Abstract The measurements of the production of prompt $${{\mathrm{D}}^0}$$ D0 , $${{\mathrm{D}}^+}$$ D+ , $${{\mathrm{D}}^{*+}}$$ D∗+ , and $${{\mathrm{D}}^+_{\mathrm{s}}}$$ Ds+ mesons in ...proton–proton (pp) collisions at $$\sqrt{s}=5.02~\mathrm {TeV}$$ s=5.02TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity ($$|y|<0.5$$ |y|<0.5 ) via their hadronic decay channels $$\mathrm{D}^0 \rightarrow {\mathrm{K}}^-\pi ^+$$ D0→K-π+ , $$\mathrm{D}^+\rightarrow {\mathrm{K}}^-\pi ^+\pi ^+$$ D+→K-π+π+ , $${\mathrm{D}}^{*+} \rightarrow {\mathrm{D}}^0 \pi ^+ \rightarrow {\mathrm{K}}^- \pi ^+ \pi ^+$$ D∗+→D0π+→K-π+π+ , $${{\mathrm{D}}^{+}_{\mathrm{s}}\rightarrow \phi \pi ^+\rightarrow {\mathrm{K}}^{+} {\mathrm{K}}^{-} \pi ^{+}}$$ Ds+→ϕπ+→K+K-π+ , and their charge conjugates. The production cross sections were measured in the transverse momentum interval $$0<p_{\mathrm{T}}<36~\mathrm {GeV}/c$$ 0<pT<36GeV/c for $${{\mathrm{D}}^0}$$ D0 , $$1<p_{\mathrm{T}}<36~\mathrm {GeV}/c$$ 1<pT<36GeV/c for $${{\mathrm{D}}^+}$$ D+ and $${{\mathrm{D}}^{*+}}$$ D∗+ , and in $$2<p_{\mathrm{T}}<24~\mathrm {GeV}/c$$ 2<pT<24GeV/c for $${{\mathrm{D}}^+_{\mathrm{s}}}$$ Ds+ mesons. Thanks to the higher integrated luminosity, an analysis in finer $$p_{\mathrm{T}}$$ pT bins with respect to the previous measurements at $$\sqrt{s}=7~\mathrm {TeV}$$ s=7TeV was performed, allowing for a more detailed description of the cross-section $$p_{\mathrm{T}}$$ pT shape. The measured $$p_{\mathrm{T}}$$ pT -differential production cross sections are compared to the results at $$\sqrt{s}=7$$ s=7 TeV and to four different perturbative QCD calculations. Its rapidity dependence is also tested combining the ALICE and LHCb measurements in pp collisions at $$\sqrt{s}=5.02~\mathrm {TeV}$$ s=5.02TeV . This measurement will allow for a more accurate determination of the nuclear modification factor in p–Pb and Pb–Pb collisions performed at the same nucleon–nucleon centre-of-mass energy.
Abstract The pseudorapidity density of charged particles, $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη , in p–Pb collisions has been measured at a centre-of-mass energy per nucleon–nucleon ...pair of $$\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}$$ sNN = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, $$|\eta |<1.8$$ |η|<1.8 . The $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη value is $$19.1\pm 0.7$$ 19.1±0.7 at $$|\eta |<0.5$$ |η|<0.5 . This quantity divided by $$\langle N_{\mathrm{part}} \rangle $$ ⟨Npart⟩ / 2 is $$4.73\pm 0.20$$ 4.73±0.20 , where $$\langle N_{\mathrm{part}} \rangle $$ ⟨Npart⟩ is the average number of participating nucleons, is 9.5% higher than the corresponding value for p–Pb collisions at $$\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}$$ sNN = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agree within uncertainties with data in the Pb-going side, while HIJING overestimates, showing a symmetric behaviour, and EPOS underestimates the p-going side of the $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη distribution. Saturation-based models reproduce the distributions well for $$\eta >-1.3$$ η>-1.3 . The $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη is also measured for different centrality estimators, based both on the charged-particle multiplicity and on the energy deposited in the Zero-Degree Calorimeters. A study of the implications of the large multiplicity fluctuations due to the small number of participants for systems like p–Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity.
Abstract First results on $$\hbox {K}/\pi $$ K/π , $$\hbox {p}/\pi $$ p/π and K/p fluctuations are obtained with the ALICE detector at the CERN LHC as a function of centrality in $$\text{ Pb--Pb }$$ ...Pb--Pb collisions at $$\sqrt{s_\mathrm{{NN}}} =2.76\hbox { TeV}$$ sNN=2.76TeV . The observable $$\nu _{\mathrm{dyn}}$$ νdyn , which is defined in terms of the moments of particle multiplicity distributions, is used to quantify the magnitude of dynamical fluctuations of relative particle yields and also provides insight into the correlation between particle pairs. This study is based on a novel experimental technique, called the Identity Method, which allows one to measure the moments of multiplicity distributions in case of incomplete particle identification. The results for $$\hbox {p}/\pi $$ p/π show a change of sign in $$\nu _{\mathrm{dyn}}$$ νdyn from positive to negative towards more peripheral collisions. For central collisions, the results follow the smooth trend of the data at lower energies and $$\nu _{\mathrm{dyn}}$$ νdyn exhibits a change in sign for $$\hbox {p}/\pi $$ p/π and K/p.
Abstract The ALICE Collaboration reports a search for jet quenching effects in high-multiplicity (HM) proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV, using the semi-inclusive ...azimuthal-difference distribution ∆φ of charged-particle jets recoiling from a high transverse momentum (high-p T,trig) trigger hadron. Jet quenching may broaden the ∆φ distribution measured in HM events compared to that in minimum bias (MB) events. The measurement employs a p T,trig-differential observable for data-driven suppression of the contribution of multiple partonic interactions, which is the dominant background. While azimuthal broadening is indeed observed in HM compared to MB events, similar broadening for HM events is observed for simulations based on the PYTHIA 8 Monte Carlo generator, which does not incorporate jet quenching. Detailed analysis of these data and simulations show that the azimuthal broadening is due to bias of the HM selection towards events with multiple jets in the final state. The identification of this bias has implications for all jet quenching searches where selection is made on the event activity.
Abstract Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV and ...the corresponding nuclear modification factor R pPb ch jet $$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region |η jet| < 0.5 from charged particles using the anti-k T algorithm with resolution parameters R = 0.2, 0.3, and 0.4. The p T-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10 < p T , jet ch $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 140 GeV/c and 10 < p T , jet ch $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 160 GeV/c, respectively, together with the nuclear modification factor R pPb ch jet $$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ in the range 10 < p T , jet ch $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 140 GeV/c. The analysis extends the p T range of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD Powheg calculations with parton shower provided by Pythia8 as well as by Jetscape simulations.
Abstract The production yields of the Σ(1385) ± and Ξ(1530)0 resonances are measured in pp collisions at s $$ \sqrt{s} $$ = 13 TeV with ALICE. The measurements are performed as a function of the ...charged-particle multiplicity ⟨dN ch /dη⟩, which is related to the energy density produced in the collision. The results include transverse momentum (p T) distributions, p T-integrated yields, mean transverse momenta of Σ(1385) ± and Ξ(1530)0, as well as ratios of the p T-integrated resonance yields relative to yields of other hadron species. The Σ(1385) ± /π ± and Ξ(1530)0 /π ± yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the Σ(1385) ± and Ξ(1530)0 production in pp collisions at s $$ \sqrt{s} $$ = 13 TeV.
Abstract Results on the transverse spherocity dependence of light-flavor particle production (π, K, p, ϕ, K*0, K S 0 $$ {\textrm{K}}_{\textrm{S}}^0 $$ , Λ, Ξ) at midrapidity in high-multiplicity pp ...collisions at s $$ \sqrt{s} $$ = 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator S O p T = 1 $$ \left({S}_{\textrm{O}}^{p_{\textrm{T}}=1}\right) $$ categorizes events by their azimuthal topology. Utilizing narrow selections on S O p T = 1 $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The S O p T = 1 $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ estimator is found to effectively constrain the hardness of the events when the midrapidity (|η| < 0.8) estimator is used. The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced. The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of S O p T = 1 $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ .
Abstract Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at s $$ \sqrt{s} $$ = 13 TeV and p–Pb collisions at s NN ...$$ \sqrt{s_{\textrm{NN}}} $$ = 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 < p T < 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.
Abstract 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 s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV are extended to a pseudorapidity gap of ∆η ~ 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 ∆η ~ 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, v 2(η), is extracted from the long-range correlations. The v 2(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 v 2(η) measurements are compared with 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.
Abstract The transverse momentum (p T) and centrality dependence of the nuclear modification factor R AA of prompt and non-prompt J/ψ, the latter originating from the weak decays of beauty hadrons, ...have been measured by the ALICE collaboration in Pb–Pb collisions at s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV. The measurements are carried out through the e+e − decay channel at midrapidity (|y| < 0.9) in the transverse momentum region 1.5 < p T < 10 GeV/c. Both prompt and non-prompt J/ψ measurements indicate a significant suppression for p T > 5 GeV/c, which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping p T intervals, and cover the kinematic region down to p T = 1.5 GeV/c at midrapidity, not accessible by other LHC experiments. The suppression of prompt J/ψ in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J/ψ production from recombination of c and c ¯ $$ \overline{\textrm{c}} $$ quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J/ψ. For non-prompt J/ψ, the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quark-gluon plasma is consistent with measurements within uncertainties.
PDF