1,827 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
Efficient computation of matched solutions of the Kapchinskij-Vladimirskij envelope equations for periodic focusing lattices
A new iterative method is developed to numerically calculate the periodic,
matched beam envelope solution of the coupled Kapchinskij-Vladimirskij (KV)
equations describing the transverse evolution of a beam in a periodic, linear
focusing lattice of arbitrary complexity. Implementation of the method is
straightforward. It is highly convergent and can be applied to all usual
parameterizations of the matched envelope solutions. The method is applicable
to all classes of linear focusing lattices without skew couplings, and also
applies to all physically achievable system parameters -- including where the
matched beam envelope is strongly unstable. Example applications are presented
for periodic solenoidal and quadrupole focusing lattices. Convergence
properties are summarized over a wide range of system parameters.Comment: 20 pages, 5 figures, Mathematica source code provide
Event Anisotropy in High Energy Nucleus-Nucleus Collisions
The predictions of event anisotropy parameters from transport model RQMD are
compared with the recent experimental measurements for 158 GeV Pb+Pb
collisions. Using the same model, we study the time evolution of event
anisotropy at 2 GeV and 158 GeV for several colliding systems. For the
first time, both momentum and configuration space information are studied using
the Fourier analysis of the azimuthal angular distribution. We find that, in
the model, the initial geometry of the collision plays a dominant role in
determining the anisotropy parameters.Comment: 18 pages, 7 figures, 2 table
Quantum Mechanical Localization Effects for Bose-Einstein Correlations
For a set of N identical massive boson wavepackets with optimal initial quantum mechanical localization, we derive the Hanbury-Brown/Twiss (HBT) two-particle correlation function. Our result provides finite multiplicity corrections to the coherent state formalism and allows to trace back an error in the so-called cos-prescription. It suggests that what the HBT radius parameters in very small boson emitting systems (e.g. Z_0-decays, p-pbar annihilation) measure is essentially the initial spatial wavepacket width. Both one- and two-particle spectra depend explicitly on this width. Our derivation gives an algorithm for calculating one-particle spectra and two-particle correlations from an arbitrary phase space occupation (q_i,p_i,t_i) as e.g. returned by event generators of heavy ion collisions
Two-particle interferometry for non-central heavy-ion collisions
In non-central heavy ion collisions, identical two particle
Hanbury-Brown/Twiss (HBT) correlations C(K,q) depend on the azimuthal direction
of the pair momentum K. We investigate the consequences for a harmonic analysis
of the corresponding HBT radius parameters. Our discussion includes both, a
model- independent analysis of these parameters in the Gaussian approximation,
and the study of a class of hydrodynamical models which mimic essential
geometrical and dynamical properties of peripheral heavy ion collisions. Also,
we discuss the additional geometrical and dynamical information contained in
the harmonic coefficients of these HBT radius parameters. The leading
contribution of their first and second harmonics are found to satisfy simple
constraints. This allows for a minimal, azimuthally sensitive parametrization
of all first and second harmonic coefficients in terms of only two additional
fit parameters. We determine to what extent these parameters can be extracted
from experimental data despite finite multiplicity fluctuations and the
resulting uncertainty in the reconstruction of the reaction plane.Comment: 14 pages, RevTeX, 7 eps-figures include
Flow effects on the freeze-out phase-space density in heavy ion collisions
The strong longitudinal expansion of the reaction zone formed in relativistic
heavy-ion collisions is found to significantly reduce the spatially averaged
pion phase-space density, compared to naive estimates based on thermal
distributions. This has important implications for data interpretation and
leads to larger values for the extracted pion chemical potential at kinetic
freeze-out.Comment: 5 pages, 3 figures included via epsfig, added discussion of different
transverse density profiles, 1 new figur
Morphology of High-Multiplicity Events in Heavy Ion Collisions
We discuss opportunities that may arise from subjecting high-multiplicity
events in relativistic heavy ion collisions to an analysis similar to the one
used in cosmology for the study of fluctuations of the Cosmic Microwave
Background (CMB). To this end, we discuss examples of how pertinent features of
heavy ion collisions including global characteristics, signatures of collective
flow and event-wise fluctuations are visually represented in a Mollweide
projection commonly used in CMB analysis, and how they are statistically
analyzed in an expansion over spherical harmonic functions. If applied to the
characterization of purely azimuthal dependent phenomena such as collective
flow, the expansion coefficients of spherical harmonics are seen to contain
redundancies compared to the set of harmonic flow coefficients commonly used in
heavy ion collisions. Our exploratory study indicates, however, that these
redundancies may offer novel opportunities for a detailed characterization of
those event-wise fluctuations that remain after subtraction of the dominant
collective flow signatures. By construction, the proposed approach allows also
for the characterization of more complex collective phenomena like higher-order
flow and other sources of fluctuations, and it may be extended to the
characterization of phenomena of non-collective origin such as jets.Comment: Matches version accepted for publication in Physical Review C. 13
pages, 9 figure
The Coulomb Interaction between Pion-Wavepackets: The piplus-piminus Puzzle
The time dependent Schr\"odinger equation for -- pairs, which
are emitted from the interaction zone in relativistic nuclear collisions, is
solved using wavepacket states. It is shown that the Coulomb enhancement in the
momentum correlation function of such pairs is smaller than obtained in earlier
calculations based on Coulomb distorted plane waves. These results suggest that
the experimentally observed positive correlation signal cannot be caused by the
Coulomb interaction between pions emitted from the interaction zone. But other
processes which involve long-lived resonances and the related extended source
dimensions could provide a possible explanation for the observed signal.Comment: 12 pages, LaTeX, 1 figur
A Spin-Mechanical Device for Detection and Control of Spin Current by Nanomechanical Torque
We propose a spin-mechanical device to control and detect spin currents by
mechanical torque. Our hybrid nano-electro-mechanical device, which contains a
nanowire with a ferromagnetic-nonmagnetic interface, is designed to measure or
induce spin polarized currents. Since spin carries angular momentum, a spin
flip or spin transfer process involves a change in angular momentum--and hence,
a torque--which enables mechanical measurement of spin flips. Conversely, an
applied torque can result in spin polarization and spin current.Comment: 6 pages, 2 figure
Observing Non-Gaussian Sources in Heavy-Ion Reactions
We examine the possibility of extracting non-Gaussian sources from
two-particle correlations in heavy-ion reactions. Non-Gaussian sources have
been predicted in a variety of model calculations and may have been seen in
various like-meson pair correlations. As a tool for this investigation, we have
developed an improved imaging method that relies on a Basis spline expansion of
the source functions with an improved implementation of constraints. We examine
under what conditions this improved method can distinguish between Gaussian and
non-Gaussian sources. Finally, we investigate pion, kaon, and proton sources
from the p-Pb reaction at 450 GeV/nucleon and from the S-Pb reaction at 200
GeV/nucleon studied by the NA44 experiment. Both the pion and kaon sources from
the S-Pb correlations seem to exhibit a Gaussian core with an extended,
non-Gaussian halo. We also find evidence for a scaling of the source widths
with particle mass in the sources from the p-Pb reaction.Comment: 16 pages, 15 figures, 5 tables, uses RevTex3.
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