Vub extraction using the Analytic Coupling model
We summarize the main characteristics and recent results on B->Xulnu decays of a model based on soft-gluon resummation and an analytic time-like QCD coupling.
hep-ex↗
arXiv subjects
U. Aglietti
Publications and source records attributed to U. Aglietti.
Tevatron-for-LHC Report: Higgs
The search for Higgs bosons in both the standard model and its extensions is well under way at the Tevatron. As the integrated luminosity collected increases into the multiple inverse femptobarn range, these searches are becoming very interesting indeed. Meanwhile, the construction of the Large Hadron Collider (LHC) and its associated experiments at CERN are nearing completion. In this TeV4LHC workshop, it was realized that any experience at the Tevatron with respect to backgrounds, experimental techniques and theoretical calculations that can be verified at the Tevatron which have relevance for future measurements at the LHC were important. Studies and contributions to these efforts were made in three broad categories: theoretical calculations of Higgs production and decay mechanisms; theoretical calculations and discussions pertaining to non-standard model Higgs bosons; and experimental reviews, analyses and developments at both the Tevatron and the upcoming LHC experiments. All of these contributions represent real progress towards the elucidation of the mechanism of electroweak symmetry breaking.
hep-ph↗
The Two Loop Crossed Ladder Vertex Diagram with Two Massive Exchanges
We compute the (three) master integrals for the crossed ladder diagram with two exchanged quanta of equal mass. The differential equations obeyed by the master integrals are used to generate power series expansions centered around all the singular (plus some regular) points, which are then matched numerically with high accuracy. The expansions allow a fast and precise numerical calculation of the three master integrals (better than 15 digits with less than 30 terms in the whole real axis). A conspicuous relation with the equal-mass sunrise in two dimensions is found. Comparison with a previous large momentum expansion is made finding complete agreement.
hep-ph↗
Analytic Results for Virtual QCD Corrections to Higgs Production and Decay
We consider the production of a Higgs boson via gluon-fusion and its decay into two photons. We compute the NLO virtual QCD corrections to these processes in a general framework in which the coupling of the Higgs boson to the external particles is mediated by a colored fermion and a colored scalar. We present compact analytic results for these two-loop corrections that are expressed in terms of Harmonic Polylogarithms. The expansion of these corrections in the low and high Higgs mass regimes, as well as the expression of the new Master Integrals which appear in the reduction of the two-loop amplitudes, are also provided. For the fermionic contribution, we provide an independent check of the results already present in the literature concerning the Higgs boson and the production and decay of a pseudoscalar particle.
hep-ph↗
Two-loop electroweak corrections to Higgs production in proton-proton collisions
We study the impact of the two-loop electroweak corrections on the production of a Higgs boson via gluon-fusion in proton-proton collisions at LHC energies. We discuss the prescritpion to include the corrections to the hard scattering matrix element in the calculation of the hadronic cross-section sigma (p+p\to H+X). Under the hypothesis of factorization of the electroweak corrections with respect to the dominant soft and collinear QCD radiation, we observe an increase of the total cross-section from 4 to 8 %, for MH <=160 GeV. This increase is comparable with the present QCD uncertainties originating from hard scattering matrix elements.
hep-ph↗
Non-Universal Effects in Semi-Inclusive B Decays
We show that most spectra in the semileptonic decay B -> X_u + l + nu, such as for example the distribution in the light-cone momentum p_+ = E_X - p_X recently considered, do not have the same long-distance structure of the photon spectrum in the radiative decay B -> X_s + gamma. On the contrary, the semileptonic distribution in the final hadron energy E_X is connected to the radiative spectrum via short-distance factors only. The E_X distribution also has a specific infrared structure known as the ``Sudakov shoulder''. We also discuss an explicit check of the resummation formula for the semileptonic decays, based on a recent second-order computation.
hep-ph↗
The evaluation of loop amplitudes via differential equations
The evaluation of loop amplitudes via differential equations and harmonic polylogarithms is discussed at an introductory level. The method is based on evolution equations in the masses or in the external kinematical invariants and on a proper choice of the basis of the trascendental functions. The presentation is pedagogical and goes through specific one-loop and two-loop examples in order to illustrate the general elements and ideas.
hep-ph↗
Master integrals for the two-loop light fermion contributions to $gg \to H$ and $H \to γγ$
We give the analytic expressions of the eight master integrals entering our previous computation of two-loop light fermion contributions to $gg \to H$ and $H \to γγ$. The results are expressed in terms of generalized harmonic polylogarithms with maximum weight four included.
hep-ph↗
Two-loop light fermion contribution to Higgs production and decays
We compute the electroweak corrections due to the light fermions to the production cross section $σ(g g \to H)$ and to the partial decay widths $Γ(H \to γγ)$ and $Γ(H \to g g)$. We present analytic results for these corrections that are expressed in terms of Generalized Harmonic Polylogarithms. We find that for the gluon fusion production cross section and for the decay width $Γ(H \to g g)$ the corrections are large in the Higgs mass region below 160 GeV where they reach up to 9% of the lowest order term. For the decay width $Γ(H \to γγ)$ the corrections for Higgs mass above 160 GeV can reach $-$10% of the lowest order term.
hep-ph↗
Master integrals with 2 and 3 massive propagators for the 2-loop electroweak form factor - planar case
We compute the master integrals containing 2 and 3 massive propagators entering the planar amplitudes of the 2-loop electroweak form factor. The masses of the $W$, $Z$ and Higgs bosons are assumed to be degenerate. This work is a continuation of our previous evaluation of master integrals containing at most 1 massive propagator. The 1/εpoles and the finite parts are computed exactly in terms of a {\it new} class of 1-dimensional harmonic polylogarithms of the variable x, with ε=2-D/2 and D the pace-time dimension. Since thresholds and pseudothresholds in s=\pm 4m^2 do appear in addition to the old ones in s=0,\pm m^2, an extension of the basis function set involving complex constants and radicals is introduced, together with a set of recursion equations to reduce integrals with semi-integer powers. It is shown that the basic properties of the harmonic polylogarithms are maintained by the generalization. We derive small-momentum expansions |s| << m^2 of all the 6-denominator amplitudes. We also present large momentum expansions |s| >> m^2 of all the 6-denominator amplitudes which can be represented in terms of ordinary harmonic polylogarithms. Comparison with previous results in the literature is performed finding complete agreement.
hep-ph↗
Full O(alpha_S) Evaluation for b->s+gamma Transverse Momentum Distribution
The full O(alpha_S) transverse momentum distribution for the b -> s+gamma decay is computed. Results are presented in analytic form. An improved expression for the coefficient function taking into account subleading operators is given and an exact expression for the remainder function associated with the leading operator O_7 is also derived.
hep-ph↗
Master integrals with one massive propagator for the two-loop electroweak form factor
We compute the master integrals containing one massive propagator entering the two-loop electroweak form factor, i.e. the process f fbar --> X, where f fbar is an on-shell massless fermion pair and X is a singlet particle under SU(2)L x U(1)Y, such as a virtual gluon or an hypothetical Z'. The method used is that of the differential equation in the evolution variable x = -s/m^2, where s is the c.m. energy squared and m is the mass of the W or Z bosons (assumed to be degenerate). The 1/εpoles and the finite parts are computed exactly in terms of one-dimensional harmonic polylogarithms of the variable x, H(w;x), with ε=2-D/2 and D the space-time dimension. We present large-momentum expansions of the master integrals, i.e. expansions for |s| >> m^2, which are relevant for the study of infrared properties of the Standard Model. We also derive small-momentum expansions of the master integrals, i.e. expansions in the region |s| << m^2, related to the threshold behaviour of the form factor (soft probe). Comparison with previous results in the literature is performed finding complete agreement.
hep-ph↗
A new sum rule to determine Vub/Vcb
We present a new sum rule which does not contain any Landau-pole effect and allows a determination of Vub/Vcb with a theoretical error of O(5%).
hep-ph↗
Next-to-leading resummed coefficient function for the shape function
We present a next-to-leading evaluation of the resummed coefficient function for the shape function. The results confirm our previous leading order analysis, namely that the coefficient function is short-distance-dominated, and allow relating the shape function computed with a non-perturbative technique to the physical QCD distributions.
hep-ph↗
Transverse Momentum Distributions in B-Decays
We consider transverse momentum distributions in B-decays. The O(alpha_S) coefficients for soft and collinear logarithms are computed to next-to-leading accuracy. Resummation of large logarithmic contributions is performed in impact parameter space within the general formalism for transverese momentum distributions. It is shown that the shape-function approach as used for the threshold distribution case cannot be extended to the transverse momentum one.
hep-ph↗
Resummed B -> X_u l nu Decay Distributions to Next-to-Leading Order
We perform factorization of the most general distribution in semileptonic B -> X_u decays and we resum the threshold logarithms to next-to-leading order. From this (triple-differential) distribution, any other distribution is obtained by integration. As an application of our method, we derive simple analytical expressions for a few distributions, resummed to leading approximation. It is shown that the shape function can be directly determined by measuring the distribution in m_X^2/E_X^2, not in m_X^2/m_B^2. We compute the resummed hadron energy spectrum, which has a ``Sudakov shoulder'', and we show how the distribution in the singular region is related to the shape function. We also present an improved formula for the photon spectrum in B->X_s gamma which includes soft-gluon resummation and non-leading operators in the effective hamiltonian. We explicitly show that the same non-perturbative function - namely the shape function - controls the non-perturbative effects in all the distributions in the semi-leptonic and in the rare decay.
hep-ph↗
A sum rule from the shape function
We present a sum rule relating the electron energy spectrum and the hadron mass distribution in semileptonic b -> u decays close to threshold. The relation found is free from non-perturbative effects and the theoretical error is expected to be O(5%). An experimental confirmation of this prediction can provide a check of the basic assumptions at the root of the theory of the shape function.
hep-ph↗
Resummed coefficient function for the shape function
We present a leading evaluation of the resummed coefficient function for the shape function. It is also shown that the coefficient function is short-distance-dominated. Our results allow relating the shape function computed on the lattice to the physical QCD distributions.
hep-ph↗