Multiplicity dependence of charged-particle production in pp, p–Pb, Xe–Xe and Pb–Pb collisions at the LHC

Multiplicity (Nch) distributions and transverse momentum (pT) spectra of inclusive primary charged particles in the kinematic range of |η|<0.8 and 0.15 GeV/c<pT<10 GeV/c are reported for pp, p–Pb, Xe–Xe and Pb–Pb collisions at centre-of-mass energies per nucleon pair ranging from sNN=2.76 TeV up to 13 TeV. A sequential two-dimensional unfolding procedure is used to extract the correlation between the transverse momentum of primary charged particles and the charged-particle multiplicity of the corresponding collision. This correlation sharply characterises important features of the final state of a collision and, therefore, can be used as a stringent test of theoretical models. The multiplicity distributions as well as the mean and standard deviation derived from the pT spectra are compared to state-of-the-art model predictions. Providing these fundamental observables of bulk particle production consistently across a wide range of collision energies and system sizes can serve as an important input for tuning Monte Carlo event generators

Measurement of the low-energy antitriton inelastic cross section

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 [Formula presented] 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

Study of the p–p–K+^{+} and p–p–K−^{-} dynamics using the femtoscopy technique

AbstractThe interactions of kaons (K) and antikaons ($$\mathrm {\overline{K}}$$ K ¯ ) with few nucleons (N) were studied so far using kaonic atom data and measurements of kaon production and interaction yields in nuclei. Some details of the three-body KNN and $$\mathrm {\overline{K}}$$ K ¯ NN dynamics are still not well understood, mainly due to the overlap with multi-nucleon interactions in nuclei. An alternative method to probe the dynamics of three-body systems with kaons is to study the final state interaction within triplet of particles emitted in pp collisions at the Large Hadron Collider, which are free from effects due to the presence of bound nucleons. This Letter reports the first femtoscopic study of p–p–K$$^+$$ + and p–p–K$$^-$$ - correlations measured in high-multiplicity pp collisions at $$\sqrt{s}$$ s = 13 TeV by the ALICE Collaboration. The analysis shows that the measured p–p–K$$^+$$ + and p–p–K$$^-$$ - correlation functions can be interpreted in terms of pairwise interactions in the triplets, indicating that the dynamics of such systems is dominated by the two-body interactions without significant contributions from three-body effects or bound states.</jats:p

Multiplicity and event-scale dependent flow and jet fragmentation in pp collisions at s \sqrt{s} = 13 TeV and in p–Pb collisions at sNN \sqrt{s_{\textrm{NN}}} = 5.02 TeV

Abstract Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at $$\sqrt{s}$$ s = 13 TeV and p–Pb collisions at $$\sqrt{s_{\textrm{NN}}}$$ s 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| &lt; 0.9 and the transverse-momentum interval 1 &lt; pT&lt; 4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6 &lt; |∆η| &lt; 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.</jats:p

Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p-Pb collisions

Abstract Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at $$\sqrt{s}$$ s = 13 TeV at midrapidity with the ALICE detector are presented down to a transverse momentum (pT) of 0.2 GeV/c and up to pT = 35 GeV/c, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p-Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the pT range 0.5 &lt; pT&lt; 26 GeV/c at $$\sqrt{s_{\textrm{NN}}}$$ s NN = 8.16 TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p-Pb collisions grow faster than linear with the self-normalised multiplicity. A strong pT dependence is observed in pp collisions, where the yield of high-pT electrons increases faster as a function of multiplicity than the one of low-pT electrons. The measurement in p-Pb collisions shows no pT dependence within uncertainties. The self-normalised yields in pp and p-Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations.</jats:p

<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>K</mml:mi><mml:mo>*</mml:mo></mml:msup><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:mn>892</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>±</mml:mo></mml:msup></mml:mrow></mml:math> resonance production in Pb-Pb collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>5.02</mml:mn></mml:mrow></mml:math> TeV

The production of K∗(892)± meson resonance is measured at midrapidity (|y|8 GeV/c, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium

Production of KS0{\rm K}^{0}_{\rm{S}}, Λ\Lambda (Λˉ\bar{\Lambda}), Ξ±\Xi^{\pm} and Ω±\Omega^{\pm} in jets and in the underlying event in pp and p−-Pb collisions

International audienceThe production of strange hadrons (${\textrm{K}}_{\textrm{S}}^0$, Λ, Ξ$^{±}$, and Ω$^{±}$), baryon-to-meson ratios (Λ/${\textrm{K}}_{\textrm{S}}^0$, Ξ/${\textrm{K}}_{\textrm{S}}^0$, and Ω/${\textrm{K}}_{\textrm{S}}^0$), and baryon-to-baryon ratios (Ξ/Λ, Ω/Λ, and Ω/Ξ) associated with jets and the underlying event were measured as a function of transverse momentum (p$_{T}$) in pp collisions at $\sqrt{s}$ = 13 TeV and p Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV with the ALICE detector at the LHC. The inclusive production of the same particle species and the corresponding ratios are also reported. The production of multi-strange hadrons, Ξ$^{±}$ and Ω$^{±}$, and their associated particle ratios in jets and in the underlying event are measured for the first time. In both pp and p–Pb collisions, the baryon-to-meson and baryon-to-baryon yield ratios measured in jets differ from the inclusive particle production for low and intermediate hadron p$_{T}$ (0.6–6 GeV/c). Ratios measured in the underlying event are in turn similar to those measured for inclusive particle production. In pp collisions, the particle production in jets is compared with Pythia 8 predictions with three colour-reconnection implementation modes. None of them fully reproduces the data in the measured hadron p$_{T}$ region. The maximum deviation is observed for Ξ$^{±}$ and Ω$^{±}$ which reaches a factor of about six. The event multiplicity dependence is further investigated in p−Pb collisions. In contrast to what is observed in the underlying event, there is no significant event-multiplicity dependence for particle production in jets. The presented measurements provide novel constraints on hadronisation and its Monte Carlo description. In particular, they demonstrate that the fragmentation of jets alone is insufficient to describe the strange and multi-strange particle production in hadronic collisions at LHC energies.[graphic not available: see fulltext