) in the limit of small parton masses, in accordance with mass factorization theorems proposed in the literature. On the other hand, they are unsuppressed and diverge logarithmically near the threshold for pair production of two heavy particles. As an applica…
Feasibility study for the measurement of πN transition distribution amplitudes at P¯ANDA in p¯p→J/ψπ0
2017
The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is show…
Radiative decays χcJ→Vγ within the QCD factorization framework
2017
We present a discussion of radiative decays ${\ensuremath{\chi}}_{cJ}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\rho}(\ensuremath{\omega},\ensuremath{\phi})$. The decay amplitudes are computed within the QCD factorization framework. NRQCD has been used in the heavy meson sector as well as a collinear expansion in order to describe the overlap with light mesons in the final state. The color-singlet contributions to all helicity amplitudes have been computed using the light-cone distribution amplitudes of twist-2 and twist-3. All obtained expressions are well defined at least in the leading-order approximation. The color-octet contributions have also been studied in the Coulomb li…
The present status of the EPS nuclear PDFs
2010
The recent global analyses of the nuclear parton distribution functions (nPDFs) lend support to the validity of the factorization theorem of QCD in high-energy processes involving bound nucleons. With a special attention on our latest global analysis EPS09, we review the recent developements in the domain of nuclear PDFs.