A multi-step setup for heavy-flavor studies in high-energy nucleus-nucleus (
AA
) collisions—addressing within a comprehensive framework the initial
production, the propagation in the hot medium ...until decoupling and the final hadronization and decays—is presented. The initial hard production of
pairs is simulated using the POWHEG pQCD event generator, interfaced with the PYTHIA parton shower. Outcomes of the calculations are compared to experimental data in
pp
collisions and are used as a validated benchmark for the study of medium effects. In the
AA
case, the propagation of the heavy quarks in the medium is described in a framework provided by the relativistic Langevin equation. For the latter, different choices of transport coefficients are explored (either provided by a perturbative calculation or extracted from lattice-QCD simulations) and the corresponding numerical results are compared to experimental data from RHIC and the LHC. In particular, outcomes for the nuclear modification factor
R
AA
and for the elliptic flow
v
2
of
D
/
B
mesons, heavy-flavor electrons and non-prompt
J
/
ψ
’s are displayed.
We present results for the quenching, elliptic flow and azimuthal correlations of heavy-flavor particles in high-energy nucleus-nucleus collisions obtained through the POWLANG transport setup, ...developed in the past to study the propagation of heavy quarks in the Quark–Gluon Plasma and here extended to include a modeling of their hadronization in the presence of a medium. Hadronization is described as occurring via the fragmentation of strings with endpoints given by the heavy (anti-) quark
Q
(
Q
¯
)
and a thermal parton
q
¯
(
q
)
from the medium. The flow of the light quarks is shown to affect significantly the
R
AA
and
v
2
of the final
D
mesons, leading to a better agreement with the experimental data. The approach allows also predictions for the angular correlation between heavy-flavor hadrons (or their decay electrons) and the charged particles produced in the fragmentation of the heavy-quark strings.
We report on broadly based systematic investigations of the modeling components for open heavy-flavor diffusion and energy loss in strongly interacting matter in their application to heavy-flavor ...observables in high-energy heavy–ion collisions, conducted within an EMMI Rapid Reaction Task Force framework. Initial spectra including cold-nuclear-matter effects, a wide variety of space-time evolution models, heavy-flavor transport coefficients, and hadronization mechanisms are scrutinized in an effort to quantify pertinent uncertainties in the calculations of nuclear modification factors and elliptic flow of open heavy-flavor particles in nuclear collisions. We develop procedures for error assessments and criteria for common model components to improve quantitative estimates for the (low-momentum) heavy-flavor diffusion coefficient as a long-wavelength characteristic of QCD matter as a function of temperature, and for energy loss coefficients of high-momentum heavy-flavor particles.
The propagation of the heavy quarks produced in relativistic nucleus–nucleus collisions at RHIC and LHC is studied within the framework of Langevin dynamics in the background of an expanding ...deconfined medium described by ideal and viscous hydrodynamics. The transport coefficients entering into the relativistic Langevin equation are evaluated by matching the hard-thermal-loop result for soft collisions with a perturbative QCD calculation for hard scatterings. The heavy-quark spectra thus obtained are employed to compute the differential cross sections, the nuclear modification factors
R
AA
and the elliptic-flow coefficients
v
2
of electrons from heavy-flavor decay.
We present a new model for the description of heavy-flavor hadronization in relativistic heavy-ion collisions. We explore its effect on the charmed hadron yields and kinematic distributions once the ...latter is applied at the end of transport calculations used to simulate the propagation of heavy quarks in the deconfined fireball produced in the collision. The model is based on the formation of color-singlet clusters through the recombination of charm quarks with light antiquarks or diquarks from the same fluid cell. This local mechanism of color neutralization leads to a strong space-momentum correlation, which provides a substantial enhancement of charmed baryon production and of the collective flow of all charmed hadrons.
A multi-step setup for heavy-flavour studies in high-energy nucleus–nucleus collisions is presented. The initial hard production of QQ¯ pairs is simulated with the POWHEG pQCD event generator, ...interfaced with the PYTHIA parton shower. In a nucleus–nucleus collision the propagation of the heavy quarks in the medium is described through the relativistic Langevin equation. The numerical results are compared to experimental data from the RHIC and the LHC. In particular we show the comparisons of the nuclear modification factor of D-mesons, non-prompt J/ψ's and heavy-flavour electrons. Furthermore, first results on azimuthal correlations of heavy quark pair and open charm/beauty meson pairs are presented.
We present results for the quenching, elliptic flow and azimuthal correlations of heavy flavour particles in high-energy nucleus-nucleus collisions obtained through the POWLANG transport setup, ...developed in the past to study the propagation of heavy quarks in the Quark-Gluon Plasma and here extended to include a modeling of their hadronization in the presence of a medium. Hadronization is described as occurring via the fragmentation of strings with endpoints given by the heavy (anti-)quark and a thermal parton from the medium. The flow of the light quarks is shown to affect significantly the RAA and v2 of the final D mesons, leading to a better agreement with the experimental data.
A refined version of a multi-step calculation of heavy-flavor observables in pp and AA collisions has been developed, based on pQCD at NLO accuracy followed by parton shower evolution to describe ...heavy-quark production and on the relativistic Langevin equation to describe their stochastic evolution in the QCD plasma. Then, hadronization is modeled through an implementation of fragmentation functions based on pQCD and constrained by e+e− collider data. Results of our calculations can be compared with recent measurements performed at the LHC in Pb–Pb collisions at sNN=2.76TeV: nuclear modification factor RAA of the pT spectra at mid-rapidity of heavy-flavor decay electrons and of exclusively reconstructed open-charm mesons at different centralities, as well as their elliptic-flow v2(pT) in semi-central collisions. To test the validity of our setup for such studies, its predictions are also checked against the pT spectra measured in pp collisions at s=7TeV and 2.76 TeV.
Characterization of a neutron imaging setup at the INES facility Durisi, E.A.; Visca, L.; Albertin, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2013, Letnik:
726
Journal Article
Recenzirano
Odprti dostop
The Italian Neutron Experimental Station (INES) located at the ISIS pulsed neutron source (Didcot, United Kingdom) provides a thermal neutron beam mainly used for diffraction analysis. A neutron ...transmission imaging system was also developed for beam monitoring and for aligning the sample under investigation. Although the time-of-flight neutron diffraction is a consolidated technique, the neutron imaging setup is not yet completely characterized and optimized. In this paper the performance for neutron radiography and tomography at INES of two scintillator screens read out by two different commercial CCD cameras is compared in terms of linearity, signal-to-noise ratio, effective dynamic range and spatial resolution. In addition, the results of neutron radiographies and a tomography of metal alloy test structures are presented to better characterize the INES imaging capabilities of metal artifacts in the cultural heritage field.
A full characterization of the present INES imaging set-up was carried out.Two CCD cameras and two scintillators (ZnS/6LiF) of different thicknesses were tested.Linearity, effective dynamic range and spatial resolution were determined.Radiographies of steep wedges were performed using the highest dynamic range setup.Tomography of a bronze cube was performed using the best spatial resolution setup.
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