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[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

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.

/pdf/the-automated-computation-of-tree-level-and-next-to-leading-4etm0g6w46.pdf

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

The Pythia program can be used to generate high-energy-physics ''events'', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

/pdf/pythia-6-4-physics-and-manual-3dvwmijpnq.pdf

PYTHIA 6.4 Physics and Manual

We discuss finite-volume computations of two-body hadronic decays below the inelastic threshold (e.g. $K\to\pi\pi$ decays). The relation between finite-volume matrix elements and physical amplitudes, recently derived by Lellouch and L\"uscher, is extended to all elastic states under the inelastic threshold. We present a detailed comparison of our approach with that of Lellouch and L\"uscher and discuss the possible limitations of the method which could arise due to the presence of inelastic thresholds. We also examine a standard alternative method which can be used to extract the real part of the decay amplitude from correlators of the form $ $. We show that in this case there are finite-volume corrections which vanish as inverse powers of the volume, which cannot be removed by a multiplicative factor.

https://arxiv.org/pdf/hep-lat/0104006.pdf

$K \to \pi\pi$ Decays in a Finite Volume

A lattice computation of the decay constant of the B-meson

We describe the computation of the amplitude ${A}_{2}$ for a kaon to decay into two pions with isospin $I=2$. The results presented in [T. Blum et al., Phys. Rev. Lett. 108, 141601 (2012)] from an analysis of 63 gluon configurations are updated to 146 configurations giving $\mathrm{Re}{A}_{2}=1.381(46{)}_{\mathrm{stat}}(258{)}_{\mathrm{syst}}{10}^{\ensuremath{-}8}\text{ }\text{ }\mathrm{GeV}$ and $\mathrm{Im}{A}_{2}=\ensuremath{-}6.54(46{)}_{\mathrm{stat}}(120{)}_{\mathrm{syst}}{10}^{\ensuremath{-}13}\text{ }\text{ }\mathrm{GeV}$. $\mathrm{Re}{A}_{2}$ is in good agreement with the experimental result, whereas the value of $\mathrm{Im}{A}_{2}$ was hitherto unknown. We are also working toward a direct computation of the $K\ensuremath{\rightarrow}(\ensuremath{\pi}\ensuremath{\pi}{)}_{I=0}$ amplitude ${A}_{0}$ but, within the Standard Model, our result for $\mathrm{Im}{A}_{2}$ can be combined with the experimental results for $\mathrm{Re}{A}_{0}$, $\mathrm{Re}{A}_{2}$ and ${\ensuremath{\epsilon}}^{\ensuremath{'}}/\ensuremath{\epsilon}$ to give $\mathrm{Im}{A}_{0}/\mathrm{Re}{A}_{0}=\ensuremath{-}1.61(28)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Our result for $\mathrm{Im}{A}_{2}$ implies that the electroweak penguin (EWP) contribution to ${\ensuremath{\epsilon}}^{\ensuremath{'}}/\ensuremath{\epsilon}$ is $\mathrm{Re}({\ensuremath{\epsilon}}^{\ensuremath{'}}/\ensuremath{\epsilon}{)}_{\mathrm{EWP}}=\ensuremath{-}(6.25\ifmmode\pm\else\textpm\fi{}{0.44}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.19}_{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$.

Lattice determination of the K → ( π π ) I = 2 decay amplitude A 2

A lattice study of nucleon structure

We report on the first complete calculation of the K L - K S mass difference, Δ M K , using lattice QCD. The calculation is performed on a 2 + 1 flavor, domain wall fermion ensemble with a 330 MeV pion mass and a 575 MeV kaon mass. We use a quenched charm quark with a 949 MeV mass to implement Glashow-Iliopoulos-Maiani cancellation. For these heavier-than-physical particle masses, we obtain Δ M K = 3.19 ( 41 ) ( 96 ) × 10 - 12 MeV , quite similar to the experimental value. Here the first error is statistical, and the second is an estimate of the systematic discretization error. An interesting aspect of this calculation is the importance of the disconnected diagrams, a dramatic failure of the Okubo-Zweig-Iizuka rule.

/pdf/k-l-k-s-mass-difference-from-lattice-qcd-1nz95qx9y0.pdf

Christopher T. Sachrajda

Papers

$K \to \pi\pi$ Decays in a Finite Volume

A lattice computation of the decay constant of the B-meson

Lattice determination of the K → ( π π ) I = 2 decay amplitude A 2

A lattice study of nucleon structure

K L − K S mass difference from Lattice QCD