### Proceedings Series

#### Cosmic Ray Measurements with IceCube

abstract

We report on measurements of cosmic rays in the energy range between some 100 TeV and about 1 EeV using the IceCube Neutrino Observatory at the South Pole. The IceCube facility combines the in-ice detector with the 1-km$^2$ surface detector IceTop. The combination offers a unique possibility to study the air-shower development at the surface together with the high-energy muons and neutrinos generated in the first interactions in the upper atmosphere. The report gives an overview of experimental results and a discussion of their impact on the understanding of cosmic rays and of hadronic air-shower models. Finally, we briefly discuss the ongoing upgrade activities for the current surface detector and for the future extensions (IceCube-Gen2).

all authors

A. Haungs, J.C. Arteaga-Velázquez, M. Bertaina, A. Chiavassa, K. Daumiller, V. de Souza, F. Di Pierro, R. Engel, A. Gherghel-Lascu, C. Grupen, J.R. Hörandel, T. Huege, K.-H. Kampert, D. Kang, K. Link, H.J. Mathes, S. Ostapchenko, T. Pierog, D. Rivera-Rangel, M. Roth, H. Schieler, F.G. Schröder, O. Sima, A. Weindl, J. Wochele, J. Zabierowski

#### KASCADE-Grande Results and Future Prospects for the Transition Energy Range of Cosmic Rays

abstract

Investigations of the energy spectrum as well as the mass composition of cosmic rays in the energy range of PeV to EeV are important for understanding both, the origin of the galactic and the extragalactic cosmic rays. The multi-detector arrangement of KASCADE and its extension KASCADE-Grande was designed for observations of cosmic ray air showers in this energy range. The experimental installation was completed in 2013, however, the collaboration continues to analyse the recorded data. In this contribution, we discuss the status and results of recent analyses in particular in view of tests of the validity of hadronic interaction models used for the interpretation of measured air-shower data.

#### Digital Radio Arrays for the Detection of Air Showers Initiated by Ultra-High-Energy Particles

abstract

Digital radio arrays have become an effective tool to measure air showers at energies around and above 100 PeV. Compared to optical techniques, the radio technique is not restricted to clear nights. Thanks to a recent progress in computational analysis techniques, radio arrays can provide an equally accurate measurement of the energy and the depth of the shower maximum. Stand-alone radio arrays offer an economic way towards huge apertures, e.g. , for the search for ultra-high-energy neutrinos, but still require technical demonstration on large scales. Hybrid arrays combining radio antennas and particle detectors have already started to contribute to cosmic-ray physics in the energy range of the presumed galactic-to-extragalactic transition. In particular, the combination of radio and muon detectors can pave a path to unprecedented accuracy for the mass composition of cosmic rays. These proceedings paper reviews recent developments regarding the radio technique and highlights selected running and planned antenna arrays, such as GCOS, GRAND, the SKA, the AugerPrime Upgrade of the Pierre Auger Observatory, and IceCube-Gen2.

#### Origin of Spectral Hardening of Secondary Cosmic Ray Nuclei

abstract

We discuss the production, acceleration and escape of secondary cosmic-ray (CR) nuclei, such as lithium, beryllium, and boron, produced by spallation of primary CR nuclei at the shock in supernova remnants (SNRs). We find that if the SNR is surrounded by a dense circumstellar medium which has a wind-like profile, the spectra of the escaping secondary nuclei are harder than those of the escaping primary nuclei. We show that if there was a past supernova surrounded by a dense wind-like CSM at a distance of $\sim 1.6~{\rm kpc}$, we could simultaneously reproduce the spectral hardening of primary and secondary CRs above $\sim 200~{\rm GV}$ that have recently been reported by AMS-02.

#### Search for Cosmic Ray Bursts at PeV Energies

abstract

Over the past forty years, there have been occasional reports of the observations of ‘bursts’ by small air-shower arrays operating at energies of about 1 PeV. These would seem to be of astrophysical origin and related to the thrust of studies pursued by the CREDO program. The bursts are rare and few burst searches have extended past a time required to record more than a handful of potential events. There have also been discussions of the burst data which offer alternative non-astrophysical explanations. This paper will critically review some burst results, which may suggest that interesting burst events have been detected at a rate of $\sim 1$ per year. If these exist, the astrophysical processes of their origin need to be examined and some possibilities will be briefly discussed in the paper.

#### Very High Energy Astronomy with VERITAS

abstract

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) consists of four atmospheric Cherenkov telescopes fully operating in the northern hemisphere since 2007. It is located at the Fred Lawrence Whipple Observatory in southern Arizona, USA and is sensitive to gamma rays from 85 GeV to 30 TeV energy range. One of the major focuses of the broad science topics of the multinational VERITAS Collaboration is indirect measurements of cosmic rays and their spectra via the study of very high energy gamma-ray emission. So far, the gamma-ray observation has resulted in detection of 23 galactic and 41 extragalactic sources, which include supernovae remnants, pulsar wind nebulae, gamma-ray binaries, active galactic nuclei, gamma-ray bursts, starburst galaxies, etc. VERITAS participates in multi-wavelength studies with several observatories and maintains an active multi-wavelength campaign with HAWC and LHAASO. Additionally, there is also a multi-messenger program with multiple collaborations to follow up on gravitational waves and high-energy neutrino signals originating from the very energetic regions of the Universe. In this presentation, we summarize the recent results from VERITAS in gamma-ray physics along with the multi-wavelength and the multi-messenger efforts.

#### The MAGIC of Acceleration

abstract

MAGIC is an array of two 17-m diameter Cherenkov telescopes observing gamma rays in the very-high-energy (VHE; above a few tens of GeV) range. MAGIC has been in operation since 2003, leading a successful observational program covering a broad range of scientific topics. Observations of gamma-ray emission from Galactic or extragalactic sources allow us to probe the conditions of acceleration of charged particles in them. We will report on the recent highlight results of MAGIC, shedding light on acceleration and radiative cooling processes in cosmic sources. In particular, we will discuss the recently added new member of the VHE Flat Spectrum Radio Quasar family: B2 1420+32 during its 2020 flaring state, the steepest source detected in VHE gamma rays: the Geminga pulsar, and the newly discovered at VHE gamma-rays nova RS Ophiuchi.

#### Multiwavelength and Multimessenger Observations of Blazars and Theoretical Modeling: Blazars as Astrophysical Neutrino Sources

abstract

This contribution reviews recent advances in the possible identification of blazars as potential sources of at least some of the very-high-energy neutrinos detected by the IceCube neutrino detector at the South Pole. The basic physical requirements for neutrino production and physics constraints that may be drawn from neutrino–blazar associations are reviewed. Several individual cases of possible associations will be discussed in more detail. It is emphasized that due to $\gamma \gamma$ opacity constraints in efficiently neutrino-producing blazars, an association between X-ray to soft $\gamma$-ray activity and very-high-energy neutrino production is more naturally expected than a connection between neutrino and high-energy/very-high-energy $\gamma$-ray activity.

#### Recent Very-high-energy Results on Pulsars and Pulsar Wind Nebulae

abstract

For many years, high-energy pulsar models were rather uncertain regarding expectations of detectable pulsed TeV spectral components from pulsars. Surprising detections of pulsations from the Crab pulsar up to 1.5 TeV opened a new window in pulsar science. H.E.S.S.-II next detected pulsed emission from the Vela pulsar (initially from 20–120 GeV and now up to a few TeV). Additionally, pulsations were detected by MAGIC from the Geminga pulsar (15–75 GeV) and by H.E.S.S.-II from PSR B1706$-$44 (sub-100 GeV). These new detections challenge established theoretical frameworks that explain the origin and nature of gamma-ray emission from pulsars. Moreover, these developments feed into the study of very-high-energy pulsar wind nebulae that surround some energetic pulsars. In 2018, H.E.S.S. released a pulsar wind nebula catalogue revealing new correlations and spurring on theoretical progress. HAWC detected spatially-extended TeV sources (pulsar halos) that surround several pulsars, generating new questions regarding PeV accelerators. Millisecond pulsar binaries are another class of pulsar-related systems that may manifest modulated TeV signals. In this review article, I will discuss some recent developments in the field and assess theoretical progress and challenges, also mentioning relevant questions that the Cherenkov Telescope Array may tackle.

#### It’s a Blazar… It’s a Radio Galaxy… It’s PKS 0625-354!

abstract

The catalogue of TeV gamma-ray emitting objects includes about 90 extragalactic sources, among which only a few belong to the class of radio galaxies or misaligned blazars. This smaller class includes PKS 0625-354, a source detected as a TeV gamma-ray emitter already in 2012. Here, we report on H.E.S.S. observations of this active galaxy performed in November 2018. The classification of the object is still a matter of debate in the context of blazar and radio-galaxy scenarios. With the recent H.E.S.S. observations, supported with multi-wavelength observations collected with Fermi-LAT, Swift-XRT, and Swift-UVOT, we report on the detection of TeV gamma-ray variability of the sources. Ten days of H.E.S.S. observations revealed an outburst observed on November 1 followed by a decrease in the gamma-ray flux. We report on the result of H.E.S.S. and multi-wavelength observations of PKS 0625-354. We also discuss the possible interpretation of the broadband spectral energy distribution of the source and the implication of the TeV gamma-ray variability detected.

#### Study of Optical and Gamma-ray Long-term Variability in Blazars

abstract

Blazars, a subset of powerful active galactic nuclei, feature relativistic jets that shine in a broadband electromagnetic radiation, e.g. from radio to TeV emission. Here, I present the results of the studies that explore gamma-ray and optical variability properties of a sample of gamma-ray bright sources. Several methods of time-series analyses are performed on the decade-long optical and Fermi-LAT observations. The main results are as follows: The sources are found highly variable in both the bands, and the gamma-ray power spectral density is found to be consistent with the flicker noise suggesting long-memory processes at work. While comparing two emissions, not only the overall optical and the $\gamma$-ray emission are highly correlated but also both the observation distributions exhibit heavy-tailed log-normal distribution and linear RMS-flux relation. In addition, in some of the sources, indications of quasi-periodic oscillation were revealed with similar characteristic timescales in both the bands. We discuss the results in light of current blazar models with relativistic shocks propagating down the jet viewed close to the line of sight.

#### An Expanding Model to Explain Blazars Emission

abstract

Blazars have their jet pointing towards us and are known for their emission that covers practically all electromagnetic spectrum frequencies. These sources, in some cases, exhibit a correlation between $\gamma$-ray and radio emission, especially during flaring episodes. Adopting the hypothesis that high-energy photon emission by relativistic electrons occurs close to the central black hole, we study the evolution of this population of particles as they move along the jet and lose energy by radiation and adiabatic expansion. In this scenario, radio emission is produced at a later time when the emission region becomes optically thin to synchrotron self-absorption due to expansion. We develop an expanding one-zone code to calculate the emitted spectrum by simultaneously solving the kinetic equations of particles and photons. We will discuss the parameters entering our calculations, such as the magnetic field strength, the density of relativistic electrons, etc., in connection to the observational data by applying our results to the case of blazars.

#### The Low Number of Galactic Supernova Remnant Pevatrons

abstract

Although supernova remnants remain the main suspects as sources of galactic cosmic rays up to the knee, the supernova paradigm still has many loose ends. The weakest point in this construction is the possibility that individual supernova remnants can accelerate particles to the rigidity of the knee, $10^6$ GV. This scenario heavily relies upon the possibility to excite current-driven non-resonant hybrid modes, while the shock is still at the beginning of the Sedov phase. These modes can enhance the rate of particle scattering thereby leading to potentially very-high maximum energies. Here, we calculate the spectrum of particles released into the interstellar medium from the remnants of different types of supernovae. We find that only the remnants of very powerful, rare core-collapse supernova explosions can accelerate light elements such as hydrogen and helium nuclei to the knee rigidity, and that the local spectrum of cosmic rays directly constrains the rate of such events if they are also the source of PeV cosmic rays. This would imply that the possibility to detect SNR pevatrons with future gamma-ray observatories is drastically limited.

#### A Marginally Fast-cooling Proton-synchrotron Model for Prompt GRB Emission

abstract

A small fraction of Gamma Ray Bursts (GRBs) with available data down to soft X-rays ($\sim 0.5$ keV) have been detected to feature a spectral break in the low-energy part of their prompt emission spectrum. The overall spectral shape is consistent with optically thin synchrotron emission from a population of marginally fast cooling particles. In this work, we consider that such radiating particles are hadrons and investigate the idea of the marginally fast-cooling proton-synchrotron emission. We compute the source parameters required for such a scenario to work and investigate numerically how additional processes, namely photohadronic interactions and $\gamma \gamma$ pair production, contribute to the overall spectrum. We also construct analytically and numerically the expected neutrino flux from this model.

#### A Connection Between TeV Gamma-ray Flux and Cosmic Rays in the Seyfert Galaxy NGC 1068

abstract

Hadronic interactions in cosmic-ray propagation can produce charged and neutral pions. The neutron pion decays into photons, while positrons and electrons are produced due to the decay of charged pions. The basic mechanisms that can produce gamma-ray fluxes associated with jets of cosmic rays are the decay of neutral pions electron/positron bremsstrahlung, and inverse Compton scattering. These cascade processes show a correlation between the upper limit on the integral GeV–TeV gamma-ray flux and the ultra-high energy cosmic rays (UHECR) luminosity. We calculate the UHECR cosmic-ray luminosity for the NGC 1068 galaxy using the upper limits on TeV gamma-ray flux by H.E.S.S. and MAGIC observatories. We compare our neutrino flux to current estimates of NGC 1068 neutrino flux.

#### Ultra-high Energy Cosmic Rays Luminosity from Multi-messenger Analysis

abstract

The ultra-high energy cosmic rays (UHECR) originate probably from extragalactic sources, e.g. , Starburst, Radio Galaxies, and Active Galactic Nuclei (AGNs). In the present work, we obtain the upper limits of the cosmic-ray luminosity of Starburst galaxies. The method described in A.D. Supanitsky, V. de Souza, J. Cosmol. Astropart. Phys. 2013, 023 (2013) and R.C. Anjos, A.D. Supanitsky, V. de Souza, J. Cosmol. Astropart. Phys. 2014, 049 (2014) is a productive tool for obtaining the upper limits of the cosmic-rays luminosity and illustrates techniques to study the origin of UHECR from gamma rays at GeV–TeV. The method has been used with the upper limit on the GeV–TeV gamma-ray flux measured by space and ground instruments, such as Fermi-LAT, VERITAS, H.E.S.S., and MAGIC. It connects a measured upper limit on the integral flux of GeV–TeV gamma-rays and the UHECR cosmic-ray luminosity of a point source.

#### Jets and Winds from Gamma-ray Bursts

abstract

We investigate the properties of short and long gamma-ray burst jets launched from accreting black holes. We run the numerical general relativistic simulations in a magneto-hydrodynamic setup and we study the connection between properties of the jet and the accretion disk as its central engine. Our simulations show that the formation of magnetically arrested disk state is important for the jet launching process. The variability of the jets as measured at their base is intrinsically related to the timescales of magneto-rotational instability in the accretion disk. In addition, magnetically driven winds from the accretion disk influence the jet properties and, in some cases, may lead to its quenching. Finally, in short GRB engines, these winds are sites of r-process nucleosynthesis and contribute to the kilonova signal, observed at longer wavelengths after the prompt GRB emission.

#### Magnetic Reconnection in Relativistic Jets

abstract

Relativistic jets are produced by accreting black holes around which accumulation of magnetic fields leads to relativistic magnetizations; they are the dominant feature of blazars, a class of active galactic nuclei. Blazars are defined by very broad and luminous spectral energy distributions (SEDs) that are both strongly (stochastically) variable and spectrally stable. The maximum energy of electrons (and positrons) producing these SEDs must be robustly regulated. The prevalent view is that the regulating factor is radiative cooling, however, this implies extremely weak electric fields relative to magnetic fields, $E/B\sim 10^{-9}$ (this is equivalent to the separation of Larmor and cooling time scales; this is also why the synchrotron SEDs of blazars extend to much lower energies than that of the Crab pulsar wind nebula). The alternative regulating factor could be local (highly inhomogeneous) magnetization. Relativistic magnetic reconnection has been proposed to explain rapid (a few minutes) gamma-ray flares of blazars. Two particular scenarios have been developed: minijets (Alfvénic outflows) and plasmoids (magnetic flux ropes). It was recently demonstrated that plasmoids are better suited to produce rapid flares (by tail-on mergers), because their higher density is a decisive advantage over the higher Lorentz factors of minijets. Magnetic reconnection can be triggered in relativistic jets by instabilities of toroidal magnetic fields, driven either by electric currents or by gas pressure, which were recently shown to lead to efficient particle acceleration.

#### PIC Simulations of SNR’s Shock Waves with a Turbulent Upstream Medium

abstract

Investigation of astrophysical shocks has major importance in understanding the physics of the cosmic rays acceleration. Electrons to be accelerated at shocks must have suprathermal energy, which implies that they should undergo some pre-acceleration mechanism. Many numerical studies examined possible injection mechanisms, however, most of them considered homogenous upstream medium, which is an unreal assumption for astrophysical environments. We will investigate electron acceleration at high Mach number and low plasma beta shocks using a 2D3V particle-in-cell simulations with a turbulent upstream medium. Here, we discuss a method of generation of the compression-dominated turbulence. It is sufficiently long-living to be inserted into a shock simulation and its parameters represent the high Mach number and low beta regime.

#### Numerical Study of Statistical Behaviors of Galactic Cosmic Rays Invading the Heliosphere

abstract

The statistics of galactic cosmic rays (GCRs) invading the heliosphere are investigated using numerical simulations. First, a time stationary global heliosphere is reproduced using an MHD simulation. Then, motions of a large number of GCR protons with initial Lorentz factor 10 ($\sim 10$ GeV) and 1000 ($\sim 1$ TeV), distributed in the interstellar space around the heliosphere, are numerically solved. We map the positional distribution of the GCRs arriving at 50 AU from the Sun. Our results show that the arrival position of GCRs depends on their energies. We discuss the statistical behavior of the arriving GCRs at each energy.

#### Hydrodynamics and Radiation from Colliding Pulsar and Stellar Winds in a High-mass Binary System

abstract

In this work, we discuss a semi-analytical model of the shocked wind of a pulsar embedded in a non-shocked wind of a massive star in the context of a high-mass binary system. Both winds collide at scales of the binary system, producing a contact discontinuity that creates shocked flows that go away from the system and are affected by the orbital motion. The shocked wind is made of charged particles and is assumed to be a relativistic, adiabatic, and ideal fluid. Under these assumptions, we compute the hydrodynamics of the wind as well as the non-thermal radiation emitted by the accelerated particles within the plasma in the region close to the binary system. Using this model, we predict the observed luminosity curves along the orbit that give us information about the inclination of the system, non-thermal processes, and the properties of both the massive star and the pulsar.

#### Relativistic MHD Cylindrical Jets and Their Linear Stability

abstract

We find cylindrical steady-state jet configurations, which are shaped and carry the traits of the acceleration and collimation processes occurring in the launching region, as governed by the equations of ideal relativistic magnetohydrodynamics (RMHD). The resulting solutions correspond to a two-component structure having a fast propagating inner core surrounded by a slower outer sheath. After we thoroughly present the algorithm to find such steady-state solutions, we study their linear stability. For both axisymmetric and non-axisymmetric modes, we find similar behaviour and typical growth timescales for the instabilities of the order of a few tenths of jet radius light-crossing time.

#### The Latest T2K Neutrino Oscillation Results and the Future of the T2K and Hyper-Kamiokande Experiments

abstract

T2K is an accelerator neutrino experiment conducted in Japan, which studies neutrino oscillations: muon (anti)neutrinos disappearance and electron (anti)neutrinos appearance at a distance of 295 km. It has already provided world-best measurements of the two oscillation parameters: $\theta _{23}$ mixing angle and $\delta _{\mathrm {CP}}$ phase, describing the CP symmetry conservation/violation for neutrinos, as well as many neutrino cross-section measurements. T2K is now heading towards its phase II (T2KII), which goal is to confirm CP symmetry violation at the $3\sigma$ level. The successor of the T2K experiment will be the Hyper-Kamiokande (HK) experiment. The HK physics program includes confirmation of CP violation at the $5\sigma$ level, searching for proton decay and cosmic neutrino studies. The start of T2KII and HK is scheduled for 2023 and 2027, respectively. The latest T2K neutrino oscillation results and the status of the work performed for T2KII and HK, as well as their physics program, are presented in this document.

#### Experimental Detection of the CNO Cycle

abstract

Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sun’s total energy production, the associated neutrino flux is remarkably low compared to that of the $pp$ chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of $^{210}$Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe.

all authors

M. Bagheri, E. Gazda, O. Romero Matamala, A. Nepomuk Otte, E.G. Judd, E.N. Kuznetsov, P.J. Reardon, M.J. Miller, Y. Onel

#### A Very-High-Energy Neutrino Telescope On-board EUSO-SPB2 Mission

abstract

We present the status of the development of a Cherenkov telescope on-board the Extreme Universe Space Observatory Super Pressure Balloon 2 (EUSO-SPB2). EUSO-SPB2 is an approved NASA balloon mission that is planned to fly in 2023 from Wanaka, NZ and is a pathfinder for future space-based missions to detect astrophysical neutrinos. The objectives of this mission are to classify the sources of background and make the first observation of Very-High-Energy (VHE) cosmic rays via Cherenkov technique from suborbital altitude. We also intend to perform target of opportunity searches in response to multi-messenger alerts and use the Earth-skimming technique to search for VHE-tau neutrinos below the Earth’s limb ($E \gt 10$ PeV). The 0.785 m$^2$ Cherenkov telescope is equipped with a 512-pixel SiPM camera, covering $12.8^\circ \times 6.4^\circ$ (Horizontal $\times$ Vertical) field of view. The camera signals are digitized with a 100 MS/s readout system. In this paper, we report the status of the camera development and its performance, and the integration of the telescope.

#### Gamma-ray Follow-up Observations of Dwarf Nova AT2021afpi as a Possible Neutrino Counterpart with the VERITAS Instrument

abstract

AT2021afpi was a 10 mag outburst seen by the MASTER-Tavrida auto-detection system in temporal coincidence with the astrophysical neutrino candidate IC211125A. The object was observed as an optical bright transient, initially classified as a classical nova. Follow-up observations by the VERITAS instrument at gamma-ray energies $\gt 100$ GeV on the nova location resulted in no detection for an exposure of 5.5 hours. Further spectroscopic reports reclassified AT2021afpi as a dwarf nova of the type WZ Sge-Type, which are not expected to be neutrino emitters. A possible blazar detected by Fermi-LAT, 4FGL J0248.0$+$2232, which lies within the 90% localisation region of IC211125A, was observed in a flaring radio state four days after the neutrino alert. A further combined analysis with 1 hour of exposure time on 4FGL J0248.0$+$2232 at the position of AT2021afpi still resulted in no detection.

#### Fast Method for Simulation of Photon Propagation for Large-scale Underwater Neutrino Cherenkov Telescopes

abstract

Large-scale neutrino telescopes, such as Baikal-GVD or ORCA, require calibration and testing of the optical modules. The calibration methods typically use laser and LED-based systems to test the telescope’s response to light. These systems are also used in monitoring the optical parameters of water which has strong seasonal variation. The high-energy laser is an intense light source that can damage the optical modules. In the present work, an efficient and fast simulation has been developed for light propagation in a medium. The parameters of the light source such as its wavelength/energy, intensity, and direction as well as the properties of the medium such as its absorption and scattering lengths are used as inputs to the simulation. This simulation can be used in the optimization of the parameters of an intense light source like laser such that the optical modules are not damaged. In this paper, the simulation technique is presented and the results obtained using this approach are compared with the output of Geant4 simulations.

#### Compact Star Twins with a Dark Matter Core

abstract

We present a model of compact stars with a dark matter core. The hadronic equation of state is based on the parity doublet model and does not present a phase transition to quark matter. Instead, a strong first-order phase transition to dark matter described by a constant speed-of-sound model leads to the scenario of compact star mass twins. Compact star structural properties which obey the state-of-the-art measurements and constraints are presented.

#### Direct Searches for Cold Dark Matter in DarkSide-20k

abstract

The DarkSide scientific program concentrated on the dark matter search using low-radioactivity argon proposes the new generation DarkSide-20k detector as a next step. For this purpose, the Global Argon Dark Matter Collaboration was formed by joining together main current argon-based experiments. The DarkSide-20k detector is designed as a 20 tons fiducial mass liquid argon Time Projection Chamber capable of identifying nuclear recoils from WIMP over the course of a very large exposure. It will be using custom-designed large area cryogenic silicon photo-multiplier’s arrays as a light detection system. Additionally, a huge effort to limit the radioactivity sources in construction materials and procedures is undertaken to fulfill the ‘background free’ operation goal. The construction is about to start in the INFN-LNGS underground laboratory in Italy. Due to its unique light emission properties and pulse shape discrimination abilities, liquid argon can provide excellent sensitivity for WIMP collisions and strong background suppression. The proposed experiment will reach the cross section versus mass range in the search for dark matter of $6.3\times 10^{-48}~{\mathrm {cm}}^{2}$ for the $90\%$ C.L. exclusion significance for a 1 TeV/$c^2$ WIMP after a 200 t yr exposure. This will allow DarkSide-20k to discover, confirm, or exclude the WIMP dark matter hypothesis down the so-called neutrino floor barrier.

#### Probing the QCD Phase Diagram with HBT Femtoscopy

abstract

Intensity interferometry, however, originates from the field of radio astronomy, it evolved to be the most important tool to access the spatio-temporal properties of the matter under extreme conditions on subatomic scales. In this paper, I review recent experimental results from energies of the CERN super proton synchrotron (SPS), through Relativistic Heavy Ion Collider (RHIC) to the Large Hadron Collider (LHC) and discuss their possible implication on the equation of state of the QCD matter.

#### Early Charm Results at Belle II

abstract

Time-dependent analyses of $D$ mesons provide access to the fundamental Standard Model parameters and probe natural non-SM scales at 10–100 TeV energies. Outstanding vertexing performances are the key enablers of this program. We prove the capabilities of the Belle II detector by measuring the lifetimes of the $D^{0}$ and $D^{+}$ mesons. The results are the most precise to date, owing to a vertexing resolution 2 times better than that of Belle and BaBar. First results obtained on relevant channels with early data sets are discussed.

#### Strong Evidence of the $\rho$(1250) from a Unitary Multichannel Reanalysis of Elastic Scattering Data with Crossing-symmetry Constraints

abstract

We present an analysis of elastic $P$-wave $\pi \pi$ phase shifts and inelasticities up to $2$ GeV in order to identify the corresponding $J^{PC}=1^{--}$ excited $\rho$ resonances focusing on the $\rho (1250)$ vs. $\rho (1450)$ controversy. In our approach, we employed an improved parametrization in terms of a manifestly unitary and analytic three-channel S-matrix with its complex-energy pole positions. The included channels were $\pi \pi$, $\rho 2\pi$, and $\rho \rho$. The improvement with respect to prior work amounts to the enforcement of maximum crossing symmetry through once-subtracted dispersion relations called GKPY equations. A clear picture emerges from this analysis, identifying five vector $\rho$ states below 2 GeV which are $\rho (770)$, $\rho (1250)$, $\rho (1450)$, $\rho (1600)$, and $\rho (1800)$, with $\rho (1250)$ being indisputably the most important excited $\rho$ resonance.

#### Evidence of Double Parton Scattering at LHCb

abstract

Results showing the contribution from Double Parton Scattering were reported by the LHCb experiment based on Run 2 data sample. The production cross section of $J/\psi$ pairs was measured in $pp$ collisions at a centre-of-mass energy $\sqrt {s}=13$ TeV and compared to theoretical predictions. Pairs of prompt charm hadrons were studied in proton–lead collisions at $\sqrt {s_{NN}}=8.16$ TeV and confirmed the enhancement of DPS compared to single parton scattering production.

#### Event Reconstruction in MUonE Experiment at the SPS Accelerator

abstract

The MUonE experiment planned to be operating at the SPS accelerator in 2021–2022 (pilot run) and 2023–2026 provides a great potential to search for new physics in the sector of the anomalous muon magnetic moment $a_\mu$. The discrepancy between the most accurate determination of $a_\mu$ and the Standard Model predictions is about 4 standard deviations. Since the new experiments dedicated to highly precise measurements of the anomalous magnetic moment of the muon will allow for the measurement with an accuracy of about 0.05%, a serious limitation in increasing the significance of a possible discovery will be the theoretical error, dominated by uncertainties from hadronic contributions. The MUonE experiment will allow for a precise measurement of hadronic contribution to $a_\mu$ employing the measurement of the differential cross section for the $\mu e \rightarrow \mu e$ elastic process. This would help to increase the significance of the observed discrepancy to the level of 7 standard deviations. The crucial issue in this kind of study is the development of the event reconstruction procedures, allowing to control the systematic effects and, at the same time, to achieve high angular resolution.

#### Theoretical Aspects of Relativistic Perfect-fluid Spin Hydrodynamic Framework

abstract

We review the recently proposed perfect-fluid spin hydrodynamic formalism, which provides a new tool for the description of the spin polarization of ${\mit \Lambda }(\bar {{\mit \Lambda }})$ particles. This formalism is based on the de Groot–van Leeuwen–van Weert definitions of the energy-momentum and spin tensors.

#### Second Generation Machine Learning Based Algorithm for Long-lived Particles Reconstruction in Upgraded LHCb Experiment

abstract

The paper presents the developments and preliminary results related to the implementation of a Machine Learning based Algorithm for reconstruction of the long-lived particles in an upgraded LHCb experiment. The analysis is based on a Monte-Carlo simulation prepared for LHC Run 3 data-taking conditions. Studied tracks are reconstructed with an official LHCb software application Moore in configuration that is very close to the one that will be operated as a part of the final software trigger system.

#### Charmonium as a Probe of Hot Quark Matter in Nuclear Collisions with ALICE at the LHC

abstract

Ultrarelativistic nuclear collisions offer an opportunity to study the properties of the quark–gluon plasma (QGP) by achieving extreme conditions in terms of temperature and energy density in the laboratory. Charmonia, bound states of charm and anti-charm quarks, serve as an efficient probe of the QGP in nuclear collisions. In these proceedings, charmonium measurements performed by the ALICE Collaboration in Pb–Pb collisions are discussed. In particular, observables sensitive to the transport and thermodynamic properties of the QGP, such as nuclear modification factor ($R_{AA}$) and elliptic flow ($v_2$) of inclusive $J/\psi$ meson in Pb–Pb collisions at $\sqrt {s_{NN}} = 5.02$ TeV, are reported. The measurements are compared with available theoretical models.

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