QCD coherence and the soft limit of the particle spectrum

Abstract

The analytical perturbative approach, if taken to the limit of its applicability, allows one to predict an energy independent limit for the one-particle invariant density in QCD jets E dn d 3 p at very small momenta p. This is a direct consequence of the colour coherence in soft gluon branching. The existing data on the charged and identified particle inclusive spectra follow this prediction surprisingly well. Further tests of the perturbatively based picture in the soft region are discussed. 1

Low and high energy limits of particle spectra in QCD jets

“…A iterative approximate solution of the MLLA equations which is valid in the soft region and goes to zero for ξ → Y has been given in [23]:…”

Topology of hadronic flow for Higgs production at hadron colliders

“…The dominant irreducible background comes from the qq → Z 0 Z 0 process. In the language of Section 2, the antenna patterns for these signal and background processes are simply 2N c [12] and 2C F [12] respectively. In other words, soft hadrons or jets with fixed transverse momentum should be uniformly distributed in the (η, φ) plane in both cases, but with an enhancement of 9/4 for the signal relative to the background.…”

“…(3). Note that the Higgs pattern is the same as for gg → H → bb apart from colour factor replacement N c → C F for the initial-state [12] antenna. In order to illustrate the quantitative differences between these radiation patterns it is necessary to define appropriate kinematics.…”

“…We next consider the patterns for arbitrary η and Θ. With the exception of [12] all antennae exhibit an η dependence. We are again especially interested in the value of R H Θ and R QCD Θ at the symmetric point between the two jets at P c = (∆η = −η, ∆φ = π/2), as the massless study suggests that at this point the differences between the signal and background radiation patterns should be maximal.…”

“…The soft hadrons paint the colour portrait of the parton hard scattering, and can therefore act as a 'partonometer' [1][2][3][4][5][6][7][8][9][10][11][12]. Since signal and background processes at hadron colliders can have very different colour structures (compare for example the s-channel colour singlet process qq → Z ′ → q ′q′ with the colour octet process qq → g * → q ′q′ ), the distribution of accompanying soft hadronic radiation in the events can provide a useful additional diagnostic tool for identifying new physics processes.…”