397 research outputs found

    Measurement of inclusive charged-particle b-jet production in pp and p-Pb collisions at √sNN = 5.02 TeV

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    A measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at sNN = 5.02 TeV, using data collected with the ALICE detector at the LHC. The jets were reconstructed in the central rapidity region |η| T algorithm with resolution parameter R = 0.4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The pT-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10 ≤ pT,ch jet≤ 100 GeV/c, together with the nuclear modification factor, RpPbb−jet. The analysis thus extends the lower pT limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at sNN = 5.02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation. [Figure not available: see fulltext.]

    First measurement of quarkonium polarization in nuclear collisions at the LHC

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    The polarization of inclusive J/psi and Upsilon(1S) produced in Pb-Pb collisions at root s(NN) = 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5 < y < 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters lambda(theta), lambda(phi) and lambda(theta phi) are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2 < p(T) < 10 GeV/c and p(T) < 15 GeV/c for the J/psi and Upsilon(1S), respectively. The polarization parameters for the J/psi are found to be compatible with zero, within a maximum of about two standard deviations at low p(T), for both reference frames and over the whole p(T) range. The values are compared with the corresponding results obtained for pp collisions at root s = 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for Upsilon(1S) production in Pb-Pb collisions are also consistent with zero. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

    Measurement of strange baryon–antibaryon interactions with femtoscopic correlations

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    Two-particle correlation functions were measured for p (p) over bar, p (Lambda) over bar, (p) over bar Lambda, and Lambda(Lambda) over bar pairs in Pb-Pb collisions at root sNN = 2.76 TeV and root sNN = 5.02 TeV recorded by the ALICE detector. From a simultaneous fit to all obtained correlation functions, real and imaginary components of the scattering lengths, as well as the effective ranges, were extracted for combined p (Lambda) over bar and (p) over bar Lambda pairs and, for the first time, for Lambda(Lambda) over bar pairs. Effective averaged scattering parameters for heavier baryon-antibaryon pairs, not measured directly, are also provided. The results reveal similarly strong interaction between measured baryon-antibaryon pairs, suggesting that they all annihilate in the same manner at the same pair relative momentum k*. Moreover, the reported significant non-zero imaginary part and negative real part of the scattering length provide motivation for future baryon-antibaryon bound state searches. (C) 2020 The Author(s). Published by Elsevier B.V

    Investigating the role of strangeness in baryon-antibaryon annihilation at the LHC

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    Annihilation dynamics plays a fundamental role in the baryon-antibaryon interaction (B-(B) over bar) at low-energy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the p-(p) over bar system but not in the low relative momentum region. Data regarding the B-(B) over bar interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon-antinucleon (N-(N) over bar) results, when available. In this letter we present a measurement of the p-(p) over bar, p-(Lambda) over bar circle plus(p) over bar-Lambda and Lambda-(Lambda) over bar interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at root s = 13 TeV recorded by ALICE at the LHC. In the p-(p) over bar system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent chi EFT potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednicky-Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental p-(Lambda) over bar circle plus(p) over bar-Lambda and Lambda-(Lambda) over bar correlations. The model describes the Lambda-(Lambda) over bar data and underestimates the p-(Lambda) over bar circle plus(p) over bar-Lambda data in the region of momenta below 200 MeV/c. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons. (C) 2022 European Organization for Nuclear Research. Published by Elsevier B.V

    Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

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    Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

    Prompt and non-prompt J/ψ production cross sections at midrapidity in proton-proton collisions at s = 5.02 and 13 TeV

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    The production of J/ψ is measured at midrapidity (|y| &lt; 0.9) in proton-proton collisions at ss \sqrt{s} = 5.02 and 13 TeV, through the dielectron decay channel, using the ALICE detector at the Large Hadron Collider. The data sets used for the analyses correspond to integrated luminosities of LL \mathcal{L} int = 19.4 ± 0.4 nb−1 and LL \mathcal{L} int = 32.2 ± 0.5 nb−1 at ss \sqrt{s} = 5.02 and 13 TeV, respectively. The fraction of non-prompt J/ψ mesons, i.e. those originating from the decay of beauty hadrons, is measured down to a transverse momentum pT = 2 GeV/c (1 GeV/c) at ss \sqrt{s} = 5.02 TeV (13 TeV). The pT and rapidity (y) differential cross sections, as well as the corresponding values integrated over pT and y, are carried out separately for prompt and non-prompt J/ψ mesons. The results are compared with measurements from other experiments and theoretical calculations based on quantum chromodynamics (QCD). The shapes of the pT and y distributions of beauty quarks predicted by state-of-the-art perturbative QCD models are used to extrapolate an estimate of the bb¯bb \mathrm{b}\overline{\mathrm{b}} pair cross section at midrapidity and in the total phase space. The total bb¯bb \mathrm{b}\overline{\mathrm{b}} cross sections are found to be σbb¯σbb {\sigma}_{\mathrm{b}\overline{\mathrm{b}}} = 541 ± 45 (stat.) ± 69 syst.−12+10(syst.)12+10 {\left(\mathrm{syst}.\right)}_{-12}^{+10} (extr.) μb and σbb¯σbb {\sigma}_{\mathrm{b}\overline{\mathrm{b}}} = 218±37 (stat.)±31 syst.−9.1+8.2(syst.)9.1+8.2 {\left(\mathrm{syst}.\right)}_{-9.1}^{+8.2} (extr.) μb at ss \sqrt{s} = 13 and 5.02 TeV, respectively. The value obtained from the combination of ALICE and LHCb measurements in pp collisions at ss \sqrt{s} = 13 TeV is also provided

    Femtoscopic study of the proton-proton and proton-deuteron systems in heavy-ion collisions at the LHC

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    This work reports femtoscopic correlations of p-−p(p ̅-−p ̅) and p−−d(p ̅-−d ̅) pairs measured in Pb–Pb collisions at center-of-mass energy per nucleon sNN = 5.02 TeV in the ALICE Collaboration. A fit to the measured proton-proton correlation functions allows one to extract the dependence of the nucleon femtoscopic radius of the particle-emitting source on the pair transverse mass (mT) and on the average charge particle multiplicity 〈dNch/dη〉1/3 for three centrality intervals (0–10%,10−−30%,30−−50%). In both cases, the expected power-law and linear scalings are observed, respectively. The measured p–d correlations can be described by both two- and three-body calculations, indicating that the femtoscopy observable is not sensitive to the short-distance features of the dynamics of the p-(p-n) system, due to the large inter-particle distances in Pb–Pb collisions at the LHC. Indeed, in this study, the minimum measured femtoscopic source sizes for protons and deuterons have a minimum value at 2.73−0.05+0.05 and 3.10−0.86+1.04 fm, respectively, for the 30–50% centrality collisions. Moreover, the m T-scaling obtained for the p–p and p–d systems is compatible within 1 σ of the uncertainties. These findings provide new input for fundamental studies on the production of light (anti)nuclei under extreme conditions

    First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production

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    The first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V

    Erratum to “Rapidity and transverse momentum dependence of inclusive J/ψ production in pp collisions at s=7 TeV” [Phys. Lett. B 704 (5) (2011) 442]

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    Multiplicity dependence of (anti-)deuteron production in pp collisions at root s=7 TeV

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    In this letter, the production of deuterons and anti-deuterons in pp collisions at s=7 TeV is studied as a function of the charged-particle multiplicity density at mid-rapidity with the ALICE detector at the LHC. Production yields are measured at mid-rapidity in five multiplicity classes and as a function of the deuteron transverse momentum (pT). The measurements are discussed in the context of hadron–coalescence models. The coalescence parameter B2, extracted from the measured spectra of (anti-)deuterons and primary (anti-)protons, exhibits no significant pT-dependence for pT2 parameter is found to decrease smoothly from low multiplicity pp to Pb–Pb collisions, in qualitative agreement with more elaborate coalescence models. The measured mean transverse momentum of (anti-)deuterons in pp is not reproduced by the Blast-Wave model calculations that simultaneously describe pion, kaon and proton spectra, in contrast to central Pb–Pb collisions. The ratio between the pT-integrated yield of deuterons to protons, d/p, is found to increase with the charged-particle multiplicity, as observed in inelastic pp collisions at different centre-of-mass energies. The d/p ratios are reported in a wide range, from the lowest to the highest multiplicity values measured in pp collisions at the LHC
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