Monte Carlo mass production for the ZEUS experiment on the Grid
The detector and collider upgrades for HERA-II have considerably increased the demand on computing resources for Monte Carlo production for the ZEUS experiment. In order to close the gap, the existing production system was extended to be able to use Grid resources as well. This integrated system has been successfully in production since November 2004. A total of 275 million events have been simulated by thirty different Grid sites within eight months exceeding the capacity of the old system. We present the production setup and introduce the toolkit that has been developed by ZEUS for efficient use of the existing Grid middleware.

title: Inclusive-jet photoproduction at HERA and determination of alpha(s)
abstract: Inclusive-jet cross sections have been measured in the reaction e p → e + jet + X for photon virtuality Q 2 1 GeV 2 and γp centre-of-mass energies in the region 142 W γ p 293 GeV with the ZEUS detector at HERA using an integrated luminosity of 300 pb − 1 . Jets were identified using the k T , anti- k T or SIScone jet algorithms in the laboratory frame. Single-differential cross sections are presented as functions of the jet transverse energy, E T jet , and pseudorapidity, η jet , for jets with E T jet > 17 GeV and − 1 η jet 2.5 . In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of E T jet in different regions of η jet . Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low E T jet and high η jet . The influence of non-perturbative effects not related to hadronisation was studied. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O ( α s 2 ) terms. Values of α s ( M Z ) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of α s ( M Z ) extracted from the measurements based on the k T jet algorithm is α s ( M Z ) = 0.1206 − 0.0022 + 0.0023 ( exp . ) − 0.0035 + 0.0042 ( th . ) ; the results from the anti- k T and SIScone algorithms are compatible with this value and have a similar precision.

title: Study of taupair production at HERA
abstract: A study of events containing two tau leptons with high transverse momentum has been performed with the ZEUS detector at HERA, using a data sample corresponding to an integrated luminosity of 0.33 fb−1. The tau candidates were identified from their decays into electrons, muons or hadronic jets. The number of tau-pair candidates has been compared with the prediction from the Standard Model, where the largest contribution is expected from Bethe-Heitler processes. The total visible cross section was extracted. Standard Model expectations agree well with the measured distributions, also at high invariant mass of the tau pair.

title: HERA signature-based searches I: events with isolated leptons and missing transverse momentum at HERA
abstract: Recent results of searches for events containing isolated leptons and missing transverse momentum at HERA are presented. Searches in this final state have yielded notable excesses over Standard Model expectations in the past. Searches for isolated leptons in channels corresponding to all three generations of leptons over the full HERA running period are now available. The combined H1+ZEUS results for searches for electrons and muons are compatible with the Standard Model.

title: Exclusive electroproduction of two pions at HERA
abstract: The exclusive electroproduction of two pions in the mass range 0.4<Mππ<2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb−1. The analysis was carried out in the kinematic range of 2<Q2<80 GeV2, 32<W<180 GeV and |t|<0.6 GeV2, where Q2 is the photon virtuality, W is the photon-proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, |F(Mππ)|, assuming that the studied mass range includes the contributions of the ρ, ρ′ and ρ′′ vector-meson states. The masses and widths of the resonances were obtained and the Q2 dependence of the cross-section ratios σ(ρ′→ππ)/σ(ρ) and σ(ρ′′→ππ)/σ(ρ) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e+e−→π+π−.

title: Triggering on Long-Lived Neutral Particles in the ATLAS Detector
abstract: Neutral particles with long decay paths that decay to many-particle final states represent, from an experimental point of view, a challenge both for the trigger and for the reconstruction capabilities of the ATLAS apparatus. The Hidden Valley scenario serves as an excellent setting for the purpose of exploring the challenges to the trigger posed by long-lived particles.

title: On the Bel radiative gravitational fields
abstract: We analyze the concept of intrinsic radiative gravitational fields defined by Bel and we show that the three radiative types, N, III and II, correspond with the three following different physical situations: pure radiation, asymptotic pure radiation and generic (non-pure, non-asymptotic pure) radiation. We introduce the concept of observer at rest with respect to the gravitational field and that of proper super-energy of the gravitational field and we show that, for non-radiative fields, the minimum value of the relative super-energy density is the proper super-energy density, which is acquired by the observers at rest with respect to the field. Several super-energy inequalities are also examined.

title: Rainich theory for type D aligned Einstein–Maxwell solutions
abstract: The original Rainich theory for the non-null Einstein–Maxwell solutions consists of a set of algebraic conditions and the Rainich (differential) equation. We show here that the subclass of type D aligned solutions can be characterized just by algebraic restrictions.

title: Positioning with stationary emitters in a two-dimensional space-time
abstract: The basic elements of the relativistic positioning systems in a two-dimensional space-time have been introduced in a previous work  where geodesic positioning systems, constituted by two geodesic emitters, have been considered in a flat space-time. Here, we want to show in what precise senses positioning systems allow to make relativistic gravimetry. For this purpose, we consider stationary positioning systems, constituted by two uniformly accelerated emitters separated by a constant distance, in two different situations: absence of gravitational field (Minkowski plane) and presence of a gravitational mass (Schwarzschild plane). The physical coordinate system constituted by the electromagnetic signals broadcasting the proper time of the emitters are the so called emission coordinates, and we show that, in such emission coordinates, the trajectories of the emitters in both situations, the absence and presence of a gravitational field, are identical. The interesting point is that, in spite of this fact, particular additional information on the system or on the user allows us not only to distinguish both space-times, but also to complete the dynamical description of emitters and user and even to measure the mass of the gravitational field. The precise information under which these dynamical and gravimetricmore » results may be obtained is carefully pointed out.« less

title: Positioning systems in Minkowski space-time: Bifurcation problem and observational data
abstract: In the framework of relativistic positioning systems in Minkowski space-time, the determination of the inertial coordinates of a user involves the {\em bifurcation problem} (which is the indeterminate location of a pair of different events receiving the same emission coordinates). To solve it, in addition to the user emission coordinates and the emitter positions in inertial coordinates, it may happen that the user needs to know {\em independently} the orientation of its emission coordinates. Assuming that the user may observe the relative positions of the four emitters on its celestial sphere, an observational rule to determine this orientation is presented. The bifurcation problem is thus solved by applying this observational rule, and consequently, {\em all} of the parameters in the general expression of the coordinate transformation from emission coordinates to inertial ones may be computed from the data received by the user of the relativistic positioning system.

title: On the classification of type D space–times
abstract: We give a classification of the type D space–times based on the invariant differential properties of the Weyl principal structure. Our classification is established using tensorial invariants of the Weyl tensor and, consequently, besides its intrinsic nature, it is valid for the whole set of the type D metrics and it applies on both, vacuum and nonvacuum solutions. We consider the Cotton-zero type D metrics and we study the classes that are compatible with this condition. The subfamily of space–times with constant argument of the Weyl eigenvalue is analyzed in more detail by offering a canonical expression for the metric tensor and by giving a generalization of some results about the nonexistence of purely magnetic solutions. The usefulness of these results is illustrated in characterizing and classifying a family of Einstein–Maxwell solutions. Our approach permits us to give intrinsic and explicit conditions that label every metric, obtaining in this way an operational algorithm to detect them. In partic...