The measurement of the production of charm jets, identified by the presence of a D$^{0}$ meson in the jet constituents, is presented in proton–proton collisions at centre-of-mass energies of $ ...\sqrt{s} $ = 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The D$^{0}$ mesons were reconstructed from their hadronic decay D$^{0}$ → K$^{−}$π$^{+}$ and the respective charge conjugate. Jets were reconstructed from D$^{0}$-meson candidates and charged particles using the anti-k$_{T}$ algorithm, in the jet transverse momentum range 5 < p$_{T,chjet}$< 50 GeV/c, pseudorapidity |η$_{jet}$| < 0.9 − R, and with the jet resolution parameters R = 0.2, 0.4, 0.6. The distribution of the jet momentum fraction carried by a D$^{0}$ meson along the jet axis $ \left({z}_{\Big\Vert}^{\textrm{ch}}\right) $ was measured in the range 0.4 <$ {z}_{\Big\Vert}^{\textrm{ch}} $< 1.0 in four ranges of the jet transverse momentum. Comparisons of results for different collision energies and jet resolution parameters are also presented. The measurements are compared to predictions from Monte Carlo event generators based on leading-order and next-to-leading-order perturbative quantum chromodynamics calculations. A generally good description of the main features of the data is obtained in spite of a few discrepancies at low p$_{T,chjet}$. Measurements were also done for R = 0.3 at $ \sqrt{s} $ = 5.02 and are shown along with their comparisons to theoretical predictions in an appendix to this paper.graphic not available: see fulltext
We propose a new fixed-target experiment for the study of electromagnetic and hard probes of the Quark-Gluon Plasma (QGP) in heavy-ion collisions at the CERN SPS. The experiment aims at performing ...measurements of the dimuon spectrum from threshold up to the charmonium region, and of hadronic decays of charm and strange hadrons. It is based on a muon spectrometer, which includes a toroidal magnet and six planes of tracking detectors, coupled to a vertex spectrometer, equipped with Si MAPS immersed in a dipole field. High luminosity is an essential requirement for the experiment, with the goal of taking data with 10\(^6\) incident ions/s, at collision energies ranging from \(\sqrt{s_{\rm NN}} = 6.3\) GeV (\(E_{\rm lab}= 20\) A GeV) to top SPS energy (\(\sqrt{s_{\rm NN}} = 17.3\) GeV, \(E_{\rm lab}= 158\) A GeV). This document presents the physics motivation, the foreseen experimental set-up including integration and radioprotection studies, the current detector choices together with the status of the corresponding R&D, and the outcome of physics performance studies. A preliminary cost evaluation is also carried out.
Three-body nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron ...stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the three-nucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the three-body forces. In this work, we present the first direct measurement of the p–p–p and p–p–
Λ
systems in terms of three-particle correlation functions carried out for pp collisions at
s
=
13
TeV. Three-particle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the three-particle interaction contribution to these correlations can be isolated after subtracting the known two-body interaction terms. A negative cumulant is found for the p–p–p system, hinting to the presence of a residual three-body effect while for p–p–
Λ
the cumulant is consistent with zero. This measurement demonstrates the accessibility of three-baryon correlations at the LHC.
A bstract The ALICE Collaboration reports a search for jet quenching effects in high-multiplicity (HM) proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, using the semi-inclusive ...azimuthal-difference distribution ∆ φ of charged-particle jets recoiling from a high transverse momentum (high- p T , trig ) trigger hadron. Jet quenching may broaden the ∆ φ distribution measured in HM events compared to that in minimum bias (MB) events. The measurement employs a p T , trig -differential observable for data-driven suppression of the contribution of multiple partonic interactions, which is the dominant background. While azimuthal broadening is indeed observed in HM compared to MB events, similar broadening for HM events is observed for simulations based on the PYTHIA 8 Monte Carlo generator, which does not incorporate jet quenching. Detailed analysis of these data and simulations show that the azimuthal broadening is due to bias of the HM selection towards events with multiple jets in the final state. The identification of this bias has implications for all jet quenching searches where selection is made on the event activity.
A bstract Results on the transverse spherocity dependence of light-flavor particle production ( π , K, p, ϕ , K *0 , $$ {\textrm{K}}_{\textrm{S}}^0 $$ K S 0 , Λ, Ξ) at midrapidity in ...high-multiplicity pp collisions at $$ \sqrt{s} $$ s = 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator $$ \left({S}_{\textrm{O}}^{p_{\textrm{T}}=1}\right) $$ S O p T = 1 categorizes events by their azimuthal topology. Utilizing narrow selections on $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ S O p T = 1 , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ S O p T = 1 estimator is found to effectively constrain the hardness of the events when the midrapidity (| η | < 0.8) estimator is used. The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced. The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ S O p T = 1 .
A bstract Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV and ...the corresponding nuclear modification factor $$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ R pPb ch jet are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region | η jet | < 0 . 5 from charged particles using the anti- k T algorithm with resolution parameters R = 0 . 2, 0 . 3, and 0 . 4. The p T -differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10 < $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ p T , jet ch < 140 GeV/ c and 10 < $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ p T , jet ch < 160 GeV/ c , respectively, together with the nuclear modification factor $$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ R pPb ch jet in the range 10 < $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ p T , jet ch < 140 GeV/ c . The analysis extends the p T range of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD P owheg calculations with parton shower provided by P ythia 8 as well as by J etscape simulations.
A bstract Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at $$ \sqrt{s} $$ s = 13 TeV and p–Pb collisions at $$ ...\sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV. The correlation functions are measured as a function of relative azimuthal angle ∆ φ and pseudorapidity separation ∆ η for pairs of primary charged particles within the pseudorapidity interval | η | < 0 . 9 and the transverse-momentum interval 1 < p T < 4 GeV/ c . Flow coefficients are extracted for the long-range correlations (1 . 6 < |∆ η | < 1 . 8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.
A bstract The transverse momentum ( p T ) and centrality dependence of the nuclear modification factor R AA of prompt and non-prompt J/ ψ , the latter originating from the weak decays of beauty ...hadrons, have been measured by the ALICE collaboration in Pb–Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5.02 TeV. The measurements are carried out through the e + e − decay channel at midrapidity (| y | < 0.9) in the transverse momentum region 1.5 < p T < 10 GeV/ c . Both prompt and non-prompt J/ ψ measurements indicate a significant suppression for p T > 5 GeV/ c , which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping p T intervals, and cover the kinematic region down to p T = 1.5 GeV/ c at midrapidity, not accessible by other LHC experiments. The suppression of prompt J/ ψ in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J/ ψ production from recombination of c and $$ \overline{\textrm{c}} $$ c ¯ quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J/ ψ . For non-prompt J/ ψ , the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quark-gluon plasma is consistent with measurements within uncertainties.
