arXiv subjects

Kai Gallmeister

Publications and source records attributed to Kai Gallmeister.

At least 19 recordsLinked to original sources

arXiv2026

Understanding the impact of nuclear effects on proton decay searches with the GiBUU model

Proton decay searches in the next generation of water Cherenkov detectors, such as Hyper-Kamiokande, are expected to probe the $10^{35}$-year lifetime regime where atmospheric neutrino backgrounds and systematic uncertainties begin to play an increasingly important role. In this study, we employ the GiBUU framework and reevaluate the proton decay search sensitivity for the $\textrm{p}\rightarrow\textrm{e}^{+}π^{0}$ channel by incorporating a typical event reconstruction performance in water Cherenkov detectors. Using sophisticated models implemented in GiBUU -- most notably the mean-field potential and Boltzmann transport -- which have been benchmarked against accelerator neutrino scattering data, in particular pion production, we find that the resulting proton decay signal detection efficiency and atmospheric neutrino background rate are comparable to those previously evaluated for the current and near future water Cherenkov experiments using $\textit{ad hoc}$ nuclear models. In addition to pion final-state interactions, we evaluate the impact of differences in the Fermi momentum distribution of nucleons in the nucleus, as a source of systematic uncertainty, on the signal detection efficiency and the expected background event rate. We find that the uncertainty associated with pion final-state interactions is moderate, whereas the choice of Fermi momentum distribution can significantly affect the estimated atmospheric neutrino background rate and constitutes the dominant contribution. Our study provides an independent and complementary characterisation of nuclear effects on proton decay searches and helps to refine sensitivity estimates in the regime where systematic uncertainties become more relevant.

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arXiv2025

Understanding neutrino pion production with the GiBUU model

Pion production is a major source of systematic uncertainty in neutrino oscillation measurements. We report a systematic investigation of neutrino-induced pion production using MINERvA and MicroBooNE data within the GiBUU theoretical framework. The analysis begins by establishing baseline model parameters using inclusive and pionless data from MINERvA, MicroBooNE, and T2K experiments. We then examine the role of in-medium effects, including resonance broadening and nucleon-nucleon final-state interactions. While agreement with individual datasets can be achieved through specific model configurations, we demonstrate the difficulty of a unified description across all experiments: MINERvA measurements prefer minimum in-medium modifications, whereas MicroBooNE data require the maximum in-medium enhancement, revealing the complexity and richness of the underlying nuclear dynamics.

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arXiv2025

Calorimetric analysis for long-baseline neutrino experiments

In neutrino long-baseline experiments the energy of the incoming neutrino must be reconstructed from observations of the final state. We first discuss the problems that arise for energy conservation during the final-state interactions in a momentum-dependent potential. We then show, for the example of the Deep Underground Neutrino Experiment, that the presence of such a potential is necessarily connected with a large uncertainty in the reconstructed energy. This same uncertainty also affects the determination of energy- and four-momentum-transfers in neutrino-nucleus reactions. We analyze the origins of these uncertainties using transport theory for the description of the evolution of the final state of the reaction. We show that the spectral functions of target nuclei play an essential role not only for the initial neutrino-nucleus interaction but also for the final state evolution.

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arXiv2024

Medium modification of pion production in low energy Au+Au collisions

There is a major mismatch between the charged pion yields in Au+Au collisions at low energies calculated by various transport models and the experimental measured values from the Hades collaboration. In this work, reasonable improvements on the equation of state, in-medium modification of cross sections, and the influence of the nuclear potential for Delta resonances will be investigated in the framework of the GiBUU transport model. As a result, we demonstrate that theoretical calculations can indeed describe the charged pion yields measured by Hades for Au+Au collisions rather well, but that a mismatch then remains between calculations and data for the yields of neutral pions extracted from dileptons within the same experiment.

nucl-th↗

arXiv2022

The Forward Physics Facility at the High-Luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential.

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arXiv2022

Neutrinos at FPF

The GiBUU model is used to obtain information on possible neutrino-nucleus events at the proposed Forward Physics Facility (FPF) at CERN. An FPF neutrino program could contribute to fundamental questions such as formation times, color transparency and the EMC effect for neutrinos.

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arXiv2021

Bjorken flow attractors with transverse dynamics

In the context of the longitudinally boost-invariant Bjorken flow with transverse expansion, we use three different numerical methods to analyze the emergence of attractor solutions in an ideal gas of massless particles exhibiting constant shear viscosity to entropy density ratio $η/ s$. The fluid energy density is initialized using a Gaussian profile in the transverse plane, while the ratio $χ= \mathcal{P}_L / \mathcal{P}_T$ between the longitudinal and transverse pressures is set at initial time $τ_0$ to a constant value $χ_0$ throughout the system employing the Romatschke-Strickland distribution. We introduce the hydrodynamization time $δτ_H = (τ_H - τ_0)/ τ_0$ based on the time $τ_H$ when the standard deviation $σ(χ)$ of a family of solutions with different $χ_0$ reaches a minimum value at the point of maximum convergence of the solutions. In the $0+1{\rm D}$ setup, $δτ_H$ exhibits scale invariance, being a function only of $(η/ s) / (τ_0 T_0)$. With transverse expansion, we find a similar $δτ_H$ computed with respect to the local initial temperature, $T_0(r)$. We highlight the transition between the regimes where the longitudinal and transverse expansions dominate. We find that the hydrodynamization time required for the attractor solution to be reached increases with the distance from the origin, as expected based on the properties of the $0+1{\rm D}$ system defined by the local initial conditions. We argue that hydrodynamization is predominantly the effect of the longitudinal expansion, being significantly influenced by the transverse dynamics only for small systems or for large values of $η/ s$.

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arXiv2021

Solving the puzzle of high temperature light (anti)-nuclei production in ultra-relativistic heavy ion collisions

The creation of loosely bound objects in heavy ion collisions, e.g. light clusters, near the phase transition temperature $\left(T_{\rm ch} \approx 155 \, \rm{MeV} \right)$ has been a puzzling observation that seems to be at odds with Big Bang nucleosynthesis suggesting that deuterons and other clusters are formed only below a temperature $T\approx 0.1-1 \, \text{MeV}$. We solve this puzzle by showing that the light cluster abundancies in heavy ion reactions stay approximately constant from chemical freeze-out to kinetic freeze-out. To this aim we develop an extensive network of coupled reaction rate equations including stable hadrons and hadronic resonances to describe the temporal evolution of the abundancies of light (anti-)(hyper-)nuclei in the late hadronic environment of an ultrarelativistic heavy ion collision. It is demonstrated that the chemical equilibration of the light nuclei occurs on a very short timescale as a consequence of the strong production and dissociation processes. However, because of the partial chemical equilibrium of the stable hadrons, including the nucleon feeding from $Δ$ resonances, the abundancies of the light nuclei stay nearly constant during the evolution and cooling of the hadronic phase. This solves the longstanding contradiction between the thermal fits and the late stage coalescence (and the Big Bang nucleosynthesis) and explains why the observed light cluster yields are compatible with both a high chemical production temperature and a late state emission as modelled by coalescence. We also note in passing that the abundancies of the light clusters in the present approach are in excellent agreement with those measured by ALICE at LHC.

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arXiv2020

Production of Light Nuclei in Heavy Ion Collisions via Hagedorn Resonances

The physical processes behind the production of light nuclei in heavy ion collisions are unclear. The nice theoretical description of experimental yields by thermal models conflicts with the very small binding energies of the observed states, being fragile in such a hot and dense environment. Other available ideas are delayed production via coalescence, or a cooling of the system after the chemical freeze-out according a Saha equation, or a `quench' instead of a thermal freeze-out. A recently derived prescription of an (interacting) Hagedorn gas is applied to consolidate the above pictures. The tabulation of decay rates of Hagedorn states into light nuclei allows to calculate yields usually unaccessable due to very poor Monte Carlo statistics. Decay yields of stable hadrons and light nuclei are calculated. While the scale-free decays of Hagedorn states alone are not compatible with the experimental data, a thermalized hadron and Hagedorn state gas is able to describe the experimental data. Applying a cooling of the system according a Saha-equation with conservation of nucleons and anti-nucleons in number leads to (nearly) temperature independent yields, thus a production of the light nuclei at temperatures much lower than the chemical freeze-out temperature is possible.

hep-ph↗

arXiv2019

Nucleosynthesis in heavy-ion collisions at the LHC via the Saha equation

The production of light (anti-)(hyper-)nuclei in heavy-ion collisions at the LHC is considered in the framework of the Saha equation, making use of the analogy between the evolution of the early universe after the Big Bang and that of "Little Bangs" created in the lab. Assuming that disintegration and regeneration reactions involving light nuclei proceed in relative chemical equilibrium after the chemical freeze-out of hadrons, their abundances are determined through the famous cosmological Saha equation of primordial nucleosynthesis and show no exponential dependence on the temperature typical for the thermal model. A quantitative analysis, performed using the hadron resonance gas model in partial chemical equilibrium, shows agreement with experimental data of the ALICE collaboration on d, $^3$He, $^3_Λ$H, and $^4$He yields for a very broad range of temperatures at $T \lesssim 155$ MeV. The presented picture is supported by the observed suppression of resonance yields in central Pb-Pb collisions at the LHC.

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arXiv2019

The Shear Viscosity to Entropy Density Ratio of Hagedorn States

The fireball concept of Rolf Hagedorn, developed in the 1960's, is an alternative description of hadronic matter. Using a recently derived mass spectrum, we use the transport model GiBUU to calculate the shear viscosity of a gas of such Hagedorn states, applying the Green-Kubo method to Monte-Carlo calculations. Since the entropy density is rising ad infinitum near $T_H$, this leads to a very low shear viscosity to entropy density ratio near $T_H$. Further, by comparing our results with analytic expressions, we find a nice extrapolation behavior, indicating that a gas of Hagedorn states comes close or even below the boundary $1/4π$ from AdS-CFT.

hep-ph↗

arXiv2018

Sensitivity of Neutrino-Nucleus Interaction Measurements to 2p2h Excitations

We calculate the charged-current cross sections obtained at the T2K off-axis near detector for $ν_μ$-induced events without pions and any number of protons in the final state using transport theory as encoded in the GiBUU model. In a comparison with recent T2K data the strength of the 2p2h multinucleon correlations is determined. Linking this to the isospin (T) of the initial nuclear state, it is found that T=0 leads to a significantly better fit of the recent cross sections obtained by T2K, thus achieving consistency of the 2p2h multi-nucleon correlation contributions between electron-nucleus and neutrino-nucleus reactions.

hep-ex↗

arXiv2015

Glueballs amass at RHIC and LHC Colliders! - The early quarkless 1st order phase transition at $T=270$ MeV - from pure Yang-Mills glue plasma to GlueBall-Hagedorn states

The early stage of high multiplicity pp, pA and AA collider is represented by a nearly quarkless, hot, deconfined pure gluon plasma. According to pure Yang-Mills Lattice Gauge Theory, this hot pure glue matter undergoes, at a high temperature, $T_c = 270$ MeV, a first order phase transition into a confined Hagedorn-GlueBall fluid. These new scenario should be characterized by a suppression of high $p_T$ photons and dileptons, baryon suppression and enhanced strange meson production. We propose to observe this newly predicted class of events at LHC and RHIC.

hep-ph↗

arXiv2014

Energy reconstruction in the Long-Baseline Neutrino Experiment

The Long-Baseline Neutrino Experiment aims at measuring fundamental physical parameters to high precision and exploring physics beyond the standard model. Nuclear targets introduce complications towards that aim. We investigate the uncertainties in the energy reconstruction, based on quasielastic scattering relations, due to nuclear effects. The reconstructed event distributions as a function of energy tend to be smeared out and shifted by several 100 MeV in their oscillatory structure if standard event selection is used. We show that a more restrictive experimental event selection offers the possibility to reach the accuracy needed for a determination of the mass ordering and the $CP$-violating phase. Quasielastic-based energy reconstruction could thus be a viable alternative to the calorimetric reconstruction also at higher energies.

nucl-th↗

arXiv2011

Description of fully differential Drell-Yan pair production

We investigate Drell-Yan pair production in a QCD inspired model, which takes into account all relevant hard processes up to $O(α_s)$. To address the known shortfalls of such a fixed order calculation we introduce phenomenological parton distributions for initial transverse momentum and quark mass, and devise a subtraction scheme to avoid double-counting when utilizing the standard longitudinal parton distribution functions. We show that we can reproduce Drell-Yan transverse momentum and invariant mass spectra from different proton-proton, proton-nucleus and antiproton-nucleus experiments and at different energies without the need for a $K$ factor. Fixing our parameters at these spectra, we make predictions for Drell-Yan transverse momentum spectra at low hadronic energies, which will be measured for example at $\bar{\text{P}}$ANDA in antiproton-proton collisions.

hep-ph↗

arXiv2011

In-Medium Properties of Vector Mesons in a Transport Approach

We present dilepton spectra from p+p and p+Nb collisions at a kinetic beam energy of 3.5 GeV, which were simulated with the GiBUU transport model assuming different in-medium scenarios. We compare these spectra to preliminary HADES data and show that GiBUU can describe the data reasonably well. Our simulations indicate that the intermediate dilepton-mass region is sensitive to the N-Delta electromagnetic transition form factor, which up to now is unmeasured in the time-like region.

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arXiv2009

Pionic transparency in semi-exclusive electroproduction off nuclei

We investigate the early onset of pionic color transparency ($π$CT) observed at Jefferson Laboratory (JLAB) in semi--exclusive pion electroproduction reaction $A(e,e'π^+)$ off nuclei. In the present description the primary $γ^*p \to π^+ n$ interaction is described very well both for the longitudinal and the transverse polarizations. For the final state interactions a coupled--channel treatment of the interactions of transmitted hadrons allows to go beyond the Glauber approximation. We show that a proper distinction between the soft hadronic and hard partonic components of the electroproduction amplitude is essential for a quantitative description of the measured nuclear transparency. The data are well reproduced if one assumes that point--like configurations are produced in the regime of hard deep--inelastic scattering (DIS) off partons and dominate the transverse channel.

nucl-th↗

arXiv2009

Deeply inelastic pions in the exclusive reaction $p(e,e'π^+)n$ above the resonance region

A model for the $p(e,e'π^+)n$ reaction which combines an improved treatment of gauge invariant meson--exchange currents and hard deep--inelastic scattering (DIS) of virtual photons off nucleons is proposed. It is shown that DIS dominates and explains the transverse response at moderate and high photon virtualities $Q^2$ whereas the longitudinal response is dominated by hadronic degrees of freedom and the pion electromagnetic form factor. This leads to a combined description of the longitudinal and transverse components of the cross section in a wide range of photon virtuality $Q^2$ and momentum transfer to the target $t$ and solves the longstanding problem of the observed large transverse cross sections. The latter are shown to be sensitive to the intrinsic transverse momentum distribution of partons.

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