Hadron multiplicity fluctuations in perturbative QCD

Abstract

We examine hadron multiplicity fluctuations in hard processes and confront analytic QCD predictions with the pattern of multiplicity fluctuations observed in $e^{+}{e}^{-}$ annihilation and high-$p_t$ jets produced in $pp$ collisions at the LHC. Special emphasis is placed on high-multiplicity fluctuations in jets. Selecting events with hadronic multiplicity exceeding the average value by a factor of 3 or more in various processes has been a source of conundrums for many years. We discuss two recent high-multiplicity puzzles and attempt to reveal their common origin.

36 pages, 22 figures, version for publication