Transparencies pdf - Desy

P H Y S I C A L R E V I E W L E T T E R S week ending
17 JUNE 2005
lative transverse moentation
is performed
in PYTHIA [18]. This
CD event generator,
utations (Sibyll v2.1
peripheral collisions
f the nucleus is not
ron-nucleus collision
ade equations which
the air shower [20].
ntation are published
before discussing res,
such as the variable
ed predominantly by
region, since this is
d to number of partiton-air
reactions at
model deposits about
the region xF > 10 3
ent of forward quark
n the saturation mo-
tered quarks fragment
imum x F. In contrast,
leading diquark with
momentum. This core
when the saturation
X max [g/cm 2 ]
850
800
750
700
650
600
550
10 8
Sibyll (proton,Iron)
BBL running coupling (proton)
BBL fixed coupling (proton)
Hires Stereo data
p
10 9
energy [GeV]
Fe (Sibyll only)
10 10
Seneca 1.2
10 11
FIG. 1 (color online). Mean Xmax as a function of primary
energy for the pQCD model Sibyll (proton and iron primaries),
the saturation model BBL (proton primaries, fixed- and runningcoupling
evolution of Qs), and the Hires stereo data [1].
Mean Xmax as a function of primary energy for the pQCD model Sibyll
(proton and iron primaries), the saturation model BDL (proton primaries,
fixed- and running- coupling evolution of Q corresponding to the disk body
limit), and the Hires stereo data .
PRL 94, 231801 (2005)
This is due to the ‘‘breakup’’ of the projectile’s coherence
[15] together with the suppression of forward parton scattering
(for central collisions). The comparison to the data
suggests High-Density a light QCDcomposition and Cosmic-Ray Air Showers at those energies. Although
H. J. Drescher, the curve for running-coupling evolution appears to be
parallel to that from Sibyll, the two curves actually approach
at lower energies.
1 A. Dumitru, 1 and M. Strikman 2
P H Y S I C A L R E V I E W L E T T E R S week ending
17 JUNE 2005
1
Johann Wolfgang Goethe University, Postfach 11 19 32, 60054 Frankfurt, Germany
(Received 18 August 2004; published 15 June 502005)
2 Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
We discuss particle production in the high-energy, small-x limit of QCD where the gluon density of
hadrons is expected to become nonperturbatively large. Strong modifications of the phase-space distribution
of produced particles as compared to leading-twist models are predicted, which reflect in the
50