arXiv subjects

Richard Ruiz

Publications and source records attributed to Richard Ruiz.

At least 19 recordsLinked to original sources

arXiv2026

Polarization interference in exclusive $V+$jets at all orders in $\alpha_s$

Using new methods for computing helicity amplitudes with intermediate helicity-polarized gauge bosons, we revisit the transverse-longitudinal polarization interference in the $pp\to V+{\rm jets}$ process for $V=\gamma^*,Z^{(*)},W^{(*)}$ decaying to massless leptons. At each order of the strong coupling constant $\alpha_s$ and remaining exclusive with respect to jet kinematics, we show that the polarization interference in $\gamma^*\to\ell^+\ell^-$ vanishes after phase-space integration over the kinematics of $\ell^\pm$, thereby extending well-known results for the inclusive process. Due to parity violation, cancellations are softened for the $W$ and $Z$ bosons. We give a simple formula to account for fiducial cuts. We comment on the implications for multiboson processes, and the applicability of our results to chiral gauge bosons in new physics scenarios and to polarization measurements of weak bosons in heavy ion collisions.

hep-ph↗

arXiv2025

The Four Polarizations of the $W$ at High Energies

We investigate polarization-induced interference, off-shell effects, and gauge cancellations in predictions for high-energy, multi-leg processes with (near) resonant weak bosons. Building on the ``polarized propagator'' paradigm, we carry out our analysis at the level of helicity amplitudes and squared amplitudes, computing polarization interference directly. We introduce analytical decompositions of polarized propagators, valid for covariant and axial gauges, that simplify the organization and evaluation of polarized amplitudes, and make power counting of mass-over-energy factors manifest. We show: (i) For the fully massive case, polarization interference can exceed $\mathcal{O}(\Gamma_V^2/M_V^2)$ width-over-mass corrections, limiting the applicability of the narrow width and pole approximation at low energies. (ii) At the fully differential level, interference can naturally be larger than squared longitudinal amplitudes but can also vanish when bosons are emitted by unpolarized sources. (iii) When weak bosons decay to massless fermions, the non-interference of polarization after angular integration extends to the off-shell regime but remains approximate due to $V-A$ couplings. Guided by BRST invariance, we propose a simple scheme for grouping together polarizations that reduces gauge ambiguities in predictions for polarized scattering rates and is applicable to the fully massive case. As case studies, we examine polarization interference in $W$(+jets), top quark decay, and neutrino deep-inelastic scattering. For decays of unpolarized top quarks, interference exactly cancels at the totally unintegrated level.

hep-ph↗

arXiv2025

Are arXiv submissions on Wednesday better cited? Introducing Big Data methods in undergraduate courses on scientific computing

Extracting information from big data sets, both real and simulated, is a modern hallmark of the physical sciences. In practice, students face barriers to learning ``Big Data'' methods in undergraduate physics and astronomy curricula. As an attempt to alleviate some of these challenges, we present a simple, farm-to-table data analysis pipeline that can collect, process, and plot data from the 800k entries common to the arXiv preprint repository and the bibliographical database inSpireHEP. The pipeline employs contemporary research practices and can be implemented using open-sourced Python libraries common to undergraduate courses on Scientific Computing. To support the use such pipelines in classroom contexts, we make public an example implementation, authored by two undergraduate physics students, that runs on off-the-shelf laptops. For advanced students, we discuss applications of the pipeline, including for online DAQ monitoring and commercialization.

physics.ed-ph↗

arXiv2025

Precise Standard-Model predictions for polarised Z-boson pair production and decay at the LHC

Providing accurate theoretical predictions in the Standard Model for processes with polarised electroweak bosons is crucial to understand more in-depth the electroweak-symmetry breaking mechanism and to enhance the sensitivity to potential new-physics effects. Motivated by the rapidly increasing number of polarisation analyses of di-boson processes with LHC data, we carry out a comprehensive study of the inclusive production of two polarised Z bosons in the decay channel with four charged leptons. We perform a detailed comparison of fixed-order predictions obtained with various Monte Carlo programs which rely on different signal-definition strategies, assessing non-resonant and interference effects by contrasting polarised results with unpolarised and full off-shell ones. For the first time, we accomplish the combination of NNLO QCD and NLO EW corrections, setting the new state-of-the-art perturbative accuracy for polarised Z-boson pairs at the LHC. The impact of parton-shower matching and multi-jet merging is investigated by scrutinising calculations obtained with event generators that are typically used in experimental analyses. Integrated and differential results are discussed in a realistic fiducial setup and compared to publicly available ATLAS results.

hep-ph↗

arXiv2025

Weak bosons as partons below 10 TeV partonic center-of-momentum

We investigate the modeling of weak boson number densities for leptons and hadrons in practical calculations in the Standard Model. In the framework of the Effective $W$ Approximation (EWA) and in the $R_\xi$ and axial gauges, we derive the unrenormalized, tree-level parton number densities for weak bosons from massless fermions at next-to-leading power in the collinear expansion. Corrections exhibit various pathologies and properties, including those conjectured but not proven, and parallel heavy quark factorization. We suppress pathologies through a new set of kinematical consistency conditions. When satisfied, shapes and normalizations of full matrix elements for many-leg processes can be well approximated by the EWA and fragmentation contributions at leading power, suggesting the onset of tree-level factorization. Findings also suggest that the EWA is testable at the LHC with $\mathcal{L}=450$ fb$^{-1}$ of same-sign $WW$ scattering data at $\sqrt{s}=13.6$ TeV.

hep-ph↗

arXiv2024

Hard processes in multi-TeV ion collisions

Motivated by the ion-collision program at the Large Hadron Collider, plans for its high-luminosity upgrade, and on-going discussions for multi-TeV future hadron colliders, we systematically investigate hard-scattering, Standard Model processes in many-TeV ion-ion collisions. We focus on the symmetric beam configurations $^{208}$Pb-$^{208}$Pb, $^{131}$Xe-$^{131}$Xe, $^{12}$C-$^{12}$C, and $pp$, and we catalog total and fiducial cross sections for dozens of processes, ranging from associated-Higgs and multiboson production to associated-top pair production, at next-to-leading order in QCD for nucleon-nucleon collision energies from $\sqrt{s_{NN}}=1$ to $100$ TeV. We report the residual scale uncertainties at this order as well as the uncertainties originating from fits of nuclear parton densities. We also discuss the propagation of nuclear dynamics (as encoded in nuclear parton densities) into parton luminosities, and ultimately into predictions for cross sections. Finally, we report on the emergence of trends and the reliability of extrapolating cross sections across different nuclei. For Pb-Pb collisions at a hypothetical Future Circular Collider with $\sqrt{s_{NN}}=39$ TeV, $\mathcal{O}(10^{8})$ weak bosons, $\mathcal{O}(10^5)$ diboson pairs, $\mathcal{O}(10^4)$ $WH$ and $ZH$ pairs, $\mathcal{O}(10^3)$ triboson events, $\mathcal{O}(10^5)$ high-$p_T$ photons events, and $\mathcal{O}(10^7)$ $t\overline{t}$ pairs can be produced with $\mathcal{L}=33$~nb$^{-1}$ of data. At $\sqrt{s_{NN}}=5.52$ TeV, one can expect $\mathcal{O}(10-10^6)$ single, multiboson, and top events per $1$ nb$^{-1}$. Decay rates and experimental selection/acceptance rates will impact final event yields, and merits further study; as an illustrative example, we focus on select diboson and triboson channels in lead-lead collisions and discuss their observability at the high-luminosity phase of the LHC and the FCC.

hep-ph↗

arXiv2024

Polarized ZZ pairs in gluon fusion and vector boson fusion at the LHC

Pair production of helicity-polarized weak bosons $(V_\lambda=W^\pm_\lambda, Z_\lambda)$ from gluon fusion $(gg\to V_\lambda V'_{\lambda'})$ and weak boson fusion $(V_1V_2\to V_\lambda V'_{\lambda'})$ are powerful probes of the Standard Model, new physics, and properties of quantum systems. Measuring cross sections of polarized processes is a chief objective of the Large Hadron Collider's (LHC) Run 3 and high luminosity programs, but progress is limited by the simulation tools that are presently available. We propose a method for computing polarized cross sections that works by directly modifying Feynman rules instead of (squared) amplitudes. The method is applicable to loop-induced processes, and can capture the interference between arbitrary polarization configurations, interference with non-resonant diagrams, as well as off-shell/finite-width effects. By construction, previous results that work at the (squared) amplitude level are recoverable. As a demonstration, we report the prospect of observing and studying polarized $Z_\lambda Z_{\lambda'}$ pairs when produced via gluon fusion and electroweak processes in final-states with four charged leptons at the LHC, using the new method to simulate the gluon fusion process. Our Feynman rules are publicly available as a set of \textit{Universal FeynRules Object} libraries called \texttt{SM\_Loop\_VPolar}.

hep-ph↗

arXiv2023

Testing the Scalar Triplet Solution to CDF's Fat $W$ Problem at the LHC

The Type II Seesaw model remains a popular and viable explanation of neutrino masses and mixing angles. By hypothesizing the existence of a scalar that is a triplet under the weak gauge interaction, the model predicts strong correlations among neutrino oscillation parameters, signals at lepton flavor experiments, and collider observables at high energies. We investigate reports that the Type II Seesaw can naturally accommodate recent measurements by the CDF collaboration, which finds the mass of the $W$ boson to be significantly larger than allowed by electroweak precision data, while simultaneously evading constraints from direct searches. Experimental scrutiny of this parameter space in the Type II Seesaw has long been evaded since it is not characterized by ``golden channels'' at colliders but instead by cascade decays, moderate mass splittings, and many soft final states. In this work, we test this parameter space against publicly released measurements made at the Large Hadron Collider. By employing a newly developed tool chain combining MadGraph5\_aMC@NLO and Contur, we find that most of the favored space for this discrepancy is already excluded by measurements of Standard Model final states. We give suggestions for further exploration at Run III of the LHC, which is now underway.

hep-ph↗

arXiv2022

Report of the Topical Group on Electroweak Precision Physics and Constraining New Physics for Snowmass 2021

The precise measurement of physics observables and the test of their consistency within the standard model (SM) are an invaluable approach, complemented by direct searches for new particles, to determine the existence of physics beyond the standard model (BSM). Studies of massive electroweak gauge bosons (W and Z bosons) are a promising target for indirect BSM searches, since the interactions of photons and gluons are strongly constrained by the unbroken gauge symmetries. They can be divided into two categories: (a) Fermion scattering processes mediated by s- or t-channel W/Z bosons, also known as electroweak precision measurements; and (b) multi-boson processes, which include production of two or more vector bosons in fermion-antifermion annihilation, as well as vector boson scattering (VBS) processes. The latter categories can test modifications of gauge-boson self-interactions, and the sensitivity is typically improved with increased collision energy. This report evaluates the achievable precision of a range of future experiments, which depend on the statistics of the collected data sample, the experimental and theoretical systematic uncertainties, and their correlations. In addition it presents a combined interpretation of these results, together with similar studies in the Higgs and top sector, in the Standard Model effective field theory (SMEFT) framework. This framework provides a model-independent prescription to put generic constraints on new physics and to study and combine large sets of experimental observables, assuming that the new physics scales are significantly higher than the EW scale.

hep-ph↗

arXiv2022

Doubly Charged Higgs Boson Production at Hadron Colliders II: A Zee-Babu Case Study

Motivated by searches for so-called leptonic scalars at the LHC and the recent measurement of the $W$ boson's mass at the Tevatron, we revisit the phenomenology of the Zee-Babu model for neutrino masses and the ability to differentiate it from the Type II Seesaw model at the LHC. We conclude that this task is much more difficult than previously believed. All inputs equal in the two scenarios, we find that total and differential rates for producing pairs of doubly and singly charged scalars are identical in shape and only differ in normalization. The normalization is given by the ratio of hadronic cross sections and can be unity. Differences in cross sections are small and can be hidden by unknown branching rates. This holds for Drell-Yan, $γγ$ fusion, and $gg$ fusion, as well as observables at LO and NLO in QCD. This likeness allows us to reinterpret Run II limits on the Type II Seesaw and estimate projections for the HL-LHC. Using updated neutrino oscillation data, we also find that some collider observables, e.g., lepton flavor-violating branching ratios, are now sufficiently precise to provide a path forward. Other means of discrimination are also discussed. As a byproduct of this work, we report the availability of new Universal \texttt{FeynRules} Object libraries, the \texttt{SM\_ZeeBabu} UFO, that enable fully differential simulations up to NLO+LL(PS) with tool chains employing \texttt{MadGraph5\_aMC@NLO}.

hep-ph↗

arXiv2022

On Baryon and Lepton Number Violation

In this report we discuss the main theories to understand the origin of baryon and lepton number violation in physics beyond the Standard Model. We present the theoretical predictions for rare processes such as neutrinoless double beta decay, proton decay, and neutron-antineutron oscillation, and overview the prospects to discover these rare processes in the near future. The possibility to observe baryon and lepton violating signatures at current and future colliders and through precision studies of other rare processes, and the testability of different baryogenesis mechanisms is discussed in detail. A healthy and broad experimental program looking for proton decay, neutrinoless double beta decay and neutron-antineutron oscillations is essential to make new discoveries in this field. These searches are carried out at various experimental facilities in the US and abroad, and use instrumentation arching across traditional HEP/NP boundaries. In addition, experiments such as those at the Large Hadron Collider could discover exotic baryon and/or lepton number violating signatures connected to low energy scale theories for neutrino masses, supersymmetric models with R-parity violation, new gauge theories or other mechanisms for physics beyond the Standard Model. The landscape presented in this report could be crucial to discover the underlying mechanism for neutrino masses and the matter-antimatter asymmetry in the universe.

hep-ph↗

arXiv2022

The Effective Vector Boson Approximation in High-Energy Muon Collisions

Due to the inclination for forward gauge radiation, lepton colliders beyond a few TeV are effectively electroweak (EW) boson colliders, suggesting the treatment of EW bosons as constituents of high-energy leptons. In the context of a muon collider, we revisit the validity of $W$ and $Z$ parton distribution functions (PDFs) at leading order in $2\to n$ process. We systematically investigate universal and quasi-universal power-law and logarithmic corrections that arise when deriving (polarized) weak boson PDFs in the collinear limit. We go on to survey a multitude of $2\to n$ processes at $\sqrt{s}=2-30$ TeV via polarized and unpolarized EW boson fusion/scattering. To conduct this study, we report a public implementation of the Effective $W/Z$ and Weizsäcker-Williams Approximations, which we collectively call the Effective Vector Boson Approximation, into the Monte Carlo event generator \texttt{MadGraph5\_aMC@NLO}. This implementation lays the groundwork for developing matrix-element matching prescriptions involving EW parton showers and renormalized EW PDFs. To further with this agenda, we give recommendations on using $W/Z$ PDFs.

hep-ph↗

arXiv2022

Muon Collider Physics Summary

The perspective of designing muon colliders with high energy and luminosity, which is being investigated by the International Muon Collider Collaboration, has triggered a growing interest in their physics reach. We present a concise summary of the muon colliders potential to explore new physics, leveraging on the unique possibility of combining high available energy with very precise measurements.

hep-ph↗

arXiv2022

Vector Boson Scattering Processes: Status and Prospects

Insight into the electroweak (EW) and Higgs sectors can be achieved through measurements of vector boson scattering (VBS) processes. The scattering of EW bosons are rare processes that are precisely predicted in the Standard Model (SM) and are closely related to the Higgs mechanism. Modifications to VBS processes are also predicted in models of physics beyond the SM (BSM), for example through changes to the Higgs boson couplings to gauge bosons and the resonant production of new particles. In this review, experimental results and theoretical developments of VBS at the Large Hadron Collider, its high luminosity upgrade, and future colliders are presented.

hep-ph↗

arXiv2022

Neutrinoless Double-Beta Decay: A Roadmap for Matching Theory to Experiment

The observation of neutrino oscillations and hence non-zero neutrino masses provided a milestone in the search for physics beyond the Standard Model. But even though we now know that neutrinos are massive, the nature of neutrino masses, i.e., whether they are Dirac or Majorana, remains an open question. A smoking-gun signature of Majorana neutrinos is the observation of neutrinoless double-beta decay, a process that violates the lepton-number conservation of the Standard Model. This white paper focuses on the theoretical aspects of the neutrinoless double-beta decay program and lays out a roadmap for future developments. The roadmap is a multi-scale path starting from high-energy models of neutrinoless double-beta decay all the way to the low-energy nuclear many-body problem that needs to be solved to supplement measurements of the decay rate. The path goes through a systematic effective-field-theory description of the underlying processes at various scales and needs to be supplemented by lattice quantum chromodynamics input. The white paper also discusses the interplay between neutrinoless double-beta decay, experiments at the Large Hadron Collider and results from astrophysics and cosmology in probing simplified models of lepton-number violation at the TeV scale, and the generation of the matter-antimatter asymmetry via leptogenesis. This white paper is prepared for the topical groups TF11 (Theory of Neutrino Physics), TF05 (Lattice Gauge Theory), RF04 (Baryon and Lepton Number Violating Processes), NF03 (Beyond the Standard Model) and NF05 (Neutrino Properties) within the Theory Frontier, Rare Processes and Precision Frontier, and Neutrino Physics Frontier of the U.S. Community Study on the Future of Particle Physics (Snowmass 2021).

hep-ph↗

arXiv2022

The Present and Future Status of Heavy Neutral Leptons

The existence of non-zero neutrino masses points to the likely existence of multiple SM neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as Heavy Neutral Leptons (HNLs). In this white paper we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding on key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios.

hep-ph↗

arXiv2022

BSM $ν$ physics: complementarity across energies -- a white paper for Snowmass 2021

We reiterate that there is significant complementarity between low-energy experiments and high-energy colliders in exploring new physics associated with neutrino properties and their mass generation mechanisms. Signals of the new physics in the two energy regimes may be correlated with each other from the same underlying dynamics. We demonstrate the complementary nature by presenting the physics reaches for the Seesaw models of Type I, II and III, and for general neutrino interactions in an effective field theory framework, and in a $Z'$ model.

hep-ph↗

arXiv2021

Leptonic anomalous magnetic moments in $ν$SMEFT

We investigate contributions to the anomalous magnetic moments of charged leptons in the neutrino-extended Standard Model Effective Field Theory ($ν$SMEFT). We discuss how $ν$SMEFT operators can contribute to a lepton's magnetic moment at one- and two-loop order. We show that only one operator can account for existing electronic and muonic discrepancies, assuming new physics appears above $1$ TeV. In particular, we find that a right-handed charged current in combination with minimal sterile-active mixing can explain the discrepancy for sterile neutrino masses of $\mathcal O(100)$ GeV while avoiding direct and indirect constraints. We discuss how searches for sterile neutrino production at the (HL-)LHC, measurements of $h\rightarrow μ^+ μ^-$ and searches for $h\rightarrow e^+ e^-$, neutrinoless double beta decay experiments, and improved unitarity tests of the CKM matrix can further probe the relevant parameter space.

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