50 research outputs found
A model-free procedure to correct for volume fluctuations in E-by-E analyses of particle multiplicities
We develop an innovative and unbiased procedure, based on event mixing, to
account for unavoidable contributions from volume (or system size) fluctuations
to experimentally measured moments of particle multiplicity distributions
produced in relativistic nuclear collisions. Within the wounded-nucleon model
they are characterized by fluctuations of the number of wounded nucleons, the
latter usually referred to as participants. For the first time we extract
participant fluctuations directly from the data used for the fluctuation
analysis, i.e., without involving model calculations. To achieve this we
constructed a dedicated event-mixing algorithm that eliminates all possible
correlations between produced particles while preserving the volume
fluctuations. The procedure provides direct access to the cumulants of
wounded-nucleon distributions, which can be used to account for non-critical
contributions to the experimentally measured cumulants of multiplicity
distributions
Constraints on the kinetic mixing parameter for the light dark photons from dilepton production in heavy-ion collisions in the few-GeV energy range
The vector -bosons, or so called 'dark photons', are one of the possible
candidates for the dark matter mediators. They are supposed to interact with
the standard matter via a 'vector portal' due to the
symmetry group mixing which might make them visible in particle and heavy-ion
experiments. While there is no confirmed observation of dark photons, the
detailed analysis of different experimental data allows to estimate the upper
limit for the kinetic mixing parameter depending on the mass
of -bosons which is also unknown. In this study we present theoretical
constraints on the upper limit of in the mass range GeV from the comparison of the calculated dilepton spectra with the
experimental data from the HADES Collaboration at SIS18 energies where the dark
photons are not observed. Our analysis is based on the microscopic
Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces well
the measured dilepton spectra in , and collisions.
Additionally to the different dilepton channels originating from interactions
and decays of ordinary matter particles (mesons and baryons), we incorporate
the decay of hypothetical -bosons to dileptons, , where the
-bosons themselves are produced by the Dalitz decay of pions , -mesons and Delta resonances . Our analysis can help to estimate the requested accuracy for future
experimental searches of 'light' dark photons by dilepton experiments.Comment: 11 pages, 5 figures, extended version, to be published in Phys. Rev.
Defect-Driven Superfluid Crossover for Two-Dimensional Dipolar Excitons Trapped at Thermodynamic Equilibrium
We study ultra-cold dipolar excitons confined in a 10m trap of a double
GaAs quantum well. Based on the local density approximation, we unveil for the
first time the equation of state of excitons at pure thermodynamic equilibrium.
In this regime we show that, below a critical temperature of about Kelvin,
a superfluid forms in the inner region of the trap at a local exciton density
, encircled by a more dilute and normal
component in the outer rim of the trap. Remarkably, this spatial arrangement
correlates directly with the concentration of defects in the exciton density
which exhibits a sudden decrease at the onset of superfluidity, thus pointing
towards an underlying Berezinskii-Kosterlitz-Thouless mechanism.Comment: 8 pages, 8 figure
Pluto: a Monte Carlo simulation tool for hadronic physics
Pluto is a Monte-Carlo event generator designed for hadronic interactions from Pion production threshold to intermediate energies of a few GeV per nucleon, as well as for studies of heavy ion reactions. The package is entirely based on ROOT, without the need of additional packages, and uses the embedded C++ interpreter of ROOT to control the event production. The generation of events based on a single reaction chain and the storage of the resulting particle objects can be done with a few lines of a ROOT-macro. However, the complete control of the package can be taken over by the steering macro and user-defined models may be added without a recompilation of the framework. Multi-reaction cocktails can be facilitated as well using either mass-dependent or user-defined static branching ratios. The included physics uses resonance production with mass-dependent Breit-Wigner sampling. The calculation of partial and total widths for resonances producing unstable particles is performed recursively in a coupled-channel approach. Here, particular attention is paid to the electromagnetic decays, motivated by the physics program of HADES. The thermal model supports 2-component thermal distributions, longitudinal broadening, radial blast, direct and elliptic flow, and impact-parameter sampled multiplicities. The interface allows angular distribution models (e.g. for the primary meson emission) to be attached by the user as well as descriptions of multi-particle correlations using decay chain templates. The exchange of mass sampling or momentum generation models is also possible. The first feature allows for consistent coupled-channel calculations, needed for a correct description of hadronic interactions. For elementary reactions, angular distribution models for selected channels are already part of the framework, based on parameterizations of existing data. This report gives an overview of the design of the package, the included models and the user interface
Study of exclusive one-pion and one-eta production using hadron and dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and 2.2 GeV with HADES
We present measurements of exclusive ensuremathπ+,0 and η production in pp reactions at 1.25GeV and 2.2GeV beam kinetic energy in hadron and dielectron channels. In the case of π+ and π0 , high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance-corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of Δ (1232) and higher-lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross-sections are of special interest in the case of pp → pp η , since controversial data exist at 2.0GeV; we find \ensuremathσ=0.142±0.022 mb. Using the dielectron channels, the π0 and η Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance-corrected helicity angle distributions are found in good agreement with model predictions
Metadata standards and practical guidelines for specimen and DNA curation when building barcode reference libraries for aquatic life
DNA barcoding and metabarcoding is increasingly used to effectively and precisely assess and monitor biodiversity in aquatic ecosystems. As these methods rely on data availability and quality of barcode reference libraries, it is important to develop and follow best practices to ensure optimal quality and traceability of the metadata associated with the reference barcodes used for identification. Sufficient metadata, as well as vouchers, corresponding to each reference barcode must be available to ensure reliable barcode library curation and, thereby, provide trustworthy baselines for downstream molecular species identification. This document (1) specifies the data and metadata required to ensure the relevance, the accessibility and traceability of DNA barcodes and (2) specifies the recommendations for DNA harvesting and for the storage of both voucher specimens/samples and barcode data.info:eu-repo/semantics/publishedVersio