Mean Free Path of High-Energy Nucleons in the Atmosphere

We address a recent puzzling result from the LHC: the jet fragmentation functions measured in Pb–Pb and pp collisions appear very similar in spite of a large medium-induced energy loss (we will call this jet fragmentation scaling (JFS)). To model the real-time nonperturbative effects in the propagation of a high energy jet through the strongly coupled QCD matter, we adopt an effective dimensionally reduced description in terms of the (1+1) quasi-Abelian–Schwinger theory. This theory is exactly soluble at any value of the coupling and shares with QCD the properties of dynamical generation of "mesons" with a finite mass and the screening of "quark" charge that are crucial for describing the transition of the jet into hadrons. We find that this approach describes quite well the vacuum jet fragmentation in e+e- annihilation at z≥0.2 at jet energies in the range of the LHC heavy ion measurements (z is the ratio of hadron and jet momenta). In QCD medium, we find that the JFS is reproduced if the mean free path λ of the jet is short, λ≤0.3 fm, which is in accord with the small shear viscosity inferred from the measurements of the collective flow. The JFS holds since at short mean free path the quantum interference (analogous to the Landau–Pomeranchuk–Migdal (LPM) effect in QED) causes the produced mesons to have low momenta p~m, where m≃0.6 GeV is the typical meson mass. Meanwhile the induced jet energy loss at short mean free path is much larger than naively expected in string models.

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Determination of Inelastic Mean Free Path of High Energy Electrons from Shape Analysis of K-Auger and K-conversion Spectra Emitted from Thin Films

Journal of Surface Analysis ◽

10.1384/jsa.9.281 ◽

2002 ◽

Vol 9 (3) ◽

pp. 281-284

Author(s):

L. Kövér ◽

S. Tougaard ◽

J. Tóth ◽

D. Varga ◽

O. Dragoun ◽

...

Keyword(s):

Thin Films ◽

Free Path ◽

Shape Analysis ◽

Mean Free Path ◽

High Energy ◽

High Energy Electrons ◽

Inelastic Mean Free Path

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High-energy pion interactions

Canadian Journal of Physics ◽

10.1139/p68-320 ◽

1968 ◽

Vol 46 (10) ◽

pp. S655-S659 ◽

Cited By ~ 5

Author(s):

C. B. A. McCusker ◽

L. S. Peak ◽

R. L. S. Woolcott

Keyword(s):

Free Path ◽

Average Energy ◽

Mean Free Path ◽

High Energy ◽

Average Multiplicity ◽

Multiple Collision ◽

Average Value ◽

Narrow Angle ◽

Pion Interaction ◽

Primary Jets

In this paper the results of a line scan of 640 cm of narrow-angle secondary tracks (EPt > 100 GeV) from proton primary jets in emulsions are presented. The proton component was eliminated by disregarding the smallest-angle track unless there was clear evidence that it did not represent a proton. The energy of each pion interaction found was estimated by the following procedure. The various energy estimators were modified to take account of multiple-collision events and then the energy and inelasticity which gave the closest agreement between the energy estimators E(charged), E(median), E(Castagnoli), E(quartile), and Ept were used.The π-meson mean free path was found to be 40 cm (~26 mb) at an average energy of 450 GeV. The average multiplicity of the sample (of pion interactions) was found and shown to be consistent with a log E dependence. The average value of Nh was found and contrasted with previous results at lower energies. The results also show that on the average one pion carries away ~40% of the incident energy.In tracing the above path-length seven examples of direct pair production were identified giving a mean free path of 90 cm.

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