Journal of Physics G: Nuclear and Particle Physics

The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector.

Theoretical predictions for particle production cross sections and decays at colliders rely heavily on perturbative Quantum Chromodynamics (QCD) calculations, expressed as an expansion in powers of the strong coupling constant α_S. The current ${ \mathcal O }(1 \% )$ uncertainty of the QCD coupling evaluated at the reference Z boson mass, ${\alpha }_{S}({m}_{{\rm{Z}}}^{2})=0.1179\pm 0.0009$, is one of the limiting factors to more precisely describe multiple processes at current and future colliders. A reduction of this uncertainty is thus a prerequisite to perform precision tests of the Standard Model as well as searches for new physics. This report provides a comprehensive summary of the state-of-the-art, challenges, and prospects in the experimental and theoretical study of the strong coupling. The current ${\alpha }_{S}({m}_{{\rm{Z}}}^{2})$ world average is derived from a combination of seven categories of observables: (i) lattice QCD, (ii) hadronic τ decays, (iii) deep-inelastic scattering and parton distribution functions fits, (iv) electroweak boson decays, hadronic final-states in (v) e⁺e⁻, (vi) e–p, and (vii) p–p collisions, and (viii) quarkonia decays and masses. We review the current status of each of these seven ${\alpha }_{S}({m}_{{\rm{Z}}}^{2})$ extraction methods, discuss novel α_S determinations, and examine the averaging method used to obtain the world-average value. Each of the methods discussed provides a 'wish list' of experimental and theoretical developments required in order to achieve the goal of a per-mille precision on ${\alpha }_{S}({m}_{{\rm{Z}}}^{2})$ within the next decade.

Collective modes emerge as the relevant degrees of freedom that govern low-energy excitations of atomic nuclei. These modes—rotations, pairing rotations, and vibrations—are separated in energy from non-collective excitations, making it possible to describe them in the framework of effective field theory. Rotations and pairing rotations are the remnants of Nambu–Goldstone modes from the emergent breaking of rotational symmetry and phase symmetries in finite deformed and finite superfluid nuclei, respectively. The symmetry breaking severely constrains the structure of low-energy Lagrangians and thereby clarifies what is essential and simplifies the description. The approach via effective field theories exposes the essence of nuclear collective excitations and is defined with a breakdown scale in mind. This permits one to make systematic improvements and to estimate and quantify uncertainties. Effective field theories of collective excitations have been used to compute spectra, transition rates, and other matrix elements of interest. In particular, predictions of the nuclear matrix element for neutrinoless double beta decay then come with quantified uncertainties. This review summarizes these results and also compares the approach via effective field theories to well-known models and ab initio computations.

The main objectives of the KM3NeT Collaboration are (i) the discovery and subsequent observation of high-energy neutrino sources in the Universe and (ii) the determination of the mass hierarchy of neutrinos. These objectives are strongly motivated by two recent important discoveries, namely: (1) the high-energy astrophysical neutrino signal reported by IceCube and (2) the sizable contribution of electron neutrinos to the third neutrino mass eigenstate as reported by Daya Bay, Reno and others. To meet these objectives, the KM3NeT Collaboration plans to build a new Research Infrastructure consisting of a network of deep-sea neutrino telescopes in the Mediterranean Sea. A phased and distributed implementation is pursued which maximises the access to regional funds, the availability of human resources and the synergistic opportunities for the Earth and sea sciences community. Three suitable deep-sea sites are selected, namely off-shore Toulon (France), Capo Passero (Sicily, Italy) and Pylos (Peloponnese, Greece). The infrastructure will consist of three so-called building blocks. A building block comprises 115 strings, each string comprises 18 optical modules and each optical module comprises 31 photo-multiplier tubes. Each building block thus constitutes a three-dimensional array of photo sensors that can be used to detect the Cherenkov light produced by relativistic particles emerging from neutrino interactions. Two building blocks will be sparsely configured to fully explore the IceCube signal with similar instrumented volume, different methodology, improved resolution and complementary field of view, including the galactic plane. One building block will be densely configured to precisely measure atmospheric neutrino oscillations.

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential.

This biennial Review summarizes much of particle physics. Using data from previous editions, plus 2633 new measurements from 689 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 110 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V_ud & V_us, V_cb & V_ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.      A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.

This biennial Review summarizes much of particle physics. Using data from previous editions, plus 2158 new measurements from 551 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on neutrino mass, mixing, and oscillations, QCD, top quark, CKM quark-mixing matrix, V_ud & V_us, V_cb & V_ub, fragmentation functions, particle detectors for accelerator and non-accelerator physics, magnetic monopoles, cosmological parameters, and big bang cosmology.

A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: pdg.lbl.gov.

Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton–proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments—as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER—to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity 'dark showers', highlighting opportunities for expanding the LHC reach for these signals.

Organising Committee

Xiang-Zhou Cai (SINAP) Xu Cai (CCNU), Co-chair Zhan-Jun He (SINAP) TD Lee (Columbia University, CCAST), Honorary chair Ya-Hong Li Zuo-Tang Liang (Shandong University) Feng Liu (CCNU) Bo-Qiang Ma (Beijing University) Yu-Gang Ma (SINAP), Scientific secretary Ru-Keng Su (Fudan University) En-Ke Wang (CCNU), Scientific secretary Fan Wang (Nanjing University) Xiao-Lian Wang (USTC) Hu-Shan Xu (IMP) Wei-Qin Zhao (CCAST) Dai-Cui Zhou (CCNU) Shu-Hua Zhou (CIAE) Wei Zhou (SINAP) Zhi-Yuan Zhu (SINAP, CAS), Co-chair Peng-Fei Zhuang (Tsinghua University) Bing-Song Zou (IHEP)

International Advisory Committee

Jean Paul Blaizot, France Peter Braun Münzinger, Germany Igor M Dremin, Russia Christian Fabjan, Switzerland Jens Jorgen Gaardhoje, Denmark Hans-Ake Gustaffson, Sweden Hans Gutbrod, Germany Miklos Gyulassy, USA Timothy Hallman, USA Hideki Hamagaki, Japan John W Harris, USA Tetsuo Hatsuda, Japan Huan-Zhong Huang, USA Barbara Jacak, USA Peter Kevi, Hungary Thomas W Ludlam, USA Luciano Maiani, Italy Larry McLerran, USA Berndt Müller, USA Lodovico Riccati, Italy Hans Georg Ritter, USA Vesa Ruuskanen, Finland Jurgen Schukraft, Switzerland Wen-Qing Shen, China Edward V Shuryak, USA Bikash Sinha, India Johanna Stachel, Germany Horst Stöcker, Germany Itzhak Tserruya, Israel Xin-Nian Wang, USA Bolek Wyslouch, USA Fu-Jia Yang, China Glenn R Young, USA William A Zajc, USA Wen-Long Zhan, China Zong-Ye Zhang, China

It is well known that the coupling of an axion-like particle with a photon modifies the Maxwell equations. One of the main consequences of these modifications is the conversion of axions into photons. Little has been said about other possible effects. In this paper we show that the trajectory of an electron can be significantly altered because of the emergence of an electric field due to the dark matter background of the axion-like particles in this modified axion-electrodynamics. Different dark matter densities and magnetic field strengths are considered and it is shown that an axion-like particle with a mass m_a ∼ 10⁻²² eV generates an electric field that can significantly change the trajectory of an electron in these scenarios.

Using the ab initio symmetry-adapted no-core–shell model, we compute sum rules and response functions for light to medium-mass nuclei, starting from interactions that are derived in the chiral effective field theory. Specifically, we investigate electromagnetic transitions of monopole, dipole and quadrupole nature for ⁴He, and explore dominant features of giant monopole resonances in symmetric nuclei such as the closed-shell ⁴He and ¹⁶O light nuclei, the intermediate-mass open-shell ²⁰Ne and the medium-mass closed-shell ⁴⁰Ca. Furthermore, for the NNLO_opt chiral potential, we determine parameter-free monopole sum rules, which can provide information on the incompressibility of symmetric nuclear matter. We report 213(10) MeV as an estimate for the compression modulus for infinite nuclear matter, which overlaps with the lower range of values often used in current astrophysical applications.

We investigate the chiral phase diagram in the NJL model with a modified coupling strength. Moreover, we delve deeply into the fluctuations of baryon numbers. A temperature damping factor for the coupling strength is introduced to mimic the temperature dependence of quantum chromodynamics (QCD) in the low and middle temperature ranges. This novel parameter is fitted by using the quark condensate from lattice QCD at finite temperature. Our approach provides a significant enhancement to the chiral phase diagram, accurately reproducing the pseudocritical temperature at μ_B = 0 and aligning the crossover boundary with lattice QCD results. The quark condensate is used to ascertain the location of the phase transition, and we find an area where both phases coexist. The chiral susceptibility is employed to identify the pseudo-critical line in the crossover region. The skewness ratios and the kurtosis ratios varying with T at several different μ_B are calculated meticulously, and the results demonstrate that they experience a significant change around the pseudo-critical line. Additionally, the skewness ratios and the kurtosis ratios along the pseudo-critical line (T_c(μ_B)) and the lines deviating from T_c(μ_B) are computed to gain a better understanding of the experimental results. This implies that the freeze-out line is relatively far from the critical end point.

Form-factor analysis of pseudoscalar ${\pi }^{\pm }-$ and vector ${\rho }^{\pm }-$ mesons with zero transmitted momentum has been carried out in the model based on the point form of Poincaré-invariant quantum mechanics. The original method of model parameters' calculations from leptonic decays ${\pi }^{\pm }\to {\ell }^{\pm }{\nu }_{{\ell }^{\pm }}$, ${\tau }^{\pm }\to {\rho }^{\pm }{\nu }_{{\tau }^{\pm }}$ using pseudoscalar density ${g}_{{\pi }^{\pm }}$ constant is proposed. The method is generalized in radiative decays ${\rho }^{0}\to {\ell }^{+}{\ell }^{-}$ and ${\rho }^{\pm }\to {\pi }^{\pm }\gamma$ with the following anomalous magnetic moments calculation of constituent $u-$ and $d-$ quarks. It has been shown that the obtained parameters lead to the values of magnetic and quadrupole moment of ${\rho }^{\pm }-$ meson which are comparable with other models as well as hadronic transition ${\rho }^{\pm }\to {\pi }^{\pm }{\pi }^{0}$ observables. A comparative analysis of the obtained values of ${\mu }_{u}$ and ${\mu }_{d}$ quark magnetic moments has been carried out. It has been found that the proposed model gives numerical evaluations which are comparable to other approaches and models.

We investigate the relative yields of various like and unlike mass hadrons in ultra-relativistic heavy-ion collisions (URHIC). In the framework of thermal model, a strong evidence of strangeness imbalance is observed in the experiments at lower collision energies relative to non-strange particles, particularly pions. The study indicates that like mass particle ratios in the system at the chemical freeze-out in URHIC can be described effectively by considering baryons (antibaryons) as point like as well as finite size particles which imitates hard-core repulsive interactions leading to an excluded volume type effect. In this analysis, we employ the statistical hadron resonance gas model for both cases. A comparison between the two cases is provided. However, the importance of considering baryons (antibaryons) as finite size particles is revealed in the description of baryon to meson ratios. Best fits to particle ratios are obtained using χ²-minimization procedure. For the case of finite-size baryons (antibaryons), we find that considering their hard-core radii allows us to fit the available antibaryon-to-baryon and baryon (antibaryon)-to-pion ratio experimental data simultaneously quite well with the same model parameter values. Moreover, our results align well with the proton radius puzzle observed in the muonic hydrogen measurement data. Furthermore, the study reveals two distinct chemical freeze-out stages in both cases, where the earlier one corresponds to baryonic (hyperonic) and antibaryonic (antihyperonic) states and a later one to mesonic degrees of freedom. A comparison of freeze-out lines obtained from both the cases is made along with the results of some earlier studies.

Collective modes emerge as the relevant degrees of freedom that govern low-energy excitations of atomic nuclei. These modes—rotations, pairing rotations, and vibrations—are separated in energy from non-collective excitations, making it possible to describe them in the framework of effective field theory. Rotations and pairing rotations are the remnants of Nambu–Goldstone modes from the emergent breaking of rotational symmetry and phase symmetries in finite deformed and finite superfluid nuclei, respectively. The symmetry breaking severely constrains the structure of low-energy Lagrangians and thereby clarifies what is essential and simplifies the description. The approach via effective field theories exposes the essence of nuclear collective excitations and is defined with a breakdown scale in mind. This permits one to make systematic improvements and to estimate and quantify uncertainties. Effective field theories of collective excitations have been used to compute spectra, transition rates, and other matrix elements of interest. In particular, predictions of the nuclear matrix element for neutrinoless double beta decay then come with quantified uncertainties. This review summarizes these results and also compares the approach via effective field theories to well-known models and ab initio computations.

In modern high energy physics (HEP) experiments, triggers perform the important task of selecting, in real time, the data to be recorded and saved for physics analyses. As a result, trigger strategies play a key role in extracting relevant information from the vast streams of data produced at facilities like the large hadron collider (LHC). As the energy and luminosity of the collisions increase, these strategies must be upgraded and maintained to suit the experimental needs. This whitepaper presents a high-level overview and reviews recent developments of triggering practices employed at the LHC. The general trigger principles applied at modern HEP experiments are highlighted, with specific reference to the current trigger state-of-the-art within the ALICE, ATLAS, CMS and LHCb collaborations. Furthermore, a brief synopsis of the new trigger paradigm required by the upcoming high-luminosity upgrade of the LHC is provided. This whitepaper, compiled by Early Stage Researchers of the SMARTHEP network, is not meant to provide an exhaustive review or substitute documentation and papers from the collaborations themselves, but rather offer general considerations and examples from the literature that are relevant to the SMARTHEP network.

Collective anisotropic flow, where particles are correlated over the entire event, is a prominent phenomenon in relativistic heavy-ion collisions and is sensitive to the properties of the matter created in those collisions. It is often measured by two- and multi-particle correlations and is therefore contaminated by nonflow, those genuine few-body correlations unrelated to the global event-wise correlations. Many methods have been devised to estimate nonflow contamination with various degrees of successes and difficulties. Here, we review those methods pedagogically, discussing the pros and cons of each method, and give examples of ballpark estimate of nonflow contamination and associated uncertainties in relativistic heavy-ion collisions. We hope such a review of the various nonflow estimation methods in a single place would prove helpful to future researches.

Heavy-ion collisions provide a window into the properties of many-body systems of deconfined quarks and gluons. Understanding the collective properties of quarks and gluons is possible by comparing models of heavy-ion collisions to measurements of the distribution of particles produced at the end of the collisions. These model-to-data comparisons are extremely challenging, however, because of the complexity of the models, the large amount of experimental data, and their uncertainties. Bayesian inference provides a rigorous statistical framework to constrain the properties of nuclear matter by systematically comparing models and measurements. This review covers model emulation and Bayesian methods as applied to model-to-data comparisons in heavy-ion collisions. Replacing the model outputs (observables) with Gaussian process emulators is key to the Bayesian approach currently used in the field, and both current uses of emulators and related recent developments are reviewed. The general principles of Bayesian inference are then discussed along with other Bayesian methods, followed by a systematic comparison of seven recent Bayesian analyses that studied quark-gluon plasma properties, such as the shear and bulk viscosities. The latter comparison is used to illustrate sources of differences in analyses, and what it can teach us for future studies.

Baryon number conservation is not guaranteed by any fundamental symmetry within the standard model, and therefore has been a subject of experimental and theoretical scrutiny for decades. So far, no evidence for baryon number violation has been observed. Large underground detectors have long been used for both neutrino detection and searches for baryon number violating processes. The next generation of large neutrino detectors will seek to improve upon the limits set by past and current experiments and will cover a range of lifetimes predicted by several Grand Unified Theories. In this White Paper, we summarize theoretical motivations and experimental aspects of searches for baryon number violation in neutrino experiments.

The European Spallation Source (ESS) will be the world's brightest neutron source and will open a new intensity frontier in particle physics. The HIBEAM collaboration aims to exploit the unique potential of the ESS with a dedicated ESS instrument for particle physics which offers world-leading capability in a number of areas. The HIBEAM program includes the first search in thirty years for free neutrons converting to antineutrons and searches for sterile neutrons, ultralight axion dark matter and nonzero neutron electric charge. This paper outlines the capabilities, design, infrastructure, and scientific potential of the HIBEAM program, including its dedicated beamline, neutron optical system, magnetic shielding and control, and detectors for neutrons and antineutrons. Additionally, we discuss the long-term scientific exploitation of HIBEAM, which may include measurements of the neutron electric dipole moment and precision studies of neutron decays.

Lattice QCD calculations of the 2s radial excitation of the nucleon place the state at an
energy of approximately 1.9 GeV, raising the possibility that it is associated with the N1/2⁺(1880)
and N1/2⁺(1710) resonances through mixing with two-particle meson-baryon states. The discovery
of the N1/2⁺(1880) resonance in pion photoproduction but not in πN scattering and the small
width of the N1/2⁺(1710) resonance suggest that a state associated with these resonances would
be insensitive to the manner in which pions are permitted to dress it. To explore this possibility,
we examine the spectrum of nucleon radial excitations in both 2+1 flavour QCD and in simulations
where the coupling to meson-baryon states is significantly modified through quenching. We find the
energy of the 2s radial excitation to be insensitive to this modification for quark masses close to the
physical point. This invariance provides further evidence that the 2s radial excitation of the nucleon
is associated with the N1/2⁺(1880) and N1/2⁺(1710) resonances.

Inspired by the discrepancies observed in the b → s ℓ⁺ℓ^- neutral current decays, we study the decay channel B_c → D_s^(∗) ℓ⁺ℓ^- (ℓ=μ,τ), which is based on the same flavor changing neutral current (FCNC) transition at the quark level. The current study shows that this decay channel can provide a useful probe for physics beyond the standard model. We use the helicity formalism while employing the effective theory approach where we include the effects of vector and axial vector `new' physics (NP) operators. In this study, we have computed the branching ratio B_r, the D^∗ helicity fraction f_L , the lepton forward-backward asymmetry A_FB , and the lepton flavor universality ratio (LFU) R^μτ_Ds^∗. In addition, as a complementary check on the LFU, we also calculate the various other LFU observables, R_i^μτ where i=A_AB, f_L . We assume that the NP universal coupling is present for both muons and tauons, while the non-universal coupling is only present for muons. Regarding these couplings, we employ the latest global fit to the b → s ℓ⁺ℓ^- data, which is recently computed in \cite{Alguero:2023jeh}. We give predictions of some of the mentioned observables within the SM and the various NP scenarios. We have found that not only are the considered observables sensitive to NP but are also helpful in distinguishing among the different NP scenarios. These results can be tested at the LHCb, HL-LHC, and FCC-ee, and therefore, a precise measurements of these observables not only deepens our understanding of the b → s ℓ⁺ℓ^- process but also provides a window of opportunity to possibly study various NP scenarios.

We consider the electromagnetic form factors ratio in the Rosenbluth and polarization methods. We explore the impact of adding new particles as the mediators in the electron-proton scattering on these ratios. We show that such new particles can compensate the difference between the two methods and potentially solve this paradox. Consequently, we find some bound on the scalar coupling as $\alpha_{sc}\sim 10^{-5}$ for $m_{sc}\sim$ 5 MeV-2 GeV and $\alpha_{sc}\sim 10^{-4}-10^{-3}$ for $m_{sc}\sim$ 2-10 GeV. Meanwhile, the vector coupling is bounded as $\alpha_v\sim 10^{-5}$ for $m_v\sim$ 5 MeV-1.1 GeV and $\alpha_v\sim 10^{-4}-10^{-3}$ for $m_v\sim$ 1.2-10 GeV. These constraints are in complete agreement with those which is found from other independent terrestrial experiments.

Quantum Chromodynamics admits a CP violating contribution to the action, the $\theta$ term, which is expected to give rise to a nonvanishing electric dipole moment of the neutron. Despite intensive search, no CP violations have been found in the strong interaction. This puzzle is referred to as the strong CP problem. There is evidence that CP is conserved in the confining theory, to the extent that color charges are totally screened for $\theta > 0$ at large distances. It is not immediately obvious that this implies a vanishing dipole moment though. With this Letter I will close the gap. It is shown that in the infinite volume hadron correlation functions decouple from the topological charge, expressed in terms of the zero modes. The reason is that hadrons have a limited range of interaction, while the density of zero modes vanishes with the inverse root of the volume, thus reducing the probability of finding a zero mode in the vicinity to zero. This implies that CP is conserved in the strong interaction,

The European Spallation Source (ESS) will be the world's brightest neutron source and will open a new intensity frontier in particle physics. The HIBEAM collaboration aims to exploit the unique potential of the ESS with a dedicated ESS instrument for particle physics which offers world-leading capability in a number of areas. The HIBEAM program includes the first search in thirty years for free neutrons converting to antineutrons and searches for sterile neutrons, ultralight axion dark matter and nonzero neutron electric charge. This paper outlines the capabilities, design, infrastructure, and scientific potential of the HIBEAM program, including its dedicated beamline, neutron optical system, magnetic shielding and control, and detectors for neutrons and antineutrons. Additionally, we discuss the long-term scientific exploitation of HIBEAM, which may include measurements of the neutron electric dipole moment and precision studies of neutron decays.

It is well known that the coupling of an axion-like particle with a photon modifies the Maxwell equations. One of the main consequences of these modifications is the conversion of axions into photons. Little has been said about other possible effects. In this paper we show that the trajectory of an electron can be significantly altered because of the emergence of an electric field due to the dark matter background of the axion-like particles in this modified axion-electrodynamics. Different dark matter densities and magnetic field strengths are considered and it is shown that an axion-like particle with a mass m_a ∼ 10⁻²² eV generates an electric field that can significantly change the trajectory of an electron in these scenarios.

Lattice QCD calculations of the 2s radial excitation of the nucleon place the state at an
energy of approximately 1.9 GeV, raising the possibility that it is associated with the N1/2⁺(1880)
and N1/2⁺(1710) resonances through mixing with two-particle meson-baryon states. The discovery
of the N1/2⁺(1880) resonance in pion photoproduction but not in πN scattering and the small
width of the N1/2⁺(1710) resonance suggest that a state associated with these resonances would
be insensitive to the manner in which pions are permitted to dress it. To explore this possibility,
we examine the spectrum of nucleon radial excitations in both 2+1 flavour QCD and in simulations
where the coupling to meson-baryon states is significantly modified through quenching. We find the
energy of the 2s radial excitation to be insensitive to this modification for quark masses close to the
physical point. This invariance provides further evidence that the 2s radial excitation of the nucleon
is associated with the N1/2⁺(1880) and N1/2⁺(1710) resonances.

Collective modes emerge as the relevant degrees of freedom that govern low-energy excitations of atomic nuclei. These modes—rotations, pairing rotations, and vibrations—are separated in energy from non-collective excitations, making it possible to describe them in the framework of effective field theory. Rotations and pairing rotations are the remnants of Nambu–Goldstone modes from the emergent breaking of rotational symmetry and phase symmetries in finite deformed and finite superfluid nuclei, respectively. The symmetry breaking severely constrains the structure of low-energy Lagrangians and thereby clarifies what is essential and simplifies the description. The approach via effective field theories exposes the essence of nuclear collective excitations and is defined with a breakdown scale in mind. This permits one to make systematic improvements and to estimate and quantify uncertainties. Effective field theories of collective excitations have been used to compute spectra, transition rates, and other matrix elements of interest. In particular, predictions of the nuclear matrix element for neutrinoless double beta decay then come with quantified uncertainties. This review summarizes these results and also compares the approach via effective field theories to well-known models and ab initio computations.

Starting from the measurements conducted in 2004 with the ADAMO silicon spectrometer, we have performed a 2D fit procedure to diverse combinations of muon flux datasets documented in the literature. The fit employed three different formulas describing the energy and angular distribution of atmospheric muons at the Earth's surface. The analysis revealed that some measurements showed discrepancies in their compatibility with the expected results or between them with variations greater than a few sigmas. For example, vertical measurements expand over a wide range of flux values even for similar setup experiments. However, we have identified a formula capable of furnishing comprehensive spectrum coverage utilizing a singular set of parameters. Despite inherent limitations, we have achieved a satisfactory agreement with the Guan parameterization. Subsequently, we have integrated this optimized parameterization into the EcoMug library and a Geant4-based muon generator. The model's predictive capabilities have been validated by comparing it with experimental flux measurements and against other measurements in the literature. Through this process, we have shown and tested the reliability and accuracy of different muon flux modelling, facilitating advancements in domains reliant on the precise characterization of atmospheric muon phenomena.

Transverse momentum correlations were recently measured by the ALICE collaboration at the LHC [Acharya etal (2020 Phys. Lett. B804 135375)]. A long-range structure in terms of relative pseudorapidity of particle pairs is observed. This may imply some signal of the initial state owing to the sheer spread of the correlation. However, the fluctuations inside a thermally equilibrated medium have to be taken into account, serving as motivation for this paper. Using lattice Quantum Chromodynamics constraints, we predicted the development and spread of balancing correlations caused by energy-momentum conservation. At the same time, we propagated the Gaussian-shaped initial correlation using hydrodynamics to estimate its effects. Our findings suggest that the resulting correlation, known as 'the ridge,' is sensitive both to flucutations seeded in the pre-equilibrium stage and to those seeded in the equilibrated medium. This can provide important insight into the early stages of the collision.

In modern high energy physics (HEP) experiments, triggers perform the important task of selecting, in real time, the data to be recorded and saved for physics analyses. As a result, trigger strategies play a key role in extracting relevant information from the vast streams of data produced at facilities like the large hadron collider (LHC). As the energy and luminosity of the collisions increase, these strategies must be upgraded and maintained to suit the experimental needs. This whitepaper presents a high-level overview and reviews recent developments of triggering practices employed at the LHC. The general trigger principles applied at modern HEP experiments are highlighted, with specific reference to the current trigger state-of-the-art within the ALICE, ATLAS, CMS and LHCb collaborations. Furthermore, a brief synopsis of the new trigger paradigm required by the upcoming high-luminosity upgrade of the LHC is provided. This whitepaper, compiled by Early Stage Researchers of the SMARTHEP network, is not meant to provide an exhaustive review or substitute documentation and papers from the collaborations themselves, but rather offer general considerations and examples from the literature that are relevant to the SMARTHEP network.

We consider a general model for a quasi-spherical explosion in which a part of the explosion energy is thermalized, forming an expanding photosphere around a compact object, and the second part of energy is taken by the expanding shell of material which forms a shock wave in the surrounding medium. Different types of particles (electrons, hadrons) can, in principle, be accelerated at the shock. They interact with the thermal radiation from the photosphere and also with the material at the shell. We determine the equilibrium spectra of particles in the shell as a function of time after explosion and calculate the time-dependent γ-ray spectra by taking into account the effects which are due to the anisotropy of the photo-spheric radiation field on the Inverse Compton (IC) process; we also include the absorption of IC γ-rays in the photosphere radiation. We conclude that, in principle, both leptonic and hadronic models can explain the GeV-TeV gamma-ray emission recently detected from the Nova RS Oph. However, the hadronic model, in comparison to the leptonic model, is more energetically demanding and requires much stronger magnetization of the nova shell.

We present progress towards the first unpolarized gluon quasi-parton distribution function (PDF) from lattice quantum chromodynamics using high-statistics measurements for hadrons at two valence pion masses M_π ≈ 310 and 690 MeV computed on an a ≈ 0.12 fm ensemble with 2 + 1 + 1-flavors of highly improved staggered quark generated by the MILC collaboration. In this study, we consider two gluon operators for which the hybrid-ratio renormalization matching kernels have been recently derived and a third operator that has been used in prior pseudo-PDF studies of the gluon PDFs. We compare the matrix elements for each operator for both the nucleon and pion, at both pion masses, and using two gauge-smearing techniques. Focusing on the more phenomenologically studied nucleon gluon PDF, we compare the ratio and hybrid-ratio renormalized matrix elements at both pion masses and both smearings to those reconstructed from the nucleon gluon PDF from the CT18 global analysis. We identify the best choice of operator to study the gluon PDF and present the first gluon quasi-PDF under some caveats. Additionally, we explore the recent idea of Coulomb gauge fixing to improve signal at large Wilson-line displacement and find it could be a major help in improving the signal in the gluon matrix elements. This work helps identify the best operator for studying the gluon quasi-PDF, shows higher hadron boost momentum is needed to implement hybrid-ratio renormalization reliably, and suggests the need to study more diverse set of operators with their corresponding perturbative calculations for hybrid-ratio renormalization to further gluon quasi-PDF study.

The quantum molecular dynamics (QMD) part of the UrQMD model is extended to allow implementation of momentum dependent potentials from a parity doubling chiral mean field (CMF) model. Important aspects like energy conservation and effects on particle production and flow are discussed. It is shown, that this new implementation reproduces qualitatively and quantitatively available data over a wide range of beam energies and improves the description of observables without exception. In particular the description of hyperon and pion production at SIS18 energies is improved. From a comparison with HADES data one could conclude that the present parametrization of the CMF model leads to a slightly too weak momentum dependence. However, a more firm conclusion will require a systematic comparison with flow and multiplicity data over a range of beam energies and system sizes. Our work serves as an important step towards such future studies where the properties of dense QCD matter, through parameters of the CMF model, can be constraint using a comparison of the UrQMD model with high precision heavy ion data, finally also allowing direct comparisons with neutron star and neutron star merger observables.