87 research outputs found
Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions
The global polarization of {\Lambda} hyperons along the total orbital angular
momentum of a relativistic heavy-ion collision is presented based on the high
statistics data samples collected in Au+Au collisions at \sqrt{s_{NN}} = 2.4
GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer
(HADES) at GSI, Darmstadt. This is the first measurement below the strangeness
production threshold in nucleon-nucleon collisions. Results are reported as a
function of the collision centrality as well as a function of the hyperon
transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality
0--40%. We observe a strong centrality dependence of the polarization with an
increasing signal towards peripheral collisions. For mid-central (20--40%)
collisions the polarization magnitudes are (%) = 6.0 \pm 1.3
(stat.) \pm 2.0 (syst.) for Au+Au and (%) = 4.6 \pm 0.4 (stat.)
\pm 0.5 (syst.) for Ag+Ag, which are the largest values observed so far. This
observation thus provides a continuation of the increasing trend previously
observed by STAR and contrasts expectations from recent theoretical
calculations predicting a maximum in the region of collision energies about 3
GeV. The observed polarization is of a similar magnitude as predicted by 3D
fluid dynamics and the UrQMD plus thermal vorticity model and significantly
above results from the AMPT model.Comment: 8 pages, 4 figure
Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions
In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pionâpion momentum correlations is investigated in Au + Au collisions at = 2.4 GeV. We show that the low-m region (m < 0.2 GeV / c) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields
Inclusive ee production in collisions of pions with protons and nuclei in the second resonance region of baryons
Inclusive ee production has been studied with HADES in + p,
+ C and reactions, using the GSI pion beam at
= 1.49 GeV. Invariant mass and transverse momentum
distributions have been measured and reveal contributions from Dalitz decays of
, mesons and baryon resonances. The transverse momentum
distributions are very sensitive to the underlying kinematics of the various
processes. The baryon contribution exhibits a deviation up to a factor seven
from the QED reference expected for the dielectron decay of a hypothetical
point-like baryon with the production cross section constrained from the
inverse n p reaction. The enhancement is attributed
to a strong four-momentum squared dependence of the time-like electromagnetic
transition form factors as suggested by Vector Meson Dominance (VMD). Two
versions of the VMD, that differ in the photon-baryon coupling, have been
applied in simulations and compared to data. VMD1 (or two-component VMD)
assumes a coupling via the meson and a direct coupling of the photon,
while in VMD2 (or strict VMD) the coupling is only mediated via the
meson. The VMD2 model, frequently used in transport calculations for dilepton
decays, is found to overestimate the measured dielectron yields, while a good
description of the data can be obtained with the VMD1 model assuming no phase
difference between the two amplitudes. Similar descriptions have also been
obtained using a time-like baryon transition form factor model where the pion
cloud plays the major role.Comment: (HADES collaboration
Inspired or foolhardy: sensemaking, confidence and entrepreneurs' decision-making.
The purpose of this paper is to investigate the role of confidence in how both new and experienced entrepreneurs interpret and make sense of their business environment to inform decision-making. We illustrate our conceptual arguments with descriptive results from a large-scale (n = 6289) survey on entrepreneurs' perception of business performance and their decisions taken at a time of uncertainty in an economic downturn. Quantitative findings are stratified along experiential lines to explore heterogeneity in entrepreneurial decision-making and directly inform our conceptual arguments, while qualitative data from open questions are used to explain the role of confidence. Newer entrepreneurs are found to be more optimistic in the face of environmental risk, which impacts on their decision-making and innovative capabilities. However, the more experienced entrepreneurs warily maintain margin and restructure to adapt to environmental changes. Instead of looking directly at the confidence of individuals, we show how confidence impacts sensemaking, and ultimately, decision-making. These insights inform research on the behaviour of novice and experienced entrepreneurs in relation to innovative business activities. Specifically, blanket assumptions on the role of confidence may be misplaced as its impact changes with experience to alter how entrepreneurs make sense of their environment
Una metodologia per la scelta e la misurazione del grado di apertura delle pratiche di open innovation
Negli ultimi anni il termine open Ăš stato adottato in ambiti molto differenti â ad esempio lâopen innovation (OI) e lâopen manufacturing â e con significati diversi, persino con riferimento allo stesso ambito. Dopo aver analizzato le principali accezioni del termine, il lavoro esplora il tema dellâOI, che nellâultimo decennio Ăš stato oggetto di crescente attenzione da parte della comunitĂ scientifica e delle imprese. Per queste ultime, in particolare, lâadozione di pratiche di OI consente di accedere a expertise non disponibili in house, di ridurre i costi e condividere con altri soggetti i rischi associati allo sviluppo delle innovazioni. In questo lavoro si propone una metodologia che le imprese possono utilizzare a supporto (i) della scelta della pratica piĂč adatta al contesto nel quale lâinnovazione Ăš sviluppata e (ii) della misurazione del grado di openness della pratica stess
Assessing The Openness Degree Of Knowledge Supply Chains
Organizations need to engage in collaboration networks to develop innovations. Such networks are defined as Knowledge Supply Chains (KSCs) and the involved collaborations as Knowledge Supplies (KSs). The paper proposes a methodology to map the KSs that an organization needs in developing innovation and to assess its openness degree, an evaluation in turn depending on the characteristics and the criticality of each supply. By taking into consideration different dimensions of the KSs and providing a measurement of their criticality, the methodology contributes to make the concept of openness clearer. The methodology can also be used by organizations to support (i) decision making and priority assessment in the allocation of resources, (ii) ex-post learning (lesson learnt) as to the knowledge acquired and used during New Product Development (NPD) and the degree, if any, of openness adopted
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