Search results for "hadron"
showing 10 items of 3505 documents
Precision physics with QCD
2016
The four-loop determination of the strong coupling from fully inclusive observables is reviewed. Special attention is given to the low-energy measurement extracted from the hadronic $\tau$ decay width. A recent exhaustive analysis of the ALEPH data, exploring several complementary methodologies with very different sensitivities to inverse power corrections and duality violations, confirms the strong suppression of non-perturbative contributions to $R_\tau$. It gives the value $\alpha_s(m_\tau^2)= 0.328 \pm 0.013$, which implies $\alpha_s(M_Z^2)= 0.1197 \pm 0.0015$. The excellent agreement with the direct measurement at the $Z$ peak, $\alpha_s(M_Z^2)= 0.1196 \pm 0.0030$, provides a beautiful…
Determination of the Transverse Momentum of W Bosons in Hadronic Collisions via Forward Folding Techniques
2015
The measurement of the transverse momentum of W bosons in hadron collisions provides not only an important test of QCD calculations, but also is an important input for the precision measurement of the W boson mass. While the measurement of the Z boson transverse momentum is experimentally well under control, the available unfolding techniques for the W boson final states lead generically to relatively large uncertainties. In this paper, we present a new methodology to estimate the W boson transverse momentum spectrum, significantly improving the systematic uncertainties of current approaches.
Non-perturbative momentum dependence of the coupling constant and hadronic models
2011
Models of hadron structure are associated with a hadronic scale which allows by perturbative evolution to calculate observables in the deep inelastic region. The resolution of Dyson-Schwinger equations leads to the freezing of the QCD running coupling (effective charge) in the infrared, which is best understood as a dynamical generation of a gluon mass function, giving rise to a momentum dependence which is free from infrared divergences. We use this new development to understand why perturbative treatments are working reasonably well despite the smallness of the hadronic scale.
τ→πππντdecays in the resonance effective theory
2004
$\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ decays are analyzed within the framework of the resonance effective theory of QCD. We work out the relevant Lagrangian that describes the axial-vector current hadronization contributing to these processes, in particular the local ${a}_{1}(1260)\ensuremath{-}\ensuremath{\rho}(770)$-Goldstone interactions. The new coupling constants are constrained by imposing the asymptotic behavior of the corresponding spectral function within QCD. Hence we compare the theoretical framework with the experimental data, obtaining a good quality fit from the ALEPH spect…
Measuring KS0K± interactions using Pb–Pb collisions at sNN=2.76 TeV
2019
We present the first measurements of femtoscopic correlations between the KS0 and K± particles in pp collisions at s=7 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding solely via the a0(980) resonance. The extracted kaon source radius and correlation strength parameters for KS0K− are found to be equal within the experimental uncertainties to those for KS0K+ . Results of the present study are compared with those from identical-kaon femtoscopic studies also performed with pp collisions at s=7 TeV by ALICE and with a KS0K± measurement in Pb–Pb collisions at sNN=2.76 TeV. Combined with the Pb–Pb results, our pp a…
Hadron polarizability data analysis: GoAT
2015
The A2 Collaboration at the Institute for Nuclear Physics in Mainz, Germany, is working towards determining the polarizabilities of hadrons from nonperturbative quantum chromodynamics through Compton scattering experiments at low energies. The asymmetry observables are directly related to the scalar and spin polarizabilities of the hadrons. Online analysis software, which will give real-time feedback on asymmetries, efficiencies, energies, and angle distributions, has been developed. The new software is a big improvement over the existing online code and will greatly develop the quality of the acquired data.
W+W−Production at Hadron Colliders in Next to Next to Leading Order QCD
2014
Charged gauge boson pair production at the Large Hadron Collider allows detailed probes of the fundamental structure of electroweak interactions. We present precise theoretical predictions for on-shell W+ W- production that include, for the first time, QCD effects up to next to next to leading order in perturbation theory. As compared to next to leading order, the inclusive W+ W- cross section is enhanced by 9% at 7 TeV and 12% at 14 TeV. The residual perturbative uncertainty is at the 3% level. The severe contamination of the W+ W- cross section due to top-quark resonances is discussed in detail. Comparing different definitions of top-free W+ W- production in the four and five flavor numbe…
Multiple polylogarithms with algebraic arguments and the two-loop EW-QCD Drell-Yan master integrals
2020
We consider Feynman integrals with algebraic leading singularities and total differentials in $\epsilon\,\mathrm{d}\ln$ form. We show for the first time that it is possible to evaluate integrals with singularities involving unrationalizable roots in terms of conventional multiple polylogarithms, by either parametric integration or matching the symbol. As our main application, we evaluate the two-loop master integrals relevant to the $\alpha \alpha_s$ corrections to Drell-Yan lepton pair production at hadron colliders. We optimize our functional basis to allow for fast and stable numerical evaluations in the physical region of phase space.
Unraveling the organization of the QCD tapestry
2015
I review some key aspects of the ongoing progress in our understanding of the infrared dynamics of the QCD Green's functions, derived from the close synergy between Schwinger-Dyson equations and lattice simulations. Particular attention is dedicated to the elaborate nonperturbative mechanisms that endow the fundamental degrees of freedom (quarks and gluons) with dynamical masses. In addition, the recently established connection between the effective interaction obtained from the gauge sector of the theory and that needed for the veracious description of the ground-state properties of hadrons is briefly presented.
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…