[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

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

FeynRules 2.0 - A complete toolbox for tree-level phenomenology

Theory and phenomenology of two-Higgs-doublet models

We present NNPDF3.0, the first set of parton distribution functions (PDFs) determined with a methodology validated by a closure test. NNPDF3.0 uses a global dataset including HERA-II deep-inelastic inclusive cross-sections, the combined HERA charm data, jet production from ATLAS and CMS, vector boson rapidity and transverse momentum distributions from ATLAS, CMS and LHCb, W+c data from CMS and top quark pair production total cross sections from ATLAS and CMS. Results are based on LO, NLO and NNLO QCD theory and also include electroweak corrections. To validate our methodology, we show that PDFs determined from pseudo-data generated from a known underlying law correctly reproduce the statistical distributions expected on the basis of the assumed experimental uncertainties. This closure test ensures that our methodological uncertainties are negligible in comparison to the generic theoretical and experimental uncertainties of PDF determination. This enables us to determine with confidence PDFs at different perturbative orders and using a variety of experimental datasets ranging from HERA-only up to a global set including the latest LHC results, all using precisely the same validated methodology. We explore some of the phenomenological implications of our results for the upcoming 13 TeV Run of the LHC, in particular for Higgs production cross-sections.

/pdf/parton-distributions-for-the-lhc-run-ii-3k5n4fqkie.pdf

Parton distributions for the LHC Run II

We compute the next-to-next-to-leading order (NNLO) quantum chromodynamics (QCD) correction to the total cross section for the reaction $gg\ensuremath{\rightarrow}t\overline{t}+X$. Together with the partonic channels we computed previously, the result derived in this Letter completes the set of NNLO QCD corrections to the total top pair-production cross section at hadron colliders. Supplementing the fixed order results with soft-gluon resummation with next-to-next-to-leading logarithmic accuracy, we estimate that the theoretical uncertainty of this observable due to unknown higher order corrections is about 3% at the LHC and 2.2% at the Tevatron. We observe a good agreement between the standard model predictions and the available experimental measurements. The very high theoretical precision of this observable allows a new level of scrutiny in parton distribution functions and new physics searches.

/pdf/total-top-quark-pair-production-cross-section-at-hadron-4ckugwhsqk.pdf

Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through O ( α S 4 )

Top++: a program for the calculation of the top-pair cross-section at hadron colliders

Top-pair production at hadron colliders with next-to-next-to-leading logarithmic soft-gluon resummation

We compute the next-to-next-to-leading order QCD correction to the total inclusive top pair production cross-section in the reaction $ qg\to t\overline{t}+X $
 . We find moderate $ \mathcal{O} $
 (1%) correction to central values at both Tevatron and LHC. The scale variation of the cross-section remains unchanged at the Tevatron and is significantly reduced at the LHC. We find that recently introduced approximation based on the high-energy limit of the top pair cross-section significantly deviates from the exact result. The results derived in the present work are included in version 1.4 of the program Top++. Work towards computing the reaction $ gg\to t\overline{t}+X $
 is ongoing.

/pdf/nnlo-corrections-to-top-pair-production-at-hadron-colliders-3ztw3dhgv9.pdf

NNLO corrections to top pair production at hadron colliders: the quark-gluon reaction

This is a second paper in our ongoing calculation of the next-to-next-to-leading order (NNLO) QCD correction to the total inclusive top-pair production cross-section at hadron colliders. In this paper we calculate the reaction $ q\overline{q}\to t\overline{t}+q\overline{q} $
 which was not considered in our previous work on $ q\overline{q}\to t\overline{t}+X $
 [1] due to its phenomenologically negligible size. We also calculate all remaining fermion-pair-initiated partonic channels $ q{q^{\prime }} $
 , $ q{{\overline{q}}^{\prime }} $
 and qq that contribute to top-pair production starting from NNLO. The contributions of these reactions to the total cross-section for top-pair production at the Tevatron and LHC are small, at the permil level. The most interesting feature of these reactions is their characteristic logarithmic rise in the high energy limit. We compute the constant term in the leading power behavior in this limit, and achieve precision that is an order of magnitude better than the precision of a recent theoretical prediction for this constant. All four partonic reactions computed in this paper are included in our numerical program Top++. The calculation of the NNLO corrections to the two remaining partonic reactions, $ qg\to t\overline{t}+X $
 and $ gg\to t\overline{t}+X $
 , is ongoing.

/pdf/nnlo-corrections-to-top-pair-production-at-hadron-colliders-th7dotip28.pdf

Michal Czakon

Papers

Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through O ( α S 4 )

Top++: a program for the calculation of the top-pair cross-section at hadron colliders

Top-pair production at hadron colliders with next-to-next-to-leading logarithmic soft-gluon resummation

NNLO corrections to top pair production at hadron colliders: the quark-gluon reaction

NNLO corrections to top-pair production at hadron colliders: the all-fermionic scattering channels