1,485 research outputs found
New observables in longitudinal single-spin asymmetries in semi-inclusive DIS
We analyze longitudinal beam and target single-spin asymmetries in
semi-inclusive deep inelastic scattering and in jet deep inelastic scattering,
including all possible twist-3 contributions as well as quark mass corrections.
We take into account the path-ordered exponential in the soft correlators and
show that it leads to the introduction of a new distribution and a new
fragmentation function contributing to the asymmetries.Comment: 8 page
Double spin asymmetry A_{LT} in direct photon production
We study the longitudinal-transverse double spin asymmetry for
direct photon production in nucleon-nucleon scattering by using the collinear
twist-3 approach. This asymmetry, which, for instance, could be measured at
RHIC, contains a complete set of collinear twist-3 correlation functions in a
transversely polarized nucleon.Comment: 9 pages, 1 figur
A dynamical trichotomy for structured populations experiencing positive density-dependence in stochastic environments
Positive density-dependence occurs when individuals experience increased
survivorship, growth, or reproduction with increased population densities.
Mechanisms leading to these positive relationships include mate limitation,
saturating predation risk, and cooperative breeding and foraging. Individuals
within these populations may differ in age, size, or geographic location and
thereby structure these populations. Here, I study structured population models
accounting for positive density-dependence and environmental stochasticity i.e.
random fluctuations in the demographic rates of the population. Under an
accessibility assumption (roughly, stochastic fluctuations can lead to
populations getting small and large), these models are shown to exhibit a
dynamical trichotomy: (i) for all initial conditions, the population goes
asymptotically extinct with probability one, (ii) for all positive initial
conditions, the population persists and asymptotically exhibits unbounded
growth, and (iii) for all positive initial conditions, there is a positive
probability of asymptotic extinction and a complementary positive probability
of unbounded growth. The main results are illustrated with applications to
spatially structured populations with an Allee effect and age-structured
populations experiencing mate limitation
Momentum sum rules for fragmentation functions
Momentum sum rules for fragmentation functions are considered. In particular,
we give a general proof of the Sch\"afer-Teryaev sum rule for the transverse
momentum dependent Collins function. We also argue that corresponding sum rules
for related fragmentation functions do not exist. Our model-independent
analysis is supplemented by calculations in a simple field-theoretical model.Comment: 12 pages; v2: Eqs. (44,46) added, minor additional changes, to appear
in Phys. Lett.
Sivers vs. Collins effect in azimuthal single spin asymmetries in pion production in SIDIS
Recently it has been argued that the transverse momentum dependent twist-2
Sivers distribution function does not vanish in QCD. Therefore both, the
Collins and Sivers effects, should be considered in order to explain the
azimuthal single spin asymmetries A(UL) in pion production in semi-inclusive
deeply inelastic lepton scattering of a longitudinally polarized target. On the
basis of presently available phenomenological information on the Sivers
function we estimate that for those asymmetries A(UL) in the kinematic region
of the HERMES experiments the Sivers effect can be neglected with respect to
the Collins effect. It is argued that the same feature holds also for the
COMPASS and CLAS experiments. This justifies theoretical approaches to
understand the HERMES data on the basis of the Collins effect only.Comment: 8 pages, 4 figures. References added, small changes in text, Appendix
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Azimuthal single spin asymmetries in SIDIS in the light of chiral symmetry breaking
An attempt is made to understand the z-dependence of the azimuthal single
spin asymmetries observed by the HERMES collaboration in terms of chiral models
based on effective quark and Goldstone boson degrees of freedom. The effects of
respectively neglecting and considering Gaussian intrinsic parton transverse
momenta and the Sivers effect are explored. Predictions for the transverse
target polarization experiment at HERMES are presented.Comment: 14 pages, 18 figure
Transverse spin asymmetries for W-production in proton-proton collisions
We study parity-even and parity-odd polarization observables for the process
, where the lepton comes from the decay of a
-boson. By using the collinear twist-3 factorization approach, we consider
the case when one proton is transversely polarized, while the other is either
unpolarized or longitudinally polarized. These observables give access to two
particular quark-gluon-quark correlation functions, which have a direct
relation to transverse momentum dependent parton distributions. We present
numerical estimates for RHIC kinematics. Measuring, for instance, the
parity-even transverse single spin correlation would provide a crucial test of
our current understanding of single spin asymmetries in the framework of QCD.Comment: 10 page
Thermophysical properties of the lanthanide sesquisulfides. II. Schottky contributions and magnetic and electronic properties of Îłâphase Pr2S3, Tb2S3, and Dy2S3
Heatâcapacity measurements by adiabatic equilibrium calorimetry are reported for Îłâphase Pr2S3, Tb2S3, and Dy2S3 between 5 and 350 K. Highly purified samples were prepared and their composition verified by chemical analysis. Precision lattice parameters were determined for each compound and are compared with literature values. The total heat capacity has been resolved into lattice, magnetic, and Schottky components by a volumetric approach. The experimental Schottky contributions accord with the calculated curves based on the crystalâfield splitting of the 2S+1LJ ground state of the lanthanide ions occupying sites of S4 symmetry in the Th3P4 lattice. The individual crystalâfield electronic energy levels have been obtained in part from an analysis of the hotâband data observed in the absorption spectra of Pr2S3, Tb2S3, and Dy2S3, and from a calculated splitting in which the crystalâfield parameters Bkm, were determined from a latticeâsum calculation. Molar thermodynamic properties are reported for all three compounds. The entropy at 298.15 K {S0âS0 (7 K)}, is 22.78R, 22.93R, and 23.36R, for Îłâphase Pr2S3, Tb2S3, and Dy2S3, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70592/2/JCPSA6-95-3-1964-1.pd
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