arXiv subjects

ALICE Collaboration

Publications and source records attributed to ALICE Collaboration.

At least 109 records · Page 6Linked to original sources

arXiv2025

Measurement of $ω$ meson production in pp collisions at $\sqrt{s}$ = 13 TeV

The $p_{\rm T}$-differential cross section of $ω$ meson production in pp collisions at $\sqrt{s}= 13$ TeV at midrapidity ($|y|<0.5$) was measured with the ALICE detector at the LHC, covering an unprecedented transverse-momentum range of $1.6 <p_{\rm T}< 50$ GeV/$c$. The meson is reconstructed via the $ω\rightarrowπ^+π^-π^0$ 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 $p_{\rm T}$ ranges of previously available measurements. A constant ratio of $C^{ω/π^0}=0.578\pm0.006~\text{(stat.)}\pm 0.013~\text{(syst.)}$ 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.

hep-ex↗

arXiv2025

Measurement of f$_{1}$(1285) production in pp collisions at $\mathbf{\sqrt{\textit s}}$ = 13 TeV

This study presents the first measurement of the f$_{1}$(1285) resonance using the ALICE detector in inelastic proton-proton collisions at a center-of-mass energy of 13 TeV. The resonance is reconstructed at midrapidity ($|y| <$ 0.5) through the hadronic decay channel f$_{1} (1285) \rightarrow \mathrm{K^{0}_{S} K^{\pm}π^{\mp}}$. Key measurements include the determination of its mass, transverse-momentum integrated yield, and average transverse momentum. Additionally, the ratio of the transverse-momentum integrated yield of f$_{1}$(1285) to pion is compared with calculations from the canonical statistical hadronization model. The model calculation, assuming a zero total strangeness content for f$_{1}$(1285), reproduces the data within 1$σ$ deviation, shedding light on the quark composition of f$_{1}$(1285).

hep-ex↗

arXiv2025

Measurement of the inclusive isolated-photon production cross section in pp and Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

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 ($p_{\rm T}^γ$), in Pb$-$Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=5.02$ TeV. The photon transverse momentum range is between 10-14 and 40-140 GeV/$c$, depending on the collision system and on the Pb$-$Pb centrality class. The result extends to lower $p_{\rm T}^γ$ than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is $|η^γ| <0.67$. The isolation selection is based on a charged particle isolation momentum threshold $p_{\rm T}^{\rm iso,~ch} = 1.5$ GeV/$c$ within a cone of radii $R=0.2$ 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$^0$ bosons from the CMS experiment, which are all found to be in agreement.

nucl-ex↗

arXiv2025

First observation of strange baryon enhancement with effective energy in pp collisions at the LHC

The production of (multi-)strange hadrons is measured at midrapidity in proton--proton collisions at $\sqrt{s} = 13$ TeV as a function of the local charged-particle multiplicity in the pseudorapidity interval ${|η|<0.5}$ and of the very-forward energy measured by the ALICE Zero-Degree Calorimeters. The latter provides information on the effective energy, i.e. the energy available for particle production in the collision once subtracted from the centre-of-mass energy. The yields of K$^0_{\rm S}$, $Λ+{\bar Λ}$, and $Ξ^{-}+\overlineΞ^{+}$ per charged-particle increase with the effective energy. In addition, this work exploits a multi-differential approach to decouple the roles of local multiplicity and effective energy in such an enhancement. The results presented in this article provide new insights into the interplay between global properties of the collision, such as the initial available energy in the event, and the locally produced final hadronic state, connected to the charged-particle multiplicity at midrapidity. Notably, a strong increase of strange baryon production with effective energy is observed for fixed charged-particle multiplicity at midrapidity. These results are discussed within the context of existing phenomenological models of hadronisation implemented in different tunes of the PYTHIA 8 event generator.

nucl-ex↗

arXiv2025

Medium-induced modification of groomed and ungroomed jet mass and angularities in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

The ALICE Collaboration presents a new suite of jet substructure measurements in Pb-Pb and pp collisions at a center-of-mass energy per nucleon pair $\sqrt{s}_{\rm NN} = 5.02$ TeV. These measurements provide access to the internal structure of jets via the momentum and angle of their constituents, probing how the quark--gluon plasma modifies jets, an effect known as jet quenching. Jet grooming additionally removes soft wide-angle radiation to enhance perturbative accuracy and reduce experimental uncertainties. We report the groomed and ungroomed jet mass $m_{\rm jet}$ and jet angularities $λ_α^κ$ using $κ=1$ and $α>0$. Charged-particle jets are reconstructed at midrapidity using the anti-$k_\mathrm{T}$ algorithm with resolution parameter $R = 0.2$. A narrowing of the jet mass and angularity distributions in Pb-Pb collisions with respect to pp is observed and is enhanced for groomed results, confirming modification of the jet core. By using consistent jet definitions and kinematic cuts between the mass and angularities for the first time, previous inconsistencies in the interpretation of quenching measurements are resolved, rectifying a hurdle for understanding how jet quenching arises from first principles and highlighting the importance of a well-controlled baseline. These results are compared with a variety of theoretical models of jet quenching, providing constraints on jet energy-loss mechanisms in the quark--gluon plasma.

nucl-ex↗

arXiv2025

First polarisation measurement of coherently photoproduced J/$ψ$ in ultra-peripheral Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The first measurement of the polarisation of coherently photoproduced J$/ψ$ mesons in ultra-peripheral Pb-Pb collisions, using data at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, is presented. The J/$ψ$ meson is measured via its dimuon decay channel in the forward rapidity interval $-4.0 < y < -2.5$ using the ALICE detector at the CERN LHC. An event sample corresponding to an integrated luminosity of 750 $μ\text{b}^{-1}$ $\pm$ 5% (syst) is analysed. Hadronic activity is highly suppressed since the interaction is mediated by a photon. The polar and azimuthal angle distributions of the decay muons are measured, and the polarisation parameters $\mathbf{λ_θ}$, $\mathbf{λ_φ}$, $\mathbf{λ_{θφ}}$ are extracted. The analysis is carried out in the helicity frame. The results are found to be consistent with a transversely polarised J/$ψ$. These values are compared with previous measurements by the H1 and ZEUS experiments. The polarisation parameters of coherent J/$ψ$ photoproduction in Pb-Pb collisions are found to be consistent with the $s$-channel helicity conservation hypothesis.

nucl-ex↗

arXiv2025

Multimuons in cosmic-ray events as seen in ALICE at the LHC

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 ($N_μ>4$) and in the zenith angle range $0^{\circ}<θ<50^{\circ}$. 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 \times 10^{15} 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 $E_\mathrm{prim} \sim 10^{17}$ eV of these events. This result places significant constraints on more exotic production mechanisms.

astro-ph.HE↗

arXiv2025

Proton emission in ultraperipheral Pb-Pb collisions at $\sqrt{\textit{s}_{\mathrm{\textbf{NN}}}}=5.02$ TeV

The first measurements of proton emission accompanied by neutron emission in the electromagnetic dissociation (EMD) of $^{208}$Pb nuclei in the ALICE experiment at the LHC 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 $^{208}$Pb--$^{208}$Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ 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 $^{208}$Pb. 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 $^{206,205,204}$Tl.

nucl-ex↗

arXiv2025

First measurement of A = 4 (anti)hypernuclei at the LHC

In this Letter, the first evidence of the $^4_{\barΛ}\overline{\rm He}$ antihypernucleus is presented, along with the first measurement at the LHC of the production of (anti)hypernuclei with mass number $A=4$, specifically (anti)$^4_Λ\mathrm{H}$ and (anti)$^4_Λ\mathrm{He}$. In addition, the antiparticle-to-particle ratios for both hypernuclei ($^4_{\barΛ}\overline{\rm H}$ / $^4_Λ\mathrm{H}$ and $^4_{\barΛ}\overline{\rm He}$ / $^4_Λ\mathrm{He}$) 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 $\sqrt{s_{\mathrm{NN}}} = $ 5.02 TeV. The yields measured for the average of the charge-conjugated states are found to be $[0.78 \pm 0.19 \; \mathrm{(stat.)} \pm 0.17 \; \mathrm{(syst.)}] \times 10^{-6}$ for the (anti)$^4_Λ\mathrm{H}$ and $[1.08 \pm 0.34 \; \mathrm{(stat.)} \; \pm 0.20 \; \mathrm{(syst.)}] \times 10^{-6}$ for the (anti)$^4_Λ\mathrm{He}$, and the measured antiparticle-to-particle ratios are in agreement with unity. The presence of (anti)$^4_Λ\mathrm{H}$ and (anti)$^4_Λ\mathrm{He}$ 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)$^4_Λ\mathrm{H}$ and (anti)$^4_Λ\mathrm{He}$ masses are compatible with the world-average values within the uncertainties.

nucl-ex↗

arXiv2025

Energy-energy correlators in charm-tagged jets in proton-proton collisions at $\mathbf{\sqrt{s} = 13}$ TeV

In this letter, we present the first measurement of the energy-energy correlator (EEC) in charm-tagged jets from proton-proton (pp) collisions at $\sqrt{s} = 13$ TeV. EECs probe the structure of QCD radiation, providing a unique test of mass-dependent effects in parton showers involving a charm quark and offering a distinct view into non-perturbative phenomena, including the hadronization process. The EEC is measured for charm-tagged jets and flavor-untagged (inclusive) jets with transverse momenta of $10 < p_{\rm T} < 30$ GeV/$c$, where charm-quark mass effects are significant. We observe a significant suppression of the EEC amplitude in charm jets compared to inclusive ones, consistent with the expected suppression of radiation from massive quarks -- a fundamental prediction of QCD. Despite the significant amplitude difference, the observed peak positions of the charm and inclusive-jet EEC are similar, indicating a complex interplay between Casimir factor (differentiating quark and gluon jets), and quark-mass (dead-cone) effects in the QCD parton shower as well as subsequent hadronization effects. Comparisons with next-to-leading order calculations and various Monte Carlo event generators reveal the sensitivity of this observable to both mass effects in the parton shower and hadronization process. These results provide new constraints on theoretical models of heavy-quark jets and offer insights into the parton-to-hadron transition in QCD.

hep-ex↗

arXiv2025

First observation of ultra-long-range azimuthal correlations in low multiplicity pp and p-Pb collisions at the LHC

This study presents the first observation of ultra-long-range two-particle azimuthal correlations with pseudorapidity separation of ($|Δη| > 5.0$) in proton-proton (pp) and ($|Δη| > 6.5$) in proton-lead (p-Pb) collisions at the LHC, down to and below the minimum-bias multiplicity. Two-particle correlation coefficients (${V}_{2Δ}$) are measured after removing non-flow (jets and resonance decays) contributions using the template-fit method across various multiplicity classes, providing novel insights into the origin of long-range correlations in small systems. Comparisons with the 3D-Glauber + MUSIC + UrQMD hydrodynamic model reveal significant discrepancies at low multiplicities, indicating possible dynamics beyond typical hydrodynamic behavior. Initial-state models based on the Color Glass Condensate framework generate only short-range correlations, while PYTHIA simulations implemented with the string-shoving mechanism also fail to describe these ultra-long-range correlations. The results challenge existing paradigms and question the underlying mechanisms in low-multiplicity pp and p-Pb collisions. The findings impose significant constraints on models describing collective phenomena in small collision systems and advance the understanding of origin of long-range correlations at Large Hadron Collider (LHC) energies.

nucl-ex↗

arXiv2025

Particle production as a function of charged-particle flattenicity in pp collisions at $\sqrt{s}$ = 13 TeV

This paper reports the first measurement of the transverse momentum ($p_{\mathrm{T}}$) spectra of primary charged pions, kaons, (anti)protons, and unidentified particles as a function of the charged-particle flattenicity in pp collisions at $\sqrt{s}=13$ TeV. Flattenicity is a novel event shape observable that is measured in the pseudorapidity intervals covered by the V0 detector, $2.8<η<5.1$ and $-3.7<η<-1.7$. According to QCD-inspired phenomenological models, it shows sensitivity to multiparton interactions and is less affected by biases toward larger $p_{\mathrm{T}}$ due to local multiplicity fluctuations in the V0 acceptance than multiplicity. The analysis is performed in minimum-bias (MB) as well as in high-multiplicity events up to $p_{\mathrm{T}}=20$ GeV/$c$. The event selection requires at least one charged particle produced in the pseudorapidity interval $|η|<1$. The measured $p_{\mathrm{T}}$ distributions, average $p_{\mathrm{T}}$, kaon-to-pion and proton-to-pion particle ratios, presented in this paper, are compared to model calculations using PYTHIA 8 based on color strings and EPOS LHC. The modification of the $p_{\mathrm{T}}$-spectral shapes in low-flattenicity events that have large event activity with respect to those measured in MB events develops a pronounced peak at intermediate $p_{\mathrm{T}}$ ($2<p_{\mathrm{T}}<8$ GeV/$c$), and approaches the vicinity of unity at higher $p_{\mathrm{T}}$. The results are qualitatively described by PYTHIA, and they show different behavior than those measured as a function of charged-particle multiplicity based on the V0M estimator.

hep-ex↗

arXiv2025

Probing strangeness hadronization with event-by-event production of multistrange hadrons

This Letter presents the first measurement of event-by-event fluctuations of the net number (difference between the particle and antiparticle multiplicities) of multistrange hadrons $Ξ^-$ and $\overlineΞ^+$ and its correlation with the net-kaon number using the data collected by the ALICE Collaboration in pp, p$-$Pb, and Pb$-$Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\ \mathrm{TeV}$. The statistical hadronization model with a correlation over three units of rapidity between hadrons having the same and opposite strangeness content successfully describes the results. On the other hand, string-fragmentation models that mainly correlate strange hadrons with opposite strange quark content over a small rapidity range fail to describe the data.

nucl-ex↗

arXiv2025

Measurement of the inclusive isolated-photon production cross section in pp collisions at $\sqrt{s}$ = 13 TeV

The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of $\sqrt{s}=13$ TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of $|η^γ|<0.67$ and a transverse momentum range of $7<p_{\rm T}^γ<200$ GeV/$c$. The result extends to lower $p_{\rm T}^γ$ and $x_{\rm T}^γ = 2p_{\rm T}^γ/\sqrt{s}$ ranges, the lowest $x_{\rm T}^γ$ of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower $p_{\rm T}^γ$ at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties.

hep-ex↗

arXiv2025

Measurement of the production cross section of prompt $Ξ^0_{\rm c}$ baryons in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV

The transverse momentum ($p_{\rm T}$) differential production cross section of the promptly produced charm-strange baryon $Ξ_{\rm c}^{0}$ (and its charge conjugate $\overline{Ξ_{\rm c}^{0}}$) is measured at midrapidity via its hadronic decay into ${\rm π^{+}}Ξ^{-}$ in p$-$Pb collisions at a centre-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV with the ALICE detector at the LHC. The $Ξ_{\rm c}^{0}$ nuclear modification factor ($R_{\rm pPb}$), calculated from the cross sections in pp and p$-$Pb collisions, is presented and compared with the $R_{\rm pPb}$ of $Λ_{\rm c}^{+}$ baryons. The ratios between the $p_{\rm T}$-differential production cross section of $Ξ_{\rm c}^{0}$ baryons and those of $\mathrm {D^0}$ mesons and $Λ_{\rm c}^{+}$ baryons are also reported and compared with results at forward and backward rapidity from the LHCb Collaboration. The measurements of the production cross section of prompt $Ξ^0_{\rm c}$ baryons are compared with a model based on perturbative QCD calculations of charm-quark production cross sections, which includes only cold nuclear matter effects in p$-$Pb collisions, and underestimates the measurement by a factor of about 50. This discrepancy is reduced when the data is compared with a model that includes string formation beyond leading-colour approximation or in which hadronisation is implemented via quark coalescence. The $p_{\rm T}$-integrated cross section of prompt $Ξ^0_{\rm c}$-baryon production at midrapidity extrapolated down to $p_{\rm T}$ = 0 is also reported. These measurements offer insights and constraints for theoretical calculations of the hadronisation process. Additionally, they provide inputs for the calculation of the charm production cross section in p$-$Pb collisions at midrapidity.

nucl-ex↗

arXiv2025

Investigating $Λ$ baryon production in p-Pb collisions in jets and the underlying event using angular correlations

First measurements of hadron(h)$-Λ$ azimuthal angular correlations in p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV using the ALICE detector at the Large Hadron Collider are presented. These correlations are used to separate the production of associated $Λ$ baryons into three different kinematic regions, namely those produced in the direction of the trigger particle (near-side), those produced in the opposite direction (away-side), and those whose production is uncorrelated with the jet axis (underlying event). The per-trigger associated $Λ$ yields in these regions are extracted, along with the near- and away-side azimuthal peak widths, and the results are studied as a function of associated particle $p_{\rm T}$ and event multiplicity. Comparisons with the DPMJET event generator and previous measurements of the $ϕ(1020)$ meson are also made. The final results indicate that strangeness production in the highest multiplicity p$-$Pb collisions is enhanced relative to low multiplicity collisions in both the jet-like regions and the underlying event. The production of $Λ$ relative to charged hadrons is also enhanced in the underlying event when compared to the jet-like regions. Additionally, the results hint that strange quark production in the away-side of the jet is modified by soft interactions with the underlying event.

nucl-ex↗

arXiv2025

Multiplicity dependence of $Υ$ production at forward rapidity in pp collisions at $\sqrt{s}$ = 13 TeV

The measurement of $Υ$(1S), $Υ$(2S), and $Υ$(3S) yields as a function of the charged-particle multiplicity density, $\textrm{d}N_{\textrm{ch}}/\textrm{d}η$, using the ALICE experiment at the LHC, is reported in pp collisions at $\sqrt{s} =$ 13 TeV. The $Υ$ meson yields are measured at forward rapidity ($2.5 < y < 4$) in the dimuon decay channel, whereas the charged-particle multiplicity is defined at central rapidity ($|η| < 1$). Both quantities are divided by their average value in minimum bias events to compute the self-normalized quantities. The increase of the self-normalized $Υ$(1S), $Υ$(2S), and $Υ$(3S) yields is found to be compatible with a linear scaling with the self-normalized $\textrm{d}N_{\textrm{ch}}/\textrm{d}η$, within the uncertainties. The self-normalized yield ratios of excited-to-ground $Υ$ states are compatible with unity within uncertainties. Similarly, the measured double ratio of the self-normalized $Υ$(1S) to the self-normalized J/$ψ$ yields, both measured at forward rapidity, is compatible with unity for self-normalized charged-particle multiplicities beyond one. The measurements are compared with theoretical predictions incorporating initial or final state effects.

nucl-ex↗

arXiv2025

Measurement of ${}_Λ^{3}\mathrm{H}$ production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

The first measurement of $_Λ^{3}\mathrm{H}$ and $^3_ {\overlineΛ}\overline{\mathrm{H}}$ differential production with respect to transverse momentum and centrality in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV is presented. The $_Λ^{3}\mathrm{H}$ has been reconstructed via its two-charged-body decay channel, i.e., $_Λ^{3}\mathrm{H} \rightarrow {}^{3}\mathrm{He} + π^{-}$. A Blast-Wave model fit of the $p_{\rm T}$-differential spectra of all nuclear species measured by the ALICE collaboration suggests that the $_Λ^{3}\mathrm{H}$ kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of $_Λ^{3}\mathrm{H}$ and $^3\mathrm{He}$ is compared to predictions from the statistical hadronisation model and the coalescence model, with the latter being favoured by the presented measurements.

nucl-ex↗