25,268 research outputs found

    Star formation in galaxies hosting Active Galactic Nuclei up to z~1

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    We review recent evidence for a clear association between accretion onto supermassive black holes and star formation up to z~1 in the zCOSMOS survey. Star formation rates (SFRs) are determined from the [OII] emission-line strength and a correction for the AGN contribution. We find that SFRs of X-ray selected AGN span a distribution of 1-100 solar masses per year and evolve in a manner that is indistinguishable from that of massive, star-forming galaxies. The close relationship between AGN activity and star formation is further supported by an increase in the AGN fraction with bluer rest-frame colors (U-V); we further illustrate how the location of AGNs in a color-magnitude diagram can be misleading in luminosity-limited samples due to the dependence of AGN activity on the stellar mass and the low mass-to-light ratios of blue cloud galaxies. To conclude, our results support a co-evolutionary scenario up to z~1 based on the constancy with redshift of the ratio between mass accretion rate and SFR.Comment: Invited talk, to appear in the Proceedings of "AGN Feedback in Galaxy Formation", V.Antonuccio-Delogu and J. Silk, eds., in pres

    Measurement of Orbitally Excited D-Mesons at CDF II

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    Measurement of Orbitally Excited D-Mesons at CDF II Igor V. Gorelov (For the CDF Collaboration) Talk given on behalf of the CDF Collaboration at the First Meeting of the APS Topical Group on Hadronic Physics, GHP 2004, 24-26 October 2004, FERMILAB. Results on the first measurement of orbitally excited neutral D-meson states, D*_2 and D_1, produced in hadron collisions at Tevatron are presented. Using data from the displaced track trigger, CDF II collects the largest world sample of these states in decay modes D*+ pi-, D+ pi-. Masses and widths of both states have been measured with precision better than or comparable to the world average.Comment: 6 pages, 5 figures, talk given on behalf of the CDF Collaboration at the First Meeting of the APS Topical Group on Hadronic Physics, GHP 2004, Oct 24-26,2004, Fermilab, Batavia, Illinoi

    Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHIC

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    Thermal photon production at mid-rapidity in Au+Au reactions at sNN\sqrt{s_{NN}} = 200 GeV is studied in the framework of a 2D+1 hydrodynamical model that describes efficiently the bulk identified hadron spectra at RHIC. The combined thermal plus NLO pQCD photon spectrum is in good agreement with the yields measured by the PHENIX experiment for all Au+Au centralities. Within our model, we demonstrate that the correlation of the thermal photon slopes with the charged hadron multiplicity in each centrality bin provides direct empirical information on the underlying degrees of freedom and on the equation of state, s(T)/T3s(T)/T^3, of the strongly interacting matter.Comment: Version to appear in EPJ-C (extended discussion and refs. and a few corrections

    Remarks Concerning the Study of Four-Jet Events from Hadronic Decays of the Z0

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    The angular correlations of four-jet events from hadronic decays of the Z0 have been studied in the past mainly to extract from them the fundamental constants of quantum chromodynamics called colour factors. Previous studies have used all the available phase-space in order to maximize statistics. In this note we want to point out the possibility that significant differences between experiment and theory in restricted regions of phase-space might have escaped detection. Such differences could be a harbinger of the existence of new particles. Some preliminary results are presented.Comment: 9 pages, 3 figure

    The neutrino velocity anomaly as an explanation of the missing observation of neutrinos in coincidence with GRB

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    The search for neutrinos emitted in coincidence with Gamma-Bay Burst has been so far unsuccessfully. In this paper we show that the recent result reported by the OPERA Collaboration on an early arrival time of muon neutrinos with respect to the one computed assuming the speed of light in vacuum could explain the null search for neutrinos in coincidence with Gamma-Ray Burst

    Baryon Number Transfer in Hadron+Nucleus and Nucleus+Nucleus Collisions: A Link between Elementary and Complex Interactions

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    The baryon number transfer is studied in elementary and complex hadronic interactions at the CERN experiment NA49 at the SPS, at 158 AGeV beam energy (\sqrt{s}=17.2 GeV). A two component picture is proposed, which builds up the net proton distribution from a target and a projectile component. Using pion beam, the projectile component is experimentally determined for p+p and p+A interactions. A similar stopping behaviour of the projectile component is found for p+A and A+A interactions. Based on these observations, the baryon transfer is assumed to provide a common scale of inelasticity in p+p, p+A and A+A interactions. A model-independent way is proposed to predict the pion multiplicity in A+A.Comment: 10 pages, 12 figures. To appear in the proceedings of International Workshop on Quark and Hadron Dynamics in Relativistic Heavy Ion Collisions (BP 2002), Budapest, Hungary, 3-7 Mar 200

    Measurement of the B0 and B- meson lifetimes in ALEPH

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    The lifetimed of the Bbar0 and B- meson lifetimes are measured using data recorded on the Z peak with the ALEPH detector at LEP. An improved analysis based on partially reconstructed Bbar0 -> D*+l-nubar and B- -> D0l-nubar decays is presented.Comment: 3 pages, 1 figur
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