21,423 research outputs found
Forward Neutral Pion Production in p + p and d + Au Collisions at √s_(NN) = 200 GeV
Measurements of the production of forward π^0 mesons from p + p and d + Au collisions at √s_(NN) = 200 GeV are reported. The p + p yield generally agrees with next-to-leading order perturbative QCD calculations. The d + Au yield per binary collision is suppressed as η increases, decreasing to ~30% of the p + p yield at =4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward π^0 with charged hadrons at η ≈ 0 show a recoil peak in p + p that is suppressed in d + Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei
Short-Time Decoherence and Deviation from Pure Quantum States
In systems considered for quantum computing, i.e., for control of quantum
dynamics with the goal of processing information coherently, decoherence and
deviation from pure quantum states, are the main obstacles to fault-tolerant
error correction. At low temperatures, usually assumed in quantum computing
designs, some of the accepted approaches to evaluation of relaxation mechanisms
break down. We develop a new general formalism for estimation of decoherence at
short times, appropriate for evaluation of quantum computing architectures.Comment: 9 pages in plain Te
Measurement of spin-exchange rate constants between 129Xe and alkali metals
By measuring the relaxation rates of the nuclear spin polarization of Xe-129 in the presence of alkali-metal vapor at different densities, we have extracted the spin-exchange rates between Xe-129 and the three alkali metals K, Rb, and Cs. By studying the alkali-metal-Xe-129 spin-exchange rates as functions of the cell number density from 0.2 to 0.7 amagat, the binary collision and van der Waals molecular terms are separated, and constants governing both mechanisms are determined. The results from our work can be used to optimize the parameter space for polarizing Xe-129, a promising agent for magnetic resonance imaging and other applications
Directed flow in Au + Au collisions at √s_(NN) = 62.4 GeV
We present the directed flow (v1) measured in Au+Au collisions at √s_(NN) = 62.4 GeV in the midpseudorapidity
region |η| < 1.3 and in the forward pseudorapidity region 2.5 < |η| < 4.0. The results are obtained using the
three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the
Relativistic Heavy Ion Collider, the standard method with the event plane reconstructed from spectator neutrons.
Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle
directed flow is in the direction opposite to that of fragmentation neutrons
Measurement of a Quantum System Coupled to Independent Heat-Bath and Pointer Modes
We present an exact derivation of a process in which a microscopic measured
system interacts with heat-bath and pointer modes of a measuring device, via a
coupling involving a general Hermitian operator of the system. In the
limit of strong interaction with these modes, over a small time interval, we
derive the exact effective many-body density matrix of the measured system plus
pointer. We then discuss the interpretation of the dynamics considered as the
first stage in the process of quantum measurement, eventually involving the
wave-function collapse due to interactions with "the rest of the universe." We
establish that the effective density matrix represents the required framework
for the measured system and the pointer part of the measuring device to evolve
into a statistical mixture described by direct-product states such that the
system is in each eigenstate of with the correct quantum-mechanical
probability, whereas the expectation values of pointer-space operators retain
amplified information of the system's eigenstate.Comment: 19 pages in plain Te
An Improved NSGA-II and its Application for Reconfigurable Pixel Antenna Design
Based on the elitist non-dominated sorting genetic algorithm (NSGA-II) for multi-objective optimization problems, an improved scheme with self-adaptive crossover and mutation operators is proposed to obtain good optimization performance in this paper. The performance of the improved NSGA-II is demonstrated with a set of test functions and metrics taken from the standard literature on multi-objective optimization. Combined with the HFSS solver, one pixel antenna with reconfigurable radiation patterns, which can steer its beam into six different directions (θDOA = ± 15°, ± 30°, ± 50°) with a 5 % overlapping impedance bandwidth (S11 < − 10 dB) and a realized gain over 6 dB, is designed by the proposed self-adaptive NSGA-II
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