Search results for "Exponent"
showing 10 items of 896 documents
Determination of the Pseudoscalar Decay Constant fDs+ via Ds+→μ+νμ
2019
Using a 3.19 fb^{-1} data sample collected at an e^{+}e^{-} center-of-mass energy of E_{cm}=4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay D_{s}^{+}→μ^{+}ν_{μ} to be B_{D_{s}^{+}→μ^{+}ν_{μ}}=(5.49±0.16_{stat}±0.15_{syst})×10^{-3}. Combining our branching fraction with the masses of the D_{s}^{+} and μ^{+} and the lifetime of the D_{s}^{+}, we determine f_{D_{s}^{+}}|V_{cs}|=246.2±3.6_{stat}±3.5_{syst} MeV. Using the c→s quark mixing matrix element |V_{cs}| determined from a global standard model fit, we evaluate the D_{s}^{+} decay constant f_{D_{s}^{+}}=252.9±3.7_{stat}±3.6_{syst} MeV. Alternatively, using the value of f_{D_{s}^{+}} calculat…
Testing chiral effective theory with quenched lattice QCD
2008
We investigate two-point correlation functions of left-handed currents computed in quenched lattice QCD with the Neuberger-Dirac operator. We consider two lattice spacings a ~ 0.09, 0.12 fm and two different lattice extents L ~ 1.5, 2.0 fm; quark masses span both the p- and the epsilon-regimes. We compare the results with the predictions of quenched chiral perturbation theory, with the purpose of testing to what extent the effective theory reproduces quenched QCD at low energy. In the p-regime we test volume and quark mass dependence of the pseudoscalar decay constant and mass; in the epsilon-regime, we investigate volume and topology dependence of the correlators. While the leading order b…
correction to ƒB
1991
Abstract The 1/m corrections to the B-meson decay constant ƒB (and the D-meson decay constant ƒD) of the heavy quark effective theory are calculated in the Green function approach. The corrections are found to be sensitive to the difference of the meson mass mB and the heavy quark mass mb. For mb=4.81 GeV we obtain a 100% correction to the heavy quark limit mb=mB. The scaling law of the ratio ƒB/ƒD is, however, quite well satisfied because of cancellations. For reasonable values of quark masses we obtain ƒ B = (130±20) MeV and ƒ D = (170±10) MeV .
Nonequilibrium critical scaling in quantum thermodynamics
2016
The emerging field of quantum thermodynamics is contributing important results and insights into archetypal many-body problems, including quantum phase transitions. Still, the question whether out-of-equilibrium quantities, such as fluctuations of work, exhibit critical scaling after a sudden quench in a closed system has remained elusive. Here, we take a novel approach to the problem by studying a quench across an impurity quantum critical point. By performing density matrix renormalization group computations on the two-impurity Kondo model, we are able to establish that the irreversible work produced in a quench exhibits finite-size scaling at quantum criticality. This scaling faithfully …
Scaling of Berry's phase close to the Dicke quantum phase transition
2006
We discuss the thermodynamic and finite size scaling properties of the geometric phase in the adiabatic Dicke model, describing the super-radiant phase transition for an $N$ qubit register coupled to a slow oscillator mode. We show that, in the thermodynamic limit, a non zero Berry phase is obtained only if a path in parameter space is followed that encircles the critical point. Furthermore, we investigate the precursors of this critical behavior for a system with finite size and obtain the leading order in the 1/N expansion of the Berry phase and its critical exponent.
Dynamical bifurcation as a semiclassical counterpart of a quantum phase transition
2011
We illustrate how dynamical transitions in nonlinear semiclassical models can be recognized as phase transitions in the corresponding -- inherently linear -- quantum model, where, in a Statistical Mechanics framework, the thermodynamic limit is realized by letting the particle population go to infinity at fixed size. We focus on lattice bosons described by the Bose-Hubbard (BH) model and Discrete Self-Trapping (DST) equations at the quantum and semiclassical level, respectively. After showing that the gaussianity of the quantum ground states is broken at the phase transition, we evaluate finite populations effects introducing a suitable scaling hypothesis; we work out the exact value of the…
The pion distribution amplitude and the pion-photon transition form factor in a nonlocal chiral quark model
2014
We study the pion Distribution Amplitude (\pi DA) in the context of a nonlocal chiral quark model. The corresponding Lagrangian reproduces the phenomenological values of the pion mass and decay constant, as well as the momentum dependence of the quark propagator obtained in lattice calculations. It is found that the obtained \pi DA has two symmetric maxima, which arise from the new contributions generated by the nonlocal character of the interactions. This \pi DA is applied to leading order and next-to-leading order calculations of the pion-photon transition form factor. Implications of the results are discussed.
Queuing transitions in the asymmetric simple exclusion process
2003
Stochastic driven flow along a channel can be modeled by the asymmetric simple exclusion process. We confirm numerically the presence of a dynamic queuing phase transition at a nonzero obstruction strength, and establish its scaling properties. Below the transition, the traffic jam is macroscopic in the sense that the length of the queue scales linearly with system size. Above the transition, only a power-law shaped queue remains. Its density profile scales as $\delta \rho\sim x^{-\nu}$ with $\nu={1/3}$, and $x$ is the distance from the obstacle. We construct a heuristic argument, indicating that the exponent $\nu={1/3}$ is universal and independent of the dynamic exponent of the underlying…
Results of the measurements carried out in order to verify the validity of the poisson-exponential distribution in radioactive decay events
1978
Abstract Berkson, examining a series of 250,000 disintegration time intervals, found a significant departure of the distribution from the Poisson-exponential law. Therefore he proposed to repeat the experiment using a large number of intervals and to check the interval recordings by using more than one recording instrument simultaneously. Accepting these suggestions we developed two systems of data collecting provided with different controls. In several experiments we collected data for more than one million decay intervals. The results elaborated using the Pearson ξ 2 test reflect a Poisson process of the radioactive decay events.
Application of a radiative cooling model to daily minimum temperature prediction
1985
A model of exponential decrease of temperature is applied to the study of night cooling in an agricultural area of citrus orchards located near the Valentian Coast (Spain). A set of annual average parameters which determine that cooling is obtained by using temperature measurements at different levels during two years. These parameters appear to be representative of the thermal behaviour of the area of study. The attainment of such parameters allows a prediction of the minimum temperatures of the area to an accuracy of £1.5 K, knowing the temperature at sunset and some time later.