arXiv subjects

Stefan Schmitt

Publications and source records attributed to Stefan Schmitt.

17 recordsLinked to original sources

arXiv2026

A high-flux electron detection system to measure non-linear Compton scattering at LUXE

This paper presents the development and testing of a high-flux electron detection system designed to measure the energy spectrum of more than $10^9$ electrons from laser-electron collisions at the LUXE experiment, planned at DESY. The system is intended to enable precision measurements of non-linear Compton scattering in the strong-field regime of quantum electrodynamics. It combines a scintillating screen observed by a camera system with a spatially segmented detector based on the Cherenkov effect. Prototype tests were conducted at two accelerator facilities, where the performance of the system was evaluated under realistic beam conditions. The results demonstrate the feasibility of the detector concept, characterize its current performance and limitations, and provide input for the optimization and final design of the detection system to be used in the experiment.

physics.ins-det↗

arXiv2026

A dump leakage calorimeter to measure the flux of high-energy electrons and photons

We developed a novel apparatus based on a lead-glass calorimeter that can measure the flux of high-energy electrons or photons. Our detector uses the electromagnetic shower leakage from the beam dump, where the particles are disposed of at the beamline's end. A prototype of such a calorimeter was set up at the FLASHForward experiment at DESY. We show that it can measure the electron bunch charge with a typical precision on the order of 10% and an accuracy at the few-percent level. Additionally, it is capable of determining the beam's position with a precision on the order of tens of micrometers. Finally, we demonstrate applicability to high-energy photons.

hep-ex↗

arXiv2025

A High-Flux Electron Detector System to Measure Non-linear Compton Scattering at LUXE

Recently, advancements in high-intensity laser technology have enabled the exploration of non-perturbative Quantum Electrodynamics (QED) in strong-field regimes. Notable aspects include non-linear Compton scattering and Breit-Wheeler pair production, observable when colliding high-intensity laser pulses and relativistic electron beams. The LUXE experiment at DESY and the E-320 experiment at SLAC aim to study these phenomena by measuring the created high-flux Compton electrons and photons. We propose a novel detector system featuring a segmented gas-filled Cherenkov detector with a scintillator screen and camera setup, designed to efficiently detect high-flux Compton electrons. Preliminary results from E-320 measurement campaigns demonstrate methods for reconstructing electron energy spectra, aiming to reveal crucial features of non-perturbative QED.

physics.ins-det↗

arXiv2023

High-rate electron detectors to study Compton scattering in non-perturbative QED

Research in non-perturbative QED in strong-field backgrounds has gained interest in recent years, due to advances in high-intensity laser technologies that make extreme fields accessible in the laboratory. One key signature of strong-field QED is non-linear Compton scattering in collisions between a relativistic electron beam and a high-intensity laser pulse. In the vicinity of strong fields, the electron gains a larger effective mass, which leads to a laser-intensity-dependent shift of the kinematic Compton edge and the appearance of higher-order harmonics in the energy spectrum. One of the challenges of measuring the Compton energy spectrum in laser-electron-beam collisions is the enormous flux of outgoing Compton-scattered electrons and photons, ranging from $10^3$ to $10^9$ particles per collision. We present a combined detector system for high-rate Compton electron detection in the context of the planned LUXE experiment, consisting of a spatially segmented gas-filled Cherenkov detector and a scintillator screen imaged by an optical camera system. The detectors are placed in a forward dipole spectrometer to resolve the electron energy spectrum. Finally, we discuss techniques to reconstruct the non-linear Compton electron energy spectrum from the high-rate electron detection system and to extract the features of non-perturbative QED from the spectrum.

hep-ex↗

arXiv2021

Conceptual Design Report for the LUXE Experiment

This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) effective field strengths to be probed at and beyond the Schwinger limit and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout.

hep-ex↗

arXiv2021

Preservation through modernisation: The software of the H1 experiment at HERA

The lepton-proton collisions produced at the HERA collider represent a unique high energy physics data set. A number of years after the end of collisions, the data collected by the H1 experiment, as well as the simulated events and all software needed for reconstruction, simulation and data analysis, were migrated into a preserved operational mode at DESY. A recent modernisation of the H1 software architecture has been performed, which will not only facilitate on going and future data analysis efforts with the new inclusion of modern analysis tools, but also ensure the long-term availability of the H1 data and associated software. The present status of the H1 software stack, the data, simulations and the currently supported computing platforms for data analysis activities are discussed.

hep-ex↗

arXiv2020

The impact of applying WildCards to disabled modules for FTK pattern banks on efficiency and data flow

Online selection is an essential step to collect the most relevant collisions from the very large number of collisions inside the ATLAS detector at the Large Hadron Collider (LHC). The Fast TracKer (FTK) is a hardware based track finder, built to greatly improve the ATLAS trigger system capabilities for identifying interesting physics processes through track-based signatures. The FTK is reconstructing after each Level-1 trigger all tracks with $ p_{\textrm T}>1 $ GeV, such that the high-level trigger system gains access to track information at an early stage. FTK track reconstruction starts with a pattern recognition step. Patterns are found with hits in seven out of eight possible detector layers. Disabled detector modules, as often encountered during LHC operation, lead to efficiency losses. To recover efficiency, WildCards (WC) algorithms are implemented in the FTK system. The WC algorithm recovers inefficiency but also causes high combinatorial background and thus increased data volumes in the FTK system, possibly exceeding hardware limitations. To overcome this, a refined algorithm to select patterns is developed and investigated in this article.

physics.ins-det↗

arXiv2019

The Tensor Pomeron and Small-x Deep Inelastic Scattering

We apply the tensor-pomeron model to small-$x$ deep-inelastic lepton-proton scattering and photoproduction. Our model includes a soft and a hard tensor pomeron as well as a reggeon contribution. Data with c.m. energies $6 < \sqrt{s} < 318$ GeV and virtualities $Q^2 < 50 \,\mbox{GeV}^2$ are considered. Our fit gives a very good description of the available data in this kinematic region, including the latest HERA data for $x < 0.01$. In particular, the transition region from low to high $Q^2$ is well described. Within the errors, the hard pomeron is absent in photoproduction. The intercepts of the soft and hard pomeron in the two-tensor-pomeron model are found to be $1.0935\, ({}^{+76}_{-64})$ and $1.3008 \,({}^{+73}_{-84})$, respectively. We argue that a vector pomeron would not give any contribution to photoproduction.

hep-ph↗

arXiv2019

The Tensor Pomeron and Low-x Deep Inelastic Scattering

The tensor-pomeron model is applied to low-x deep-inelastic lepton-nucleon scattering and photoproduction. We consider c.m. energies in the range 6 - 318 GeV and Q^2 < 50 GeV^2. In addition to the soft tensor pomeron, which has proven quite successful for the description of soft hadronic high-energy reactions, we include a hard tensor pomeron. We also include f_2-reggeon exchange which turns out to be particularly relevant for real-photon-proton scattering at c.m. energies in the range up to 30 GeV. The combination of these exchanges permits a description of the absorption cross sections of real and virtual photons on the proton in the same framework. In particular, a detailed comparison of this two-tensor-pomeron model with the latest HERA data for x < 0.01 is made. Our model gives a very good description of the transition from the small-Q^2 regime where the real or virtual photon behaves hadron-like to the large-Q^2 regime where hard scattering dominates. Our fit allows us, for instance, a determination of the intercepts of the hard pomeron as 1.3008(+73,-84), of the soft pomeron as 1.0935(+76,-64), and of the f_2 reggeon. We find that in photoproduction the hard pomeron does not contribute within the errors of the fit. We show that assuming a vector instead of a tensor character for the pomeron leads to the conclusion that it must decouple in real photoproduction.

hep-ph↗

arXiv2016

Data Unfolding Methods in High Energy Physics

A selection of unfolding methods commonly used in High Energy Physics is compared. The methods discussed here are: bin-by-bin correction factors, matrix inversion, template fit, Tikhonov regularisation and two examples of iterative methods. Two procedures to choose the strength of the regularisation are tested, namely the L-curve scan and a scan of global correlation coefficients. The advantages and disadvantages of the unfolding methods and choices of the regularisation strength are discussed using a toy example.

physics.data-an↗

arXiv2015

Measurement of Dijet Production in Diffractive Deep-Inelastic Scattering at HERA

The production of dijets is measured in diffractive deep-inelastic scattering at HERA. The data were recorded with the H1 detector at DESY in the years 2003-2007. Diffractive events are selected by requiring a gap in the rapidity distribution of the hadronic systen, where no particles are produced. Two jets are selected with transverse momenta in the hadronic-centre-of-mass system larger than 4 and 5.5GeV, respectively. Cross sections are measured single- and doubledifferentially in various kinematic quantities. The data are found to be in good agreement with NLO QCD calculations based on diffractive parton densities determined frominclusive diffractive cross section measurements.

hep-ex↗

arXiv2015

Diffractive Dijet Production with a Leading Proton in ep Collisions at HERA

The production of dijets with a tagged forward proton is measured at HERA. The data were recorded with the H1 detector at DESY in the years 2006-2007. Events with a leading proton are detected using the very forward proton spectrometer of the H1 detector. Two jets are selected with transverse momenta transverse momenta in the hadronic-centre-of-mass larger than 4 and 5.5GeV, respectively. The analysis is performed both in the regime of deep-inelastic scattering (DIS), with momentum transfer $Q{^2} > 4$ GeV${^2}$ and for photoproduction (γp), with $Q{^2} < 2$ GeV${^2}$. Cross sections are measured single-differentially in various kinematic quantities. For DIS, the data are found to be in good agreement with NLO QCD calculations based on diffractive parton densities determined from inclusive diffractive cross section measurements. For γp, the cross sections are found to be overestimated by approximately a factor of two.

hep-ex↗

arXiv2015

Graphene layer on Rh(111): combined DFT, STM, and NC-AFM studies

The simultaneous combination of scanning probe methods (tunnelling and force microscopies, STM and AFM) is a unique way to get an information about crystallographic and electronic structure of the studied surface. Here we apply these methods accompanied by the state-of-the-art density functional theory (DFT) calculations to shed a light on the structure and electronic properties of the strongly-corrugated graphene/Rh(111) system. The atomically resolved images are obtained for both STM and AFM modes and compared with the DFT results showing good agreement between theory and experiment.

cond-mat.mtrl-sci↗

arXiv2012

TUnfold: an algorithm for correcting migration effects in high energy physics

TUnfold is a tool for correcting migration and background effects in high energy physics for multi-dimensional distributions. It is based on a least square fit with Tikhonov regularisation and an optional area constraint. For determining the strength of the regularisation parameter, the L-curve method and scans of global correlation coefficients are implemented. The algorithm supports background subtraction and error propagation of statistical and systematic uncertainties, in particular those originating from limited knowledge of the response matrix. The program is interfaced to the ROOT analysis framework.

physics.data-an↗

arXiv2012

Polarisation at HERA - Reanalysis of the HERA II Polarimeter Data -

In this technical note we briefly present the analysis of the HERA polarimeters (transversal and longitudinal) as of summer 2011. We present the final reanalysis of the TPOL data, and discuss the systematic uncertainties. A procedure to combine and average LPOL and TPOL data is presented.

physics.ins-det↗

arXiv2009

Recent Results from the H1 Collaboration

An overview of recent physics results from the H1 collaboration is given. The covered areas are: rare processes and searches for new physics, structure functions and inclusive measurements, heavy flavour production, QCD and hadronic final states, diffractive scattering.

hep-ex↗

arXiv2008

Recent HERA Results on Leptoquarks and other SUSY-related Signatures

The HERA ep collider and the experiments H1 and ZEUS operated from 1994-2007. A total integrated luminosity of almost 1 fb^-1 was collected at centre-of-mass energies up to 320 GeV. Results from searches for leptoquarks and squarks, final states with an isolated lepton and missing transverse momentum and final states with multi-leptons are presented. The leptoquark limits are interpreted in terms of limits on squark production in SUSY models with R-parity violating couplings.

hep-ex↗