Showing papers in "Epj Web of Conferences in 2022"

Systematics in the global polarization measurements of Λ hyperons with HADES at SIS18

Abstract: The global polarization of Λ hyperons has been measured in Au+Au and Ag+Ag collisions at √SNN = 2.4 and 2.55 GeV recorded with HADES. An increase of the polarization is observed following the trend measured by the STAR Collaboration. The high statistics Ag+Ag data allowed for differential measurements of the polarization. The study of acceptance effects is very important in the fixed target setup, as the phase-space coverage is not symmetric. These studies are reported together with the evaluation procedure of the systematic uncertainties.

Origin of the Proton Mass

Abstract: Atomic nuclei lie at the core of everything visible; and at the first level of approximation, their atomic weights are simply the sum of the masses of all the neutrons and protons (nucleons) they contain. Each nucleon has a mass mN ≈ 1 GeV ≈ 2000-times the electron mass. The Higgs boson – discovered at the large hadron collider in 2012, a decade ago – produces the latter, but what generates the nucleon mass? This is a pivotal question. The answer is widely supposed to lie within quantum chromodynamics (QCD), the strong-interaction piece of the Standard Model. Yet, it is far from obvious. In fact, removing Higgs-boson couplings into QCD, one arrives at a scale invariant theory, which, classically, can’t support any masses at all. This contribution sketches forty years of developments in QCD, which suggest a solution to the puzzle, and highlight some of the experiments that can validate the picture.

Another look at the Landau gauge three-gluon vertex

Abstract: We revisit the computation of the three-gluon vertex in the Landau gauge using lattice QCD simulations with large physical volumes of ~ (6.5 fm) 4 and ~ (8 fm) 4 and large statistical ensembles. For the kinematical configuration analysed, that is described by a unique form factor, an evaluation of the lattice artefacts is also performed. Particular attention is given to the low energy behavior of vertex and its connection with evidence (or lack of it) of infrared ghost dominance.

Low-pT μ+μ− pair production in Au+Au collisions at √SNN = 200 GeV at STAR

Abstract: We report the measurements of μ+μ− pair production for pT < 0.10 GeV/c in 40-80% Au+Au collisions at √SNN = 200 GeV at STAR. A significant enhancement with respect to the hadronic cocktail is observed. The pT2 and ∆ϕ distributions of the excess yields are also reported and compared with model calculations. The EPA-QED calculations can describe the data very well within uncertainties.

New methods for theranostic radioisotope production with solid targets at the Bern medical cyclotron

Abstract: The production of theranostic radionuclides using solid targets is challenging and requires an accurate knowledge of the production crosssections as well as the energy, positioning and focusing of the beam. A research program is ongoing at the 18 MeV Bern medical cyclotron, equipped with a Solid Target Station (STS) and a 6 m Beam Transfer Line (BTL) ending in a separate bunker with independent access. A novel target coin was designed and built to irradiate compressed powder pellets, together with a compact focalization system to optimize the irradiation procedure. Furthermore, methods were developed to measure the beam energy, the production cross-sections and the EoB-activity.

Muonium Lamb shift: theory update and experimental prospects

Abstract: We review the theory of the Lamb shift for muonium, provide an updated numerical value and present the prospects of the Mu-MASS collaboration at PSI to improve upon their recent measurement. Due to its smaller nuclear mass, the contributions of the higher-order recoil corrections (160 kHz level) and nucleus self-energy (40 kHz level) are enhanced for muonium compared to hydrogen where those are below the level of the latest measurement performed by Hessels et al. and thus could not be tested yet. The ongoing upgrades to the Mu-MASS setup will open up the possibility to probe these contributions and improve the sensitivity of this measurement to searches for new physics in the muonic sector.

Role of the effective range in the weak-binding relation

Abstract: We study the range correction in the weak-binding relation, which relates the internal structure of hadrons with the scattering length and the binding energy. Utilizing the effective field theories, we show that the effective range originates from the derivative coupling interaction as well as from the channel coupling to the bare state, and that the different contributions are not distinguishable. By examining the compositeness in the effective field theories, it is demonstrated that the effective range induces the finite range correction for the weak-binding relation in addition to the previously known contributions. We thus propose to include the range correction in the uncertainty terms of the weak-binding relation.

Gravitational Waves from dark composite dynamics

Abstract: We discuss the stochastic gravitational-wave spectrum from dark confinement and chiral phase transitions in the early Universe. Specifically, we look at pure Yang-Mills theory for an arbitrary number of colours as well as SU(3) with quarks in different representations. We utilise thermodynamic Lattice data and map it to effective models, such as the Polyakov-loop and the PNJL model. This allows us to compute gravitational-wave parameters and the corresponding gravitational-wave signal. We compare the signal to future gravitational-wave observatories such as the Big Bang Observer and DECIGO.

Overview of recent lattice QCD results: phase diagram, fluctuations and strangeness

Abstract: In recent years there has been much progress on the investigation of the QCD phase diagram with lattice QCD. This work will focus on the developments in the last few years with physical parameters and low chemical potential which are obtained by extrapolations from zero or imaginary chemical potential.

Three-gluon vertex in Landau-gauge from quenched-lattice QCD in general kinematics

Abstract: We report on a novel and extensive lattice QCD analysis for the three-gluon vertex from quenched lattice-QCD simulations. Using standard Wilson action, we have computed the three-gluon vertex beyond the usual kinematic restriction to the symmetric (q2 = r2 = p2) and soft-gluon (p = 0) cases where it depends on a single momentum scale. The so-dubbed bisectoral case (r2 = q2 ≠ p2), where the transversely projected vertex can be cast in terms of three independent tensors, have been the object of a recent exhaustive scrutiny [1], also shown in this communication. Herein, beyond this special case, results for kinematic configurations with three different squared momenta are also presented. All data considered, the lattice estimate of the three-gluon vertex exhibits a clear dominance of the tree-level tensor form factor.

Fusion: a true challenge for an enormous reward

Abstract: A source of energy which would be inexhaustible, inherently safe and environmentally friendly, is this not a marvellous prospect? Nuclear fusion is a possible candidate for this role. It has been the energy source of our Sun and the stars in the universe for billions of years. The process requires temperatures of tens of millions of degrees, so extremely high and foreign to our daily experience that it seems out of reach. Nevertheless, these extremely high temperatures are routinely realised in several laboratories all over the world. Since the early 1990s, tens of MW of fusion power have been released from fusion reactions. Progress in the last years shows that fusion holds the promise to be a clean and safe solution for mankind’s long-term energy needs. We are witnessing the birth of a new technology destined to meet the gigantic future energy needs of mankind with minimal impact on the environment.

Midrapidity cluster formation in heavy-ion collisions

Abstract: We study the production of clusters and hypernuclei at midrapidity employing the Parton-Hadron- Quantum-Molecular-Dynamics (PHQMD) approach, a microscopic n-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent 2-body potential interactions. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at relativistic energies. PHQMD allows to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the ’ice in the fire’ puzzle. To investigate whether this explanation of the ’ice in the fire’ puzzle applies only to the MST results we study also the deuterons production by coalescence. We embed MST and coalescence in the PHQMD and UrQMD transport approaches in order to obtain model independent results. We find that both clustering procedures give very similar results for the deuteron observables in the UrQMD as well as in the PHQMD environment. This confirms that our solution for the ’ice in the fire’ puzzle is common to MST and coalescence and independent of the transport approach.

HADES Overview

Abstract: In March 2019 the HADES experiment recorded 14 billion Ag+Ag collisions at √SNN = 2.55 GeV as a part of the FAIR phase-0 physics program. With the capabilities to measure and analyze particles forming the bulk matter, namely pions, protons and light nuclei, as well as rare probes like dilepton decays of vectormesons and strange hadrons, the HADES experiment allows to study the properties of matter at high densities in great detail. In this contribution a special focus is put on the reconstruction of weakly decaying strange hadrons.

CONCERTO at APEX: Installation and first phase of on-sky commissioning

Abstract: CONCERTO (CarbON CII line in post-rEionisation and ReionisaTiOn) is a large field-of-view (FoV) spectro-imager that has been installed on the Cassegrain Cabin of Atacama Pathfinder EXperiment (APEX) telescope in April 2021. CONCERTO hosts 2 focal planes and a total number of 4000 Kinetic Inductance Detectors (KID), with an instantaneous FoV of 18.6 arcminutes in the range of 130-310 GHz. The spectral resolution can be easily tuned down to 1 GHz depending on the scientific target. The scientific program of CONCERTO has many objectives, with two main programs focused on mapping the fluctuations of the [CII] line intensity in the reionisation and postreionisation epoch (4.5<z<8.5), and on studying galaxy clusters via the thermal and kinetic Sunyaev-Zel’dovich (SZ) effect. CONCERTO will also measure the dust and molecular gas contents of local and intermediate-redshift galaxies, it will study the Galactic star-forming clouds and finally it will observe the CO intensity fluctuations arising from 0.3<z<2 galaxies. The design of the instrument, installation at APEX and current status of the commissioning phase and science verification will be presented. Also we describe the deployment and first on-sky tests performed between April and June 2021.

Commissioning of Underground Nuclear Astrophysics Experiment JUNA in China

Abstract: Underground Nuclear Astrophysics Experiment in China (JUNA) has been commissioned by taking the advantage of the ultra-low background in Jinping underground lab. High current mA level 400 KV accelerator with an ECR source and BGO detectors were commissioned. JUNA studies directly a number of nuclear reactions important to hydrostatic stellar evolution at their relevant stellar energies. In the first quarter of 2021, JUNA performed the direct measurements of 25Mg(p,γ)26Al, 19F(p,α)16O, 13C(α,n)16O and 12C(α,γ)16O near the Gamow window. The experimental results reflect the potential of JUNA with higher statistics, precision and sensitivity of the data. The preliminary results of JUNA experiment and future plan are given.

Nonequilibrium evolution of quarkonium in medium

Abstract: We review recent progress in open quantum system approach to the description of quarkonium in the quark-gluon plasma. A particular emphasis is put on the Lindblad equations for quarkonium and its numerical simulations.

The density of states method in Yang-Mills theories and first order phase transitions

Abstract: Extensions of the standard model that lead to first-order phase transitions in the early universe can produce a stochastic background of gravitational waves, which may be accessible to future detectors. Thermodynamic observables at the transition, such as the latent heat, can be determined by lattice simulations, and then used to predict the expected signatures in a given theory. In lattice calculations, the emergence of metastabilities in proximity of the phase transition may make the precise determination of these observables quite challenging, and may lead to large uncontrolled numerical errors. In this contribution, we discuss as a prototype lattice calculation the first order deconfinement transition that arises in the strong SU(3) Yang-Mills sector. We adopt the novel logarithmic linear relaxation method, which can provide a determination of the density of states of the system with exponential error suppression. Thermodynamic observables can be reconstructed with a controlled error, providing a promising direction for accurate model predictions in the future.

Inverse problems, real-time dynamics and lattice simulations

Abstract: The determination of real-time dynamics of strongly coupled quantum fields is a central goal of modern nuclear and particle physics, which requires insight into quantum field theory beyond the weak-coupling approximation. While lattice QCD has provided vital insights into the non-perturbative static properties of quarks and gluons it hides their real-time dynamics behind an ill-posed inverse problem. In this proceeding I will discuss developments in tackling the inverse problem on the lattice and touch upon progress in the direct simualtion of real-time dynamics.

Static quark anti-quark interactions at non-zero temperature from lattice QCD

Abstract: We present results on the in-medium interactions of static quark antiquark pairs using realistic 2+1 HISQ flavor lattice QCD. Focus is put on the extraction of spectral information from Wilson line correlators in Coulomb gauge using four complementary methods. Our results indicate that on HISQ lattices, the position of the dominant spectral peak associated with the real-part of the interquark potential remains unaffected by temperature. This is in contrast to prior work in quenched QCD and we present follow up comparisons to newly generated quenched ensembles.

The hydrostatic mass bias in The Three Hundred clusters

Abstract: The assumption of Hydrostatic equilibrium (HE) is often used in observations to estimate galaxy clusters masses. We use a set of almost 300 simulated clusters from T he T hree H undred Project, to estimate the cluster HE mass and the bias deriving from it. We study the dependence of the bias on several dynamical state indicators across a redshift range from 0.07 to 1.3, finding no dependence between them. Moreover, we focus our attention on the evolution of the HE bias during the merger phase, where the bias even reaches negative values due to an overestimation of the mass with HE.

The ¹²C+¹²C fusion reaction at stellar energies

Abstract: The carbon fusion reaction is crucial in stellar evolution. Despite six decades of studies, there is still a large uncertainty in the reaction rate which limits our understanding of various stellar objects, such as massive stars, type Ia supernovae, and superbursts. In this paper, we review the experimental and theoretical studies of the carbon fusion reaction at sub-barrier energies. An outlook for future studies is also presented.

Panther — the new thermal neutron time-of-flight spectrometer at the ILL

Abstract: Panther is a new high-flux medium-resolution direct-geometry thermal-neutron time-of-flight spectrometer at the Institut Laue-Langevin (ILL). It is designed for inelastic neutron-scattering measurements of excitations in condensed matter using single crystals, polycrystalline samples, and liquids. Panther uses double focusing graphite or Cu monochromators, a Fermi chopper, and position-sensitive 3He detectors covering 2 steradians of solid angle. A system of disc choppers and an optional sapphire filter are used to reduce the epithermal neutron background. Thermal neutron background is reduced by a radial oscillating collimator, a beam dump, and an elaborate set of Cd shielding inside the evacuated detector tank. The outside of the tank is covered by a 0.3 m thick layer of borated high-density polyethylene to reduce ambient and cosmic background. The design and performance of the instrument in its current status are described, as well as planned developments.

A comparison of spectral reconstruction methods applied to non-zero temperature NRQCD meson correlation functions

Abstract: We present results from the fastsum collaboration's programme to determine the spectrum of the bottomonium system as a function of temperature. Three different methods of extracting spectral information are discussed: a Maximum Likelihood approach using a Gaussian spectral function for the ground state, the Backus Gilbert method, and the Kernel Ridge Regression machine learning procedure. We employ the fastsum anisotropic lattices with 2+1 dynamical quark flavours, with temperatures ranging from 47 to 375 MeV.

Thermal model description of the particle spectra in the few-GeV energy regime

Abstract: It has been demonstrated that Statistical Hadronization Model fits perfectly to particle yields at freeze-out in heavy-ion and hadron collisions at LHC, RHIC and SPS, where quark-gluon plasma is created. It is however entirely not clear if particles emitted in the few-GeV energy regime can be understood as emerging from thermalized hadronic medium. Our recent work suggests that this might be the case. By implementing appropriate fireball geometry and expansion pattern in the THERMINATOR (THERMal heavy IoN generATOR) it was possible to describe not only yields, but also the spectra of most abundant particles measured at GSI SIS18. Most of the latter are pure prediction of the model. We present details of the model and extended comparison with experimental data and discuss further developments.

Quarkonia dynamics in the QGP with open quantum systems

Abstract: We investigate the real-time dynamics of a correlated heavy quarkantiquark pair inside the Quark-Gluon Plasma using new quantum master equations derived from first QCD principles and based on the work of Blaizot & Escobedo [4]. The full equations are directly numerically solved in one-dimension to reduce computing costs and is used to gain insight on the dynamics in both a static and evolving medium following a Björken-like temperature evolution. The effect of the initial state on the dynamics is also studied.

The static potential using trial states from Laplacian eigenmodes

Abstract: We compute the static potential of a quark-antiquark pair in lattice QCD using a method which is not based on Wilson loops, but where the trial states are formed by eigenvector components of the covariant lattice Laplace operator. The computational effort of this method is significantly lower than the standard Wilson loop calculation, when computing the static potential not only for on-axis, but also for many off-axis quark-antiquark separations, i.e., when a fine spatial resolution is required, e.g., for string breaking calculations. We further improve the signal by using multiple eigenvector pairs, weighted with Gaussian profile functions of the eigenvalues, providing a basis for a generalized eigenvalue problem (GEVP), as it was recently introduced to improve distillation in meson spectroscopy. We show results from the new method for the static potential with dynamical fermions and demonstrate its efficiency compared to traditional Wilson loop calculations.

Event-by-event correlations and fluctuations with strongly intensive quantities in heavy-ion collisions with ALICE

Abstract: The strongly intensive quantity Σ is a new observable, introduced recently to the domain of heavy-ion physics. In superposition models which assume independent particle production from statistically identical sources, Σ is insensitive to the number of sources and its fluctuations, contrary to the standard forward-backward correlation coefficient (bcorr). Therefore it provides direct information on the multiplicity correlations and fluctuations from a single source. This paper presents new results on forward-backward correlations studied with the quantity Σ, measured by ALICE at the LHC in Xe–Xe collisions at √sNN = 5.44 TeV and in Pb–Pb collisions at √sNN = 2.76 and 5.02 TeV. These results are compared with ALICE measurements in pp collisions at √s = 13 TeV.

Unitarizing infinite-range forces: Graviton-graviton scattering, the graviball, and Coulomb scattering

Abstract: We study graviton-graviton scattering in partial-wave amplitudes after unitarizing their Born terms. In order to apply S -matrix techniques, based on unitarity and analyticity, we introduce an S -matrix associated to this resummation that is free of infrared divergences. This is achieved by removing the diverging phase factor calculated by Weinberg that multiplies the S matrix, and that stems from the virtual infrared gravitons. A scalar graviton-graviton resonance with vacuum quantum numbers is obtained as a pole in the nonperturbative S -wave amplitude, which is called the graviball. Its resonant effects along the physical real s-axis may peak at values substantially lower than the UV cutoff squared of the theory, similarly to the σ resonance in QCD. These techniques are also applied to study nonrelativistic Coulomb scattering up to next-to-leading order in the unitarization program. A comparison with the exact known solution is very illuminating.

Deciphering the phases of QCD matter with fluctuations and correlations of conserved charges

Abstract: A review is given on recent experimental and theoretical/phenomenological developments regarding the phase structure of the strongly interacting matter. Specifically, evolution with collision energy of netproton number fluctuations as measured by several experiments are presented and their implications for the QCD phase diagram are outlined. In addition, theoretical calculations on correlations between conserved charges are presented and prospects for their experimental explorations are addressed.

The high-energy limit of perturbative QCD: Theory and phenomenology

Abstract: After a brief introduction of formal and phenomenological progresses in the study of the high-energy limit of perturbative QCD, we present arguments supporting the statement that the inclusive emission of Higgs bosons or heavy-flavored hadrons acts as fair stabilizer of high-energy resummed differential distributions. We come out with the message that the hybrid high-energy and collinear factorization, built in term of the next-to-leading logarithmic resummation à la BFKL and supplemented by collinear parton distributions and fragmentation functions, is a valid and powerful tool to gauge the feasibility of precision analyses of QCD in its high-energy limit.