Top quark pair production in association with a jet at NLO accuracy with parton showering

6,220

5,572

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.

Section: Jhep07(2014)079mentioning

confidence: 99%

Section: Jhep07(2014)079mentioning

confidence: 99%

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

Alwall

Frederix

Frixione

et al. 2014

6,220

5,572

“…The systematic uncertainties are 20% for charge flips, and 50% for both fake and rare SM backgrounds. The next-to-leading order ttW and ttZ production cross sections used to normalize the MC predictions are 232 fb [23] and 208 fb [24,25], respectively.…”

Section: Jhep03(2013)037mentioning

confidence: 99%

Search for new physics in events with same-sign dileptons and b jets in pp collisions at $ \sqrt{s}=8 $ TeV

Chatrchyan

Khachatryan

Sirunyan

et al. 2013

A search for new physics is performed using events with isolated same-sign leptons and at least two bottom-quark jets in the final state. Results are based on a sample of proton-proton collisions collected at a center-of-mass energy of 8 TeV with the CMS detector and corresponding to an integrated luminosity of 10.5 fb −1 . No excess above the standard model background is observed. Upper limits are set on the number of events from non-standard-model sources and are used to constrain a number of new physics models. Information on acceptance and efficiencies is also provided so that the results can be used to confront an even broader class of new physics models.

“…A conservative systematic uncertainty of 50% is assigned to the total number of background events from simulation, since these are rare SM processes which have yet to be observed. The production cross sections used to normalize the dominant tt W and tt Z contributions are 0.16 pb [28] and 0.14 pb [29,30], respectively. In the baseline sample the simulated rare SM backgrounds are determined to contribute 0.9 ± 0.5, 1.1 ± 0.6, and 2.0 ± 1.0 events in the ee, µµ, and eµ final states, respectively.…”

Section: Background Estimationmentioning

confidence: 99%

Search for new physics in events with same-sign dileptons and b-tagged jets in pp collisions at $ \sqrt {s} = 7 $ TeV

Chatrchyan

Khachatryan

Sirunyan

et al. 2012

A search for new physics is performed using isolated same-sign dileptons with at least two b-quark jets in the final state. Results are based on a 4.98 fb −1 sample of protonproton collisions at a centre-of-mass energy of 7 TeV collected by the CMS detector. No excess above the standard model background is observed. Upper limits at 95% confidence level are set on the number of events from non-standard-model sources. These limits are used to set constraints on a number of new physics models. Information on acceptance and efficiencies are also provided so that the results can be used to confront additional models in an approximate way.