[Paper Review] Automated Neutrino Jet and Top Jet Predictions at Next-to-Leading-Order with Parton Shower Matching in Effective Left-Right Symmetric Models

Olivier Mattelaer, Manimala Mitra+1 more|arXiv (Cornell University)|Oct 27, 2016

Particle physics theoretical and experimental studies68 references17 citations

TL;DR

This paper presents an automated framework for next-to-leading-order (NLO) QCD corrections matched to parton showers in an effective Left-Right Symmetric Model (LRSM), enabling precise predictions for $W_R^\pm$, $Z_R$, and heavy Majorana neutrino ($N$) production at the LHC and future colliders. The key finding is that neutrino jets from $W_R$ decays are robust against parton shower and QCD radiation effects, allowing aggressive kinematic cuts with minimal signal loss—unlike top jets, which are significantly altered by hard radiation.

ABSTRACT

Hadronic decays of boosted resonances, e.g., top quark jets, at hadronic super colliders are frequent predictions in TeV-scale extensions of the Standard Model of Particle Physics. In such scenarios, accurate modeling of QCD radiation is necessary for trustworthy predictions. We present the automation of fully differential, next-to-leading-order (NLO) in QCD corrections with parton shower (PS) matching for an effective Left-Right Symmetric Model (LRSM) that features $W_R^\pm, Z_R$ gauge bosons and heavy Majorana neutrinos $N$. Publicly available universal model files require remarkably fewer user inputs for predicting benchmark collider processes than leading order LRSM constructions. We present predictions for inclusive $W_R^\pm, Z_R$ production at the $\sqrt{s} = 13$ TeV Large Hadron Collider (LHC) and a hypothetical future 100 TeV Very Large Hadron Collider (VLHC), as well as inclusive $N$ production for a hypothetical Large Hadron Electron Collider (LHeC). As a case study, we investigate at NLO+PS accuracy the properties of heavy neutrino (color-singlet) jets and top quark (color-triplet) jets from decays of high-mass $W_R$ bosons at the LHC. Contrary to top jets, we find that the kinematic properties of heavy neutrinos jets, and in particular jet mass, are resilient against the effects of parton showers and hard QCD radiation. This suggests that in searches for neutrino jets, aggressive selection cuts that would otherwise be inappropriate for top jets can be imposed with minimal signal loss.

Motivation & Objective

• To develop a fully automated, publicly available model for NLO QCD corrections with parton shower matching in an effective Left-Right Symmetric Model (LRSM).
• To enable precise, differential predictions for $W_R^\pm$, $Z_R$, and heavy Majorana neutrino ($N$) production at the 13 TeV LHC and future 100 TeV VLHC and LHeC.
• To investigate the impact of QCD radiation and parton shower effects on the kinematics of top quark jets and neutrino jets from high-mass $W_R$ decays.
• To provide a user-friendly, minimal-input framework using FeynRules, NLOCT, and MG5_aMC@NLO for collider phenomenology in LRSM.

Proposed method

• The authors implement the effective LRSM in the FeynRules (FR) framework to generate universal model files (UFO), enabling automated model deployment.
• They use the MG5_aMC@NLO framework with parton shower matching (PS) to compute fully differential NLO QCD corrections for $pp \to W_R^\pm, Z_R$, and $pp \to N$ processes.
• The model includes $W_R^\pm$, $Z_R$, and heavy Majorana neutrinos $N$ with $W_R \to N\ell^\pm$ and $N \to \ell^\pm W_R^{\mp*} \to \ell^\pm q\bar{q}'$ decays.
• Spin-correlated decays of $N$ and $t$ are modeled using improved MadSpin, preserving full spin correlations with hard matrix elements.
• Generator-level cuts are implemented via custom modifications to the MG5_aMC@NLO cuts.f file to enforce $p_T > 750$ GeV on final-state top quarks and $N$ particles.
• The framework supports both hadron-hadron ($pp$) and hadron-electron ($ep$) collisions, enabling simulations for LHC, VLHC, and LHeC.

Experimental results

Research questions

• RQ1 How do NLO QCD corrections and parton shower effects alter the kinematic distributions of top quark jets from $W_R$ decays at the LHC?
• RQ2 To what extent are neutrino jet properties, particularly jet mass, affected by parton shower and hard QCD radiation in $W_R \to N\ell^\pm$ decays?
• RQ3 Can aggressive selection cuts be applied to neutrino jets without significant signal loss due to QCD radiation, unlike in top jet searches?
• RQ4 How does the inclusion of NLO corrections and PS matching improve the reliability of collider predictions for $W_R$, $Z_R$, and $N$ production in the LRSM?
• RQ5 What is the performance of the automated, minimal-input model framework in predicting inclusive cross sections and differential distributions at NLO+PS accuracy?

Key findings

• Neutrino jets from $W_R$ decays exhibit minimal distortion from parton shower and hard QCD radiation, particularly in their jet mass distributions.
• In contrast, top quark jets show significant kinematic shifts due to wide-angle final-state radiation not captured by parton showers, leading to substantial changes in jet mass and $p_T$ distributions.
• The resilience of neutrino jet kinematics allows for the application of aggressive selection cuts—such as $p_T > 750$ GeV—without significant signal loss, unlike in top jet analyses.
• The automated framework achieves accurate, differential NLO+PS predictions for $W_R^\pm$, $Z_R$, and $N$ production at the 13 TeV LHC and future 100 TeV VLHC and LHeC.
• The public availability of universal model files (UFO) drastically reduces user input requirements compared to traditional LO-only LRSM constructions.
• The study confirms that $W_R \to N\ell^\pm$ decays produce distinct, stable jet signatures that are promising for discovering heavy Majorana neutrinos in high-energy collider experiments.