15 research outputs found
Resummation of nuclear enhanced higher twist in the Drell Yan process
We investigate higher twist contributions to the transverse momentum
broadening of Drell Yan pairs in proton nucleus collisions. We revisit the
contribution of matrix elements of twist-4 and generalize this to matrix
elements of arbitrary twist. An estimate of the maximal nuclear broadening
effect is derived. A model for nuclear enhanced matrix elements of arbitrary
twist allows us to give the result of a resummation of all twists in closed
form. Subleading corrections to the maximal broadening are discussed
qualitatively.Comment: 10 pages, 5 figures; v2: minor changes in text, acknowledgement
added; v3: mistake in fig. 1 correcte
Shadowing in photo-production : role of in-medium hadrons
We study the effects of in-medium hadronic properties on shadowing in
photon-nucleus interactions in Glauber model as well as in the multiple
scattering approach. A reasonable agreement with the experimental data is
obtained in a scenario of downward spectral shift of the hadrons. Shadowing is
found to be insensitive to the broadening of the spectral functions. An impact
parameter dependent analysis of shadowing might shed more light on the role of
in-medium properties of hadrons.Comment: Title modified; version to appear in PRC, Rapid Communication
Nonperturbative Effects in Gluon Radiation and Photoproduction of Quark Pairs
We introduce a nonperturbative interaction for light-cone fluctuations
containing quarks and gluons. The interaction squeezes the transverse
size of these fluctuations in the photon and one does not need to simulate this
effect via effective quark masses. The strength of this interaction is fixed by
data. Data on diffractive dissociation of hadrons and photons show that the
nonperturbative interaction of gluons is much stronger. We fix the parameters
for the nonperturbative quark-gluon interaction by data for diffractive
dissociation to large masses (triple-Pomeron regime). This allows us to predict
nuclear shadowing for gluons which turns out to be not as strong as
perturbative QCD predicts. We expect a delayed onset of gluon shadowing at shadowing of quarks. Gluon shadowing turns out to be nearly scale
invariant up to virtualities due to presence of a semihard
scale characterizing the strong nonperturbative interaction of gluons. We use
the same concept to improve our description of gluon bremsstrahlung which is
related to the distribution function for a quark-gluon fluctuation and the
interaction cross section of a fluctuation with a nucleon. We expect
the nonperturbative interaction to suppress dramatically the gluon radiation at
small transverse momenta compared to perturbative calculations.Comment: 58 pages of Latex including 11 figures. Shadowing for soft gluons and
Fig. 6 are added as well as a few reference
Nuclear shadowing in Glauber-Gribov theory with Q2-evolution
We consider deep inelastic scattering off nuclei in the Regge limit within
the Glauber-Gribov model. Using unitarized parton distribution functions for
the proton, we find sizeable shadowing effects on the nuclear total and
longitudinal structure functions, and , in the low-x limit.
Extending a fan-diagram analysis for the large-mass region of coherent
diffraction off nuclei to high Q2, we also find significant shadowing effects
in this kinematical regime. Finally, we discuss shortcomings of our approach
and possible extensions of the model to other kinematical regimes.Comment: 16 pages, 9 figure
Contributions of gluon recombination to saturation phenomena
Parton distributions in the small region are numerically predicted by
using a modified DGLAP equation with the GRV-like input distributions. We find
that gluon recombination at twist-4 level obviously suppresses the rapid growth
of parton densities with decrease. We show that before the saturation scale
is reached, saturation and partial saturation appear in the small
behavior of parton distributions in nucleus and free proton, respectively. The
antishadowing contributions to the saturation phenomena are also discussed.Comment: 23 pages, LATEX, 22 figures, to appear in Phys. Rev.
Is the Public Motivated to Engage in Open Data Innovation?
Part 3: Policy and StakeholdersInternational audienceGovernments aim to increase democracy by engaging the public in using open data to develop mobile apps and citizen services. They make information available (open data) and organize innovation contests to stimulate innovation with the goal to make new services available for the public to use. But will the public take on the challenge to both develop and provide services to each other? In this paper we use a case study from public transportation to investigate the motivation for individuals and teams to participate in innovation contests. The results show that the motivation for participating is primarily related to fun and enjoyment. We argue that in order to better meet the goals of open data innovation, governments need to follow through the full service innovation cycle and also care for making citizen coproduction in the execution and monitoring phases fun and enjoyable. Currently there is little chance for participants to make profit on a competitive market so governments need to provide other mechanisms to ensure service provisioning. For future research it is suggested to investigate how the later stages of open data innovation can be supported in order to meet the overall goals of open data innovation