{"id":"5e901d44-7200-4eff-8187-81ca98a05474","arxiv_id":"1101.2672","paper_version":3,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"The PowHel framework delivers the first next-to-leading-order plus parton-shower predictions for top-antitop plus jet production, validated against independent fixed-order calculations and applied to Tevatron and LHC kinematics.","lead":"The authors combine three public particle-physics codes to produce the first simulation of a top-quark pair plus one jet at next-to-leading-order accuracy matched to parton showers, giving hadron-level predictions for the Tevatron and the LHC. The result matters because this final state is a major background for new-physics searches and a calibration channel for top-quark measurements.","discovery_kind":"new_method","skeptic_critique":{"model":"selfhosted/deepseek-v4.1-flash","headline":"The HERWIG-based hadron-level predictions carry an unquantified truncated-shower uncertainty; the PYTHIA/HERWIG agreement invoked to bound it is at the same 3% level as the negative-weight systematic and is not a valid proxy for the truncated-shower effect.","rationale":"The reader's weakest_assumption correctly identifies the truncated-shower omission in Section 2 as the load-bearing soft spot, and the paper is transparent about it. My refinement is that the empirical argument used to bound the effect is weaker than the reader's rationale implies: the PYTHIA/HERWIG agreement is not a direct test of the truncated-shower contribution because PYTHIA's pT-ordered shower does not need one, and the 3% level coincides with the negative-weight systematic. The [27] citation is published and supports smallness in a different process, so it is legitimate support but not a direct bound here. I also note that the reader's rationale slightly overstates the independence of the one-loop check: check (ii) compares HELAC-Oneloop to the PowHel interface that uses it, which is an internal consistency check, not an independent implementation. The external validation of the virtual comes instead from the total cross section and distributions agreeing with Dittmaier-Uwer-Weinzierl (1.78 vs 1.791 pb, Fig. 1), which is a genuine external check and keeps correctness risk low. The scale-uncertainty gap on the LHC predictions is acknowledged and deferred, and the r = 4.29 shape rescaling is disclosed. None of these overturns ACCEPT: the central claim survives through the PYTHIA-based predictions and the fixed-order validation, and the paper states its limitations where they arise. My concern sharpens the reader's but does not change the verdict, so UNCHANGED is the honest recommendation; a follow-up should quantify the truncated-shower effect directly rather than infer it from PYTHIA/HERWIG agreement.","tokens_in":12704,"tokens_out":5849,"duration_ms":110845,"concrete_test":"Run the same LHE events through a shower that does implement truncated showers (e.g. HERWIG++ with the appropriate POWHEG matching, or SHERPA) and compare the LHC ttbar+jet observables of Figs. 4-7 (leading jet pT, antilepton rapidity, H_perp) to HERWIG 6.5.20. If the difference exceeds the quoted 3% and the statistical uncertainty, the truncated-shower effect is not negligible and the HERWIG-based predictions need a stated uncertainty; if it stays within 3%, the concern does not land.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is NLO-accurate hadron-level predictions for ttbar+jet. For POWHEG, formal NLO accuracy of the hardest emission requires both (i) a veto on shower emissions harder than the POWHEG emission and (ii) a truncated shower to populate wide-angle soft emission before the first emission. Section 2 states that HERWIG 6.5.20 driven by external LHE files has no truncated shower, so (ii) is absent from the HERWIG predictions. The authors argue the effect is small by citing Ref. [27] and by finding PYTHIA and HERWIG agree within 3%. Neither argument closes the gap. Ref. [27] is a study for a different process, so its smallness does not automatically transfer to ttbar+jet at the LHC. More importantly, the PYTHIA/HERWIG agreement is not a valid test of the truncated-shower contribution: PYTHIA's default pT-ordered shower does not require a truncated shower in the first place, so agreement between the two codes can reflect cancellation of different approximations rather than smallness of the missing piece. The paper then uses that same agreement in Section 6 to argue the LHC predictions are 'insensitive to the version of the parton shower' and that 'the effect of the missing truncated shower must be small' (Figs. 4-7). That inference is not established. The concern is not that the calculation is wrong; it is that the HERWIG-based hadron-level shapes carry an unquantified modeling uncertainty that the paper's own robustness argument does not bound. The 3% agreement is also the same size as the disclosed negative-weight effect (146.9 vs 143.2 vs 147 fb), so it sits at the level of known systematics rather than providing a precise validation.","agreement_with_reader":"agree"},"referee_report":{"model":"selfhosted/deepseek-v4.1-flash","summary":"The manuscript reports an NLO+parton-shower calculation of t tbar + jet production at hadron colliders, implemented by interfacing the POWHEG BOX with the HELAC family of codes (HELAC-Dipoles for the Born and real-emission helicity amplitudes and colour correlations, HELAC-Oneloop for the one-loop virtual corrections). The authors describe the input required by the POWHEG BOX for this 2→3 process, the treatment of the technical cut on the Born-level massless parton (and the alternative Born-suppression), and a set of validation checks: the LO cross section against MadGraph, the virtual amplitudes against an independent implementation, the soft and collinear limits of the real-emission matrix elements, and the independence of the NLO cross section from the technical cut (Table 3). The fixed-order NLO result, 1.78±0.01 pb, is compared with the Dittmaier–Uwer–Weinzierl value of 1.791±0.001 pb, and jet pT and rapidity distributions are compared with that work in Fig. 1. Hadron-level predictions are then presented for the Tevatron at 1.96 TeV in the semileptonic channel, with PYTHIA and HERWIG showers and with a decay-only sample, compared against the narrow-width NLO result of Melnikov and Schulze (Figs. 2–3), and for the LHC at 7 TeV in the dileptonic channel (Figs. 4–7), including a comparison of two scale choices.","tokens_in":12983,"tokens_out":6393,"duration_ms":121448,"significance":"If the results hold, this is a useful and non-trivial step: a semi-automatic NLO+PS generator for a genuine 2→3 process, with the one-loop amplitudes obtained from a general numerical unitarity method rather than a process-specific analytic calculation. The validation strategy is the right one and is carried out against independent published fixed-order results rather than only against the authors' own tooling, and the technical-cut independence study in Table 3 is exactly the check this kind of POWHEG implementation needs. The hadron-level event samples are of direct use for LHC top-quark analyses, and the observation that the H⊥ distribution softens substantially under the full shower is a concrete, falsifiable statement. The paper is also candid about what it does not do: the absence of a truncated shower in the HERWIG configuration and the absence of spin correlations in the decays are both stated explicitly in the text, which is to the authors' credit.","major_comments":[{"comment":"The sentence in §6 that the agreement between PYTHIA and HERWIG 'shows that the effect of the missing truncated shower must be small' is not supported by the evidence offered. PYTHIA's default pT-ordered shower does not require a truncated shower in the first place, so agreement between the two codes is consistent with two different approximations coinciding rather than with the missing wide-angle soft contribution being small; the comparison therefore does not bound the quantity it is invoked to bound. The same 3% figure is quoted in §5 as the size of the effect of including versus neglecting negative-weight events, so the PYTHIA/HERWIG comparison has a systematic floor at the level of the effect being bounded. Since this inference is what licenses the claim that the LHC predictions are insensitive to the shower version, it should either be reworded as 'consistent with being small' with the truncated-shower contribution flagged as an unquantified modelling uncertainty for the HERWIG-based shapes, or supported by a direct estimate (for example a variation of the veto/ordering treatment, or an independent estimate of the wide-angle soft-emission contribution).","section":"§6, Figs. 4–7","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The hadron-level predictions contain no spin correlations, because the top decays are performed in the shower at LO. The authors acknowledge this and use the decay-level comparison in Figs. 2–3 to argue that spin correlations make the NLO lepton rapidity distribution slightly wider. However, the observable in this paper most sensitive to spin correlations in the dileptonic channel is the lepton-pair invariant mass of Fig. 7, and no such comparison is shown for it, even though the two samples needed (NLO+decay, which carries spin correlations, and PowHel+decay, which does not) are already in hand. Either show the NLO+decay versus PowHel+decay ratio for m(l+l-) and for a lepton angular observable, or state explicitly in §6 that Fig. 7 and lepton angular distributions should not be interpreted at NLO accuracy for this reason.","section":"§5, Figs. 2–3 and §6, Fig. 7","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The veto on events containing an additional charged lepton with transverse momentum above 20 GeV is applied to the showered samples but is necessarily vacuous at fixed order, where no such leptons exist. This makes the comparison in Figs. 2–3 asymmetric: the SMC samples lose events that the NLO+decay sample retains, so part of the difference attributed to the shower may come from the selection rather than from showering. Please report the fraction of events removed by this veto and show, at least for one distribution, the comparison with the veto removed from the SMC side (or with an equivalent requirement imposed on the decay-level sample).","section":"§5, selection cut (x)","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The validation of the fixed-order result rests on agreement at the 1% level with Ref. [31], but the only uncertainty quoted anywhere for the fixed-order cross section is the integration error (1.78±0.01 pb against 1.791±0.001 pb). Without at least a rough scale-variation estimate, the reader cannot tell whether the agreement is meaningful at that precision or whether both numbers sit inside a common 5–10% theory uncertainty. The paper defers a scale study to a separate publication, which is reasonable for the LHC spectra, but a single number for the Tevatron setup of Ref. [31] would materially strengthen the validation claim and should be added.","section":"§3 and §4","authors_acknowledge":null,"authors_acknowledge_p":null}],"minor_comments":[{"comment":"The statement that the LO cross section agrees 'completely' with MadGraph should be accompanied by the two numbers and their integration errors.","section":"§3","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"It is not stated which of the two treatments of the underlying Born configuration (the technical cut or the Born-suppression factor) was used to produce the results in §5 and §6, nor what value of the technical cut was adopted there. Please state this explicitly for each set of predictions.","section":"§3","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The entries 'q qbar → t tbar g g' and 'qbar q → t tbar g g' appear to denote the same flavour structure, as do several other pairs in the table. Please clarify the organizing principle of the columns and check the table for repeated entries.","section":"Table 2","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The text notes that the jet rapidity distribution from the LHE events is more central than the NLO one. This is a visible discrepancy in a validation figure and deserves a sentence of interpretation, including whether it is expected from the absence of radiation beyond the first emission and whether it propagates to the hadron-level predictions.","section":"Fig. 1","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The label 'NLO+Decay' denotes the Ref. [32] result rescaled by r = 4.29. This should be stated in the figure captions, not only in the body text, since the figures are likely to be read on their own.","section":"Figs. 2 and 3","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The negative-weight events are reported only through their effect on the total cross section. Please give the fraction of negative-weight events in the sample and state whether their inclusion affects the shapes in Figs. 2–3 at the same 3% level.","section":"§5","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The statement that the jet pT spectra are 'rather robust against the choice of the default scale (2–6% variation, not shown here)' would be more useful with the variation shown for at least one distribution, given that the scale choice is one of the two main theory inputs of the LHC predictions.","section":"§6","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"Reference [1] is listed as arXiv:803.4180, which should read arXiv:0803.4180.","section":"References","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"'Rapdity' should be 'Rapidity' in the Fig. 5 caption.","section":"Figs. 5 and 6 captions","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The sentence 'We use the polarization vectors to project the helicity amplitudes to Lorentz basis for writing the spin-correlated squared matrix elements' is difficult to parse; please rephrase so that the role of the Lorentz basis in the spin-correlated matrix elements is clear.","section":"§2","authors_acknowledge":null,"authors_acknowledge_p":null},{"comment":"The sentence 'the effect of the truncated showers is absent from our predictions' should read 'the effect of the truncated shower is absent'; the plural is used inconsistently with the preceding sentence.","section":"§2","authors_acknowledge":null,"authors_acknowledge_p":null}],"recommendation":"minor_revision","confidential_remarks":"The paper is a letter that defers two things a reader will want: scale uncertainties and spin correlations. Both deferrals are stated, and the fixed-order validation against Refs. [30, 31] is genuine, so I do not regard the central claim as at risk. The one place where the text overreaches is the inference in §6 that PYTHIA/HERWIG agreement bounds the missing truncated-shower contribution; that sentence should be softened. The authors also note at the end a concurrent work by Alioli, Moch and Uwer; the novelty claim is appropriately worded given that disclosure."},"author_rebuttal":null,"desk_editor":{"model":"selfhosted/deepseek-v4.1-flash","letter":"Worth your time, with one caveat about how far the HERWIG numbers can be pushed. What's new: this is the first NLO+PS treatment of a 2-to-3 process, ttbar+jet, with the matching done semi-automatically through POWHEG-BOX fed by HELAC amplitudes. The fixed-order NLO result itself is not new (Dittmaier-Uwer-Weinzierl, Melnikov-Schulze); what is new is the hadron-level event sample and the automated amplitude pipeline behind it. The checks are the right ones and they are done properly: LO against MadGraph, the one-loop amplitudes cross-checked against an independent implementation, soft and collinear limits of the real matrix elements, and the technical-cut independence scan in Table 3. The NLO cross section, 1.78 plus or minus 0.01 pb, lands on the DUW value. That is external validation, not self-validation, and it counts. Soft spots, in order of how much they matter. The truncated shower: Section 2 says plainly that HERWIG 6.5.20 driven by external LHE files has no truncated shower, so it is absent from the HERWIG predictions. Fine, they disclose it. But then Section 6 uses PYTHIA/HERWIG agreement to argue that the effect of the missing truncated shower must be small. That inference does not hold. PYTHIA's pT-ordered shower does not need a truncated shower in the first place, so agreement between the two codes does not bound the missing piece; it can just as easily reflect two different approximations landing in the same place. The 3 percent agreement is also the same size as the negative-weight systematic they quote (146.9 versus 143.2 versus 147 fb), so it sits at the level of known systematics rather than acting as a precision test. The HERWIG shapes carry an unquantified modeling uncertainty. That does not break the central claim, but the robustness sentence should be softened. Second: scale dependence on the LHC predictions is quoted as 2 to 6 percent and deferred to a follow-up. For a paper whose selling point is hadron-level predictions, that is the number experimenters will want. Third, minor: decays are LO and spin correlations are dropped, which they say. Who should read it: anyone using ttbar+jet as a background or measuring top properties at 7 TeV, and anyone building NLO+PS for higher multiplicity. Send it out.","headline":"A solid, properly cross-checked first NLO+PS treatment of ttbar+jet; the one real soft spot is that the PYTHIA/HERWIG agreement is used to bound a truncated-shower effect it cannot actually bound.","tokens_in":13756,"tokens_out":1551,"would_cite":true,"duration_ms":30115,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"pith_extraction":{"msc":[],"pacs":["12.38.-t","13.87.-a","14.65.Ha"],"model":"selfhosted/deepseek-v4.1-flash","headline":"The authors compute top–antitop pair production in association with a jet at next-to-leading-order accuracy matched to parton showers, producing hadron-level events whose fixed-order limit reproduces an independent NLO calculation.","keywords":["top quark pair production","jet production","next-to-leading order QCD","parton shower matching","POWHEG","hadronization","LHC phenomenology","Tevatron"],"falsifier":"Implement a truncated shower for the angular-ordered program when reading external event files, or compare against an independent matched calculation with a different matching prescription, and check whether the hadron-level distributions — particularly the antilepton rapidity and the scalar sum of transverse momenta — move by more than the quoted 3 percent spread between the two showers.","tokens_in":13982,"feed_emoji":"⚛️","tokens_out":2624,"duration_ms":40342,"temperature":0.7,"pith_summary":"This paper reports the first matched next-to-leading-order plus parton-shower calculation of a three-body final state at a hadron collider: a top–antitop pair recoiling against a hard jet. The physics motivation is that at LHC energies top pairs with large transverse momentum are copious, so the probability that they radiate an extra hard gluon is high enough that the $tbar{t}+$jet final state is measurable with high statistics and needs a prediction that can be compared directly to detector data. The authors assemble the calculation from existing general-purpose pieces — a framework that organizes the NLO subtraction and generates positive-weight events with the hardest emission ordered in transverse momentum, a numerical amplitude library that supplies the tree-level, colour-correlated, spin-correlated and one-loop ingredients, and a standard shower and hadronization program — so that the whole chain runs semi-automatically. The claim that matters is validation: the fixed-order cross section agrees with an independent published NLO result, the distributions agree except in jet rapidity, and two different shower programs give hadron-level predictions that agree within about 3 percent. If that holds, the community gains a working, reusable route to NLO-accurate hadron-level predictions for processes with one more hard object than the two-body cases that were already standard.","feed_headline":"Top pairs plus a jet now come with full showering","feed_subtitle":"A three-body final state gets NLO accuracy matched to parton showers; two shower programs agree within 3 percent.","key_machinery":"The load-bearing construction is the combination of a NLO event generator built on the FKS subtraction scheme, which produces positive-weight events in which the hardest emission is the first one and is ordered in transverse momentum, with a numerical amplitude framework that supplies all the required ingredients on demand: Born and real-emission helicity amplitudes, colour-correlated squared matrix elements, spin-correlated squared matrix elements obtained by projecting helicity amplitudes onto a Lorentz basis with polarization vectors, and one-loop corrections from a unitary-based numerical method. The generator needs only these inputs plus a Born phase-space parametrization for one massless and two massive momenta, which is what makes the approach semi-automatic and extensible to further processes. Because the generator starts from an underlying Born configuration and adds emissions, a technical cut on the transverse momentum of the single massless parton at Born level is required to keep the parton-level calculation finite; the authors show the NLO cross section is stable against this cut below about 5 GeV, and note the alternative of a suppression factor on the underlying Born configuration.","core_discovery":"The paper's central claim is that $tbar{t}+$jet production can be computed at NLO accuracy and then matched to parton showers, with the resulting hadron-level events correct order by order up to NLO when expanded in the strong coupling. The authors establish this in stages. They check the LO cross section against an independent tree-level generator and find complete agreement. They check the one-loop amplitudes point by point against a separate implementation, and check that the ratio of real-emission matrix elements to their subtraction terms tends to one in every unresolved limit. They then reproduce the published NLO cross section of an earlier fixed-order calculation, $(1.78pm0.01)$ pb versus $(1.791pm0.001)$ pb for the same setup, and reproduce that paper's transverse-momentum and rapidity distributions, with the one noted exception that the jet rapidity distribution from the generated events is more central than the fixed-order one. Finally they shower two million events with two different shower programs and compare hadron-level distributions, finding agreement between the two showers within 3 percent and a substantial, roughly uniform shower and hadronization effect of up to about 20 percent on some distributions, including a marked softening of the scalar sum of transverse momenta.","pith_inferences":["The validation strategy used here — agreement of the fixed-order limit with an independent calculation plus agreement between two showers — is a template that could be applied to any future NLO-plus-shower implementation before its hadron-level shapes are trusted.","The observation that jet rapidity from the generated events is more central than the fixed-order prediction is a concrete, checkable discrepancy that a dedicated study of the matching in that observable could resolve.","Since the shower is where top decays are handled, spin correlations in the decay products are absent from these predictions; adding decays at the hard-matrix-element level, which the authors defer, would let the two treatments be compared directly.","The technical cut on the Born-level massless parton is a practical workaround rather than a physical ingredient, so a systematic study of its interplay with jet clustering at small jet transverse momentum would be a natural next check."],"forward_implications":["Hadron-level predictions for $tbar{t}+$jet become available as unweighted events that can be passed through the same analysis chain as collision data, allowing direct theory-to-data comparison and Standard Model background estimates for this final state.","The fixed-order limit of the generator reproduces an independent NLO calculation for the same process, so the matching procedure does not distort the NLO result.","Because the ingredients come from a general numerical amplitude framework, the same route extends to other processes with three hard objects without new analytic work.","Shower and hadronization effects on this final state are large and roughly uniform in some observables, so NLO parton-level predictions alone are insufficient for several of the distributions shown.","Distributions of the three hardest jets are insensitive to which shower program is used and vary only a few percent with the choice of default scale, which supports the stability of the predictions in that region."],"supporting_citations":[{"why":"The NLO-plus-shower framework that organizes the subtraction, generates positive-weight events and produces the event files everything else feeds into.","marker":"[13]"},{"why":"Supplies the automated one-loop amplitude method used for the virtual corrections.","marker":"[2]"},{"why":"Provides the tree-level and colour-correlated squared matrix elements, including the dipole subtraction ingredients.","marker":"[16]"},{"why":"The subtraction scheme on which the NLO organization of the calculation rests.","marker":"[15]"},{"why":"Defines the matching method that gives the hardest emission its transverse-momentum ordering and positive weights.","marker":"[12]"},{"why":"The independent NLO calculation of $tbar{t}+$jet whose cross section and distributions this paper reproduces as its main validation.","marker":"[31]"},{"why":"The NLO calculation including top decays in the narrow-width approximation, used as the comparison point for decay-level and shower-level distributions.","marker":"[32]"},{"why":"Cited for the finding that the truncated-shower effect is small, which underwrites the decision to omit it for the angular-ordered shower.","marker":"[27]"},{"why":"One of the two shower and hadronization programs used to produce the hadron-level predictions and the cross-program agreement check.","marker":"[33]"},{"why":"The second shower program, whose angular ordering motivates the vetoed-shower treatment discussed in the text.","marker":"[34]"}],"fun_headline_variants":["Top pairs plus a jet get NLO matching to two showers","Two showers agree within 3 percent for top pairs plus a jet","Showering shifts top-pair-plus-jet distributions by up to 20 percent","NLO top pairs plus jet pass tree, loop, and subtraction checks","Jet rapidity from showered events is more central than fixed order"],"cache_read_input_tokens":0,"weakest_assumption_plain":"The hadron-level predictions assume that a transverse-momentum-ordered hardest emission can be handed to a shower whose own ordering variable is different without a truncated shower, and the authors state plainly that no truncated shower is implemented for the angular-ordered case, so that contribution is simply absent from those predictions and its size is argued rather than computed.","fun_headline_variants_meta":{"raw":{"variants":["Top pairs plus a jet get NLO matching to two showers","Two showers agree within 3 percent for top pairs plus a jet","Showering shifts top-pair-plus-jet distributions by up to 20 percent","NLO top pairs plus jet pass tree, loop, and subtraction checks","Jet rapidity from showered events is more central than fixed order"]},"model":"selfhosted/deepseek-v4.1-flash","effort":"low","attempts":1,"cost_usd":0.0,"raw_usage":{"total_tokens":1687,"prompt_tokens":906,"completion_tokens":781,"prompt_tokens_details":null,"completion_tokens_details":{"reasoning_tokens":700}},"tokens_in":906,"tokens_out":781,"duration_ms":13354,"image_pages":[],"temperature":1.0,"reasoning_budget":50,"reasoning_tokens":700,"transport_provider":"selfhosted","cache_read_input_tokens":0,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-11-10T18:15:39.320636+00:00","model_set":{"reader":"selfhosted/deepseek-v4.1-flash"},"falsifier":"Implement a truncated shower for the angular-ordered program when reading external event files, or compare against an independent matched calculation with a different matching prescription, and check whether the hadron-level distributions — particularly the antilepton rapidity and the scalar sum of transverse momenta — move by more than the quoted 3 percent spread between the two showers.","supporting_citations":[{"cited_title":"A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX","cited_arxiv_id":"1002.2581","evidence_quote":"The NLO-plus-shower framework that organizes the subtraction, generates positive-weight events and produces the event files everything else feeds into."},{"cited_title":"Automated one-loop calculations: a proof of concept","cited_arxiv_id":"0903.4665","evidence_quote":"Supplies the automated one-loop amplitude method used for the virtual corrections."},{"cited_title":"Polarizing the Dipoles","cited_arxiv_id":"0905.0883","evidence_quote":"Provides the tree-level and colour-correlated squared matrix elements, including the dipole subtraction ingredients."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The subtraction scheme on which the NLO organization of the calculation rests."},{"cited_title":"Matching NLO QCD computations with parton shower simulations: the POWHEG method","cited_arxiv_id":"0709.2092","evidence_quote":"Defines the matching method that gives the hardest emission its transverse-momentum ordering and positive weights."},{"cited_title":"Hadronic top-quark pair production in association with a hard jet at next-to-leading order QCD: Phenomenological studies for the Tevatron and the LHC","cited_arxiv_id":"0810.0452","evidence_quote":"The independent NLO calculation of $tbar{t}+$jet whose cross section and distributions this paper reproduces as its main validation."},{"cited_title":"NLO QCD corrections to top quark pair production in association with one hard jet at hadron colliders","cited_arxiv_id":"1004.3284","evidence_quote":"The NLO calculation including top decays in the narrow-width approximation, used as the comparison point for decay-level and shower-level distributions."},{"cited_title":"A Positive-Weight Next-to-Leading-Order Monte Carlo for e+e- Annihilation to Hadrons","cited_arxiv_id":"hep-ph/0612281","evidence_quote":"Cited for the finding that the truncated-shower effect is small, which underwrites the decision to omit it for the angular-ordered shower."},{"cited_title":"PYTHIA 6.4 Physics and Manual","cited_arxiv_id":"hep-ph/0603175","evidence_quote":"One of the two shower and hadronization programs used to produce the hadron-level predictions and the cross-program agreement check."},{"cited_title":"HERWIG 6.5 Release Note","cited_arxiv_id":"hep-ph/0210213","evidence_quote":"The second shower program, whose angular ordering motivates the vetoed-shower treatment discussed in the text."}],"review_version":1}