GEV Parameters Research Articles

Contributions of hyperon-hyperon scattering to subthreshold cascade production in heavy ion collisions

Using a gauged flavor SU(3)-invariant hadronic Lagrangian, we calculate the cross sections for the strangeness-exchange reactions $YY\ensuremath{\leftrightarrow}N\ensuremath{\Xi}$ ($Y=\ensuremath{\Lambda},\ensuremath{\Sigma}$) in the Born approximation. These cross sections are then used in the relativistic Vlasov-Uehling-Uhlenbeck transport model to study $\ensuremath{\Xi}$ production in $\mathrm{Ar}+\mathrm{KCl}$ collisions at incident energy of 1.76A GeV and impact parameter $b=3.5$ fm. We find that including the contributions of hyperon-hyperon scattering channels strongly enhances the yield of $\ensuremath{\Xi}$, leading to the abundance ratio ${\ensuremath{\Xi}}^{\ensuremath{-}}/(\ensuremath{\Lambda}+{\ensuremath{\Sigma}}^{0})=3.38\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which is essentially consistent with the recently measured value of $(5.6\ifmmode\pm\else\textpm\fi{}{1.2}_{\ensuremath{-}1.7}^{+1.8})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ by the HADES Collaboration at GSI.

Climate change impacts on extreme precipitation in Morocco

Morocco is a North African country highly vulnerable to extreme precipitation events. In the present study, past trends in extreme precipitation and future projections using an ensemble of regional climate models (RCM) are evaluated. The extreme precipitation distributions during the extended winter season (October to April) in 10 stations are fitted with Generalized Extreme Value models (GEV). The dependence of the GEV parameters with time, winter North Atlantic Oscillation (NAO) and Mediterranean Oscillation (MO) indexes have been tested. Results indicate no significant trends in extreme precipitation during the observation period 1961–2007. However, dependences between precipitation extremes and NAO or MO indexes are detected, in particular for the Atlantic stations. Then 15 RCM simulations provided by the ENSEMBLES European project ran with the A1B scenario are considered to provide future projections. The Cramér–von Mises (CM) statistic is introduced as a measure of adequacy between the observed extreme precipitation distributions at the different stations and the distributions simulated by the RCMs. The CM statistic can thus provide weights to build a multi-model ensemble of future projections based on model performance in the present climate. Even if some models exhibit good skills, there is a great variability in the RCM performances to reproduce the seasonal cycle and the extreme precipitation distributions at the different stations. The projected changes on extreme precipitation at the stations are evaluated with quantiles computed for different return periods, ranging from 2 to 40years, during the control period 1961–2007 and two projection periods, 2020–2050 and 2070–2099. The climate change scaling factors on extreme quantiles provided by the different RCMs are averaged with equal weights, or with weights obtained from the inverse of the CM statistic. The climate change signal in the RCM simulations indicate a decrease in extreme precipitation quantiles, −12% in average for the projection period 2070–2099 but a great variability and lower convergence between models is found for the projection period 2020–2050. Overall, there is a good model convergence towards a decrease for the Atlantic stations. For the Mediterranean stations, the projected changes are difficult to assess due to the great variability. The two weighting schemes tested for model outputs provide similar results.

Effects of triangular flow on di-hadron azimuthal correlations in relativistic heavy ion collisions

Using the AMPT model for relativistic heavy ion collisions, we have studied the di-hadron azimuthal angular correlations triggered by emitted jets in Au+Au collisions at center of mass energy $\sqrt{s_{NN}}=200$ GeV and impact parameter $b=8$ fm. A double-peak structure for the associated particles at the away side of trigger particles is obtained after subtracting background correlations due to the elliptic flow. Both the near-side peak and the away-side double peaks in the azimuthal angular correlations are, however, significantly suppressed (enhanced) in events of small (large) triangular flow, which are present as a result of fluctuations in the initial collision geometry. After subtraction of background correlations due to the triangular flow, the away-side double peaks change into a single peak with broad shoulders on both sides. The away side of the di-hadron correlations becomes essentially a single peak after further subtraction of higher-order flows.

Cento e vinte anos de totais extremos de precipitação pluvial máxima diária em Campinas, Estado de São Paulo: análises estatísticas

O objetivo do trabalho foi descrever, com base na distribuição geral dos valores extremos (GEV), a probabilidade de ocorrência associada aos totais máximos anuais de precipitação pluvial diária (Preabs), observados na localidade de Campinas entre 1890 e 2009, verificando também qual método, máxima verossimilhança ou momentos-L, resultam no melhor desempenho da GEV no referido propósito. Após verificação estatística da inexistência de significativas correlações seriais, tendências e periodicidades, observou-se que a GEV pode ser utilizada na descrição das probabilidades associadas aos dados de Preabs, na localidade de Campinas. O método da máxima verossimilhança mostrou-se, por meio do teste Lilliefors e de gráficos Quantil-Quantil, o melhor algoritmo para estimação dos parâmetros da GEV. Verificou-se ganho de energia no sinal temporal da série analisada após 1990. Essa característica espectral, também verificada entre 1920 e 1935, indica concentração dos valores mais elevados de Preabs nos referidos períodos.

Relativistic multirank interaction kernels of the neutron–proton system

The multirank separable kernels of the neutron–proton interaction for uncoupled S and P partial waves (with the total angular momentum J = 0 , 1 ) are proposed. Two different methods of a relativistic generalization of initially nonrelativistic form factors parametrizing the kernel are considered. Using the constructed kernels the experimental data for phase shifts in the elastic neutron–proton scattering for the laboratory energy up to 3 GeV and low-energy parameters are described. The comparison of our results with other model calculations are presented.

Downscaling and Projection of Winter Extreme Daily Precipitation over North America

Abstract Large-scale atmospheric variables have been statistically downscaled to derive winter (December–March) maximum daily precipitation at stations over North America using the generalized extreme value distribution (GEV). Here, the leading principal components of the sea level pressure field and local specific humidity are covariates of the distribution parameters. The GEV parameters are estimated using data from 1949 to 1999 and the r-largest method. This statistical downscaling procedure is found to yield skill over the southern and northern West Coast, central United States, and areas of western and eastern Canada when tested with independent data. The projected changes in covariates or predictors are obtained from transient climate change simulations conducted with the Canadian Centre for Climate Modelling and Analysis (CCCma) Coupled General Circulation Model, version 3.1 (CGCM3.1) forced by the Intergovernmental Panel on Climate Change (IPCC) A2 forcing scenario. They are then used to derive the GEV distribution parameters for the period 2050–99. The projected frequency of the current 20-yr return maximum daily precipitation for that period suggests that extreme precipitation risk will increase heavily over the south and central United States but decrease over the Canadian prairies. The difference between the statistical downscaling results and those estimated using GCM simulation is also discussed.

Linear Regression with Extreme Value Residuals

We propose a method of estimating the p + 3 parameters of a random sample consisting of a trend with p covariates plus residuals from the three-parameter generalized extreme value distribution (GEV). The estimates are the p maximum likelihood estimates for the p-variate slope β, combined iteratively with the L-moment estimates for the three GEV parameters. An application is illustrated to annual maximum rainfall data from Orlando, Florida. With p = 1, we show how to compute by simulation the densities and percentiles of and , where α is the GEV scale parameter and is its estimate. We do this for both ‘2-sample’ covariates and linear covariates, and for a range of values of the GEV shape parameter k. These two distributions are invariant to the location and scale parameters but do depend on the covariates. Also, their percentiles do not vary greatly for the shape parameter k near 0. Thus, the percentiles of provide a convenient confidence region for β at least when the shape parameter estimate is near 0. The method can be applied to any choice of covariates. A similar analysis is carried out for the Gumbel (EV1) distribution with trend, that is, for the case k = 0. A variation of this confidence region is suggested when p > 1.

Coherent effects of a macro-bunch in an undulator

The longitudinal radiative force of an electron bunch moving in an undulator has been investigated in [1] assuming an 1D density distribution. To obtain the contribution of pure curvature effects and to avoid singular fields, the 1D linear motion field was subtracted. To relate these results to the 3D case we present analytical and numerical field calculations using the field solver of TRAFIC4. The 1D and 3D cases have been calculated in the transient regime, the steady-state regime and the steady-state regime averaged over one undulator period for the 1 GeV parameter set of the TESLA FEL.

Processes with a t-channel singularity in the physical region: finite beam sizes make cross sections finite

It is known that some high-energy processes have a t-channel singularity in the physical region. In this paper we show that this singularity is regularized if one takes into account the finite sizes of the colliding beams, i.e. the realistic situation which takes place at high-energy colliders. In this way we obtain a finite cross section which is linearly proportional to the transverse sizes of the colliding beams. As an application of the above result we study the production of a single W boson at μ + μ − colliders in the reaction μ − μ + → e v eW + . For the total energy √ s ≈ 95 GeV and reasonable parameters of the muon beams the “beam-size” dependent part of the cross section for this reaction is of the order of the standard cross section of the μ − μ + → μ − v μW + process.