We report on the measurement of inclusive, non-prompt, and prompt J/$ψ$-hadron correlations by the ALICE Collaboration at the CERN Large Hadron Collider in pp collisions at a center-of-mass energy of $13~\text{TeV}$. The correlations are studied at midrapidity ($|y| < 0.9$) in the transverse momentum ranges $p_{\rm T} < 40~\text{GeV}/c$ for the J/$ψ$ and $0.15 < p_{\rm T} < 10~\text{GeV}/c$ and $|η|<0.9$ for the associated hadrons. The measurement is based on minimum bias and high multiplicity data samples corresponding to integrated luminosities of $L_{\text{int}} = 34~\text{nb}^{-1}$ and $L_{\text{int}} = 6.9~\text{pb}^{-1}$, respectively. In addition, two more data samples are employed, requiring, on top of the minimum bias condition, a threshold on the tower energy of $E = 4$ and $9~\text{GeV}$ in the ALICE electromagnetic calorimeters, which correspond to integrated luminosities of $L_{\text{int}} = 0.9~\text{pb}^{-1}$ and $L_{\text{int}} = 8.4~\text{pb}^{-1}$, respectively. The azimuthally integrated near and away side yields of associated charged hadrons per J/$ψ$ trigger are presented as a function of the J/$ψ$ and associated hadron transverse momentum. The measurements are discussed in comparison to PYTHIA calculations.
Near side asociated charged particle yield per trigger in the range $0.15<p_T<1$ GeV/$c$ for inclusive J/$\psi$, as a function of $p_T$, using the MB and EMCal event samples.
Near side asociated charged particle yield per trigger in the range $0.15<p_T<1$ GeV/$c$ for inclusive J/$\psi$, as a function of $p_T$, using the HM event samples.
Near side asociated charged particle yield per trigger in the range $0.15<p_T<1$ GeV/$c$ for prompt J/$\psi$, as a function of $p_T$, using the MB and EMCal event samples.
Short-range correlations between charged particles are studied via two-particle angular correlations in pp collisions at ${\sqrt{{\textit s}}}=13$~TeV. The correlation functions are measured as a function of the relative azimuthal angle $\Delta\varphi$ and the pseudorapidity separation $\Delta\eta$ for pairs of primary charged particles within the pseudorapidity interval $|\eta| < 0.9$ and the transverse-momentum range $1 < p_{\rm T} < 8$ GeV/$c$. Near-side ($|\Delta\varphi|<1.3$) peak widths are extracted from a generalised Gaussian fitted over the correlations in full pseudorapidity separation ($|\Delta\eta|<1.8$), while the per-trigger associated near-side yields are extracted for the short-range correlations ($|\Delta\eta|<1.3$). Both are evaluated as a function of charged-particle multiplicity obtained by two different event activity estimators. The width of the near-side peak decreases with increasing multiplicity, and this trend is reproduced qualitatively by the Monte Carlo event generators PYTHIA 8, AMPT, and EPOS. However, the models overestimate the width in the low transverse-momentum region ($p_{\rm T} < 3$ GeV/$c$). The per-trigger associated near-side yield increases with increasing multiplicity. Although this trend is also captured qualitatively by the considered event generators, the yield is mostly overestimated by the models in the considered kinematic range. The measurement of the shape and yield of the short-range correlation peak can help us understand the interplay between jet fragmentation and event activity, quantify the narrowing trend of the near-side peak as a function of transverse momentum and multiplicity selections in pp collisions, and search for final-state jet modification in small collision systems.
Multiplicity dependence of the near-side width $\sigma$ in pp collisions at $\sqrt{s_{\rm NN}} = 13$ TeV. Obtained in transverse momentum intervals $1.0 < p_\mathrm{T, assoc} < p_\mathrm{T, trig} < 2.0$ GeV/$c$. The multiplicity is estimated with midrapidity multiplicity estimator ($|\eta|<1.0,\,p_\mathrm{T}>0.2$ GeV/$c$).
Multiplicity dependence of the near-side width $\sigma$ in pp collisions at $\sqrt{s_{\rm NN}} = 13$ TeV. Obtained in transverse momentum intervals $2.0 < p_\mathrm{T, trig} < 3.0$ GeV/$c$ and $1.0 < p_\mathrm{T, assoc} < 2.0$ GeV/$c$. The mulitplicity is estimated with midrapidity multiplicity estimator ($|\eta|<1.0,\,p_\mathrm{T}>0.2$ GeV/$c$).
Multiplicity dependence of the near-side width $\sigma$ in pp collisions at $\sqrt{s_{\rm NN}} = 13$ TeV. Obtained in transverse momentum intervals $2.0 < p_\mathrm{T, assoc} < p_\mathrm{T, trig} < 3.0$ GeV/$c$. The multiplicity is estimated with midrapidity multiplicity estimator ($|\eta|<1.0,\,p_\mathrm{T}>0.2$ GeV/$c$).
The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of $\sqrt{s}=13$ TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of $|\eta^{\gamma}|<0.67$ and a transverse momentum range of $7<p_{\rm T}^{\gamma}<200$ GeV/$c$. The result extends to lower $p_{\rm T}^{\gamma}$ and $x_{\rm T}^{\gamma} = 2p_{\rm T}^{\gamma}/\sqrt{s}$ ranges, the lowest $x_{\rm T}^{\gamma}$ of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower $p_{\rm T}^{\gamma}$ at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties.
Differential cross section of isolated photons measured in pp collisions at 13 TeV.
pQCD NLO calculations with JETPHOX of the isolated-photon cross section as a function of $p_\mathrm{T}^{\gamma}$. The calculations were obtained by choosing factorisation, normalisation, and fragmentation scales equal to the photon transverse momentum ($\mu_{f}=\mu_{R}=\mu_{F}=p_\mathrm{T}^{\gamma}$). The parton distribution function used in the calculations is NNPDF4.0, and the fragmentation function is BFG II.
Ratio of isolated-photon cross sections measured in pp collisions at $\sqrt{s}=$13 TeV over the previous ALICE measurement at $\sqrt{s}=$7 TeV.
The transverse momentum ($p_{\rm T}$) differential production cross section of the promptly produced charm-strange baryon $\Xi_{\rm c}^{0}$ (and its charge conjugate $\overline{\Xi_{\rm c}^{0}}$) is measured at midrapidity via its hadronic decay into ${\rm \pi^{+}}\Xi^{-}$ in p$-$Pb collisions at a centre-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV with the ALICE detector at the LHC. The $\Xi_{\rm c}^{0}$ nuclear modification factor ($R_{\rm pPb}$), calculated from the cross sections in pp and p$-$Pb collisions, is presented and compared with the $R_{\rm pPb}$ of $\Lambda_{\rm c}^{+}$ baryons. The ratios between the $p_{\rm T}$-differential production cross section of $\Xi_{\rm c}^{0}$ baryons and those of $\mathrm {D^0}$ mesons and $\Lambda_{\rm c}^{+}$ 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 $\Xi^0_{\rm c}$ 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 that includes string formation beyond leading-colour approximation or in which hadronisation is implemented via quark coalescence. The $p_{\rm T}$-integrated cross section of prompt $\Xi^0_{\rm c}$-baryon production at midrapidity extrapolated down to $p_{\rm T}$ = 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.
Prompt $\Xi_\mathrm{c}^0$ productions cross-section as a function of $p_\mathrm{T}$ in p–Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
$\Xi_\mathrm{c}^0~R_\mathrm{pPb}$ as a function of $p_\mathrm{T}$ in p–Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
$\Xi_\mathrm{c}^0/\mathrm{D}^0$ ratio as a function of $p_\mathrm{T}$ in p–Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
A study of strange hadron production associated with hard scattering processes and with the underlying event is conducted to investigate the origin of the enhanced production of strange hadrons in small collision systems characterised by large charged-particle multiplicities. For this purpose, the production of the single-strange meson ${\rm K^0_S}$ and the double-strange baryon $\Xi^{\pm}$ is measured, in each event, in the azimuthal direction of the highest-$p_{\rm T}$ particle (``trigger" particle), related to hard scattering processes, and in the direction transverse to it in azimuth, associated with the underlying event, in pp collisions at $\sqrt{s}=5.02$ TeV and $\sqrt{s}=13$ TeV using the ALICE detector at the LHC. The per-trigger yields of ${\rm K^0_S}$ and $\Xi^{\pm}$ are dominated by the transverse-to-leading production (i.e., in the direction transverse to the trigger particle), whose contribution relative to the toward-leading production is observed to increase with the event charged-particle multiplicity. The transverse-to-leading and the toward-leading $\Xi^{\pm}$/${\rm K^0_S}$ yield ratios increase with the multiplicity of charged particles, suggesting that strangeness enhancement with multiplicity is associated with both hard scattering processes and the underlying event. The relative production of $\Xi^{\pm}$ with respect to ${\rm K^0_S}$ is higher in transverse-to-leading processes over the whole multiplicity interval covered by the measurement. The ${\rm K}^{0}_{\rm{S}}$ and $\Xi^{\pm}$ per-trigger yields and yield ratios are compared with predictions of three different phenomenological models, namely PYTHIA 8.2 with the Monash tune, PYTHIA 8.2 with ropes and EPOS LHC. The comparison shows that none of them can quantitatively describe either the transverse-to-leading or the toward-leading yields of ${\rm K}^{0}_{\rm{S}}$ and $\Xi^{\pm}$.
Yields of $\rm K^{0}_\rm{S}$ per trigger particle per unit $\Delta\eta\Delta\varphi$ area in pp collisions at $\sqrt{s}=13$ TeV, as a function of the $\rm K^{0}_\rm{S}$ $p_\rm{T}$. Trigger particles are charged particles with $p_\rm{T}>3$ GeV/c. The trigger-particle-$\rm K^{0}_\rm{S}$ correlation is integrated in the ranges $-1.2<\Delta\eta<1.2$ and $-\pi/2<\Delta\varphi<3/2\pi$.
Transverse-to-leading yields of $\rm K^{0}_\rm{S}$ per trigger particle per unit $\Delta\eta\Delta\varphi$ area in pp collisions at $\sqrt{s}=13$ TeV, as a function of the $\rm K^{0}_\rm{S}$ $p_\rm{T}$. Trigger particles are charged particles with $p_\rm{T}>3$ GeV/c. The trigger-particle-$\rm K^{0}_\rm{S}$ correlation is integrated in the ranges $0.86<|\Delta\eta|<1.2$ and $0.96<\Delta\varphi<1.8$.
Toward-leading yields of $\rm K^{0}_\rm{S}$ per trigger particle per unit $\Delta\eta\Delta\varphi$ area in pp collisions at $\sqrt{s}=13$ TeV, as a function of the $\rm K^{0}_\rm{S}$ $p_\rm{T}$. Trigger particles are charged particles with $p_\rm{T}>3$ GeV/c. The trigger-particle-$\rm K^{0}_\rm{S}$ correlation is integrated in the ranges $|\Delta\eta|<0.86$ and $|\Delta\varphi|<1.1$.
The total charm-quark production cross section per unit of rapidity $\mathrm{d}\sigma({\rm c\overline{c}})/\mathrm{d}y$, and the fragmentation fractions of charm quarks to different charm-hadron species $f(\mathrm{c}\rightarrow {\rm h_{c}})$, are measured for the first time in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV at midrapidity ($-0.96<y<0.04$ in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species: $\mathrm{D}^{0}$, $\mathrm{D}^{+}$, $\mathrm{D}_\mathrm{s}^{+}$, and $\mathrm{J/\psi}$ mesons, and $\Lambda_\mathrm{c}^{+}$ and $\Xi_{\rm c}^{0}$ baryons. The resulting cross section is $\mathrm{d}\sigma({\rm c\overline{c}})/\mathrm{d}y =219.6 \pm 6.3\;(\mathrm{stat.}) {\;}_{-11.8}^{+10.5}\;(\mathrm{syst.}) {\;}_{-2.9}^{+8.3}\;(\mathrm{extr.})\pm 5.4\;(\mathrm{BR})\pm 4.6\;(\mathrm{lumi.}) \pm 19.5\;(\text{rapidity shape})+15.0\;(\Omega_{\rm c}^{0})$ mb, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at $\sqrt{s} = 5.02$ and $13$ TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p$-$Pb collisions compared with $\mathrm{e^{+}e^{-}}$ and $\mathrm{e^{-}p}$ collisions. The $p_\mathrm{T}$-integrated nuclear modification factor of charm quarks, $R_\mathrm{pPb}({\rm c\overline{c}})= 0.91 \pm 0.04\;{\rm (stat.)}{}^{+0.08}_{-0.09}\;{\rm (syst.)}{}^{+0.05}_{-0.03}\;{\rm (extr.)}{}\pm 0.03\;{\rm (lumi.)}$, is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.
The $p_\mathrm{T}$-integrated rapidity-differential cross sections for all measured charm-hadron species at midrapidity in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
The fragmentation fractions $f(\mathrm{c}\rightarrow\mathrm{h}_{\mathrm{c}})$ of charm hadrons in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
The total $\mathrm{c\overline{c}}$ production cross section at midrapidity in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
Measurements of the $p_{\rm T}$-dependent flow vector fluctuations in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}} = 5.02~\mathrm{TeV}$ using azimuthal correlations with the ALICE experiment at the Large Hadron Collider are presented. A four-particle correlation approach [1] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the $p_{\rm T}$-dependent flow vector fluctuations at $\sqrt{s_{_{\rm NN}}} = 5.02~\mathrm{TeV}$ with two-particle correlations. Significant $p_{\rm T}$-dependent fluctuations of the $\vec{V}_{2}$ flow vector in Pb-Pb collisions are found across different centrality ranges, with the largest fluctuations of up to $\sim$15% being present in the 5% most central collisions. In parallel, no evidence of significant $p_{\rm T}$-dependent fluctuations of $\vec{V}_{3}$ or $\vec{V}_{4}$ is found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more than $5\sigma$ significance in central collisions. These observations in Pb-Pb collisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high $p_{\rm T}$, which might be biased by $p_{\rm T}$-dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be re-examined to improve our understanding of initial conditions, quark--gluon plasma properties, and the dynamic evolution of the created system.
The ratio $v_{2}{2}/v_2[2]$ as a function of $p_{\rm T}$ in different centrality intervals
The ratio $v_{3}{2}/v_3[2]$ as a function of $p_{\rm T}$ in different centrality intervals
The ratio $v_{4}{2}/v_4[2]$ as a function of $p_{\rm T}$ in different centrality intervals
The $p_{\rm T}$-differential production cross sections of non-prompt ${\rm D^0}$, ${\rm D^+}$, and ${\rm D_s^+}$ mesons originating from beauty-hadron decays are measured in proton$-$proton collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV. The measurements are performed at midrapidity, $|y| < 0.5$, with the data sample collected by ALICE from 2016 to 2018. The results are in agreement with predictions from several perturbative QCD calculations. The fragmentation fraction of beauty quarks to strange mesons divided by the one to non-strange mesons, $f_{\rm{s}}/(f_{\rm{u}} + f_{\rm{d}})$, is found to be $0.114 \pm 0.016~{\rm (stat.)} \pm 0.006~{\rm (syst.)} \pm 0.003~{\rm (BR)} \pm 0.003~{\rm (extrap.)}$. This value is compatible with previous measurements at lower centre-of-mass energies and in different collision systems in agreement with the assumption of universality of fragmentation functions. In addition, the dependence of the non-prompt D meson production on the centre-of-mass energy is investigated by comparing the results obtained at $\sqrt{s} = 5.02$ and 13 TeV, showing a hardening of the non-prompt D-meson $p_{\rm T}$-differential production cross section at higher $\sqrt{s}$. Finally, the ${\rm b\overline{b}}$ production cross section per unit of rapidity at midrapidity is calculated from the non-prompt ${\rm D^0}$, ${\rm D^+}$, ${\rm D_s^+}$, and $\Lambda_{\rm c}^+$ hadron measurements, obtaining ${\rm d}\sigma/{\rm d}y = 75.2\pm 3.2~(\mathrm{stat.}) \pm 5.2~(\mathrm{syst.})^{+12.3}_{-3.2} ~(\mathrm{extrap.})\text{ } \rm \mu b \;.$
$p_{\mathrm{T}}$-differential non-prompt $\mathrm{D}^{0}$ 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 non-prompt $\mathrm{D}^{+}$ 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 $\mathrm{D}^{+}_\mathrm{s}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{+}_\mathrm{s}\rightarrow\phi\pi^+\rightarrow\mathrm{K}^+\mathrm{K}^-\pi^+$: $(2.22 \pm 0.06)\%$. Global relative uncertainty on BR: $2.7\%$ Global relative uncertainty on luminosity: $1.6\%$
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.
The first measurements of femtoscopic correlations with the particle pair combinations $\pi^\pm$K$^0_{\rm S}$ in pp collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider (LHC) are reported by the ALICE experiment. Using the femtoscopic approach, it is shown that it is possible to study the elusive K$^*_0(700)$ particle that has been considered a tetraquark candidate for over forty years. Source and final-state interaction parameters are extracted by fitting a model assuming a Gaussian source to the experimentally measured two-particle correlation functions. The final-state interaction in the $\pi^\pm$K$^0_{\rm S}$ system is modeled through a resonant scattering amplitude, defined in terms of a mass and a coupling parameter. The extracted mass and Breit-Wigner width, derived from the coupling parameter, of the final-state interaction are found to be consistent with previous measurements of the K$^*_0(700)$. The small value and increase of the correlation strength with increasing source size support the hypothesis that the K$^*_0(700)$ is a four-quark state, i.e. a tetraquark state of the form $({\rm q_1},\overline{\rm q_2}, {\rm q_3}, \overline{\rm q_3})$ in which ${\rm q_1}$, ${\rm q_2}$, and ${\rm q_3}$ indicate the flavor of the valence quarks of the $\pi$ and K$^0_{\rm S}$. This latter trend is also confirmed via a simple geometric model that assumes a tetraquark structure of the K$^*_0(700)$ resonance.
Experimental $C(k^*)$, 0-100% mult. class, $k_{\rm T}>0$.
PYTHIA $C(k^*)$, 0-100% mult. class, $k_{\rm T}>0$.
Experimental $C(k^*)$, 0-100% mult. class, $k_{\rm T}<0.5$ GeV/$c$.
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