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The first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced ρ0 mesons is presented. The ρ0 mesons are reconstructed through their decay into a pion pair. The measured anisotropy corresponds to the amplitude of the cos(2ϕ) modulation, where ϕ is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb−Pb collisions at a center-of-mass energy of sNN−−−√ = 5.02 TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the cos(2ϕ) modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations, which describe the measurement, explain the cos(2ϕ) anisotropy as the result of a quantum interference effect at the femtometer scale that arises from the ambiguity as to which of the nuclei is the source of the photon in the interaction.
Cryophytic steppes in the Minusinskaya intermountain basin containing plant species that are predominantly distributed in the alpine zone such as Androsace dasyphylla, Dryas oxyodonta, Festuca sphagnicola, Kobresia myosuroides, K. filifolia, Minuartia verna, Oxytropis bracteata, Sagina saginoides, Papaver nudicaule, Patrinia sibirica, Pedicularis lasiostachys, Pulsatilla ambigua, Saussurea schanginiana, which are considered remnants of the Pleistocene vegetation. Based on 89 relevés, we classified cryophytic steppes using the Braun-Blanquet method within two phytosociological classes: Central Asian steppes of the Cleistogenetea squarrosae and West Palearctic steppes of the Festuco-Brometea. Three associations (Androsaco dasyphyllae-Caricetum pediformis, Pulsatillo patentis-Caricetum pediformis and Bupleuro multinervi-Helictotrichetum desertori) with three subassociations and three variants were described with respect to their phytosociological affinities and ecology. DCA ordination showed floristic differences between syntaxa, while correlations of DCA axes and floristic and environmental variables detected substrate type and temperature regime as presumably main drivers for vegetation differentiation. Another driver for vegetation differentiation seems to be continentality of the climate. Small scale distribution of cryophytic steppes were mapped using satellite images with resolution of 1.8 m. Cryophytic steppes always occupy only small areas in landscapes, on convex parts of undulated microrelief of mountain slopes and summits characterised by drought in summer and deep soil freezing in winter. These special micro-ecological conditions play an essential role for the existence of alpine flora in the Minusinskaya intermountain basin.