arXiv subjects

J. Michel

Publications and source records attributed to J. Michel.

At least 19 recordsLinked to original sources

arXiv2026

Measurement of Differential Cross Sections and Integrated Luminosity using Proton-Proton Elastic Scattering with HADES at T = 4.53 GeV and T = 1.60 GeV

This work presents an investigation of elastic proton-proton scattering based on data collected with the recently upgraded HADES detector using beams of protons with kinetic energies of $T = 4.53$ GeV and $T = 1.60$ GeV impinging on a liquid hydrogen target. This is the first measurement emerging from the upgraded detector setup, including a Forward Detector with straw-tube tracking planes designed for the PANDA experiment. The well-constrained two-body kinematic relations of elastic scattering have been exploited to study the detector alignment, the beam alignment, and to provide the final measurement of the beam energy. In addition, the recorded luminosity of the experiment has been determined by normalizing the HADES data in a range of the squared four-momentum transfer $t$ that overlaps with measurements by previous experiments worldwide. Furthermore, the differential cross sections have been determined over a large range of $t$ from which the slope parameter $B$ is extracted, yielding $B = 8.98 \pm 0.3$ (GeV/$c$)$^{-2}$ and $7.3 \pm 0.1$ (GeV/$c$)$^{-2}$ at $T = 4.53$ GeV and $1.60$ GeV, respectively. This contribution to the world database on elastic proton-proton scattering provides input to theoretical modeling and serves as a reference for luminosity determinations by future experiments in the same energy range.

hep-ex↗

arXiv2025

Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV

We present the first observation of $\mathrm{^{3}_\Lambda H}$ and $\mathrm{^{4}_\Lambda H}$ in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV, emitted around mid-rapidity. The hypernuclei are reconstructed via their two-body decay channels and identified through their weak-decay topology, employing an artificial neural network for enhanced discrimination. The analysis methodology is validated using $\Lambda$ hyperons. The resulting rapidity distributions, dN/dy, exhibit a bell shape centered at mid-rapidity. The yield of $\mathrm{^{4}_\Lambda H}$ is equal to or exceeds that of $\mathrm{^{3}_\Lambda H}$, which contrasts the measurement from the STAR collaboration at $\mathrm{\sqrt{s_{NN}}}$ = 3 GeV and is consistent with a scenario in which hypernuclei receive feed-down from excited states. The data enable a high-precision measurement of the hypernuclei lifetimes. For the $\mathrm{^{3}_\Lambda H}$, a lifetime of $\mathrm{\tau_{^{3}_\Lambda H}}$ = $(239 \pm 23{\mathrm{(stat)}} \pm 18{\mathrm{(sys)}})\,\mathrm{ps}$, is extracted, consistent on the 1$\sigma$ level with that of the free $\Lambda$. In contrast, the $\mathrm{^{4}_\Lambda H}$ lifetime of $\mathrm{\tau_{^{4}_\Lambda H}}$ = $(209 \pm 7{\mathrm{(stat)}} \pm 10{\mathrm{(sys)}})\,\mathrm{ps}$, shows a 4.5 $\sigma$ deviation from the free $\Lambda$ lifetime. The results consolidate the available world data.

nucl-ex↗

arXiv2024

Electronics design and testing of the CMS Fast Beam Condition Monitor for HL-LHC

The high-luminosity upgrade of the LHC (HL-LHC) brings unprecedented requirements for precision bunch-by-bunch luminosity measurement and beam-induced background monitoring in real time. A key component of the CMS Beam Radiation Instrumentation and Luminosity detector system is a stand-alone luminometer, the Fast Beam Condition Monitor (FBCM), which is able to operate independently at all times with a triggerless asynchronous readout. FBCM utilizes a dedicated front-end ASIC to amplify the signals from CO$_2$-cooled silicon-pad sensors with 1 ns timing resolution. Front-end (FE) electronics are subject to high-radiation conditions, thus all components are radiation hardened: sensors, ASICs, transceivers, etc. The FBCM ASIC contains 6 channels, each outputting a high-speed binary signal carrying the time-of-arrival and time-over-threshold information. This signal is sent via a gigabit optical link to the back-end electronics for analysis. A dedicated test system is designed for the FBCM FE electronics with a modular setup for all testing needs of the project from initial ASIC validation test to system-level testing with the full read-out chain. The paper reports on the design, read-out architecture, and testing program for the FBCM electronics.

physics.ins-det↗

arXiv2024

Status of QCD precision predictions for Drell-Yan rapidity distributions

We compute differential distributions for Drell-Yan processes at the LHC and the Tevatron colliders at next-to-next-to-leading order in perturbative QCD, including fiducial cuts on the decay leptons in the final state. The comparison of predictions obtained with four different codes shows excellent agreement, once linear power corrections from the fiducial cuts are included in those codes that rely on phase-space slicing subtraction schemes. For Z-boson production we perform a detailed study of the symmetric cuts on the transverse momenta of the decay leptons. Predictions at fixed order in perturbative QCD for those symmetric cuts, typically imposed in experiments, suffer from an instability. We show how this can be remedied by an all-order resummation of the fiducial transverse momentum spectrum, and we comment on the choice of cuts for future experimental analyses.

hep-ph↗

arXiv2024

The CMS Fast Beam Condition Monitor for HL-LHC

The high-luminosity upgrade of the LHC brings unprecedented requirements for real-time and precision bunch-by-bunch online luminosity measurement and beam-induced background monitoring. A key component of the CMS Beam Radiation, Instrumentation and Luminosity system is a stand-alone luminometer, the Fast Beam Condition Monitor (FBCM), which is fully independent from the CMS central trigger and data acquisition services and able to operate at all times with a triggerless readout. FBCM utilizes a dedicated front-end application-specific integrated circuit (ASIC) to amplify the signals from CO$_2$-cooled silicon-pad sensors with a timing resolution of a few nanoseconds, which enables the measurement of the beam-induced background. FBCM uses a modular design with two half-disks of twelve modules at each end of CMS, with four service modules placed close to the outer edge to reduce radiation-induced aging. The electronics system design adapts several components from the CMS Tracker for power, control and read-out functionalities. The dedicated FBCM23 ASIC contains six channels and adjustable shaping time to optimize the noise with regards to sensor leakage current. Each ASIC channel outputs a single binary high-speed asynchronous signal carrying time-of-arrival and time-over-threshold information. The chip output signal is digitized, encoded and sent via a radiation-hard gigabit transceiver and an optical link to the back-end electronics for analysis. This paper reports on the updated design of the FBCM detector and the ongoing testing program.

physics.ins-det↗

arXiv2023

Inclusive e$^+$e$^-$ production in collisions of pions with protons and nuclei in the second resonance region of baryons

Inclusive e$^+$e$^-$ production has been studied with HADES in $π^-$ + p, $π^-$ + C and $π^- + \mathrm{CH}_2$ reactions, using the GSI pion beam at $\sqrt{s_{πp}}$ = 1.49 GeV. Invariant mass and transverse momentum distributions have been measured and reveal contributions from Dalitz decays of $π^0$, $η$ mesons and baryon resonances. The transverse momentum distributions are very sensitive to the underlying kinematics of the various processes. The baryon contribution exhibits a deviation up to a factor seven from the QED reference expected for the dielectron decay of a hypothetical point-like baryon with the production cross section constrained from the inverse $γ$ n$\rightarrow π^-$ p reaction. The enhancement is attributed to a strong four-momentum squared dependence of the time-like electromagnetic transition form factors as suggested by Vector Meson Dominance (VMD). Two versions of the VMD, that differ in the photon-baryon coupling, have been applied in simulations and compared to data. VMD1 (or two-component VMD) assumes a coupling via the $ρ$ meson and a direct coupling of the photon, while in VMD2 (or strict VMD) the coupling is only mediated via the $ρ$ meson. The VMD2 model, frequently used in transport calculations for dilepton decays, is found to overestimate the measured dielectron yields, while a good description of the data can be obtained with the VMD1 model assuming no phase difference between the two amplitudes. Similar descriptions have also been obtained using a time-like baryon transition form factor model where the pion cloud plays the major role.

nucl-ex↗

arXiv2023

Hadron Production and Propagation in Pion-Induced Reactions on Nuclei

Hadron production ($π^\pm$, proton, $Λ$, $K_S^0$, $K^\pm$) in $π^- + \mathrm{C}$ and $π^- + \mathrm{W}$ collisions is investigated at an incident pion beam momentum of $1.7~\mathrm{GeV}/c$. This comprehensive set of data measured with HADES at SIS18/GSI significantly extends the existing world data on hadron production in pion induced reactions and provides a new reference for models that are commonly used for the interpretation of heavy-ion collisions. The measured inclusive differential production cross-sections are compared with state-of-the-art transport model (GiBUU, SMASH) calculations. The (semi-) exclusive channel $π^- + A \rightarrow Λ+ K_S^0 +X$, in which the kinematics of the strange hadrons are correlated, is also investigated and compared to a model calculation. Agreement and remaining tensions between data and the current version of the considered transport models are discussed.

nucl-ex↗

arXiv2023

Investigation of the $\mathbf{Σ^{0}}$ Production Mechanism in p(3.5 GeV)+p Collisions

The production of $Σ^0$ hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES setup. The total production cross section is found to be $\mathrm{σ(pK^{+}Σ^{0}) [μb] = 17.7 \pm 1.7 (stat) \pm 1.6 (syst)}$. Differential cross section distributions of the exclusive channel $\mathrm{pp \rightarrow pK^{+}Σ^{0}}$ were analyzed in the center-of-mass, Gottfried-Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to $\mathrm{K^{+}Σ^{0}}$. The Bonn-Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710 $\mathrm{GeV/c^{2}}$ ($\mathrm{N^{*}(1710)}$) and 1.900 $\mathrm{GeV/c^{2}}$ ($\mathrm{N^{*}(1900)}$ or $\mathrm{Δ^{*}(1900)}$) are preferred by the fit.

nucl-ex↗

arXiv2023

Production of hydrogen isotopes and charged pions in p (3.5 GeV) + Nb reactions

The double differential production cross sections, $d^2σ/dΩdE$, for hydrogen isotopes and charged pions in the reaction of p + Nb at 3.5 GeV proton beam energy have been measured by the High Acceptance DiElectron Spectrometer (HADES). Thanks to the high acceptance of HADES at forward emission angles and usage of its magnetic field, the measured energy range of hydrogen isotopes could be significantly extended in comparison to the relatively scarce experimental data available in the literature. The data provide information about the development of the intranuclear cascade in the proton-nucleus collisions. They can as well be utilized to study the rate of energy/momentum dissipation in the nuclear systems and the mechanism of elementary and composite particle production in excited nuclear matter at normal density. Data of this type are important also for technological and medical applications. Our results are compared to models developed to describe the processes relevant to nuclear spallation (INCL++) or oriented to probe either the elementary hadronic processes in nuclear matter or the behavior of compressed nuclear matter (GiBUU).

nucl-ex↗

arXiv2022

Resistive Plate Chambers for Precise Measurement of High-Momentum Protons in Short Range Correlations at R$^3$B

The Reactions with Relativistic Radioactive Beams (R$^3$B) collaboration of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, has constructed an experimental setup to perform fundamental studies of nuclear matter, using as a probe reactions with exotic nuclei at relativistic energies. Among the various detection systems, one of the most recent upgrades consisted on the installation of a large area, around 2 m$^2$, multi-gap Resistive Plate Chamber (RPC), equipped with twelve 0.3 mm gaps and readout by 30 mm pitch strips, exhibiting a timing precision down to 50 ps and efficiencies above 98% for MIPs in a previous characterization of the detector. The RPC was part of the setup of the FAIR Phase 0 experiment that focused on measuring, for the first time, nucleon-nucleon short-range correlations (SRC) inside an exotic nucleus ($^{16}$C) that occurred in Spring 2022. The excellent timing precision of this detector will allow the measurement of the forward emitted proton momentum with a resolution of around 1%. In beam measurements show an RPC efficiency above 95% and a time precision better than 100 ps (including the contribution of a reference scintillator and the momentum spread of the particles) for forward emitted particles.

physics.ins-det↗

arXiv2022

Report of the Topical Group on Top quark physics and heavy flavor production for Snowmass 2021

This report summarizes the work of the Energy Frontier Topical Group on EW Physics: Heavy flavor and top quark physics (EF03) of the 2021 Community Summer Study (Snowmass). It aims to highlight the physics potential of top-quark studies and heavy-flavor production processes (bottom and charm) at the HL-LHC and possible future hadron and lepton colliders and running scenarios.

hep-ph↗

arXiv2022

Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisions

The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au collisions at \sqrt{s_{NN}} = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality 0--40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20--40%) collisions the polarization magnitudes are (%) = 6.8 \pm 1.3 (stat.) \pm 2.1 (syst.) for Au+Au and (%) = 6.2 \pm 0.4 (stat.) \pm 0.6 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D fluid dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.

nucl-ex↗

arXiv2022

Proton, deuteron and triton flow measurements in Au+Au collisions at $\sqrt{s_{NN}} = 2.4$ GeV

High precision measurements of flow coefficients $v_{n}$ ($n = 1 - 4$) for protons, deuterons and tritons relative to the first-order spectator plane have been performed in Au+Au collisions at $\sqrt{s_{NN}} = 2.4$ GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at the SIS18/GSI. Flow coefficients are studied as a function of transverse momentum $p_{t}$ and rapidity $y_{cm}$ over a large region of phase space and for several classes of collision centrality. A clear mass hierarchy is found for the slope of $v_{1}$, $d v_{1}/d y^{\prime}|_{y^{\prime} = 0}$ where $y^{\prime}$ is the scaled rapidity, and for $v_{2}$ at mid-rapidity. Scaling with the number of nucleons is observed for the $p_{t}$ dependence of $v_{2}$ and $v_{4}$ at mid-rapidity, which is indicative for nuclear coalescence as the main process responsible for light nuclei formation. $v_{2}$ is found to scale with the initial eccentricity $\langle \epsilon_{2} \rangle$, while $v_{4}$ scales with $\langle \epsilon_{2} \rangle^{2}$ and $\langle \epsilon_{4} \rangle$. The multi-differential high-precision data on $v_{1}$, $v_{2}$, $v_{3}$, and $v_{4}$ provides important constraints on the equation-of-state of compressed baryonic matter.

nucl-ex↗

arXiv2022

Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions

In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged pion transverse-mass and rapidity spectra, as well as on pion-pion momentum correlations is investigated in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV. We show that the low-mt part of the data ($m_t < 0.2$ GeV/c$^2$) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential deviates strongly from a $A_{part}^{2/3}$ scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields.

nucl-ex↗

arXiv2022

First measurement of massive virtual photon emission from N* baryon resonances

First information on the time-like electromagnetic structure of baryons in the second resonance region has been obtained from measurements of dielectron (e+ e-) invariant-mass and angular distributions in the quasi-free reaction $\pi-$ p $\rightarrow$ n e+ e- at $\sqrt{s_{\pi p}}$ = 1.49 GeV with the High Acceptance Di-Electron Spectrometer (HADES) at GSI using the pion beam impinging on a CH$_2$ target. We find a total cross section $\sigma$ = 2.97 $\pm$ 0.07data $\pm$ 0.21acc $\pm$ 0.31Zeff $\mu$b. In complement to the analysis of the inclusive e+ e- channel, this data set provides a crucial test of the description of baryon time-like transitions. Approaches based on a Vector Meson Dominance amplitude containing direct photon and vector meson ($\rho$) couplings to the baryon provide a satisfactory agreement with the data. A good description is also obtained by electromagnetic time-like baryon transition form factors in a covariant spectator-quark model, pointing to the dominance of meson-cloud effects. The dielectron angular distributions exhibit the contributions of virtual photons ($\gamma^*$) with longitudinal polarization, in contrast to real photons. The virtual photon angular dependence supports the dominance of J=3/2, I=1/2 contributions observed in both the $\gamma^*$n and the $\pi \pi$n channels.

nucl-ex↗

arXiv2021

Production and electromagnetic decay of hyperons: a feasibility study with HADES as a Phase-0 experiment at FAIR

A feasibility study has been performed in order to investigate the performance of the HADES detector to measure the electromagnetic decays of the hyperon resonances $Σ(1385)^0$, $Λ(1405)$ and $ΛΛ(1520)$ as well as the production of double strange baryon systems $Ξ^-$ and $ΛΛ$ in p+p reactions at a beam kinetic energy of 4.5 GeV. The existing HADES detector will be upgraded by a new Forward Detector, which extends the detector acceptance into a range of polar angles that plays a crucial role for these investigations. The analysis of each channel is preceded by a consideration of the production cross-sections. Afterwards the expected signal count rates using a target consisting of either liquid hydrogen or polyethylene are summarized.

nucl-ex↗

arXiv2021

Performance study and calibration strategy of the HADES scintillator TOF Wall with fast digital readout

We present in this work the calibration procedure and a performance study of long scintillator bars used for the time-of-flight (TOF) measurement in the HADES experiment. The digital front-end electronics installed at the TOF detector required to develop novel calibration methods. The exceptional performance of the spectrometer for particle identification and pointing accuracy allows one to determine in great detail the response of scintillators to minimum ionizing particles. A substantial position sensitivity of the calibration parameters has been found, in particular for the signal time walk. After including the position dependence, the timing accuracy for minimum ionizing particles was improved from 190~ps to 135~ps for the shortest rods (1475 mm) and to 165~ps for the longest (2356 mm). These results are in accordance with the time degradation length of the scintillator bars, as determined from previous measurements.

physics.ins-det↗

arXiv2020

Correlated pion-proton pair emission off hot and dense QCD matter

In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at \sqrt{s_{NN}} = 2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπpdpTdy distributions of correlated πp pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1 < Minv (GeV/c2) < 1.4, the yield is found to be similar for π+p and π-p pairs, and to follow a power law ^α, where is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α = 1.5 \pm 0.08stat \pm 0.2sys.

nucl-ex↗