New chronology for the Middle Palaeolithic of the southern Caucasus suggests early demise of Neanderthals in this region.

Neanderthal populations of the southern and northern Caucasus became locally extinct during the Late Pleistocene. The timing of their extinction is key to our understanding of the relationship between Neanderthals and anatomically modern humans (AMH) in Eurasia. Recent re-dating of the end of the Middle Palaeolithic (MP) at Mezmaiskaya Cave, northern Caucasus, and Ortvale Klde, southern Caucasus, suggests that Neanderthals did not survive after 39 ka cal BP (thousands of years ago, calibrated before present). Here we extend the analysis and present a revised regional chronology for MP occupational phases in western Georgia, based on a series of model-based Bayesian analyses of radiocarbon dated bone samples obtained from the caves of Sakajia, Ortvala and Bronze Cave. This allows the establishment of probability intervals for the onset and end of each of the dated levels and for the end of the MP occupation at the three sites. Our results for Sakajia indicate that the end of the late Middle Palaeolithic (LMP) and start of the Upper Palaeolithic (UP) occurred between 40,200 and 37,140 cal BP. The end of the MP in the neighboring site of Ortvala occurred earlier at 43,540-41,420 cal BP (at 68.2% probability). The dating of MP layers from Bronze Cave confirms that it does not contain LMP phases. These results imply that Neanderthals did not survive in the southern Caucasus after 37 ka cal BP, supporting a model of Neanderthal extinction around the same period as reported for the northern Caucasus and other regions of Europe. Taken together with previous reports of the earliest UP phases in the region and the lack of archaeological evidence for an in situ transition, these results indicate that AMH arrived in the Caucasus a few millennia after the Neanderthal demise and that the two species probably did not interact.

Observation of an "ABC" Effect in proton-proton collisions.

The cross section for inclusive multipion production in the pp-->ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasiparticle is in the 1S0 state. At the three higher energies, the missing-mass M_{X} spectra show a strong enhancement at low M_{X}, corresponding to an Abashian-Booth-Crowe effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with M_{X} and beam energy are consistent with two-pion production being mediated through the excitation of two Delta(1232) isobars, coupled to S and D states of the initial pp system. There is no sign of any resonancelike structure in the energy dependence of the type recently observed for the pn-->dpi;{0}pi;{0} total cross section.

Near-threshold production of phi mesons in pp collisions.

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair.

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.

Earliest Pleistocene hominid cranial remains from Dmanisi, Republic of Georgia: taxonomy, geological setting, and age.

Archaeological excavations at the site of Dmanisi in the Republic of Georgia have uncovered two partial early Pleistocene hominid crania. The new fossils consist of a relatively complete cranium and a second relatively complete calvaria from the same site and stratigraphic unit that yielded a hominid mandible in 1991. In contrast with the uncertain taxonomic affinity of the mandible, the new fossils are comparable in size and morphology with Homo ergaster from Koobi Fora, Kenya. Paleontological, archaeological, geochronological, and paleomagnetic data from Dmanisi all indicate an earliest Pleistocene age of about 1.7 million years ago, supporting correlation of the new specimens with the Koobi Fora fossils. The Dmanisi fossils, in contrast with Pleistocene hominids from Western Europe and Eastern Asia, show clear African affinity and may represent the species that first migrated out of Africa.