Measurement of non-prompt D0-meson elliptic flow in Pb–Pb collisions at sNN=5.02 TeV

The elliptic flow (v2) of D mesons from beauty-hadron decays (non-prompt D) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed at midrapidity (| y| < 0.8) from their hadronic decay D → K -π + , in the transverse momentum interval 2 < pT< 12 GeV/c. The result indicates a positive v2 for non-prompt D mesons with a significance of 2.7 σ . The non-prompt D -meson v2 is lower than that of prompt non-strange D mesons with 3.2 σ significance in

Measurement of the Λ hyperon lifetime

A new, more precise measurement of the Λ hyperon lifetime is performed using a large data sample of Pb-Pb collisions at sNN=5.02 TeV with ALICE. The Λ and Λ¯ hyperons are reconstructed at midrapidity using their two-body weak decay channel Λ→p+π- and Λ¯→p¯+π+. The measured value of the Λ lifetime is τΛ=[261.07±0.37(stat.)±0.72(syst.)] ps. The relative difference between the lifetime of Λ and Λ¯, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value (τΛ-τΛ¯)/τΛ=0.0013±0.0028(stat.)±0.0021(syst.) is consistent with zero within the uncertainties. Both measurements of the Λ hyperon lifetime and of the relative difference between τΛ and τΛ¯ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise

Study of flavor dependence of the baryon-to-meson ratio in proton-proton collisions at s=13 TeV

The production cross sections of D0 and Λc+ hadrons originating from beauty-hadron decays (i.e., nonprompt) were measured for the first time at midrapidity (|y|<0.5) by the ALICE Collaboration in proton-proton collisions at a center-of-mass energy s=13 TeV. They are described within uncertainties by perturbative QCD calculations employing the fragmentation fractions of beauty quarks to baryons measured at forward rapidity by the LHCb Collaboration. The bb¯ production cross section per unit of rapidity at midrapidity, estimated from these measurements, is dσbb¯/dy||y|<0.5=83.1±3.5(stat)±5.4(syst)-3.2+12.3(extrap) μb. The baryon-to-meson ratios are computed to investigate the hadronization mechanism of beauty quarks. The nonprompt Λc+/D0 production ratio has a similar trend to the one measured for the promptly produced charmed particles and to the p/π+ and Λ/KS0 ratios, suggesting a similar baryon-formation mechanism among light, strange, charm, and beauty hadrons. The pT -integrated nonprompt Λc+/D0 ratio is found to be significantly higher than the one measured in e+e- collisions

Study of the p–p–K+ and p–p–K- dynamics using the femtoscopy technique

The interactions of kaons (K) and antikaons (K ¯) with few nucleons (N) were studied so far using kaonic atom data and measurements of kaon production and interaction yields in nuclei. Some details of the three-body KNN and K ¯ NN dynamics are still not well understood, mainly due to the overlap with multi-nucleon interactions in nuclei. An alternative method to probe the dynamics of three-body systems with kaons is to study the final state interaction within triplet of particles emitted in pp collisions at the Large Hadron Collider, which are free from effects due to the presence of bound nucleons. This Letter reports the first femtoscopic study of p–p–K + and p–p–K - correlations measured in high-multiplicity pp collisions at s = 13 TeV by the ALICE Collaboration. The analysis shows that the measured p–p–K + and p–p–K - correlation functions can be interpreted in terms of pairwise interactions in the triplets, indicating that the dynamics of such systems is dominated by the two-body interactions without significant contributions from three-body effects or bound states

Multiplicity dependence of charged-particle production in pp, p–Pb, Xe–Xe and Pb–Pb collisions at the LHC

Multiplicity (Nch) distributions and transverse momentum (pT) spectra of inclusive primary charged particles in the kinematic range of |η|<0.8 and 0.15 GeV/c<pT<10 GeV/c are reported for pp, p–Pb, Xe–Xe and Pb–Pb collisions at centre-of-mass energies per nucleon pair ranging from sNN=2.76 TeV up to 13 TeV. A sequential two-dimensional unfolding procedure is used to extract the correlation between the transverse momentum of primary charged particles and the charged-particle multiplicity of the corresponding collision. This correlation sharply characterises important features of the final state of a collision and, therefore, can be used as a stringent test of theoretical models. The multiplicity distributions as well as the mean and standard deviation derived from the pT spectra are compared to state-of-the-art model predictions. Providing these fundamental observables of bulk particle production consistently across a wide range of collision energies and system sizes can serve as an important input for tuning Monte Carlo event generators

Enhanced Deuteron Coalescence Probability in Jets

International audienceThe transverse-momentum (pT) spectra and coalescence parameters B2 of (anti)deuterons are measured in p-p collisions at s=13  TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest pT in the event (pTlead&gt;5  GeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the B2Jet is not reproduced by the models, which instead give a decreasing trend