ALICE INDICO

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ALICE Calendar

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ALICE is optimized to study the collisions of nuclei at the ultra-relativistic energies provided by the LHC. The aim is to study the physics of strongly interacting matter at the highest energy densities reached so far in the laboratory. In such conditions, an extreme phase of matter - called the quark-gluon plasma - is formed. Our universe is thought to have been in such a primordial state for the first few millionths of a second after the Big Bang, before quarks and gluons were bound together to form protons and neutrons. Recreating this primordial state of matter in the laboratory and understanding how it evolves will allow us to shed light on questions about how matter is organized and the mechanisms that confine quarks and gluons. For this purpose, we are carrying out a comprehensive study of the hadrons, electrons, muons, and photons produced in the collisions of heavy nuclei (²⁰⁸Pb). ALICE is also studying proton-proton and proton-nucleus collisions both as a comparison with nucleus-nucleus collisions and in their own right. In 2021, the collaboration completed a major upgrade, denoted ALICE 2, to enhance its detector capabilities and continue its scientific journey at the LHC in Runs 3 and 4. Further detector upgrades are being carried out for Run 4 until the end of 2033. At the same time, preparations are in progress for ALICE 3, the next-generation heavy-ion experiment for HL-LHC Run 5.

Diversity and Inclusivity in ALICE

The ALICE Collaboration embraces and values the diversity of its team members and colleagues. We are committed to fostering an inclusive environment for all people regardless of their nationality/culture, profession, age/generation, family situation and gender, as well as individual differences such as but not limited to ethnic origin, sexual orientation, belief, disability, or opinions provided that they are consistent with the Organization’s values.

Recent highlights

Latest ALICE Submissions

Correlations and fluctuations of flow with event shape engineering in Pb-Pb and Xe-Xe collisions at the LHCMeasurements of anisotropic flow provide some of the strongest constraints on the collective expansion and transport properties of the quark-gluon plasma produced in ultra-relativistic heavy-ion collisions. In this paper, correlations and fluctuations of the anisotropic flow coefficients $v_{2}$, $v_{3}$, and $v_{4}$ are measured in Pb-Pb and Xe-Xe collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ and $5.44$ TeV, respectively, with the ALICE detector. The Event Shape Engineering technique, based on the reduced flow vector $q_{n}$, is used to study flow correlations for different initial-state geometries. A strong anticorrelation between $v_2$ and $v_3$ and a positive correlation between $v_2$ and $v_4$ are observed. A small anticorrelation is seen between $v_3$ and $v_4$. From the $v_2$-$v_4$ correlation, the linear and nonlinear components of $v_4$ are extracted and compared to those extracted using multiparticle correlations. The linear and nonlinear components of $v_{4}$ are also measured directly as a function of $q_2$ for the first time in Pb-Pb and Xe-Xe, revealing a strong coupling of the nonlinear term to the initial-state ellipticity $\varepsilon_2$, while the linear component shows little dependence on initial-state geometry. Additionally, the coupling coefficient $χ_{4,22}$, which measures the nonlinear contribution of $v_2^2$ to $v_4$, is extracted and shows little dependence on $q_2$, except in very central collisions. The effects of flow fluctuations for constrained initial-state geometries are studied for the first time using Event Shape Engineering with the ratio of $v_2\{2\}$ and $v_2\{4\}$; the results show that collisions with the lowest $q_2$ exhibit more significant $v_2$ fluctuations compared to the unbiased ratio.	2611.08473
Exploring the limit of partonic collectivity in small collision systems at the LHCThe existence of a partonic phase in small collision systems has been investigated previously through measurements of the elliptic flow ($v_{2}$) of mesons ($π^{\pm}$, K$^{\pm}$, and K$_{S}^{0}$) and baryons ($\rm{p}(\overline{\rm{p}})$, $Λ(\overlineΛ)$) in high-multiplicity p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and pp collisions at $\sqrt{s} = 13$ TeV recorded by ALICE. The results have revealed a grouping and splitting behavior of $v_{2}$ for baryons and mesons at intermediate transverse momentum ($p_{\rm{T}}$), establishing that partonic collectivity, as observed in heavy-ion collisions, is also present in these systems. In this Letter, the $p_{\rm{T}}$-differential $v_{2}$ of various hadronic species is investigated in p-Pb collisions for the multiplicity intervals $N_{\rm ch} \geq 50$, $25 \leq N_{\rm ch} < ~ 50$, and $15 \leq N_{\rm ch} < ~ 25$, as well as in pp collisions for $25 \leq N_{\rm ch} < ~ 50$ and $15 \leq N_{\rm ch} < ~ 25$. Here, $N_{\rm ch}$ is the efficiency-corrected number of charged particles produced in the kinematic region of $\|η\| < ~ 0.8$ and $0.2 < ~ p_{\rm T} < ~ 3.0$ GeV/$c$. The characteristic mass dependence of $v_{2}$, as well as the grouping and splitting patterns among identified particles, are examined. The results in both p-Pb and pp collisions with $N_{\rm ch} \geq 25$ are consistent with the development of partonic collectivity. In the low-multiplicity region, $15 \leq N_{\rm ch} < ~ 25$, the baryon-to-meson $v_{2}$ splitting, as quantified by the baryon-to-meson $v_2$ ratios, remains broadly consistent with that at higher multiplicities. However, its significance decreases to $\sim2σ$ in p-Pb collisions and to less than $1σ$ in pp collisions owing to the sizable experimental uncertainties. These measurements constitute the first steps towards identifying the limits of partonic flow in small collision systems at the LHC.	2611.08327
Measurement of antideuteron and net-$Λ$ number fluctuations at the Large Hadron ColliderThe recent measurements of event-by-event correlations between the antideuteron and antiproton numbers in Pb$-$Pb collisions at the LHC deviate from the statistical hadronization model parameterizations that describe the yields and fluctuations of light-flavored hadrons. This discrepancy may stem from nucleosynthesis processes involved in the formation of composite states like antideuterons. In this letter, we present the first measurement of the antideuteron$-$net-$Λ$ number correlation obtained in Pb$-$Pb collisions with the ALICE detector. This quantity is mostly sensitive to the quantum-number correlations induced by the hadronization process, as $Λ$ hyperons are not constituents of antideuterons. Both the antideuteron$-$net-$Λ$ number correlation and the normalized second-order cumulant of the net-$Λ$ number are well described by the statistical hadronization model implemented in Thermal-FIST. This establishes strong evidence that the antideuteron$-$antiproton correlation is driven by the nucleosynthesis processes, while the correlation between antideuterons and non-nucleonic hadrons is primarily sensitive to the hadronization mechanism.	2610.36307
Evidence of partonic collectivity in OO collisions through the measurement of $φ$, K$^0_{\rm S}$, and $Λ$ elliptic flowThe first measurement of the elliptic-flow coefficient ($v_{2}$) of $φ$, K$^0_{\rm S}$, and $Λ(\overlineΛ)$ hadrons performed in OO collisions at $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV with the ALICE detector is presented as a function of transverse momentum ($p_{\rm T}$) in central and semi-central collisions. For the $φ$ meson, in particular, this is the first measurement of the elliptic flow in a small collision system. At low $p_{\rm T}$, a characteristic mass ordering of $v_{2}$ is observed, consistent with collective expansion of the system, in which heavier hadrons are shifted to higher $p_{\rm T}$ by a common velocity field. At intermediate $p_{\rm T}$, above 3 GeV/$c$, a baryon$-$meson splitting with a $10σ$ significance emerges, with the $Λ(\overlineΛ)$ baryon exhibiting larger $v_{2}$ values than mesons, while, despite its mass being close to the mass of the $Λ$, the $φ$ follows the K$^{0}_{\rm S}$. The $φ$ meson behavior disfavors a purely mass-driven interpretation of the observed patterns and supports the role of hadronization via quark recombination from a collectively flowing partonic medium. These results provide complementary evidence that key signatures of partonic collectivity observed in Pb$-$Pb collisions persist in light nucleus$-$nucleus systems.	2610.36237
Measurement of prompt and non-prompt ${\rm D}^{\rm +}$-meson spin alignment in pp collisions at $\sqrt{s}$ = 13.6 TeVA precise measurement of prompt and non-prompt ${\rm D}^{\rm +}$-meson spin alignment with respect to the helicity and production axes in proton-proton (pp) collisions at $\sqrt{s} = 13.6$ TeV is presented, using data collected with the ALICE experiment at the LHC. The spin alignment is quantified by measuring the diagonal spin density matrix element $ρ_{\rm 00}$ for ${\rm D}^{\rm +}$ mesons at midrapidity ($\|y\| < ~0.8$). The measurement is performed in the transverse-momentum ($p_{\rm T}$) range $3 < ~p_{\rm T} < ~100$ GeV/$c$ for prompt ${\rm D}^{\rm +}$ mesons and $3 < ~p_{\rm T} < ~30$ GeV/$c$ for non-prompt ${\rm D}^{\rm +}$ mesons, respectively. The measured $ρ_{\rm 00}$ values for prompt ${\rm D}^{\rm +}$ mesons are consistent with the unpolarised expectation of $1/3$ over the entire $p_{\rm T}$ range, indicating no evidence of spin alignment. In contrast, $ρ_{\rm 00}$ of non-prompt ${\rm D}^{\rm +}$ mesons exhibit a deviation from $1/3$, consistent with expectations from weak beauty-hadron decays and well described by PYTHIA 8 simulations coupled with the EvtGen decay package. These results confirm and extend previous measurements, providing a precise baseline for future studies of ${\rm D}^{\rm +}$ spin alignment in heavy-ion collisions.	2609.39713