We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505±22(stat)-36+28(syst)] mb is found.
COBISS.SI-ID: 2468347
A thorough search of the sky exposed at the Pierre Auger Cosmic Ray Observatory reveals no statistically significant excess of events in any small solid angle that would be indicative of a flux of neutral particles from a discrete source. The search covers from –90° to +15° in declination using four different energy ranges above 1 EeV (1018 eV). The method used in this search is more sensitive to neutrons than to photons. The upper limit on a neutron flux is derived for a dense grid of directions for each of the four energy ranges. These results constrain scenarios for the production of ultrahigh energy cosmic rays in the Galaxy.
COBISS.SI-ID: 2611707
We report the first observations of the spin-singlet bottomonium states hb(1P) and hb(2P). The states are produced in the reaction e+e-→hb(nP)π+π- using a 121.4 fb-1 data sample collected at energies near the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We determine M[hb(1P)]=(9898.2-1.0-1.1+1.1+1.0) MeV/c2 and M[hb(2P)]=(10 259.8±0.6-1.0+1.4) MeV/c2, which correspond to P-wave hyperfine splittings ΔMHF=(+1.7±1.5) and (+0.5-1.2+1.6) MeV/c2, respectively. The significances of the hb(1P) and hb(2P) are 5.5σ and 11.2σ, respectively. We find that the production of the hb(1P) and hb(2P) is not suppressed relative to the production of the Υ(1S), Υ(2S), and Υ(3S).
COBISS.SI-ID: 25645351
We present predictions for the production cross section of a standard model Z0 boson in association with a t anti-t pair at the next-to-leading order accuracy in QCD, matched with shower Monte Carlo programs to evolve the system down to the hadronization energy scale. We adopt a framework based on three well-established numerical codes, namely, the powheg-box, used for computing the cross section, helac-nlo, which generates all necessary input matrix elements, and finally a parton shower program, such as pythia or herwig, which allows for including t-quark and Z0-boson decays at leading-order accuracy and generates shower emissions, hadronization and hadron decays.
COBISS.SI-ID: 2586619
We analyse two issues that arise in the context of (matrix) string theories in plane wave backgrounds, namely (1) the use of Brinkmann- versus Rosen-variables in the quantum theory for general plane waves (which we settle conclusively in favour of Brinkmann variables), and (2) the regularisation of the quantum dynamics for a certain class of singular plane waves (discussing the benefits and limitations of regularisations of the plane-wave metric itself).
COBISS.SI-ID: 2281467