# Christoph HeroldSuranaree University of Technology | sut · School of Physics

Christoph Herold

PhD

## About

60

Publications

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Introduction

## Publications

Publications (60)

The pion-to-proton ratio is identified as a potential signal for a non-equilibrium first-order chiral phase transition in heavy-ion collisions, as the pion multiplicity is directly related to entropy production. To showcase this effect, a non-equilibrium Bjorken expansion starting from realistic initial conditions along a Taub adiabat is used to si...

We investigate the coalescence factors $B_2$ and $B_3$ at low collision energies ($\sqrt{s_\mathrm{NN}}<6$ GeV) with special focus on the HADES and RHIC-BES experiments. It is shown that, in order to properly interpret the coalescence factors $B_A$, two important corrections are necessary: I) $B_2$ has to be calculated using the proton $\times$ neu...

We study cumulants of the chiral order parameter as function of beam energy as a possible signal for the presence of a critical end point and first-order phase transition in the QCD phase diagram. We model the expansion of a heavy-ion collision by a fluid dynamic expansion coupled to the explicit propagation of the chiral order parameter sigma via...

Correlations between the harmonic flow coefficients $$v_1$$ v 1 , $$v_2$$ v 2 , $$v_3$$ v 3 and $$v_4$$ v 4 of nucleons in semi-peripheral Au+Au collisions at a beam energy of 1.23 AGeV are investigated within the hadronic transport approach ultra-relativistic quantum molecular dynamics (UrQMD). In contrast to ultra-relativistic collision energies...

We study cumulants of the chiral order parameter as function of beam energy as a possible signal for the presence of a critical end point and first-order phase transition in the QCD phase diagram. We model the expansion of a heavy-ion collision by a fluid dynamic expansion coupled to the explicit propagation of the chiral order parameter sigma via...

STAR's beam energy scan program at RHIC provides data on net-proton number fluctuations with the goal to detect the QCD critical point and first-order phase transition. Interpreting these experimental signals requires a vital understanding of the interplay of critical phenomena and the nonequilibrium dynamics of the rapidly expanding fireball. We s...

Correlations between the harmonic flow coefficients $v_1$, $v_2$, $v_3$ and $v_4$ of nucleons in semi-peripheral Au+Au collisions at a beam energy of 1.23~AGeV are investigated within the hadronic transport approach Ultra-relativistic Quantum Molecular Dynamics (UrQMD). In contrast to ultra-relativistic collision energies (where the flow coefficien...

We study (anti)deuteron formation rates in heavy-ion collisions in the framework of a wave-function based coalescence model. The main feature of our model is that nucleons are emitted from the whole spherically symmetric fireball volume, while antinucleons are emitted only from a spherical shell close to the surface. In this way, the model accounts...

We study (anti)deuteron formation rates in heavy-ion collisions in the framework of a wave-function based coalescence model. The main feature of our model is that nucleons are emitted from the whole spherically symmetric fireball volume, while antinucleons are emitted only from a spherical shell close to the surface. In this way, the model accounts...

Based on $14.7~\textrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected with the BESIII detector at the BEPCII collider at 17 different center-of-mass energies between $3.7730~\textrm{GeV}$ and $4.5995~\textrm{GeV}$, Born cross sections of the two processes $e^+e^- \to p\bar{p}\eta$ and $e^+e^- \to p\bar{p}\omega$ are measured for the first time....

In Ref. [1] the BESIII collaboration published a cross section measurement of the process e+e−→π+π− in the energy range between 600 and 900 MeV. In this corrigendum, we report a corrected evaluation of the statistical errors in terms of a fully propagated covariance matrix. The correction also yields a reduced statistical uncertainty for the hadron...

We study the influence of the centrality definitionCentrality definition and detector efficiency on the net-proton kurtosis for minimum bias AuAu collisions at a beam energy of GeV by using the UrQMD model. We find that different ways of defining the centrality lead to different cumulant ratiosCumulant ratios. Moreover, we demonstrate that the kurt...

We explore the scaling properties of the elliptic and quadrangular flow of deuterons and protons in Au+Au reactions at a beam energy of 1.23 AGeV within the UrQMD approach. These investigations are of great interest for the HADES experiment at GSI that has recently studied the flow of light nuclei. In the present studies, deuterons are formed via p...

We investigate the collision energy dependence of deuteron and antideuteron emission in the RHIC-BES low- to mid-energy range sNN = 4.6–200 GeV where the formation rate of antinuclei compared to nuclei is strongly suppressed. In the coalescence picture, this can be understood as bulk emission for nuclei in contrast to surface emission for antinucle...

We present different methods of unsupervised learning which can be used for outlier detection in high energy nuclear collisions. The UrQMD model is used to generate the bulk background of events as well as different variants of outlier events which may result from misidentified centrality or detector malfunctions. The methods presented here can be...

We investigate the collision energy dependence of deuteron and antideuteron emission in the RHIC-BES low- to mid-energy range $\sqrt{s_{NN}} = 4.6-200$ GeV where the formation rate of antinuclei compared to nuclei is strongly suppressed. In the coalescence picture, this can be understood as bulk emission for nuclei in contrast to surface emission f...

We study the influence of the centrality definition and detector efficiency on the net-proton kurtosis for minimum bias Au+Au collisions at a beam energy of $\sqrt{s_{\mathrm{NN}}}= 7.7$ GeV by using the UrQMD model. We find that different ways of defining the centrality lead to different cumulant ratios. Moreover, we demonstrate that the kurtosis...

We explore the directed, elliptic, triangular and quadrangular flow of deuterons in Au+Au reactions at a beam energy of 1.23 AGeV within the UrQMD approach. These investigations are of direct relevance for the HADES experiment at GSI that has recently presented first data on the flow of light clusters in Au+Au collisions at 1.23 AGeV. To address th...

This study is motivated by upcoming data from the high acceptance di‐electron spektrometer (HADES) collaboration at gesellschaft für schwerionenforschung, which presented preliminary data on a possible mass shift of the Δ(1232) resonance in central Au + Au reactions at Elab = 1.23 AGeV. This effect is explored via the Ultra Relativistic Quantum Mol...

The production of deuterons and heavy clusters such as triton and helium (or even hypertriton) has gained increased attention during the last years. This attention was mainly stimulated by the recent hypertriton data and has led to the question of whether cluster production is driven by coalescence of its constituents or by thermal emission of the...

We explore the rapidity and transverse momentum dependence of collective flow harmonics of deuterons and protons in Au + Au reactions at a beam energy of 1.23 AGeV within the UrQMD approach. These investigations are of direct relevance for the high acceptance di electron spectrometer (HADES) experiment at the GSI Helmholtzzentrum für Schwerionenfor...

The HADES experiment at GSI will soon provide data on the production and properties of Δ(1232) baryons from Au + Au reactions at 1.23 AGeV. Using the Ultra Relativistic Quantum Molecular Dynamics model, we predict the yield and spectra of Δ(1232) resonances. In addition we show that one expects to observe a mass shift of the Δ(1232) resonance on th...

We explore the directed, elliptic, triangular and quadrangular flow of deuterons in Au+Au reactions at a beam energy of 1.23 AGeV within the UrQMD approach. These investigations are of direct relevance for the HADES experiment at GSI that has recently presented first data on the flow of light clusters in Au+Au collisions at 1.23 AGeV. To address th...

The HADES experiment at GSI will soon provide data on the production and properties of $\Delta$ baryons from Au+Au reactions at 1.23 AGeV. Using the UrQMD model, we predict the yield and spectra of $\Delta$ resonances. In addition we show that one expects to observe a mass shift of the $\Delta$ resonance on the order of 40 MeV in the reconstructabl...

We study the production of entropy in the context of a nonequilibrium chiral phase transition. The dynamical symmetry breaking is modeled by a Langevin equation for the order parameter coupled to the Bjorken dynamics of a quark plasma. We investigate the impact of dissipation and noise on the entropy and explore the possibility of reheating for cro...

Ultrarelativistic quantum molecular dynamics phase-space coalescence calculations for the production of deuterons are compared with available data for various reactions from the Facility for Antiproton and Ion Research energy regime energy regime over the CERN Super Proton Synchrotron–Relativistic Heavy Ion Collider Beam Energy Scan region up to CE...

We study the production of entropy in the context of a nonequilibrium chiral phase transition. The dynamical symmetry breaking is modeled by a Langevin equation for the order parameter coupled to the Bjorken dynamics of a quark plasma. We investigate the impact of dissipation and noise on the entropy and explore the possibility of reheating for cro...

UrQMD phase-space coalescence calculations for the production of deuterons are compared with available data for various reactions from the GSI/FAIR energy regime up to LHC. It is found that the production process of deuterons, as reflected in their rapidity and transverse momentum distributions in p+p, p+A and A+A collisions at a beam energies star...

Recent lattice QCD data on higher order susceptibilities of Charm quarks provide the opportunity to explore Charm quark equilibration in the early quark gluon plasma (QGP) phase. Here, we propose to use the lattice data on second and fourth order net Charm susceptibilities to infer the Charm quark equilibration temperature and the corresponding vol...

To classify clusters of hits in the electromagnetic calorimeter (EMC) of ANDA (antiProton ANnihilation at DArmstadt), one has to match these EMC clusters with tracks of charged particles reconstructed from hits in the tracking system. Therefore the tracks are propagated to the surface of the EMC and associated with EMC clusters which are nearby and...

We investigate higher cumulants of the sigma field as the chiral order parameter at the QCD phase transition. We derive a thermodynamic expression for the skewness and kurtosis from susceptibilities and use these to determine \( S\sigma\) and \( \kappa\sigma^2\) for the sigma field in equilibrium. In a next step, we study the behavior of these cumu...

We study the production of charged particles (K+, K−, p, and p¯) in proton-proton (pp) collisions at s=0.9TeV within the paciae model whose parameters we fix by comparing the yield of charged particles with experimental data from ALICE. We analyze the production of K−p and K+p¯ bound states with the paciae+dcpc model. Results of our work indicate t...

We study fluctuations of the sigma field and the net-baryon number on the crossover side of the critical point within the model of nonequilibrium chiral fluid dynamics (NχFD). Herein, the sigma field as the chiral order parameter is propagated explicitly and coupled to a fluid of quarks. Before investigating these fluctuations in an expanding noneq...

We investigate higher cumulants of the sigma field as the chiral order parameter at the QCD phase transition. We derive a thermodynamic expression for the skewness and kurtosis from susceptibilities and use these to determine $S\sigma$ and $\kappa\sigma^2$ for the sigma field in equilibrium. In a next step, we study the behavior of these cumulants...

We study the dependence of the normalized moments of the net-proton multiplicity distributions on the definition of centrality in relativistic nuclear collisions at a beam energy of $\sqrt{s_{\mathrm{NN}}}= 7.7$ GeV. Using the UrQMD model as event generator we find that the centrality definition has a large effect on the extracted cumulant ratios....

We study the formation of domain structures due to spontaneous breakdown of center symmetry at high temperatures in quenched QCD. We develop a phenomenological model for the explicit propagation of the Polyakov loop as the relevant order parameter of the deconfinement phase transition. The surface tension in the equation of motion is fit in compari...

We present an analysis of the net-proton kurtosis on the crossover side of the critical point within the model of nonequilibrium chiral fluid dynamics (NχFD). The chiral order parameter is propagated explicitly and coupled to an expanding fluid of quarks and gluons to describe the dynamical situation in a heavy-ion collision. After implementing a p...

Heavy-ion collisions performed in the beam energy range accessible by the NICA collider facility are expected to produce systems of extreme net-baryon densities and can thus reach yet unexplored regions of the QCD phase diagram. Here, one expects the phase transition between the plasma of deconfined quarks and gluons and the hadronic matter to be o...

We investigate the evolution of the net-proton kurtosis and the kurtosis of
the chiral order parameter near the critical point in the model of
nonequilibrium chiral fluid dynamics. The order parameter is propagated
explicitly and coupled to an expanding fluid of quarks and gluons in order to
describe the dynamical situation in a heavy-ion collision...

The region of large net-baryon densities in the QCD phase diagram is expected
to exhibit a first-order phase transition. Experimentally, its study will be
one of the primaryobjectives for the upcoming FAIR accelerator. We model the
transition between quarks and hadrons in a heavy-ion collision using a fluid
which is coupled to the explicit dynamics...

We study the variance and kurtosis of the net-baryon number in a fluid
dynamical model for heavy-ion collisions. It is based on an effective chiral
model with dilatons for the strong coupling regime of QCD. Taking into account
spinodal instabilities, we demonstrate that this model exhibits a diverging
quark number susceptibility and kurtosis all al...

Experimental signals for a possible QCD critical point and first-order phase transition are strongly influenced by the rapid nonequilibrium dynamics during a heavy-ion collision. In order to estimate and understand these effects we study the cooling through the phase transition within a nonequilibrium chiral fluid dynamics model. The order paramete...

We consider the (3+1) dimensional expansion and cooling of the chirally-restored and deconfined matter at finite net-baryon densities as expected in heavy-ion collisions at moderate energies. In our approach, we consider chiral fields and the Polyakov loop as dynamical variables coupled to a medium represented by a quark-antiquark fluid. The intera...

The FAIR facility will make the region of high net-baryon densities experimentally accessible, where a first-order phase transition is conjectured. We investigate the dynamics of chiral symmetry breaking and the onset of confinement during a heavy-ion collision at large baryochemical potentials within a nonequilibrium chiral fluid dynamics model in...

We consider the (3+1) dimensional expansion and cooling of the
chirally-restored and deconfined matter at finite net-baryon densities as
created in heavy-ion collisions. In our approach, chiral fields and the
Polyakov loop propagate explicitly within a medium represented by a
quark-antiquark fluid. The interaction between the fields and the fluid l...

We present a fully dynamical model to study the chiral and deconfinement
transition of QCD simultaneously. The quark degrees of freedom constitute a
heat bath in local equilibrium for both order parameters, the sigma field and a
dynamical Polyakov loop. The nonequilibrium evolution of these fields is
described by Langevin equations including dissip...

The search for the critical point is one of the central issues that will
be investigated in the upcoming FAIR project. For a profound theoretical
understanding of the expected signals we go beyond thermodynamic studies
and present a fully dynamical model for the chiral and deconfinement
phase transition in heavy ion collisions. The corresponding or...

According to a fluid dynamic expansion of the fireball we investigate how the
inhomogeneity of the system influences the chiral phase transition of QCD. We
compare the averaged values of the order parameter in equilibrium with that of
a homogeneous system. If the temperature is averaged over a certain region of
the fireball the corresponding correl...

We present a fully dynamical model to study nonequilibrium effects in both
the chiral and the deconfinement phase transition. The sigma field and the
Polyakov loop as the corresponding order parameters are propagated by Langevin
equations of motion. The locally thermalized background is provided by a fluid
of quarks and antiquarks. Allowing for an...

We study nonequilibrium effects at the QCD phase transition within the
framework of Polyakov loop extended chiral fluid dynamics. The quark degrees of
freedom act as a locally equilibrated heat bath for the sigma field and a
dynamical Polyakov loop. Their evolution is described by a Langevin equation
with dissipation and noise. At a critical point...

We study the impact of nonequilibrium effects on the relevant signals within a chiral fluid dynamics model including explicit propagation of the Polyakov loop. An expanding heat bath of quarks is coupled to the Langevin dynamics of the order parameter fields. The model is able to describe relaxational processes, including critical slowing down and...

We review the physics potential at FAIR in the light of the existing
data of the RHIC-BES program and the NA49/NA61 beam and system size
scan. Special emphasize will be put on the potential of fluctuations, as
well as dilepton observables.

We investigate the nonequilibrium evolution of the sigma field coupled to a fluid dynamic expansion of a hot fireball to model the chiral phase transition in heavy-ion collisions. The dissipative processes and fluctuations are allowed under the assumption that the total energy of the coupled system is conserved. We use the linear sigma model with c...

We present a consistent theoretical approach for the study of nonequilibrium
effects in chiral fluid dynamics within the framework of the linear sigma model
with constituent quarks. Treating the quarks as an equilibrated heat bath we
use the influence functional formalism to obtain a Langevin equation for the
sigma field. This allows us to calculat...

We present the current status of hybrid approaches to describe heavy ion
collisions and their future challenges and perspectives. First we present a
hybrid model combining a Boltzmann transport model of hadronic degrees of
freedom in the initial and final state with an optional hydrodynamic evolution
during the dense and hot phase. Second, we prese...