S. H. Lim’s research while affiliated with Pusan National University and other places

The ALICE Collaboration at the CERN LHC has measured the inclusive production cross section of isolated photons at midrapidity as a function of the photon transverse momentum ( $p_{\textrm{T}}^{\gamma }$ p T γ ), in Pb–Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of $\sqrt{s_{\textrm{NN}}}~=~5.02$ s NN = 5.02 TeV. The photon transverse momentum range is between 10–14 and 40–140 GeV/ c c , depending on the collision system and on the Pb–Pb centrality class. The result extends to lower $p_{\textrm{T}}^{\gamma }$ p T γ than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is $|\eta ^{\gamma } | <0.67$ | η γ | < 0.67 . The isolation selection is based on a charged particle isolation momentum threshold $p_{\textrm{T}}^\mathrm{iso,~ch} = 1.5$ p T iso , ch = 1.5 GeV/ c c within a cone of radii R=0.2 R = 0.2 and 0.4. The nuclear modification factor is calculated and found to be consistent with unity in all centrality classes, and also consistent with the HG-PYTHIA model, which describes the event selection and geometry biases that affect the centrality determination in peripheral Pb–Pb collisions. The measurement is compared to next-to-leading order perturbative QCD calculations and to the measurements of isolated photons and Z $^{0}$ 0 bosons from the CMS experiment, which are all found to be in agreement.

The first measurements of proton emission accompanied by neutron emission in the electromagnetic dissociation (EMD) of Pb 208 nuclei in the ALICE experiment at the Large Hadron Collider are presented. The EMD protons and neutrons emitted at very forward rapidities are detected by the proton and neutron zero degree calorimeters of the ALICE experiment. The emission cross sections of zero, one, two, and three protons accompanied by at least one neutron were measured in ultraperipheral Pb 208 − Pb 208 collisions at a center-of-mass energy per nucleon pair s N N = 5.02 TeV . The 0p and 3p cross sections are described by the RELDIS model within their measurement uncertainties, while the 1p and 2p cross sections are underestimated by the model by 17–25%. According to this model, these 0p, 1p, 2p, and 3p cross sections are associated, respectively, with the production of various isotopes of Pb, Tl, Hg, and Au in the EMD of Pb 208 . The cross sections of the emission of a single proton accompanied by the emission of one, two, or three neutrons in EMD were also measured. The data are significantly overestimated by the RELDIS model, which predicts that the (1p,1n), (1p,2n), and (1p,3n) cross sections are very similar to the cross sections for the production of the thallium isotopes Tl 206 , 205 , 204 . ©2025 CERN, for the ALICE Collaboration 2025 CERN

In this Letter, the first evidence of the He ¯ Λ ¯ 4 antihypernucleus is presented, along with the first measurement at the LHC of the production of (anti)hypernuclei with mass number A = 4 , specifically ( anti ) H Λ 4 and ( anti ) He Λ 4 . In addition, the antiparticle-to-particle ratios for both hypernuclei ( H ¯ Λ ¯ 4 / H Λ 4 and He ¯ Λ ¯ 4 / He Λ 4 ) are shown, which are sensitive to the baryochemical potential of the strongly interacting matter created in heavy-ion collisions. The results are obtained from a data sample of central Pb-Pb collisions, collected during the 2018 LHC data taking at a center-of-mass energy per nucleon pair of s NN = 5.02 TeV . The yields measured for the average of the charge-conjugated states are found to be [ 0.78 ± 0.19 ( stat ) ± 0.17 ( syst ) ] × 10 − 6 for the ( anti ) H Λ 4 and [ 1.08 ± 0.34 ( stat ) ± 0.20 ( syst ) ] × 10 − 6 for the ( anti ) He Λ 4 , and the measured antiparticle-to-particle ratios are in agreement with unity. The presence of ( anti ) H Λ 4 and ( anti ) He Λ 4 excited states is expected to strongly enhance the production yield of these hypernuclei. The yield values exhibit a combined deviation of 3.3 σ from the theoretical ground-state-only expectation, while the inclusion of the excited states in the calculations leads to an agreement within 0.6 σ with the present measurements. Additionally, the measured ( anti ) H Λ 4 and ( anti ) He Λ 4 masses are compatible with the world-average values within the uncertainties. © 2025 CERN, for the ALICE Collaboration 2025 CERN

A bstract The p T -differential cross section of ω meson production in pp collisions at $\sqrt{s}$ s = 13 TeV at midrapidity ( |y| < 0 . 5) was measured with the ALICE detector at the LHC, covering an unprecedented transverse-momentum range of 1 . 6 < p T < 50 GeV/ c . The meson is reconstructed via the ω → π ⁺ π − π ⁰ decay channel. The results are compared with various theoretical calculations: PYTHIA8.2 with the Monash 2013 tune overestimates the data by up to 50%, whereas good agreement is observed with Next-to-Leading Order (NLO) calculations incorporating ω fragmentation using a broken SU(3) model. The ω/π ⁰ ratio is presented and compared with theoretical calculations and the available measurements at lower collision energies. The presented data triples the p T ranges of previously available measurements. A constant ratio of C ω/π 0 = 0 . 578 ± 0 . 006 (stat.) ± 0 . 013 (syst.) is found above a transverse momentum of 4 GeV/ c , which is in agreement with previous findings at lower collision energies within the systematic and statistical uncertainties.

The PHENIX experiment at the Relativistic Heavy Ion Collider measured the second Fourier component $v_2$ of the direct-photon azimuthal anisotropy at midrapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The results are presented in 10\% wide bins of collision centrality and cover the transverse-momentum range of $1<p_T<20$ GeV/c, and are in quantitative agreement with findings published earlier, but provide better granularity and higher $p_T$ reach. Above a $p_T$ of 8--10 GeV/c, where hard scattering dominates the direct-photon production, $v_2$ is consistent with zero. Below that in each centrality bin $v_2$ as a function of $p_T$ is comparable to the $\pi^0$ anisotropy albeit with a tendency of being somewhat smaller. The results are compared to recent theory calculations that include, in addition to thermal radiation from the quark-gluon plasma and hadron gas, sources of photons from pre-equilibrium, strong magnetic fields, or radiative hadronization. While the newer theoretical calculations describe the data better than previous models, none of them alone can fully explain the results, particularly in the region of $p_T=4$--8 GeV/c.

ALICE is a large experiment at the CERN Large Hadron Collider. Located 52 meters underground, its detectors are suitable to measure muons produced by cosmic-ray interactions in the atmosphere. In this paper, the studies of the cosmic muons registered by ALICE during Run 2 (2015–2018) are described. The analysis is limited to multimuon events defined as events with more than four detected muons (Nμ > 4) and in the zenith angle range 0° < θ < 50°. The results are compared with Monte Carlo simulations using three of the main hadronic interaction models describing the air shower development in the atmosphere: QGSJET-II-04, EPOS-LHC, and SIBYLL 2.3d. The interval of the primary cosmic-ray energy involved in the measured muon multiplicity distribution is about 4 × 10¹⁵ < E prim < 6 × 10¹⁶ eV. In this interval none of the three models is able to describe precisely the trend of the composition of cosmic rays as the energy increases. However, QGSJET-II-04 is found to be the only model capable of reproducing reasonably well the muon multiplicity distribution, assuming a heavy composition of the primary cosmic rays over the whole energy range, while SIBYLL 2.3d and EPOS-LHC underpredict the number of muons in a large interval of multiplicity by more than 20% and 30%, respectively. The rate of high muon multiplicity events (Nμ > 100) obtained with QGSJET-II-04 and SIBYLL 2.3d is compatible with the data, while EPOS-LHC produces a significantly lower rate (55% of the measured rate). For both QGSJET-II-04 and SIBYLL 2.3d, the rate is close to the data when the composition is assumed to be dominated by heavy elements, an outcome compatible with the average energy E prim ∼ 10¹⁷ eV of these events. This result places significant constraints on more exotic production mechanisms.

A bstract Short-range correlations between charged particles are studied via two-particle angular correlations in pp collisions at $\sqrt{s}$ s = 13 TeV. The correlation functions are measured as a function of the relative azimuthal angle ∆ φ and the pseudorapidity separation ∆ η for pairs of primary charged particles within the pseudorapidity interval | η | < 0 . 9 and the transverse-momentum range 1 < p T < 8 GeV/ c . Near-side (|∆ φ | < 1 . 3) peak widths are extracted from a generalised Gaussian fitted over the correlations in full pseudorapidity separation (|∆ η | < 1 . 8), while the per-trigger associated near-side yields are extracted for the short-range correlations (|∆ η | < 1 . 3). Both are evaluated as a function of charged-particle multiplicity obtained by two different event activity estimators. The width of the near-side peak decreases with increasing multiplicity, and this trend is reproduced qualitatively by the Monte Carlo event generators PYTHIA 8, AMPT, and EPOS. However, the models overestimate the width in the low transverse-momentum region ( p T < 3 GeV/ c ). The per-trigger associated near-side yield increases with increasing multiplicity. Although this trend is also captured qualitatively by the considered event generators, the yield is mostly overestimated by the models in the considered kinematic range. The measurement of the shape and yield of the short-range correlation peak can help us understand the interplay between jet fragmentation and event activity, quantify the narrowing trend of the near-side peak as a function of transverse momentum and multiplicity selections in pp collisions, and search for final-state jet modification in small collision systems.

This corrects the article DOI: 10.1103/PhysRevLett.116.122301.