Top-quark processes at NLO in production and decay

Campbell, John M.; Ellis, R. Keith

doi:10.48550/arxiv.1204.1513

Cited by 57 publications

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“…This has motivated tremendous activity on the theory side to match the experimental precision by computing higher order corrections in Quantum Chromodynamics (QCD) and we briefly recapitulate the status for inclusive t t-pair production, i.e., no additional jets or other tagged final states. Predictions for the total cross section are complete to next-to-next-to-leading order (NNLO) [6][7][8][9] while differential distributions are known to next-to-leading order (NLO) [10,11], including topquark decay [12,13], though. Additional corrections beyond NLO based on threshold logarithms have been obtained for distributions in the top-quark's transverse momentum and rapidity, p t T and y t , as well as in the invariant mass m t t of the top-quark pair [14,15].…”

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confidence: 99%

“…Using the relations presented here, we have computed the differential cross sections for t tproduction in terms of p t T , y t and m t t . We have used the program MCFM [32] for the NLO corrections [13,33] in the conventional pole mass m pole t scheme and a custom routine for the Born and mass derivative terms. The calculations were carried out using the ABM11 [25] and CT10 [30] PDFs at NLO.…”

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confidence: 99%

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Differential distributions for top-quark hadro-production with a running mass

Dowling

Moch

2014

Eur. Phys. J. C

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We take a look at how the differential distributions for top-quark production are affected by changing to the running mass scheme. Specifically we consider the transverse momentum, rapidity and pair-invariant mass distributions at next-to-leading order for the top-quark mass in the MS scheme. It is found that, similar to the total cross section, the perturbative expansion converges faster and the scale dependence improves using the mass in the MS scheme as opposed to the on-shell scheme. We also update the analysis for the total cross section using the now available full next-to-next-to-leading order contribution.The measurement of top-quark pair production cross sections at hadron colliders has entered the era of precision physics with the analysis of data available from the Large Hadron Collider (LHC) in the runs at center-of-mass energies √ S = 7 and 8 TeV. Measurements of the total cross section for tt-production from ATLAS and CMS reach by now an accuracy of typically better than O(10 %), with the systematic and luminosity uncertainties already dominating over the small statistical uncertainty, see, e.g., [1][2][3]. First results of differential distributions for tt-production from the LHC are appearing as well [4,5]. Thus, given the present experimental accuracy hadro-production of tt-pairs is currently being established as a standard model (SM) benchmark process.This has motivated tremendous activity on the theory side to match the experimental precision by computing higher order corrections in quantum chromodynamics (QCD) and we briefly recapitulate the status for inclusive tt-pair production, i.e., no tagged final states. Predictions for the total cross section are complete to next-to-next-to-leading order (NNLO) [6][7][8][9] while differential distributions are known to next-to-leading order (NLO) [10,11], including top-quark decay [12][13][14][15][16], though. Additional corrections beyond NLO based on threshold logarithms have been obtained for distria e-mail: matthew.dowling@desy.de butions in the top-quark's transverse momentum and rapidity, p t T and y t , as well as in the invariant mass m tt of the top-quark pair [17][18][19][20].Comparison of these theory predictions to experimental data can be used to determine parameters such as the strong coupling constant, the parton luminosity and the top-quark mass and to study their correlations. Of these parameters, the top-quark mass is certainly the most interesting one with prominent implications for the electro-weak vacuum of the SM, see, e.g., [21,22]. It is a particularly attractive feature of cross sections measurements that they offer the opportunity for an unambiguous and theoretically well-defined determination of the top-quark mass in a particular renormalization scheme [23,24].The conventional scheme choice for the quark mass renormalization is the pole mass, which has its short-comings [25,26], though, since it is based on the idea of quarks appearing as asymptotic states. It exhibits poor convergence of the perturbative series and ...

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confidence: 99%

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confidence: 99%

Differential distributions for top-quark hadro-production with a running mass

Dowling

Moch

2014

Eur. Phys. J. C

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“…We note that the jets have been clustered using the standard k t -algorithm with jet resolution parameter D jet = 0.7. The implementation of the factorizable corrections to production and decay subprocesses has been checked in the limit of on-shell top quarks against the di-lepton channel implementation in MCFM [63]. Very good agreement was found both for inclusive cross sections and for all distributions we have checked.…”

Section: Resultsmentioning

confidence: 86%

“…Results in the NWA, including the on-shell decay of the top-antitop pair to the physical final state W + W − b b, were given in Refs. [60][61][62][63]. The fully differential semi-leptonic decay of on-shell top quarks is also now known to NNLO [64,65].…”

Section: Top-antitop Production At Hadron Collidersmentioning

confidence: 99%

Finite-width effects in unstable-particle production at hadron colliders

Falgari

Papanastasiou

Signer

2013

J. High Energ. Phys.

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We present a general formalism for the calculation of finite-width contributions to the differential production cross sections of unstable particles at hadron colliders. In this formalism, which employs an effective-theory description of unstable-particle production and decay, the matrix element computation is organized as a gauge-invariant expansion in powers of Γ X /m X , with Γ X and m X the width and mass of the unstable particle. This framework allows for a systematic inclusion of off-shell and non-factorizable effects whilst at the same time keeping the computational effort minimal compared to a full calculation in the complex-mass scheme. As a proof-of-concept example, we give results for an NLO calculation of top-antitop production in the qq partonic channel. As already found in a similar calculation of single-top production, the finite-width effects are small for the total cross section, as expected from the naïve counting ∼ Γ t /m t ∼ 1%. However, they can be sizeable, in excess of 10%, close to edges of certain kinematical distributions. The dependence of the results on the mass renormalization scheme, and its implication for a precise extraction of the top-quark mass, is also discussed.

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“…The replacement above leads to an exact factorization of the matrix elements into terms describing the production and the decay of on-shell top quarks. This factorization can be combined with a strict expansion of Γ t in α s to yield results correct to O(α s ) [30,31]. Maintaining a finite width and subsequently relaxing the on-shell assumption in standard fixed-order perturbation theory entails the computation of much more than the resonant diagrams (i.e., those that feature an s-channel top-quark propagator) required in the NWA.…”

Section: Unstable Single-top Productionmentioning

confidence: 99%

Single-top t-channel production with off-shell and non-resonant effects

Papanastasiou¹,

Frederix²,

Frixione³

et al. 2013

Physics Letters B

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This letter details and discusses the next-to-leading order QCD corrections to t-channel electro-weak W + bj production, where finite top-width effects are consistently taken into account. The computation is done within the aMC@NLO framework and includes both resonant and non-resonant contributions as well as interferences between the two. Results are presented for the LHC and compared to those of the narrow-width approximation and effective theory approaches.It is of no surprise therefore that over the last three decades much effort has been invested in providing accurate predictions for single-top cross sections. Stable single-top production was first discussed at the leading order (LO) in [4]. Next-to-leading order (NLO) QCD corrections in the five-flavour (5F) scheme were first computed in [5] and in the four-flavour (4F) scheme in [6,7], whilst electroweak (EW) corrections were investigated in [8]. Furthermore, soft and collinear gluon resummation has been studied in [9,10,11,12] and stable single-top at NLO matched to parton showers has been achieved in [13,14,15] for both the 5F and 4F schemes. Incorporating the decay of the top quark, t → W + b, as part of the hard process matrix elements was accomplished via the narrow-width approximation (NWA) in [16,17,18], in which NLO corrections to both production and decay were included. Going beyond the NWA, a study of off-shell and non-resonant effects at LO was performed in [19] and final-state non-factorizable corrections in the s-channel were examined in [20]. In [21,22], effective theory (ET) techniques were employed to relax the assumption of an on-shell top quark in the amplitudes, allowing for a systematic study of finite top-width (Γ t ) effects in the resonant regions of phase space.The full computation of α s -corrections to EW W + bj production (i.e. the process that includes single-top production) has so far been missing in the literature. Given the opportunity for precision top physics provided by the LHC, it is of phenomenological interest to understand the effects of off-shell top quarks versus top quarks in the NWA. In this letter we present such a computation for the tchannel process in the 5F scheme, and make a direct comparison to results in the NWA as well as to those obtained by using the ET method. The s-channel and W t-production processes are not considered here.The expectation is that for inclusive observables off-shell effects are small [23,24,25] (i.e., parametrically of O(Γ t /m t )), whilst they should be noticeable in the case of less inclusive observables, such as the invariant or transverse masses of the reconstructed top. Indeed, differences between NWA and ET or off-shell calculations have already been highlighted for 5F scheme single-top [21,22] and top-pair [26,27,28,29] production. We shall confirm these findings here.This paper is organized as follows. In Sect. 2 we briefly discuss the NWA, ET, and off-shell approaches in view of their application to single-top production; results for total rates and for a few selected distri...

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Top-quark processes at NLO in production and decay

Cited by 57 publications

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Differential distributions for top-quark hadro-production with a running mass

Differential distributions for top-quark hadro-production with a running mass

Finite-width effects in unstable-particle production at hadron colliders

Single-top t-channel production with off-shell and non-resonant effects

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