Kirill Melnikov

Bio: Kirill Melnikov is an academic researcher from University of Hawaii. The author has contributed to research in topics: Quantum chromodynamics & Muon. The author has an hindex of 36, co-authored 74 publications receiving 6754 citations. Previous affiliations of Kirill Melnikov include Stanford University & University of Hawaii at Manoa.

High-precision QCD at hadron colliders: Electroweak gauge boson rapidity distributions at next-to-next-to leading order

Abstract: We compute the rapidity distributions of W and Z bosons produced at the Tevatron and the LHC through next-to-next-to leading order in QCD. Our results demonstrate remarkable stability with respect to variations of the factorization and renormalization scales for all values of rapidity accessible in current and future experiments. These processes are therefore ''gold-plated'': current theoretical knowledge yields QCD predictions accurate to better than one percent. These results strengthen the proposal to use $W$ and $Z$ production to determine parton-parton luminosities and constrain parton distribution functions at the LHC. For example, LHC data should easily be able to distinguish the central parton distribution fit obtained by MRST from that obtained by Alekhin.

Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment reexamined

Abstract: We discuss the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment ${a}_{\ensuremath{\mu}}^{\mathrm{l}\mathrm{b}\mathrm{l}}$, paying particular attention to the consistent matching between the short- and the long-distance behavior of the light-by-light scattering amplitude. We argue that short-distance QCD imposes strong constraints on this amplitude overlooked in previous analyses. We find that accounting for these constraints leads to approximately 50% increase in the central value of ${a}_{\ensuremath{\mu}}^{\mathrm{l}\mathrm{b}\mathrm{l}}$, compared to commonly accepted estimates (see, e.g., [M. Davier, S. Eidelman, A. Hocker, and Z. Zhang, Eur. Phys. J. C 31, 503 (2003).]). The hadronic light-by-light scattering contribution becomes ${a}_{\ensuremath{\mu}}^{\mathrm{l}\mathrm{b}\mathrm{l}}=136(25)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$, thereby shifting the standard model prediction closer to the experimental value.

Electroweak gauge boson production at hadron colliders through O(α s 2 )

Abstract: We describe a calculation of the O({alpha}{sub s}{sup 2}) QCD corrections to the fully differential cross section for W and Z boson production in hadronic collisions. The result is fully realistic in that it includes spin correlations, finite width effects, {gamma}-Z interference and allows for the application of arbitrary cuts on the leptonic decay products of the W and Z. We have implemented this calculation into a numerical program. We demonstrate the use of this code by presenting phenomenological results for several future LHC analyses and recent Tevatron measurements, including the W cross section in the forward rapidity region and the central over forward cross section ratio.

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.