We present a next-to-leading order (NLO) global DGLAP analysis of nuclear parton distribution functions (nPDFs) and their uncertainties. Carrying out an NLO nPDF analysis for the first time with three different types of experimental input -- deep inelastic $\ell$+A scattering, Drell-Yan dilepton production in p+$A$ collisions, and inclusive pion production in d+Au and p+p collisions at RHIC -- we find that these data can well be described in a conventional collinear factorization framework. Although the pion production has not been traditionally included in the global analyses, we find that the shape of the nuclear modification factor $R_{\rm dAu}$ of the pion $p_T$-spectrum at midrapidity retains sensitivity to the gluon distributions, providing evidence for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method to quantify the nPDF uncertainties which originate from the uncertainties in the data. In this method the sensitivity of $χ^2$ to the variations of the fitting parameters is mapped out to orthogonal error sets which provide a user-friendly way to calculate how the nPDF uncertainties propagate to any factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the corresponding error sets are collected in our new release called {\ttfamily EPS09}. These results should find applications in precision analyses of the signatures and properties of QCD matter at the LHC and RHIC.
Inspecting the power of parton showering the generated events by comparing the events generated in NLO+PS to NLO and NNLO without parton shower in $e^+e^-$ at 91.2 GEV
本文介绍了在克拉科夫IFJ PAN建立一个完整的NLO级部分子簇射蒙特卡罗程序的计划。讨论了四个问题：（1）将标准的包含共线分解扩展为一个新的完全排他的方案;（2）在新方案中重建LO Parton Shower;（3）将排他的NLO修正包含到硬过程中;（4）将排他的NLO修正包含到演化（阶梯）部分中。
We present the matching of NLO QCD and NLO EW corrections to parton showers for vector-boson pair production at the LHC. We consider leptonic final states, including resonant and non-resonant diagrams, spin correlations and off-shell effects. Our results are obtained interfacing the Recola2-Collier one-loop provider with the POWHEG-BOX-RES framework. We discuss our implementation, we validate it at fixed order, and we show our final results matched to parton shower. A by-product of our work is also a general interface between Recola2-Collier and POWHEG-BOX-RES. This is the first time that EW a…
We present a selection of results from our recent study of $pp\to t\bar{t}W^\pm$ production matched to partons showers at NLO QCD at the LHC. Theoretical predictions are obtained at perturbative orders $\mathcal{O}(α_s^3α)$ and $\mathcal{O}(α_sα^3)$, where the different contributions are studied first separately at the inclusive level before being combined within a realistic two same-sign lepton signature. We investigate in detail uncertainties originating from missing higher-order corrections and from the parton-shower matching scheme employed.
We propose a new approach for combining next-to-leading order (NLO) and parton shower (PS) calculations so as to obtain three core features: (a) applicability to general showers, as with the MCatNLO and POWHEG methods; (b) positive-weight events, as with the KrkNLO and POWHEG methods; and (c) all showering attributed to the parton shower code, as with the MCatNLO and KrkNLO methods. This is achieved by using multiplicative matching in phase space regions where the shower overestimates the matrix element and accumulative (additive) matching in regions where the shower underestimates the matrix …
Nuclear modification factors of single hadrons and dihadrons at large transverse momentum ($p_{\rm T}$) in high-energy heavy-ion collisions are studied in a next-to-leading-order (NLO) perturbative QCD parton model. Parton fragmentation functions (FFs) in $A+A$ collisions are modified due to jet energy loss which is proportional to the jet transport coefficient $\hat{q}$ characterizing the interaction between the parton jet and the produced medium. By confronting 6 current sets of NLO parton FFs for large $p_{\rm T}$ hadron productions, we extract $\hat{q}$ quantitatively via a global fit to d…
Matching NLO QCD computations and parton shower simulations
提出了一种将QCD过程的次领先级（NLO）计算与部分子簇射蒙特卡罗（MC）模拟相匹配的方法。该方法具有以下特点：完全互斥事件的产生，根据MC模型进行强子化;总互斥率精确到NLO;分布的NLO结果在$α_S$中展开后恢复;硬发射处理为NLO计算，而软/共线发射由MC模拟处理，具有与MC相同的对数精度;并且硬和软/共线发射区域之间的匹配是平滑的。生成具有负权重的事件的一小部分，但是以合理的效率取消权重仍然是可能的。该方法是澄清使用一个简单的玩具模型，并说明了应用程序的hadroproduction的W $^+$ W $^-$对。
NLO predictions for Higgs boson pair production with full top quark mass dependence matched to parton showers
我们提出了第一个组合的非线性光学QCD矩阵元素的双希格斯生产，保留完整的顶夸克质量的依赖性，与部分子淋浴。结果在POWHEG-BOX和MadGraph5_aMC@NLO Monte Carlo框架内提供。我们详细评估的理论不确定性，并提供差分结果。我们发现，正如预期的那样，簇射效应对于像希格斯玻色子对的横向动量这样的观测量是相对较大的，这对额外的辐射是敏感的。然而，这些簇射效应仍然比Born改进的HEFT近似和完全NLO计算在分布尾部之间的差异小得多。
We present results for Higgs boson pair production with variations of the trilinear Higgs boson self-coupling at next-to-leading order (NLO) in QCD including the full top quark mass dependence. Differential results at 14 TeV are presented, and we discuss the implications of anomalous trilinear couplings as well as differences between the PYTHIA 8.2 and HERWIG 7.1 parton showers in combination with POWHEG. The implementation of the NLO QCD calculation with variable Higgs boson self-coupling is made publicly available in the POWHEG-BOX-V2 Monte Carlo framework. A simple method for using the new …
