The formation of light (anti)nuclei with mass number A of a few units (e.g., d, $^3$He, and $^4$He) in high-energy hadronic collisions presents a longstanding mystery in nuclear physics [1,2]. It is not clear how nuclei bound by a few MeV can emerge in environments characterized by temperatures above 100 MeV [3-5], about 100,000 times hotter than the center of the Sun. Despite extensive studies, this question remained unanswered. The ALICE Collaboration now addresses it with a novel approach using deuteron-pion momentum correlations in proton-proton (pp) collisions at the Large Hadron Collider (LHC). Our results provide model-independent evidence that about 80% of the observed (anti)deuterons are produced in nuclear fusion reactions [6] following the decay of short-lived resonances, such as the $\Delta (1232)$. These findings resolve a crucial gap in our understanding of nucleosynthesis in hadronic collisions. Beyond answering the fundamental question on how nuclei are formed in hadronic collisions, the results can be employed in the modeling of the production of light and heavy nuclei in cosmic rays [7] and dark matter decays [8,9].
Measured $\pi^{+}$–d$\oplus\pi^{-}$–$\overline{\mathrm{d}}$ (left panel) correlation function.
Measured $\pi^{-}$–d$\oplus\pi^{+}$–$\overline{\mathrm{d}}$ (right panel) correlation function.
The extracted kinetic decoupling temperature is derived from $\pi^{+}$–d correlation functions.
The pseudorapidity distribution of charged hadrons produced in Au+Au collisions at a center-of-mass energy of $\sqrt{s_\mathrm{NN}} = 200$ GeV is measured using data collected by the sPHENIX detector. Charged hadron yields are extracted by counting cluster pairs in the inner and outer layers of the Intermediate Silicon Tracker, with corrections applied for detector acceptance, reconstruction efficiency, combinatorial pairs, and contributions from secondary decays. The measured distributions cover $|\eta| < 1.1$ across various centralities, and the average pseudorapidity density of charged hadrons at mid-rapidity is compared to predictions from Monte Carlo heavy-ion event generators. This result, featuring full azimuthal coverage at mid-rapidity, is consistent with previous experimental measurements at the Relativistic Heavy Ion Collider, thereby supporting the broader sPHENIX physics program.
Nch, Npart, and Nch/(Npart/2) values in Table 4, presented in Figure 6.
Nch as a function of $\eta$, presented in Figure 5.
This paper reports measurements of the transverse energy per unit pseudorapidity ($dE_{T}/dη$) produced in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, performed with the sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The results cover the pseudorapidity range $\left|η\right| < 1.1$ and constitute the first such measurement performed using a hadronic calorimeter at RHIC. Measurements of $dE_{T}/dη$ are presented for a range of centrality intervals and the average $dE_{T}/dη$ as a function of the number of participating nucleons, $N_{\mathrm{part}}$, is compared to a variety of Monte Carlo heavy-ion event generators. The results are in agreement with previous measurements at RHIC, and feature an improved granularity in $η$ and improved precision in low-$N_{\mathrm{part}}$ events.
An example of a reconstructed EMCal di-cluster invariant mass distribution, similar to those used for in situ EMCal tower calibrations. The distributions are made from EMCal cluster pairs using Run 2024 Au+Au data. The prominent peak arises from $\pi^{0}\to\gamma\gamma$ decays.
An example of a reconstructed EMCal di-cluster invariant mass distribution, similar to those used for in situ EMCal tower calibrations. The distributions are made from EMCal cluster pairs using a GEANT-4 simulation of HIJING events. The prominent peak arises from $\pi^{0}\to\gamma\gamma$ decays.
An example of the measured energy distribution in a single OHCal tower, showing the MIP distribution from cosmic-ray data from the detector.
We measure the spin-density matrix elements (SDMEs) for the photoproduction of $ϕ(1020)$ off of the proton in its decay to $K_S^0K_L^0$, using 105 pb$^{-1}$ of data collected with a linearly polarized photon beam using the GlueX experiment. The SDMEs are measured in nine bins of the squared four-momentum transfer $t$ in the range $-t=0.15-1.0$ GeV$^2$, providing the first measurement of their $t$-dependence for photon beam energies $E_γ= 8.2-8.8$ GeV. We confirm the dominance of Pomeron exchange in this region, and put constraints on the contribution of other Regge exchanges. We also find that helicity amplitudes where the helicity of the photon and the $ϕ(1020)$ differ by two units are negligible.
Spin-density matrix elements of $\phi(1020)$ mesons produced by a linearly polarized photon beam in the helicity system. For each bin of $-t$, the limits of the bin range are given, along with the average $-\bar t$ and root-mean-square deviation $-t_\text{RMS}$ of all events that fall within the bin.
This paper presents a study of the inclusive forward $J/ψ$ yield as a function of forward charged-particle multiplicity in pp collisions at $\sqrt{s} =13$ TeV using data collected by the ALICE experiment at the CERN LHC. The results are presented in terms of relative $J/ψ$ yields and relative charged-particle multiplicities with respect to these quantities obtained in inelastic collisions having at least one charged particle in the pseudorapidity range $|η| < 1$. The $J/ψ$ mesons are reconstructed via their decay into $μ^+ μ^-$ pairs in the forward rapidity region ($2.5 < y < 4$). The relative multiplicity is estimated in the forward pseudorapidity range which overlaps with the $J/ψ$ rapidity region. The results show a steeper-than-linear increase of the $J/ψ$ yields versus the multiplicity. They are compared with previous measurements and theoretical model calculations.
Forward inclusive J/$\psi$ relative yield as a function of the relative multiplicity in −3.7 < $\eta$ < −1.7 in INEL > 0 pp collisions at $\sqrt{s}$ = 13 TeV.
The first measurement of prompt D$^{*+}$-meson spin alignment in ultrarelativistic heavy-ion collisions with respect to the direction orthogonal to the reaction plane is presented. The spin alignment is quantified by measuring the element $ρ_{00}$ of the diagonal spin-density matrix for prompt D$^{*+}$ mesons with $4<p_{\rm T}<30$ GeV/$c$ in two rapidity intervals, $|y|<0.3$ and $0.3<|y|<0.8$, in central ($0-10$%) and midcentral ($30-50$%) Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. Evidence of spin alignment $ρ_{00}>1/3$ has been found for $p_{\rm T}>15$ GeV/$c$ and $0.3<|y|<0.8$ with a significance of $3.1σ$. The measured spin alignment of prompt D$^{*+}$ mesons is compared with the one of inclusive J$/ψ$ mesons measured at forward rapidity ($2.5 < y < 4$).
$\rho_{00}$ of prompt D$^{*\pm}$ mesons as a function of transverse momentum ($p_{\rm T}$) in the rapidity interval $0.0 < |y| < 0.3$ for mid-central (30--50\%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02~TeV$.
$\rho_{00}$ of prompt D$^{*\pm}$ mesons as a function of transverse momentum ($p_{\rm T}$) in the rapidity interval $0.3 < |y| < 0.8$ for mid-central (30--50\%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02~TeV$.
$\rho_{00}$ of prompt D$^{*\pm}$ mesons as a function of transverse momentum ($p_{\rm T}$) in the rapidity interval $0.0 < |y| < 0.3$ for central (0--10\%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02~TeV$.
Correlations among conserved quantum numbers, such as the net-electric charge, the net-baryon, and the net-strangeness in heavy-ion collisions, are crucial for exploring the QCD phase diagram. In this paper, these correlations are investigated using net-proton number (as a proxy for the net-baryon), net-kaon number (for the net-strangeness), and net-charged particle number in Pb--Pb collisions at $\sqrt{s_\text{NN}}=5.02$ TeV with the ALICE detector. The observed correlations deviate from the Poissonian baseline, with a more pronounced deviation at LHC energies than at RHIC. Theoretical calculations of the Thermal-FIST hadron resonance gas model, HIJING, and EPOS LHC event generators are compared with experimental results, where a significant impact of resonance decays is observed. Thermal-FIST calculations under the grand canonical and canonical ensembles highlight significant differences, underscoring the role of local charge conservation in explaining the data. Recent lattice QCD studies have demonstrated that the magnetic field generated by spectator protons in heavy-ion collisions affects susceptibility ratios, in particular those related to the net-electric charge and the net-baryon numbers. The experimental findings are in qualitative agreement with the expectations of lattice QCD.
$\kappa^{2}_{\pi}$ as a function of centrality (%) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for Set 1 $p_\mathrm{T}$ acceptance.
$\kappa^{2}_{\pi}$ as a function of centrality (%) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for Set 2 $p_\mathrm{T}$ acceptance.
$\kappa^{2}_\mathrm{K}$ as a function of centrality (%) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for Set 1 $p_\mathrm{T}$ acceptance.
The interaction between pions and nucleons plays a crucial role in hadron physics. It represents a fundamental building block of the low-energy QCD dynamics and is subject to several resonance excitations. This work studies the p-$\pi^{\pm}$ dynamics using femtoscopic correlations in high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV measured by ALICE at the LHC. As the final-state interaction between protons and pions is well constrained by scattering experiments and the study of pionic hydrogen, the results give access to information on the particle-emitting source in pp collisions using the femtoscopy methods. The scaling of the source size of primordial protons and pions against their pair transverse mass is extracted. The results are compared with the source sizes studied with p-p, p-K$^+$, and $\pi^{\pm}$-$\pi^{\pm}$ pairs by ALICE in the same collision system and are found to be in agreement for the different particle pairs. This reinforces recent findings by ALICE of a common emission source for all hadron-pairs in pp collisions at LHC energies. Furthermore, the p-p-$\pi^{\pm}$ systems are studied using three-particle femtoscopy in pp collisions at $\sqrt{s} = 13$ TeV. The presence of three-body effects is analyzed utilizing the cumulant expansion method. In this formalism, the known two-body interactions are subtracted in order to isolate the three-body effects. For both, p-p-$\pi^{+}$ and p-p-$\pi^{-}$, a non-zero cumulant is found, indicating effects beyond pairwise interactions. These results give information on the coupling of the pion to multiple nucleons.
p-$\pi^{+}$ + antip-$\pi^{-}$ correlation function in high-multiplicity (0-0.17%) pp collisions at $\sqrt{s}=13$ TeV for $m_\text{T} \in [0.54, 0.75)$ GeV/$c^2$
p-$\pi^{+}$ + antip-$\pi^{-}$ correlation function in high-multiplicity (0-0.17%) pp collisions at $\sqrt{s}=13$ TeV for $m_\text{T} \in [0.75, 0.95)$ GeV/$c^2$
p-$\pi^{+}$ + antip-$\pi^{-}$ correlation function in high-multiplicity (0-0.17%) pp collisions at $\sqrt{s}=13$ TeV for $m_\text{T} \in [0.95, 1.20)$ GeV/$c^2$
We present the measurement of the $p_{\rm T}$-differential production cross section of $ω$ mesons in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at midrapidity by ALICE. In addition, the first measurement of the nuclear modification factor $R_{\text{pPb}}$ for $ω$ mesons at LHC energies is presented, complementing the existing measurements of lighter neutral mesons such as the $π^0$ and $η$. Within the measured $p_{\rm T}$-range, the $R_{\text{pPb}}$ of $ω$ mesons is compatible with no cold nuclear matter effects within the uncertainties, consistent with previous measurements at lower energies. The $ω/π^0$ ratio is presented for both collision systems, showing no collision system dependence within the uncertainties. The comparison to previously published $ω/π^0$ ratios at lower and higher collision energies in pp collisions suggests a decreasing trend of the ratio above $p_{\rm T}=~4 $ GeV/$c$ with increasing collision energy. The data in both collision systems are compared to predictions from PYTHIA, EPOS LHC and DPMJET event generators, revealing significant shortcomings in these models' ability to describe the production of $ω$ mesons.
Differential production cross section of $\omega$ mesons in pp collisions at 5.02 TeV. In addition to the edges of the $p_{\rm T}$ intervals, the table shows the corresponding $p_{\rm T}$ position as described in the publication.
Differential production cross section of $\omega$ mesons in p--Pb collisions at 5.02 TeV. In addition to the edges of the $p_{\rm T}$ intervals, the table shows the corresponding $p_{\rm T}$ position as described in the publication.
Production ratio of $\omega$ to $\pi^{0}$ mesons in pp collisions at 5.02 TeV.
The mass of the top quark is measured using top-antitop-quark pair events with high transverse momentum top quarks. The dataset, collected with the ATLAS detector in proton--proton collisions at $\sqrt{s}=13$ TeV delivered by the Large Hadron Collider, corresponds to an integrated luminosity of 140 fb$^{-1}$. The analysis targets events in the lepton-plus-jets decay channel, with an electron or muon from a semi-leptonically decaying top quark and a hadronically decaying top quark that is sufficiently energetic to be reconstructed as a single large-radius jet. The mean of the invariant mass of the reconstructed large-radius jet provides the sensitivity to the top quark mass and is simultaneously fitted with two additional observables to reduce the impact of the systematic uncertainties. The top quark mass is measured to be $m_t = 172.95 \pm 0.53$ GeV, which is the most precise ATLAS measurement from a single channel.
Values and uncertainties for the parameters of interest in the profile likelihood fit to $\overline{m_J}$, $m_{jj}$, and $m_{tj}$ using data. The parameters of interest are the top quark mass, $m_t$, and the ratio of the measured cross-section to the Standard Model expectation of the $t\bar{t}$ cross-section, $\mu$.
Post-fit central values and uncertaintes for the nuisance parameters (including MC stat uncertainty terms) used in the profile likelihood fit to $\overline{m_J}$, $m_{jj}$, and $m_{tj}$ using data.
Covariance matrix for the profile likelihood fit to $\overline{m_J}$, $m_{jj}$, and $m_{tj}$ using data.
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