218 research outputs found
Threshold scans in Central Diffraction at the LHC
We propose a new set of measurements which can be performed at the LHC using
roman pot detectors. The method exploits excitation curves in central
diffractive pair production, and is illustrated using the examples of the W
boson and top quark mass measurements. Further applications are mentioned.Comment: 11 page
Asymptotic perfect fluid dynamics as a consequence of AdS/CFT
We study the dynamics of strongly interacting gauge-theory matter (modelling
quark-gluon plasma) in a boost-invariant setting using the AdS/CFT
correspondence. Using Fefferman-Graham coordinates and with the help of
holographic renormalization, we show that perfect fluid hydrodynamics emerges
at large times as the unique nonsingular asymptotic solution of the nonlinear
Einstein equations in the bulk. The gravity dual can be interpreted as a black
hole moving off in the fifth dimension. Asymptotic solutions different from
perfect fluid behaviour can be ruled out by the appearance of curvature
singularities in the dual bulk geometry. Subasymptotic deviations from perfect
fluid behaviour remain possible within the same framework.Comment: 19 pages, 1 figure; v2: free streaming example changed to s=1;
conclusions unchange
Unified description of Bjorken and Landau 1+1 hydrodynamics
We propose a generalization of the Bjorken in-out Ansatz for fluid
trajectories which, when applied to the (1+1) hydrodynamic equations, generates
a one-parameter family of analytic solutions interpolating between the
boost-invariant Bjorken picture and the non boost-invariant one by Landau. This
parameter characterises the proper-time scale when the fluid velocities
approach the in-out Ansatz. We discuss the resulting rapidity distribution of
entropy for various freeze-out conditions and compare it with the original
Bjorken and Landau results.Comment: 20 pages, 5 figure
Universality and tree structure of high energy QCD
Using non-trivial mathematical properties of a class of nonlinear evolution
equations, we obtain the universal terms in the asymptotic expansion in
rapidity of the saturation scale and of the unintegrated gluon density from the
Balitsky-Kovchegov equation. These terms are independent of the initial
conditions and of the details of the equation. The last subasymptotic terms are
new results and complete the list of all possible universal contributions.
Universality is interpreted in a general qualitative picture of high energy
scattering, in which a scattering process corresponds to a tree structure
probed by a given source.Comment: 4 pages, 3 figure
Phenomenology on the QCD dipole picture revisited
We perform an adjust to the most recent structure function data, considering
the QCD dipole picture applied to ep scattering. The structure function F2 at
small x and intermediate Q2 can be described by the model containing an
economical number of free-parameters, which encodes the hard Pomeron physics.
The longitudinal structure function and the gluon distribution are predicted
without further adjustments. The data description is effective, whereas a
resummed next-to-leading level analysis is deserved.Comment: 18 pages, 6 figures. Version to be published in Eur. Phys. J.
Universality of traveling waves with QCD running coupling
``Geometric scaling'', i.e. the dependence of DIS cross-sections on the ratio
Q/Q_S, where Q_S(Y) is the rapidity-dependent \saturation scale, can be
theoretically obtained from universal ``traveling wave'' solutions of the
nonlinear Balitsky-Kovchegov (BK) QCD evolution equation at fixed coupling. We
examine the similar mean-field predictions beyond leading-logarithmic order,
including running QCD coupling.Comment: 4 pages, 3 figures,, Invited talk given at the DIS 2007 Conference,
Munich, Germany, April 2007; Change of titl
Threshold scans in diffractive W pair production via QED processes at the LHC
We propose a new set of measurements which can be performed at the LHC using
roman pot detectors. This new method is based on exploiting excitation curves
to measure kinematical properties of produced particles. We illustrate it in
the case of central diffractive W pair production.Comment: Accepted by Phys. Lett. B - 1 reference adde
Geometric scaling as traveling waves
We show the relevance of the nonlinear Fisher and Kolmogorov-Petrovsky-
Piscounov (KPP) equation to the problem of high energy evolution of the QCD
amplitudes. We explain how the traveling wave solutions of this equation are
related to geometric scaling, a phenomenon observed in deep-inelastic
scattering experiments. Geometric scaling is for the first time shown to result
from an exact solution of nonlinear QCD evolution equations. Using general
results on the KPP equation, we compute the velocity of the wave front, which
gives the full high energy dependence of the saturation scale.Comment: 4 pages, 1 figure. v2: references adde
Factorial Moments of Continuous Order
The normalized factorial moments are continued to noninteger values of
the order , satisfying the condition that the statistical fluctuations
remain filtered out. That is, for Poisson distribution for all .
The continuation procedure is designed with phenomenology and data analysis in
mind. Examples are given to show how can be obtained for positive and
negative values of . With being continuous, multifractal analysis is
made possible for multiplicity distributions that arise from self-similar
dynamics. A step-by-step procedure of the method is summarized in the
conclusion.Comment: 15 pages + 9 figures (figures available upon request), Late
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