Parton distributions and the LHC: W and Z production

W and Z bosons will be produced copiously at the LHC proton-proton collider. We study the parton distribution dependence of the total production cross sections and rapidity distributions, paying particular attention to the uncertainties arising from uncertainties in the parton distributions themselves. Variations in the gluon, the strong coupling, the sea quarks and the overall normalisation are shown to lead to small but non-negligible variations in the cross section predictions. Ultimately, therefore, the measurement of these cross sections will provide a powerful cross check on our knowledge of parton distributions and their evolution. Received: 23 November 1999 / Published online: 6 April 2000     

W\gamma and Z\gamma production at hadron colliders

We present a general purpose Monte Carlo program for the calculation of any infrared safe observable in and production at hadron colliders at next-to-leading order in . We treat the leptonic decays of the W and Z-boson in the narrow-width approximation, but retain all spin information via decay angle correlations. The effect of anomalous triple gauge boson couplings is investigated and we give the analytical expressions for the corresponding amplitudes. Furthermore, we propose a way to study the effect of anomalous couplings without introducing the ambiguity of form factors. Received: 14 February 2000 / Published online: 18 May 2000     

Parton counting: physical and computational complexity of multi-jet production at hadron colliders

We present an enumeration of all possible amplitudes that contribute to an n-jet process in QCD. We estimate the number of amplitudes for large number of jets and determine the actual number of amplitudes to be calculated, which is smaller due to relabelling among (massless) quark flavours. Received: 15 June 2000 / Published online: 25 September 2000     

PHOTOS Monte Carlo: a precision tool for QED correctionsin Z and W decays

We present a discussion of the precision for the PHOTOS Monte Carlo algorithm, with improved implementation of QED interference and multiple-photon radiation. The main application of PHOTOS is the generation of QED radiative corrections in decays of any resonances, simulated by a "host" Monte Carlo generator. By careful comparisons automated with the help of the MC-TESTER tool specially tailored for that purpose, we found that the precision of the current version of PHOTOS is of 0.1% in the case of Z and W decays. In the general case, the precision of PHOTOS was also improved, but this will not be quantified here. Received: 7 June 2005, Revised: 5 August 2005, Published online: 21 October 2005 Z. Was: Supported in part by the EU grant MTKD-CT-2004-510126, in partnership with the CERN Physics department, and Polish State Committee for Scientific Research (KBN) grant 2 P03B 091 27 for the years 2004-2006     

Diphoton plus Z production at the ILC at \mathcal{O}(\alpha ^4)

In this paper, we consider a system of gravitating bodies in Kaluza–Klein models with toroidal compactification of the extra dimensions. To simulate the astrophysical objects (e.g., our Sun and pulsars) with energy density much greater than the pressure, we assume that these bodies are pressureless in the external space, i.e., the space we inhabit. At the same time, they may have nonzero parameters $\omega _{({\bar{\alpha }} -3)} \, ({\bar{\alpha }} =4,\ldots , D)$ in the equations of state in the extra dimensions. We construct the Lagrange function of this many-body system for any value of $\Sigma =\sum _{{\bar{\alpha }}} \omega _{({\bar{\alpha }} -3)}$ . Moreover, the gravitational tests (PPN parameters, perihelion and periastron advances) require a negligible deviation from the latent soliton value $\Sigma =-(D-3)/2$ . However, the presence of pressure/tension in the internal space results necessarily in the smearing of the gravitating masses over the internal space and in the absence of KK modes. This looks very unnatural from the point of view of quantum physics.     

Lepton-hadron correlations to\mathcal{O}(\alpha _s^2 ) in (2+1) jet production at electron-proton colliders

We present one-loop corrected results on the four parity-conserving structure functions that describe deep inelastic (2+1)-jet production at high energy electron-proton colliders.Supported in part by the BMFT, FRG under contract 06MZ760     

The three-adatom non-pairwise (“trio”) interaction,with implications for Monte Carlo simulations of O/W(110)

Ching et al.¹ found that three-adatom non-pairwise interactions, with a repulsive energy greater than a quarter the nearest pair attraction, can explain the pronounced asymmetries in the phase diagram of O/W(110). In the first explicit calculations of such short-range “trio” interactions, we find that electronic indirect interactions have strengths consistent with their parameters. In general the closest-spaced trios are stronger than all but the few shortest-range pair interactions which determine the adlayer symmetry. We further show that triad configurations with similar shorter legs should have comparable magnitude; when applied to O/W(110), this idea doubles the number of trios entering the equations of Ching et al.¹ and thus can halve the minimum required trio strength. Such trio interactions (as well as linear triad configurations) have a substantial quantitative effect on the pair interaction strengths extracted from Monte Carlo simulations.     

DFT and Monte Carlo study of the W(001) surface reconstruction

The driving force for the W(001) surface reconstruction and electronic structures of pristine and H-covered W(001) surfaces are studied by means of relativistic DFT calculations. The spin-orbit coupling leads to the splitting of the bands. Adsorbed physical monolayer of hydrogen due to forming adsorption bonds stabilizes the (1 × 1) structure of the H/W(001) surface. The performed calculations have not revealed any substantial nesting of Fermi surface, so do not support the Peierls-like charge-density-wave mechanism of the surface reconstruction. The total energy of the (√2 × √2)R45° W(001) surface structure is found to be lower, by 0.14 eV per atom, than for the (1 × 1 W(001). The dependence of the relative intensity of the characteristic LEED reflection on temperature, obtained with the help of Monte Carlo simulations using the interaction energies estimated from DFT calculations, is in good agreement with available experimental data, thus supporting the concept of the order-disorder type of the transition between the low-temperature ((√2 × √2)R45° and room-temperature (1 × 1) surface structures of W(001).     

Heavy-quarkonium creation and annihilation with O(alpha(3)(s)ln(alpha(s)) accuracy

We calculate the O(alpha(3)(s)ln(alpha(s)) contributions to the heavy-quarkonium production and annihilation rates. Our result sheds new light on the structure of the high-order perturbative corrections and opens a new perspective for a high-precision theoretical analysis. We also determine the three-loop anomalous dimensions of the nonrelativistic vector and pseudoscalar currents.     

W Boson production cross section at the Large Hadron cCllider with Omicron(alpha(2)(s)) corrections

We compute the Omicron(alpha(2)(s)) QCD corrections to the fully differential cross section pp --> WX --> lnuX, retaining all effects from spin correlations. The knowledge of these corrections makes it possible to calculate with high precision the boson production rate and acceptance at the CERN Large Hadron Collider (LHC), subject to realistic cuts on the lepton and missing energy distributions. For certain choices of cuts we find large corrections when going from next-to-leading order (NLO) to next-to-next-to-leading order in perturbation theory. These corrections are significantly larger than those obtained by parton-shower event generators merged with NLO calculations. Our result may be used to assess and significantly reduce the QCD uncertainties in the many studies of boson production planned at the LHC.     

Monte Carlo simulations with Symanzik's improved actions in the lattice O(3) non-linear σ-model

The scaling properties of the lattice O(3) non-linear σ-model are studied. The mass-gap, energy momentum dispersion, correlation functions are measured by numerical Monte Carlo methods. Symanzik's tree-level and one loop improved actions are compared to the standard (nearest neighbour) action.