Search results for "PARAMETRIZATION"

The scale dependent nuclear effects in parton distributions for practical applications

1999

The scale dependence of the ratios of parton distributions in a proton of a nucleus $A$ and in the free proton, $R_i^A(x,Q^2)=f_{i/A}(x,Q^2)/f_i(x,Q^2)$, is studied within the framework of the lowest order leading-twist DGLAP evolution. By evolving the initial nuclear distributions obtained with the GRV-LO and CTEQ4L sets at a scale $Q_0^2$, we show that the ratios $R_i^A(x,Q^2)$ are only moderately sensitive to the choice of a specific modern set of free parton distributions. We propose that to a good first approximation, this parton distribution set-dependence of the nuclear ratios $R_i^A(x,Q^2)$ can be neglected in practical applications. With this result, we offer a numerical parametriz…

Temperature dependence of η/s : uncertainties from the equation of state

2018

We perform a global model-to-data comparison on Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Pb+Pb collisions at $2.76$ TeV and $5.02$ TeV, using a 2+1D hydrodynamics model with the EKRT initial state and a shear viscosity over entropy density ratio $(\eta/s)(T)$ with a linear $T$ dependence. To quantify the amount of uncertainty due to the choice of the equation of state (EoS), we compare analysis results based on four different EoSs: the well known $s95p$ parametrisation, an updated parametrisation based on the same list of particles in hadron resonance gas, but using recent lattice results for the partonic part of the EoS, and two new parametrisations based on the Particle Data Group …

nPDF constraints from the large hadron electron collider

2016

An updated analysis regarding the expected nuclear PDF constraints from the future Large Hadron Electron Collider (LHeC) experiment is presented. The new study is based on a more flexible small-$x$ parametrization which provides less biased uncertainty estimates in the region where there are currently no data constraints. The effect of the LHeC is quantified by directly including a sample of pseudodata according to the expected precision of this planned experiment. As a result, a significant reduction of the small-$x$ uncertainties in sea quarks and gluons is observed.

2021

Abstract IceCube is a cubic-kilometer Cherenkov telescope operating at the South Pole. The main goal of IceCube is the detection of astrophysical neutrinos and the identification of their sources. High-energy muon neutrinos are observed via the secondary muons produced in charge current interactions with nuclei in the ice. Currently, the best performing muon track directional reconstruction is based on a maximum likelihood method using the arrival time distribution of Cherenkov photons registered by the experiment's photomultipliers. A known systematic shortcoming of the prevailing method is to assume a continuous energy loss along the muon track. However at energies >1 TeV the light yie…

Analytic estimation of transition between instantaneous eigenstates of quantum two-level system

2018

AbstractTransition amplitudes between instantaneous eigenstates of a quantum two-level system are evaluated analytically on the basis of a new parametrization of its evolution operator, which has recently been proposed to construct exact solutions. In particular, the condition under which the transitions are suppressed is examined analytically. It is shown that the analytic expression of the transition amplitude enables us, not only to confirm the adiabatic theorem, but also to derive the necessary and sufficient condition for quantum two-level system to remain in one of the instantaneous eigenstates.

Initial state in heavy ion collisions

2016

Abstract We briefly review advances in understanding the initial stages of a heavy ion collision. In particular the focus is on moving from parametrizing the initial state to calculating its properties from QCD, consistently with the description of hard probes and dilute-dense scattering experiments. Modeling the event-by-event fluctuating nuclear geometry in initial state calculations has significantly improved in recent years. We also discuss prospects of directly seeing effects of particle correlations created in the initial state in the experimental observables.

A global reanalysis of nuclear parton distribution functions

2007

We determine the nuclear modifications of parton distribution functions of bound protons at scales $Q^2\ge 1.69$ GeV$^2$ and momentum fractions $10^{-5}\le x\le 1$ in a global analysis which utilizes nuclear hard process data, sum rules and leading-order DGLAP scale evolution. The main improvements over our earlier work {\em EKS98} are the automated $\chi^2$ minimization, simplified and better controllable fit functions, and most importantly, the possibility for error estimates. The resulting 16-parameter fit to the N=514 datapoints is good, $\chi^2/{\rm d.o.f}=0.82$. Within the error estimates obtained, the old {\em EKS98} parametrization is found to be fully consistent with the present an…

A model study of nuclear structure functions

1994

We calculate the structure function for a deuteron using the hadronic quark cluster decomposition. By assuming that nuclei might be composed of quasi deuterons, we study their structure functions. The procedure enables a quantum mechanical parametrization of various scenarios, among them nuclear dynamics and nucleon swelling. Moreover it is specially suited to study quark exchange effects. We show, within a scheme where perturbative evolution effects are minimized, that the region around x=1 is very sensitive to these two mechanisms and their effects can be disentangled.

Exchange-correlation energy of a multicomponent two-dimensional electron gas

2003

We discuss the exchange-correlation energy of a multicomponent (multi-valley) two-dimensional electron gas and show that an extension of the recent parametrisation of the exchange-correlation energy by Attacalite et al (Phys. Rev. Lett. 88, 256601 (2002)) describes well also the multicomponent system. We suggest a simple mass dependence of the correlation energy and apply it to study the phase diagram of the multicomponent 2D electron (or hole) gas. The results show that even a small mass difference of the components (e.g. heavy and light holes) decreases the concentration of the lighter components already at relatively high densities.

A simple equation for determining sea surface emissivity in the 3–15 µm region

2009

The high level of accuracy demanded for the sea surface temperature retrieval from infrared data requires an accurate determination of directional sea surface emissivity (SSE). Previous models have permitted calculating SSEs using a physical characterization of sea surface roughness and emission. However, these result in complex equations, and make an operational application difficult. This paper presents a simple SSE algorithm based on a parametrization of one of these models, which was selected as a reference since it reproduces SSE experimental data to a reasonable level of accuracy. The parametrization provides the SSE variation with observation angle and wind speed from a given nadir S…