The first measurement of $_{\Lambda}^{3}\mathrm{H}$ and $^3_ {\overline{\Lambda}}\overline{\mathrm{H}}$ differential production with respect to transverse momentum and centrality in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV is presented. The $_{\Lambda}^{3}\mathrm{H}$ has been reconstructed via its two-charged-body decay channel, i.e., $_{\Lambda}^{3}\mathrm{H} \rightarrow {}^{3}\mathrm{He} + \pi^{-}$. A Blast-Wave model fit of the $p_{\rm T}$-differential spectra of all nuclear species measured by the ALICE collaboration suggests that the $_{\Lambda}^{3}\mathrm{H}$ kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of $_{\Lambda}^{3}\mathrm{H}$ 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.
We report on the measurement of inclusive, non-prompt, and prompt J/$ψ$-hadron correlations by the ALICE Collaboration at the CERN Large Hadron Collider in pp collisions at a center-of-mass energy of $13~\text{TeV}$. The correlations are studied at midrapidity ($|y| < 0.9$) in the transverse momentum ranges $p_{\rm T} < 40~\text{GeV}/c$ for the J/$ψ$ and $0.15 < p_{\rm T} < 10~\text{GeV}/c$ and $|η|<0.9$ for the associated hadrons. The measurement is based on minimum bias and high multiplicity data samples corresponding to integrated luminosities of $L_{\text{int}} = 34~\text{nb}^{-1}$ and $L_{\text{int}} = 6.9~\text{pb}^{-1}$, respectively. In addition, two more data samples are employed, requiring, on top of the minimum bias condition, a threshold on the tower energy of $E = 4$ and $9~\text{GeV}$ in the ALICE electromagnetic calorimeters, which correspond to integrated luminosities of $L_{\text{int}} = 0.9~\text{pb}^{-1}$ and $L_{\text{int}} = 8.4~\text{pb}^{-1}$, respectively. The azimuthally integrated near and away side yields of associated charged hadrons per J/$ψ$ trigger are presented as a function of the J/$ψ$ and associated hadron transverse momentum. The measurements are discussed in comparison to PYTHIA calculations.
Differential two-particle normalized cumulants ($R_2$) and transverse momentum correlations ($P_2$) are measured as a function of the relative pseudorapidity and azimuthal angle difference $( Δη, Δφ)$ of charged particle pairs in minimum bias pp collisions at $\sqrt{\textit{s}}$ = 13 TeV. The measurements use charged hadrons in the pseudorapidity region of $|η| < 0.8$ and the transverse momentum range \mbox{0.2 $< \textit{p}_{\mathrm T} < $ 2.0 $\mathrm{GeV}/\textit{c}$} in order to focus on soft multiparticle interactions and to complement prior measurements of these correlation functions in p-Pb and Pb-Pb collisions. The correlation functions are reported for both unlike-sign and like-sign pairs and their charge-independent and charge-dependent combinations. Both the $R_2$ and $P_2$ measured in pp collisions exhibit features qualitatively similar to those observed in p--Pb and Pb--Pb collisions. The $Δη$ and $Δφ$ root mean square widths of the near-side peak of the correlation functions are evaluated and compared with those observed in p-Pb and Pb-Pb collisions and show smooth evolution with the multiplicity of charged particles produced in the collision. The comparison of the measured correlation functions with predictions from PYTHIA8 shows that this model qualitatively captures their basic structure and characteristics but feature important differences. In addition, the $R_2^{\rm CD}$ is used to determine the charge balance function of hadrons produced within the detector acceptance of the measurements. The integral of the balance function is found to be compatible with those reported by a previous measurement in Pb--Pb collisions.
Ultrarelativistic heavy-ion collisions create a quark-gluon plasma (QGP), a hot and dense state of strongly interacting QCD matter. In ultracentral collisions, the QGP volume remains nearly constant event-by-event, while its total entropy can fluctuate due to quantum effects, leading to temperature variations. These features allow the correlation between the mean transverse momentum $(\langle p_{\mathrm{T}} \rangle)$ of charged hadrons and their multiplicity to serve as a probe of the QGP's speed of sound, $c_{s}$. This study extracts $c_{s}$ by analyzing the relative increase in $\langle p_{\mathrm{T}} \rangle$ with respect to the charged-particle density $(\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle)$ at midrapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$, using data from the ALICE detector. Centrality is determined with estimators based on multiplicity and transverse energy, applying a pseudorapidity gap to reduce selection biases. The extracted value of $c_{s}^{2}$ is found to strongly depend on the employed centrality estimator and ranges between $0.1146 \pm 0.0028 \,\mathrm{(stat.)} \pm 0.0065 \,\mathrm{(syst.)}$ and $0.4374 \pm 0.0006 \mathrm{(stat.)} \pm 0.0184 \mathrm{(syst.)}$ in natural units. Additionally, the event-by-event $[p_{\mathrm{T}}]$ distribution is studied through its variance, skewness, and kurtosis. A pronounced decrease in the self-normalized variance and a peak followed by a drop in skewness suggest the suppression of impact-parameter fluctuations in ultracentral collisions. These observations provide new insights into the thermodynamic properties and initial-state fluctuations of the QGP.
The transverse momentum spectra and integrated yields of $\overlineΣ^{\pm}$ have been measured in pp and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV with the ALICE experiment. Measurements are performed via the newly accessed decay channel $\overlineΣ^{\pm} \rightarrow {\rm\overline{n}}π^{\pm}$. A new method of antineutron reconstruction with the PHOS electromagnetic spectrometer is developed and applied to this analysis. The $p_{\rm T}$ spectra of $\overlineΣ^{\pm}$ are measured in the range $0.5 < p_{\rm T} < 3$ GeV/$c$ and compared to predictions of the PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4 models. The EPOS LHC and EPOS4 models provide the best descriptions of the measured spectra both in pp and p-Pb collisions, while models which do not account for multiparton interactions provide a considerably worse description at high $p_{\rm T}$. The total yields of $\overlineΣ^{\pm}$ in both pp and p-Pb collisions are compared to predictions of the Thermal-FIST model and dynamical models PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4. All models reproduce the total yields in both colliding systems within uncertainties. The nuclear modification factors $R_{\rm pPb}$ for both $\overlineΣ^{+}$ and $\overlineΣ^{-}$ are evaluated and compared to those of protons, $Λ$ and $Ξ$ hyperons, and predictions of EPOS LHC and EPOS4 models. No deviations of $R_{\rm pPb}$ for $\overlineΣ^{\pm}$ from the model predictions or measurements for other hadrons are found within uncertainties.
The coherent J/$\psi$ photoproduction cross section is measured for the first time at midrapidity in peripheral to semicentral Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. The centrality differential cross section ${\rm d} \sigma/ {\rm d}y$ is reported for the centrality range 40-90%, together with the doubly-differential cross section ${\rm d}^2 \sigma /{\rm d}y {\rm d} p_{\rm T}$, extracted in two peripheral centrality classes. The J/$\psi$ mesons are reconstructed in the dielectron channel, in the rapidity interval $|y| <$ 0.9 using the ALICE central barrel detectors. The J/$\psi$ cross section at midrapidity is statistically compatible to the earlier ALICE measurement at forward rapidity and at the same centre-of-mass energy, and shows only a mild centrality dependence over the covered range. Several sets of theoretical calculations taking into account the hadronic overlap in the collisions but ignoring possible final-state effects from a hot expanding medium are found to give a fairly good description of the current measurements within uncertainties.
First measurements of hadron(h)$-\Lambda$ 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 $\Lambda$ 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 $\Lambda$ 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 $\phi(1020)$ 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 $\Lambda$ 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.
This article presents the first measurement of the interaction between charm hadrons and nucleons. The two-particle momentum correlations of $\mathrm{pD^-}$ and $\mathrm{\overline{p}D}^+$ pairs are measured by the ALICE Collaboration in high-multiplicity pp collisions at $\sqrt{s} = 13~\mathrm{TeV}$. The data are compatible with the Coulomb-only interaction hypothesis within (1.1-1.5)$\sigma$. The level of agreement slightly improves if an attractive nucleon(N)$\overline{\mathrm{D}}$ strong interaction is considered, in contrast to most model predictions which suggest an overall repulsive interaction. This measurement allows for the first time an estimation of the 68% confidence level interval for the isospin $\mathrm{I}=0$ inverse scattering length of the $\mathrm{N\overline{D}}$ state ${f_{0,~\mathrm{I}=0}^{-1} \in [-0.4,0.9]~\mathrm{fm^{-1}}}$, assuming negligible interaction for the isospin $\mathrm{I}=1$ channel.
The production yields of non-prompt $\mathrm{D_s}^{+}$ mesons, namely $\mathrm{D_s}^{+}$ mesons from beauty-hadron decays, were measured for the first time as a function of the transverse momentum ($p_{\rm T}$) at midrapidity ($|y|<0.5$) in central and semi-central Pb$-$Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV with the ALICE experiment at the LHC. The $\mathrm{D_s}^{+}$ mesons and their charge conjugates were reconstructed from the hadronic decay channel $\mathrm{D_s}^{+} \to \phi\pi^+$, with $\phi \to {\rm K}^-{\rm K}^+$, in the $4 < p_{\rm T}<36$ GeV/$c$ and $2 < p_{\rm T}<24$ GeV/$c$ intervals for the 0$-$10% and 30$-$50% centrality classes, respectively. The measured yields of non-prompt $\mathrm{D_s}^{+}$ mesons are compared to those of prompt $\mathrm{D_s}^{+}$ and non-prompt $\mathrm{D^0}$ mesons by calculating the ratios of the production yields in Pb$-$Pb collisions and the nuclear modification factor $R_\mathrm{AA}$. The ratio between the $R_\mathrm{AA}$ of non-prompt $\mathrm{D_s}^{+}$ and prompt $\mathrm{D_s}^{+}$ mesons, and that between the $R_\mathrm{AA}$ of non-prompt $\mathrm{D_s}^{+}$ and non-prompt $\mathrm{D^0}$ mesons in central Pb$-$Pb collisions are found to be on average higher than unity in the $4< p_{\rm T}<12$ GeV/$c$ interval with a statistical significance of about $1.6\,\sigma$ and $1.7\,\sigma$, respectively. The measured $R_\mathrm{AA}$ ratios are compared with the predictions of theoretical models of heavy-quark transport in a hydrodynamically expanding QGP that incorporate hadronisation via quark recombination.
The production of non-prompt ${\rm D}^{0}$ mesons from beauty-hadron decays was measured at midrapidity ($\left| y \right| < 0.5$) in Pb-Pb collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\rm NN}}=5.02~\mathrm{TeV}$ with the ALICE experiment at the LHC. Their nuclear modification factor ($R_{\rm AA}$), measured for the first time down to $p_{\rm T}=1~\mathrm{GeV}/c$ in the $0-10$% and $30-50$% centrality classes, indicates a significant suppression, up to a factor of about three, for $p_{\rm T} > 5~\mathrm{GeV}/c$ in the $0-10$% central Pb-Pb collisions. The data are described by models that include both collisional and radiative processes in the calculation of beauty-quark energy loss in the quark-gluon plasma, and quark recombination in addition to fragmentation as a hadronisation mechanism. The ratio of the non-prompt to prompt ${\rm D}^{0}$-meson $R_{\rm AA}$ is larger than unity for $p_{\rm T} > 4~\mathrm{GeV}/c$ in the $0-10$% central Pb-Pb collisions, as predicted by models in which beauty quarks lose less energy than charm quarks in the quark-gluon plasma because of their larger mass.