abstract

The \(B \rightarrow K\tau \ell \) decays (where \(\ell =e,\mu \)) are not allowed in the Standard Model (SM) at the tree level due to lepton flavor violation (LFV). In some New Physics (NP) models, their branching fractions are within the reach of the current experimental sensitivities. The Belle and Belle II experiments provide ideal conditions for their search. We used the basic kinematic constraints of the experiments to reconstruct them. A multivariate classifier score is used to model the signal and background. For the estimation of statistical upper limits (ULs), the Bayesian approach is used. To validate the analysis method, two control channel modes are used.

abstract

An intermediate 48 V to 11 V DC/DC conversion stage, located in Patch Panel 2 (PP2), constitutes a key element of the power delivery chain for the ATLAS Inner Tracker (ITk) Strip detector. The design, based on commercial off-the-shelf components, meets the detector constraints and radiation tolerance requirements. Pre-production DC/DC boards demonstrate efficiencies above 81% across the full load range and low output noise, confirming the robustness of the PP2 system.

abstract

During the summer of 2025, the LHC collided protons with oxygen, oxygen with oxygen, and neon with neon. The ATLAS experiment recorded these data with its Forward Proton detectors (AFP) inserted on both: the proton and ion sides. This allows access to many interesting studies with scattered fragments being tagged. A few analysis ideas are presented followed by preliminary studies of what could be visible in the AFP.

abstract

The anomalous magnetic moment of the muon is one of the promising sectors for probing New Physics. Recent results from \(g-2\) experiments indicate a possible deviation of about \(5\sigma \) from the Standard Model prediction. The MUonE experiment was designed to precisely measure the hadronic contribution to the muon anomalous magnetic moment, which could increase the significance to at least \(7\sigma \) and thereby confirm potential discovery. Several crucial milestones have already been achieved by the MUonE project, and the results of the ongoing 2025 test run analysis will serve as the foundation for the full-scale 40 station proposal to be implemented after the LHC Long Shutdown 3. However, classical event reconstruction will face a significant challenge due to combinatorial scaling in this final configuration. To address these challenges, the use of Graph Neural Networks (GNNs) is proposed for the pattern recognition stage, as they offer the flexibility to process irregular geometries while maintaining the low latency required for a trigger. This allows for robust track reconstruction even in scenarios where detector hits may be missing, ensuring accurate performance under imperfect or incomplete data conditions.

abstract

A successor to the PACIFIC front-end ASIC, currently used in the LHCb Scintillating Fibre (SciFi) Tracker, is being developed for the second foreseen upgrade of the LHCb experiment. The new ASIC, referred to as PACIFIC++, is implemented in 65 nm CMOS technology and extends the architecture of the existing PACIFIC, designed in 130 nm CMOS technology. The new design introduces a 10-bit ADC and a 6-bit TDC measurement in each channel, together with on-chip clustering. The PACIFIC++ is proposed for the readout of the Mighty SciFi Tracker and Magnet Station detectors in the LHCb Upgrade II. An 8-channel prototype version of PACIFIC++, called PACIFIC+8, including all key functionalities, is currently being prepared for submission. This paper discusses the PACIFIC++ architecture and its current state of development.

abstract

An overview of charm-quark hadronisation within the PYTHIA/Angantyr model is provided. The improvements to the junction formation and fragmentation mechanisms in the context of charm-quark hadronisation are discussed. We discuss these changes in the context of the recently developed global colour reconnection mechanism, which is based on the QCD-inspired colour reconnection model. We show the enhancement in \({\mit \Lambda }_c\) baryon yield in \(\pp \) and \(\pPb \) collisions at the LHC at \(\sqrt {s_{NN}} = 5.02\) TeV collision energy using the PYTHIA/Angantyr model.

abstract

Studies of the internal structure of hadrons have been a main focus in particle physics since perturbative Quantum Chromodynamics (p-QCD) was established as the theory of the strong interaction. While the constituent quark model provided a successful framework for the investigation of many hadrons, recent decades have unveiled exotic states that defy simple classification. An example is the \(X(6900)\) resonance, identified in the di-\(J/\psi \) mass spectrum by LHCb, ATLAS, and CMS. As a tetraquark composed of \(c\bar {c}c\bar {c}\), its existence confirms the possibility of such multi-quark states. Its fundamental nature — whether it is a compact diquark–antidiquark entity or a diffuse molecule of two charmonia — remains an open question. We propose a study for the exclusive \(\gamma \gamma \to X(6900)\) process, accessible in ultraperipheral heavy-ion collisions (UPCs), which serves as a clean probe to differentiate between these inner structures. In this work, we calculate the respective two-photon decay width, \({\mit \Gamma }_{\gamma \gamma }\), using a leading-order Non-Relativistic QCD (NRQCD) framework. The long-distance matrix elements are determined from the wave functions at origin obtained in an extended relativized quark model. For the \(X(6900)\) as a radially excited (\(2s\)) compact state, we predict sizable widths of \({\mit \Gamma }_{\gamma \gamma }(2^{++}_{2s}) \approx 0.22\) keV and \({\mit \Gamma }_{\gamma \gamma }(0^{++}_{2s}) \approx 0.15\)–0.69 keV. These values are significantly larger than expected for a molecular state, providing a clear experimental discriminant.

abstract

NA61/SHINE is a multipurpose fixed-target experiment located at the CERN SPS. One of its main goals is to study the onset of deconfinement and the properties of strongly interacting matter. For this purpose, a unique two-dimensional scan in collision energy (\(\sqrt {s_{NN}} = 5.12\)–\(16.8/17.3\) GeV) and system size (from \(p\)+\(p\) to Pb+Pb) was performed. Results on hadron spectra produced in nucleus–nucleus collisions, including the recent data on charged hadrons produced in central Xe+La collisions and baryons in central Ar+Sc collisions, are presented. The kinematic distributions and the measured multiplicities of identified hadrons are compared with NA49 Pb+Pb results and with available world data. The obtained results, particularly the \(K^+/\pi ^+\) ratio, are crucial for understanding the phenomena of the onset of deconfinement, which is one of the main aims of the strong interaction program of the NA61/SHINE Collaboration. Additionally, a comparison of proton rapidity spectra in nucleus–nucleus collisions from NA61/SHINE and NA49 is presented, providing a complete picture of the energy and system-size dependence of the mechanism of transport of baryon number at SPS energies.

abstract

These proceedings give an overview of the latest measurements in light-ion collision systems with the ATLAS detector at the LHC using the 5.36 TeV \(^{16}\)O+\(^{16}\)O and \(^{20}\)Ne+\(^{20}\)Ne collisions data recorded in July 2025. The increased Sub Farm Output rate enabled higher rates for low-\(p_{\mathrm {T}}\) and minimum-bias triggers. The measurement of azimuthal anisotropies in O\(+\)O and Ne\(+\)Ne collisions, utilising two-particle correlations with template-fit subtraction and four-particle subevent cumulants, is presented. The preliminary measurement of the dijet transverse momentum balance in O\(+\)O and \(pp\) collisions at 5.36 TeV is also presented.

abstract

The ATLAS heavy-ion physics program includes the study of ultraperipheral collisions. In these interactions, the ions serve as a source of high-energy quasi-real photons. These photons can interact with another nucleus, giving rise to a variety of photon-induced processes. One of these is exclusive vector meson production. This process allows for the study of the spatial and momentum structure of the nuclear parton distribution functions and may provide insight into low Bjorken-\(x\) phenomena such as nuclear shadowing and parton saturation. This study shows the first ATLAS measurement of coherent exclusive \(J/\psi \) production in ultraperipheral Pb+Pb collisions at \(\sqrt {s_{NN}} = 5.36\) TeV. The differential cross section for this process is measured as a function of \(J/\psi \) rapidity.

abstract

Ultraperipheral heavy-ion collisions (UPC) at the Large Hadron Collider (LHC) provide a unique environment to study photon-induced processes. This overview highlights recent ATLAS measurements of UPC in Pb+Pb collisions at \(\sqrt {s_{NN}} = 5.02\) TeV and 5.36 TeV. The measurements address important physics questions on nuclear parton structure, onset of quark–gluon plasma formation, and multiple photon-induced processes.

abstract

The Transition Radiation Tracker (TRT) is the outermost part of the ATLAS Inner Detector and its main purpose is improving momentum resolution of charged particles by providing measurements at large radial distances. In the TRT, the particle position is inferred from the time at which the ionisation signal reaches the wire located at the centre of the straw. This drift time measurement is translated into a one-dimensional spatial constraint — a circle around the wire, referred to as the drift circle. The uncertainty of the drift circle measurement (drift circle error) is determined from the distribution of unbiased residuals, which depends on the drift time and on the position of the straw within the detector, and must be periodically updated to account for changing detector conditions. This work presents the latest Run 3 calibration performed using 2024 data with muon tracks at low pile-up, as well as the evaluation of the detector performance after the calibration. The results show an improvement in the region of high local detector occupancy.

abstract

Jet production has been studied extensively in heavy-ion collisions to measure its modification in the presence of the quark–gluon plasma. Several recent measurements performed by the ATLAS experiment at the LHC are highlighted, including studies of the jet suppression as a function of jet radius and jet substructure. Additionally, results of the search for jet-induced wake are presented.

abstract

The ATLAS small-system program began in 2012 with the first \(p\)+Pb collisions delivered by the LHC. Measurements across several collision systems and energies show that small systems exhibit collective phenomena similar to those observed in large collision systems. In contrast, hard-probe measurements in \(p\)+Pb collisions show no significant modification consistent with jet quenching, and observed centrality dependencies are largely explained by initial-state effects and event-activity biases.

abstract

The ATLAS experiment at the Large Hadron Collider performs a broad heavy-ion physics programme aimed at studying strongly interacting matter at extreme energy density, as well as probing QCD and electroweak phenomena in nuclear environments. This contribution presents an overview of recent ATLAS results obtained in heavy-ion, light-ion, and ultra-peripheral collisions. Measurements include jet quenching observables in Pb+Pb and O+O collisions, top-quark observation in Pb+Pb collisions, collective behaviour in heavy-ion and light-ion systems, photon-induced processes in ultra-peripheral collisions, and searches for physics beyond the Standard Model.

abstract

An overview of recent results from the sPHENIX Collaboration spanning the full scientific program is presented. Recent publications on standard-candle measurements are presented in addition to photon and jet cross sections, which demonstrate how sPHENIX can extend to higher momentum measurements than previous RHIC experiments. Transverse Single Spin Asymmetries for neutral mesons and jets are also discussed. The evolution of the dijet-momentum imbalance as a function of centrality in Au+Au collisions is also compared to the imbalance in \(pp\) collisions. Finally, invariant mass distributions of several resonances and heavy-flavor hadrons are presented to demonstrate the significant progress made on tracking calibrations and corrections.