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T. Mertens

Publications and source records attributed to T. Mertens.

At least 19 recordsLinked to original sources
arXiv2021

Measurement of the EMC effect in light and heavy nuclei

Inclusive electron scattering from nuclear targets has been measured to extract the nuclear dependence of the inelastic cross section in Hall C at the Thomas Jefferson National Accelerator facility. Results are presented for 2H, 3He, 4He, 9B, 12C, 63Cu and 197Au at an incident electron beam energy of 5.77 GeV for a range of momentum transfer from Q^2 = 2 to 7 (GeV/c)^2. These data improve the precision of the existing measurements of the EMC effect in the nuclear targets at large x, and allow for more detailed examinations of the A dependence of the EMC effect.

nucl-ex↗
arXiv2021

Performance and luminosity models for heavy-ion operation at the CERN Large Hadron Collider

A good understanding of the luminosity performance in a collider, as well as reliable tools to analyse, predict, and optimise the performance, are of great importance for the successful planning and execution of future runs. In this article, we present two different models for the evolution of the beam parameters and the luminosity in heavy-ion colliders. The first, Collider Time Evolution (CTE) is a particle tracking code, while the second, the Multi-Bunch Simulation (MBS), is based on the numerical solution of ordinary differential equations for beam parameters. As a benchmark, we compare simulations and data for a large number of physics fills in the 2018 Pb-Pb run at the CERN Large Hadron Collider (LHC), finding excellent agreement for most parameters, both between the simulations and with the measured data. Both codes are then used independently to predict the performance in future heavy-ion operation, with both Pb-Pb and p-Pb collisions, at the LHC and its upgrade, the High-Luminosity LHC. The use of two independent codes based on different principles gives increased confidence in the results.

physics.acc-ph↗
arXiv2015

High statistics study of the reaction $γp\to p\;2π^0$

The photoproduction of 2$π^0$ mesons off protons was studied with the Crystal Barrel/TAPS experiment at the electron accelerator ELSA in Bonn. The energy of photons produced in a radiator was tagged in the energy range from 600\,MeV to 2.5\,GeV. Differential and total cross sections and $pπ^0π^0$ Dalitz plots are presented. Part of the data was taken with a diamond radiator producing linearly polarized photons, and beam asymmetries were derived. Properties of nucleon and $Δ$ resonances contributing to the $pπ^0π^0$ final state were determined within the BnGa partial wave analysis. The data presented here allow us to determine branching ratios of nucleon and $Δ$ resonances for their decays into $pπ^0π^0$ via several intermediate states. Most prominent are decays proceeding via $Δ(1232)π$, $N(1440)1/2^+π$, $N(1520)3/2^-π$, $N(1680)5/2^+π$, but also $pf_0(500)$, $pf_0(980)$, and $pf_2(1270)$ contribute to the reaction.

nucl-ex↗
arXiv2015

Photoproduction of ω Mesons off the Proton

The differential cross sections and unpolarized spin-density matrix elements for the reaction $γp\to pω$ were measured using the CBELSA/TAPS experiment for initial photon energies ranging from the reaction threshold to 2.5 GeV. These observables were measured from the radiative decay of the $ω$ meson, $ω\toπ^0γ$. The cross sections cover the full angular range and show the full extent of the $t$-channel forward rise. The overall shape of the angular distributions in the differential cross sections and unpolarized spin-density matrix elements are in fair agreement with previous data. In addition, for the first time, a beam of linearly-polarized tagged photons in the energy range from 1150 MeV to 1650 MeV was used to extract polarized spin-density matrix elements. These data were included in the Bonn-Gatchina partial wave analysis (PWA). The dominant contribution to $ω$ photoproduction near threshold was found to be the $3/2^+$ partial wave, which is primarily due to the sub-threshold $N(1720)\,3/2^+$ resonance. At higher energies, pomeron-exchange was found to dominate whereas $π$-exchange remained small. These $t$-channel contributions as well as further contributions from nucleon resonances were necessary to describe the entire dataset: the $1/2^-$, $3/2^-$, and $5/2^+$ partial waves were also found to contribute significantly.

nucl-ex↗
arXiv2014

Fréchet derivative for light-like Wilson Loops

We address the equations of motion for the light-like QCD Wilson exponentials defined in the generalized loop space. We attribute an important class of the infinitesimal shape variations of the rectangular light-like Wilson loops to the Fréchet derivative associated to a diffeomorphism in loop space what enables the derivation of the law of the classically conformal-invariant shape variations. We show explicitly that the Fréchet derivative coincides (at least in the leading perturbative or- der) with the area differential operator introduced in the previous works. We discuss interesting implications of this result which will allow one to relate the rapidity evolution and ultra-violet evolution of phenomenologically important quantum correlation functions (such as 3-dimensional parton distribution functions) and geometrical properties of the light-like cusped Wilson loops.

hep-th↗
arXiv2014

Generalized Loop Space and Evolution of the Light-Like Wilson Loops

Equations of motion for the light-like QCD Wilson loops are studied in the generalized loop space (GLS) setting. To this end, the classically conformal-invariant non-local variations of the cusped Wilson exponentials lying (partially) on the light-cone are formulated in terms of the Fréchet derivative. The rapidity and renormalization-group behaviour of the gauge-invariant quantum correlation functions (in particular, the three-dimensional parton densities) are demonstrated to be connected to certain geometrical properties of the Wilson loops defined in the GLS.

hep-ph↗
arXiv2014

Measurement of polarisation observables in $K^0_sΣ^+$ photoproduction off the proton

The reaction $γ\, p \rightarrow K^0_S\,Σ^+$ is studied in the photon energy range from threshold. Linearly polarised photon beams from coherent bremsstrahlung enabled the first measurement of photon beam asymmetries in this reaction up to $E_γ= 2250$ MeV. In addition, the recoil hyperon polarisation was determined through the asymmetry in the weak decay $Σ^+ \rightarrow p π^0$ up to $E_γ= 1650$ MeV. The data are compared to partial wave analyses, and the possible impact on the interpretation of a recently observed cusp-like structure near the $K^*$ thresholds is discussed.

nucl-ex↗
arXiv2014

On Geometric Scaling of Light-Like Wilson Polygons: Higher Orders in $α_s$

We address the scaling behaviour of contour-shape-dependent ultra-violet singularities of the light-like cusped Wilson loops in Yang-Mills and ${\cal N} = 4$ super-Yang-Mills theories in the higher orders of the perturbative expansion. We give the simple arguments to support the idea that identifying of a special type of non-local infinitesimal shape variations of the light-like Wilson polygons with the Fréchet differentials results in the combined geometric and renormalization-group evolution equation, which is applicable beyond the leading order exponentiated Wilson loops.

hep-th↗
arXiv2013

Characterization and performances of a monitoring ionization chamber dedicated to IBA-universal irradiation head for Pencil Beam Scanning

Every radiotherapy center has to be equipped with real-time beam monitoring devices. In 2008, the medical application group from the Laboratory of Corpuscular Physics (LPC Caen) developed an Ionization Chamber in collaboration with the company IBA (Ion Beam Applications). This monitoring device called IC2/3 was developed to be used in IBAs universal irradiation head for Pencil Beam Scanning (PBS). The objectives presented in this article are to characterize the IC2/3 monitor in the energy and ux ranges used in protontherapy. The equipment has been tested with an IBAs cyclotronable to deliver proton beams from 70 to 230 MeV. This beam monitoring device has been validated and is now installed at the Westdeutsches Protonentherapiezentrum Essen protontherapy center (WPE, Germany). The results obtained in both terms of spatial resolution and dose measurements are at least equal to the initials speci cations needed for PBS purposes. The detector measures the dose with a relative precision better than 1% in the range 0.5 Gy/min to 8 Gy/min while the spatial resolution is higher than 250 m. The technology has been patented and ve IC2/3 chambers were delivered to IBA. Nowadays, IBA produces the IC2/3 beam monitoring device as part of its Proteus 235 product

physics.ins-det↗
arXiv2013

Evolution of Light-Like Wilson Loops with a Self-Intersection in Loop Space

Recently, we proposed a general evolution equation for single quadrilateral Wilson loop on the light-cone. In present work, we study the energy evolution of a combination of two such loops that partially overlap or have a self-intersection. We show that, for a class of geometric variations, then evolution is consistent with our previous conjecture, and we are able to handle the intricacies associated with the self-intersections and overlaps. This way, a step forward is made towards the understanding of loop space, with the hope of studying more complicated structures appearing in phenomenological relevant objects, such as parton distributions.

hep-ph↗
arXiv2013

Evolution of transverse-distance dependent parton densities at large-$x_B$ and geometry of the loop space

We discuss possible applications of the equations of motion in the generalized Wilson loop space to the phenomenology of the three-dimensional parton distribution functions in the large-$x_B$ approximation. This regime is relevant for future experimental programs to be launched at the (approved) Jefferson Lab 12 GeV upgrade and the (planned) Electron-Ion Collider. We show that the geometrical evolution of the Wilson loops corresponds to the combined rapidity and renormalization-group equation of the transverse-distance dependent parton densities in the large-$x_B$ factorization scheme.

hep-ph↗
arXiv2013

Cusped light-like Wilson loops in gauge theories

We propose and discuss a new approach to the analysis of the correlation functions which contain light-like Wilson lines or loops, the latter being cusped in addition. The objects of interest are therefore the light-like Wilson null-polygons, the soft factors of the parton distribution and fragmentation functions, high-energy scattering amplitudes in the eikonal approximation, gravitational Wilson lines, etc. Our method is based on a generalization of the universal quantum dynamical principle by J. Schwinger and allows one to take care of extra singularities emerging due to light-like or semi-light-like cusps. We show that such Wilson loops obey a differential equation which connects the area variations and renormalization group behavior of those objects and discuss the possible relation between geometrical structure of the loop space and area evolution of the light-like cusped Wilson loops.

hep-ph↗
arXiv2012

Evolution of cusped light-like Wilson loops and geometry of the loop space

We discuss the possible relation between certain geometrical properties of the loop space and energy evolution of the cusped Wilson exponentials defined on the light-cone. Analysis of the area differential equations for this special class of the Wilson loops calls for careful treatment of the ultraviolet and rapidity divergences which make those loops non-multiplicatively-renormalizable. We propose to consider the renormalization properties of the light-cone cusped Wilson loops from the point of view of the universal quantum dynamical approach introduced by Schwinger. We conjecture and discuss the relevance of the Makeenko-Migdal loop equations supplied with the modified Schwinger principle to the energy evolution of some phenomenologically significant objects, such as transverse-momentum dependent distribution functions, collinear parton densities at large-$x$, etc.

hep-th↗
arXiv2012

Loop space and evolution of the light-like Wilson polygons

We address a connection between the energy evolution of the polygonal light-like Wilson exponentials and the geometry of the loop space with the gauge invariant Wilson loops of a variety of shapes being the fundamental degrees of freedom. The renormalization properties and the differential area evolution of these Wilson polygons are studied by making use of the universal Schwinger quantum dynamical approach. We discuss the appropriateness of the dynamical differential equations in the loop space to the study of the energy evolution of the collinear and transverse-momentum dependent parton distribution functions.

hep-th↗
arXiv2012

Transparency ratio in γA -> η' A' and the in-medium η' width

The photoproduction of η'-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500 - 2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations describing the propagation of η'-mesons in nuclei. The comparison indicates a width of the η' -meson of the order of Γ= 15-25 MeV at ρ=ρ_0 for an average momentum p_{η'} = 1050 MeV/c, at which the η'-meson is produced in the nuclear rest frame. The inelastic η' N cross section is estimated to be 3 - 10 mb. Parameterizing the photoproduction cross section of η'-mesons by σ(A) = σ_0 A^α, a value of α= 0.84\pm0.03 has been deduced.

nucl-ex↗
arXiv2011

Anomaly in the K^0_S Sigma^+ photoproduction cross section off the proton at the K* threshold

The $γ+ p \rightarrow K^0 + Σ^+$ photoproduction reaction is investigated in the energy region from threshold to $E_γ= 2250$\,MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the $K^*$ threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the $K^*Λ$ and $K^*Σ$ thresholds. It is speculated whether this signals the turnover of the reaction mechanism from t-channel exchange below the $K^*$ production threshold to an s-channel mechanism associated with the formation of a dynamically generated $K^*$-hyperon intermediate state.

nucl-ex↗
arXiv2011

Photoproduction of Neutral Pions off Protons

Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction $γp\to pπ^0$ for photon energies between 0.85 and 2.50 GeV. The $π^0$ mesons are observed in their dominant neutral decay mode: $π^0\toγγ$. For the first time, the differential cross sections cover the very forward region, $θ_{\rm c.m.}<60^\circ$. A partial-wave analysis of these data within the Bonn-Gatchina framework observes the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).

nucl-ex↗