Inclusive Particle Spectra From QCD Cascades

Abstract

New results in applications of the analytical perturbative approach to the description of particle distributions in QCD jets are presented. We study inclusive energy spectra of partons from QCD cascades truncated at different values of the cutoff parameter Q0, which can be used to model the energy distributions of massive hadrons in the framework of the local parton-hadron duality hypothesis. Results of straightforward numerical calculations of parton distributions which solve the MLLA evolution equations are compared to approximate formulas representing the spectra in terms of a few analytically calculated shape parameters.

Screened-Coulomb ansatz for the nonfactorizable radiative corrections to off-shell $W^+W^-$ production

“…Another example of the cancellation of the off-shell effects at relativistic energies has been known for quite a while (see e.g. [6,13]). When considering the gluon radiation corresponding to the top production and decay at very high energies, one observes that the width-dependent effects vanish when the emission at the production and decay stages are added coherently.…”

Low and high energy limits of particle spectra in QCD jets

“…Recently, the first such moment analysis, based on the analytical results [17], has been performed over the full cms energy range available in e + e − annihilation [18]. There are a number of advantages of the moment analysis over the analysis of the spectrum itself: (a) there are analytical formulae which keep the two essential parameters of the theory Q 0 and Λ independent [17], whereas explicit formulae for the spectrum are only available for the limiting case Q 0 = Λ; (b) the moments evolve with energy independently of each other. Their absolute size is determined by the initial condition at the threshold of the process; (c) the moments of order q ≥ 1 are independent of the overall normalization and depend only on the two essential parameters of the LPHD approach; (d) the difference between the theory with running coupling and an artificial theory with fixed coupling can be studied directly and (e) the flavour thresholds can be included in the theoretical calculations.…”

Jet Quenching in Relativistic Heavy Ion Collisions at the LHC

“…This has led to development of calculations using a modified leading log approximation (MLLA), which include corrections for next-to-leading effects [65][66][67][68][69]. In general, the behavior of these enhancements is to cause the "hump-backed plateau" behavior, 32) with ξ = ln 1/x and the width and peak approximately given by [70],…”

“…In the AMY approach [47,48,65,66], the gluon emission rates are calculated fully at leading order in ↵ s by resumming an infinite number of ladder diagrams in the Clearly the assumption of collinearity is badly violated: for values of x ⇠ µ/E, dN g /dxdk T reaches its maximum value at k T ⇠ xE. For these values of x the emission spectrum is highly sensitive to the choice of k max : dN g /dx ⇠ k 2 max .…”

“…In the AMY approach [47,48,65,66], the gluon emission rates are calculated fully at leading order in ↵ s by resumming an infinite number of ladder diagrams in the made it difficult to consistently fix parameters for a direct comparison of models. However a recent comparison was performed by applying the GLV, AMY and ASW (both MS and SH) formalisms to a "brick" of QGP matter of fixed length [150].…”