Bound-free pair production in ultra-relativistic ion collisions at the LHC collider: Analytic approach to the total and differential cross sections

A theoretical investigation of the bound-free electron-positron pair production in relativistic heavy ion collisions is presented. Special attention is paid to the positrons emitted under large angles with respect to the beam direction. The measurement of these positrons in coincidence with the down--charged ions is in principle feasible by LHC experiments. In order to provide reliable estimates for such measurements, we employ the equivalent photon approximation together with the Sauter approach and derive simple analytic expressions for the differential pair--production cross section, which compare favorably to the results of available numerical calculations. Based on the analytic expressions, detailed calculations are performed for collisions of bare Pb$^{82+}$ ions, taking typical experimental conditions of the LHC experiments into account. We find that the expected count rate strongly depends on the experimental parameters and may be significantly enhanced by increasing the positron-detector acceptance cone.Comment: 10 pages, 4 figure

Longitudinal scaling property of the charge balance function in Au + Au collisions at 200 GeV

We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage [-1.3, 1.3]. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes.Comment: 6 pages, 3 figure

Measurement of an Elongation of the Pion Source in Z Decays

We measure Bose-Einstein correlations between like-sign charged pion pairs in hadronic Z decays with the L3 detector at LEP. The analysis is performed in three dimensions in the longitudinal center-of-mass system. The pion source is found to be elongated along the thrust axis with a ratio of transverse to longitudinal radius of $0.81\pm 0.02 ^{+0.03}_{-0.19}$

On the paradox of 'organised' encounter

Encounters are politically and pedagogically charged. They have long been celebrated for their ability to chip away at prejudices, enact cultural destabilisations, shape subjectivities, and produce new knowledges. Yet encounters come with risk. The paper argues that encounters should be taken as very specific genres of contact and offers a conceptual interrogation of the notion of encounter, and its (dis)organisation, as a way of reflecting on the paradox of ‘organised encounter’. In particular, the paper suggests that the promise and hope of organised encounter stands in tension with the recognition that encounters are inherently unpredictable –that they are about rupture and surprise. Taking this tension forward, the paper asks what possibilities remain for forms of planned encounter in intercultural contexts and focuses on two concerns. First, a concern with what happens when something that is inherently unpredictable becomes a site of intervention and secondly, a concern with the risks of encounter, and for whom the risks are most acutely felt. It finishes by reflecting on what it might mean to keep hold of the unpredictability of encounter in organised settings and what it means for questions of difference, power, and privilege

Rapanea ferruginea (Ruiz & Pav.) Mez. (Myrsinacea) como uma importante fonte alimentar para as aves em uma mata de galeria no interior do Estado de São Paulo Rapanea ferruginea (Ruiz & Pav.) Mez. (Myrsinacea) as an important food resource birds in a gallery forest in São Paulo, southeastern Brasil

Espécie típica de ambientes úmidos, Rapanea ferruginea produz diásporos globosos contendo uma única semente, envolta por um delgado pericarpo negro-arroxeado. Os comportamentos alimentares e a contribuição das aves na dispersão de sementes de R. ferruginea foram investigados em uma área de borda de mata de galeria, no município de São Manuel (22°43’S, 48°34’W), estado de São Paulo, sudeste do Brasil. Em 38 horas e 40 minutos de observações realizadas entre 20 de outubro e 12 de novembro de 2005, foram consumidos 11618 frutos por 31 espécies de aves, sendo a alta taxa de remoção de diásporos provavelmente devido à superabundância de frutos e à exposição dos mesmos na planta. Das 31 espécies registradas, 25 foram consideradas como potenciais dispersores por engolirem o diásporo inteiro e por realizarem visitas freqüentes e de curta duração. Turdus amaurochalinus Cabanis, 1851 foi a espécie que mais se alimentou em R. ferruginea, seguida por Dryocopus lineatus (Linnaeus, 1766) e Turdus leucomelas Vieillot, 1818, responsáveis por 43% do total de frutos consumidos, sendo ainda a primeira a espécie mais freqüente. A técnica de captura de frutos mais empregada foi "picking", enquanto "hanging" foi a menos utilizada, mas predominante em Vireo olivaceus(Vieillot, 1817) e D.lineatus. Foram registrados poucos encontros agonísticos, sendo Mimus saturninus Hellmayr, 1903 a espécie responsável pelo maior número de encontros interespecíficos, enquanto que as interações intraespecíficas foram lideradas por T. amaurochalinus e por T. leucomelas.<br>Characteristic of humid habitats, Rapanea ferruginea produces globose drupes containing a single seed covered by a thin black-purplish pulp. The feeding behavior and the contribution of birds in dispersing R. ferrugineafruits was examined in a gallery forest edge in São Manuel (22°43’S, 48°34’W), state of São Paulo, southeastern Brazil. In 38 hours and 40 minutes of focal observations carried out between October 20 to November 12, 2005, an amount of 11618 fruits were consumed by 31 bird species, probably due to both superabundance of food and exposure of fruits on tree. From the total, 25 species could be considered potential seed dispersers by swallowing the whole diaspore and having short and frequent visits. The most common feeder were Turdus amaurochalinus Cabanis, 1851, Dryocopus lineatus (Linnaeus, 1766) and Turdus leucomelas Vieillot, 1818, accounting for 43% of the total fruits consumed, being the former the most frequent in R. ferruginea. The birds involved removed fruits mainly by the picking technique, while hanging was the least employed, but for Vireo olivaceus (Vieillot, 1817) and D. lineatus. Aggressive interactions were minimal, being Mimus saturninus Hellmayr, 1903 the responsible for most interespecific encounters, in contrast to intraspecific actions dominated by T. amaurochalinus and T.leucomelas