2,546 research outputs found
Centrality dependence of heavy flavor production from single electron measurement
We present preliminary measurements of electron production in p+p, d+Au, and
Au+Au collisions at =200 GeV for transverse momenta 1.5 GeV/
8 GeV/ as a function of centrality. These measurements were carried
out using the STAR Time Projection Chamber and Barrel Electromagnetic
Calorimeter. In this manuscript we describe the measurement techniques used to
discriminate electrons from hadrons and the method used to evaluate the
non-photonic contributions from semi-leptonic decays of heavy flavor mesons.
The observed nuclear modification factors, , of non-photonic electrons
indicate at substantial energy loss of heavy quarks at moderate to high .Comment: 4 pages, 3 figures, presented in Quark Matter 2005 in Budapes
Coherent multiple scattering effect in DIS
We present a QCD calculation of the coherent multiple scattering effect on
single hadron production in semi-inclusive lepton-nucleus deep inelastic
scattering (DIS). We show that the destructive interference of coherent
multiple scattering leads to suppression in hadron productions. The suppression
is similar to the expectations of energy loss calculations. We compare our
calculation with experimental data.Comment: 4 pages, talk given at Hard Probe 2006 conferenc
Heavy Flavor Production at STAR
e present measurements on meson production via direct reconstruction of
its hadronic decay channel in minimum bias +Au and Au+Au
collisions at =200 GeV with up to 3 GeV/.
Non-photonic electron spectra from the charm semi-leptonic decays are analyzed
from the same data set as well as in + collision at =200 GeV
using the STAR Time-of-Flight (TOF) and Barrel EMC (BEMC) detectors,
respectively. Results of the charm-decayed single muon (prompt muon) spectra
are also presented at low in Au+Au collisions measured by the TOF
detector. The charm production total cross-section per nucleon-nucleon
collision is measured to be 1.260.09(stat.)0.23(sys.) mb in minimum
bias Au+Au collisions, which is consistent with the scaling compared
to 1.40.4 mb in minimum bias +Au collisions, and supports the
idea that charm quarks should be produced mostly via parton fusion at early
stage in relativistic heavy-ion collisions. A Blast-Wave model fit to the low
( GeV/c) non-photonic electrons, prompt muons and spectra shows
that charm hadrons may kinetically freeze-out earlier than light hadrons with a
smaller collective velocity. The nuclear modification factors () of the
non-photonic electrons in central Au+Au collisions are significantly below
unity at 2 GeV/, which indicates a significant amount of energy
loss for heavy quarks in Au+Au collisions. The charm transverse momentum
distribution must have been modified by the hot and dense matter created in
central Au+Au collisions at RHIC.Comment: 7 pages, 4 figures, proceedings for the Strange Quark Matter 2006
conferenc
Fungal growth response to recurring heating events is modulated by species interactions
An increasing frequency of heat events can affect key organisms related to ecosystem functions. Soil saprobic fungi have important roles in carbon and nutrient cycling in soils, and they are clearly affected by heat events. When tested individually, saprobic soil fungi showed a variety of growth responses to a series of two heat events. However, in nature these fungi rarely grow alone. Coexistence theory predicts that diversity in the response to stressors can influence the outcome of species interactions and growth. This means that the co-cultivation of different fungi may affect their growth response to heat events. To test if recurring heat events affect fungal growth in small synthetic communities, we evaluated fungi previously known to respond to recurring heat events in experimental small communities composed of two and three species. For the fungi growing in pairs, surprisingly, most of the responses could not be predicted by how the isolates responded individually. In some cases, facilitation or increased competition were observed. For the three fungi growing together, results were also not predicted by the individual or pair responses. Both the heat events and the small communities influenced the growth of the fungi and growth properties emerged from the interactions among isolates and the heat stress. We show that not only do environmental conditions influence fungal interactions and growth rates, but also that the co-cultivation of different fungi affects fungal response to recurring heat events. These results indicate that more complex experimental designs are needed to better understand the effects of recurring heat events and climate change on soil fungi
Heavy-Quark Diffusion, Flow and Recombination at RHIC
We discuss recent developments in assessing heavy-quark interaction in the
Quark-Gluon Plasma (QGP). While induced gluon radiation is expected to be the
main energy-loss mechanism for fast-moving quarks, we focus on elastic
scattering which prevails toward lower energies, evaluating both perturbative
(gluon-exchange) and nonperturbative (resonance formation) interactions in the
QGP. The latter are treated within an effective model for D- and B-meson
resonances above T_c as motivated by current QCD lattice calculations.
Pertinent diffusion and drag constants, following from a Fokker-Planck
equation, are implemented into an expanding fireball model for Au-Au collisions
at RHIC using relativistic Langevin simulations. Heavy quarks are hadronized in
a combined fragmentation and coalescence framework, and resulting
electron-decay spectra are compared to recent RHIC data. A reasonable
description of both nuclear suppression factors and elliptic flow up to momenta
of ~5 GeV supports the notion of a strongly interacting QGP created at RHIC.
Consequences and further tests of the proposed resonance interactions are
discussed.Comment: 8 pages, 14 figures, contribution to the proceedings for the
"International Conference on Strangeness in Quark Matter 2006
Overview of charm production at RHIC
In this presentation, I discussed a) the charm total cross-section and its
comparisons to measurements at other beam energies and pQCD calculations; b)
the semileptonic decay of charmed hadrons and the sensitivity of non-photonic
leptons to charm quark collective flow and freeze-out; c) semileptonic decayed
electron spectrum at high transverse momentum, its comparison to FONLL in p+p
and d+Au collisions, and heavy-quark energy loss in Au+Au collisions.Comment: 8 pages, 4 figures, overview talk at SQM2006: Strangeness in Quark
Matter Los Angeles, CA, Mar. 26-31, 2006; minor text changes and references
adde
Local buffer mechanisms for population persistence
Assessing and predicting the persistence of populations is essential for the conservation and control of species. Here, we argue that local mechanisms require a better conceptual synthesis to facilitate a more holistic consideration along with regional mechanisms known from metapopulation theory. We summarise the evidence for local buffer mechanisms along with their capacities and emphasise the need to include multiple buffer mechanisms in studies of population persistence. We propose an accessible framework for local buffer mechanisms that distinguishes between damping (reducing fluctuations in population size) and repelling (reducing population declines) mechanisms. We highlight opportunities for empirical and modelling studies to investigate the interactions and capacities of buffer mechanisms to facilitate better ecological understanding in times of ecological upheaval.acceptedVersio
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