21 research outputs found
KNO scaling 30 years later
KNO scaling, i.e. the collapse of multiplicity distributions P_n onto a
universal scaling curve manifests when P_n is expressed as the distribution of
the standardized multiplicity (n-c)/lambda with c and lambda being location and
scale parameters governed by leading particle effects and the growth of average
multiplicity. At very high energies, strong violation of KNO scaling behavior
is observed (p-pbar) and expected to occur (e+e-). This challenges one to
introduce novel, physically well motivated and preferably simple scaling rules
obeyed by high-energy data. One possibility what I find useful and which
satisfies the above requirements is the repetition of the original scaling
prescription (shifting and rescaling) in Mellin space, that is, for the
multiplicity moments' rank. This scaling principle is discussed here,
illustrating its capabilities both on model predictions and on real data.Comment: 8 pages LaTeX, 9th Int. Workshop on Multiparticle Production, Torino,
Ital
Multiplicity with a Thrust Cut
We evaluate the multiplicity of hadrons in the -annihilation at a
given thrust in the modified leading-log approximation, including
corrections. The calculation is done at a large value of
by the use of the factorisation which takes place in the
one-particle-inclusive cross section at a given . At a small , a
different type of factorisation takes place, which also enable us to evaluate
the multiplicity. Two approaches are compared numerically. Measuring this
quantity near , we can determine the multiplicity ratio between a
gluon-jet and a quark-jet.Comment: OCHA-PP-32, LATEX FILE, 21
Corrections to Angular Ordering in Multiple Hadroprodroproduction
One of the key ideas in describing the multiparticle production at high
energies in the perturbative QCD is the angular ordering in successive
soft-gluon emission. We analyse the angular distribution of particles in a jet,
and investigate the corrections to the angular ordering. At a small angle from
the jet direction, the angular ordering is exact at the next-to-leading order.
At a large angle, the angular ordering overestimates the angular particle
density by a factor , where is the
anomalous dimension of the multiplicity. The correction restores
the boost invariance of the cross section.Comment: Latex fil
Higher Twist Distribution Amplitudes of the Nucleon in QCD
We present the first systematic study of higher-twist light-cone distribution
amplitudes of the nucleon in QCD. We find that the valence three-quark state is
described at small transverse separations by eight independent distribution
amplitudes. One of them is leading twist-3, three distributions are twist-4 and
twist-5, respectively, and one is twist-6. A complete set of distribution
amplitudes is constructed, which satisfies equations of motion and constraints
that follow from conformal expansion. Nonperturbative input parameters are
estimated from QCD sum rules.Comment: 29 pages, 4 figures, eqn in (3.19) corrected, table 3 accordingly
changed, some typos fixe
Baryon Distribution Amplitudes in QCD
We develop a new theoretical framework for the description of leading twist
light-cone baryon distribution amplitudes which is based on integrability of
the helicity evolution equation to leading logarithmic accuracy.
A physical interpretation is that one can identify a new `hidden' quantum
number which distinguishes components in the distribution
amplitudes with different scale dependence. The solution of the corresponding
evolution equation is reduced to a simple three-term recurrence relation. The
exact analytic solution is found for the component with the lowest anomalous
dimension for all moments , and the WKB-type expansion is constructed for
other levels, which becomes asymptotically exact at large . Evolution
equations for the distribution amplitudes (e.g. for the nucleon)
are studied as well. We find that the two lowest anomalous dimensions for the
operators (one for each parity) are separated from the rest of
the spectrum by a finite `mass gap'. These special states can be interpreted as
scalar diquarks.Comment: 75 pages, LaTeX style, 18 figures embedded with epsf.st
The Uses of Conformal Symmetry in QCD
The Lagrangian of Quantum Chromodynamics is invariant under conformal
transformations. Although this symmetry is broken by quantum corrections, it
has important consequences for strong interactions at short distances and
provides one with powerful tools in practical calculations. In this review we
give a short exposition of the relevant ideas, techniques and applications of
conformal symmetry to various problems of interest.Comment: 110 pages, invited review for "Prog. Part. Nucl. Phys