On specific QCD properties of heavy quark fragmentation ('dead cone')

SQM 2006: theory summary and perspectives

“…Among the novelties presented was the work by K. Tuchin, who discussed heavy quark production in High Parton Density QCD in a quasi-classical approximation, including low-x quantum evolution, as well as heavy-quark production based on the effect of pair production in external fields [108]. For moderate transverse momenta (p T ≤ a few GeV/c) the energy loss of heavy quarks is thought to be dominated by inelastic collisions with medium constituents, rather than gluon radiation [109,110], because the heavy quarks are not ultra-relativistic and gluon radiation is suppressed by the so-called dead-cone effect [111]. These findings were highlighted in a comprehensive analysis of the non-photonic electron nuclear suppression factors measured at RHIC presented by M. Djordjevic [112,113].…”

Exposing the dead cone effect with jet substructure techniques

“…1 In the soft and collinear limit, the probability for a top quark to emit a FSR gluon with energy fraction z and opening angle θ is [1][2][3] 1 σ…”

“…This process is familiar in quantum electrodynamics, where electrons radiate photons, as well as in quantum chromodynamics (QCD), where quarks (and gluons) radiate gluons. The pattern of radiation depends crucially on the mass of the emitter but not on its spin, leading to the famous dead cone effect [1][2][3] where radiation from quarks with mass m q and energy E q is suppressed for emission angles θ ≲ m q =E q . The dead cone is a fundamental prediction of QCD and other gauge theories, relying on only the behavior of radiation from massive particles in the soft (and collinear) limit.…”

Multiparticle production and perturbative QCD

“…For heavy quarks the accompanying radiation of gluons should be stronger depleted in the forward direction (dead-cone or ring-like emission). It was predicted [30,31] that it should result in the energy-independent difference of companion mean multiplicities for heavy-and light-quark jets of equal energy. The naive model of energy rescaling [32,33,34] predicts the decreasing difference.…”