3,942 research outputs found
Consistency of data on soft photon production in hadronic interactions
The glob model of Lichard and Van Hove and the modified soft annihilation
model (MSAM) of Lichard and Thompson are used as a phenomenological tool for
relating results from various experiments on soft photon production in high
energy collisions. The total phenomenological expectation is composed of
contributions from classical bremsstrahlung, the soft annihilation model and
the glob model. The empirical excess above the background from hadronic decays
at very small longitudinal momenta of photons is well reproduced, as well as
that for transverse momenta pT >~ 10 MeV/c. Some data do not require the glob
model and MSAM components in the phenomenological mixture, but do not exclude
them. On the basis of consistency of all data with the total theoretical
expectation we argue that the results of all experiments are mutually
consistent. The models are unable to describe the excess of ultrasoft photons
(pT <~ 10 MeV/c), seen by some, but not all, experiments. This may indicate an
as yet unknown projectile-mass-dependent production mechanism. Possible
relations of soft photon production to other phenomena are discussed. A
simple-to-use, but physically equivalent version of the glob model is
developed, which enables an easy check of presented results.Comment: 25 pages, RevTeX, epsf.sty, 12 embedded figure
Soft Photoproduction Physics
Several topics of interest in soft photoproduction physics are discussed.
These include jet universality issues (particle flavour composition), the
subdivision into event classes, the buildup of the total photoproduction cross
section and the effects of multiple interactions.Comment: 10 pages, LaTeX2e, no figures, to appear in the proceedings of the
Durham Workshop on HERA Physics, ``Proton, Photon and Pomeron Structure'',
17--23 September 1995, Durham, U.
Aspects of four-jet production in polarized proton-proton collisions
We examine the intrinsic spin-dependence of the dominant subprocess contribution to four-jet production in polarized proton-proton
collisions using helicity amplitude techniques. We find that the partonic
level, longitudinal spin-spin asymmetry, , is intrinsically large
in the kinematic regions probed in experiments detecting four isolated jets.
Such events may provide another qualitative or semi-quantitative test of the
spin-structure of QCD in planned polarized collisions at RHIC.Comment: 9 pages, LaTeX, 2 uuencoded postscript files attache
Anthropogenic and climatic impacts on a coastal environment in the Baltic Sea over the last 1000 years
Coastal environments have experienced large ecological changes as a result of human activities over the last 100-200 years. To understand the severity and potential consequences of such changes, paleoenvironmental records provide important contextual information. The Baltic Sea coastal zone is naturally a vulnerable system and subject to significant human-induced impacts. To put the recent environmental degradation in the Baltic coastal zone into a long-term perspective, and to assess the natural and anthropogenic drivers of environmental change, we present sedimentary records covering the last 1000 years obtained from a coastal inlet (Gasfjarden) and a nearby lake (Lake Storsjon) in Sweden. We investigate the links between a pollen-based land cover reconstruction from Lake Storsjon and paleoenvironmental variables from Gasfjarden itself, including diatom assemblages, organic carbon (C) and nitrogen (N) contents, stable C and N isotopic ratios, and biogenic silica contents. The Lake Storsjon record shows that regional land use was characterized by small-scale agricultural activity between 900 and 1400 CE, which slightly intensified between 1400 and 1800 CE. Substantial expansion of cropland was observed between 1800 and 1950 CE, before afforestation between 1950 and 2010 CE. From the Gasfjarden record, prior to 1800 CE, relatively minor changes in the diatom and geochemical proxies were found. The onset of cultural eutrophication in Gasfjarden can be traced to the 1800s and intensified land use is identified as the main driver. Anthropogenic activities in the 20th century have caused unprecedented ecosystem changes in the coastal inlet, as reflected in the diatom composition and geochemical proxies. (c) 2018 Elsevier Ltd. All rights reserved.Peer reviewe
Behavior of the diffractive cross section in hadron-nucleus collisions
A phenomenological analysis of diffractive dissociation of nuclei in
proton-nucleus and meson-nucleus collisions is presented. The theoretical
approach employed here is able to take into account at once data of the HELIOS
and EHS/NA22 collaborations that exhibit quite different atomic mass
dependences. Possible extensions of this approach to hard diffraction in
nuclear processes are also discussed.Comment: 5 pages, 2 figure
Multi-boson effects and the normalization of the two-pion correlation function
The two-pion correlation function can be defined as a ratio of either the
measured momentum distributions or the normalized momentum space probabilities.
We show that the first alternative avoids certain ambiguities since then the
normalization of the two-pion correlator contains important information on the
multiplicity distribution of the event ensemble which is lost in the second
alternative. We illustrate this explicitly for specific classes of event
ensembles.Comment: 6 pages, three figures,submit to PR
A partial wave analysis of the centrally produced pi0pi0 system in pp interactions at 450 GeV/c
A partial wave analysis of the centrally produced pi0pi0 channel has been
performed in pp collisions using an incident beam momentum of 450 GeV/c. An
unambiguous physical solution has been found. Evidence is found for the
f0(980), f0(1300) and f0(1500) in the the S-wave. and the f2(1270) is observed
dominantly in the D0-wave. In addition, there is evidence for a broad
enhancement in the D-wave below 1 GeV.Comment: 12 pages, Latex, 4 Figure
Thermal phenomenology of hadrons from 200 AGeV S+S collisions
We develop a complete and consistent description for the hadron spectra from
heavy ion collisions in terms of a few collective variables, in particular
temperature, longitudinal and transverse flow. To achieve a meaningful
comparison with presently available data, we also include the resonance decays
into our picture. To disentangle the influences of transverse flow and
resonance decays in the -spectra, we analyse in detail the shape of the
-spectra.Comment: 31 pages, 13 figs in seperate uuencoded file, for LaTeX, epsf.sty and
dvips, TPR-93-16 and BNL-(no number yet
Measurement of the mid-rapidity transverse energy distribution from GeV Au+Au collisions at RHIC
The first measurement of energy produced transverse to the beam direction at
RHIC is presented. The mid-rapidity transverse energy density per participating
nucleon rises steadily with the number of participants, closely paralleling the
rise in charged-particle density, such that E_T / N_ch remains relatively
constant as a function of centrality. The energy density calculated via
Bjorken's prescription for the 2% most central Au+Au collisions at
sqrt(s_NN)=130 GeV is at least epsilon_Bj = 4.6 GeV/fm^3 which is a factor of
1.6 larger than found at sqrt(s_NN)=17.2 GeV (Pb+Pb at CERN).Comment: 307 authors, 6 pages, 4 figures, 1 table, submitted to PRL 4/18/2001;
revised version submitted to PRL 5/24/200
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