The pseudorapidity density of charged particles with minimum transverse momentum ($p_{\rm T}$) thresholds of 0.15, 0.5, 1, and 2 GeV$/c$ is measured in pp collisions at the centre of mass energies of $\sqrt{s} =$ 5.02 and 13 TeV with the ALICE detector. The study is carried out for inelastic collisions with at least one primary charged particle having a pseudorapidity ($\eta$) within $\pm0.8$ and $p_{\rm T}$ larger than the corresponding threshold. In addition, measurements without $p_{\rm T}$-thresholds are performed for inelastic and non-single-diffractive events as well as for inelastic events with at least one charged particle having $|\eta|<1$ in pp collisions at $\sqrt{s} =$ 5.02 TeV for the first time at the LHC. These measurements are compared to the PYTHIA 6, PYTHIA 8, and EPOS-LHC models. In general, the models describe the $\eta$ dependence of particle production well. However, discrepancies are observed for the highest transverse momentum threshold ($p_{\rm T}>2 {\rm\ GeV}/c$), highlighting the importance of such measurements for tuning event generators. The new measurements agree within uncertainties with results from the ATLAS and CMS experiments obtained at $\sqrt{s} = 13$ TeV.
The distributions of $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ for INEL event classes in pp collisions at $\sqrt{s} = 5.02$ TeV
The distributions of $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ for NSD event classes in pp collisions at $\sqrt{s} = 5.02$ TeV
The distributions of $\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta$ for INEL>0 event classes in pp collisions at $\sqrt{s} = 5.02$ TeV
The transverse-momentum ($p_{\rm T}$) spectra and coalescence parameters $B_2$ of (anti)deuterons are measured in pp collisions at $\sqrt{s} = 13$ TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest $p_{\rm T}$ in the event ($p_{\rm T}^{\rm{ lead}} > 5$ GeV/$c$) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions and the jet signal is obtained as the difference between the Toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the Transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons inside the jet cone as compared to the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase space distributions of nucleons are generated using PYTHIA 8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in PYTHIA 8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the $B^{\rm Jet}_2$ is not reproduced by the models, which instead give a decreasing trend.
Transverse momentum spectra for the transverse azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).
Transverse momentum spectra for the toward azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).
Transverse momentum spectra for the away azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).
Multiplicity ($N_{\rm ch}$) distributions and transverse momentum ($p_{\rm T}$) spectra of inclusive primary charged particles in the kinematic range of $|\eta| < 0.8$ and 0.15 GeV/$c$$< p_{T} <$ 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 $\sqrt{s_{\rm NN}} = 2.76$ 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 $p_{\rm T}$ 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.
Charged-particle multiplicity distribution for pp collisions at 2.76 TeV.
Koba-Nielsen-Olesen scaled charged-particle multiplicity distribution for pp collisions at 2.76 TeV.
Charged-particle transverse momentum spectra as a function of charged-particle multiplicity for pp collisions at 2.76 TeV.
The production of strange hadrons (K$^{0}_{\rm S}$, $\Lambda$, $\Xi^{\pm}$, and $\Omega^{\pm}$), baryon-to-meson ratios ($\Lambda/{\rm K}^0_{\rm S}$, $\Xi/{\rm K}^0_{\rm S }$, and $\Omega/{\rm K}^0_{\rm S}$), and baryon-to-baryon ratios ($\Xi/\Lambda$, $\Omega/\Lambda$, and $\Omega/\Xi$) associated with jets and the underlying event were measured as a function of transverse momentum ($p_{\rm T}$) in pp collisions at $\sqrt{s} = 13$ TeV and p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ 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, $\Xi^{\pm}$ and $\Omega^{\pm}$, 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 $p_{\rm T}$ (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 $p_{\rm T}$ region. The maximum deviation is observed for $\Xi^{\pm}$ and $\Omega^{\pm}$, which reaches a factor of about six. In p-Pb collisions, there is no significant event-multiplicity dependence for particle production in jets, in contrast to what is observed in the underlying event. 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.
$p_{\rm T}$-differential density of inclusive ${\rm K}_{\rm S}^{0}$ and $\Lambda$ ($\overline{\Lambda}$) in pp collisions at $\sqrt{s} = 13$ TeV.
$p_{\rm T}$-differential densities of ${\rm K}_{\rm S}^{0}$ and $\Lambda$ ($\overline{\Lambda}$) in jets and the underlying event in pp collisions at $\sqrt{s} = 13$ TeV.
$p_{\rm T}$-differential density of inclusive $\Xi^{\pm}$ in pp collisions at $\sqrt{s} = 13$ TeV.
The measurement of $\Upsilon$(1S), $\Upsilon$(2S), and $\Upsilon$(3S) yields as a function of the charged-particle multiplicity density, $\textrm{d}N_{\textrm{ch}}/\textrm{d}\eta$, using the ALICE experiment at the LHC, is reported in pp collisions at $\sqrt{s} =$ 13 TeV. The $\Upsilon$ meson yields are measured at forward rapidity ($2.5 < y < 4$) in the dimuon decay channel, whereas the charged-particle multiplicity is defined at central rapidity ($|\eta| < 1$). Both quantities are divided by their average value in minimum bias events to compute the self-normalized quantities. The increase of the self-normalized $\Upsilon$(1S), $\Upsilon$(2S), and $\Upsilon$(3S) yields is found to be compatible with a linear scaling with the self-normalized $\textrm{d}N_{\textrm{ch}}/\textrm{d}\eta$, within the uncertainties. The self-normalized yield ratios of excited-to-ground $\Upsilon$ states are compatible with unity within uncertainties. Similarly, the measured double ratio of the self-normalized $\Upsilon$(1S) to the self-normalized J/$\psi$ yields, both measured at forward rapidity, is compatible with unity for self-normalized charged-particle multiplicities beyond one. The measurements are compared with theoretical predictions incorporating initial or final state effects.
Self-normalized Upsilon(1S) yield as a function of the self-normalized charged-particle multiplicity.
Self-normalized Upsilon(2S) yield as a function of the self-normalized charged-particle multiplicity.
Self-normalized Upsilon(3S) yield as a function of the self-normalized charged-particle multiplicity.
Three-body nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the three-nucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the three-body forces. In this work, we present the first direct measurement of the p$-$p$-$p and p$-$p$-\Lambda$ systems in terms of three-particle correlation functions carried out for pp collisions at $\sqrt{s} = 13$ TeV. Three-particle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the three-particle interaction contribution to these correlations can be isolated after subtracting the known two-body interaction terms. A negative cumulant is found for the p$-$p$-$p system, hinting to the presence of a residual three-body effect while for p$-$p$-\Lambda$ the cumulant is consistent with zero. This measurement demonstrates the accessibility of three-baryon correlations at the LHC.
The (p-p)-p correlation function obtained using the data-driven approach
The (p-p)-$\Lambda$ correlation function obtained using the data-driven approach
The p-(p-$\Lambda$) correlation function obtained using the data-driven approach
The inclusive production of the charm-strange baryon $\rm \Omega_c^0$ is measured for the first time via its hadronic decay into $\rm \Omega^-\pi^+$ at midrapidity ($|y|<0.5$) in proton-proton (pp) collisions at the centre-of-mass energy $\sqrt{s}=13$ TeV with the ALICE detector at the LHC. The transverse momentum ($p_{\rm T}$) differential cross section multiplied by the branching ratio is presented in the interval $2
The $p_{\rm T}$-differential production cross section of inclusive $\rm \Omega_c^0$ baryons multiplied by the branching ratio into $\rm \Omega^-\pi^+$ for $|{\it y}|<0.5$ in pp collisions at $\sqrt{s}=13$ TeV.
$\rm BR(\Omega_{c}^{0} \rightarrow \Omega^{-}\pi^{+}) \times {\it \sigma}(\Omega_{c}^{0})/{\it \sigma}(D^{0})$ as a function of $p_{\rm T}$ in pp collisions at $\sqrt{s}=13$ TeV for $|{\it y}|<0.5$.
$\rm BR(\Omega_{c}^{0} \rightarrow \Omega^{-}\pi^{+}) \times {\it \sigma}(\Omega_{c}^{0})/{\it \sigma}(\Xi_c^0)$ as a function of $p_{\rm T}$ in pp collisions at $\sqrt{s}=13$ TeV for $|{\it y}|<0.5$.
The first experimental information on the strong interaction between $\Lambda$ and $\Xi^-$ strange baryons is presented in this Letter. The correlation function of $\Lambda-\Xi^-$ and $\overline{\Lambda}-\overline{\Xi}^{+}$ pairs produced in high-multiplicity proton-proton (pp) collisions at $\sqrt{s}$ = 13 TeV at the LHC is measured as a function of the relative momentum of the pair. The femtoscopy method is used to calculate the correlation function, which is then compared with theoretical expectations obtained using a meson exchange model, chiral effective field theory, and Lattice QCD calculations close to the physical point. Data support predictions of small scattering parameters while discarding versions with large ones, thus suggesting a weak $\Lambda-\Xi^{-}$ interaction. The limited statistical significance of the data does not yet allow one to constrain the effects of coupled channels like $\Sigma-\Xi$ and N$-\Omega$.
The $\Lambda$--$\Xi^{-}$ $\oplus$ $\overline{\Lambda}$--$\overline{\Xi}^{+}$ correlation function and the $\lambda$ parameters with the parametrization of the background contribution $C_\mathrm{mis.}(k^*)$
The measurement of the production of charm jets, identified by the presence of a ${\rm D^0}$ meson in the jet constituents, is presented in proton-proton collisions at centre-of-mass energies of $\sqrt{s}$ = 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The ${\rm D^0}$ mesons were reconstructed from their hadronic decay ${\rm D^0} \rightarrow {\rm K^-}\pi^+$ and the respective charge conjugate. Jets were reconstructed from ${\rm D^0}$-meson candidates and charged particles using the anti-$k_{\rm T}$ algorithm, in the jet transverse momentum range $5
$p_{\mathrm{T,ch\ jet}}$-differential cross section of charm jets tagged with $\mathrm{D^{0}}$ mesons for $R=0.2$, $0.4$, and $0.6$ in pp collisions at $\sqrt{s}=13$ TeV.
$p_{\mathrm{T,ch\ jet}}$-differential cross section of charm jets tagged with $\mathrm{D^{0}}$ mesons for $R=0.2$, $0.4$, and $0.6$ in pp collisions at $\sqrt{s}=5.02$ TeV.
Ratio of $p_{\mathrm{T,ch\ jet}}$-differential cross section of charm jets tagged with $\mathrm{D^{0}}$ mesons in pp collisions at $\sqrt{s}=13$ TeV to $\sqrt{s}=5.02$ TeV for $R=0.2$, $0.4$, and $0.6$.
Production of inclusive charmonia in pp collisions at center-of-mass energy of $\sqrt{s}$ = 13 TeV and p-Pb collisions at center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/$\psi$, $\psi$(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame $2.5 < y_{\rm cms} < 4.0$ for pp collisions, and $2.03 < y_{\rm cms} < 3.53$ and $-4.46 < y_{\rm cms} < -2.96$ for p-Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity ($|\eta|<1.0$). 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 $\psi$(2S) yield increases with the charged-particle pseudorapidity density. The ratio of $\psi$(2S) over J/$\psi$ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/$\psi$ and $\psi$(2S) yields with respect to charged-particle pseudorapidity density. Results for the $\psi$(2S) yield and its ratio with respect to J/$\psi$ agree with available model calculations.
Ratio of measured PSI(2S) cross section in charged-particle multiplicity intervals and integrated in multiplicity.
Ratio of measured PSI(2S) cross section in charged-particle multiplicity intervals and integrated in multiplicity.
Ratio of measured PSI(2S) cross section in charged-particle multiplicity intervals and integrated in multiplicity.
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