A signal consistent with the $\Omega$(2012) baryon has been observed with a significance of $15\sigma$ in pp collisions at $\sqrt{s} = 13$ TeV at the LHC. In this paper, the analysis technique is described and measurements of the mass and width of the $\Omega$(2012) are reported, along with the first measurement of its transverse-momentum spectrum and yield. This paper corroborates the observation by Belle of this excited $\Omega$ state and the observation that the $\Omega$(2012) has a rather narrow width for a strongly decaying resonance. The yield measurement is combined with a statistical thermal model calculation of strange baryon yield ratios to obtain estimates of the $\Omega{\rm (2012)}^{-} \rightarrow \Xi\overline{\rm K}$ branching ratios. These results will improve our understanding of the internal structure and mass spectrum of excited baryon states and serve as a baseline for searches regarding modifications of these properties in high-temperature media.
The measured mass of $\Omega(2012)^{-}$ and $\overline{\Omega}(2012)^{+}$ (anti)baryons. The uncertainties are (1) statistical and (2) systematic.
The measured width of $\Omega(2012)^{-}$ and $\overline{\Omega}(2012)^{+}$ (anti)baryons. The uncertainties are (1) statistical and (2) systematic.
The measured $p_{\mathrm{T}}$ spectrum of $\Omega(2012)^{-}$ and $\overline{\Omega}(2012)^{+}$ (anti)baryons in high-multiplicity proton-proton collisions at $\sqrt{s}=13$ TeV. The uncertainties are (1) statistical, (2) total systematic, and (3) the part of the systematic uncertainties that is uncorrelated between $p_{\mathrm{T}}$ bins. The yield values have not been corrected for the $\Omega(2012)^{-}\rightarrow\Xi^{-}\mathrm{K^{0}_{S}}$ branching ratio.
Hard-scattered partons ejected from high-energy proton-proton collisions undergo parton shower and hadronization, resulting in collimated collections of particles that are clustered into jets. A substructure observable that highlights the transition between the perturbative and non-perturbative regimes of jet evolution in terms of the angle between two particles is the two-point energy correlator (EEC). In this letter, the first measurement of the EEC at RHIC is presented, using data taken from 200 GeV $p$+$p$ collisions by the STAR experiment. The EEC is measured both for all the pairs of particles in jets and separately for pairs with like and opposite electric charges. These measurements demonstrate that the transition between perturbative and non-perturbative effects occurs within an angular region that is consistent with expectations of a universal hadronization regime that scales with jet momentum. Additionally, a deviation from Monte-Carlo predictions at small angles in the charge-selected sample could result from mechanics of hadronization not fully captured by current models.
Corrected distributions of the normalized EEC differential in $R_{L}$ for $R_{\rm jet}=$ 0.6, with jet transverse momentum selections 15 $< p_{\rm T, jet} <$ 20 GeV/c and 30 $< p_{\rm T, jet} <$ 50 GeV/c
Corrected distributions of the normalized EEC within jets, differential in $ \left\langle p_{\rm T,jet} \right\rangle R_{L} $ at $R_{\rm jet} =$ 0.6 for one $p_{\rm T, jet}$ selection. Each distribution is normalized to integrate to one in $R_{L}$ prior to shifting.
Corrected distributions of the normalized EEC within jets, differential in $ \left\langle p_{\rm T,jet} \right\rangle R_{L} $ at $R_{\rm jet} =$ 0.6 for one $p_{\rm T, jet}$ selection. Each distribution is normalized to integrate to one in $R_{L}$ prior to shifting.
We report measurements of $\varUpsilon(1S)$, $\varUpsilon(2S)$ and $\varUpsilon(3S)$ production in $\textit{p+p}$ collisions at $\sqrt{s}=500\:\mathrm{GeV}$ by the STAR experiment in year 2011, corresponding to an integrated luminosity $\mathcal{L}_{int}=13\:\mathrm{pb^{-1}}$. The results provide precise cross sections, transverse momentum ($p_{T}$) and rapidity ($y$) spectra, as well as cross section ratios for $p_{\mathrm{T}}<10\:\mathrm{GeV/c}$ and $|y|<1$. The dependence of the $\varUpsilon$ yield on charged particle multiplicity has also been measured, offering new insights into the mechanisms of quarkonium production. The data are compared to various theoretical models: the Color Evaporation Model (CEM) accurately describes the $\varUpsilon(1S)$ production, while the Color Glass Condensate + Non-relativistic Quantum Chromodynamics (CGC+NRQCD) model overestimates the data, particularly at low $p_{T}$. Conversely, the Color Singlet Model (CSM) underestimates the rapidity dependence. These discrepancies highlight the need for further development in understanding the production dynamics of heavy quarkonia in high-energy hadronic collisions. The trend in the multiplicity dependence is consistent with CGC/Saturation and String Percolation models or $\varUpsilon$ production happening in multiple parton interactions modeled by PYTHIA8.
The invariant mass distribution of electron pairs collected from p+p collisions at 500 GeV.
Single electron efficiencies.
Upsilon reconstruction efficiencies.
Correlations between event-by-event fluctuations of anisotropic flow harmonics are measured in Pb-Pb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV, as recorded by the ALICE detector at the LHC. This study presents correlations up to the hexagonal flow harmonic, $v_6$, which was measured for the first time. The magnitudes of these higher-order correlations are found to vary as a function of collision centrality and harmonic order. These measurements are compared to viscous hydrodynamic model calculations with EKRT initial conditions and to the iEBE-VISHNU model with TRENTo initial conditions. The observed discrepancies between the data and the model calculations vary depending on the harmonic combinations. Due to the sensitivity of model parameters estimated with Bayesian analyses to these higher-order observables, the results presented in this work provide new and independent constraints on the initial conditions and transport properties in theoretical models used to describe the system created in heavy-ion collisions.
NSC(5,2) vs centrality in Pb-Pb collisions at 5.02 TeV
NSC(5,3) vs centrality in Pb-Pb collisions at 5.02 TeV
NSC(6,2) vs centrality in Pb-Pb collisions at 5.02 TeV
The STAR Collaboration reports precise measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for dijet production with at least one jet at intermediate pseudorapidity $0.8 < η_{\rm jet} < 1.8$ in polarized proton-proton collisions at a center-of-mass energy of 200 GeV. This study explores partons scattered with a longitudinal momentum fraction ($x$) from 0.01 to 0.5, which are predominantly characterized by interactions between high-$x$ valence quarks and low-$x$ gluons. The results are in good agreement with previous measurements at 200 GeV with improved precision and are found to be consistent with the predictions of global analyses that find the gluon polarization to be positive. In contrast, the negative gluon polarization solution from the JAM Collaboration is found to be strongly disfavored.
$A_{LL}$ as a function of parton-level invariant mass for dijets with the East barrel-endcap.
$A_{LL}$ as a function of parton-level invariant mass for dijets with the West barrel-endcap.
$A_{LL}$ as a function of parton-level invariant mass for dijets with the endcap-endcap.
In this letter, we present the first measurement of direct photons at the transverse momentum of $ 1 < p_{\rm T} < 6$ GeV/$c$ at midrapidity $|η| < 0.8$ in inelastic and high-multiplicity proton--proton collisions at a centre-of-mass energy of $\sqrt{s} =$ 13 TeV. The fraction of virtual direct photons in the inclusive virtual photon spectrum is obtained from a fit to the dielectron invariant mass spectrum. In the limit of zero invariant mass, this fraction is equal to the relative contribution of real direct photons in the inclusive real photon spectrum. Contributions from decays of light-flavour neutral mesons are estimated using independent measurements in proton-proton collisions at the same energy and the same event class. For the first time at the LHC energies, a direct-photon signal is observed at low $p_{\rm T}$ in both inelastic and high-multiplicity event classes, with a significance of 3.2$σ$ and 1.9$σ$ in terms of standard deviations, correspondingly. The yield of direct photons in inelastic pp collisions is compared to perturbative QCD calculations. The integrated photon yield is studied as a function of charged-particle multiplicity and is compared to the results from other experiments and theoretical calculations. The results show a significant increase of direct-photon yield with charged-particle multiplicity.
The dielectron cross section in inelastic pp collisions at $\sqrt{s}$ = 13 TeV as a function of invariant mass for 2 < $p_{\rm T,ee}$ < 3 GeV/$c$.
The dielectron cross section in high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV as a function of invariant mass for 2 < $p_{\rm T,ee}$ < 3 GeV/$c$.
The direct-photon fraction r in inelastic pp collisions at $\sqrt{s}$ = 13 TeV as a function of transverse momentum for 1 < $p_{\rm T}$ < 6 GeV/$c$. r is the ratio of direct GAMMA to inclusive GAMMA.
The distribution of angular correlations between prompt charm hadrons and primary charged particles in pp collisions is sensitive to the charm-quark hadronisation process. In this letter, charm-baryon correlations are measured for the first time by studying the azimuthal-angle difference between charged particles and prompt $Λ_{\rm c}^{+}$ baryons produced in pp collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, with the ALICE detector. $Λ_{\rm c}^{+}$ baryons are reconstructed at midrapidity ($|y| < 0.5$) in the transverse-momentum interval $3 < p_{\rm T} < 16$ GeV/$c$, and correlated with charged particles with $p_{\rm T} > 0.3$ GeV/$c$ and pseudorapidity $|η| < 0.8$. For $3< p_{\rm T}^{Λ_{\rm c}^{+},{\rm D}} <5$ GeV/$c$, the comparison with published measurements of D-meson and charged-particle correlations in the same collision system hints at a larger number of low-momentum particles associated with $Λ_{\rm c}^{+}$-baryon triggers than with D-meson triggers, both in the collinear and opposite directions with respect to the trigger particle. These differences can be quantified by the comparison of the properties of the near- and away-side correlation peaks, and are not reproduced by predictions of various Monte Carlo event generators, generally underpredicting the associated particle yields at $p_{\rm T}^{\rm assoc}<1$ GeV/$c$. This tension between $Λ_{\rm c}^{+}$-baryon and D-meson associated peak yields could suggest a modified fragmentation of the charm quark, or a different hadronisation process, when a charm baryon is produced in the final state.
Azimuthal-correlation distributions of $\Lambda_\mathrm{c}^{+}$ baryons with associated particles in pp collisions at $\sqrt{s} = 13$ TeV, compared to the average of the azimuthal-correlation distributions of D$^{0}$, D$^{+}$, and D$^{*+}$ mesons with associated particles in the same collision system. The distributions are shown after the baseline subtraction. Charm hadrons are reported for $3 < p_{\rm T} < 5$ GeV/$c$, associated particles for $0.3 < p_{\rm T} < 1$ GeV/$c$. The rapidity range for the D mesons and $\Lambda_\mathrm{c}^{+}$ baryons is $|y^{\rm D,\Lambda_\mathrm{c}^{+}}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D,\Lambda_{c}^{+}}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Azimuthal-correlation distributions of $\Lambda_\mathrm{c}^{+}$ baryons with associated particles, i.e. primary charged particles, in pp collisions at $\sqrt{s} = 13$ TeV, compared to the average of the azimuthal-correlation distributions of D$^{0}$, D$^{+}$, and D$^{*+}$ mesons with associated particles in the same collision system. The distributions are shown after the baseline subtraction. Charm hadrons are reported for $5 < p_{\rm T} < 8$ GeV/$c$, associated particles for $0.3 < p_{\rm T} < 1$ GeV/$c$. The rapidity range for the D mesons and $\Lambda_\mathrm{c}^{+}$ baryons is $|y^{\rm D,\Lambda_\mathrm{c}^{+}}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D,\Lambda_{c}^{+}}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Azimuthal-correlation distributions of $\Lambda_\mathrm{c}^{+}$ baryons with associated particles, i.e. primary charged particles, in pp collisions at $\sqrt{s} = 13$ TeV, compared to the average of the azimuthal-correlation distributions of D$^{0}$, D$^{+}$, and D$^{*+}$ mesons with associated particles in the same collision system. The distributions are shown after the baseline subtraction. Charm hadrons are reported for $8 < p_{\rm T} < 16$ GeV/$c$, associated particles for $p_{\rm T} > 1$ GeV/$c$. The rapidity range for the D mesons and $\Lambda_\mathrm{c}^{+}$ baryons is $|y^{\rm D,\Lambda_\mathrm{c}^{+}}| < 0.5$. Correlations are integrated for $|\Delta\eta|=|\eta_{\rm ch}-\eta_{\rm D,\Lambda_{c}^{+}}| < 1$. The azimuthal-correlation distributions are reported in the range $0 < \Delta\varphi < \pi$.
Quantum Chromodynamics predicts a phase transition from ordinary hadronic matter to the quark-gluon plasma (QGP) at high temperatures and energy densities, where quarks and gluons (partons) are not confined within hadrons. The QGP is generated in ultrarelativistic heavy-ion collisions. Anisotropic flow coefficients, quantifying the anisotropic azimuthal expansion of the produced matter, provide a unique tool to unravel QGP properties. Flow measurements in high-energy heavy-ion collisions show a distinctive grouping of anisotropic flow for baryons and mesons at intermediate transverse momentum, a feature associated with flow being imparted at the quark level, confirming the existence of the QGP. The observation of QGP-like features in relativistic proton-proton and proton-ion collisions has sparked debate about possible QGP formation in smaller collision systems, which remains unresolved. In this article, we demonstrate for the first time the distinctive grouping of anisotropic flow for baryons and mesons in high-multiplicity proton-lead and proton-proton collisions at the Large Hadron Collider (LHC). These results are described by a model that includes hydrodynamic flow followed by hadron formation via quark coalescence, replicating features observed in heavy-ion collisions. This observation is consistent with the formation of a partonic flowing system in proton-proton and proton-lead collisions at the LHC.
$v_2${2, $1.1<|\Delta\eta|< 7.8$} of $\mathrm{\pi}^{\pm}$ as a function of $p_{\mathrm{T}}$ in high-multiplicity p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.
$v_2${2, $1.1<|\Delta\eta|< 7.8$} of $\mathrm{K}^{\pm}$ as a function of $p_{\mathrm{T}}$ in high-multiplicity p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.
$v_2${2, $1.1<|\Delta\eta|< 7.8$} of p + $\rm\overline p$ as a function of $p_{\mathrm{T}}$ in high-multiplicity p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.
Event-by-event fluctuations of the event-wise mean transverse momentum, $\langle p_{\mathrm{T}}\rangle$, of charged particles produced in proton$-$proton (pp) collisions at $\sqrt{s}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_{\mathrm{NN}}} =$ 5.44 TeV, and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}} =$ 5.0 TeV are studied using the ALICE detector based on the integral correlator $\langle\langle Δp_{\rm T}Δp_{\rm T}\rangle\rangle $. The correlator strength is found to decrease monotonically with increasing produced charged-particle multiplicity measured at midrapidity in all three systems. In Xe$-$Xe and Pb$-$Pb collisions, the multiplicity dependence of the correlator deviates significantly from a simple power-law scaling as well as from the predictions of the HIJING and AMPT models. The observed deviation from power-law scaling is expected from transverse radial flow in semicentral to central Xe$-$Xe and Pb$-$Pb collisions. In pp collisions, the correlation strength is also studied by classifying the events based on the transverse spherocity, $S_0$, of the particle production at midrapidity, used as a proxy for the presence of a pronounced back-to-back jet topology. Low-spherocity (jetty) events feature a larger correlation strength than those with high spherocity (isotropic). The strength and multiplicity dependence of jetty and isotropic events are well reproduced by calculations with the PYTHIA 8 and EPOS LHC models.
Normalized transverse momentum correlator, $\sqrt{ \langle\langle \Delta p_{{\rm T}1}\Delta p_{{\rm T}2} \rangle\rangle }$$/\langle\langle p_{\rm T} \rangle\rangle $, as a function of the charged-particle multiplicity density, $\langle{\rm d}N_{\rm ch}/{\rm d}\eta \rangle$, in pp collisions at $\sqrt{s}$ = 5.02 TeV.
Normalized transverse momentum correlator, $\sqrt{ \langle\langle \Delta p_{{\rm T}1}\Delta p_{{\rm T}2} \rangle\rangle }$$/\langle\langle p_{\rm T} \rangle\rangle $, as a function of the charged-particle multiplicity density, $\langle{\rm d}N_{\rm ch}/{\rm d}\eta \rangle$, in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
Normalized transverse momentum correlator, $\sqrt{ \langle\langle \Delta p_{{\rm T}1}\Delta p_{{\rm T}2} \rangle\rangle }$$/\langle\langle p_{\rm T} \rangle\rangle $, as a function of the charged-particle multiplicity density, $\langle{\rm d}N_{\rm ch}/{\rm d}\eta \rangle$, in Xe--Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV.
The $p_{\rm T}$-differential cross section of $\omega$ meson production in pp collisions at $\sqrt{s}= 13$ TeV at midrapidity ($|y|<0.5$) was measured with the ALICE detector at the LHC, covering an unprecedented transverse-momentum range of $1.6 <p_{\rm T}< 50$ GeV/$c$. The meson is reconstructed via the $\omega\rightarrow\pi^+\pi^-\pi^0$ decay channel. The results are compared with various theoretical calculations: PYTHIA8.2 with the Monash 2013 tune overestimates the data by up to 50%, whereas good agreement is observed with Next-to-Leading Order (NLO) calculations incorporating $\omega$ fragmentation using a broken SU(3) model. The $\omega/\pi^0$ ratio is presented and compared with theoretical calculations and the available measurements at lower collision energies. The presented data triples the $p_{\rm T}$ ranges of previously available measurements. A constant ratio of $C^{\omega/\pi^0}=0.578\pm0.006~\text{(stat.)}\pm 0.013~\text{(syst.)}$ is found above a transverse momentum of $4$ GeV/$c$, which is in agreement with previous findings at lower collision energies within the systematic and statistical uncertainties.
Invariant differential cross section of OMEGA mesons produced in inelastic pp collisions at center-of-mass energy 13 TeV, the uncertainty of sigma_{MB} of 1.58% is not included in the systematic error.
The measured ratio of cross sections for inclusive OMEGA to PI0 production at a centre-of-mass energy of 13 TeV.
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