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Item type:Publication, Multiplicity dependence of (multi-)strange hadron production in proton-proton collisions at √s = 13 TeV(Springer, 2020-02-01)Abstract The production rates and the transverse momentum distribution of strange hadrons at mid-rapidity ( $$\left| y\right| < 0.5$$ y < 0.5 ) are measured in proton-proton collisions at $$\sqrt{s}$$ s = 13 TeV as a function of the charged particle multiplicity, using the ALICE detector at the LHC. The production rates of $$\mathrm{K}^{0}_{S}$$ K S 0 , $$\Lambda $$ Λ , $$\Xi $$ Ξ , and $$\Omega $$ Ω increase with the multiplicity faster than what is reported for inclusive charged particles. The increase is found to be more pronounced for hadrons with a larger strangeness content. Possible auto-correlations between the charged particles and the strange hadrons are evaluated by measuring the event-activity with charged particle multiplicity estimators covering different pseudorapidity regions. When comparing to lower energy results, the yields of strange hadrons are found to depend only on the mid-rapidity charged particle multiplicity. Several features of the data are reproduced qualitatively by general purpose QCD Monte Carlo models that take into account the effect of densely-packed QCD strings in high multiplicity collisions. However, none of the tested models reproduce the data quantitatively. This work corroborates and extends the ALICE findings on strangeness production in proton-proton collisions at 7 TeV. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Multiplicity dependence of π, K, and p production in pp collisions at √s=13 TeV(Institute for Ionics, 2020-08-01)Abstract This paper presents the measurements of $$\pi ^{\pm }$$ π± , $$\mathrm {K}^{\pm }$$ K± , $$\text {p}$$ p and $$\overline{\mathrm{p}} $$ p¯ transverse momentum ( $$p_{\text {T}}$$ pT ) spectra as a function of charged-particle multiplicity density in proton–proton (pp) collisions at $$\sqrt{s}\ =\ 13\ \text {TeV}$$ s=13TeV with the ALICE detector at the LHC. Such study allows us to isolate the center-of-mass energy dependence of light-flavour particle production. The measurements reported here cover a $$p_{\text {T}}$$ pT range from 0.1 to 20 $$\text {GeV}/c$$ GeV/c and are done in the rapidity interval $$|y|<0.5$$ |y|<0.5 . The $$p_{\text {T}}$$ pT -differential particle ratios exhibit an evolution with multiplicity, similar to that observed in pp collisions at $$\sqrt{s}\ =\ 7\ \text {TeV}$$ s=7TeV , which is qualitatively described by some of the hydrodynamical and pQCD-inspired models discussed in this paper. Furthermore, the $$p_{\text {T}}$$ pT -integrated hadron-to-pion yield ratios measured in pp collisions at two different center-of-mass energies are consistent when compared at similar multiplicities. This also extends to strange and multi-strange hadrons, suggesting that, at LHC energies, particle hadrochemistry scales with particle multiplicity the same way under different collision energies and colliding systems. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Measurement of Λ (1520) production in pp collisions at √s=7TeV and p–Pb collisions at √sNN=5.02TeV(Institute for Ionics, 2020-02-01)Abstract The production of the $$\Lambda $$ Λ (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at $$\sqrt{s} = 7\ \hbox {TeV}$$ s=7TeV and in p–Pb collisions at $$\sqrt{s_{\mathrm{NN}}} = 5.02\ \hbox {TeV}$$ sNN=5.02TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel $$\Lambda $$ Λ (1520) $$\rightarrow \hbox {pK}^{-}$$ →pK- and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons ( $$\pi $$ π , K, $$\hbox {K}_{\mathrm{S}}^0$$ KS0 , p, $$\Lambda $$ Λ ) describes the shape of the $$\Lambda $$ Λ (1520) transverse momentum distribution up to $$3.5\ \hbox {GeV}/c$$ 3.5GeV/c in p–Pb collisions. In the framework of this model, this observation suggests that the $$\Lambda $$ Λ (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of $$\Lambda (1520)$$ Λ(1520) to the yield of the ground state particle $$\Lambda $$ Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the $$\Lambda $$ Λ (1520) yield. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p-Pb collisions at √sNN = 5.02 TeV(Springer, 2020-02-01)Abstract The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval −1.07 < ycms< 0.14 and transverse momentum interval 2 < pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at √sNN = 5.02 TeV(Springer, 2020-05-01)Abstract Anisotropic flow coefficients, v n , non-linear flow mode coefficients, χ n,mk , and correlations among different symmetry planes, ρ n,mk are measured in Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV. Results obtained with multi-particle correlations are reported for the transverse momentum interval 0.2 < p T < 5.0 GeV/c within the pseudorapidity interval 0.4 < |η| < 0.8 as a function of collision centrality. The v n coefficients and χ n,mk and ρ n,mk are presented up to the ninth and seventh harmonic order, respectively. Calculations suggest that the correlations measured in different symmetry planes and the non-linear flow mode coefficients are dependent on the shear and bulk viscosity to entropy ratios of the medium created in heavy-ion collisions. The comparison between these measurements and those at lower energies and calculations from hydrodynamic models places strong constraints on the initial conditions and transport properties of the system. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Production of (anti-)He3 and (anti-)H3 in p-Pb collisions at sNN =5.02 TeV(American Physical Society, 2020-04-01)The transverse momentum (${p}_{\mathrm{T}}$) differential yields of (anti-)$^{3}\mathrm{He}$ and (anti-)$^{3}\mathrm{H}$ measured in $p$-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV with ALICE at the Large Hadron Collider (LHC) are presented. The ratios of the ${p}_{\mathrm{T}}$-integrated yields of (anti-)$^{3}\mathrm{He}$ and (anti-)$^{3}\mathrm{H}$ to the proton yields are reported, as well as the ${p}_{\mathrm{T}}$ dependence of the coalescence parameters ${B}_{3}$ for (anti-)$^{3}\mathrm{He}$ and (anti-)$^{3}\mathrm{H}$. For (anti-)$^{3}\mathrm{He}$, the results obtained in four classes of the mean charged-particle multiplicity density are also discussed. These results are compared to predictions from a canonical statistical hadronization model and coalescence approaches. An upper limit on the total yield of ${}^{4}\overline{\mathrm{He}}$ is determined. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Jet-hadron correlations measured relative to the second order event plane in Pb-Pb collisions at sNN =2.76 TeV(American Physical Society, 2020-06-01)The quark gluon plasma produced in ultrarelativistic heavy-ion collisions at the Large Hadron Collider (LHC) can be studied by measuring the modifications of jets formed by hard scattered partons which interact with the medium. We studied these modifications via angular correlations of jets with charged hadrons for jets with momenta $20<{p}_{\mathrm{T}}^{\mathrm{jet}}<40$ GeV/$c$ as a function of the associated particle momentum. The reaction plane fit method is used in this analysis to remove the flow modulated background. The analysis of angular correlations for different orientations of the jet relative to the second order event plane allows for the study of the path length dependence of medium modifications to jets. We present the dependence of azimuthal angular correlations of charged hadrons with respect to the angle of the axis of a reconstructed jet relative to the event plane in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 2.76 TeV. The dependence of particle yields associated with jets on the angle of the jet with respect to the event plane is presented. Correlations at different angles relative to the event plane are compared through ratios and differences of the yield. No dependence of the results on the angle of the jet with respect to the event plane is observed within uncertainties, which is consistent with no significant path length dependence of the medium modifications for this observable. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Probing the Effects of Strong Electromagnetic Fields with Charge-Dependent Directed Flow in Pb-Pb Collisions at the LHC(American Physical Society, 2020-07-10)The first measurement at the LHC of charge-dependent directed flow (${v}_{1}$) relative to the spectator plane is presented for Pb-Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\text{ }\text{ }\mathrm{TeV}$. Results are reported for charged hadrons and ${\mathrm{D}}^{0}$ mesons for the transverse momentum intervals ${p}_{\mathrm{T}}>0.2\text{ }\text{ }\mathrm{GeV}/c$ and $3<{p}_{\mathrm{T}}<6\text{ }\text{ }\mathrm{GeV}/c$ in the 5%--40% and 10%--40% centrality classes, respectively. The difference between the positively and negatively charged hadron ${v}_{1}$ has a positive slope as a function of pseudorapidity $\ensuremath{\eta}$, $\mathrm{d}\mathrm{\ensuremath{\Delta}}{v}_{1}/\mathrm{d}\ensuremath{\eta}=\phantom{\rule{0ex}{0ex}}[1.68\ifmmode\pm\else\textpm\fi{}0.49(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.41(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. The same measurement for ${\mathrm{D}}^{0}$ and ${\overline{\mathrm{D}}}^{0}$ mesons yields a positive value $\mathrm{d}\mathrm{\ensuremath{\Delta}}{v}_{1}/\mathrm{d}\ensuremath{\eta}=[4.9\ifmmode\pm\else\textpm\fi{}1.7(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}$, which is about 3 orders of magnitude larger than the one of the charged hadrons. These measurements can provide new insights into the effects of the strong electromagnetic field and the initial tilt of matter created in noncentral heavy ion collisions on the dynamics of light (u, d, and s) and heavy (c) quarks. The large difference between the observed $\mathrm{\ensuremath{\Delta}}{v}_{1}$ of charged hadrons and ${\mathrm{D}}^{0}$ mesons may reflect different sensitivity of the charm and light quarks to the early time dynamics of a heavy ion collision. These observations challenge some recent theoretical calculations, which predicted a negative and an order of magnitude smaller value of $\mathrm{d}\mathrm{\ensuremath{\Delta}}{v}_{1}/\mathrm{d}\ensuremath{\eta}$ for both light flavor and charmed hadrons. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Evidence of Spin-Orbital Angular Momentum Interactions in Relativistic Heavy-Ion Collisions(American Physical Society, 2020-07-03)The first evidence of spin alignment of vector mesons (K^{*0} and ϕ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ_{00} is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at a center-of-mass energy (sqrt[s_{NN}]) of 2.76 TeV with the ALICE detector. ρ_{00} values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum (p_{T}<2 GeV/c) for K^{*0} and ϕ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the K_{S}^{0} meson (spin=0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Unveiling the strong interaction among hadrons at the LHC(Nature Research, 2020-12-10)Abstract One of the key challenges for nuclear physics today is to understand from first principles the effective interaction between hadrons with different quark content. First successes have been achieved using techniques that solve the dynamics of quarks and gluons on discrete space-time lattices 1,2 . Experimentally, the dynamics of the strong interaction have been studied by scattering hadrons off each other. Such scattering experiments are difficult or impossible for unstable hadrons 3–6 and so high-quality measurements exist only for hadrons containing up and down quarks 7 . Here we demonstrate that measuring correlations in the momentum space between hadron pairs 8–12 produced in ultrarelativistic proton–proton collisions at the CERN Large Hadron Collider (LHC) provides a precise method with which to obtain the missing information on the interaction dynamics between any pair of unstable hadrons. Specifically, we discuss the case of the interaction of baryons containing strange quarks (hyperons). We demonstrate how, using precision measurements of proton–omega baryon correlations, the effect of the strong interaction for this hadron–hadron pair can be studied with precision similar to, and compared with, predictions from lattice calculations 13,14 . The large number of hyperons identified in proton–proton collisions at the LHC, together with accurate modelling 15 of the small (approximately one femtometre) inter-particle distance and exact predictions for the correlation functions, enables a detailed determination of the short-range part of the nucleon-hyperon interaction.