arXiv subjects

R. Vogt

Publications and source records attributed to R. Vogt.

At least 19 recordsLinked to original sources

arXiv2026

Improving the Predictive Capability of the Fission Reaction Event Yield Algorithm ($\mathtt{FREYA}$)

We determine the optimal parameters for thermal neutron-induced fission of $^{233,235}$U and $^{239,241}$Pu in the complete event fission model $\mathtt{FREYA}$. First, we revisit and, in most cases, improve the prior values determined for spontaneous fission using a genetic algorithm. Our optimization procedure is then applied to thermal neutron-induced fission, replacing the empirically-chosen parameters previously employed in $\mathtt{FREYA}$. Finally, the optimized parameter values are used to make predictions for spontaneous and thermal neutron-induced fission observables not included in the fits. This work represents the first step in a broader program to study neutron-induced fission as a function of incident neutron energy, to systematically improve the performance of $\mathtt{FREYA}$, capturing any energy-dependent trends of the physics-based $\mathtt{FREYA}$ parameters.

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arXiv2026

Dilepton Correlations from Heavy Flavor Decays

Background: Azimuthal correlations between heavy flavor hadrons have been previously studied in $p+p$ collisions (Phys. Rev. C {\bf 98}, 034907 (2018), {\bf 101}, 034910 (2020)). These studies found good agreement with the data and provide a baseline for further studies in $p+A$ and $A+A$ collisions. Purpose: This work extends those studies to heavy flavor hadron decays to low mass lepton pairs. The low mass dilepton region is important for heavy ion collisions because of the interest in thermal dilepton production as a signature of the early time dynamics of the medium. Methods: Building on previous work, azimuthal correlations between leptons from semileptonic decays of heavy flavor hadrons are examined. The exclusive \textsc{HVQMNR} code is used in the calculations, made in the PHENIX acceptance at $\sqrt{s} = 200$~GeV and for dielectrons in ALICE at $\sqrt{s} = 13$~TeV. The $b \overline b$ decay contributions subtract like-sign lepton pairs from the opposite-sign signal. Results: The next-to-leading order calculations reproduce the trends of the PHENIX data. The calculations at 13~TeV show a change in signal as electron pair $p_T$ is increased, with the peak of the $\Delta \phi$ distribution moving from $\Delta \phi \sim \pi$ to $\sim 0$ and the contribution from bottom decays becoming dominant. The sensitivity of the signal to $k_T$ broadening is also studied and found to be small. Conclusions: It is found that the dependence on $k_T$ broadening previously observed is significantly reduced by the decay process. Despite this, the correlations between decay leptons retains some memory of the correlations between the parent hadrons in $p+p$ collisions. However, to study these correlations in heavy-ion collisions, it is necessary to separate them from thermal dilepton production in the same mass region.

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arXiv2026

Physics Opportunities with a Fixed-Target Program at the Electron-Ion Collider

A fixed-target program at the Electron-Ion Collider (EIC) would broaden the facility's scientific reach by providing key measurements for studies of cold nuclear matter (CNM), the QCD phase diagram, and nuclear reactions relevant for space radiation. Constraining CNM effects is essential for interpreting observables in proton-nucleus ($p+A$) and nucleus-nucleus ($A+A$) collisions, yet these effects are poorly understood at low center-of-mass energies. In particular, the range $\sqrt{s}\approx10$--20 GeV, where several CNM effects may compete at similar scales, has not been explored with high statistical precision. Mapping the QCD phase diagram similarly requires high-statistics $A+A$ data with broad rapidity and transverse-momentum coverage to probe the onset of deconfinement and the possible location of the QCD critical point (CP). Currently, such data are limited at 4.5 GeV $< \sqrt{s_{NN}} < 7.7$ GeV A fixed-target program at the EIC would fill these gaps, providing CNM baselines and complementary data for QCD CP studies. By delivering high luminosity and systematic measurements across a broad range of nuclear targets, the program would link $p+A$ and $A+A$ systems at the same center-of-mass energies, enabling a unified, quantitative description of cold QCD matter and clarifying the interpretation of QGP signatures in $A+A$ collisions at low energies where comparable $p+A$ data are lacking. Finally, the program would offer a unique opportunity to measure nuclear cross sections critical for improving cosmic-ray models, including studies of space-radiation protection for both autonomous spacecraft and long-duration human spaceflight.

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arXiv2025

Nuclear Cold QCD: Review and Future Strategy

This review examines data from hadron-nucleus collisions, primarily focusing on hard processes like Drell-Yan, heavy flavor and quarkonium production. It highlights observed modifications of particle yields as functions of momentum and rapidity, aiming to clarify the underlying QCD effects in cold nuclear matter (CNM). The paper outlines strategies for future experiments, including the Electron-Ion Collider (EIC), to distinguish between these effects. Key questions address the universality of suppression mechanisms and the role of non-perturbative physics, providing a road map for upcoming nuclear data.

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arXiv2024

Tetraquarks from Intrinsic Heavy Quarks

A number of new four-quark states containing from one to four charm or anti-charm quarks have been observed recently. Many of these new states have been discovered at the LHC. The production of these states via intrinsic charm in the proton is investigated. The tetraquark masses obtained in this approach, while dependent on the internal transverse momenta of the partons in the state, are shown to agree well with the measured masses. These calculations can provide some insight into the nature of the tetraquark candidates, whether as a bound meson pair or as a looser configuration of four individual partons. The kinematic distributions of these states as a function of rapidity and transverse momentum are also studied. The possible cross sections for these states are finally considered.

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arXiv2024

Comparative Study of Quarkonium Transport in Hot QCD Matter

This document summarizes the efforts of the EMMI Rapid Reaction Task Force on "Suppression and (re)generation of quarkonium in heavy-ion collisions at the LHC", centered around their 2019 and 2022 meetings. It provides a review of existing experimental results and theoretical approaches, including lattice QCD calculations and semiclassical and quantum approaches for the dynamical evolution of quarkonia in the quark-gluon plasma as probed in high-energy heavy-ion collisions. The key ingredients of the transport models are itemized to facilitate comparisons of calculated quantities such as reaction rates, binding energies, and nuclear modification factors. A diagnostic assessment of the various results is attempted and coupled with an outlook for the future.

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arXiv2023

Contribution from Intrinsic Charm Production to Fixed-Target Interactions at the LHC

Background: Intrinsic charm, nonperturbative charm in the hadron wavefunction, has long been speculated but has never been satisfactorily proven. Open charm and $J/\psi$ measurements in a fixed-taget configuration at the LHCb searched for this contribution but reported no evidence. Purpose: $\overline D$ meson and $J/\psi$ production is calculated for the SMOG fixed-target configuration in the LHCb experiment using a combination of perturbative QCD and intrinsic charm to see whether intrinsic chaarm would indeed be observable in the SMOG kinematics. Methods: Open charm and $J/\psi$ production is calculated to next-to-leading order in perturbative QCD. Because a gas jet nuclear target is used, cold nuclear matter effects are included in the perturbative calculations. The intrinsic charm is calculated assuming production from a $|uud c \overline c \rangle$ Fock state. Results: The differential rapidity and transverse momentum distributions in $p+{\rm Ne}$, $p+{\rm He}$ and $p+{\rm Ar}$ fixed-target interactions are calculated in the SMOG acceptance and compared to data. The predicted asymmetries between $\overline D$ (leading charm) and $D$ (nonleading charm) are also shown. Conclusions: The contribution from intrinisic charm is small and decreases with center of mass energy. The calculations agree well with the current SMOG data, with or without intrinsic charm.

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arXiv2022

Energy Dependence of Intrinsic Charm Production: What is the Best Energy for Observation?

Background: A nonperturbative charm production contribution, known as intrinsic charm, was predicted in the early 1980s. Recent results have provided new evidence for its existence but further confirmation is needed. Purpose: $J/ψ$ and $\bar D$ meson production are calculated with a combination of perturbative QCD and intrinsic charm to determine the best energy range to study intrinsic charm production. Methods: $J/ψ$ and $\bar D$ meson production are calculated in perturbative QCD to next-to-leading order in the cross section. Cold nuclear matter effects, including nuclear modification of the parton densities and $p_T$ broadening by multiple scattering are taken into account in the production of both; absorption by nucleons is also included for the $J/ψ$. Contributions from intrinsic charm are calculated assuming production from a $|uud c \bar c \rangle$ Fock state. Results: The $J/ψ$ and $\bar D$ meson rapidity and $p_T$ distributions are calculated as a function of rapidity and transverse momentum $p_T$ over a wide range of center-of-mass energies with and without intrinsic charm in $p+p$ collisions. The nuclear modification factor, $R_{pA}$, is also calculated for $p+{\rm Pb}$ interactions at appropriate energies. Previous fixed-target data as a function of Feynman $x$, $x_F$, are also compared to calculations within the approach. Good agreement with the data is found when intrinsic charm is included. Conclusions: The intrinsic charm signal may be largest at midrapidity for future low energy fixed target experiments such as the proposed NA60+.

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arXiv2021

Bottom Tetraquark Production at RHIC?

Background: A resonance has been observed by the ANDY Collaboration at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory in Cu+Au collisions at center-of-mass energy $\sqrt{s} = 200$ GeV and at forward rapidity with an average mass of 18.15 GeV. The Collaboration suggests that it is a $b \overline b b \overline b$ tetraquark state decaying to two $Υ$(1S) states, each measured through the $Υ\rightarrow ggg$ channel. Purpose: Their suggestion is investigated assuming that the two $Υ$ states are produced through the materialization of a $|uud b\overline b b \overline b \rangle$ Fock state in the projectile. Methods: The $Υ$ pair mass and rapidity distributions arising from such a state are calculated. The production of an $X_b(b \overline b b \overline b)$ tetraquark state from the same Fock configuration is also investigated. The dependence on bottom quark mass and their transverse momentum range is also studied. Results: It is found that double $Υ$ production from these $|uud b \overline b b \overline b \rangle$ states peak in the rapidity range of the ANDY detector. The $Υ$ pair and $X_b$ masses are, however, higher than the mass reported by the ANDY Collaboration. Conclusions: The results obtained from these calculations are incompatible with the ANDY result. They are, however, compatible with previous predictions of $b \overline b b \overline b$ tetraquark masses.

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arXiv2021

Generation of fragment angular momentum in fission

A recent analysis of experimental data [J. Wilson $et. al$, Nature $\mathbf 590$, 566 (2021)] found that the angular momenta of nuclear fission fragments are uncorrelated. Based on this finding, the authors concluded that the spins are therefore determined only $after$ scission has occurred. We show here that the nucleon-exchange mechanism, as implemented in the well-established event-by-event fission model $\mathtt{FREYA}$, while agitating collective rotational modes in which the two spins are highly correlated, nevertheless leads to fragment spins that are largely uncorrelated. This fact invalidates the reasoning of those authors. Furthermore, it was reported [J. Wilson $et. al$, Nature $\mathbf 590$, 566 (2021)] that the mass dependence of the average fragment spin has a sawtooth structure. We demonstrate that such a behavior naturally emerges when shell and deformation effects are included in the moments of inertia of the fragments at scission.

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arXiv2021

Limits on Intrinsic Charm Production from the SeaQuest Experiment

Background: A nonperturbative charm production contribution, known as intrinsic charm, has long been speculated but has never been satisfactorily proven. The SeaQuest experiment at FNAL is in an ideal kinematic region to provide evidence of $J/ψ$ production by intrinsic charm. Purpose: $J/ψ$ production in the SeaQuest kinematics is calculated with a combination of perturbative QCD and intrinsic charm to see whether the SeaQuest data can put limits on an intrinsic charm contribution. Methods: $J/ψ$ production in perturbative QCD is calculated to next-to-leading order in the cross section. Cold nuclear matter effects include nuclear modification of the parton densities, absorption by nucleons, and $p_T$ broadening by multiple scattering. The $J/ψ$ contribution from intrinsic charm is calculated assuming production from a $|uud c \overline c \rangle$ Fock state. Results: The nuclear modification factor, $R_{pA}$, is calculated as a function of $x_F$ and $p_T$ for $p+$C, $p+$Fe, and $p+$W interactions relative to $p+$d. Conclusions: The SeaQuest kinematic acceptance is ideal for testing the limits on intrinsic charm in the proton.

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arXiv2020

Study of angular momentum effects in fission

Background: The role of angular momentum in fission has long been discussed but the observable effects are difficult to quantify. Purpose: We discuss a variety of effects associated with angular momentum in fission and present quantitative illustrations. Methods: We employ the fission simulation model $\mathtt{FREYA}$ which is well suited for this purpose because it obeys all conservation laws, including linear and angular momentum conservation at each step of the process. We first discuss the implementation of angular momentum in $\mathtt{FREYA}$ and then assess particular observables, including various correlated observables. We also study potential effects of neutron-induced fission of the low-lying isomeric state of $^{235}$U relative to the ground state. Results: The fluctuations inherent in the fission process ensure that the spin of the initial compound nucleus has only a small influence on the fragment spins which are therefore nearly uncorrelated. There is a marked correlation between the spin magnitude of the fission fragments and the photon multiplicity. We also consider the dynamical anisotropy caused by the rotation of an evaporating fragment and study especially the distribution of the projected neutron-neutron opening angles, showing that while it is dominated by the effect of the evaporation recoils, it is possible to extract the signal of the dynamical anisotropy by means of a Fourier decomposition. Finally, we note that the use of an isomeric target, $^{235 {\rm m}}$U($n_{\rm th}$,f), may enhance the symmetric yields and can thus result in higher neutron multiplicities for low total fragment kinetic energy.

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arXiv2020

$b \bar b$ Kinematic Correlations in Cold Nuclear Matter

Background: The LHCb Collaboration has studied a number of kinematic correlations between $B$-hadron pairs through their subsequent decays to $J/ψ$ pairs at 7 and 8 TeV for four minimum values of the $J/ψ$ $p_T$. Purpose: In this work, these measurements are compared to calculations of $b \bar b$ pairs and their hadronization and inclusive decays to $J/ψJ/ψ$ are compared to the same observables. Potential cold matter effects on the $b \bar b$ pair observables are discussed to determine which are most likely to provide insights about the system and why. Methods: The calculations, employing the exclusive HVQMNR code, assume the same intrinsic $k_T$-broadening and fragmentation as in [R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907]. The pair distributions presented by LHCb are calculated in this approach, both for the parent $b \bar b$ and the $J/ψJ/ψ$ pairs produced in their decay. The sensitivity of the results to the intrinsic $k_T$ broadening is shown. The theoretical uncertainties due to the $b$ quark mass and scale variations on both the initial $b \bar b$ pairs and the resulting $J/ψ$ pairs are also shown. Possible effects due to the presence of the nucleus are studied by increasing the size of the $k_T$ broadening and modification of the fragmentation parameter. Results: Good agreement with the LHCb data is found for all observables. The parent $b \bar b$ distributions are more sensitive to the $k_T$ broadening than are the final-state $J/ψ$ pairs. Conclusions: Next-to-leading order calculations with $k_T$ broadening, as in [R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907], can describe all correlated observables. Multiple measurements of correlated observables are sensitive to different nuclear effects which can help distinguish between them.

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arXiv2019

Review of predictions of hard probes in $p+$Pb collisions at $\sqrt{s_{NN}} = 5.02$ and 8.16 TeV and comparison with data

Predictions have been compiled for the $p+$Pb LHC runs, focusing on production of hard probes in cold nuclear matter. These predictions were first made for the $\sqrt{s_{_{NN}}} = 5.02$ TeV $p+$Pb run and were later compared to the available data. A similar set of predictions were published for the 8.16~TeV $p+$Pb run. A selection of the predictions are reviewed here.

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arXiv2018

High resolution measurement of tagged two-neutron energy and angle correlations in Cf-252(sf)

Background: Spontaneous fission events emit prompt neutrons correlated with one another in emission angle and energy. Purpose: We explore the relationship in energy and angle between correlated prompt neutrons emitted from 252Cf spontaneous fission. Methods: Measurements with the Chi-Nu array provide experimental data for coincident neutrons tagged with a fission chamber signal with 10 degree angular resolution and 1 ns timing resolution for time-of-flight energy calculations. The experimental results are compared to simulations produced by the fission event generators CGMF, FREYA, and MCNPX-POLIMI IPOL(1)=1. Results: We find that the measurements and the simulations all exhibit anisotropic neutron emission, though differences exist between fission event generators. Conclusions: This work shows that the dependence of detected neutron energy on the energy of a neutron detected in coincidence, although weak, is non-negligible, indicating that there may be correlations in energy between two neutrons emitted in the same fission event.

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arXiv2018

Heavy Flavor Azimuthal Correlations in Cold Nuclear Matter

Background: It has been proposed that the azimuthal distributions of heavy flavor quark-antiquark pairs may be modified in the medium of a heavy-ion collision. Purpose: This work tests this proposition through next-to-leading order (NLO) calculations of the azimuthal distribution, $dσ/dϕ$, including transverse momentum broadening, employing $ $ and fragmentation in exclusive $Q \bar Q$ pair production. While these studies were done for $p+p$, $p + \bar p$ and $p+$Pb collisions, understanding azimuthal angle correlations between heavy quarks in these smaller, colder systems is important for their interpretation in heavy-ion collisions. Methods: First, single inclusive $p_T$ distributions calculated with the exclusive HVQMNR code are compared to those calculated in the fixed-order next-to-leading logarithm approach. Next the azimuthal distributions are calculated and sensitivities to $ $, $p_T$ cut, and rapidity are studied at $\sqrt{s} = 7$ TeV. Finally, calculations are compared to $Q \bar Q$ data in elementary $p+p$ and $p + \bar p$ collisions at $\sqrt{s} = 7$ TeV and 1.96 TeV as well as to the nuclear modification factor $R_{p {\rm Pb}}(p_T)$ in $p+$Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV measured by ALICE. Results: The low $p_T$ ($p_T < 10$ GeV) azimuthal distributions are very sensitive to the $k_T$ broadening and rather insensitive to the fragmentation function. The NLO contributions can result in an enhancement at $ϕ\sim 0$ absent any other effects. Agreement with the data was found to be good. Conclusions: The NLO calculations, assuming collinear factorization and introducing $k_T$ broadening, result in significant modifications of the azimuthal distribution at low $p_T$ which must be taken into account in calculations of these distributions in heavy-ion collisions.

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arXiv2018

Correlated Prompt Fission Data in Transport Simulations

Detailed information on the fission process can be inferred from the observation, modeling and theoretical understanding of prompt fission neutron and $γ$-ray~observables. Beyond simple average quantities, the study of distributions and correlations in prompt data, e.g., multiplicity-dependent neutron and \gray~spectra, angular distributions of the emitted particles, $n$-$n$, $n$-$γ$, and $γ$-$γ$~correlations, can place stringent constraints on fission models and parameters that would otherwise be free to be tuned separately to represent individual fission observables. The FREYA~and CGMF~codes have been developed to follow the sequential emissions of prompt neutrons and $γ$-rays~from the initial excited fission fragments produced right after scission. Both codes implement Monte Carlo techniques to sample initial fission fragment configurations in mass, charge and kinetic energy and sample probabilities of neutron and $γ$~emission at each stage of the decay. This approach naturally leads to using simple but powerful statistical techniques to infer distributions and correlations among many observables and model parameters. The comparison of model calculations with experimental data provides a rich arena for testing various nuclear physics models such as those related to the nuclear structure and level densities of neutron-rich nuclei, the $γ$-ray~strength functions of dipole and quadrupole transitions, the mechanism for dividing the excitation energy between the two nascent fragments near scission, and the mechanisms behind the production of angular momentum in the fragments, etc. Beyond the obvious interest from a fundamental physics point of view, such studies are also important for addressing data needs in various nuclear applications. (See text for full abstract.)

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arXiv2017

Improved modeling of photon observables with FREYA

The event-by-event fission model FREYA has been improved, in particular to address deficiencies in the calculation of photon observables. We discuss the improvements that have been made and introduce several new variables, some detector dependent, that affect the photon observables. We show the sensitivity of FREYA to these variables. We then compare the results to the available photon data from spontaneous and thermal neutron-induced fission.

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