arXiv subjects

P. Pagano

Publications and source records attributed to P. Pagano.

At least 19 recordsLinked to original sources

arXiv2026

MHD Modelling of magnetic reconnection heating and jets in the solar corona

Magnetic reconnection is seen as the lead mechanism to explain the persistent and bursty heating of the solar corona that keeps its thermal structure. Lately the observations and modelling of magnetic reconnection outflows, i.e. nanojets, has empowered our capabilities to scrutinise this mechanisms, however more needs to be understood on the relation between the energetic and kinematic events. The aim of this paper is to study in details the properties of the heating events (nanoflare) and the kinematic counterparts (nanojets) in order to augment detection capabilities of magnetic reconnection events. We use MHD simulations of the interaction of two magnetic flux tubes where magnetic reconnection occurs and such reconnection outflows are generated. We vary key parameters, such as the critical current and the size of the domain to study the heating and slingshot mechanisms. We find that the properties of the nanojets can give away much information on the magnetic reconnection that generated it, while it is difficult to directly link the amount of heating and the jet speeds. We also find that such reconnection model can explain a wide range of heating events. Magnetic reconnection still is invariably linked to both heating and outflows and our simulations show the complex interplay between these two byproducts of the magnetic reconnection and how their properties can be studied in observations.

astro-ph.SR↗

arXiv2025

Coronal energy release by MHD avalanches III. Identification of a reconnection outflow from a nanoflare

Outflows perpendicular to the guide field are believed to be a possible signature of magnetic reconnection in the solar corona and specifically a way to detect the occurrence of ubiquitous small-angle magnetic reconnection. The aim of this work is to identify possible diagnostic techniques of such outflows in hot coronal loops with SDO/AIA and the forthcoming MUltislit Solar Explorer (MUSE), in a realistically dynamic coronal loop environment in which an MHD avalanche is occurring. We consider a 3D MHD model of two magnetic flux tubes, including a stratified, radiative and thermal-conducting atmosphere, twisted by footpoint rotation. The faster rotating flux tube becomes kink-unstable and soon involves the other one in the avalanche. The turbulent decay of this magnetic structure on a global scale leads to the formation, fragmentation, and dissipation of current sheets driving impulsive heating akin to a nanoflare storm. We captured a clear outflow from a reconnection episode soon after the initial avalanche and synthesized its emission as detectable with AIA and MUSE. The outflow has a maximum temperature around 8 MK, a total energy of 1024 erg, a velocity of a few hundred km/s, and a duration of less than 1 min. We show the emission in the AIA 94 A channel (Fe XVIII line) and in the MUSE 108 A Fe XIX spectral line. his outflow shares many features with nanojets recently detected at lower temperatures. Its low emission measure makes, however, its detection difficult with AIA, but Doppler shifts can be measured with MUSE. Conditions become different in a later steady state phase when the flux tubes are filled with denser and relatively cooler plasma.

astro-ph.SR↗

arXiv2024

Coronal energy release by MHD avalanches II. EUV line emission from a multi-threaded coronal loop

MHD kink instability can trigger the fragmentation of a twisted magnetic flux tube into small-scale current sheets that dissipate as aperiodic impulsive heating events. This instability propagates as an avalanche to nearby flux tubes and leads to a nanoflare storm. Our previous work was devoted to related 3D MHD numerical modeling with a stratified and realistic atmosphere. This work addresses predictions for the EUV imaging spectroscopy of such structure and evolution of a loop, with an average temperature of 2.5 MK in the solar corona. We set a particular focus on the forthcoming MUSE mission. From the output of the numerical simulations, we synthesized the intensities, Doppler shifts, and non-thermal line broadening in 3 EUV spectral lines in the MUSE passbands: Fe IX 171A, Fe XV 284 A, and Fe XIX 108 A, at 1 MK, 2 MK, and 10 MK, respectively, according to the MUSE expected pixel size, temporal resolution, and temperature response functions. We provide maps showing different view angles and realistic spectra. Finally, we discuss the relevant evolutionary processes from the perspective of possible observations. We find that the MUSE observations might be able to detect the fine structure determined by tube fragmentation. In particular, the Fe IX line is mostly emitted at the loop footpoints, where we track the motions that drive the magnetic stressing and detect the upward motion of evaporating plasma from the chromosphere. In Fe XV, we see the bulk of the loop with increasing intensity. The Fe XIX line is very faint within the chosen simulation parameters; thus, any transient brightening around the loop apex may possibly be emphasized by the folding of sheet-like structure. In conclusion, we show that coronal loop observations with MUSE can pinpoint some crucial features of MHD-modeled ignition processes, such as the related dynamics, helping to identify the heating processes.

astro-ph.SR↗

arXiv2023

Coronal energy release by MHD avalanches. Effects on a structured, active region, multi-threaded coronal loop

A possible key element for large-scale energy release in the solar corona is an MHD kink instability in a single twisted magnetic flux tube. An initial helical current sheet fragments in a turbulent way into smaller-scale sheets, similarly to a nanoflare storm. As the loop expands in the radial direction during the relaxation process, an unstable loop can disrupt nearby stable loops and trigger an MHD avalanche. Exploratory investigations have been conducted in previous works with relatively simplified loop configurations. Here, we address a more realistic environment that comprehensively accounts for most of the physical effects involved in a stratified atmosphere, typical of an active region. The question is whether the avalanche process will be triggered, with what timescales, and how it will develop, as compared with the original, simpler approach. Three-dimensional MHD simulations describe the interaction of magnetic flux tubes, which have a stratified atmosphere, including chromospheric layers, the thin transition region to the corona, and the related transition from high-beta to low-beta regions. The model also includes the effects of thermal conduction and of optically thin radiation. Our simulations address the case where one flux tube among a few is twisted at the footpoints faster than its neighbours. We show that this flux tube becomes kink unstable first, in conditions in agreement with those predicted by analytical models. It rapidly involves nearby stable tubes, instigating significant magnetic reconnection and dissipation of energy as heat. The heating determines the development of chromospheric evaporation, while the temperature rises up to about 10 MK, close to microflares observations. This work confirms that avalanches are a viable mechanism for the storing and release of magnetic energy in plasma confined in closed coronal loops, as a result of photospheric motions.

astro-ph.SR↗

arXiv2021

C-Ports: a proposal for a comprehensive standardization and implementation plan of digital services offered by the "Port of the Future"

In this paper we address the topic of a possible path to standardize the ICT services expected to be delivered by the so-called "Port of the Future". How the most relevant technologies and Information Systems are used by the Port Communities for their businesses is discussed together with a detailed analysis of the on-going actions carried on by Standard Setting Organizations. Considering the examples given by the C-ITS Platform and the C-Roads programme at EU level, a proposal of contents to be considered in a comprehensive standardization action is given. The innovation services are therefore grouped into four bundles: (i) Vessel \& Marine Navigation, (ii) e-Freight \& (Intermodal) Logistics, (iii) Passenger Transport, (iv) Environmental sustainability. The standardized version of these applications will be finally labeled as C-Port services. Alongside the standardization plan, a proposal for ranking the ports on the basis of a specially-defined C- Port vector is discussed with the purpose of addressing the well-known lack of consensus around the mathematical definition of the Smart Port Index. Considering the good practice and the background offered by the Port of Livorno in terms of innovation actions, the prospected final user applications are then labeled as Day 1, Day 1.5, and Day 2 services in consideration of the technical and commercial gaps to be filled. As a case study about the evolution in the C-Port vector experienced by the Port of Livorno in the last years will also be discussed.

cs.CY↗

arXiv2021

A fast multi-dimensional magnetohydrodynamic formulation of the transition region adaptive conduction (TRAC) method

We have demonstrated that the Transition Region Adaptive Conduction (TRAC) method permits fast and accurate numerical solutions of the field-aligned hydrodynamic equations, successfully removing the influence of numerical resolution on the coronal density response to impulsive heating. This is achieved by adjusting the parallel thermal conductivity, radiative loss, and heating rates to broaden the transition region (TR), below a global cutoff temperature, so that the steep gradients are spatially resolved even when using coarse numerical grids. Implementing the original 1D formulation of TRAC in multi-dimensional magnetohydrodynamic (MHD) models would require tracing a large number of magnetic field lines at every time step in order to prescribe a global cutoff temperature to each field line. In this paper, we present a highly efficient formulation of the TRAC method for use in multi-dimensional MHD simulations, which does not rely on field line tracing. In the TR, adaptive local cutoff temperatures are used instead of global cutoff temperatures to broaden any unresolved parts of the atmosphere. These local cutoff temperatures are calculated using only local grid cell quantities, enabling the MHD extension of TRAC to efficiently account for the magnetic field evolution, without tracing field lines. Consistent with analytical predictions, we show that this approach successfully preserves the properties of the original TRAC method. In particular, the total radiative losses and heating remain conserved under the MHD formulation. Results from 2D MHD simulations of impulsive heating in unsheared and sheared arcades of coronal loops are also presented. These simulations benchmark the MHD TRAC method against a series of 1D models and demonstrate the versatility and robustness of the method in multi-dimensional magnetic fields. We show, for the first time, that pressure differences, ...

astro-ph.SR↗

arXiv2020

Effect of Coronal Loop Structure on Wave Heating by Phase Mixing

The mechanism behind coronal heating still elude direct observation and modelling of viable theoretical processes and the subsequent effect on coronal structures is one of the key tools available to assess possible heating mechanisms. Wave-heating via phase-mixing of Magnetohydrodynamics (MHD) transverse waves has been proposed as a possible way to convert magnetic energy into thermal energy but increasingly, MHD models suggest this is not a sufficiently efficient mechanism. We model heating by phase-mixing of transverse MHD waves in various configurations, to investigate whether certain circumstances can enhance the heating sufficiently to sustain the million degree solar corona and to assess the impact of the propagation and phase-mixing of transverse MHD waves on the structure of the boundary shell of coronal loops. We use 3D MHD simulations of a pre-existing density enhancement in magnetised medium and a boundary driver to trigger the propagation of transverse waves with the same power spectrum as measured by the COmP. We consider different density structures, boundary conditions at the non-drive footpoint, characteristics of the driver, and different forms of magnetic resistivity. We find that different initial density structures affect the evolution of the boundary shell and some driver configurations enhance the heating generated from the dissipation of the MHD waves. In particular, drivers coherent on a larger spatial scale and higher dissipation coefficients generate significant heating, although it is still insufficient. We conclude that while phase-mixing of transverse MHD waves is unlikely to sustain the thermal structure of the corona, there are configurations that allow for an enhanced efficiency of this mechanism. We provide possible signatures to identify the presence of such configurations, such as the location of where the heating is deposited along the coronal loop

astro-ph.SR↗

arXiv2020

Hydrogen Non-Equilibrium Ionisation Effects in Coronal Mass Ejections

A new generation of coronagraphs to study the solar wind and CMEs are being developed and launched. These coronagraphs will heavily rely on multi-channel observations where visible light (VL) and UV-EUV observations provide new plasma diagnostics. One of these instruments, Metis on board ESA-Solar Orbiter, will simultaneously observe VL and the UV Lyman-$α$ line. The number of neutral Hydrogen atoms (a small fraction of coronal protons) is a key parameter for deriving plasma properties such as temperature from the observed Lyman-$α$ line intensity. However, these measurements are significantly affected if non-equilibrium ionisation effects occur. The aim of this work is to determine if non-equilibrium ionisation effects are relevant in CMEs and in particular when and in which regions of the CME. We use a magneto-hydrodynamic simulation of a magnetic flux rope ejection to generate a CME. From this we then reconstruct the ionisation state of Hydrogen atoms in the CME by evaluating both the advection of neutral and ionised Hydrogen atoms and the ionisation and recombination rates in the MHD simulation. We find that the equilibrium ionisation assumption holds mostly in the core of the CME. In contrast non-equilibrium ionisation effects are significant at the CME front, where we find about 100 times more neutral Hydrogen atoms than prescribed by ionisation equilibrium conditions, even if this neutral Hydrogen excess might be difficult to identify due to projection effects. This work provides key information for the development of a new generation of diagnostic techniques that aim at combining visible light and Lyman-$α$ line emissions. The results show that non-ionisation equilibrium effects need to be considered when we analyse CME fronts. To incorrectly assume equilibrium ionisation in these regions would lead to a systematic underestimate of plasma temperatures.

astro-ph.SR↗

arXiv2020

Chromospheric evaporation and phase mixing of Alfvén waves in coronal loops

Phase mixing of Alfvén waves has been studied extensively as a possible coronal heating mechanism but without the full thermodynamic consequences considered self-consistently. It has been argued that in some cases, the thermodynamic feedback of the heating could substantially affect the transverse density gradient and even inhibit the phase mixing process. In this paper, we use MHD simulations with the appropriate thermodynamical terms included to quantify the evaporation following heating by phase mixing of Alfvén waves in a coronal loop and the effect of this evaporation on the transverse density profile. The numerical simulations were performed using the Lare2D code. We set up a 2D loop model consisting of a field-aligned thermodynamic equilibrium and a cross-field (background) heating profile. A continuous, sinusoidal, high-frequency Alfvén wave driver was implemented. As the Alfvén waves propagate along the field, they undergo phase mixing due to the cross-field density gradient in the coronal part of the loop. We investigated the presence of field-aligned flows, heating from the dissipation of the phase-mixed Alfvén waves, and the subsequent evaporation from the lower atmosphere. We find that phase mixing of Alfvén waves leads to modest heating in the shell regions of the loop and evaporation of chromospheric material into the corona with upflows of the order of only 5-20 m/s. Although the evaporation leads to a mass increase in the shell regions of the loop, the effect on the density gradient and, hence, on the phase mixing process, is insignificant. This paper self-consistently investigates the effect of chromospheric evaporation on the cross-field density gradient and the phase mixing process in a coronal loop. We found that the effects in our particular setup (small amplitude, high frequency waves) are too small to significantly change the density gradient.

astro-ph.SR↗

arXiv2019

A New Space Weather Tool for Identifying Eruptive Active Regions

One of the main goals of solar physics is the timely identification of eruptive active regions. Space missions such as Solar Orbiter or future Space Weather forecasting missions would largely benefit from this achievement. Our aim is to produce a relatively simple technique that can provide real time indications or predictions that an active region will produce an eruption. We expand on the theoretical work of \citet{Pagano2019fp} that was able to distinguish eruptive from non-eruptive active regions. From this we introduce a new operational metric that uses a combination of observed line-of-sight magnetograms, 3D data-driven simulations and the projection of the 3D simulations forward in time. Results show that the new metric correctly distinguishes active regions as eruptive when observable signatures of eruption have been identified and as non-eruptive when there are no observable signatures of eruption. After successfully distinguishing eruptive from non-eruptive active regions we illustrate how this metric may be used in a "real-time" operational sense were three levels of warning are categorised. These categories are: high risk (red), medium risk (amber) and low risk (green) of eruption. Through considering individual cases we find that the separation into eruptive and non-eruptive active regions is more robust the longer the time series of observed magnetograms used to simulate the build up of magnetic stress and free magnetic energy within the active region. Finally, we conclude that this proof of concept study delivers promising results where the ability to categorise the risk of an eruption is a major achievement.

astro-ph.SR↗

arXiv2019

A Prospective New Diagnostic Technique for Distinguishing Eruptive and Non-Eruptive Active Regions

Active regions are the source of the majority of magnetic flux rope ejections that become Coronal Mass Ejections (CMEs). To identify in advance which active regions will produce an ejection is key for both space weather prediction tools and future science missions such as Solar Orbiter. The aim of this study is to develop a new technique to identify which active regions are more likely to generate magnetic flux rope ejections. The new technique will aim to: (i) produce timely space weather warnings and (ii) open the way to a qualified selection of observational targets for space-borne instruments. We use a data-driven Non-linear Force-Free Field (NLFFF) model to describe the 3D evolution of the magnetic field of a set of active regions. We determine a metric to distinguish eruptive from non-eruptive active regions based on the Lorentz force. Furthermore, using a subset of the observed magnetograms, we run a series of simulations to test whether the time evolution of the metric can be predicted. The identified metric successfully differentiates active regions observed to produce eruptions from the non-eruptive ones in our data sample. A meaningful prediction of the metric can be made between 6 to 16 hours in advance. This initial study presents an interesting first step in the prediction of CME onset using only LOS magnetogram observations combined with NLFFF modelling. Future studies will address how to generalise the model such that it can be used in a more operational sense and for a variety of simulation approaches.

astro-ph.SR↗

arXiv2019

MHD simulations of the in-situ generation of kink and sausage waves in the solar corona by collision of dense plasma clumps

MHD waves are ubiquitous in the solar corona where the highly structured magnetic fields provide efficient wave guides for their propagation. While MHD waves have been observed originating from lower layers of the solar atmosphere, recent studies have shown that some can be generated in-situ by the collision of dense counter propagating flows. In this theoretical study, we analyse the mechanism that triggers the propagation of kink and sausage modes in the solar corona, following the collision of counter-propagating flows and how the properties of the flows affect the properties of the generated waves. In order to study in detail such a mechanism we run a series of ideal 2D and 3D MHD simulations where we vary the properties of the counter-propagating flows and by means of a simple technique to estimate the amplitudes of the kink and sausage modes, we investigate their role on the generation and propagation of the MHD waves. We find that the amplitude of the waves is largely dependent on the kinetic energy of the flows and that the onset of kink or sausage modes depends on the asymmetries between the colliding blobs. Moreover, the initial wavelength of the MHD waves is associated with the magnetic configuration resulting from the collision of the flows. We also find that genuine 3D systems respond with smaller wave amplitudes. In this study, we present a parameter space description of the mechanism that leads to the generation of MHD waves from the collision of flows in the corona. Future observations of these waves can be used to understand the properties of the plasma and magnetic field of the solar corona.

astro-ph.SR↗

arXiv2018

Contribution of phase-mixing of Alfvén waves to coronal heating in multi-harmonic loop oscillations

Kink oscillations of a coronal loop are observed and studied in detail because they provide a unique probe into the structure of coronal loops through MHD seismology and a potential test of coronal heating through the phase-mixing of Alfvén waves. In particular, recent observations show that standing oscillations of loops often involve also higher harmonics, beside the fundamental mode. The damping of these kink oscillations is explained by mode coupling with Alfvén waves. We investigate the consequences for wave-based coronal heating of higher harmonics and what coronal heating observational signatures we may use to infer the presence of higher harmonic kink oscillations. We perform a set of non-ideal MHD simulations where the damping of the kink oscillation of a flux tube via mode coupling is modelled. Our MHD simulation parameters are based on the seismological inversion of an observation for which the first three harmonics are detected. We study the phase-mixing of Alfvén waves that leads to the deposition of heat in the system, and we apply the seismological inversion techniques to the MHD simulation output. We find that the heating due to phase-mixing of the Alfvén waves triggered by the damping of the kink oscillation is relatively small, however we can illustrate i) how the heating location drifts due to the subsequent damping of lower order harmonics. We also address the role of the higher order harmonics and the width of the boundary shell in the energy deposition. We conclude that the coronal heating due to phase-mixing seems not to provide enough energy to maintain the thermal structure of the solar corona even when multi-harmonics oscillations are included, and these oscillations play an inhibiting role in the development of smaller scale structures.

astro-ph.SR↗

arXiv2018

A new technique for observationally derived boundary conditions for space weather

In recent years, space weather research has focused on developing modelling techniques to predict the arrival time and properties of coronal mass ejections (CMEs) at the Earth. The aim of this paper is to propose a new modelling technique suitable for the next generation of Space Weather predictive tools that is both efficient and accurate. The aim of the new approach is to provide interplanetary space weather forecasting models with accurate time dependent boundary conditions of erupting magnetic flux ropes in the upper solar corona. To produce boundary conditions, we couple two different modelling techniques, MHD simulations and a quasi-static non-potential evolution model. Both are applied on a spatial domain that covers the entire solar surface. The non-potential model uses a time series of observed synoptic magnetograms to drive the non-potential quasi-static evolution of the coronal magnetic field. This allows us to follow the formation and loss of equilibrium of magnetic flux ropes. Following this a MHD simulation captures the dynamic evolution of the erupting flux rope. The present paper focuses on the MHD simulations that follow the ejection of magnetic flux ropes to 4$R_\odot$. We first propose a technique for specifying the pre-eruptive plasma properties in the corona. Next, time dependent MHD simulations describe the ejection of two magnetic flux ropes, that produce time dependent boundary conditions for the magnetic field and plasma at 4$R_{\odot}$. In the present paper, we show that the dual use of quasi-static non-potential magnetic field simulations and full time dependent MHD simulations can produce realistic inhomogeneous boundary conditions for space weather forecasting tools. Before a fully operational model can be produced there are a number of technical and scientific challenges that still need to be addressed.

astro-ph.SR↗

arXiv2017

Origin and Ion Charge State Evolution of Solar Wind Transients during 4 -- 7 August 2011

We present study of the complex event consisting of several solar wind transients detected by Advanced Composition Explorer (ACE) on 4 -- 7 August 2011, that caused a geomagnetic storm with Dst$=-$110 nT. The supposed coronal sources -- three flares and coronal mass ejections (CMEs) occurred on 2 -- 4 August 2011 in the active region (AR) 11261. To investigate the solar origin and formation of these transients we studied kinematic and thermodynamic properties of the expanding coronal structures using the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) EUV images and the differential emission measure (DEM) diagnostics. The Helioseismic and Magnetic Imager (HMI) magnetic field maps were used as the input data for the 3D magnetohydrodynamic (MHD) model to describe the flux rope ejection. We characterize the early phase of the flux rope ejection in the corona, where the usual three-component CME structure formed. The flux rope ejected with a speed of about 200~km~s$^{-1}$ to the height of 0.25~R$_{\odot}$. The kinematics of the modeled CME front agrees well with the Solar Terrestrial Relations Observatory (STEREO) EUV measurements. Using the results of the plasma diagnostics and MHD modeling, we calculated the ion charge ratios of carbon and oxygen as well as the mean charge state of iron ions of the 2 August 2011 CME, taking into account the processes of heating, cooling, expansion, ionization, and recombination of the moving plasma in the corona up to the frozen-in region. We estimated a probable heating rate of the CME plasma in the low corona by matching the calculated ion composition parameters of the CME with those measured in situ for the solar wind transients. We also consider the similarities and discrepancies between the results of the MHD simulation and the observations.

physics.space-ph↗

arXiv2008

Modeling magnetohydrodynamics and non equilibrium SoHO/UVCS line emission of CME shocks

We provide a guideline to interpret the UVCS emission lines (in particular O VI and Si XII) during shock wave propagation in the outer solar corona. We use a numerical MHD model performing a set of simulations of shock waves generated in the corona and from the result we compute the plasma emission for the O VI and Si XII including the effects of NEI. We analyze the radiative and spectral properties of our model with the support of a detailed radiation model including Doppler dimming and an analytical model for shocks, and, finally, we synthesize the expected O VI 1032A line profile. We explain several spectral features of the observations like the absence of discontinuities in the O VI emission during the shock passage, the brightening of Si XII emission and the width of the lines. We use our model also to give very simple and general predictions for the strength of the line wings due to the ions shock heating and on the line shape for Limb CMEs or Halo CMEs. The emission coming from post-shock region in the solar corona roughly agrees with the emission from a simple planar and adiabatic shock, but the effect of thermal conduction and the magnetic field may be important depending on the event parameters. Doppler dimming significantly influences the O VI emission while Si XII line brightens mainly because of the shock compression. Significant shock heating is responsible for the wide and faint component of the O VI line usually observed which may be taken as a shock signature in the solar corona.

astro-ph↗

arXiv2008

The importance of magnetic-field-oriented thermal conduction in the interaction of SNR shocks with interstellar clouds

We explore the importance of magnetic-field-oriented thermal conduction in the interaction of supernova remnant (SNR) shocks with radiative gas clouds and in determining the mass and energy exchange between the clouds and the hot surrounding medium. We perform 2.5D MHD simulations of a shock impacting on an isolated gas cloud, including anisotropic thermal conduction and radiative cooling; we consider the representative case of a Mach 50 shock impacting on a cloud ten-fold denser than the ambient medium. We consider different configurations of the ambient magnetic field and compare MHD models with or without the thermal conduction. The efficiency of the thermal conduction in the presence of magnetic field is, in general, reduced with respect to the unmagnetized case. The reduction factor strongly depends on the initial magnetic field orientation, and it is minimum when the magnetic field is initially aligned with the direction of shock propagation. The thermal conduction contributes to suppress hydrodynamic instabilities, reducing the mass mixing of the cloud and preserving the cloud from complete fragmentation. Depending on the magnetic field orientation, the heat conduction may determine a significant energy exchange between the cloud and the hot surrounding medium which, while remaining always at levels less than those in the unmagnetized case, leads to a progressive heating and evaporation of the cloud. This additional heating may contrast the radiative cooling of some parts of the cloud, preventing the onset of thermal instabilities.

astro-ph↗

arXiv2007

Multiplicity Studies and Effective Energy in ALICE at the LHC

In this work we explore the possibility to perform ``effective energy'' studies in very high energy collisions at the CERN Large Hadron Collider (LHC). In particular, we focus on the possibility to measure in $pp$ collisions the average charged multiplicity as a function of the effective energy with the ALICE experiment, using its capability to measure the energy of the leading baryons with the Zero Degree Calorimeters. Analyses of this kind have been done at lower centre--of--mass energies and have shown that, once the appropriate kinematic variables are chosen, particle production is characterized by universal properties: no matter the nature of the interacting particles, the final states have identical features. Assuming that this universality picture can be extended to {\it ion--ion} collisions, as suggested by recent results from RHIC experiments, a novel approach based on the scaling hypothesis for limiting fragmentation has been used to derive the expected charged event multiplicity in $AA$ interactions at LHC. This leads to scenarios where the multiplicity is significantly lower compared to most of the predictions from the models currently used to describe high energy $AA$ collisions. A mean charged multiplicity of about 1000-2000 per rapidity unit (at $η\sim 0$) is expected for the most central $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 5.5 TeV$.

hep-ph↗