International Journal of Modern Physics A

The central exclusive production of charged hadron pairs in pp collisions at a center-of-mass energy of 13TeV is examined, based on data collected in a special high-${\beta }^{*}$ run of the LHC. Events are selected by requiring both scattered protons detected in the TOTEM Roman pots, exactly two oppositely charged identified particles in the CMS silicon tracker, and the energy–momentum balance of these four particles. The nonresonant continuum processes are studied with the invariant mass of the centrally produced two-pion system in the resonance-free region, $m<0.7$GeV or $m>1.8$GeV. Differential cross sections as functions of the azimuthal angle between the surviving protons, squared four-momenta, and two-hadron invariant mass are measured in a wide region of scattered protons with transverse momentum between 0.2 and 0.8GeV and for pion rapidities $|y|<2$. A rich structure of interactions related to double pomeron exchange emerges. The parabolic minimum in the distribution of the two-proton azimuthal angle is observed for the first time. It can be understood as an effect of additional pomeron exchanges between the protons, and of the interference between the bare and the rescattered amplitudes. After model tuning, various physical quantities related to the pomeron cross section, proton–pomeron and hadron–pomeron form factors, trajectory slopes and intercepts, as well as coefficients of diffractive eigenstates of the proton are determined.

Jet substructure in heavy-ion collisions is a rapidly evolving area with lots of intriguing new measurements. This contribution presents a selection of recent jet-substructure measurements from experiments at the LHC, in particular, soft-drop groomed radii of jets and reclustered large-radius jets from ATLAS, jet axis difference and generalized jet angularities from ALICE, as well as dijet shapes and b-jet shapes from the CMS experiment.

In the recent decades of high energy physics research, it was demonstrated that strongly interacting quark-gluon plasma (sQGP) is created in ultra-relativistic nucleus–nucleus collisions. Investigation and understanding of properties of the hadronic matter is among the important goals of NA61/SHINE collaboration at CERN SPS. Mapping of the phase diagram is achieved by varying the collision energy ($5\mathrm{\text{GeV}}<\sqrt{s_{\mathrm{\text{NN}}}}<17\mathrm{\text{GeV}}$) and by changing the collision system ($\mathrm{\text{p}}+\mathrm{\text{p}}$, $\mathrm{\text{p}}+\mathrm{\text{Pb}}$, $\mathrm{\text{Be}}+\mathrm{\text{Be}}$, $\mathrm{\text{Ar}}+\mathrm{\text{Sc}}$, $\mathrm{\text{Xe}}+\mathrm{\text{La}}$, $\mathrm{\text{Pb}}+\mathrm{\text{Pb}}$).

We report on the measurement of femtoscopic correlations in intermediate systems at intermediate SPS energies. Interpreting the results of measurements within the symmetric Lévy source formalism, we discuss the values of Lévy source parameters as a function of average pair transverse mass. One of the physical parameters is particularly important, the Lévy exponent $\alpha$, which describes the shape of the source and may be related to the critical exponent $\eta$ in the proximity of the critical point. Therefore, measuring it may shed light on the location of the critical endpoint of the QCD phase diagram.

Studying heavy-flavor production in high-energy heavy-ion collisions (HIC) can enhance our comprehension of parton interactions with the quark-gluon plasma (QGP) created in these collisions. Due to their significant mass, heavy quarks (charm and bottom) are mainly generated during the initial phase of HIC when hard scatterings are prevalent, and experience the entire evolution of the QGP. One way to study heavy quarks is through the measurement of electrons from heavy-flavor hadron decay, heavy-flavor electrons (HFE). In this contribution, we present the analysis of HFE at low transverse momentum ($p_{\mathrm{\text{T}}}$) in Au+Au collisions at $\sqrt{s_{\mathrm{\text{NN}}}}=54.4$GeV using data taken in 2017 by the STAR experiment. The strong HFE suppression was already observed in the central Au+Au collisions at $\sqrt{s_{\mathrm{\text{NN}}}}=200$GeV. Measuring heavy-flavor quark nuclear modification factors below the RHIC top energy offers new insights on the in-medium energy loss, especially the collisional energy loss which is dominant at low $p_{\mathrm{\text{T}}}$.

For most high-precision experiments in particle physics, it is essential to know the luminosity at highest accuracy. The luminosity is determined by the convolution of particle densities of the colliding beams. In special van der Meer transverse beam separation scans, the convolution function is sampled along the horizontal and vertical axes with the purpose of determining the beam convolution and getting an absolute luminosity calibration. For this purpose, the van der Meer data of luminometer rates are separately fitted in the two directions with analytic functions giving the best description. With the assumption that the 2D convolution shape is factorizable, one can calculate it from the two 1D fits. The task of XY factorization analyses is to check this assumption and give a quantitative measure of the effect of nonfactorizability on the calibration constant to improve the accuracy of luminosity measurements.

We perform a dedicated analysis to study XY nonfactorization on proton–proton data collected in 2022 at $\sqrt{s}=13.6$TeV by the CMS experiment [The CMS Collab., Luminosity measurement in proton-proton collisions at $\sqrt{s}=13.6$ TeV in 2022 at CMS (2024). A detailed examination of the shape of the bunch convolution function is presented, studying various biases, and choosing the best-fit analytic 2D functions to finally obtain the correction and its uncertainty.

The ALICE setup for LHC Run 3 aims to collect all minimum bias data at the targeted 1MHz interaction rate for protons and 50kHz for heavy-ion collisions. The projected maximum ALICE data rate will be $\sim$3TB/s, two orders of magnitude higher than in Run 1 and Run 2. ALICE detectors, front-end readout electronics and data processing systems were upgraded to meet these challenges. One of the upgrades is the Fast Interaction Trigger (FIT). The custom-designed front-end electronics (FEE) process the detectors’ signals in $\sim$200ns. The three main detectors of FIT are FT0, FV0 and FDD. These detectors provide trigger generation, luminosity monitoring, online vertex determination, collision time measurement, multiplicity detection, event plane and centrality determination and diffractive event measurements. This contribution will present an overview of the FIT and its performance based on the p–p and Pb–Pb collisions collected in 2022 and 2023, respectively. The FIT FEE upgrade, planned for the LHC Run 4, will also be discussed.

In high-energy physics, quantum statistical correlation measurements are very important for getting a good picture of how a particle-emitting source is structured in space and time, as well as its thermodynamic properties and inner dynamics. It is necessary to take into account the various final state effects since they have the potential to alter the observed femtoscopic correlation functions. Protons are affected mostly by the strong interaction, whereas other charged particles are mostly influenced by the Coulomb interaction. The interaction of the particles under investigation with the fireball or the expanding cloud of the other particles in the final state might also have significant consequences. This may case the trajectories of the particles to shift. This phenomenon can be viewed as an Aharonov–Bohm effect since the pair’s alternate tracks reveal a closed loop with an internal field. We investigate a numerical solution for a toy model to study the modifications of Bose–Einstien correlation function strength, which is sensitive to this effect.

Constraining the nuclear equation of state (EoS) parameters makes it possible to better understand the properties of the matter that constitutes our Universe. Many probes can be used to test the EoS, from the observation of neutron star mergers to heavy-ion collisions at intermediate energies. The fragments and particles emitted in collisions need to be identified with isotopic discrimination in order to give valuable information. In this regard, a specifically designed apparatus, such as FAZIA, may be used to study the equation of state. This review summarizes the advanced characteristics of the FAZIA detector array and the achievements obtained by the FAZIA collaboration in the last 15 years.

This paper presents the preliminary results on the anisotropies of the azimuthal angle of K${}^{+}$ mesons produced in Ag+Ag collisions at a beam energy of 1.58AGeV measured by the HADES spectrometer. The transverse flow effect is measured with the harmonic coefficients of the cosine series describing the azimuthal angle distributions in the transverse momentum-rapidity phase space. The coefficients are corrected for the finite event-plane reconstruction resolution, however, occupancy effects in the detector have not yet been studied. Some indications of the K${}^{+}$ antiflow are visible in the $v_1$ distribution.

We investigate the formation and evolution of hot systems comprising charmed and light hadrons using non-extensive thermodynamics. We analyze data from pp, p–Pb, and Pb–Pb collisions at center-of-mass energies ranging from $\sqrt{s_{\mathrm{\text{NN}}}}=2.76$TeV to 13TeV, measured by the CERN LHC ALICE experiment. The hadron species examined include charged pions and kaons, ${\mathrm{\text{K}}}_{\mathrm{\text{s}}}^0$, (anti)protons, $\varphi$ mesons, ${\mathrm{\Lambda }}^0$ hyperons, and D mesons. Employing our previously established methods, we determine the common Tsallis parameters $T_{\mathrm{\text{eq}}}$ and $q_{\mathrm{\text{eq}}}$ for each hadron type. While charm comes from earlier than light hadrons, we see that $T_{\mathrm{\text{eq}}}$ is ordered by mass, reflecting a similar ordering in the time-scale relevant for the spectrum. Our results also allow for constraining the heat capacity of the system. The current analysis thus enhances our understanding of hadron production dynamics and thermal properties in high-energy collisions.

We study the nature of charm degrees of freedom near the chiral crossover based on lattice QCD calculations of the second and fourth-order cumulants of charm fluctuations, and their correlations with net baryon number, electric charge, and strangeness fluctuations. We show that below the chiral crossover temperature, $T_{pc}$, the thermodynamics of charm can be very well understood in terms of charmed hadrons. We present evidence that above $T_{pc}$, however, charm quark-like excitations emerge as new degrees of freedom contributing to the partial charm pressure. Nonetheless, up to temperatures as high as 175MeV, charmed hadron-like excitations significantly contribute to the partial charm pressure.