939 research outputs found
Direct Photons in Nuclear Collisions at FAIR Energies
Using the extrapolation of existing data estimations of prompt photon
production at FAIR energies have been made. At the rapidity
density of prompt photons with 1.5 GeV/c per central Au+Au event at 25
AGeV is estimated as . With the planed beam intensity
per second and 1% interaction probability, for 10% of most central events one
can expect the prompt photon rate photons per second.
Direct photons from the hadron scenario of ion collisions generated by the
Hadron-String-Dynamics (HSD) transport approach with implemented meson
scatterings have been analyzed.
Photons from short-living resonances (e.g. )
decaying during the dense phase of the collision should be considered as direct
photons. They contribute significantly in the direct photon spectrum at
GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions
the HSD generator predicts, as a lower estimate,
0.5% in the region
GeV/c. At GeV/c 2%.
Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics
(BHD) model. The BHD spectra differ strongly from the HSD predictions. The
direct photon spectrum is very sensitive to the initial temperature parameter
of the model. The 10 MeV increase in the value leads to
2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of
Sciences, ITEP, Moscow, 26 - 30 November 200
A Unified Picture for Single Transverse-Spin Asymmetries in Hard Processes
Using Drell-Yan pair production as an example, we explore the relation
between two well-known mechanisms for single transverse-spin asymmetries in
hard processes: twist-three quark-gluon correlations when the pair's transverse
momentum is large, , and time-reversal-odd and
transverse-momentum-dependent parton distributions when is much less
than the pair's mass. We find that although the two mechanisms have their own
domain of validity, they describe the same physics in the kinematic region
where they overlap. This unifies the two mechanisms and imposes an important
constraint on phenomenological studies of single spin asymmetries.Comment: 4 pages, 3 figure
MC-Simulation of the Transverse Double Spin Asymmetry for RHIC
Using {\sc Sphinx tt}, a new MC simulation program for transverse polarized
nucleon--nucleon scattering based on {\sc Pythia~5.6}, we calculate the
transverse double spin asymmetry in the Drell-Yan process. If one
assumes (quite arbitrarily) that the transversity parton distribution equals the helicity distribution at some low
scale, the resulting asymmetry is of order 1\%. In this case is
would hardly be be measurable with PHENIX at RHIC.Comment: 17 pages, 5 figure
Polarized semi-inclusive electroweak structure functions at next-to-leading-order
We present a next-to-leading order (NLO) computation of the full set of
polarized and unpolarized electroweak semi-inclusive DIS (SIDIS) structure
functions, whose knowledge is crucial for a precise extraction of polarized
parton distributions. We focus on the phenomenology of the polarized structure
functions for the kinematical conditions that could be reached in an
Electron-Ion-Collider.
We show that the NLO corrections are sizeable, particularly in the small-
range. We test the sensitivity of these structure functions on certain quark
distributions and compare it to the situation of inclusive DIS and
electromagnetic SIDIS.Comment: 17 pages, 5 figure
Drell-Yan forward-backward and spin asymmetries for arbitrary vector boson production at next-to-leading order
Longitudinally polarized, unpolarized and forward-backward mass differential
cross sections for Drell-Yan lepton-pair production by arbitrary vector bosons
are calculated in next-to-leading order (NLO) QCD. Analytical results are
presented in a form valid for all consistent -dimensional regularization
schemes, with the mass factorization scheme kept general. NLO predictions for
all Drell-Yan type processes (, and ) at BNL's
relativistic heavy ion collider (RHIC) are made using polarized parton
distributions which fit the recent deep-inelastic scattering data. These are
examined as tools in the determination of the polarized parton distributions
and the unpolarized ratio. NLO predictions for the
forward-backward lepton asymmetry at Fermilab are made and the precision
determination of from future runs is studied. In all the
above, the QCD corrections are found to be significant. An introductory
discussion is given of various theoretical issues, such as allowable
factorization and regularization schemes, and scale dependences.Comment: 34 pages, figures included, revtex. Some discussions and references
added/modified. In more compact form. To appear in Phys. Rev.
Single Transverse-Spin Asymmetry in Drell-Yan Production at Large and Moderate Transverse Momentum
We study the single-transverse spin asymmetry for the Drell-Yan process. We
consider production of the lepton pair at large transverse momentum,
, where is the pair's mass. The spin asymmetry is then of
higher twist and may be generated by twist-three quark-gluon correlation
functions. Expanding the result for , we make contact with the
transverse-momentum-dependent QCD factorization involving the so-called Sivers
functions. We find that the two mechanisms, quark-gluon correlations on one
hand and the Sivers effect on the other, contain the same physics in this
region. This ties the two together and imposes an important constraint on
phenomenological studies of single transverse spin asymmetries.Comment: 29 pages, 10 figure
Detection and quantification of Aβ−3–40 (APP669‐711) in cerebrospinal fluid
Neurochemical biomarkers can support the diagnosis of Alzheimer’s disease and may facilitate clinical trials. In blood plasma, the ratio of the amyloid-β (Aβ) peptides Aβ−3– 40/Aβ1–42 can predict cerebral amyloid-β pathology with high accuracy (Nakamura et al., 2018). Whether or not Aβ−3–40 (aka. amyloid precursor protein (APP) 669– 711) is also present in cerebrospinal fluid (CSF) is not clear. Here, we investigated whether Aβ−3–40 can be detected in CSF and to what extent the CSF Aβ−3–40/Aβ42 ratio is able to differentiate between individuals with or without amyloid-β positron emission tomography (PET) evidence of brain amyloid. The occurrence of Aβ−3–40 in human CSF was assessed by immunoprecipitation followed by mass spectrometry. For quantifying the CSF concentrations of Aβ−3–40 in 23 amyloid PET- negative and 17 amyloid PET- positive subjects, we applied a sandwich-type immunoassay. Our findings provide clear evidence of the presence of Aβ−3–40 and Aβ−3–38 in human CSF. While there was no statistically significant difference in the CSF concentration of Aβ−3–40 between the two diagnostic groups, the CSF Aβ−3–40/Aβ42 ratio was increased in the amyloid PET- positive individuals. We conclude that Aβ−3– 40 appears to be a regular constituent of CSF and may potentially serve to accentuate the selec- tive decrease in CSF Aβ42 in Alzheimer's disease
NNLO corrections to massive lepton-pair production in longitudinally polarized proton-proton collisions
We present the full next-to-next-to-leading order (NNLO) coefficient
functions for the polarized cross section for the Drell-Yan
process . Here denotes any inclusive hadronic
state and represents the invariant mass of the lepton pair. All QCD
partonic subprocesses have been included provided the lepton pair is created by
a virtual photon, which is a valid approximation for GeV. Unlike the
differential distribution w.r.t. transverse momentum the dominant subprocess
for the integrated cross section is given by and
its higher order corrections so that massive lepton pair production provides us
with an excellent tool to measure the polarized anti-quark densities. Our
calculations are carried out using the method of -dimensional regularization
by making a special choice for the matrix. We give predictions for
double longitudinal spin asymmetry measurements at the RHIC.Comment: 45 pages, 22 figures. Due to a bug in our program the mass
factorization plots in fig. 8-11 are changed. All parton density sets, in
particular the set BB1 (J. Blumlein, H. Bottcher), lead to an improvement in
the scale dependence while going from LO to NLO and then to NNL
Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data
We present a combined next-to-leading order QCD analysis to data on both
inclusive and semi-inclusive polarized deep inelastic scattering asymmetries.
Performing NLO QCD global fits with different sets of observables, we evaluate
the impact of the very recent semi-inclusive results presented by SMC in the
extraction of NLO polarized parton distributions.Comment: 22 pages, 4 figures include
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