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The jet angularities are a class of jet substructure observables which characterize the angular and momentum distribution of particles within jets. These observables are sensitive to momentum scales ranging from perturbative hard scatterings to nonperturbative fragmentation into final-state hadrons. We report measurements of several groomed and ungroomed jet angularities in pp collisions at s√ = 5.02 TeV with the ALICE detector. Jets are reconstructed using charged particle tracks at midrapidity (|η| < 0.9). The anti-kT algorithm is used with jet resolution parameters R = 0.2 and R = 0.4 for several transverse momentum pchT jet intervals in the 20–100 GeV/c range. Using the jet grooming algorithm Soft Drop, the sensitivity to softer, wide-angle processes, as well as the underlying event, can be reduced in a way which is well-controlled in theoretical calculations. We report the ungroomed jet angularities, λα, and groomed jet angularities, λα,g, to investigate the interplay between perturbative and nonperturbative effects at low jet momenta. Various angular exponent parameters α = 1, 1.5, 2, and 3 are used to systematically vary the sensitivity of the observable to collinear and soft radiation. Results are compared to analytical predictions at next-to-leading-logarithmic accuracy, which provide a generally good description of the data in the perturbative regime but exhibit discrepancies in the nonperturbative regime. Moreover, these measurements serve as a baseline for future ones in heavy-ion collisions by providing new insight into the interplay between perturbative and nonperturbative effects in the angular and momentum substructure of jets. They supply crucial guidance on the selection of jet resolution parameter, jet transverse momentum, and angular scaling variable for jet quenching studies.
The transverse momentum (pT) differential cross section of the charm-strange baryon Ξ0c is measured at midrapidity (|y| < 0.5) via its semileptonic decay into e+Ξ−νe in pp collisions at s√ = 5.02 TeV with the ALICE detector at the LHC. The ratio of the pT-differential Ξ0c-baryon and D0-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The pT-integrated cross section of prompt Ξ0c-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio Ξ0c/D0 = 0.20 ± 0.04 (stat.)+0.08−0.07 (syst.). These results provide an additional indication of a modification of the charm fragmentation from e+e− and e−p collisions to pp collisions.
The study of the azimuthal anisotropy of inclusive muons produced in p–Pb collisions at √sNN=8.16 TeV, using the ALICE detector at the LHC is reported. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, v2, is performed as a function of transverse momentum pT in the 0–20% high-multiplicity interval at both forward (2.03<yCMS<3.53) and backward (−4.46<yCMS<−2.96) rapidities over a wide pT range, 0.5<pT<10 GeV/c, in which a dominant contribution of muons from heavy-flavour hadron decays is expected at pT>2 GeV/c. The v2 coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward–central two-particle correlations. Both techniques give compatible results. A positive v2 is measured at both forward and backward rapidities with a significance larger than 4.7σ and 7.6σ, respectively, in the interval 2<pT<6 GeV/c. Comparisons with previous measurements in p–Pb collisions at √sNN=5.02 TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.
Production of inclusive charmonia in pp collisions at center-of-mass energy of √s = 13 TeV and p–Pb collisions at center-of-mass energy per nucleon pair of √sNN = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/ψ, ψ(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame 2.5 < ycms < 4.0 for pp collisions, and 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96 for p–Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity (|η| < 1.0). In pp collisions, the measured charged-particle multiplicity extends to about six times the average value, while in p-Pb collisions at forward (backward) rapidity a multiplicity corresponding to about three (four) times the average is reached. The ψ(2S) yield increases with the charged-particle pseudorapidity density. The ratio of ψ(2S) over J/ψ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/ψ and ψ(2S) yields with respect to charged-particle pseudorapidity density. Results for the ψ(2S) yield and its ratio with respect to J/ψ agree with available model calculations.
The most precise measurements to date of the 3ΛH lifetime τ and Λ separation energy BΛ are obtained using the data sample of Pb-Pb collisions at √= 5.02 TeV collected by ALICE at the LHC. The 3ΛH is reconsNN structed via its charged two-body mesonic decay channel (3ΛH→ 3He + π− and the charge-conjugate process). The measured values τ=[253±11 (stat.)±6 (syst.)] ps and BΛ=[102±63 (stat.)±67 (syst.)] keV are compatible with predictions from effective field theories and confirm that the 3ΛH structure is consistent with a weakly-bound system.
The measurement of the production of charm jets, identified by the presence of a D0 meson in the jet constituents, is presented in proton–proton collisions at centre-of-mass energies of √s = 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The D0 mesons were reconstructed from their hadronic decay D0 → K−π+ and the respective charge conjugate. Jets were reconstructed from D0-meson candidates and charged particles using the anti-kT algorithm, in the jet transverse momentum range 5 < pT,chjet < 50 GeV/c, pseudorapidity |ηjet| < 0.9 − R, and with the jet resolution parameters R = 0.2, 0.4, 0.6. The distribution of the jet momentum fraction carried by a D0 meson along the jet axis (z ch) was measured in the range 0.4 < z ch < 1.0 in four ranges of the jet transverse momentum. Comparisons of results for different collision energies and jet resolution parameters are also presented. The measurements are compared to predictions from Monte Carlo event generators based on leading-order and next-to-leading-order perturbative quantum chromodynamics calculations. A generally good description of the main features of the data is obtained in spite of a few discrepancies at low pT,chjet. Measurements were also done for R = 0.3 at √s = 5.02 and are shown along with their comparisons to theoretical predictions in an appendix to this paper.
This Letter presents the most precise measurement to date of the matter/antimatter imbalance at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair sNN−−−√=5.02 TeV. Using the Statistical Hadronization framework, it is possible to obtain the value of the electric charge and baryon chemical potentials, μQ=−0.18±0.90 MeV and μB=0.71±0.45 MeV, with unprecedented precision. A centrality-differential study of the antiparticle-to-particle yield ratios of charged pions, protons, Ω-baryons, and light (hyper)nuclei is performed. These results indicate that the system created in Pb-Pb collisions at the LHC is on average baryon-free and electrically neutral at midrapidity.
The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high pT) charged hadron, in pp and central Pb−Pb collisions at center of mass energy per nucleon−nucleon collision sNN−−−√=5.02 TeV. The large uncorrelated background in central Pb−Pb collisions is corrected using a data-driven statistical approach, which enables precise measurement of recoil jet distributions over a broad range in pT,chjet and jet resolution parameter R. Recoil jet yields are reported for R=0.2, 0.4, and 0.5 in the range 7<pT,chjet<140 GeV/c and π/2<Δφ<π, where Δφ is the azimuthal angular separation between hadron trigger and recoil jet. The low pT,chjet reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark-gluonnplasma generated in high-energy nuclear collisions. Comparison of pT,chjet distributions from pp and central Pb−Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.
The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high pT) charged hadron, in pp and central Pb−Pb collisions at center of mass energy per nucleon−nucleon collision sNN−−−√=5.02 TeV. The large uncorrelated background in central Pb−Pb collisions is corrected using a data-driven statistical approach, which enables precise measurement of recoil jet distributions over a broad range in pT,chjet and jet resolution parameter R. Recoil jet yields are reported for R=0.2, 0.4, and 0.5 in the range 7<pT,chjet<140 GeV/c and π/2<Δφ<π, where Δφ is the azimuthal angular separation between hadron trigger and recoil jet. The low pT,chjet reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark-gluonnplasma generated in high-energy nuclear collisions. Comparison of pT,chjet distributions from pp and central Pb−Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.
Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at s√=13 TeV and p−Pb collisions at sNN−−−√=5.02 TeV. The correlation functions are measured as a function of relative azimuthal angle Δφ and pseudorapidity separation Δη for pairs of primary charged particles within the pseudorapidity interval |η|<0.9 and the transverse-momentum interval 1<pT<4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6<|Δη|<1.8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.
Modification of charged-particle jets in event-shape engineered Pb–Pb collisions at √sNN = 5.02 TeV
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Charged-particle jet yields have been measured in semicentral Pb−Pb collisions at center-of-mass energy per nucleon-nucleon collision sNN−−−√=5 TeV with the ALICE detector at the LHC. These yields are reported as a function of the jet transverse momentum, and further classified by their angle with respect to the event plane and the event shape, characterized by ellipticity, in an effort to study the path-length dependence of jet quenching. Jets were reconstructed at midrapidity from charged-particle tracks using the anti-kT algorithm with resolution parameters R= 0.2 and 0.4, with event-plane angle and event-shape values determined using information from forward scintillating detectors. The results presented in this letter show that, in semicentral Pb−Pb collisions, there is no significant difference between jet yields in predominantly isotropic and elliptical events. However, out-of-plane jets are observed to be more suppressed than in-plane jets. Further, this relative suppression is greater for low transverse momentum (< 50 GeV/c) R= 0.2 jets produced in elliptical events, with out-of-plane to in-plane jet-yield ratios varying up to 5.2σ between different event-shape classes. These results agree with previous studies indicating that jets experience azimuthally anisotropic suppression when traversing the QGP medium, and can provide additional constraints on the path-length dependence of jet energy loss.
n this Letter, the first measurement of the inelastic cross section for antitriton−nucleus interactions is reported, covering the momentum range of 0.8≤p<2.4 GeV/c. The measurement is carried out using data recorded with the ALICE detector in pp and Pb−Pb collisions at a centre-of-mass energy per nucleon of 13 TeV and 5.02 TeV, respectively. The detector material serves as an absorber for antitriton nuclei. The raw yield of (anti)triton nuclei measured with the ALICE apparatus is compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of (anti)particles through matter, allowing one to quantify the inelastic interaction probability in the detector material. This analysis complements the measurement of the inelastic cross section of antinuclei up to A=3 carried out by the ALICE Collaboration, and demonstrates the feasibility of the study of the isospin dependence of inelastic interaction cross section with the analysis techniques presented in this Letter.
In this Letter, the first measurement of the inelastic cross section for antitriton−nucleus interactions is reported, covering the momentum range of 0.8≤p<2.4 GeV/c. The measurement is carried out using data recorded with the ALICE detector in pp and Pb−Pb collisions at a centre-of-mass energy per nucleon of 13 TeV and 5.02 TeV, respectively. The detector material serves as an absorber for antitriton nuclei. The raw yield of (anti)triton nuclei measured with the ALICE apparatus is compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of (anti)particles through matter, allowing one to quantify the inelastic interaction probability in the detector material. This analysis complements the measurement of the inelastic cross section of antinuclei up to A=3 carried out by the ALICE Collaboration, and demonstrates the feasibility of the study of the isospin dependence of inelastic interaction cross section with the analysis techniques presented in this Letter.
The measurements of the inclusive J/ψ yield at midrapidity (|y|<0.9) and forward rapidity (2.5 <y< 4) in Pb−Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector at the LHC are reported. The inclusive J/ψ production yields and nuclear modification factors, RAA, are measured as a function of the collision centrality, J/ψ transverse momentum (pT), and rapidity. The J/ψ average transverse momentum and squared transverse momentum (⟨pT⟩ and ⟨p2T⟩) are evaluated as a function of the centrality at midrapidity. Compared to the previous ALICE publications, here the entire Pb−Pb collisions dataset collected during the LHC Run 2 is used, which improves the precision of the measurements and extends the pT coverage. The pT-integrated RAA shows a hint of an increasing trend towards unity from semicentral to central collisions at midrapidity, while it is flat at forward rapidity. The pT-differential RAA shows a strong suppression at high pT with less suppression at low pT where it reaches a larger value at midrapidity compared to forward rapidity. The ratio of the pT-integrated yields of J/ψ to those of D0 mesons is reported for the first time for the central and semicentral event classes at midrapidity. Model calculations implementing charmonium production via the coalescence of charm quarks and antiquarks during the fireball evolution (transport models) or in a statistical approach with thermal weights are in good agreement with the data at low pT. At higher pT, the data are well described by transport models and a model based on energy loss in the strongly-interacting medium produced in nuclear collisions at the LHC.
Measurements of (anti)proton, (anti)deuteron, and (anti)3He production in the rapidity range −1<y<0 as a function of the transverse momentum and event multiplicity in p-Pb collisions at a center-of-mass energy per nucleon-nucleon pair sNN−−−√=8.16 TeV are presented. The coalescence parameters B2 and B3, measured as a function of the transverse momentum per nucleon and of the mean charged-particle multiplicity density, confirm a smooth evolution from low to high multiplicity across different collision systems and energies. The ratios between (anti)deuteron and (anti)3He yields and those of (anti)protons are also reported as a function of the mean charged-particle multiplicity density. A comparison with the predictions of the statistical hadronization and coalescence models for different collision systems and center-of-mass energies favors the coalescence description for the deuteron-to-proton yield ratio with respect to the canonical statistical model.
A new, more precise measurement of the Λ hyperon lifetime is performed using a large data sample of Pb−Pb collisions at sNN−−−√=5.02 TeV with ALICE. The Λ and Λ¯¯¯¯ hyperons are reconstructed at midrapidity using their two-body weak decay channel Λ→p+π− and Λ¯¯¯¯→p¯¯¯+π+. The measured value of the Λ lifetime is τΛ=[261.07±0.37 (stat.)±0.72 (syst.)] ps. The relative difference between the lifetime of Λ and Λ¯¯¯¯, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value (τΛ−τΛ¯¯¯¯)/τΛ=0.0013±0.0028 (stat.)±0.0021 (syst.) is consistent with zero within the uncertainties. Both measurements of the Λ hyperon lifetime and of the relative difference between τΛ and τΛ¯¯¯¯ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.
The measurement of the production of charm jets, identified by the presence of a D0 meson in the jet constituents, is presented in proton-proton collisions at centre-of-mass energies of s√ = 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The D0 mesons were reconstructed from their hadronic decay D0→K−π+ and the respective charge conjugate. Jets were reconstructed from D0-meson candidates and charged particles using the anti-kT algorithm, in the jet transverse momentum range 5<pT;chjet<50 GeV/c, pseudorapidity |ηjet|<0.9−R, and with the jet resolution parameters R = 0.2, 0.4, 0.6. The distribution of the jet momentum fraction carried by a D0 meson along the jet axis (zch||) was measured in the range 0.4<zch||<1.0 in four ranges of the jet transverse momentum. Comparisons of results for different collision energies and jet resolution parameters are also presented. The measurements are compared to predictions from Monte Carlo event generators based on leading-order and next-to-leading-order perturbative quantum chromodynamics calculations. A generally good description of the main features of the data is obtained in spite of a few discrepancies at low pT;chjet. Measurements were also done for R=0.3 at s√ = 5.02 TeV and are shown along with their comparisons to theoretical predictions in an appendix to this paper.
The study of the azimuthal anisotropy of inclusive muons produced in p-Pb collisions at sNN−−−√=8.16 TeV, using the ALICE detector at the LHC is reported. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, v2, is performed as a function of transverse momentum pT in the 0-20% high-multiplicity interval at both forward (2.03<yCMS<3.53) and backward (−4.46<yCMS<−2.96) rapidities over a wide pT range, 0.5<pT<10 GeV/c, in which a dominant contribution of muons from heavy-flavour hadron decays is expected at pT>2 GeV/c. The v2 coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward-central two-particle correlations. Both techniques give compatible results. A positive v2 is measured at both forward and backward rapidities with a significance larger than 4.7σ and 7.6σ, respectively, in the interval 2<pT<6 GeV/c. Comparisons with previous measurements in p-Pb collisions at sNN−−−√=5.02 TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.
The transverse-momentum (pT) spectra of K∗(892)0 and ϕ(1020) measured with the ALICE detector up to pT = 16 GeV/c in the rapidity range −1.2<y<0.3, in p-Pb collisions at the center-of-mass energy per nucleon-nucleon collision sNN−−−√ = 5.02 TeV are presented as a function of charged particle multiplicity and rapidity. The measured pT distributions show a dependence on both multiplicity and rapidity at low pT whereas no significant dependence is observed at high pT. A rapidity dependence is observed in the pT-integrated yield (dN/dy), whereas the mean transverse momentum (⟨pT⟩) shows a flat behavior as a function of rapidity. The rapidity asymmetry (Yasym) at low pT ( < 5 GeV/c) is more significant for higher multiplicity classes. At high pT, no significant rapidity asymmetry is observed in any of the multiplicity classes. Both K∗(892)0 and ϕ(1020) show similar Yasym. The nuclear modification factor (QCP) as a function of pT shows a Cronin-like enhancement at intermediate pT, which is more prominent at higher rapidities (Pb-going direction) and in higher multiplicity classes. At high pT (> 5 GeV/c), the QCP values are greater than unity and no significant rapidity dependence is observed.
Measurement of the J/ψ polarization with respect to the event plane in Pb–Pb collisions at the LHC
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We study the polarization of inclusive J/ψ produced in Pb−Pb collisions at sNN−−−√=5.02 TeV at the LHC in the dimuon channel, via the measurement of the angular distribution of its decay products. We perform the study in the rapidity region 2.5<y<4, for three transverse momentum intervals (2<pT<4, 4<pT<6, 6<pT<10 GeV/c) and as a function of the centrality of the collision for 2<pT<6 GeV/c. For the first time, the polarization is measured with respect to the event plane of the collision, by considering the angle between the positive-charge decay muon in the J/ψ rest frame and the axis perpendicular to the event-plane vector in the laboratory system. A small transverse polarization is measured, with a significance reaching 3.9σ at low pT and for intermediate centrality values. The polarization could be connected with the behaviour of the quark−gluon plasma, formed in Pb−Pb collisions, as a rotating fluid with large vorticity, as well as with the existence of a strong magnetic field in the early stage of its formation.
Measurement of the J/ψ polarization with respect to the event plane in Pb–Pb collisions at the LHC
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We study the polarization of inclusive J/ψ produced in Pb−Pb collisions at sNN−−−√=5.02 TeV at the LHC in the dimuon channel, via the measurement of the angular distribution of its decay products. We perform the study in the rapidity region 2.5<y<4, for three transverse momentum intervals (2<pT<4, 4<pT<6, 6<pT<10 GeV/c) and as a function of the centrality of the collision for 2<pT<6 GeV/c. For the first time, the polarization is measured with respect to the event plane of the collision, by considering the angle between the positive-charge decay muon in the J/ψ rest frame and the axis perpendicular to the event-plane vector in the laboratory system. A small transverse polarization is measured, with a significance reaching 3.9σ at low pT and for intermediate centrality values. The polarization could be connected with the behaviour of the quark−gluon plasma, formed in Pb−Pb collisions, as a rotating fluid with large vorticity, as well as with the existence of a strong magnetic field in the early stage of its formation.
Production of inclusive charmonia in pp collisions at center-of-mass energy of s√ = 13 TeV and p-Pb collisions at center-of-mass energy per nucleon pair of sNN−−−√ = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/ψ, ψ(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame 2.5<ycms<4.0 for pp collisions, and 2.03<ycms<3.53 and −4.46<ycms<−2.96 for p-Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity (|η|<1.0). In pp collisions, the measured charged-particle multiplicity extends to about six times the average value, while in p-Pb collisions at forward (backward) rapidity a multiplicity corresponding to about three (four) times the average is reached. The ψ(2S) yield increases with the charged-particle pseudorapidity density. The ratio of ψ(2S) over J/ψ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/ψ and ψ(2S) yields with respect to charged-particle pseudorapidity density. Results for the ψ(2S) yield and its ratio with respect to J/ψ agree with available model calculations.
This article presents measurements of the groomed jet radius and momentum splitting fraction in pp collisions at s√=5.02 TeV with the ALICE detector at the Large Hadron Collider. Inclusive charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm for transverse momentum 60<pchjetT<80 GeV/c. We report results using two different grooming algorithms: soft drop and, for the first time, dynamical grooming. For each grooming algorithm, a variety of grooming settings are used in order to explore the impact of collinear radiation on these jet substructure observables. These results are compared to perturbative calculations that include resummation of large logarithms at all orders in the strong coupling constant. We find good agreement of the theoretical predictions with the data for all grooming settings considered.
This article presents measurements of the groomed jet radius and momentum splitting fraction in pp collisions at s√=5.02 TeV with the ALICE detector at the Large Hadron Collider. Inclusive charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm for transverse momentum 60<pchjetT<80 GeV/c. We report results using two different grooming algorithms: soft drop and, for the first time, dynamical grooming. For each grooming algorithm, a variety of grooming settings are used in order to explore the impact of collinear radiation on these jet substructure observables. These results are compared to perturbative calculations that include resummation of large logarithms at all orders in the strong coupling constant. We find good agreement of the theoretical predictions with the data for all grooming settings considered.
This article presents groomed jet substructure measurements in pp and Pb−Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector. The Soft Drop grooming algorithm provides access to the hard parton splittings inside a jet by removing soft wide-angle radiation. We report the groomed jet momentum splitting fraction, zg, and the (scaled) groomed jet radius, θg. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with resolution parameters R=0.2 and R=0.4. In heavy-ion collisions, the large underlying event poses a challenge for the reconstruction of groomed jet observables, since fluctuations in the background can cause groomed parton splittings to be misidentified. By using strong grooming conditions to reduce this background, we report these observables fully corrected for detector effects and background fluctuations for the first time. A narrowing of the θg distribution in Pb−Pb collisions compared to pp collisions is seen, which provides direct evidence of the modification of the angular structure of jets in the quark−gluon plasma. No significant modification of the zg distribution in Pb−Pb collisions compared to pp collisions is observed. These results are compared with a variety of theoretical models of jet quenching, and provide constraints on jet energy-loss mechanisms and coherence effects in the quark−gluon plasma.
This article presents groomed jet substructure measurements in pp and Pb−Pb collisions at √sNN=5.02 TeV with the ALICE detector. The soft drop grooming algorithm provides access to the hard parton splittings inside a jet by removing soft wide-angle radiation. We report the groomed jet momentum splitting fraction, zg, and the (scaled) groomed jet radius, θg. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with resolution parameters R=0.2 and R=0.4. In heavy-ion collisions, the large underlying event poses a challenge for the reconstruction of groomed jet observables, since fluctuations in the background can cause groomed parton splittings to be misidentified. By using strong grooming conditions to reduce this background, we report these observables fully corrected for detector effects and background fluctuations for the first time. A narrowing of the θg distribution in Pb−Pb collisions compared to pp collisions is seen, which provides direct evidence of the modification of the angular structure of jets in the quark-gluon plasma. No significant modification of the zg distribution in Pb−Pb collisions compared to pp collisions is observed. These results are compared with a variety of theoretical models of jet quenching, and provide constraints on jet energy-loss mechanisms and coherence effects in the quark-gluon plasma.
This article presents groomed jet substructure measurements in pp and Pb−Pb collisions at sNN−−−√=5.02 TeV with the ALICE detector. The Soft Drop grooming algorithm provides access to the hard parton splittings inside a jet by removing soft wide-angle radiation. We report the groomed jet momentum splitting fraction, zg, and the (scaled) groomed jet radius, θg. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with resolution parameters R=0.2 and R=0.4. In heavy-ion collisions, the large underlying event poses a challenge for the reconstruction of groomed jet observables, since fluctuations in the background can cause groomed parton splittings to be misidentified. By using strong grooming conditions to reduce this background, we report these observables fully corrected for detector effects and background fluctuations for the first time. A narrowing of the θg distribution in Pb−Pb collisions compared to pp collisions is seen, which provides direct evidence of the modification of the angular structure of jets in the quark−gluon plasma. No significant modification of the zg distribution in Pb−Pb collisions compared to pp collisions is observed. These results are compared with a variety of theoretical models of jet quenching, and provide constraints on jet energy-loss mechanisms and coherence effects in the quark−gluon plasma.
The very forward energy is a powerful tool for characterising the proton fragmentation in pp and p-Pb collisions and, studied in correlation with particle production at midrapidity, provides direct insightsinto the initial stages and the subsequent evolution of the collision. Furthermore, the correlation between the forward energy and the production of particles with large transverse momenta at midrapidity provides information complementary to the measurements of the underlying event, which are usually interpreted in the framework of models implementing centrality-dependent multiple parton interaction. Results about the very forward energy, measured by the ALICE zero degree calorimeters (ZDC), and its dependence on the activity measured at midrapidity in pp collisions at s√=13 TeV and in p-Pb collisions at sNN−−−√=8.16 TeV are presented and discussed. The measurements performed in pp collisions are compared with the expectations of three hadronic interaction event generators: PYTHIA 6 (Perugia 2011 tune), PYTHIA 8 (Monash tune), and EPOS LHC. These results provide new constraints on the validity of models in describing the beam remnants at very forward rapidities, where perturbative QCD cannot be used.
The jet angularities are a class of jet substructure observables which characterize the angular and momentum distribution of particles within jets. These observables are sensitive to momentum scales ranging from perturbative hard scatterings to nonperturbative fragmentation into final-state hadrons. We report measurements of several infrared- and collinear-safe jet angularities in pp collisions at s√=5.02 TeV with the ALICE detector. Jets are reconstructed using charged particle tracks at midrapidity. The anti-kT algorithm is used with jet resolution parameters R=0.2 and R=0.4 for several transverse momentum pch jetT intervals in the 20−100 GeV/c range. Using the jet grooming algorithm Soft Drop, the sensitivity to softer, wide-angle processes, as well as the underlying event, can be reduced in a way which is well-controlled in theoretical calculations. We report the ungroomed jet angularities, λα, and groomed jet angularities, λα , g, to investigate the interplay between perturbative and nonperturbative effects at low jet momenta. Various angular exponent parameters α=1, 1.5, 2, and 3 are used to systematically vary the sensitivity of the observable to collinear and soft radiation. Results are compared to analytical predictions at next-to-leading-logarithmic accuracy, which provide a generally good description of the data in the perturbative regime but exhibit discrepancies in the nonperturbative regime. Moreover, these measurements serve as a baseline for future ones in heavy-ion collisions by providing new insight into the interplay between perturbative and nonperturbative effects in the angular and momentum substructure of jets. They supply crucial guidance on the selection of jet resolution parameter, jet transverse momentum and angular scaling variable for jet quenching studies.
The jet angularities are a class of jet substructure observables which characterize the angular and momentum distribution of particles within jets. These observables are sensitive to momentum scales ranging from perturbative hard scatterings to nonperturbative fragmentation into final-state hadrons. We report measurements of several groomed and ungroomed jet angularities in pp collisions at s√=5.02 TeV with the ALICE detector. Jets are reconstructed using charged particle tracks at midrapidity (|η|<0.9). The anti-kT algorithm is used with jet resolution parameters R=0.2 and R=0.4 for several transverse momentum pch jetT intervals in the 20−100 GeV/c range. Using the jet grooming algorithm Soft Drop, the sensitivity to softer, wide-angle processes, as well as the underlying event, can be reduced in a way which is well-controlled in theoretical calculations. We report the ungroomed jet angularities, λα, and groomed jet angularities, λα,g, to investigate the interplay between perturbative and nonperturbative effects at low jet momenta. Various angular exponent parameters α=1, 1.5, 2, and 3 are used to systematically vary the sensitivity of the observable to collinear and soft radiation. Results are compared to analytical predictions at next-to-leading-logarithmic accuracy, which provide a generally good description of the data in the perturbative regime but exhibit discrepancies in the nonperturbative regime. Moreover, these measurements serve as a baseline for future ones in heavy-ion collisions by providing new insight into the interplay between perturbative and nonperturbative effects in the angular and momentum substructure of jets. They supply crucial guidance on the selection of jet resolution parameter, jet transverse momentum, and angular scaling variable for jet quenching studies.
The transverse momentum (pT) differential cross section of the charm-strange baryon Ξ0c is measured at midrapidity (|y|< 0.5) via its semileptonic decay into e+Ξ−νe in pp collisions at s√ = 5.02 TeV with the ALICE detector at the LHC. The ratio of the pT-differential Ξ0c-baryon and D0-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The pT-integrated cross section of prompt Ξ0c-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio Ξ0c/D0=0.20±0.04 (stat.)+0.08−0.07 (syst.). These results provide an additional indication of a modification of the charm fragmentation from e+e− and e−p collisions to pp collisions.
The transverse momentum (pT) differential cross section of the charm-strange baryon Ξ0c is measured at midrapidity (|y|< 0.5) via its semileptonic decay into e+Ξ−νe in pp collisions at s√ = 5.02 TeV with the ALICE detector at the LHC. The ratio of the pT-differential Ξ0c-baryon and D0-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The pT-integrated cross section of prompt Ξ0c-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio Ξ0c/D0=0.20±0.04 (stat.)+0.08−0.07 (syst.). These results provide an additional indication of a modification of the charm fragmentation from e+e− and e−p collisions to pp collisions.
The pT-differential cross sections of prompt charm-strange baryons Ξ0c and Ξ+c were measured at midrapidity (|y|<0.5) in proton−proton (pp) collisions at a centre-of-mass energy s√=13 TeV with the ALICE detector at the LHC. The Ξ0c baryon was reconstructed via both the semileptonic decay (Ξ−e+νe) and the hadronic decay (Ξ−π+) channels. The Ξ+c baryon was reconstructed via the hadronic decay (Ξ−π+π+) channel. The branching-fraction ratio BR(Ξ0c→Ξ−e+νe)/BR(Ξ0c→Ξ−π+) = 1.38 ± 0.14 (stat) ± 0.22 (syst) was measured with a total uncertainty reduced by a factor of about 3 with respect to the current world average reported by the Particle Data Group. The transverse momentum (pT) dependence of the Ξ0c- and Ξ+c-baryon production relative to the D0-meson and to the Σ0,+,++c- and Λ+c-baryon production are reported. The baryon-to-meson ratio increases towards low pT up to a value of approximately 0.3. The measurements are compared with various models that take different hadronisation mechanisms into consideration. The results provide stringent constraints to these theoretical calculations and additional evidence that different processes are involved in charm hadronisation in electron−positron (e+e−) and hadronic collisions.
The pT-differential cross sections of prompt charm-strange baryons Ξ0c and Ξ+c were measured at midrapidity (|y|<0.5) in proton−proton (pp) collisions at a centre-of-mass energy s√=13 TeV with the ALICE detector at the LHC. The Ξ0c baryon was reconstructed via both the semileptonic decay (Ξ−e+νe) and the hadronic decay (Ξ−π+) channels. The Ξ+c baryon was reconstructed via the hadronic decay (Ξ−π+π+) channel. The branching-fraction ratio BR(Ξ0c→Ξ−e+νe)/BR(Ξ0c→Ξ−π+) = 1.38 ± 0.14 (stat) ± 0.22 (syst) was measured with a total uncertainty reduced by a factor of about 3 with respect to the current world average reported by the Particle Data Group. The transverse momentum (pT) dependence of the Ξ0c- and Ξ+c-baryon production relative to the D0-meson and to the Σ0,+,++c- and Λ+c-baryon production are reported. The baryon-to-meson ratio increases towards low pT up to a value of approximately 0.3. The measurements are compared with various models that take different hadronisation mechanisms into consideration. The results provide stringent constraints to these theoretical calculations and additional evidence that different processes are involved in charm hadronisation in electron−positron (e+e−) and hadronic collisions.
In this Letter, the first measurement of the inelastic cross section for antitriton−nucleus interactions is reported, covering the momentum range of 0.8≤p<2.4 GeV/c. The measurement is carried out using data recorded with the ALICE detector in pp and Pb−Pb collisions at a centre-of-mass energy per nucleon of 13 TeV and 5.02 TeV, respectively. The detector material serves as an absorber for antitriton nuclei. The raw yield of (anti)triton nuclei measured with the ALICE apparatus is compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of (anti)particles through matter, allowing one to quantify the inelastic interaction probability in the detector material. This analysis complements the measurement of the inelastic cross section of antinuclei up to A=3 carried out by the ALICE Collaboration, and demonstrates the feasibility of the study of the isospin dependence of inelastic interaction cross section with the analysis techniques presented in this Letter.
This Letter presents the most precise measurement to date of the matter/antimatter imbalance at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair sNN−−−√=5.02 TeV. Using the Statistical Hadronization framework, it is possible to obtain the value of the electric charge and baryon chemical potentials, μQ=−0.18±0.90 MeV and μB=0.71±0.45 MeV, with unprecedented precision. A centrality-differential study of the antiparticle-to-particle yield ratios of charged pions, protons, Ω-baryons, and light (hyper)nuclei is performed. These results indicate that the system created in Pb-Pb collisions at the LHC is on average baryon-free and electrically neutral at midrapidity.
The ALICE Collaboration reports a differential measurement of inclusive jet suppression using pp and Pb−Pb collision data at a center-of-mass energy per nucleon-nucleon collision sNN−−−√=5.02 TeV. Charged-particle jets are reconstructed using the anti-kT algorithm with resolution parameters R= 0.2, 0.3, 0.4, 0.5, and 0.6 in pp collisions and R= 0.2, 0.4, 0.6 in central (0−10%), semi-central (30−50%), and peripheral (60−80%) Pb−Pb collisions. A novel approach based on machine learning is employed to mitigate the influence of jet background. This enables measurements of inclusive jet suppression in new regions of phase space, including down to the lowest jet pT≥40 GeV/c at R=0.6 in central Pb−Pb collisions. This is an important step for discriminating different models of jet quenching in the quark-gluon plasma. The transverse momentum spectra, nuclear modification factors, derived cross section, and nuclear modification factor ratios for different jet resolution parameters of charged-particle jets are presented and compared to model predictions. A mild dependence of the nuclear modification factor ratios on collision centrality and resolution parameter is observed. The results are compared to a variety of jet-quenching models with varying levels of agreement.
Correlations in azimuthal angle extending over a long range in pseudorapidity between particles, usually called the "ridge" phenomenon, were discovered in heavy-ion collisions, and later found in pp and p−Pb collisions. In large systems, they are thought to arise from the expansion (collective flow) of the produced particles. Extending these measurements over a wider range in pseudorapidity and final-state particle multiplicity is important to understand better the origin of these long-range correlations in small-collision systems. In this Letter, measurements of the long-range correlations in p−Pb collisions at sNN−−−√=5.02 TeV are extended to a pseudorapidity gap of Δη∼8 between particles using the ALICE, forward multiplicity detectors. After suppressing non-flow correlations, e.g., from jet and resonance decays, the ridge structure is observed to persist up to a very large gap of Δη∼8 for the first time in p−Pb collisions. This shows that the collective flow-like correlations extend over an extensive pseudorapidity range also in small-collision systems such as p−Pb collisions. The pseudorapidity dependence of the second-order anisotropic flow coefficient, v2({\eta}), is extracted from the long-range correlations. The v2(η) results are presented for a wide pseudorapidity range of −3.1<η<4.8 in various centrality classes in p−Pb collisions. To gain a comprehensive understanding of the source of anisotropic flow in small-collision systems, the v2(η) measurements are compared to hydrodynamic and transport model calculations. The comparison suggests that the final-state interactions play a dominant role in developing the anisotropic flow in small-collision systems.
Correlations in azimuthal angle extending over a long range in pseudorapidity between particles, usually called the "ridge" phenomenon, were discovered in heavy-ion collisions, and later found in pp and p−Pb collisions. In large systems, they are thought to arise from the expansion (collective flow) of the produced particles. Extending these measurements over a wider range in pseudorapidity and final-state particle multiplicity is important to understand better the origin of these long-range correlations in small-collision systems. In this Letter, measurements of the long-range correlations in p−Pb collisions at sNN−−−√=5.02 TeV are extended to a pseudorapidity gap of Δη∼8 between particles using the ALICE, forward multiplicity detectors. After suppressing non-flow correlations, e.g., from jet and resonance decays, the ridge structure is observed to persist up to a very large gap of Δη∼8 for the first time in p−Pb collisions. This shows that the collective flow-like correlations extend over an extensive pseudorapidity range also in small-collision systems such as p−Pb collisions. The pseudorapidity dependence of the second-order anisotropic flow coefficient, v2({\eta}), is extracted from the long-range correlations. The v2(η) results are presented for a wide pseudorapidity range of −3.1<η<4.8 in various centrality classes in p−Pb collisions. To gain a comprehensive understanding of the source of anisotropic flow in small-collision systems, the v2(η) measurements are compared to hydrodynamic and transport model calculations. The comparison suggests that the final-state interactions play a dominant role in developing the anisotropic flow in small-collision systems.
Correlations in azimuthal angle extending over a long range in pseudorapidity between particles, usually called the "ridge" phenomenon, were discovered in heavy-ion collisions, and later found in pp and p−Pb collisions. In large systems, they are thought to arise from the expansion (collective flow) of the produced particles. Extending these measurements over a wider range in pseudorapidity and final-state particle multiplicity is important to understand better the origin of these long-range correlations in small-collision systems. In this Letter, measurements of the long-range correlations in p−Pb collisions at sNN−−−√=5.02 TeV are extended to a pseudorapidity gap of Δη∼8 between particles using the ALICE, forward multiplicity detectors. After suppressing non-flow correlations, e.g., from jet and resonance decays, the ridge structure is observed to persist up to a very large gap of Δη∼8 for the first time in p−Pb collisions. This shows that the collective flow-like correlations extend over an extensive pseudorapidity range also in small-collision systems such as p−Pb collisions. The pseudorapidity dependence of the second-order anisotropic flow coefficient, v2({\eta}), is extracted from the long-range correlations. The v2(η) results are presented for a wide pseudorapidity range of −3.1<η<4.8 in various centrality classes in p−Pb collisions. To gain a comprehensive understanding of the source of anisotropic flow in small-collision systems, the v2(η) measurements are compared to hydrodynamic and transport model calculations. The comparison suggests that the final-state interactions play a dominant role in developing the anisotropic flow in small-collision systems.
The ALICE Collaboration reports a differential measurement of inclusive jet suppression using pp and Pb−Pb collision data at a center-of-mass energy per nucleon-nucleon collision sNN−−−√=5.02 TeV. Charged-particle jets are reconstructed using the anti-kT algorithm with resolution parameters R= 0.2, 0.3, 0.4, 0.5, and 0.6 in pp collisions and R= 0.2, 0.4, 0.6 in central (0−10%), semi-central (30−50%), and peripheral (60−80%) Pb−Pb collisions. A novel approach based on machine learning is employed to mitigate the influence of jet background. This enables measurements of inclusive jet suppression in new regions of phase space, including down to the lowest jet pT≥40 GeV/c at R=0.6 in central Pb−Pb collisions. This is an important step for discriminating different models of jet quenching in the quark-gluon plasma. The transverse momentum spectra, nuclear modification factors, derived cross section, and nuclear modification factor ratios for different jet resolution parameters of charged-particle jets are presented and compared to model predictions. A mild dependence of the nuclear modification factor ratios on collision centrality and resolution parameter is observed. The results are compared to a variety of jet-quenching models with varying levels of agreement.
Measurements of (anti)deuteron and (anti)3He production in the rapidity range |y|< 0.5 as a function of the transverse momentum and event multiplicity in Xe−Xe collisions at a center-of-mass energy per nucleon−nucleon pair of sNN−−−√ = 5.44 TeV are presented. The coalescence parameters B2 and B3 are measured as a function of the transverse momentum per nucleon. The ratios between (anti)deuteron and (anti)3He yields and those of (anti)protons and pions are reported as a function of the mean charged-particle multiplicity density, and compared with two implementations of the statistical hadronization model (SHM) and with coalescence predictions. The elliptic flow of (anti)deuterons is measured for the first time in Xe−Xe collisions and shows features similar to those already observed in Pb−Pb collisions, i.e., the mass ordering at low transverse momentum and the meson−baryon grouping at intermediate transverse momentum. The production of nuclei is particularly sensitive to the chemical freeze-out temperature of the system created in the collision, which is extracted from a grand-canonical-ensemble-based thermal fit, performed for the first time including light nuclei along with light-flavor hadrons in Xe−Xe collisions. The extracted chemical freeze-out temperature Tchem = (154.2 ± 1.1) MeV in Xe−Xe collisions is similar to that observed in Pb−Pb collisions and close to the crossover temperature predicted by lattice QCD calculations.
The transverse momentum (pT) differential production cross section of the promptly-produced charm-strange baryon Ξ0c (and its charge conjugate Ξ0c¯¯¯¯¯¯) is measured at midrapidity via its hadronic decay into π+Ξ− in p−Pb collisions at a centre-of-mass energy per nucleon−nucleon collision sNN−−−√ = 5.02 TeV with the ALICE detector at the LHC. The Ξ0c nuclear modification factor (RpPb), calculated from the cross sections in pp and p−Pb collisions, is presented and compared with the RpPb of Λ+c baryons. The ratios between the pT-differential production cross section of Ξ0c baryons and those of D0 mesons and Λ+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 Ξ0c 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 in which hadronisation is implemented via quark coalescence. The pT-integrated cross section of prompt Ξ0c-baryon production at midrapidity extrapolated down to pT = 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.
The first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced ρ0 mesons is presented. The ρ0 mesons are reconstructed through their decay into a pion pair. The measured anisotropy corresponds to the amplitude of the cos(2ϕ) modulation, where ϕ is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb−Pb collisions at a center-of-mass energy of sNN−−−√ = 5.02 TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the cos(2ϕ) modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations, which describe the measurement, explain the cos(2ϕ) anisotropy as the result of a quantum interference effect at the femtometer scale that arises from the ambiguity as to which of the nuclei is the source of the photon in the interaction.
A new, more precise measurement of the Λ hyperon lifetime is performed using a large data sample of Pb–Pb collisions at √sNN p ¼ 5.02 TeV with ALICE. The Λ and Λ¯ hyperons are reconstructed at midrapidity using their two-body weak decay channel Λ → p þ π− and Λ¯ → p¯ þ πþ. The measured value of the Λ lifetime is τΛ ¼ ½261.07 0.37ðstat:Þ 0.72ðsyst:Þ ps. The relative difference between the lifetime of Λ and Λ¯ , which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value ðτΛ − τΛ¯Þ=τΛ ¼ 0.0013 0.0028ðstat:Þ 0.0021ðsyst:Þ is consistent with zero within the uncertainties. Both measurements of the Λ hyperon lifetime and of the relative difference between τΛ and τΛ¯ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.
Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at s√=13 TeV and p−Pb collisions at sNN−−−√=5.02 TeV. The correlation functions are measured as a function of relative azimuthal angle Δφ and pseudorapidity separation Δη for pairs of primary charged particles within the pseudorapidity interval |η|<0.9 and the transverse-momentum interval 1<pT<4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6<|Δη|<1.8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.
The inclusive production of the charm-strange baryon Ω0c is measured for the first time via its semileptonic decay into Ω−e+νe at midrapidity (|y| < 0.8) in proton–proton (pp) collisions at the centre-of-mass energy √s = 13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The branching-fraction ratio BR(Ω0c → Ω−e+νe)/BR(Ω0c → Ω−π+) is measured to be 1.12 ± 0.22 (stat.) ± 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.
The inclusive production of the charm-strange baryon Ω0c is measured for the first time via its semileptonic decay into Ω−e+νe at midrapidity (|y| < 0.8) in proton–proton (pp) collisions at the centre-of-mass energy √s = 13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The branching-fraction ratio BR(Ω0c → Ω−e+νe)/BR(Ω0c → Ω−π+) is measured to be 1.12 ± 0.22 (stat.) ± 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.
Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at √sNN = 13 TeV and p–Pb collisions at √s = 5.02 TeV. The correlation functions are measured as a function of relative azimuthal angle ∆φ and pseudorapidity separation ∆η for pairs of primary charged particles within the pseudorapidity interval |η| < 0.9 and the transverse-momentum interval 1 < pT < 4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6 < |∆η| < 1.8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.