We study entanglement entropy in Deep Inelastic Scattering (DIS) using the dipole formulation of the high-energy limit of QCD. We argue that a reduced density matrix arises in low x DIS due to a trace over unobserved color degrees of freedom and we obtain entanglement entropy in terms of dipole multiplicities, directly from the von Neumann entropy.

In this paper, we briefly present the Monte Carlo event generators BHLUMI and BHWIDE for small and large angle Bhabha scattering, respectively, and discuss possible ways of their improvements in order to satisfy precision needs of future electron-positron colliders.

In this work, we study for the first time jet-medium interactions in heavy-ion collisions with introduction of saturation and Sudakov effects with parameters tuned for upcoming forward calorimeter acceptances in experiments, in particular the ALICE FoCal detector. We focus on γ + jet correlations by taking into account in-medium parton evolution using the BDIM equation that describes jet interactions with the quark-gluon plasma (QGP) combined with vacuum-like emissions (VLE). We systematically introduce the early time gluon saturation dynamics through the small-x Improved Transverse Momentum Dependent factorization (ITMD). For our purpose, we use Monte Carlo programs KATIE and TMDICE to generate hard events and in-medium parton evolution, respectively. We present results of azimuthal correlations and nuclear modification ratios to gauge the impact of the gluon saturation effects at early time for the in-medium jet energy loss.

The Gamma Factory (GF) project aims to generate high-intensity γ-ray beams of tunable energy and relatively small energy spread. Such beams can be optimized to generate an intense photo-neutron source, capable of driving an advanced nuclear energy system (ANES) for nuclear waste transmutation and supplying electrical power that is necessary for the GF operation mode of the Large Hadron Collider storage ring. In this study, we investigate the feasibility of driving ANES with the GF beam which is optimized to maximize the neutron production rate. The dependence of the ANES thermal power on the distance between the positions of the ANES and the GF γ-ray source is evaluated. For the γ-ray beam reaching the intensity of [Formula: see text] photons per second, the ANES thermal power could exceed 500 MWt. Under the assumption that ANES operates over 20 years, the transmutation rate could reach [Formula: see text] for five typical long-lived fission products (LLFPs): [Formula: see text]Se, [Formula: see text]Tc, [Formula: see text]Pd, [Formula: see text]I, [Formula: see text]Cs. Our comparative studies show that although the neutron production efficiency of the GF γ-ray beam (per MW of the beam power) is approximately 14 times lower than that of the 500 MeV proton beam, the overall net ANES power production efficiency for the GF beam driver scheme could be comparable to that of the proton beam driver scheme, while providing additional transmutation capacity, not available for the proton beam driven scheme. It is suggested that the GF-driven ANES could provide a viable solution for the efficient transmutation of the loaded LLFPs with no prior isotopic separation, and generate the requisite electrical power for its operation, with reduced production of LLFPs over its operation cycle.

The consistent combination of Next-to-Leading-Order (NLO) perturbative QCD with the logarithmic resummation of parton shower algorithms ('NLO matching') is a workhorse of precision QCD in the LHC era.Two methods for achieving this have been widely adopted: Mc@Nlo and Powheg.The differences between them are formally Next-to-Nextto-Leading-Order (NNLO) and therefore irrelevant for NLO accuracy, but are nevertheless numerically significant for certain processes and observables.We summarise a third method, KrkNLO, and present preliminary phenomenological results from its implementation in Herwig 7.

In this paper, we argue that the only way to improve systematic precision of W-boson mass and weak-mixing angle measurements at the LHC is to replace proton beams with isoscalar-ion beams. This results in a significant simplification of relations between W- and Z-boson production processes, with the latter serving as a precision "standard candle". However, with the presently operating LHC ion injectors, partonic luminosity for ion-ion collisions is significantly lower than the one for proton-proton collisions. Therefore, statistical precision of the above measurements is lower for the former case. The proposed way out to improve the partonic luminosity in the ion-ion mode is to transversely cool the beams. The Gamma Factory project can achieve this goal with the use of laser cooling. This will allow to improve the precision of experimental determination of the above parameters to delta MW < 5 MeV and delta sin(2) theta(W) < 10(-4). The proposed calcium beams are also optimal for exclusive Higgs-boson production in multiperipheral gamma gamma collisions and studies of H -> bb decays in a clean environment.

We provide an overview of the status of Monte-Carlo event generators for high-energy particle physics. Guided by the experimental needs and requirements, we highlight areas of active development, and opportunities for future improvements. Particular emphasis is given to physics models and algorithms that are employed across a variety of experiments. These common themes in event generator development lead to a more comprehensive understanding of physics at the highest energies and intensities, and allow models to be tested against a wealth of data that have been accumulated over the past decades. A cohesive approach to event generator development will allow these models to be further improved and systematic uncertainties to be reduced, directly contributing to future experimental success. Event generators are part of a much larger ecosystem of computational tools. They typically involve a number of unknown model parameters that must be tuned to experimental data, while maintaining the integrity of the underlying physics models. Making both these data, and the analyses with which they have been obtained accessible to future users is an essential aspect of open science and data preservation. It ensures the consistency of physics models across a variety of experiments.

With the advancement of strategies for the precision physics programs for the HL-LHC, FCC-ee, FCC-hh, ILC, CLIC, CEPC, and CPPC, the need for proper control of the attendant theoretical precision tags is manifest. We discuss the role that amplitude-based resummation may play in this regard with examples from the LHC, the proposed new colliders and quantum gravity.

In this note, we discuss the precision possible for the calculation of the small-angle Bhabha process that can serve as a luminosity monitor at the future FCCee collider.We present a refined, more aggressive version of the analysis done in the previous study.We conclude that the forecasted earlier precision of 1 × 10 -4 can be reduced to 0.76 × 10 -4 with the same calculational tools.We also analyse possibilities of a further reduction of the error to the close to 10 -5 precision regime.We discuss conditions necessary for such an ambitious goal.

In this work, we explore the features of gluonic cascades in static and Bjorken expanding media by numerically solving the full BDIM evolution equations in longitudinal momentum fraction x and transverse momentum k using the Monte Carlo event generator MINCAS. Confirming the scaling of the energy spectra at low- x , discovered in earlier works, we use this insight to compare the amount of broadening in static and expanding media. We compare angular distributions for the in-cone radiation for different medium profiles with the effective scaling laws and conclude that the out-of-cone energy loss proceeds via the radiative break-up of hard fragments, followed by an angular broadening of soft fragments. While the dilution of the medium due to expansion significantly affects the broadening of the leading fragments, we provide evidence that in the low- x regime, which is responsible for most of the gluon multiplicity in the cascade, the angular distributions are very similar when comparing different medium profiles at an equivalent, effective in-medium path length. This is mainly due to the fact that in this regime, the broadening is dominated by multiple splittings. Finally, we discuss the impact of our results on the phenomenological description of the out-of-cone radiation and jet quenching.

In order to stimulate new engagement and trigger some concrete studies in areas where further work would be beneficial towards fully understanding the physics potential of an $e^+e^-$ Higgs / Top / Electroweak factory, we propose to define a set of focus topics. The general reasoning and the proposed topics are described in this document.

One of the fundamental challenges for future leptonic colliders and neutrino factories as well as for high-sensitivity studies of lepton universality is to design and construct new high-intensity sources of muons and positrons. The next-generation sources should increase the intensity of the presently operating ones by at least three orders of magnitude and include an important option of producing longitudinally polarized leptons. The main effort to achieve this goal has been focused, so far, on the proton-beam-driven muon sources and electron-beam-driven positron sources. In this paper, we present exploratory studies of an alternative scheme which is based on high-intensity megawatt-class photon beams. Such beams could be delivered in the future by the Gamma Factory (GF) project. One of the GF multiple goals is to increase the energy range (by more than one order of magnitude) and the intensity (by more than six orders of magnitude) of presently operating photon sources. Such a leap can be achieved by extending the present hadron-collider modus operandi of the LHC with a new GF-operation-mode, allowing the collisions of beams with laser pulses. The exploratory studies presented in this paper demonstrate that more than 10$^{13}$ muons of both signs and more than 10$^{16}$ electrons/positrons per second can be produced by a GF source.

For both the FCC-ee and the ILC, to exploit properly the respective precision physics program, the theoretical precision tag on the respective luminosity will need to be improved from the analogs of the $0.054 \% (0.061\%)$ results at LEP at $M_Z$, where the former (latter) LEP result has (does not have) the pairs correction. At the FCC-ee at $M_Z$ one needs improvement to $0.01\%$, for example. We present an overview of the roads one may take to reach the required $0.01\%$ precision tag at the FCC-ee and of what the corresponding precision expectations would be for the FCC-ee$_{350}$, ILC$_{500}$, ILC$_{1000}$, and CLIC$_{3000}$ setups.

The Gamma Factory (GF) initiative aims at the construction of a unique experimental tool exploiting resonant interaction of light with ultra‐relativistic partially stripped ions (PSI) stored in circular accelerators at CERN. Resonant excitation of high‐energy electronic transitions in the ions is achieved through Doppler‐boosting (by twice the Lorentz factor; from hundred to several thousand times) of light energy. In order to efficiently excite the ions, and hence generate intense beams of scattered/fluorescent photons, a detailed knowledge of the ions' electronic energy structure and the dynamics of optical excitation is required. Spectroscopic properties of PSI selected for the GF operation, as well as their optical excitation schemes, are investigated. Two regimes of the ion–light interaction are identified, leading to different dynamics of the excitation. The efficiency of the ion–light interaction, as well as the number of photons emitted from a single ion bunch, are estimated, both analytically and numerically, for three ions considered for the GF, that is, Li‐like 082208${}^{208}_{\phantom{0}82}$ Pb79 + , Li‐like 2040${}^{40}_{20}$ Ca17 + , and H‐like 082208${}^{208}_{\phantom{0}82}$ Pb81 + .

We propose a system of evolution equations that describe in-medium time-evolution of transverse-momentum-dependent quark and gluon fragmentation functions. Furthermore, we solve this system of equations using Monte Carlo methods. We then quantify the obtained solutions in terms of a few characteristic features, namely the average transverse momentum ⟨ |k|⟩ and energy contained in a cone, which allow us to see different behaviour of quark and gluon initiated final-state radiation. In particular, the later allows us to conclude that in the gluon-initiated processes there is less energy in a cone, so that the quark jet is more collimated.

We studied the evolution of jets within a medium that contains both, transverse kicks as well as medium induced coherent radiation. In this framework parton branching occurs simultaneously to scatterings within the medium, leading to the interference effects that reproduce the well known BDMPS-Z emission rates and sizeable transverse momentum broadening. We examined the relative importances of transverse momentum broadening from the coherent splittings and different types of in-medium scatterings and found a clear hierarchy of the influences from different scattering effects and deflections during branchings.

A very intense gamma beam of the Gamma Factory facility proposed at CERN can be used to generate radioactive ion beams (RIBs) with high production yields and study the structure of exotic neutron-rich nuclei. The radioactive nuclides are generated via photo-fission in several actinide targets and thermalized in high-purity cryogenic helium, filling a gas cell which is enclosing the targets. Electric fields are used to extract heavy ions and form RIBs which can be sent to various selection and measurement stations. Estimates for the production and extraction yields of exotic neutron-rich nuclei with such a setup are provided. A study of the impact of space charge, build-up inside the gas cell, on the extraction properties is presented and it is demonstrated that the beam needs to be chopped for achieving optimal extraction yields.

We study evolution equations describing jet propagation through quark--gluon plasma (QGP). In particular we investigate the contribution of momentum transfer during branching and find that such a contribution is sizeable. Furthermore, we study various approximations, such as the Gaussian approximation and the diffusive approximation to the jet-broadening term. We notice that in order to reproduce the BDIM equation (without the momentum transfer in the branching) the diffusive approximation requires a very large value of the jet-quenching parameter $\hat q$.

We present an estimation of the theoretical precision of low angle Bhabha scattering at the proposed future ILC collider at 500 GeV. The analysis is an extension of the previous analysis done for the FCCee collider at $$\sqrt{s}=M_Z$$ s = M Z . As the state-of-the-art and the reference point we use the Monte Carlo event generator. Based on the current precision status of for LEP analysis, we estimate how various error components evolve from the LEP to ILC setups. The conclusion of our work is that for the ILC the precision of the current version of 4.04 deteriorates to 0.5%, by more than an order of magnitude w.r.t. the present precision for LEP. With the expected future improvements, the precision of can change to 0.016%, nearly as good as for the FCCee at the $$M_Z$$ M Z setup (0.01%). Based on the developed methodology we present also results for ILC $$_{1000}$$ 1000 , FCCee $$_{350}$$ 350 and CLIC $$_{3000}$$ 3000 setups.

There are two main ways to increase LHC luminosity without upgrading CERN injectors: (1) modification of beam-collision optics and (2) reduction of beam transverse emittance. The former is followed in the ongoing high-luminosity upgrade of the LHC (HL-LHC), while the latter, applicable only to ion beams, is described in this contribution. The reduction of the beam emittance can be achieved by employing a laser-cooling technique to bunches of partially stripped ions at the SPS flat-top energy. In the case of the isoscalar calcium beams fulfilling the present beam-operation constrains, the transverse beam emittance can be reduced in this way by a factor of 5 during the 8 second long cooling phase. This would allow to reach the nucleon–nucleon luminosity 𝐿 𝑁 𝑁 = 4 . 2 × 10 34 s − 1 cm − 2 , which is comparable to the levelled luminosity for the HL-LHC proton–proton collisions, but with reduced pile-up background. The calcium–calcium collisions have several advantages over the proton–proton collisions for the electroweak physics, such as precision measurements of the 𝑊 -boson mass and sin 2 𝜃 𝑊 , clean observation of the Higgs-boson decay into 𝑏 ¯ 𝑏 in its photoproduction channel or BSM phenomena. If this scheme is confirmed by the future Gamma Factory proof-of-principle experiment, it could be implemented at CERN with minor infrastructure investments. This contribution is based on Ref. [1].