Parton showers and matching uncertainties in top quark pair production with Herwig 7

We evaluate the theoretical uncertainties in next-to-leading order plus parton shower predictions for top quark pair production and decay in hadronic collisions. Our work is carried out using the Herwig 7 event generator and presents an in-depth study of variations in matching schemes with two systematically different shower algorithms, the traditional angular-ordered and alternative dipole shower. We also present all of the required extensions of the Herwig dipole shower algorithm to properly take into account quark mass effects, as well as its ability to perform top quark decays. The predictions are compared at parton level as well as to Large Hadron Collider data, including in the boosted regime. We find that the regions where predictions with a non-top-quark-specific tune differ drastically from data are plagued by large uncertainties which are consistent between our two shower and matching algorithms.

Harvester : an edge service harvesting heterogeneous resources for ATLAS

The Production and Distributed Analysis (PanDA) system has been successfully used in the ATLAS experiment as a data-driven workload management system. The PanDA system has proven to be capable of operating at the Large Hadron Collider data processing scale over the last decade including the Run 1 and Run 2 data taking periods. PanDA was originally designed to be weakly coupled with the WLCG processing resources. Lately the system is revealing the difficulties to optimally integrate and exploit new resource types such as HPC and preemptible cloud resources with instant spin-up, and new workflows such as the event service, because their intrinsic nature and requirements are quite different from that of traditional grid resources. Therefore, a new component, Harvester, has been developed to mediate the control and information flow between PanDA and the resources, in order to enable more intelligent workload management and dynamic resource provisioning based on detailed knowledge of resource capabilities and their real-time state. Harvester has been designed around a modular structure to separate core functions and resource specific plugins, simplifying the operation with heterogeneous resources and providing a uniform monitoring view. This paper will give an overview of the Harvester architecture, current status with various resources, and future plans.

Regge Phenomenology at LHC Energies

At high energies the Pomeron plays a crucial part in describing the soft interactions. In the light of LHC (Large Hadron Collider) data we perform a detailed analysis of proton-proton ([Formula: see text]) and antiproton-proton ([Formula: see text]) forward scattering data in order to determine the intercept and the slope of the soft Pomeron trajectory. This analysis is performed based on Regge theory using Born-level amplitudes. We investigate the role of the proton-Pomeron vertex form and of the nearest [Formula: see text]-channel singularity. We give predictions for the total cross section and the ratio of the real part to the imaginary part of the elastic amplitude in [Formula: see text] collisions at LHC and cosmic-ray energies.

IMPLICATIONS OF THE HIGGS DISCOVERY FOR GRAVITY AND COSMOLOGY

The discovery of the Higgs boson is one of the greatest discoveries in this century. The standard model is finally complete. Apart from its significance in particle physics, this discovery has profound implications for gravity and cosmology in particular. Many perturbative quantum gravity interactions involving scalars are not suppressed by powers of Planck mass. Since gravity couples anything with mass to anything with mass, then Higgs must be strongly coupled to any other fundamental scalar in nature, even if the gauge couplings are absent in the original Lagrangian. Since the Large Hadron Collider data indicate that the Higgs is very much standard model-like, there is very little room for nonstandard model processes, e.g. invisible decays. This severely complicates any model that involves light enough scalar that the Higgs can kinematically decay to. Most notably, these are the quintessence models, models including light axions, and light scalar dark matter models.

LHC DISCOVERIES UNFOLDED

With the LHC (Large Hadron Collider) data arriving soon, carrying discoveries, we discuss a strategy for synthesizing a set of early measurements illuminating the dark matter of the universe.