Sven-Olaf Moch

Bio: Sven-Olaf Moch is an academic researcher from University of Hamburg. The author has contributed to research in topics: Quantum chromodynamics & Parton. The author has an hindex of 30, co-authored 111 publications receiving 4626 citations.

A facility to Search for Hidden Particles at the CERN SPS: the SHiP physics case

Abstract: This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (Search for Hidden Particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, $\tau\to 3\mu$ and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the Standard Model and describe interactions between new particles and four different portals - scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the Standard Model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation

Measuring the running top-quark mass

Abstract: We present the first direct determination of the running top-quark mass based on the total cross section of top-quark pair production as measured at the Tevatron Our theory prediction for the cross section includes various next-to-next-to-leading order QCD contributions, in particular, all logarithmically enhanced terms near threshold, the Coulomb corrections at two loops and all explicitly scale-dependent terms at next-to-next-to-leading order accuracy The result allows for an exact and independent variation of the renormalization and factorization scales For Tevatron and LHC we study its dependence on all scales, on the parton luminosity and on the top-quark mass using both the conventional pole mass definition as well as the running mass in the $\overline{\mathrm{MS}}$ scheme We extract for the top quark an $\overline{\mathrm{MS}}$ mass of $m(\ensuremath{\mu}=m)={1600}_{\ensuremath{-}32}^{+33}\text{ }\text{ }\mathrm{GeV}$, which corresponds to a pole mass of ${m}_{t}={1689}_{\ensuremath{-}34}^{+35}\text{ }\text{ }\mathrm{GeV}$

Higgs production via vector-boson fusion at NNLO in QCD

Abstract: We present the total cross sections at next-to-next-to-leading order in the strong coupling for Higgs boson production via weak-boson fusion. Our results are obtained via the structure function approach, which builds upon the approximate, though very accurate, factorization of the QCD corrections between the two quark lines. The theoretical uncertainty on the total cross sections at the LHC from higher order corrections and the parton distribution uncertainties are estimated at the 2% level each for a wide range of Higgs boson masses.

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

Abstract: We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5 aMC@NLO, capable of handling all these computations — parton-level fixed order, shower-matched, merged — in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV e + e − collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.

Parton distributions for the LHC

Abstract: We present updated leading-order, next-to-leading order and next-to-next-to-leading order parton distribution functions (“MSTW 2008”) determined from global analysis of hard-scattering data within the standard framework of leading-twist fixed-order collinear factorisation in the $\overline{\mathrm{MS}}$ scheme. These parton distributions supersede the previously available “MRST” sets and should be used for the first LHC data taking and for the associated theoretical calculations. New data sets fitted include CCFR/NuTeV dimuon cross sections, which constrain the strange-quark and -antiquark distributions, and Tevatron Run II data on inclusive jet production, the lepton charge asymmetry from W decays and the Z rapidity distribution. Uncertainties are propagated from the experimental errors on the fitted data points using a new dynamic procedure for each eigenvector of the covariance matrix. We discuss the major changes compared to previous MRST fits, briefly compare to parton distributions obtained by other fitting groups, and give predictions for the W and Z total cross sections at the Tevatron and LHC.