463 research outputs found
First observation of the interaction via two-particle correlations
No full textThe strong interaction among the different hadrons at relatively small momentum transfers is difficult to describe via direct solutions of Quantum Chromodynamics, due to the running of the coupling constant. Only very recently, attempts of first principle calculations based on lattice simulations have been made and these have yet to be tested. Typically, the description of the interaction among hadrons relies on phenomenological models and effective theories, where several free parameters have to be constrained from experimental observations. Since numerous measurements are available in the nucleonic sector, a sound understanding of N-N interactions is well established. In the strangeness sector however, the experimental knowledge is rather limited and the constraints to pin down precisely the interaction involving hyperons are missing. The lack of experimental data also hinders the validation of novel approaches to describe the baryon interaction based on lattice QCD, which currently provide applicable results for baryon pairs, including at least two or more strange quarks. Furthermore, the poor constraints available for descriptions of interactions involving hyperons, limit the understanding of their appearance and behavior in cold nuclear matter at extreme densities, which thereby hampers a solid modeling of the inner parts of neutron stars. Femtoscopy is based on a study of the two-particle correlation function, where final-state effects among specific particle pairs induce a signal that is characterized by the space-time extend of the particle emission source. Recent studies demonstrate that the strong interaction can be studied from this observable if the characteristics of the emission region are sufficiently constrained. This work extends this approach to investigate the strong interaction of pairs. In the first part of this analysis, the , , and correlation functions are measured in elementary p-Pb and pp collisions at the LHC with the ALICE detector. In a detailed study the source radius is measured as a function of the pair transverse mass considering, for the first time in a quantitative way, the effect of strong resonance decays. After correcting for this effect, the radii extracted for pairs of different particle species agree. This indicates that protons, antiprotons, s and s, as well as and originate from the same source. In the second part, these results are applied to constrain the source size of pairs. The two-particle correlation function of and pairs is measured with ALICE in both collision systems. The comparison of the measurement with the prediction, assuming only an attractive Coulomb interaction, is not compatible with the data. The enhancement above the Coulomb prediction indicates the presence of an additional component due to the attractive strong interaction among a proton and a baryon, which is observed in this way for the first time. Furthermore, the comparison of the data to predictions of this strong interaction from lattice QCD calculations by the HAL QCD collaboration exhibits a qualitative agreement. This serves as a first direct test of these first principle calculations, which supports the description of the N- interaction in this approach. The lattice potentials are therefore useful to investigate the role of the in the context of neutron stars. Consequently, its interaction within a neutron rich environment is expected to be more repulsive than typically assumed, which suggests a stiffening of the Equation of State of neutron star matter at large densities
Publisher Correction: Unveiling the strong interaction among hadrons at the LHC (Nature, (2020), 588, 7837, (232-238), 10.1038/s41586-020-3001-6)
No full textIn Fig. 1c of this Article, owing to an error during the production process, the equation incorrectly began ‘C(k*, r*) = …’ instead of ‘C(k*) = …’. In addition, in affiliation 71 ‘Dipartimento di Fisica dell’Università degli studi di Bari Aldo Moro’ has been corrected to read ‘Dipartimento di Fisica dell’Università degli studi di Cagliari’. The original Article has been corrected online. *A list of authors and their affiliations appears online. © 2021, The Author(s), under exclusive licence to Springer Nature Limited
Publisher Correction: Direct observation of the dead-cone effect in quantum chromodynamics (Nature, (2022), 605, 7910, (440-446), 10.1038/s41586-022-04572-w)
No full textIn the version of this article initially published, there was a typographical error in the first sentence following the “Exposing the dead cone” heading, now reading, “The measurements of R(θ), in the three radiator (charmquark) energy intervals 5 < ERadiator < 10 GeV, 10 < ERadiator < 20 GeV and 20 < ERadiator < 35 GeV…,” where “35 GeV” initially appeared as “3 GeV.” The error has been corrected in the HTML and PDF versions of the article. *A list of authors and their affiliations appears online. © The Author(s) 2022
H-3(Lambda) and (3)((Lambda)over-bar)(H)over-bar lifetime measurement in Pb-Pb collisions at root s(NN)=5.02 TeV via two-body decay
No full textAn improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb-Pb collisions at root s(NN) = 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the dN/d(ct) spectrum. The measured value, tau = 242(-38)(+34) (stat.) +/- 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle. (C) 2019 The Author. Published by Elsevier B.V
Measuring (KSK +/-)-K-0 interactions using Pb-Pb collisions at root S-NN=2.76 TeV
No full textWe present the first ever measurements of femtoscopic correlations between the K-S(0) and K-+/- particles. The analysis was performed on the data from Pb-Pb collisions at root S-NN = 2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a(0)(980) resonance. The extracted kaon source radius and correlation strength parameters for (KSK-)-K-0 are found to be equal within the experimental uncertainties to those for (KSK+)-K-0. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a(0) resonance are tested. Our results are also compatible with the interpretation of the a(0) having a tetraquark structure instead of that of a diquark. (c) 2017 The Author. Published by Elsevier B.V
Measurement of Z0-boson production at large rapidities in Pb–Pb collisions at sNN=5.02TeV
No full textThe production of Z0 bosons at large rapidities in Pb–Pb collisions at sNN=5.02TeV is reported. Z0 candidates are reconstructed in the dimuon decay channel (Z0→μ+μ−), based on muons selected with pseudo-rapidity −4.0<η<−2.5 and pT>20GeV/c. The invariant yield and the nuclear modification factor, RAA, are presented as a function of rapidity and collision centrality. The value of RAA for the 0–20% central Pb–Pb collisions is 0.67±0.11(stat.)±0.03(syst.)±0.06(corr. syst.), exhibiting a deviation of 2.6σ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by 2.3σ in the 0–90% centrality class and by 3σ in the 0–20% central collisions. © 2018 The Author(s
Coherent J/ψ photoproduction at forward rapidity in ultra-peripheral Pb–Pb collisions at s NN = 5.02 TeV
No full textThe ALICE collaboration performed the first rapidity-differential measurement of coherent J/psi photoproduction in ultra-peripheral Pb-Pbcollisions at a center-of-mass energy root s(NN) = 5.02TeV. The J/psi is detected via its dimuon decay in the forward rapidity region (-4.0 < y < -2.5) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 mu b(-1). The cross section for coherent J/psi production is presented in six rapidity bins. The results are compared with theoretical models for coherent J/psi photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of psi' to J/psi coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons. (C) 2019 The Author. Published by Elsevier B.V
First measurement of Ξc 0 production in pp collisions at s=7 TeV
No full textThe production of the charm-strange baryon Ξc 0 is measured for the first time at the LHC via its semileptonic decay into eΞ−+νe in pp collisions at s=7 TeV with the ALICE detector. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 1&lt;pT&lt;8 GeV/c at mid-rapidity, |y|&lt;0.5. The transverse momentum dependence of the Ξc 0 baryon production relative to the D0 meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio. © 2018 The Author(s
Jet-associated deuteron production in pp collisions at root s=13 TeV
No full textDeuteron production in high-energy collisions is sensitive to the space-time evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at root s = 13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (p(T) > 5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4-4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence. (C) 2021 The Author. Published by Elsevier B.V
First measurement of Xi(0)(c) production in pp collisions at root s=7 TeV
No full textThe production of the charm-strange baryon Xi(0)(c) is measured for the first time at the LHC via its semileptonic decay into e(+) Xi(-) nu(e) in ppcollisions at root s = 7 TeV with the ALICE detector. The transverse momentum ( p(T)) differential cross section multiplied by the branching ratio is presented in the interval 1 < p(T)< 8 GeV/c at mid-rapidity, vertical bar y vertical bar < 0.5. The transverse momentum dependence of the Xi(0)(c) baryon production relative to the D-0 meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio. (C) 2018 The Author(s). Published by Elsevier B.V
- …
