Paolo Torrielli, Stefano Frixione
We present the matching between a next-to-leading order computation in QCD and the PYTHIA parton shower Monte Carlo, according to the MC@NLO formalism. We study the case of initial-state radiation, and consider in particular single vector boson hadroproduction.
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We compare a NLO W gamma matrix element generator with the leading order calculation in Pythia . A matching scheme between a next-to-leading order W gamma matrix element generator by Baur et. al. and the Pythia parton shower is presented. The NLO package produces W gamma+0 jet and W gamma+1jet final states in the hard scattering and the objective is to consistently match these to the initial state radiation from Pythia parton shower. The proposed methodology preserves both the rate of the hard scattering process as well as various kinematic distributions of experimental interest.
Multiplicative NLO matching in DIS with Pythia 8
提出Pythia 8中用于电子-质子深非弹性散射的乘性次领头阶匹配方案，通过逐事件积分和矩阵元修正实现，验证与HERA数据一致，并评估对电子-离子对撞机的影响。
One of the most important developments in Monte Carlo simulation of collider events for the LHC has been the arrival of schemes and codes for matching of parton showers to matrix elements calculated at next-to-leading order in the QCD coupling. The POWHEG scheme, and particularly its implementation in the POWHEG-BOX code, has attracted most attention due to ease of use and effective portability between parton shower algorithms. But formal accuracy to NLO does not guarantee predictivity, and the beyond-fixed-order corrections associated with the shower may be large. Further, there are open ques…
Comparison of CMS measurements with predictions at NLO applying the Parton Branching Method and PYTHIA
本文介绍了DESY暑期学校项目中将未纳入RIVET的CMS分析实现并验证的工作，并将测量结果与标准部分子簇射蒙特卡洛生成器及Parton-Branching TMDs的预测进行了比较。
Matrix element corrections in the Pythia8 parton shower in the context of matched simulations at next-to-leading order
本文研究MC@NLO匹配中矩阵元修正对不稳定共振态过程的双重计数问题，提出在Pythia8窄宽度近似下保留硬反冲效应的替代MEC设置，并通过顶夸克对产生验证其有效性。
We present a next-to-leading-order calculation of W/Z production interfaced to shower Monte Carlo, implemented according to the POWHEG method. Finite width effects, Z/gamma interference and angular correlations of decay products are included. A detailed comparison with MC@NLO and PYTHIA is carried out.
We present an implementation of the calculation of the production of W^+W^+ plus two jets at hadron colliders, at next-to-leading order (NLO) in QCD, in the POWHEG framework, which is a method that allows the interfacing of NLO calculations to shower Monte Carlo programs. This is the first 2 -> 4 process to be described to NLO accuracy within a shower Monte Carlo framework. The implementation was built within the POWHEGBOX package. We discuss a few technical improvements that were needed in the POWHEGBOX to deal with the computer intensive nature of the NLO calculation, and argue that further …
A method to calculate heavy flavor visible-level cross sections at Next-to-Leading Order (NLO) in Quantum Chromodynamics (QCD), based on an interface of the FMNR program to PYTHIA, is described. It uses the NLO prediction at quark level provided by FMNR, with a statistical reduction procedure (REDSTAT) that allows a link to PYTHIA 6.2 to be made, from where the description of the full hadron fragmentation and decay chain is obtained. The method is applied to ep -> b bbar X -> D* mu X and mu+ mu- X final states at HERA. Comparisons of the data and NLO cross sections at visible and b-quark level…
We present a next-to-leading order calculation of single-top production interfaced to Shower Monte Carlo programs, implemented according to the POWHEG method. A detailed comparison with MC@NLO and PYTHIA is carried out for several observables, for the Tevatron and LHC colliders.
Achieving a precise description of multi-parton final states is crucial for many analyses at LHC. In this contribution we review the main features of the HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections for tt + 2 jet production at LHC are illustrated and discussed.
We present the calculations necessary to obtain next-to-leading order QCD precision with the Herwig++ event generator using the MC@NLO approach, and implement them for all the processes that were previously available from Fortran HERWIG with MC@NLO. We show a range of results comparing the two implementations. With these calculations and recent developments in the automatic generation of NLO matrix elements, it will be possible to obtain NLO precision with Herwig++ for a much wider range of processes
We present a next-to-leading order calculation of Higgs boson production via gluon fusion interfaced to shower Monte Carlo programs, implemented according to the POWHEG method. A detailed comparison with MC@NLO and PYTHIA is carried out for several observables, for the Tevatron and LHC colliders. Comparisons with next-to-next-to-leading order results and with resummed ones are also presented.
I summarize phenomenological LHC13 studies of the effect of dimension six effective operators on the inclusive cross section and differential distributions for the t-channel single top process at NLO in QCD.
We study the behavior of the charged particle and energy components of the "underlying event" in hard scattering proton-antiproton collisions at 1.96TeV. The goal is to produce data on the "underlying event" that is corrected to the particle level so that it can be used to tune the QCD Monte-Carlo models without requiring CDF detector simulation. Unlike the previous CDF Run 2 "underlying event" analysis which used JetClu to define "jets" and compared uncorrected data with the QCD Monte-Carlo models after detector simulation (i.e., CDFSIM), this analysis uses the MidPoint jet algorithm and corr…
We present the implementation of Higgs boson pair production in gluon fusion within a non-linear Effective Field Theory framework containing five anomalous couplings for this process. The code, available within the POWHEG-BOX-V2, includes full NLO QCD corrections with massive top quarks. All five couplings can be modified by the user. We show $m_{hh}$ distributions at seven benchmark points provided by an $m_{hh}$ shape analysis at NLO and showered $p_T^{hh}$ distributions resulting from an interface to Pythia-8 and Herwig-7.2.
We calculate next-to-leading order (NLO) QCD corrections to electroweak Higgs plus three jet production. Both vector boson fusion (VBF) and Higgs-strahlung type contributions are included along with all interferences. The calculation is implemented within the Matchbox NLO framework of the Herwig++ event generator.
We show how a careful analysis of the behaviour of a parton shower Monte Carlo in the vicinity of the soft and collinear regions allows one to formulate a modified MC@NLO-matching prescription that reduces the number of negative-weight events with respect to that stemming from the standard MC@NLO procedure. As a first practical application of such a prescription, that we dub MC@NLO-$Δ$, we have implemented it in the MadGraph5_aMC@NLO framework, by employing the Pythia8 Monte Carlo. We present selected MC@NLO-$Δ$ results at the 13 TeV LHC, and compare them with MC@NLO ones. We find that the for…
We present the results of our recent calculation of $ε^{\prime}/ ε$ at the Next-to-Leading (NLO) order in QCD and QED, in the framework of $\DSone$ Effective Hamiltonians. The operator matrix elements are taken from lattice QCD, at a scale $μ=2\,\,\mbox{GeV}$. NLO corrections seem to lower the value of $ε^{\prime}/ε$, favouring the experimental result of E731. Contributions from different operators are analyzed and dependence on $\mt$, $μ$ and $Λ_{\sss QCD}$ discussed. (Talk given at the XXVIIIth Rencontres de Moriond, ``Electro-Weak Interactions and Unified Theories'', March 13-19 1993).
I report on a formalism introduced recently to combine parton shower Monte Carlo's and next-to-leading order QCD computations.
In this paper we present the NLO QCD + NLO EW corrections to the $ZZZ$ production with subsequent $Z$-boson leptonic decays at the LHC by adopting the improved narrow width approximation, which takes into account off-shell contributions and spin correlations. Integrated cross sections at $13$, $14$, $33$ and $100~{\rm TeV}$ hadron colliders and various kinematic distributions are presented. Our numerical results show that the jet emission correction accounts for a large part of the total QCD correction, especially in the high energy region. By applying a proper cut to the jet transverse moment…
We present results on NLO-QCD corrections to the process e+ e- --> hadrons via photon-, Z- and graviton-exchange in the context of TeV-scale gravity models. The quantitative impact of these QCD corrections for searches of extra dimensions at a Linear Collider is briefly discussed.
We present results at NLO QCD for hadronic production and decay of top quark pairs, taking into account t tbar spin correlations.
We calculate the next-to-leading order (NLO) quantum chromodynamics (QCD) corrections to inclusive processes $W^+\to J/ψ(η_c)+c+\bar{s}+X$ and $W^+\to B_c(B_c^{*})+b+\bar{s}+X$ in the framework of nonrelativistic QCD (NRQCD) factorization formalism. Result indicates that the NLO corrections are significant, and the uncertainties in theoretical predictions with NLO corrections are greatly reduced. The charmonium and $B_c$ meson yielding rates at the Large Hadron Collider (LHC) are given.
We compute the differential and total rate of the semileptonic decay of polarized top-quarks $t\to \ell ν_\ell + b{\rm jet} + {\rm jet}$ at next-to-leading order (NLO) in the QCD coupling with an off-shell intermediate $W$ boson. We present several normalized distributions, in particular those that reflect the $t$-spin analyzing powers of the lepton, the b-jet and the $W^+$ boson at LO and NLO QCD.
We discuss an alternative subtraction scheme for NLO QCD calculations, which is based on the splitting kernels of an improved parton shower. As an example, we show results for the C parameter of the process e+ e- to 3 jets at NLO used for the verification of this scheme.
We report on a technique for evaluating finite unitarity cut for one-loop amplitudes in gauge theories, and discuss its application to the cut-constructible part of six-gluon amplitude in QCD.
We present theoretical predictions for the hadroproduction of t tbar W+, t tbar W- and t tbar Z at LHC as obtained by matching numerical computations at NLO accuracy in QCD with Shower Monte Carlo programs. The calculation is performed by PowHel, relying on the POWHEG-BOX framework, that allows for the matching between the fixed order computation, with input of matrix elements produced by the HELAC-NLO collection of event generators, and the Parton Shower evolution, followed by hadronization and hadron decays as described by PYTHIA and HERWIG. We focus on the dilepton and trilepton decay chann…
We present the full NLO QCD corrections to the production of a W^+W^- pair in association with two jets in hadronic collisions, which is an important background to New Physics and Higgs boson searches. We include leptonic decays of the W-bosons with full spin correlations. We find NLO corrections of the order of 10% for standard cuts at the LHC. The scale dependence is considerably reduced by the NLO corrections.
In this contribution recent results regarding the NLO electroweak corrections for vector boson production in association with jets are presented. Besides discussing the phenomenology of the fixed-order results, their corporation in existing NLO QCD parton shower matched and merged calculations, which can directly be used in experimental analyses, will be shown.
We report on the implementation of an interface between the SANC generator framework for Drell-Yan hard processes, which includes next-to-leading order electroweak (NLO EW) corrections, and the Herwig++ and Pythia8 QCD parton shower Monte Carlos. A special aspect of this implementation is that the initial-state shower evolution in both shower generators has been augmented to handle the case of an incoming photon-in-a-proton, diagrams for which appear at the NLO EW level. The difference between shower algorithms leads to residual differences in the relative corrections of 2-3% in the p_T(mu) di…
NLO QCD fits using the DGLAP formalism have been made to the high precision ZEUS $e^+p$ reduced cross-section data and to fixed target structure function data, in order to detrmine parton distribution functions and the value of $α_s(M^2_Z)$, taking full account of correlated systematic errors. Preliminary results are reported.
Hadron-Level NLO predictions for QCD Observables in Photo-Production at the Electron-Ion Collider
本文首次为电子-离子对撞机中光生过程的单举QCD及喷注观测量提供了次领头阶精度的强子级理论预言。
The decay width of $Z^0$ to $B_c$ meson is evaluated at the next-to-leading order(NLO) accuracy in strong interaction. Numerical calculation shows that the NLO correction to this process is remarkable. The quantum chromodynamics(QCD)renormalization scale dependence of the results is obviously depressed, and hence the uncertainties lying in the leading order calculation are reduced.
In this article we review recent advances in the area of QCD factorization. We begin with a brief outline of QCD factorization, as well as a description of some recent results regarding B-->VV decays. We examine what is necessary at NLO, look at recent advances towards that goal and consider what remains to be done.
We present a parton shower which implements the DGLAP evolution of parton densities and fragmentation functions at next-to-leading order precision up to effects stemming from local four-momentum conservation. The Monte-Carlo simulation is based on including next-to-leading order collinear splitting functions in an existing parton shower and combining their soft enhanced contributions with the corresponding terms at leading order. Soft double counting is avoided by matching to the soft eikonal. Example results from two independent realizations of the algorithm, implemented in the two event gene…
In this work we investigate the NLO QCD+EW corrections to the top quark pair production and their effects on the spin correlation coefficients and asymmetries at fixed-order top quark pair production and LO decay in the dilepton channel, within the narrow-width approximation. The spin correlations are implicitly measured through the lepton kinematics. Moreover we study the EW effects to the leptonic differential distributions. We find that the EW corrections to the $t \bar t$ production are within the NLO QCD theoretical uncertainties for the spin correlation coefficients and the leptonic asym…
In this talk we present a fully automated implementation of next-to-leading order electroweak (NLO EW) corrections in OpenLoops together with Sherpa and Munich. As a first application, we present NLO QCD+EW predictions for the production of positively charged W bosons in association with up to three jets and for the production of a Z boson or photon in association with one jet.
We discuss the GENEVA Monte Carlo framework, which combines higher-order resummation (NNLL) of large Sudakov logarithms with multiple next-to-leading-order (NLO) matrix-element corrections and parton showering (using PYTHIA8) to give a complete description at the next higher perturbative accuracy in alpha_s at both small and large jet resolution scales. Results for e+e- -> jets compared to LEP data and for Drell-Yan production are presented.
We update our work ``Two Higgs Doublet Model predictions for B->X_s gamma in NLO QCD'', hep-ph/9802391 by taking into account the recently calculated electromagnetic corrections. We present a new exclusion contour plot (tan(β),m_H), where these corrections are included.
In this paper we present a complete next-to-leading order QCD calculation of the $χ_J$ ($^3P_J\; ;J=0,1,2$) hadronic decay width. We include the NLO colour-octet contribution, as defined in the Bodwin, Braaten and Lepage formalism. We extract an estimate of the colour-octet parameter \height\ from the charmonium decay data.
A very brief status of next-to-leading order QCD calculations is given. As an example the next-to-leading order QCD calculations to the pp -> ttjj processes at the CERN Large Hardon Collider are presented. Results for integrated and differential cross sections are shown. They have been obtained in the framework of the HELAC-NLO system.
We revisited excited leptons ($\bar{l^*}l$) production through gauge mediation only at LHC, followed by their two body decays into Standard Model (SM) particles. We include the next-to-leading order (NLO) QCD corrections to these processes. We have shown that these corrections can be substantial and significant. We also show that the scale dependence of the NLO cross section is greatly reduced as compare to leading order (LO) cross section.
NLO QCD corrections to Higgs boson production in association with gauge bosons in proton-proton collisions at sqrt(s) = 14 TeV
研究14TeV质子-质子碰撞中Higgs玻色子与规范玻色子关联产生过程的NLOQCD修正，分析总截面和动量分布的影响。
We report on state-of-the-art theoretical predictions for $pp\to t\bar{t}b\bar{b}$ including full off-shell effects in the di-lepton decay channel at NLO QCD accuracy. We briefly discuss the impact of NLO QCD corrections on differential distributions and also asses theoretical uncertainties from scale and PDF dependence. Furthermore, we propose a simple kinematic reconstruction in order to distinguish $b$ jets originating from top-quark decays from arising from gluon splittings.
We apply the MC@NLO approach to the process of heavy flavour hadroproduction. MC@NLO is a method for matching next-to-leading order (NLO) QCD calculations and parton shower Monte Carlo (MC) simulations, with the following features: fully exclusive events are generated, with hadronisation according to the MC model; total rates are accurate to NLO; NLO results for distributions are recovered upon expansion in $\as$; hard emissions are treated as in NLO computations while soft/collinear emissions are handled by the MC simulation, with the same logarithmic accuracy as the MC; matching between the …
The next-to-leading order (NLO) quantum chromodynamics (QCD) corrections for $χ_{cJ}(^3P_J^{[1]},^3S_1^{[8]})$, the P-wave charmoniums inclusive production at $B$ factories are calculated utilizing the non-relativistic QCD (NRQCD) factorization formalism. Large NLO corrections are found, especially for $^3P_0^{[1]}$ and $^3S_1^{[8]}$ configurations. Numerical evaluation indicates that the total cross sections of $χ_{cJ}$ inclusive production processes are at the order of $10$fb, which are accessible in BELLE II(super-B) experiment.
We are reporting on the ongoing effort of the Monte Carlo (MC) modelling of NLO DGLAP QCD evolution in the fully unintegrated form. The resulting parton shower MC is performing on its own the NLO QCD evolution, contrary to all known programs of this kind which are limited to LO level only. We overview this new MC scheme, for the non-singlet subset of the gluonstrahlung diagrams. Precision numerical tests of this new scheme are also shown.
The implementation of the full next-to-leading order (NLO) QCD corrections to electroweak Higgs boson plus three jet production at hadron colliders such as the LHC within the Matchbox NLO framework of the Herwig++ event generator is discussed. We present numerical results for integrated cross sections and kinematic distributions.
We review the recent developments of the QCD shockwave approach at Next-to-Leading Order. The general method of this effective action is sketched, and illustrated by the case of diffractive processes.
In this paper we calculate the next-to-leading order (NLO) QCD $[{\cal O}(α_s α^3)]$ and electroweak (EW) $[{\cal O}(α^4)]$ corrections to the $WWW$ production at the LHC and deal with the subsequent leptonic decays from $W$ bosons by adopting an improved narrow-width approximation which takes into account the spin correlation and finite-width effects. The NLO QCD correction from the real jet radiation is discussed, which significantly enhances the production rate, particularly in the high-energy region. We also provide the integrated cross section for the $WWW$ production and various kinemati…
The trace amplitude method (TAM) provides us a straightforward way to calculate the helicity amplitudes with massive fermions analytically. In this work, we review the basic idea of this method, and then discuss how it can be applied to next-to-leading order (NLO) quantum chromodynamics (QCD) calculations, which has not been explored before. By analyzing the singularity structures of both virtual and real corrections, we show that the TAM can be generalized to NLO QCD calculations straightforwardly, the only caution is that the unitarity should be guaranteed. We also present a simple example t…
$t\bar{t}t\bar{t}$: NLO QCD corrections in production and decays for the $4\ell$ channel
本文研究了微扰 QCD 的 NLO 精度下四顶夸克在 4$\ell$ 通道的产生与衰变过程，采用窄宽度近似并保持自旋关联，评估了 NLO QCD 修正的整体大小及忽略顶夸克衰变高阶效应的影响。
The aim of this work is to describe in detail the POWHEG method, first suggested by one of the authors, for interfacing parton-shower generators with NLO QCD computations. We describe the method in its full generality, and then specify its features in two subtraction frameworks for NLO calculations: the Catani-Seymour and the Frixione-Kunszt-Signer approach. Two examples are discussed in detail in both approaches: the production of hadrons in e+e- collisions, and the Drell-Yan vector-boson production in hadronic collisions.
We present precision Monte Carlo calculations solving the QCD evolution equations up to the next-to-leading-order (NLO) level. They employ forward Markovian Monte Carlo (FMC) algorithms, which provide the rigorous solutions of the QCD evolution equations. Appropriate Monte Carlo algorithms are described in detail. They are implemented in the form of the Monte Carlo program EvolFMC, which features the NLO kernels for the QCD evolution. The presented numerical results agree with those from independent, non-MC, programs (QCDNum16, APCheb33) at the level of 0.1%. In this way we have demonstrated t…
The project of constructing a complete NLO-level Parton Shower Monte Carlo for the QCD processes developed in IFJ PAN in Krakow is reviewed. Four issues are discussed: (1) the extension of the standard inclusive collinear factorization into a new, fully exclusive scheme; (2) reconstruction of the LO Parton Shower in the new scheme; (3) inclusion of the exclusive NLO corrections into the hard process and (4) inclusion of the exclusive NLO corrections into the evolution (ladder) part.
We briefly discuss the current status of NLO QCD automation in the Monte Carlo event generator WHIZARD. The functionality is presented for the explicit study of off-shell top quark production with associated backgrounds at a lepton collider.
The semi-inclusive deep inelastic scattering (SIDIS) process is considered. It is proposed a theoretical procedure allowing the direct extraction from the SIDIS data of the first moments of the polarized valence distributions and of the first moment difference of the light sea quark polarized distributions in the next to leading (NLO) QCD order. The validity of the procedure is confirmed by the respective simulations.
We study the process of the association production of chargino and neutralino including the NLO QCD and the complete one-loop electroweak corrections in the framework of the minimal supersymmetric standard model(MSSM) at the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). In both the NLO QCD and one-loop electroweak calculations we apply the algorithm of the phase-space slicing(PSS) method. We find that the NLO QCD corrections generally increase the Born cross sections, while the electroweak relative corrections decrease the Born cross section in most of the chosen parameter space.…
We calculate the next-to-leading order (NLO) quantum chromodynamics (QCD) corrections to $γ+γ\to η_c+c+\bar{c}$, $γ+γ\to η_b+b+\bar{b}$ and $γ+γ\to B_c+b+\bar{c}$ processes in the framework of non-relativistic QCD (NRQCD) factorization formalism. The cross sections at the SuperKEKB electron-positron collider, as well as the future collider like the Circular Electron Positron Collider (CEPC), are evaluated. Numerical results indicate that the NLO corrections are significant, and the uncertainties in theoretical predictions with NLO corrections are reduced as expected. Due to the high luminosity…
NLO QCD corrections to Vector Boson Pair Production via Vector Boson Fusion have recently been calculated and implemented in a parton-level Monte-Carlo program with full experimental cuts. We briefly sketch the elements of the calculation and show numerical results for the Large Hadron Collider.
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