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Recent experimental data from $pp$ collisions have shown a significant increase in heavy baryon production leading to a baryon over meson ratio which is one order of magnitude higher than elementary collisions ($e^+e^-$, $ep$). From a theoretical point of view this large production of baryon can be explained with hadronization via quark coalescence assuming a QGP medium in $pp$ collisions. In this study, we extend this analysis to include hadrons containing bottom quarks. Employing a coalescence plus fragmentation approach, we present predictions for $p_T$ spectra and the heavy baryon/meson ratio of charmed hadrons with and without strangeness content, specifically: $\bar{B^0}$, $B_s$, $\Lambda_b$, $\Xi_b^{0,-}$, $\Omega_b$, and the $B_c$ meson. We have found that coalescence is the dominant mechanism in the B meson production, especially at low momenta, at variance with what found in the charm sector where the D meson were mainly produced via fragmentation. Our model predicts a $\Lambda_b/\bar{B^0}\approx0.5\!-\!1$ and $\Xi_b^0/\bar{B^0}$ ratio around 0.3 at very low transverse momentum, which are about $1.5$ larger then those of the corresponding charmed hadron ratios at the same collision energy. Furthermore, we discuss the relative ratios between charmed and bottomed hadrons, emphasizing how these observables can provide information about the distribution of charm and bottom quarks and, if experimentally observed, would further support the idea of quark-gluon plasma formation even in small collision systems., Comment: 9 pages, 4 Figures

This paper is a write-up of the ideas that were presented, developed and discussed at the fourth International Workshop on QCD Challenges from pp to AA, which took place in February 2023 in Padua, Italy. The goal of the workshop was to focus on some of the open questions in the field of high-energy heavy-ion physics and to stimulate the formulation of concrete suggestions for making progresses on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.

Heavy-flavor hadrons produced in ultra-relativistic heavy-ion collisions are a sensitive probe for studying hadronization mechanisms of the quark-gluon-plasma. In this work, we survey how different transport models for the simulation of heavy-quark diffusion through a quark-gluon plasma in heavy-ion collisions implement hadronization and how this affects final-state observables. Utilizing the same input charm-quark distribution in all models at the hadronization transition, we find that the transverse-momentum dependence of the nuclear modification factor of various charm hadron species has significant sensitivity to the hadronization scheme. In addition, the charm-hadron elliptic flow exhibits a nontrivial dependence on the elliptic flow of the hadronizing partonic medium., Comment: 21 pages, 12 figures

We theoretically investigate the possibility of obtaining Majorana zero modes (MZMs) in penta-silicene nanoribbons (p-SiNRs) with induced \textit{p}-wave superconductivity. The model explicitly considers an external magnetic field perpendicularly applied to the nanoribbon plane, as well as an extrinsic Rashba spin-orbit coupling (RSOC), in addition to the first nearest neighbor hopping term and \textit{p}-wave superconducting pairing. By analyzing the dispersion relation profiles, we observe the successive closing and reopening of the induced superconducting gap with a single spin component, indicating a spin-polarized topological phase transition (TPT). Correspondingly, the plots of the energy spectrum versus the chemical potential reveal the existence of zero-energy states with a preferential spin orientation characterized by nonoverlapping wave functions localized at opposite ends of the superconducting p-SiNRs. These findings strongly suggest the emergence of topologically protected, spin-polarized MZMs at the ends of the p-SiNRs with induced \textit{p}-wave superconducting pairing, which can be realized by proximitizing the nanoribbon with an \textit{s}-wave superconductor, such as lead. The proposal paves the way for silicene-based Majorana devices hosting multiple MZMs with a well-defined spin orientation, with possible applications in fault-tolerant quantum computing platforms and Majorana spintronics., Comment: 12 pages, 9 figures

Many molecules observed in the interstellar medium are thought to result from thermal desorption of ices. Parameters such as desorption energy and pre-exponential frequency factor are essential to describe the desorption of molecules. Experimental determinations of these parameters are missing for many molecules, including those found in the interstellar medium. The objective of this work is to expand the number of molecules for which desorption parameters are available, by collecting and re-analysing experimental temperature programmed desorption data that are present in the literature. Transition State Theory (TST) is used in combination with the Redhead equation to determine desorption parameters. Experimental data and molecular constants (e.g., mass, moment of inertia) are collected and given as input. Using the Redhead-TST method, the desorption parameters for 133 molecules have been determined. The Redhead-TST method is found to provide reliable results that agree well with desorption parameters determined with more rigorous experimental methods. The importance of using accurately determined pre-exponential frequency factors to simulate desorption profiles is emphasised. The large amount of data allows to look for trends, the most important is the relationship log$_{10}$($\nu$) = 2.65ln($m$) + 8.07, where $\nu$ is the pre-exponential frequency factor and $m$ the mass of the molecule. The data collected in this work allow to model the thermal desorption of molecules and help understand changes in chemical and elemental composition of interstellar environments., Comment: Accepted for Astronomy and Astrophysics

We study the production of charmed and multi-charmed hadrons in ultra-relativistic Heavy Ion Collisions coupling the transport approach for charm dynamics in the medium to an hybrid hadronization model of coalescence plus fragmentation. In this paper, we mainly discuss the particle yields for single charmed and multi-charmed baryons focusing mainly on the production of $\Xi_{cc}$ and $\Omega_{ccc}$. We provide first predictions for PbPb collision in 0-10% centrality class and then we explore the system size dependence through KrKr, to ArAr and OO collisions, planned within the ALICE3 experiment. In these cases, a monotonic behavior for the yields emerges which can be tested in future experimental data. We found about three order of magnitude increase in the production of $\Omega_{ccc}$ in PbPb collisions compared with the yield in small collision systems like OO collisions. Furthermore, we investigate the effects on the $\Omega_{ccc}$ particle production and spectra coming from the modification of the charm quark distribution due to the different size of the collision systems comparing also to the case of thermalized charm distributions. These results suggest that observation on the $\Omega_{ccc}$ spectra and their evolution across system size can give information about the partial thermalization of the charm quark distribution as well as to its wave function width., Comment: 12 pages, 8 figures; minor changes and adding of a figure

In the last decade a Quasi-Particle Model (QPM) has been developed to study charm quark dynamics in ultra-relativistic heavy-ion collisions supplying a satisfactory description of the main observables for $D$ meson and providing an estimate of the space-diffusion coefficient $D_s(T)$ from the phenomenology. In this paper, we extend the approach to bottom quarks describing their propagation in the quark-gluon plasma within an event-by-event full Boltzmann transport approach followed by a coalescence plus fragmentation hadronization. We find that QPM approach is able to correctly predict the first available data on $R_{AA}(p_T)$ and $v_{2}(p_T)$ of single-electron from B decays without any parameter modification w.r.t. the charm. We show also predictions for centralities where data are not yet available for both $v_{2}(p_T)$ and $v_{3}(p_T)$. Moreover, we discuss the significant breaking of the expected scaling of the thermalization time $\tau_{th}$ with $M_Q/T$, discussing the evolution with mass of $D_s(T)$ to better assess the comparison to lQCD calculations. We find that at $T=T_c$ charm quark $D_s(T)$ is about a factor of 2 larger than the asymptotic value for $M \rightarrow \infty$, while bottom $D_s(T)$ is only a $20-25\%$ higher. This implies a $D_{s}(T)$ which is consistent within the current uncertainty to the most recent lattice QCD calculations with dynamical quarks for $M \rightarrow \infty$., Comment: 8 pages, 5 figures

Helium (He) retention in tungsten (W) is a concern in fusion reactors since it could be detrimental to plasma facing components performance and influence the fusion fuel balance. He being not soluble in W, it tends to agglomerate on preexisting defects (vacancy, grain boundary), but it could in theory also self-trap (be immobilized on a non-preexisting vacancy) through the emission of a vacancy/self-interstitial W pair in the vicinity of a Hen interstitial cluster. In the present study, we prepared a pure single crystal W(110) sample with a clean surface in order to evidence the self-trapping of He in the W bulk at a sample temperature of 300 K and for a constant fluence of 2.0x10$^{21}$ He$^+$.m$^{-2}$. At a He$^+$ kinetic energy of 130 eV and a flux of 0.3x10$^{17}$ He$^+$.m$^{-2}$.s$^{-1}$, we only observed a small He desorption peak below 600 K. Rising the ion flux to 0.7x10$^{17}$ He$^+$.m$^{-2}$.s$^{-1}$, we observed the sudden appearance of two desorption peaks at 950 K and 1700 K. For the highest flux studied in this work, 5.0x10$^{17}$ He$^+$.m$^{-2}$.s$^{-1}$, an additional desorption peak at 1800 K and a desorption shoulder at 1900 K are observed. The temperature position of these He desorption peaks are consistent with the density functional theory literature and points to the occurrence of self-trapping once the 0.7x10$^{17}$ He$^+$.m$^{-2}$.s$^{-1}$ flux is attained at 300 K and to the possible realization of trap-mutation for the flux of 5.0x10$^{17}$ He$^+$.m$^{-2}$.s$^{-1}$. The present set of results should be used to constrain the development of He retention and He bubbles growth models based on ab initio quantities.

Acetaldehyde is one of the most common and abundant gaseous interstellar complex organic molecules, found in cold and hot regions of the molecular interstellar medium. Its presence in the gas-phase depends on the chemical formation and destruction routes, and its binding energy (BE) governs whether acetaldehyde remains frozen onto the interstellar dust grains or not. In this work, we report a combined study of the acetaldehyde BE obtained via laboratory TPD (Temperature Programmed Desorption) experiments and theoretical quantum chemical computations. BEs have been measured and computed as a pure acetaldehyde ice and as mixed with both polycrystalline and amorphous water ice. Both calculations and experiments found a BE distribution on amorphous solid water that covers the 4000--6000 K range, when a pre-exponential factor of $1.1\times 10^{18}s^{-1}$ is used for the interpretation of the experiments. We discuss in detail the importance of using a consistent couple of BE and pre-exponential factor values when comparing experiments and computations, as well as when introducing them in astrochemical models. Based on the comparison of the acetaldehyde BEs measured and computed in the present work with those of other species, we predict that acetaldehyde is less volatile than formaldehyde, but much more than water, methanol, ethanol, and formamide. We discuss the astrochemical implications of our findings and how recent astronomical high spatial resolution observations show a chemical differentiation involving acetaldehyde, which can easily explained as due to the different BEs of the observed molecules., Comment: 12 pages, 6 figures

We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of an event-by-event transport approach. In our calculations the non-perturbative interaction between heavy quarks and light quarks has been taken into account through a quasi-particle approach with thermal light quark masses tuned to reproduce lQCD thermodynamics. We found that the flow observables $v_2$ and $v_3$ of D mesons are comparable with the experimental measurements for Pb+Pb collisions at 5.02 ATeV in different ranges of centrality selections. The results are analyzed with Event-Shape Engineering technique. The comparison of the anisotropic flow coefficients $v_n$ with experimental data show a quite well agreement with experimental data for different flow vector $q_2$ selections, which confirms the strong coupling between charm quarks and light quarks in the QCD matter. Furthermore, we present here a novel study of the event-by-event correlations between flow harmonics of $D$ mesons and soft hadrons at LHC energy with the Event-Shape Engineering technique that can put further constraints on heavy quark transport coefficients toward a solid comparison between the phenomenological determination and the lattice QCD calculations., Comment: 8 pages, 8 figures

The evolution of star-forming regions and their thermal balance are strongly influenced by their chemical composition, that, in turn, is determined by the physico-chemical processes that govern the transition between the gas phase and the solid state, specifically icy dust grains (e.g., particles adsorption and desorption). Gas-grain and grain-gas transitions as well as formation and sublimation of interstellar ices are thus essential elements of understanding astrophysical observations of cold environments (e.g., pre-stellar cores) where unexpected amounts of a large variety of chemical species have been observed in the gas phase. Adsorbed atoms and molecules also undergo chemical reactions which are not efficient in the gas phase. Therefore, the parameterization of the physical properties of atoms and molecules interacting with dust grain particles is clearly a key aspect to interpret astronomical observations and to build realistic and predictive astrochemical models. In this consensus evaluation, we focus on parameters controlling the thermal desorption of ices and how these determine pathways towards molecular complexity and define the location of snowlines, which ultimately influence the planet formation process. We review different crucial aspects of desorption parameters both from a theoretical and experimental point of view. We critically assess the desorption parameters commonly used in the astrochemical community for astrophysical relevant species and provide tables with recommended values. In addition, we show that a non-trivial determination of the pre-exponential factor nu using the Transition State Theory can affect the binding energy value. Finally, we conclude this work by discussing the limitations of theoretical and experimental approaches currently used to determine the desorption properties with suggestions for future improvements., Comment: 115 pages, 17 figures

The recent experimental measurements on $pp$ collisions at $\sqrt{s}=5.02 \,\rm TeV$ have shown a very large abundance of heavy baryon production corresponding to a ratio of $\Lambda_c/D^0 \sim 0.6$, about one order of magnitude larger than what measured in $e^+e^-$, $ep$ collisions and even in $pp$ collisions at LHC, but at forward rapidity. We apply for the first time to $pp$ collisions a quark coalescence plus fragmentation approach developed for $AA$ collisions, assuming the formation of Hot QCD matter at finite temperature. An approach that has correctly predicted a $\Lambda_c/D \sim O(1)$ in AA collisions at RHIC energy. We calculate the heavy baryon/meson ratio and the $p_T$ spectra of charmed hadrons with and without strangeness content: $D^{0}$, $D_{s}$, $\Lambda_{c}^{+}$, $\Xi_c$ and $\Omega_c$ in $pp$ collisions at top LHC energies, finding a satisfactory result for the measured $\Lambda_{c}^{+}/D^0$ and the $\Xi_c/D^0$ without any specific tuning of parameters to $pp$ collisions. At variance with other approaches a coalescence approach predicts also a significant production of $\Omega_c$ such that $\Omega_c/D^0 \sim O(10^{-1})$ ., Comment: 8 pages, 5 figures; modifications in Figures 1,2,3,4,5 and corrected typos

Raman microscopy is one of the methods that could be used for future post-mortem analyses of samples extracted from ITER plasma facing. This study shows that this technique is useful for studying tungsten-based materials containing impurities including oxides and nitrides. Here, we apply pulsed laser deposition and DC argon glow discharges to produce tungsten-containing synthetic films (compact, porous) and nanoparticles and investigate the influence of their morphology on the measured Raman spectra. The amounts of oxygen and/or nitrogen in the films are also investigated. Comparative data are obtained by X-ray Photoelectrons Spectroscopy, Atomic Force Microscopy, Electron Microscopies (Scanning and Transmission), Energy Dispersive X-ray spectroscopy, Time-of-Flight Elastic Recoil Detection Analysis. The power density of the laser beam used to perform Raman microscopy is varied by up to 4 orders of magnitude (0.01-20 mW/$\mu$m 2) to investigate thermal stability of films and nanoparticles. As a first result, we give evidence that Raman microscopy is sensitive enough to detect surface native oxides. Secondly, more tungsten oxides are detected in porous materials and nanoparticles than in compact films, and the intensities of the Raman band correlate to their oxygen content. Thirdly, thermal stability of these films (i.e. structural and chemical modification under laser heating) is poor when compact films contain a sufficiently large amount of nitrogen. This finding suggests that nitrogen can be substituted by oxygen during Raman laser induced heating occurring in ambient air. Finally, our methodology can be used to rapidly characterize morphology and chemistry of the samples analyzed, and also to create oxides at the micrometer scale. keywords: PLD, Raman spectroscopy, tungsten oxide, tungsten nitride, plasma wall interaction, laser heating, post-mortem analysis 2, Comment: Nuclear Fusion, IOP Publishing, 2020

The heavy quarks (HQs) are unique probe of the hot QCD matter properties and their dynamics is coupled to the locally thermalized expanding quark gluon plasma. We present here a novel study of the event by event correlations between light and heavy flavour flow harmonics at LHC energy within a transport approach. Interaction between heavy quarks and light quarks have been taken into account exploring the impact of different temperature dependence of the transport coefficients $D_s$ and $\Gamma$. Our study indicates that $v^{heavy}_n-v^{light}_n$ correlation and the relative fluctuations of anisotropic flows, $\sigma_{v_{n}}/\langle v_n \rangle$, are novel observables to understand the heavy quark-bulk interaction and are sensitive to the temperature dependence even to moderate differences of $D_s(T)$, or $\Gamma(T)$. Hence a comparison of such new observables for HQ to upcoming experimental data at both RHIC and LHC can put further constraints on heavy quark transport coefficients and in particular on its temperature dependence toward a solid comparison between the phenomenological determination and the lattice QCD calculations., Comment: 7 pages, 6 figures

We study the propagation of heavy quarks (HQs) in the quark-gluon plasma (QGP) by means of a relativistic Boltzmann transport (RBT) approach. The non-perturbative interaction between heavy quarks and light quarks is described by means of a quasi-particle approach able to describe simultaneously the experimental data for the nuclear suppression factor $R_{\rm AA}$ and the elliptic flow $v_2(p_T)$ of D mesons from RHIC to LHC energies. In the same framework we predict the B meson nuclear modification factor at LHC. Finally, we discuss the relevance of initial state fluctuations that allows to extend the analysis to high order anisotropic flows $v_n(p_T)$ as well as to investigate the role of QCD interaction in developing correlations between the light and the heavy flavour anisotropic flows., Comment: 27th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018)

The future opportunities for high-density QCD studies with ion and proton beams at the LHC are presented. Four major scientific goals are identified: the characterisation of the macroscopic long wavelength Quark-Gluon Plasma (QGP) properties with unprecedented precision, the investigation of the microscopic parton dynamics underlying QGP properties, the development of a unified picture of particle production and QCD dynamics from small (pp) to large (nucleus--nucleus) systems, the exploration of parton densities in nuclei in a broad ($x$, $Q^2$) kinematic range and the search for the possible onset of parton saturation. In order to address these scientific goals, high-luminosity Pb-Pb and p-Pb programmes are considered as priorities for Runs 3 and 4, complemented by high-multiplicity studies in pp collisions and a short run with oxygen ions. High-luminosity runs with intermediate-mass nuclei, for example Ar or Kr, are considered as an appealing case for extending the heavy-ion programme at the LHC beyond Run 4. The potential of the High-Energy LHC to probe QCD matter with newly-available observables, at twice larger center-of-mass energies than the LHC, is investigated., Comment: 209 pages; Report from Working Group 5 of the Workshop on the Physics of the CERN HL-LHC, and Perspectives at the HE-LHC (v2: Minor updates to text and figures. Added one author.)

Probing an atomic resonance without disturbing it is an ubiquitous issue in physics. This problem is critical in high-accuracy spectroscopy or for the next generation of atomic optical clocks. Ultra-high resolution frequency metrology requires sophisticated interrogation schemes and robust protocols handling pulse length errors and residual frequency detuning offsets . This review reports recent progress and perspective in such schemes, using sequences of composite laser-pulses tailored in pulse duration, frequency and phase, inspired by NMR techniques and quantum information processing. After a short presentation of Rabi technique and NMR-like composite pulses allowing efficient compensation of electromagnetic field perturbations to achieve robust population transfers, composite laser-pulses are investigated within Ramsey's method of separated oscillating fields in order to generate non-linear compensation of probe-induced frequency shifts. Laser-pulses protocols such as Hyper-Ramsey (HR), Modified Hyper-Ramsey (MHR), Generalized Hyper-Ramsey (GHR) and hybrid schemes are reviewed. These techniques provide excellent protection against both probe induced light-shift perturbations and laser intensity variations. More sophisticated schemes generating synthetic frequency-shifts are presented. They allow to reduce or completely eliminate imperfect correction of probe-induced frequency-shifts even in presence of decoherence due to the laser line-width. Finally, two universal protocols are presented which provide complete elimination of probe-induced frequency shifts in the general case where both decoherence and relaxation dissipation effects are present by using exact analytic expressions for phase-shifts and the clock frequency detuning. These techniques might be applied to atomic, molecular and nuclear frequency metrology, mass spectrometry as well as precision spectroscopy., Comment: This is the initial version 1.0 submitted to the review Report on Progress in Physics. The formally accepted version after revision by referees is only available online since 2018 June 04. Note that this version has been corrected , references have been added and some subsections have been extended (ABRS sub section and appendix)

Using a free-running distributed-feedback quantum cascade laser (QCL) emitting at 9.54 $\mu$m, the pressure shift parameters of four intense rovibrational transitions in the $\nu_3$ fundamental band of ozone induced by oxygen (O$_2$), air and the noble gases helium (He), argon (Ar), and xenon (Xe) are obtained by employing second harmonic detection. The experimental analysis comprises a full uncertainty budget and provides line shift data which are traceable to SI. The high density of transitions in the $\nu_3$ spectral region of ozone make this region particularly difficult to study with more commonly used techniques such as Fourier transform spectroscopy. The comparatively high spectral resolution of the QCL in the MHz range, on the contrary, allows to measure molecular shifts at relatively low pressures (from 2 to 70 hPa), thus reducing the impact of spectral congestion due to pressure broadening of molecular lines. The comparison of our results with published data shows that presently recommended values for the pressure shift are too low in this region. This observation is corroborated by semi-classical calculations using the Robert-Bonamy formalism. A slight negative $J$ dependence, already observed in other ozone vibrational bands, is predicted. Systematic use of our technique could be very useful to support this hypothesis and to make up for the lack of shift parameters for ozone $\nu_3$ transitions in molecular spectral databases. A subsequent stabilization of the QCL onto an optical frequency comb will open up possibilities to perform metrological measurements of Doppler-free molecular lines.

Tunable electromagnetic sources, such as voltage controlled oscillators (VCO), micro electromechanical systems (MEMS) or diode lasers are often required to be linear during frequency-sweep modulation. In many cases, it might also be sufficient that the degree of the non-linearity can be well controlled. Without further efforts, these conditions are rarely achieved using free running sources. Based on a pre-distortion voltage ramp, we develop in this letter a simple and universal method that minimizes the non-linear frequency response of tunable electromagnetic sources. Using a current-driven Quantum Cascade Laser (QCL) as an example, we demonstrate that the non-linearity can easily be reduced by a factor of ten when using a single distortion parameter $\gamma$. In the investigation of the IR absorption spectrum of ozone at 10\,$\mu$m, an even better reduction of the frequency scale error by two orders of magnitude is obtained by using the pre-distortion method to generate an essentially purely quadratic sweep frequency dependency which can be inverted easily to retrieve precise molecular line positions. After having tested our method on a variety of electromagnetic sources, we anticipate a wide range of applications in a variety of fields., Comment: inspired by the Gamma correction on TVs and videos

In a coalescence plus fragmentation approach we calculate the heavy baryon/meson ratio and the $p_T$ spectra of charmed hadrons $D^{0}$, $D_{s}$ and $\Lambda_{c}^{+}$ in a wide range of transverse momentum from low $p_T$ up to about 10 GeV and discuss their ratios from RHIC to LHC energies without any change of the coalescence parameters. We have included the contribution from decays of heavy hadron resonances and also the one due to fragmentation of heavy quarks which do not undergo the coalescence process. The coalescence process is tuned to have all charm quarks hadronizing in the $p_T\rightarrow 0$ limit and at finite $p_T$ charm quarks not undergoing coalescence are hadronized by independent fragmentation. The $p_T$ dependence of the baryon/meson ratios are found to be sensitive to the masses of coalescing quarks, in particular the $\Lambda_{c}/D^{0}$ can reach values of about $\rm 1\div 1.5 $ at $p_T \approx \, 3$ \mbox{GeV}, or larger, similarly to the light baryon/meson ratio like $p/\pi$ and $\Lambda/K$, however a marked difference is a quite weak $p_T$ dependence with respect to the light case, such that a larger value at intermediate $p_T$ implies a relatively large value also for the integrated yields. A comparison with other coalescence model and with the prediction of thermal model is discussed., Comment: 13 pages, 9 figures. Fig. 5 updated and some minor changes in the text

We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of a Boltzmann transport approach. Non-perturbative interaction between heavy quarks and light quarks have been taken into account through a quasi-particle approach in which light partons are dressed with thermal masses tuned to lQCD thermodynamics. Such a model is able to describe the main feature of the non-perturbative dynamics: the enhancement of the interaction strength near $T_c$. We show that the resulting charm in-medium evolution is able to correctly predict simultaneously the nuclear suppression factor, $R_{AA}$, and the elliptic flow, $v_2$, at both RHIC and LHC energies and at different centralities. The hadronization of charm quarks is described by mean of an hybrid model of fragmentation plus coalescence and plays a key role toward the agreeement with experimental data. We also performed calculations within the Langevin approach which can lead to very similar $R_{AA}(p_T)$ as Boltzmann, but the charm drag coefficient as to be reduced by about a $30\%$ and also generates an elliptic flow $v_2(p_T)$ is about a $15\%$ smaller. We finally compare the space diffusion coefficient $2\pi TD_s$ extracted by our phenomenological approach to lattice QCD results, finding a satisfying agreement within the present systematic uncertainties. Our analysis implies a charm thermalization time, in the $p\rightarrow 0$ limit, of about $4-6 \, fm/c$ which is smaller than the QGP lifetime at LHC energy., Comment: 13 pages, 12 figures

The deuteration of ammonia by D atoms has been investigated experimentally in the sub-monolayer regime on realistic analogues of interstellar dust grain surfaces. About 0.8 monolayer of solid NH3 was deposited on top of an oxidized graphite surface held at 10 K, partly covered with ASW ice. Ammonia ice is subsequently exposed to D atoms for different exposure times using a differentially pumped beam-line. The deuteration experiments of ammonia were carried out by mass spectroscopy and temperature programmed desorption (TPD) technique. The experimental results showed the formation of three isotopologue ammonia species by direct exothermic H-D substitution surface reactions: NH3+D->NH2D+H, NH2D+D->NHD2+H, and NHD2+D->ND3+H. The formation of the deuterated isotopologues NH2D, NHD2, and ND3 at low surface temperature (10 K) is likely to occur through quantum tunneling process on the oxidized graphite surface. A kinetic model taking into account the diffusion of D atoms on the surface is developed to estimate the width and the hight of the activation energy barriers for the successive deuteration reactions of ammonia species by D atoms. Identical control experiments were performed using CH3OH and D atoms. The deuteration process of solid methanol is ruled by H abstraction and D addition mechanism, and is almost five orders of magnitude faster than ammonia deuteration process.