24,263 research outputs found
Hadronic and electromagnetic probes of hot and dense matter in a Boltzmann+Hydrodynamics model of relativistic nuclear collisions
We present recent results on bulk observables and electromagnetic probes
obtained using a hybrid approach based on the Ultrarelativistic Quantum
Molecular Dynamics transport model with an intermediate hydrodynamic stage for
the description of heavy-ion collisions at AGS, SPS and RHIC energies. After
briefly reviewing the main results for particle multiplicities, elliptic flow,
transverse momentum and rapidity spectra, we focus on photon and dilepton
emission from hot and dense hadronic matter.Comment: To appear in the proceedings of WISH 2010: International Workshop on
Interplay between Soft and Hard interactions in particle production at
ultrarelativistic energies, Catania, Italy, 8-10 September 201
How Sensitive are Di-Leptons from Rho Mesons to the High Baryon Density Region?
We show that the measurement of di-leptons might provide only a restricted
view into the most dense stages of heavy ion reactions. Thus, possible studies
of meson and baryon properties at high baryon densities, as e.g. done at
GSI-HADES and envisioned for FAIR-CBM, might observe weaker effects than
currently expected in certain approaches. We argue that the strong absorption
of resonances in the high baryon density region of the heavy ion collision
masks information from the early hot and dense phase due to a strong increase
of the total decay width because of collisional broadening. To obtain
additional information, we also compare the currently used approaches to
extract di-leptons from transport simulations - i.e. shining, only vector
mesons from final baryon resonance decays and instant emission of di-leptons
and find a strong sensitivity on the method employed in particular at FAIR and
SPS energies. It is shown explicitly that a restriction to rho meson (and
therefore di-lepton) production only in final state baryon resonance decays
provide a strong bias towards rather low baryon densities. The results
presented are obtained from UrQMD v2.3 calculations using the standard set-up.Comment: 8 pages, 6 figures, expanded versio
Phi meson production in In-In collisions at =158 GeV: evidence for relics of a thermal phase
Yields and transverse mass distributions of the -mesons reconstructed
in the channel in In+In collisions at =158
GeV are calculated within an integrated Boltzmann+hydrodynamics hybrid approach
based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport
model with an intermediate hydrodynamic stage. The analysis is performed for
various centralities and a comparison with the corresponding NA60 data in the
muon channel is presented. We find that the hybrid model, that embeds an
intermediate locally equilibrated phase subsequently mapped into the transport
dynamics according to thermal phase-space distributions, gives a good
description of the experimental data, both in yield and slope. On the contrary,
the pure transport model calculations tend to fail in catching the general
properties of the meson production: not only the yield, but also the
slope of the spectra, very poorly compare with the experimental
observations
Bankruptcy risk model and empirical tests
We analyze the size dependence and temporal stability of firm bankruptcy risk
in the US economy by applying Zipf scaling techniques. We focus on a single
risk factor-the debt-to-asset ratio R-in order to study the stability of the
Zipf distribution of R over time. We find that the Zipf exponent increases
during market crashes, implying that firms go bankrupt with larger values of R.
Based on the Zipf analysis, we employ Bayes's theorem and relate the
conditional probability that a bankrupt firm has a ratio R with the conditional
probability of bankruptcy for a firm with a given R value. For 2,737 bankrupt
firms, we demonstrate size dependence in assets change during the bankruptcy
proceedings. Prepetition firm assets and petition firm assets follow Zipf
distributions but with different exponents, meaning that firms with smaller
assets adjust their assets more than firms with larger assets during the
bankruptcy process. We compare bankrupt firms with nonbankrupt firms by
analyzing the assets and liabilities of two large subsets of the US economy:
2,545 Nasdaq members and 1,680 New York Stock Exchange (NYSE) members. We find
that both assets and liabilities follow a Pareto distribution. The finding is
not a trivial consequence of the Zipf scaling relationship of firm size
quantified by employees-although the market capitalization of Nasdaq stocks
follows a Pareto distribution, the same distribution does not describe NYSE
stocks. We propose a coupled Simon model that simultaneously evolves both
assets and debt with the possibility of bankruptcy, and we also consider the
possibility of firm mergers.Comment: 8 pages, 8 figure
Deterministic quantum teleportation between distant atomic objects
Quantum teleportation is a key ingredient of quantum networks and a building
block for quantum computation. Teleportation between distant material objects
using light as the quantum information carrier has been a particularly exciting
goal. Here we demonstrate a new element of the quantum teleportation landscape,
the deterministic continuous variable (cv) teleportation between distant
material objects. The objects are macroscopic atomic ensembles at room
temperature. Entanglement required for teleportation is distributed by light
propagating from one ensemble to the other. Quantum states encoded in a
collective spin state of one ensemble are teleported onto another ensemble
using this entanglement and homodyne measurements on light. By implementing
process tomography, we demonstrate that the experimental fidelity of the
quantum teleportation is higher than that achievable by any classical process.
Furthermore, we demonstrate the benefits of deterministic teleportation by
teleporting a dynamically changing sequence of spin states from one distant
object onto another
Homodyne locking of a squeezer
We report on the successful implementation of a new approach to locking the
frequencies of an OPO-based squeezed-vacuum source and its driving laser. The
technique allows the simultaneous measurement of the phase-shifts induced by a
cavity, which may be used for the purposes of frequency-locking, as well as the
simultaneous measurement of the sub-quantum-noise-limited (sub-QNL) phase
quadrature output of the OPO. The homodyne locking technique is cheap, easy to
implement and has the distinct advantage that subsequent homodyne measurements
are automatically phase-locked. The homodyne locking technique is also unique
in that it is a sub-QNL frequency discriminator.Comment: Accepted to Optics Letter
On the distribution of career longevity and the evolution of home run prowess in professional baseball
Statistical analysis is a major aspect of baseball, from player averages to
historical benchmarks and records. Much of baseball fanfare is based around
players exceeding the norm, some in a single game and others over a long
career. Career statistics serve as a metric for classifying players and
establishing their historical legacy. However, the concept of records and
benchmarks assumes that the level of competition in baseball is stationary in
time. Here we show that power-law probability density functions, a hallmark of
many complex systems that are driven by competition, govern career longevity in
baseball. We also find similar power laws in the density functions of all major
performance metrics for pitchers and batters. The use of performance-enhancing
drugs has a dark history, emerging as a problem for both amateur and
professional sports. We find statistical evidence consistent with
performance-enhancing drugs in the analysis of home runs hit by players in the
last 25 years. This is corroborated by the findings of the Mitchell Report [1],
a two-year investigation into the use of illegal steroids in major league
baseball, which recently revealed that over 5 percent of major league baseball
players tested positive for performance-enhancing drugs in an anonymous 2003
survey.Comment: 5 pages, 5 figures, 2-column revtex4 format. Revision has change of
title, a figure added, and minor changes in response to referee comment
Low mass dimuons within a hybrid approach
We analyse dilepton emission from hot and dense hadronic matter using a
hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics
(UrQMD) transport model with an intermediate hydrodynamic stage for the
description of heavy-ion collisions at relativistic energies. Focusing on the
enhancement with respect to the contribution from long-lived hadron decays
after freeze-out observed at the SPS in the low mass region of the dilepton
spectra (often referred to as "the excess"), the relative importance of the
emission from the equilibrium and the non-equilibrium stages is discussed.Comment: Proceedings of Hot Quarks 2010, 21-26 June 2010 Las Londe Les Maures;
v2: Corrected typos and added a commen
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