arXiv subjects

J. List

Publications and source records attributed to J. List.

At least 19 recordsLinked to original sources

arXiv2025

Updated baseline design for HALHF: the hybrid, asymmetric, linear Higgs factory

Particle physicists aim to construct a electron-positron Higgs factory as the next major particle collider. However, the high associated costs motivate the development of more affordable collider designs. Plasma-wakefield acceleration is a promising technology to this end. HALHF is a proposal for a Higgs factory that utilizes beam-driven plasma-wakefield acceleration to accelerate electrons to high energy with high gradient, while using radio-frequency acceleration to accelerate positrons to a lower energy. This asymmetry sidesteps a major difficulty in plasma acceleration: that of accelerating positrons with high efficiency and quality. Since publication, several challenges were identified in the original baseline design. We summarize the updated baseline design, which addresses these challenges, and describe the parameter- and cost-optimization process used to arrive at this design.

physics.acc-ph↗

arXiv2025

Status of the International Linear Collider

This paper is not a proposal for a CERN future project but provides information on the International Linear Collider (ILC) considered for Japan in order to facilitate the European Strategy discussion in a global context. It describes progress to date, ongoing engineering studies, updated cost estimate for the machine at $\sqrt{s}=250~\rm GeV$ and the situation in Japan. The physics of the ILC is not presented here, but jointly for all Linear Collider projects in a separate document ``A Linear Collider Vision for the Future of Particle Physics'' submitted for the forthcoming European Strategy deliberations.

hep-ex↗

arXiv2025

Contribution of ALEGRO to the Update of the European Strategy on Particle Physics

Advanced and novel accelerators (ANAs), driven a by laser pulse or a relativistic particle bunch, have made remarkable progress over the last decades. They accelerated electrons by 10GeV in 30cm (laser driven) and by 42GeV in 85cm (particle bunch driven). Rapid progress continues with lasers, plasma sources, computational methods, and more. In this document we highlight the main contributions made by the various major collaborations, facilities, and experiments that develop ANAs for applications to particle and high-energy physics. These include: ALiVE, ANL-AWA, AWAKE, BNL-ATF, CEPC Injector, DESY-KALDERA, ELI ERIC, EuPRAXIA, HALHF, LBNL-BELLA, LBNL-kBELLA, LCvison, PETRA IV Injector, 10TeV Collider design, SLAC-FACET II, as well as the development of structures, lasers and plasma sources, and sustainability, and demonstrate the intense activities in the field. ANAs can have, and already have, applications to particle and high-energy physics as subsystems, the so-called intermediate applications: injectors, lower energy experiments, beam dump experiments, test beds for detectors, etc. Additionally, an ANA could be an upgrade for any Higgs factory based on a linear accelerator, as proposed in the LCvison project. ANAs have advantages over other concepts for reaching multi-TeV energies: lower geographical and environmental footprints, higher luminosity to power ratio, and are thus more sustainable than other accelerators. However, ANAs must still meet a number of challenges before they can produce bunches with parameters and the luminosity required for a linear collider at the energy frontier. It is therefore extremely important to strongly support vigorous R&D of ANAs, because they are, at this time, the most sustainable acceleration scheme to reach very high energies with a linear accelerator.

physics.acc-ph↗

arXiv2025

Input to the ESPPU: The LUXE Experiment

This document presents an overview of LUXE (Laser Und XFEL Experiment), an experiment that will combine the high-quality and high-energy electron beam of the European XFEL with a high-intensity laser, to explore the uncharted terrain of strong-field quantum electrodynamics. The scientific case, facility, and detector setup are presented together with an overview of the foreseen timeline and expected capital costs.

hep-ex↗

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

Machine Learning-Assisted Measurement of Lepton-Jet Azimuthal Angular Asymmetries in Deep-Inelastic Scattering at HERA

In deep-inelastic positron-proton scattering, the lepton-jet azimuthal angular asymmetry is measured using data collected with the H1 detector at HERA. When the average transverse momentum of the lepton-jet system, $\lvert \vec{P}_\perp \rvert $, is much larger than the total transverse momentum of the system, $\lvert \vec{q}_\perp \rvert$, the asymmetry between parallel and antiparallel configurations, $\vec{P}_\perp$ and $\vec{q}_\perp$, is expected to be generated by initial and final state soft gluon radiation and can be predicted using perturbation theory. Quantifying the angular properties of the asymmetry therefore provides an additional test of the strong force. Studying the asymmetry is important for future measurements of intrinsic asymmetries generated by the proton's constituents through Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs), where this asymmetry constitutes a dominant background. Moments of the azimuthal asymmetries are measured using a machine learning method for unfolding that does not require binning.

hep-ex↗

arXiv2024

Measurement of the 1-jettiness event shape observable in deep-inelastic electron-proton scattering at HERA

The H1 Collaboration reports the first measurement of the 1-jettiness event shape observable $\tau_1^b$ in neutral-current deep-inelastic electron-proton scattering (DIS). The observable $\tau_1^b$ is equivalent to a thrust observable defined in the Breit frame. The data sample was collected at the HERA $ep$ collider in the years 2003-2007 with center-of-mass energy of $\sqrt{s}=319\,\text{GeV}$, corresponding to an integrated luminosity of $351.1\,\text{pb}^{-1}$. Triple differential cross sections are provided as a function of $\tau_1^b$, event virtuality $Q^2$, and inelasticity $y$, in the kinematic region $Q^2>150\,\text{GeV}^{2}$. Single differential cross section are provided as a function of $\tau_1^b$ in a limited kinematic range. Double differential cross sections are measured, in contrast, integrated over $\tau_1^b$ and represent the inclusive neutral-current DIS cross section measured as a function of $Q^2$ and $y$. The data are compared to a variety of predictions and include classical and modern Monte Carlo event generators, predictions in fixed-order perturbative QCD where calculations up to $\mathcal{O}(\alpha_s^3)$ are available for $\tau_1^b$ or inclusive DIS, and resummed predictions at next-to-leading logarithmic accuracy matched to fixed order predictions at $\mathcal{O}(\alpha_s^2)$. These comparisons reveal sensitivity of the 1-jettiness observable to QCD parton shower and resummation effects, as well as the modeling of hadronization and fragmentation. Within their range of validity, the fixed-order predictions provide a good description of the data. Monte Carlo event generators are predictive over the full measured range and hence their underlying models and parameters can be constrained by comparing to the presented data.

hep-ex↗

arXiv2024

Measurement of groomed event shape observables in deep-inelastic electron-proton scattering at HERA

The H1 Collaboration at HERA reports the first measurement of groomed event shape observables in deep inelastic electron-proton scattering (DIS) at $\sqrt{s}=319$ GeV, using data recorded between the years 2003 and 2007 with an integrated luminosity of $351$ pb$^{-1}$. Event shapes provide incisive probes of perturbative and non-perturbative QCD. Grooming techniques have been used for jet measurements in hadronic collisions; this paper presents the first application of grooming to DIS data. The analysis is carried out in the Breit frame, utilizing the novel Centauro jet clustering algorithm that is designed for DIS event topologies. Events are required to have squared momentum-transfer $Q^2 > 150$ GeV$^2$ and inelasticity $ 0.2 < y < 0.7$. We report measurements of the production cross section of groomed event 1-jettiness and groomed invariant mass for several choices of grooming parameter. Monte Carlo model calculations and analytic calculations based on Soft Collinear Effective Theory are compared to the measurements.

hep-ex↗

arXiv2024

Observation and differential cross section measurement of neutral current DIS events with an empty hemisphere in the Breit frame

The Breit frame provides a natural frame to analyze lepton-proton scattering events. In this reference frame, the parton model hard interactions between a quark and an exchanged boson defines the coordinate system such that the struck quark is back-scattered along the virtual photon momentum direction. In Quantum Chromodynamics (QCD), higher order perturbative or non-perturbative effects can change this picture drastically. As Bjorken-$x$ decreases below one half, a rather peculiar event signature is predicted with increasing probability, where no radiation is present in one of the two Breit-frame hemispheres and all emissions are to be found in the other hemisphere. At higher orders in $\alpha_s$ or in the presence of soft QCD effects, predictions of the rate of these events are far from trivial, and that motivates measurements with real data. We report on the first observation of the empty current hemisphere events in electron-proton collisions at the HERA collider using data recorded with the H1 detector at a center-of-mass energy of 319 GeV. The fraction of inclusive neutral-current DIS events with an empty hemisphere is found to be $0.0112 \pm 3.9\,\%_\text{stat} \pm 4.5\,\%_\text{syst} \pm 1.6\,\%_\text{mod}$ in the selected kinematic region of $150< Q^2<1500$ GeV$^2$ and inelasticity $0.14< y<0.7$. The data sample corresponds to an integrated luminosity of 351.1 pb$^{-1}$, sufficient to enable differential cross section measurements of these events. The results show an enhanced discriminating power at lower Bjorken-$x$ among different Monte Carlo event generator predictions.

hep-ex↗

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

Technical Design Report for the LUXE Experiment

This Technical Design Report presents a detailed description of all aspects of the LUXE (Laser Und XFEL Experiment), an experiment that will combine the high-quality and high-energy electron beam of the European XFEL with a high-intensity laser, to explore the uncharted terrain of strong-field quantum electrodynamics characterised by both high energy and high intensity, reaching the Schwinger field and beyond. The further implications for the search of physics beyond the Standard Model are also discussed.

hep-ex↗

arXiv2023

Unbinned Deep Learning Jet Substructure Measurement in High $Q^2$ ep collisions at HERA

The radiation pattern within high energy quark- and gluon-initiated jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event generators with numerous applications in high energy particle and nuclear physics. Looking at electron-proton collisions is of particular interest as many of the complications present at hadron colliders are absent. A detailed study of modern jet substructure observables, jet angularities, in electron-proton collisions is presented using data recorded using the H1 detector at HERA. The measurement is unbinned and multi-dimensional, using machine learning to correct for detector effects. All of the available reconstructed object information of the respective jets is interpreted by a graph neural network, achieving superior precision on a selected set of jet angularities. Training these networks was enabled by the use of a large number of GPUs in the Perlmutter supercomputer at Berkeley Lab. The particle jets are reconstructed in the laboratory frame, using the $k_{\mathrm{T}}$ jet clustering algorithm. Results are reported at high transverse momentum transfer $Q^2>150$ GeV${}^2$, and inelasticity $0.2 < y < 0.7$. The analysis is also performed in sub-regions of $Q^2$, thus probing scale dependencies of the substructure variables. The data are compared with a variety of predictions and point towards possible improvements of such models.

hep-ex↗

arXiv2022

Stau searches and measurements with the ILD concept at the International Linear Collider

One of the most interesting channels to search for SUSY is the direct pair-production of the $\tau$-lepton superpartner, $\widetilde{\tau}$. The $\widetilde{\tau}$ is with high probability the lightest of the scalar leptons, so one of the first SUSY particles that can be observerd, and the signature of $\widetilde{\tau}$ pair production signal events is one of the most difficult ones, yielding to the ``worst'' and so most global scenario for the searches. Analysis performed at LEP set the current model-independent $\widetilde{\tau}$ limits, suffering from the low energy of this facility. Only under strong model assumptions, these limits are extended to higher masses by LHC studies. In this contribution we show the capability of the ILC, a future electron-positron collider with energy up to 1 TeV, for determining $\widetilde{\tau}$ exclusion/discovery limits in a model-independent way, including an overview of the current state-of-the-art. The determination of the ``worst'' scenario for $\widetilde{\tau}$ exclusion/discovery, taking into account the effect of the $\widetilde{\tau}$ mixing on $\widetilde{\tau}$ production cross-section and efficiency, is also presented. For selected benchmarks, the prospect for measuring masses and polarised cross-sections will be shown. The studies were done studying events passed through the full detector simulation and reconstruction procedures of the International Large Detector (ILD) concept at the ILC. The simulation included all SM backgrounds, as well as the machine induced ones.

hep-ph↗

arXiv2022

Evaluating the ILC SUSY reach in the most challenging scenario: $\widetilde{\tau}$ NLSP, low $\Delta M$ , lowest cross-section

Pair-production of the superpartner of the $\tau$-lepton, the $\tilde{\tau}$, is one of the most interesting channels to search for SUSY in: The $\tilde{\tau}$ is likely to be the lightest scalar lepton, and the signature of $\tilde{\tau}$ pair production is one of the experimentally most difficult ones, thereby constituting the "worst" possible scenario for SUSY searches. The current model-independent $\tilde{\tau}$ limits comes from analyses performed at LEP but they suffer from the limited energy of this facility. Limits obtained at the LHC do extend to higher masses, but they are only valid under strong assumptions. The International Linear Collider, the ILC, is a future electron-positron collider, to operate initially at an energy of 250 GeV, then to be upgraded to 500 GeV, and possibly to 1 TeV at a later stage. ILC will be a powerful facility for SUSY searches. The capability of the ILC for determining exclusion/discovery limits for the $\tilde{\tau}$ in a model-independent way is shown in this paper. A detailed study of the "worst" scenario for $\tilde{\tau}$ exclusion/discovery, taking into account the effect of the $\tilde{\tau}$ mixing on $\tilde{\tau}$ production cross-section and detection efficiency, is presented. The study also includes an analysis of the effect of the overlay particles in the $\tilde{\tau}$ searches. The conclusion is that both the exclusion and discovery reaches for this "worst" case would extend to only a few GeV below the kinematic limit at the ILC. Also scenarios with the $\tilde{\tau}$ and the Lightest SUSY Particle (the LSP) quite close in mass can be discovered or excluded at most $\tilde{\tau}$ masses. The studies were done using detailed detector simulation of the ILD concept at the ILC. For signal, the fast detector simulation SGV was used, while the full Geant4 based DDSim was used for the standard model backgrounds.

hep-ph↗

arXiv2021

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↗

arXiv2021

$\widetilde{\tau}$ searches at the ILC

The direct pair-production of the superpartner of the $\tau$-lepton, the $\widetilde{\tau}$, is one of the most interesting channels to search for SUSY in. First of all, the $\widetilde{\tau}$ is likely to be the lightest of the scalar leptons. Secondly the signature of $\widetilde{\tau}$ pair production signal events is one of the experimentally most difficult ones, thereby constituting the "worst" possible scenario for SUSY searches. The current model-independent $\widetilde{\tau}$ limits comes from analyses performed at LEP but they suffer from the limited energy of this facility. Limits obtained at the LHC do extend to higher masses, but they are only valid under strong assumptions. ILC, a future electron-positron collider with energy up to 500 GeV and upgrade capability\footnote{The initial ILC energy is planned to be 250 GeV.}, is a promising facility for SUSY searches. The capability of the ILC for determining exclusion/discovery limits for the $\widetilde{\tau}$ in a model-independent way is shown in this paper, together with an overview of the current state-of-the-art. Results of the last studies of $\widetilde{\tau}$ pair-production at the ILC are presented, showing the improvements with respect to previous results.

hep-ph↗

arXiv2019

Letter of Intent for the LUXE Experiment

This Letter of Intent describes LUXE (Laser Und XFEL Experiment), an experiment that aims to use the high-quality and high-energy electron beam of the European XFEL and a powerful laser. The scientific objective of the experiment is to study quantum electrodynamics processes in the regime of strong fields. High-energy electrons, accelerated by the European XFEL linear accelerator, and high-energy photons, produced via Bremsstrahlung of those beam electrons, colliding with a laser beam shall experience an electric field up to three times larger than the Schwinger critical field (the field at which the vacuum itself is expected to become unstable and spark with spontaneous creation of electron-positron pairs) and access a new regime of quantum physics. The processes to be investigated, which include nonlinear Compton scattering and nonlinear Breit-Wheeler pair production, are relevant to a variety of phenomena in Nature, e.g. in the areas of astrophysics and collider physics and complement recent results in atomic physics. The setup requires in particular the extraction of a minute fraction of the electron bunches from the European XFEL accelerator, the installation of a powerful laser with sophisticated diagnostics, and an array of precision detectors optimised to measure electrons, positrons and photons. Physics sensitivity projections based on simulations are also provided.

physics.ins-det↗

arXiv2017

Determination of the strong coupling constant $\alpha_s(M_Z)$ in next-to-next-to-leading order QCD using H1 jet cross section measurements

The strong coupling constant $\alpha_s(M_Z)$ is determined from inclusive jet and dijet cross sections in neutral-current deep-inelastic $ep$ scattering (DIS) measured at HERA by the H1 collaboration using next-to-next-to-leading order (NNLO) QCD predictions. The dependence of the NNLO predictions and of the resulting value of $\alpha_s(M_Z)$ at the $Z$-boson mass $m_Z$ are studied as a function of the choice of the renormalisation and factorisation scales. Using inclusive jet and dijet data together, the strong coupling constant is determined to be $\alpha_s(M_Z)=0.1166\,(19)_{\rm exp}\,(24)_{\rm th}$. Complementary, $\alpha_s(M_Z)$ is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value $\alpha_s(M_Z)=0.1147\,(25)_{\rm tot}$ obtained is consistent with the determination from jet data alone. The impact of the jet data on the PDFs is studied. The running of the strong coupling is tested at different values of the renormalisation scale and the results are found to be in agreement with expectations.

hep-ex↗