arXiv subjects

H. Jung

Publications and source records attributed to H. Jung.

At least 19 recordsLinked to original sources

arXiv2026

Non-perturbative effects and soft-gluon dynamics in low-$p_T$ Drell-Yan production

The transverse-momentum spectrum of Drell--Yan lepton pairs at small \ptll\ probes non-perturbative QCD effects, including intrinsic partonic transverse momentum and initial-state soft-gluon radiation. The novel \pythiaPB\ approach, which implements the Parton Branching (\PB ) framework in \pythia\ while employing the same evolution ingredients, is used to study this spectrum in the low-\ptll\ region. This framework is particularly well suited for such investigations, as it allows for a systematic treatment of the dominant non-perturbative effects and their interplay. We examine in detail the implementation of primordial transverse momentum in \pythiaPB . With an improved recoil treatment, we determine the width of the intrinsic-\kt\ distribution and find a \sqrts\ dependence that is steeper than in \PB , but much flatter than in \pythia . We identify the origin of these differences. Furthermore, different treatments of the strong coupling at low scales are investigated and confronted with available experimental data. We find that, at the highest centre-of-mass energy considered, the low-\ptll\ Drell--Yan spectrum becomes sensitive to the transition between the perturbative and non-perturbative regimes.

hep-ph↗

arXiv2025

Determination of Parton Densities for QCD partons and Electroweak Bosons

Parton densities are obtained from a solution of the extended DGLAP-type evolution equation that includes both QCD and electroweak contributions. The equations are solved using the Parton-Branching (PB) approach, and the evolution is performed at next-to-leading order for QCD partons and leading order for electroweak bosons. The initial QCD parton distributions are fitted to HERA deep inelastic scattering data, while photon and weak-boson densities are generated perturbatively and validated against $d\sigma/dQ^2$. The resulting collinear and transverse-momentum dependent (TMD) densities are provided in LHApdf and TMDlib formats for direct phenomenological use.

hep-ph↗

arXiv2025

Science for Peace and the need for Civil Clauses at universities and civilian research institutions

After the end of World War II, the commitment to confine scientific activities in universities and research institutions to peaceful and civilian purposes has entered, in the form of {\it Civil Clauses}, the charters of many research institutions and universities. In the wake of recent world events, the relevance and scope of such Civil Clauses has been questioned in reports issued by some governments and by the EU Commission, a development that opens the door to a possible blurring of the distinction between peaceful and military research. This paper documents the reflections stimulated by a panel discussion on this issue recently organized by the Science4Peace Forum. We review the adoptions of Civil Clauses in research organizations and institutions in various countries, present evidence of the challenges that are emerging to such Civil Clauses, and collect arguments in favour of maintaining the purely civilian and peaceful focus of public (non-military) research.

physics.soc-ph↗

arXiv2025

A parton shower consistent with parton densities at LO and NLO: PDF2ISR

We present a method for obtaining an initial-state parton shower model where the (backward) evolution fully consistent with the (forward) evolution of the collinear parton density used. As a proof-of-concept we use parton densities obtained with the Parton Branching (PB) approach, and modify the default initial-state shower in PYTHIA8 with this method to be consistent with them. PB is ideally suited for checking the validity of our method since, in addition to producing collinear parton densities, it also produces the corresponding transverse-dependent (TMD) ones, and these can then be directly compared to the transverse momentum distribution obtained from the parton shower. We show that TMD distributions which we in this way obtain from our modified PYTHIA8 shower using leading order (LO) parton densities and splitting functions are fully consistent with the corresponding leading order TMD densities. At next-to-leading order (NLO) it is not possible to achieve the same consistency using the built-in LO splitting functions in the shower, but we show that by introducing NLO splitting functions using a reweighting procedure, we can achieve consistency also at NLO. The method presented here, which we have named PDF2ISR, can be easily extended to any collinear parton densities, as long as the exact conditions for the evolution are known. With the PDF2ISR method we obtain an initial-state parton shower which in principle has no free parameters, and is fully consistent with collinear parton densities at LO and NLO.

hep-ph↗

arXiv2025

Science4Peace: A Plea for Continued Peaceful International Scientific Cooperation (Input to the European Strategy for Particle Physics -- 2026 update)

The European Strategy for Particle Physics (ESPP) - 2026 update is taking place in a turbulent international climate. Many of the norms that have governed relations between states for decades are being broken or challenged. The future progress of science in general, and particle physics in particular, will depend on our ability to maintain peaceful international scientific collaboration in the face of political pressures. We plead that the ESPP 2026 update acknowledge explicitly the importance of peaceful international scientific collaboration, not only for the progress of science, but also as a precious bridge between geopolitical blocs. "Scientific thought is the common heritage of mankind" - Abdus Salam

physics.soc-ph↗

arXiv2024

Interplay of intrinsic motion of partons and soft gluon emissions in Drell-Yan production studied with PYTHIA

Understanding the intrinsic transverse momentum (intrinsic-$k_T$) of partons within colliding hadrons, typically modeled with a Gaussian distribution characterized by a specific width (the intrinsic-$k_T$ width), has been an extremely challenging issue. This difficulty arises because event generators like Pythia require an intrinsic-$k_T$ width that unexpectedly varies with collision energy, reaching unphysical values at high energies. This paper investigates the underlying physics behind this energy dependence in Pythia, revealing that it arises from an interplay between two non-perturbative processes: the internal transverse motion of partons and non-perturbative soft gluon emissions. These contributions are most constrained in the production of Drell-Yan pairs with very low transverse momentum, where soft gluon effects become increasingly prominent with rising collision energy-contrary to initial expectations. Through a detailed analysis of the non-perturbative Sudakov form factor and its influence on intrinsic-$k_T$ width, we clarify the observed energy scaling behavior in Pythia, providing insight into a longstanding issue in parton shower modeling.

hep-ph↗

arXiv2024

The Parton Branching evolution package uPDFevolv2

uPDFevolv2 is a software package designed for evolving collinear and Transverse Momentum Dependent (TMD) parton densities using the DGLAP evolution equation. A comprehensive description of both the theoretical framework and technical implementation is given, accompanied by a detailed guide on program usage, focusing on customizable parameters. This report is as a technical release note for uPDFevolv version 2.5.03.

hep-ph↗

arXiv2024

Element-specific ultrafast lattice dynamics in monolayer WSe2

We study monolayer WSe2 using ultrafast electron diffraction. We introduce an approach to quantitatively extract atomic-site-specific information, providing an element-specific view of incoherent atomic vibrations following femtosecond excitation. Via differences between W and Se vibrations, we identify stages in the nonthermal evolution of the lattice. Combined with a calculated phonon dispersion, this element specificity enables us to identify a long-lasting overpopulation of specific optical phonons, and to interpret the stages as energy transfer processes between specific phonon groups. These results demonstrate the appeal of resolving element-specific vibrational information in the ultrafast time domain.

cond-mat.mtrl-sci↗

arXiv2024

The non-perturbative Sudakov Form Factor and the role of soft gluons

The role of soft gluons in inclusive collinear parton densities as well as in Transverse Momentum Dependent (TMD) parton densities is discussed. Applying the Parton-Branching (PBM) method, the so-called non-perturbative Sudakov form factor could be identified with the integration range $z \to 1$, which is neglected in collinear parton shower approaches. The importance of soft gluons could be shown by investigating the transverse momentum spectrum of Drell-Yan lepton pairs, leading to a width of the intrinsic-$k_T$ distribution which is independent on $\sqrt{s}$ , in contrast to what is observed in parton shower approaches. The reason for this behavior is traced back to the non-perturbative Sudakov form factor. The role of soft gluons for observable hadron spectra is discussed and shown to be negligible. This talk is dedicated to the memory of S. Jadach.

hep-ph↗

arXiv2024

Center-of-mass energy dependence of intrinsic-$k_T$ distributions obtained from Drell-Yan production

The internal motion of partons inside hadrons has been studied through its impact on very low transverse momentum spectra of Drell-Yan (DY) pairs created in hadron-hadron collisions. We study DY production at next-to-leading order using the Parton Branching (PB) method which describes the evolution of transverse momentum dependent parton distributions. The main focus is on studying the intrinsic transverse momentum distribution (intrinsic-$k_T$) as a function of the center-of-mass energy $\sqrt s$. While collinear parton shower Monte Carlo event generators require intrinsic transverse momentum distributions strongly dependent on $\sqrt s$, this is not the case for the PB method. We perform a detailed study of the impact of soft parton emissions. We show that by requiring a minimal transverse momentum, $q_0$, of a radiated parton, a dependence of the width of the intrinsic-$k_T$ distribution as a function of $\sqrt{s}$ is observed. This dependence becomes stronger with increasing $q_0$.

hep-ph↗

arXiv2024

A Science4Peace initiative: Alleviating the consequences of sanctions in international scientific cooperation

The armed invasion of Ukraine by the Russian Federation has adversely affected the relations between Russia and Western countries. Among other aspects, it has put scientific cooperation and collaboration into question and changed the scientific landscape significantly. Cooperation between some Western institutions and their Russian and Belarusian partners were put on hold after February 24, 2022. The CERN Council decided at its meeting in December 2023 to terminate cooperation agreements with Russia and Belarus that date back a decade. CERN is an international institution with UN observer status, and has so far played a role in international cooperation which was independent of national political strategies. We argue that the Science4Peace idea still has a great value and scientific collaboration between scientists must continue, since fundamental science is by its nature an international discipline. A ban of scientists participating in international cooperation and collaboration is against the traditions, requirements and understanding of science. We call for measures to reactivate the peaceful cooperation of individual scientists on fundamental research in order to stimulate international cooperation for a more peaceful world in the future. Specifically, we plead for finding ways to continue this cooperation through international organizations, such as CERN and JINR.

physics.soc-ph↗

arXiv2023

The small kt-region in Drell-Yan production at next-to-leading order with the Parton Branching Method

The Parton Branching (PB) method describes the evolution of transverse momentum dependent (TMD) parton distributions, covering all kinematic regions from small to large transverse momenta kT. The small kT-region is very sensitive both to the contribution of the intrinsic motion of partons (intrinsic kT) and to the resummation of soft gluons taken into account by the PB TMD evolution equations. We study the role of soft-gluon emissions in TMD as well as integrated parton distributions. We perform a detailed investigation of the PB TMD methodology at next-to-leading order (NLO) in Drell-Yan (DY) production for low transverse momenta. We present the extraction of the nonperturbative "intrinsic-kT" distribution from recent measurements of DY transverse momentum distributions at the LHC across a wide range in DY masses, including a detailed treatment of statistical, correlated and uncorrelated uncertainties. We comment on the (in)dependence of intrinsic transverse momentum on DY mass and center-of-mass energy, and on the comparison with other approaches.

hep-ph↗

arXiv2023

Beyond a Year of Sanctions in Science

While sanctions in political and economic areas are now part of the standard repertoire of Western countries (not always endorsed by UN mandates), sanctions in science and culture in general are new. Historically, fundamental research as conducted at international research centers such as CERN has long been seen as a driver for peace, and the Science4Peace idea has been celebrated for decades. However, much changed with the war against Ukraine, and most Western science organizations put scientific cooperation with Russia and Belarus on hold immediately after the start of the war in 2022. In addition, common publications and participation in conferences were banned by some institutions, going against the ideal of free scientific exchange and communication. These and other points were the topics of an international virtual panel discussion organized by the Science4Peace Forum together with the "Natural Scientists Initiative - Responsibility for Peace and Sustainability" (NatWiss e.V.) in Germany and the journal "Wissenschaft und Frieden" (W&F) (see the Figure). Fellows from the Hamburg Institute for Peace Research and Security Policy (IFSH), scientists collaborating with the large physics research institutes DESY and CERN, as well as from climate and futures researchers were represented on the panel. In this Dossier we document the panel discussion, and give additional perspectives. The authors of the individual sections present their personal reflections, which should not be taken as implying that they are endorsed by the Science4Peace Forum or any other organizations. It is regrettable that some colleagues who expressed support for this document felt that it would be unwise for them to co-sign it.

physics.soc-ph↗

arXiv2023

On the role of soft gluons in collinear parton densities and parton shower event generators

The role of soft (non-perturbative) gluons in collinear parton densities and parton shower event generators is investigated with the Parton Branching method as a solution of the DGLAP evolution equations. It is found that soft gluons play a significant role. Within the Parton Branching frame, the Sudakov form factor can be split into a perturbative and non-perturbative part. The non-perturbative part can be calculated analytically under certain conditions. It is shown that the inclusion of soft (non-perturbative) gluons in the parton density evolution is essential for the proper cancellation of divergent terms. It is argued that the non-perturbative part of the Sudakov form factor has its correspondence in Transverse Momentum Dependent parton distributions. Within the Parton Branching approach, this non-perturbative Sudakov form factor is constrained by fits of inclusive, collinear parton densities. We show that the non-perturbative Sudakov form factor and soft gluon emissions are essential for inclusive distributions (collinear parton densities and Drell-Yan transverse momentum spectra). We also show by using Parton Branching TMD parton shower, that the effect of soft gluons plays essentially no role in final state hadron spectra and jets.

hep-ph↗

arXiv2022

Boson-jet and jet-jet azimuthal correlations at high transverse momenta

We discuss our recent results on azimuthal distributions in vector boson + jets and multi-jet production at the LHC, obtained from the matching of next-to-leading order (NLO) perturbative matrix elements with transverse momentum dependent (TMD) parton branching. We present a comparative analysis of boson-jet and jet-jet correlations in the back to-back region, and a study of the theoretical systematic uncertainties associated with the matching scale in the cases of TMD and collinear parton showers.

hep-ph↗

arXiv2022

Back-to-back azimuthal correlations in Z+jet events at high transverse momentum in the TMD parton branching method at next-to-leading order

Azimuthal correlations in Z+jet production at large transverse momenta are computed by matching Parton - Branching (PB) TMD parton distributions and showers with NLO calculations via MCatNLO. The predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations $Δϕ$ between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta ${\cal O}(100)$ GeV, while they become similar for very high transverse momenta ${\cal O}(1000)$ GeV. The different patterns of Z+jet and dijet azimuthal correlations can be used to search for potential {\it factorization - breaking} effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in $Δϕ$ for Z+jet - and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.

hep-ph↗

arXiv2022

xFitter: An Open Source QCD Analysis Framework. A resource and reference document for the Snowmass study

We provide an overview of the xFitter open-source software package, review the general capabilities of the program, and highlight applications relevant to the Snowmass study. An updated version of the program (2.2.0) is available on CERN GitLab, a and this has been updated to a C++ codebase with enhanced and extended features. We also discuss some of the ongoing and future code developments that may be useful for precision studies. We survey recent analyses performed by the xFitter developers' team including: W and Z production, photon PDFs, Drell-Yan forward-backward asymmetry studies, resummation of small-x contributions, heavy quark production, constraints on the strange PDF, determination of the pion PDF, and determination of the pion Fragmentation Functions. Finally, we briefly summarize selected applications of xFitter in the literature. The xFitter program is a versatile, flexible, modular, and comprehensive tool that can provide impact studies for possible future facilities. We encourage the use of xFitter, and welcome new contributions from the community.

hep-ph↗

arXiv2022

Measurement of lepton-jet correlation in deep-inelastic scattering with the H1 detector using machine learning for unfolding

The first measurement of lepton-jet momentum imbalance and azimuthal correlation in lepton-proton scattering at high momentum transfer is presented. These data, taken with the H1 detector at HERA, are corrected for detector effects using an unbinned machine learning algorithm OmniFold, which considers eight observables simultaneously in this first application. The unfolded cross sections are compared to calculations performed within the context of collinear or transverse-momentum-dependent (TMD) factorization in Quantum Chromodynamics (QCD) as well as Monte Carlo event generators. The measurement probes a wide range of QCD phenomena, including TMD parton distribution functions and their evolution with energy in so far unexplored kinematic regions.

hep-ex↗