The inclusive production of the charm-strange baryon $\Omega^{0}_{\rm c}$ is measured for the first time via its semileptonic decay into $\Omega^{-}\rm e^{+}\nu_{e}$ at midrapidity ($|y|<0.8$) 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 $2<p_{\rm T}<12~{\rm GeV}/c$. The branching-fraction ratio ${\rm BR}(\Omega^0_{\rm c} \rightarrow \Omega^{-}{\rm e}^{+}\nu_{\rm e})/ {\rm BR}(\Omega^0_{\rm c} \rightarrow \Omega^{-}{\pi}^{+})$ is measured to be 1.12 $\pm$ 0.22 (stat.) $\pm$ 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.
The $p_{\rm T}$-differential production cross sections of inclusive $\Omega^0_{\rm c}$ baryons multiplied by the branching ratios (BR) into $\Omega^{-}{\rm e}^{+}\nu_{\rm e}$ in pp collisions at $\sqrt{s} =$ 13 TeV for $|y| < 0.8$.
$p_{\rm T}$-differential branching-fraction ratio ${\rm BR}(\Omega^0_{\rm c}\rightarrow\Omega^{-}{\rm e}^{+}\nu_{\rm e})/{\rm BR}(\Omega^0_{\rm c}\rightarrow\Omega^{-}{\pi}^{+})$.
Comparison of $p_{\rm T}$-independent branching-fraction ratio ${\rm BR}(\Omega^0_{\rm c}\rightarrow\Omega^{-}{\rm e}^{+}\nu_{\rm e})/{\rm BR}(\Omega^0_{\rm c}\rightarrow\Omega^{-}{\pi}^{+})$ between experiments and theoretical calculations.
The two-particle momentum correlation functions between charm mesons ($\mathrm{D^{*\pm}}$ and $\mathrm{D}^\pm$) and charged light-flavor mesons ($\pi^{\pm}$ and K$^{\pm}$) in all charge-combinations are measured for the first time by the ALICE Collaboration in high-multiplicity proton-proton collisions at a center-of-mass energy of $\sqrt{s} =13$ TeV. For $\mathrm{DK}$ and $\mathrm{D^*K}$ pairs, the experimental results are in agreement with theoretical predictions of the residual strong interaction based on quantum chromodynamics calculations on the lattice and chiral effective field theory. In the case of $\mathrm{D}\pi$ and $\mathrm{D^*}\pi$ pairs, tension between the calculations including strong interactions and the measurement is observed. For all particle pairs, the data can be adequately described by Coulomb interaction only, indicating a shallow interaction between charm and light-flavor mesons. Finally, the scattering lengths governing the residual strong interaction of the $\mathrm{D}\pi$ and $\mathrm{D^*}\pi$ systems are determined by fitting the experimental correlation functions with a model that employs a Gaussian potential. The extracted values are small and compatible with zero.
Genuine correlation function for $D^{+}\uppi^{-}$ in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
Genuine correlation function for $D^{+}\uppi^{+}$ in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
Genuine correlation function for $D^{+}K^{-}$ in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
This Letter presents the measurement of near-side associated per-trigger yields, denoted ridge yields, from the analysis of angular correlations of charged hadrons in proton-proton collisions at $\sqrt{s}$ = 13 TeV. Long-range ridge yields are extracted for pairs of charged particles with a pseudorapidity difference of $1.4 < |\Delta\eta| < 1.8$ and a transverse momentum of $1 < p_{\rm T} < 2$ GeV/$c$, as a function of the charged-particle multiplicity measured at midrapidity. This study extends the measurements of the ridge yield to the low multiplicity region, where in hadronic collisions it is typically conjectured that a strongly-interacting medium is unlikely to be formed. The precision of the new low multiplicity results allows for the first direct quantitative comparison with the results obtained in $\mathrm {e^{+}e^{-}}$ collisions at $\sqrt{s}$ = 91 GeV and $\sqrt{s}$ = 183$-$209 GeV, where initial-state effects such as pre-equilibrium dynamics and collision geometry are not expected to play a role. In the multiplicity range $8\lesssim\langle N_\mathrm{ch}\rangle\lesssim 24$ where the $\mathrm {e^{+}e^{-}}$ results have good precision, the measured ridge yields in pp collisions are substantially larger than the limits set in $\mathrm {e^{+}e^{-}}$ annihilations. Consequently, the findings presented in this Letter suggest that the processes involved in $\mathrm {e^{+}e^{-}}$ annihilations do not contribute significantly to the emergence of long-range correlations in pp collisions.
Ridge yield $Y_\mathrm{ridge}$ extracted at $1.4<|\Delta\eta|<1.8$ with $1.0<p_\mathrm{T,trig}<2.0\,\mathrm{GeV}/c$, $1.0<p_\mathrm{T,assoc}<2.0\,\mathrm{GeV}/c$ as a function of charged particle multiplicity counted at midrapidity $|\eta|<1.0$. The first three points at $N_\mathrm{ch}<8$ represent a 95% upper confidence limit where the statistical and systematic uncertainty have been combined.
Measurements of charged-particle production in pp, p$-$Pb, and Pb$-$Pb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum ($p_{\mathrm{T}}^{\rm trig}$) in the range $8<p_{\mathrm{T}}^{\rm trig}<15$ GeV$/c$. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier, $R_{\mathrm{T}}=N_{\mathrm{ch}}^{\mathrm{T}}/\langle N_{\mathrm{ch}}^{\mathrm{T}}\rangle$, is used to group events according to their UE activity, where $N_{\mathrm{ch}}^{\mathrm{T}}$ is the charged-particle multiplicity per event in the transverse region and $\langle N_{\mathrm{ch}}^{\mathrm{T}}\rangle$ is the mean value over the whole analysed sample. The energy dependence of the $R_{\mathrm{T}}$ distributions in pp collisions at $\sqrt{s}=2.76$, 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particle $p_{\rm T}$ spectra as a function of $R_{\mathrm{T}}$ in the three azimuthal regions in pp, p$-$Pb, and Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and p$-$Pb).
$R_\mathrm{T}$ distribution using events with trigger particles $5<p_\mathrm{T}^\mathrm{trig}<40~\mathrm{GeV}/c$ in the pseudorapidity range of $|\eta|<0.8$ and with $p_\mathrm{T}>0.5~\mathrm{GeV}/c$ in pp collisions at $\sqrt{s}=2.76~\mathrm{TeV}$
$R_\mathrm{T}$ distribution using events with trigger particles $5<p_\mathrm{T}^\mathrm{trig}<40~\mathrm{GeV}/c$ in the pseudorapidity range of $|\eta|<0.8$ and with $p_\mathrm{T}>0.5~\mathrm{GeV}/c$ in pp collisions at $\sqrt{s}=5.02~\mathrm{TeV}$
$R_\mathrm{T}$ distribution using events with trigger particles $5<p_\mathrm{T}^\mathrm{trig}<40~\mathrm{GeV}/c$ in the pseudorapidity range of $|\eta|<0.8$ and with $p_\mathrm{T}>0.5~\mathrm{GeV}/c$ in pp collisions at $\sqrt{s}=7~\mathrm{TeV}$
Collective behavior has been observed in high-energy heavy-ion collisions for several decades. Collectivity is driven by the high particle multiplicities that are produced in these collisions. At the CERN Large Hadron Collider (LHC), features of collectivity have also been seen in high-multiplicity proton-proton collisions that can attain particle multiplicities comparable to peripheral Pb-Pb collisions. One of the possible signatures of collective behavior is the decrease of femtoscopic radii extracted from pion and kaon pairs emitted from high-multiplicity collisions with increasing pair transverse momentum. This decrease can be described in terms of an approximate transverse mass scaling. In the present work, femtoscopic analyses are carried out by the ALICE Collaboration on charged pion and kaon pairs produced in pp collisions at $\sqrt{s}=13$ TeV from the LHC to study possible collectivity in pp collisions. The event-shape analysis method based on transverse sphericity is used to select for spherical versus jet-like events, and the effects of this selection on the femtoscopic radii for both charged pion and kaon pairs are studied. This is the first time this selection method has been applied to charged kaon pairs. An approximate transverse-mass scaling of the radii is found in all multiplicity ranges studied when the difference in the Lorentz boost for pions and kaons is taken into account. This observation does not support the hypothesis of collective expansion of hot and dense matter that should only occur in high-multiplicity events. A possible alternate explanation of the present results is based on a scenario of common emission conditions for pions and kaons in pp collisions for the multiplicity ranges studied.
CF vs qinv
CF vs qinv
CF vs qinv
Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at $\sqrt{s}=13$ TeV and p$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The correlation functions are measured as a function of relative azimuthal angle $\Delta\varphi$ and pseudorapidity separation $\Delta\eta$ for pairs of primary charged particles within the pseudorapidity interval $|\eta| < 0.9$ and the transverse-momentum interval $1 < p_{\rm T} < 4$ GeV/$c$. Flow coefficients are extracted for the long-range correlations ($1.6 < |\Delta\eta| <1.8$) 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.
High and low multiplicity long-range delta phi correlations
Jet fragmentation yields of near and away side as a function of multiplicity class and and the ratio of them, please see the definition of x-axis
The second and third harmonic coefficients as a function of transverse momentum in pp and p--Pb collisions.
The ALICE Collaboration reports a search for jet quenching effects in high-multiplicity (HM) proton$-$proton collisions at $\sqrt{s}$ = 13 TeV, using the semi-inclusive azimuthal-difference distribution $\Delta\varphi$ of charged-particle jets recoiling from a high transverse momentum (high-$p_{\mathrm{T,trig}}$) trigger hadron. Jet quenching may broaden the $\Delta\varphi$ distribution measured in HM events compared to that in minimum bias (MB) events. The measurement employs a $p_{\mathrm{T,trig}}$-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.
Probability distribution of $\mathrm{V0M}/\langle \mathrm{V0M} \rangle$ in MB pp collisions measured at $\sqrt{s}=13$ TeV.
Fully-corrected $\Delta_{\mathrm{recoil}} (p_{\mathrm{T, jet}}^{\mathrm{ch}})$ distributions measured in MB and HM-selected events in pp collisions at $\sqrt{s}= 13$ TeV.
Fully-corrected $\Delta_{\mathrm{recoil}} (\Delta\phi)$ distributions for $p_{\mathrm{T, jet}}^{\mathrm{ch}} \in (20, 40)$ GeV/$c$ measured in MB and HM-selected events in pp collisions at $\sqrt{s}= 13$ TeV.
The production yields of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ resonances are measured in pp collisions at $\sqrt{s}=13$ TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$, which is related to the energy density produced in the collision. The results include transverse momentum ($p_{\rm T}$) distributions, $p_{\rm T}$-integrated yields, mean transverse momenta of $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$, as well as ratios of the $p_{\rm T}$-integrated resonance yields relative to yields of other hadron species. The $\Sigma(1385)^{\pm}/\pi^{\pm}$ and $\Xi(1530)^{0}/\pi^{\pm}$ 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 $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ production in pp collisions at $\sqrt{s}=13$ TeV.
Sigma(1385)+ pT spectrum in I+II+III V0M mult class
Sigma(1385)+ pT spectrum in IV+V+VI V0M mult class
Sigma(1385)+ pT spectrum in VII+VIII V0M mult class
The production cross sections of ${\rm D^0}$ and $\Lambda^+_{\rm c}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity ($|y|<0.5$) by the ALICE Collaboration in proton-proton collisions at a center-of-mass energy $\sqrt{s}=13$ TeV. They are described within uncertainties by perturbative QCD calculations employing the fragmentation fractions of beauty quarks to baryons measured at forward rapidity by the LHCb Collaboration. The ${\rm b\overline{b}}$ production cross section per unit of rapidity at midrapidity, estimated from these measurements, is ${\rm d}\sigma_{\rm b\overline{b}}/{\rm d}y|_{|y|<0.5} = 83.1 \pm 3.5 (\mathrm{stat.}) \pm 5.4(\mathrm{syst.}) ^{+12.3}_{-3.2} (\mathrm{extrap.})\,\mu$b. The baryon-to-meson ratios are computed to investigate the hadronization mechanism of beauty quarks. The non-prompt $\Lambda^+_{\rm c}/{\rm D^0}$ production ratio has a similar trend to the one measured for the promptly produced charmed particles and to the p$/\pi^+$ and $\Lambda/{\rm K^0_S}$ ratios, suggesting a similar baryon-formation mechanism among light, strange, charm, and beauty hadrons. The $p_{\rm T}$-integrated non-prompt $\Lambda_{\rm c}/{\rm D^0}$ ratio is found to be significantly higher than the one measured in e$^+$e$^-$ collisions.
$p_{\mathrm{T}}$-differential D$^{0}$ production cross section in pp collisions at $\sqrt{s}$ = 13 TeV
$p_{\mathrm{T}}$-differential $\Lambda_\mathrm{c}^{+}$ production cross section in pp collisions at $\sqrt{s}$ = 13 TeV
$p_{\mathrm{T}}$-differential non-prompt $\Lambda_\mathrm{c}^{+}$/non-prompt D$^{0}$ ratio in pp collisions at $\sqrt{s}$ = 13 TeV
Measurements of the production cross sections of prompt ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{\ast +}}$, ${\rm D_s^+}$, ${\rm \Lambda_{c}^{+}}$, and ${\rm \Xi_{c}^{+}}$ charm hadrons at midrapidity in proton$-$proton collisions at $\sqrt{s}=13$ TeV with the ALICE detector are presented. The D-meson cross sections as a function of transverse momentum ($p_{\rm T}$) are provided with improved precision and granularity. The ratios of $p_{\rm T}$-differential meson production cross sections based on this publication and on measurements at different rapidity and collision energy provide a constraint on gluon parton distribution functions at low values of Bjorken-$x$ ($10^{-5}-10^{-4}$). The measurements of ${\rm \Lambda_{c}^{+}}$ (${\rm \Xi_{c}^{+}}$) baryon production extend the measured $p_{\rm T}$ intervals down to $p_{\rm T}=0(3)$~GeV$/c$. These measurements are used to determine the charm-quark fragmentation fractions and the ${\rm c\overline{c}}$ production cross section at midrapidity ($|y|<0.5$) based on the sum of the cross sections of the weakly-decaying ground-state charm hadrons ${\rm D^0}$, ${\rm D^+}$, ${\rm D_s^+}$, ${\rm \Lambda_{c}^{+}}$, ${\rm \Xi_{c}^{0}}$ and, for the first time, ${\rm \Xi_{c}^{+}}$, and of the strongly-decaying J/$psi$ mesons. The first measurements of ${\rm \Xi_{c}^{+}}$ and ${\rm \Sigma_{c}^{0,++}}$ fragmentation fractions at midrapidity are also reported. A significantly larger fraction of charm quarks hadronising to baryons is found compared to e$^+$e$^-$ and ep collisions. The ${\rm c\overline{c}}$ production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.
$p_{\mathrm{T}}$-differential $\mathrm{D}^{0}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{0}\rightarrow\mathrm{K}^-\pi^+$: $(3.95 \pm 0.03)\%$. Global relative uncertainty on BR: $0.8\%$ Global relative uncertainty on luminosity: $1.6\%$
$p_{\mathrm{T}}$-differential $\mathrm{D}^{+}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{+}\rightarrow\mathrm{K}^-\pi^+\pi^+$: $(9.38 \pm 0.16)\%$. Global relative uncertainty on BR: $1.7\%$ Global relative uncertainty on luminosity: $1.6\%$
$p_{\mathrm{T}}$-differential $\mathrm{D}^{+}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{*+}\rightarrow\mathrm{D}^0(\rightarrow\mathrm{K}^-\pi^+)\pi^+$: $(2.67 \pm 0.03)\%$. Global relative uncertainty on BR: $1.1\%$ Global relative uncertainty on luminosity: $1.6\%$
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