2,960 research outputs found
An Inconsistency in the Simulation of Bose-Einstein Correlations
We show that the formalism commonly used to implement Bose-Einstein
correlations in Monte-Carlo simulations can lead to values of the two-particle
correlator significantly smaller than unity, in the case of sources with strong
position-momentum correlations. This is more pronounced when the phase space of
the emitted particles is strongly reduced by experimental acceptance or
kinematic analysis selections. It is inconsistent with general principles
according to which the Bose-Einstein correlator is larger than unity. This
inconsistency seems to be rooted in the fact that quantum mechanical
localization properties are not taken into account properly.Comment: 10 pages, LaTe
Restriction on the energy and luminosity of e+e- storage rings due to beamstrahlung
The role of beamstrahlung in high-energy e+e- storage-ring colliders (SRCs)
is examined. Particle loss due to the emission of single energetic
beamstrahlung photons is shown to impose a fundamental limit on SRC
luminosities at energies 2E_0 >~ 140 GeV for head-on collisions and 2E_0 >~ 40
GeV for crab-waist collisions. With beamstrahlung taken into account, we
explore the viability of SRCs in the E_0=240-500 GeV range, which is of
interest in the precision study of the Higgs boson. At 2E_0=240 GeV, SRCs are
found to be competitive with linear colliders; however, at 2E_0=400-500 GeV,
the attainable SRC luminosity would be a factor 15-25 smaller than desired.Comment: Latex, 5 pages. v2 differs only by minor changes is abstract and
introduction, one reference is added. v3 corresponds to the paper published
in PR
Dissipative Hydrodynamics and Heavy Ion Collisions
Recent discussions of RHIC data emphasized the exciting possibility that the
matter produced in nucleus-nucleus collisions shows properties of a
near-perfect fluid. Here, we aim at delineating the applicability of fluid
dynamics, which is needed to quantify the size of corresponding dissipative
effects. We start from the equations for dissipative fluid dynamics, which we
derive from kinetic theory up to second order (Israel-Stewart theory) in a
systematic gradient expansion. In model studies, we then establish that for too
early initialization of the hydrodynamic evolution (\tau_0 \lsim 1 fm/c) or
for too high transverse momentum (p_T \gsim 1 GeV) in the final state, the
expected dissipative corrections are too large for a fluid description to be
reliable. Moreover, viscosity-induced modifications of hadronic transverse
momentum spectra can be accommodated to a significant degree in an ideal fluid
description by modifications of the decoupling stage. We argue that these
conclusions, drawn from model studies, can also be expected to arise in
significantly more complex, realistic fluid dynamics simulations of heavy ion
collisions.Comment: 18 pages, 5 figures, uses revtex4; v2: references added, typos
correcte
Hadron multiplicity in pp and AA collisions at LHC from the Color Glass Condensate
We provide quantitative predictions for the rapidity, centrality and energy
dependencies of inclusive charged-hadron productions for the forthcoming LHC
measurements in nucleus-nucleus collisions based on the idea of gluon
saturation in the color-glass condensate framework. Our formulation gives very
good descriptions of the first data from the LHC for the inclusive
charged-hadron production in proton-proton collisions, the deep inelastic
scattering at HERA at small Bjorken-x, and the hadron multiplicities in
nucleus-nucleus collisions at RHIC.Comment: 7 pages, 8 figures; v3: minor changes, one reference added, results
unchanged, the version to appear in Phys. Rev.
Symmetry constraints for the emission angle dependence of Hanbury Brown--Twiss radii
We discuss symmetry constraints on the azimuthal oscillations of two-particle
correlation (Hanbury Brown--Twiss interferometry) radii for non-central
collisions between equal spherical nuclei. We also propose a new method for
correcting in a model-independent way the emission angle dependent correlation
function for finite event plane resolution and angular binning effects.Comment: 8 pages revtex4, 2 tables, no figures. Short Section VI added and
correction algorithm in Section VII made more explicit. Submitted to Physical
Review
Anti–de Sitter/Conformal-Field-Theory Calculation of Screening in a Hot Wind
One of the challenges in relating experimental measurements of the suppression in the number of J/ψ mesons produced in heavy ion collisions to lattice QCD calculations is that whereas the lattice calculations treat J/ψ mesons at rest, in a heavy ion collision a cc̅ pair can have a significant velocity with respect to the hot fluid produced in the collision. The putative J/ψ finds itself in a hot wind. We present the first rigorous nonperturbative calculation of the consequences of a wind velocity v on the screening length Ls for a heavy quark-antiquark pair in hot N=4 supersymmetric QCD. We find Ls(v,T)=f(v)[1-v2]1/4/πT with f(v) only mildly dependent on v and the wind direction. This Ls(v,T)∼Ls(0,T)/sqrt[γ] velocity scaling, if realized in QCD, provides a significant additional source of J/ψ suppression at transverse momenta which are high but within experimental reach
The relationship between particle freeze-out distributions and HBT radius parameters
The relationship between pion and kaon space-time freeze-out distributions
and the HBT radius parameters in high-energy nucleus-nucleus collisions is
investigated. We show that the HBT radius parameters in general do not reflect
the R.M.S. deviations of the single particle production points. Instead, the
HBT radius parameters are most closely related to the curvature of the
two-particle space-time relative position distribution at the origin. We
support our arguments by studies with a dynamical model (RQMD 2.4).Comment: RevTex, 10 pages including 3 figures. v2: Discussion of the lambda
parameter has been added. PRC, in prin
Cyclic mutually unbiased bases, Fibonacci polynomials and Wiedemann's conjecture
We relate the construction of a complete set of cyclic mutually unbiased
bases, i. e., mutually unbiased bases generated by a single unitary operator,
in power-of-two dimensions to the problem of finding a symmetric matrix over
F_2 with an irreducible characteristic polynomial that has a given Fibonacci
index. For dimensions of the form 2^(2^k) we present a solution that shows an
analogy to an open conjecture of Wiedemann in finite field theory. Finally, we
discuss the equivalence of mutually unbiased bases.Comment: 11 pages, added chapter on equivalenc
On the Angular Dependence of the Radiative Gluon Spectrum
The induced momentum spectrum of soft gluons radiated from a high energy
quark produced in and propagating through a QCD medium is reexamined in the
BDMPS formalism. A mistake in our published work (Physical Review C60 (1999)
064902) is corrected. The correct dependence of the fractional induced loss
as a universal function of the variable
where is the size of the medium and
the transport coefficient is presented. We add the proof that the
radiated gluon momentum spectrum derived in our formalism is equivalent with
the one derived in the Zakharov-Wiedemann approach.Comment: LaTex, 5 pages, 1 figur
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