640 research outputs found
Au4V – Moment Stability and Spin Fluctuations in the Ordered Phase
Although neither gold nor vanadium generally possess a magnetic moment, the intermetallic compound Au4V is found to be ferromagnetic below 42K. In this paper we report the results of a muon spin relaxation study of the itinerant electron moment fluctuations in Au4V above the Curie temperature. The temperature dependence of the muon spin relaxation rate is found to be similar to that of the weak itinerant helimagnet, MnSi
Multiplicities for LHC Nuclear Collisions Using HERA Structure Functions
We compute in QCD perturbation theory the transverse energy carried by
gluons, quarks and antiquarks with GeV in Pb+Pb
collisions at GeV by using structure functions compatible
with the small- increase observed at HERA. This gives a perturbative
estimate for the energy and entropy density of the bulk system at times
fm. The predicted initial gluon entropy density gives a lower
limit of about 2200...3400 for the final charged multiplicity. Sources of
further entropy increase are discussed.Comment: HU-TFT-94-6, 7 pages, 3 PostScript figures included in the end of the
tex-fil
EPS09 - a New Generation of NLO and LO Nuclear Parton Distribution Functions
We present a next-to-leading order (NLO) global DGLAP analysis of nuclear
parton distribution functions (nPDFs) and their uncertainties. Carrying out an
NLO nPDF analysis for the first time with three different types of experimental
input -- deep inelastic +A scattering, Drell-Yan dilepton production in
p+ collisions, and inclusive pion production in d+Au and p+p collisions at
RHIC -- we find that these data can well be described in a conventional
collinear factorization framework. Although the pion production has not been
traditionally included in the global analyses, we find that the shape of the
nuclear modification factor of the pion -spectrum at
midrapidity retains sensitivity to the gluon distributions, providing evidence
for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method
to quantify the nPDF uncertainties which originate from the uncertainties in
the data. In this method the sensitivity of to the variations of the
fitting parameters is mapped out to orthogonal error sets which provide a
user-friendly way to calculate how the nPDF uncertainties propagate to any
factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the
corresponding error sets are collected in our new release called {\ttfamily
EPS09}. These results should find applications in precision analyses of the
signatures and properties of QCD matter at the LHC and RHIC.Comment: 34 pages, 16 figures. The version accepted for publicatio
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Improvement in rice seed storage longevity from high-temperature drying is a consistent positive function of harvest moisture content above a critical value
Drying reduces seed moisture content which improves subsequent seed survival periods. Diverse maximum temperatures have been recommended to limit or avoid damage to seeds, but some high-temperature drying regimes may improve subsequent seed quality. Seeds from 20 different accessions of five rice (Oryza sativa L.) variety groups (aromatic, Aus, Indica, temperate Japonica, tropical Japonica) were harvested over several seasons at different stages of maturation and either dried throughout at 15°C/15% RH or for different initial periods (continuous or intermittent) in different drying regimes at 45°C before final equilibrium drying at 15°C/15% RH. Subsequent seed longevity in hermetic storage at 45°C with 10.9% moisture content was determined. In no case did initial drying at 45°C provide poorer longevity than drying at 15°C/15% RH throughout. There was a split-line relation, which did not differ amongst investigations, between longevity after initial drying at 45°C relative to that at 15°C/15% RH throughout and harvest moisture content, with a break point at 16.5% (a seed moisture status of about -14 MPa). Below 16.5%, relative longevity did not differ with harvest moisture content with little or no advantage to longevity from drying at 45°C. Above 16.5%, relative longevity showed a positive relation with harvest moisture content, with substantial benefit from drying at 45°C to subsequent longevity of seeds harvested whilst still moist. Hence there are temporal (immediately ex planta cf. subsequent air-dry storage) and water status discontinuities (above cf. below 16.5%) in the effect of temperature on subsequent air-dry longevity
Formation and Evolution of Quark-Gluon Plasma at RHIC and LHC
Initial conditions for quark-gluon plasma formation at \tau=0.1\fm are
considered in lowest order perturbative QCD. Chemical composition,
thermalization of the formed semihard quark-gluon system and especially
implications of the new HERA parton distributions with the enhancement at small
are studied. The plasma at \tau=0.1\fm is shown to be strongly gluon
dominated both at RHIC and LHC, and a possibility for rapid thermalization of
gluons at LHC is pointed out. Uncertainties in the calculations, particularly
shadowing corrections to the parton distributions, are discussed. Free
streaming and ideal hydro limits for the evolution of the gluonic plasma with
the calculated minijet initial conditions are demonstrated, and a lower limit
for final multiplicities obtained for the LHC nuclear collisions.Comment: the uuencoded ps-file is replaced by the tex-file and a separate
uuencoded file for the figures
Cold Nuclear Matter Effects on Dijet Productions in Relativistic Heavy-ion Reactions at LHC
We investigate the cold nuclear matter(CNM) effects on dijet productions in
high-energy nuclear collisions at LHC with the next-to-leading order
perturbative QCD. The nuclear modifications for dijet angular distributions,
dijet invariant mass spectra, dijet transverse momentum spectra and dijet
momentum imbalance due to CNM effects are calculated by incorporating EPS, EKS,
HKN and DS param-etrization sets of parton distributions in nucleus . It is
found that dijet angular distributions and dijet momentum imbalance are
insensitive to the initial-state CNM effects and thus provide optimal tools to
study the final-state hot QGP effects such as jet quenching. On the other hand,
the invariant mass spectra and the transverse momentum spectra of dijet are
generally enhanced in a wide region of the invariant mass or transverse
momentum due to CNM effects with a feature opposite to the expected suppression
because of the final-state parton energy loss effect in the QGP. The difference
of EPS, EKS, HKN and DS parametrization sets of nuclear parton distribution
functions is appreciable for dijet invariant mass spectra and transverse
momentum spectra at p+Pb collisions, and becomes more pronounced for those at
Pb+Pb reactions.Comment: 10 pages, 11 figure
Screening of initial parton production in ultrarelativistic heavy-ion collisions
Screening of initial parton production due to the presence of on-shell
partons in high-energy heavy-ion collisions is discussed. It is shown that the
divergent cross sections in the calculation of parton production can be
regulated self-consistently without an {\it ad hoc} cut-off, and that the
resultant parton production and transverse energy production rate are finite.
Consequences on the energy density estimates are discussed.Comment: 10 pages, REVTeX, 5 ps-figures uuencode
Scattering amplitudes with massive fermions using BCFW recursion
We study the QCD scattering amplitudes for \bar{q}q \to gg and \bar{q}q \to
ggg where q is a massive fermion. Using a particular choice of massive fermion
spinor we are able to derive very compact expressions for the partial spin
amplitudes for the 2 \to 2 process. We then investigate the corresponding 2 \to
3 amplitudes using the BCFW recursion technique. For the helicity conserving
partial amplitudes we again derive very compact expressions, but were unable to
treat the helicity-flip amplitudes recursively, except for the case where all
the gluon helicities are the same. We therefore evaluate the remaining partial
amplitudes using standard Feynman diagram techniques.Comment: 21 page
Gauge Theories on a 2+2 Anisotropic Lattice
The implementation of gauge theories on a four-dimensional anisotropic
lattice with two distinct lattice spacings is discussed, with special attention
to the case where two axes are finely and two axes are coarsely discretized.
Feynman rules for the Wilson gauge action are derived and the renormalizability
of the theory and the recovery of the continuum limit are analyzed. The
calculation of the gluon propagator and the restoration of Lorentz invariance
in on-shell states is presented to one-loop order in lattice perturbation
theory for on both 2+2 and 3+1 lattices.Comment: 27 pages, uses feynmf. Font compatibility adjuste
Medium-evolved fragmentation functions
Medium-induced gluon radiation is usually identified as the dominant
dynamical mechanism underling the {\it jet quenching} phenomenon observed in
heavy-ion collisions. In its actual implementation, multiple medium-induced
gluon emissions are assumed to be independent, leading, in the eikonal
approximation, to a Poisson distribution. Here, we introduce a medium term in
the splitting probabilities so that both medium and vacuum contributions are
included on the same footing in a DGLAP approach. The improvements include
energy-momentum conservation at each individual splitting, medium-modified
virtuality evolution and a coherent implementation of vacuum and medium
splitting probabilities. Noticeably, the usual formalism is recovered when the
virtuality and the energy of the parton are very large. This leads to a similar
description of the suppression observed in heavy-ion collisions with values of
the transport coefficient of the same order as those obtained using the {\it
quenching weights}.Comment: LaTeX, 18 pages, 13 figures included using epsfig, uses JHEP3; v2:
enlarged discussions, one figure replaced, some references added, final
versio
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