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Femtoscopic study of the proton-proton and proton-deuteron systems in heavy-ion collisions at the LHC

The ALICE collaboration Acharya, Shreyasi ; Aglieri Rinella, Gianluca ; Aglietta, Luca ; et al.
CERN-EP-2025-096, 2025.
Inspire Record 2917986 DOI 10.17182/hepdata.165812

This work reports femtoscopic correlations of p$-$p ($\bar{\rm p}-\bar{\rm p}$) and p$-$d ($\bar{\rm p}-\bar{\rm d}$) pairs measured in Pb$-$Pb collisions at center-of-mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV by the ALICE Collaboration. A fit to the measured proton-proton correlation functions allows one to extract the dependence of the nucleon femtoscopic radius of the particle-emitting source on the pair transverse mass ($m_\text{T}$) and on the average charge particle multiplicity $\langle\text{dN}_\text{ch}/\text{d}\eta\rangle^{1/3}$ for three centrality intervals (0$-$10$\%$, 10$-$30$\%$, 30$-$50$\%$). In both cases, the expected power-law and linear scalings are observed, respectively. The measured p$-$d correlations can be described by both two- and three-body calculations, indicating that the femtoscopy observable is not sensitive to the short-distance features of the dynamics of the p$-$(p$-$n) system, due to the large inter-particle distances in Pb$-$Pb collisions at the LHC. Indeed, in this study, the minimum measured femtoscopic source sizes for protons and deuterons have a minimum value at $2.73^{+0.05}_{-0.05}$ and $3.10^{+1.04}_{-0.86}$ fm, respectively, for the 30$-$50$\%$ centrality collisions. Moreover, the $m_{\rm{T}}$-scaling obtained for the p$-$p and p$-$d systems is compatible within 1$\sigma$ of the uncertainties. These findings provide new input for fundamental studies on the production of light (anti)nuclei under extreme conditions.

23 data tables

proton-proton (same charge) correlation function for centrality 0-10% from Pb-Pb collisions at 5020 GeV

proton-proton (same charge) correlation function for centrality 10-30% from Pb-Pb collisions at 5020 GeV

proton-proton (same charge) correlation function for centrality 30-50% from Pb-Pb collisions at 5020 GeV

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D$^{0}$-meson-tagged jet axes difference in proton-proton collisions at $\mathbf{\sqrt{\textit{s}} = 5.02}$ TeV

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
CERN-EP-2025-083, 2025.
Inspire Record 2907593 DOI 10.17182/hepdata.165764

Heavy-flavor quarks produced in proton-proton (pp) collisions provide a unique opportunity to investigate the evolution of quark-initiated parton showers from initial hard scatterings to final-state hadrons. By examining jets that contain heavy-flavor hadrons, this study explores the effects of both perturbative and non-perturbative QCD on jet formation and structure. The angular differences between various jet axes, $\Delta R_{\rm axis}$, offer insight into the radiation patterns and fragmentation of charm quarks. The first measurement of D$^{0}$-tagged jet axes differences in pp collisions at $\sqrt{s}=5.02$ TeV by the ALICE experiment at the LHC is presented for jets with transverse momentum $p_{\rm T}^{\rm ch~jet} \geq 10$${\rm GeV}/c$ and D$^0$ mesons with $p_{\rm T}^{\rm D^{0}} \geq 5$${\rm GeV}/c$. In this D$^0$-meson-tagged jet measurement, three jet axis definitions, each with different sensitivities to soft, wide-angle radiation, are used: the Standard axis, Soft Drop groomed axis, and Winner-Takes-All axis. Measurements of the radial distributions of D$^0$ mesons with respect to the jet axes, $\Delta R_{\mathrm{axis-D^0}}$, are reported, along with the angle, $\Delta R_{\mathrm{axis}}$, between the three jet axes. The D$^{0}$ meson emerges as the leading particle in these jets, closely aligning with the Winner-Takes-All axis and diverging from the Standard jet axis. The results also examine how varying the sensitivity to soft radiation with grooming influences the orientation of the Soft Drop jet axis, and uncover that charm-jet structure is more likely to survive grooming when the Soft Drop axis is further from the D$^{0}$ direction, providing further evidence of the dead-cone effect recently measured by ALICE.

16 data tables

$\Delta R_{\rm axis}$ distribution for $\rm STD-D^0$ for $\rm D^0$-tagged jets of $R=0.4$, in the intervals $10<p_{\rm T}^{\rm ch \ jet}<20 \ {\rm GeV}/c$ and $5<p_{\rm T}^{\rm D^0}<20 \ {\rm GeV}/c$.

$\Delta R_{\rm axis}$ distribution for $\rm WTA-D^0$ for $\rm D^0$-tagged jets of $R=0.4$, in the intervals $10<p_{\rm T}^{\rm ch \ jet}<20 \ {\rm GeV}/c$ and $5<p_{\rm T}^{\rm D^0}<20 \ {\rm GeV}/c$.

$\Delta R_{\rm axis}$ distribution for $\rm STD-WTA$ for $\rm D^0$-tagged jets of $R=0.4$, in the intervals $10<p_{\rm T}^{\rm ch \ jet}<20 \ {\rm GeV}/c$ and $5<p_{\rm T}^{\rm D^0}<20 \ {\rm GeV}/c$.

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First measurement of D$^{*+}$ vector spin alignment in Pb-Pb collisions at $\mathbf{\sqrt{s_{\rm NN}} = 5.02}$ TeV

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
CERN-EP-2025-072, 2025.
Inspire Record 2906994 DOI 10.17182/hepdata.165763

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 $\rho_{00}$ 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 $\rho_{00}>1/3$ has been found for $p_{\rm T}>15$ GeV/$c$ and $0.3<|y|<0.8$ with a significance of $3.1\sigma$. The measured spin alignment of prompt D$^{*+}$ mesons is compared with the one of inclusive J/$\psi$ mesons measured at forward rapidity ($2.5 < y < 4$).

3 data tables

$\rho_{00}$ 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 $\sqrt{s_{\rm NN}}=5.02~TeV$.


Measurement of correlations among net-charge, net-proton, and net-kaon multiplicity distributions in Pb-Pb collisions at $\sqrt{s_\text{NN}}=5.02$ TeV

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
JHEP 08 (2025) 210, 2025.
Inspire Record 2903549 DOI 10.17182/hepdata.160697

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 letter, 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.

30 data tables

$\kappa^{2}_{\pi}$ 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.

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Measurement of $\omega$ meson production in pp and p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
CERN-EP-2025-033, 2025.
Inspire Record 2895572 DOI 10.17182/hepdata.165463

We present the measurement of the $p_{\rm T}$-differential production cross section of $\omega$ 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 $R_{\rm{pPb}}$ for $\omega$ mesons at LHC energies is presented, complementing the existing measurements of lighter neutral mesons such as the $\pi^0$ and $\eta$. Within the measured $p_{\rm T}$-range, the $R_{\rm{pPb}}$ of $\omega$ mesons shows no cold nuclear matter effects within the uncertainties, consistent with previous measurements at lower energies. The $\omega/\pi^0$ ratio is presented for both collision systems, showing no collision system dependence within the uncertainties. The comparison to previously published $\omega/\pi^0$ 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 8, EPOS LHC and DPMJET event generators, revealing significant shortcomings in these models' ability to describe the production of $\omega$ mesons.

5 data tables

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.

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Measurement of isolated prompt photon production in pp and p-Pb collisions at the LHC

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
CERN-EP-2025-024, 2025.
Inspire Record 2895564 DOI 10.17182/hepdata.165479

This paper presents the measurement of the isolated prompt photon inclusive production cross section in pp and p-Pb collisions by the ALICE Collaboration at the LHC. The measurement is performed in p-Pb collisions at centre-of-mass energies per nucleon pair of $\sqrt{s_{\rm{NN}}} = 5.02$ TeV and $8.16$ TeV, as well as in pp collisions at $\sqrt{s} = 5.02$ TeV and $8$ TeV. The cross section is obtained at midrapidity $(|y|<0.7)$ using a charged-track based isolation momentum $p_{\rm T}^{\rm{iso, ch}} < 1.5$ GeV/$c$ in a cone with radius $R = 0.4$. The data for both collision systems are well reproduced by perturbative QCD (pQCD) calculations at next-to-leading order (NLO) using recent parton distribution functions for free (PDF) and bound (nPDF) nucleons. Furthermore, the nuclear modification factor $R_{\rm{pA}}$ for both collision energies is consistent with unity for $p_{\rm T} > 20$ GeV/$c$. However, deviations from unity ($R_{\rm pA}<1$) of up to 20% are observed for $p_{\rm T} < 20$ GeV/$c$ with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision. The suppression increases with decreasing $p_{\rm T}$ with a significance of $2.3\sigma$ for a non-zero slope and yields $R_{\rm pA} < 1$ with a significance of $1.8\sigma$ at $\sqrt{s_{\rm NN}} = 8.16$ TeV for $p_{\rm T} < 20$ GeV/$c$. In addition, a significance of $1.1\sigma$ is observed for $R_{\rm pA}<1$ at the lower collision energy $\sqrt{s_{\rm NN}} = 5.02$ TeV for $p_{\rm T} < 14$ GeV/$c$. The magnitude and shape of the suppression are consistent with pQCD predictions at NLO using nPDFs that incorporate nuclear shadowing effects in the Pb nucleus.

8 data tables

Differential cross section of isolated prompt photon production in pp collisions at 8 TeV.

Differential cross section of isolated prompt photon production in p--Pb collisions at 8.16 TeV.

Differential cross section of isolated prompt photon production in p--Pb collisions at 5.02 TeV.

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Charged-particle multiplicity distributions over a wide pseudorapidity range in p-Pb collisions at $\mathbf{\sqrt{s}_{NN} = 5.02}$ TeV

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
Eur.Phys.J.C 85 (2025) 919, 2025.
Inspire Record 2895567 DOI 10.17182/hepdata.160246

This paper presents the primary charged-particle multiplicity distributions in proton-lead collisions at a centre-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\rm NN}} = 5.02$ TeV. The distributions are reported for non-single diffractive collisions in different pseudorapidity ranges. The measurements are performed using the combined information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE. The multiplicity distributions are parametrised with a double negative binomial distribution function which provides satisfactory descriptions of the distributions for all the studied pseudorapidity intervals. The data are compared to models and analysed quantitatively, evaluating the first four moments (mean, standard deviation, skewness, and kurtosis). The shape evolution of the measured multiplicity distributions is studied in terms of KNO variables and it is found that none of the considered models reproduces the measurements. This paper also reports on the average charged-particle multiplicity, normalised by the average number of participating nucleon pairs, as a function of the collision energy. The multiplicity results are then compared to measurements made in proton-proton and nucleus-nucleus collisions across a wide range of collision energies.

10 data tables

Charged-particle multiplicity distributions for different pseudorapidity intervals measured in NSD p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.

The pseudorapidity dependence of the double NBD parameters $\langle n \rangle_1$, $\langle n \rangle_2$, $k_1$, and $k_2$ in NSD p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.

First four moments ($\langle N_{\mathrm{ch}}\rangle$, $\sigma$, $S$, and $\kappa$) of charged-particle multiplicity distributions for different pseudorapidity intervals in NSD p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.

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First measurement of symmetric cumulants of hexagonal flow harmonics in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
Phys.Rev.C 112 (2025) 024905, 2025.
Inspire Record 2865181 DOI 10.17182/hepdata.159493

Correlations between event-by-event fluctuations of anisotropic flow harmonics are measured in Pb-Pb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV, as recorded by the ALICE detector at the LHC. This study presents correlations up to the hexagonal flow harmonic, $v_6$, which was measured for the first time. The magnitudes of these higher-order correlations are found to vary as a function of collision centrality and harmonic order. These measurements are compared to viscous hydrodynamic model calculations with EKRT initial conditions and to the iEBE-VISHNU model with TRENTo initial conditions. The observed discrepancies between the data and the model calculations vary depending on the harmonic combinations. Due to the sensitivity of model parameters estimated with Bayesian analyses to these higher-order observables, the results presented in this work provide new and independent constraints on the initial conditions and transport properties in theoretical models used to describe the system created in heavy-ion collisions.

5 data tables

NSC(5,2) vs centrality in Pb-Pb collisions at 5.02 TeV

NSC(5,3) vs centrality in Pb-Pb collisions at 5.02 TeV

NSC(6,2) vs centrality in Pb-Pb collisions at 5.02 TeV

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System size and energy dependence of the mean transverse momentum fluctuations at the LHC

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
Eur.Phys.J.C 85 (2025) 776, 2025.
Inspire Record 2848476 DOI 10.17182/hepdata.159277

Event-by-event fluctuations of the event-wise mean transverse momentum, $\langle p_{\mathrm{T}}\rangle$, of charged particles produced in proton$-$proton (pp) collisions at $\sqrt{s}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_{\mathrm{NN}}} =$ 5.44 TeV, and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}} =$ 5.0 TeV are studied using the ALICE detector based on the integral correlator $\langle\langle Δp_{\rm T}Δp_{\rm T}\rangle\rangle $. The correlator strength is found to decrease monotonically with increasing produced charged-particle multiplicity measured at midrapidity in all three systems. In Xe$-$Xe and Pb$-$Pb collisions, the multiplicity dependence of the correlator deviates significantly from a simple power-law scaling as well as from the predictions of the HIJING and AMPT models. The observed deviation from power-law scaling is expected from transverse radial flow in semicentral to central Xe$-$Xe and Pb$-$Pb collisions. In pp collisions, the correlation strength is also studied by classifying the events based on the transverse spherocity, $S_0$, of the particle production at midrapidity, used as a proxy for the presence of a pronounced back-to-back jet topology. Low-spherocity (jetty) events feature a larger correlation strength than those with high spherocity (isotropic). The strength and multiplicity dependence of jetty and isotropic events are well reproduced by calculations with the PYTHIA 8 and EPOS LHC models.

12 data tables

Normalized transverse momentum correlator, $\sqrt{ \langle\langle \Delta p_{{\rm T}1}\Delta p_{{\rm T}2} \rangle\rangle }$$/\langle\langle p_{\rm T} \rangle\rangle $, as a function of the charged-particle multiplicity density, $\langle{\rm d}N_{\rm ch}/{\rm d}\eta \rangle$, in pp collisions at $\sqrt{s}$ = 5.02 TeV.

Normalized transverse momentum correlator, $\sqrt{ \langle\langle \Delta p_{{\rm T}1}\Delta p_{{\rm T}2} \rangle\rangle }$$/\langle\langle p_{\rm T} \rangle\rangle $, as a function of the charged-particle multiplicity density, $\langle{\rm d}N_{\rm ch}/{\rm d}\eta \rangle$, in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.

Normalized transverse momentum correlator, $\sqrt{ \langle\langle \Delta p_{{\rm T}1}\Delta p_{{\rm T}2} \rangle\rangle }$$/\langle\langle p_{\rm T} \rangle\rangle $, as a function of the charged-particle multiplicity density, $\langle{\rm d}N_{\rm ch}/{\rm d}\eta \rangle$, in Xe--Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV.

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

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
Phys.Rev.C 111 (2025) 054906, 2025.
Inspire Record 2846998 DOI 10.17182/hepdata.157600

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.

2 data tables

Measured cross sections of the emission of a given number of protons k accompanied by at least one neutron i in UPC of Pb nuclei.

Measured cross sections of the emission of a given number of neutrons i accompanied by a single proton in UPC of Pb nuclei.