Hadronic resonance production in small collision systems with ALICE at the LHC

Short-lived hadronic resonances are good probes to investigate the late-stage evolution of ultra-relativistic heavy ion collisions. Since they have lifetimes comparable to that of the system created after the collision, the measured yields may be affected by the competing rescattering and regeneration processes during the hadronic phase, which modify the particle's momentum distributions after hadronization. Measurements of the production of resonances characterized by different lifetimes, masses, quark content, and quantum numbers can be used to explore the different mechanisms that influence the shape of particle momentum spectra, the dynamical evolution and lifetime of the hadronic phase, strangeness production, and collective effects. Furthermore, multiplicity dependent analyses of resonance production in pp and p--Pb collisions contribute to the investigation of collective effects and their onset in small collision systems. The ALICE experiment has collected data from several collision systems at LHC energies and the latest results on hadronic resonance production in pp and p--Pb collisions are presented here

Event multiplicity dependence production of K∗^*(892)±^{\pm} resonance in pp collisions at s=13\sqrt{s} = 13 TeV with the ALICE detector at the LHC

This thesis reports first measurements of K$^*$(892)$^{\pm}$ produced in pp collisions at $\sqrt{s} = 13$~TeV as function of the event multiplicity. The results include, for each multiplicity class considered, the differential transverse momentum ($p$\textsubscript{T}) spectrum, the mean transverse momentum $\langle p$\textsubscript{T}$\rangle$, the integrated yield (d$N$/d$y$), and the ratio of the K$^*$(892)$^{\pm}$ yield to the K$^0_{\rm S}$ one. The K$^*$(892)$^{\pm}$ has been studied at the same energy and compared with the neutral K$^*$ resonance production, as well as with results from different event generators

Prosafe: a european endeavor to improve quality of critical care medicine in seven countries

BACKGROUND: long-lasting shared research databases are an important source of epidemiological information and can promote comparison between different healthcare services. Here we present ProsaFe, an advanced international research network in intensive care medicine, with the focus on assessing and improving the quality of care. the project involved 343 icUs in seven countries. all patients admitted to the icU were eligible for data collection. MetHoDs: the ProsaFe network collected data using the same electronic case report form translated into the corresponding languages. a complex, multidimensional validation system was implemented to ensure maximum data quality. individual and aggregate reports by country, region, and icU type were prepared annually. a web-based data-sharing system allowed participants to autonomously perform different analyses on both own data and the entire database. RESULTS: The final analysis was restricted to 262 general ICUs and 432,223 adult patients, mostly admitted to Italian units, where a research network had been active since 1991. organization of critical care medicine in the seven countries was relatively similar, in terms of staffing, case mix and procedures, suggesting a common understanding of the role of critical care medicine. conversely, icU equipment differed, and patient outcomes showed wide variations among countries. coNclUsioNs: ProsaFe is a permanent, stable, open access, multilingual database for clinical benchmarking, icU self-evaluation and research within and across countries, which offers a unique opportunity to improve the quality of critical care. its entry into routine clinical practice on a voluntary basis is testimony to the success and viability of the endeavor

Measurement of the Cross Sections of Ξc0\Xi^0_{c} and Ξc+\Xi^+_{c} Baryons and of the Branching-Fraction Ratio BR(Ξc0→Ξ−e+νe\Xi^0_{c} \rightarrow \Xi^-{e}^+\nu_{ e})/BR(Ξc0→Ξ−π+\Xi^0_{c} \rightarrow \Xi^-\pi^+) in pp collisions at 13 TeV

The $p_T$-differential cross sections of prompt charm-strange baryons Ξ$_c^0$ and Ξ$_c^+$ were measured at midrapidity (|y|<0.5) in proton-proton (pp) collisions at a center-of-mass energy $\sqrt{s}$ = 13 TeV with the ALICE detector at the LHC. The Ξ$_c^0$ baryon was reconstructed via both the semileptonic decay (Ξ$^-$e$^+$ν$_e$) and the hadronic decay (Ξ$^-$π$^+$) channels. The Ξ$_c^+$ baryon was reconstructed via the hadronic decay (Ξ$^-$π$^+$π$^+$) channel. The branching-fraction ratio BR(Ξ$_c^0$→Ξ$^-$e$^+$ν$_e$)/BR(Ξ$_c^0$→Ξ$^-$π$^+$) = 1.38±0.14(stat)±0.22(syst) was measured with a total uncertainty reduced by a factor of about 3 with respect to the current world average reported by the Particle Data Group. The transverse momentum ($p_T$) dependence of the Ξ$_c^0-$ and Ξ$_c^+$-baryon production relative to the D$^0$ meson and to the Σ$_c^{0,+,++}$- and Λ$_c^+$-baryon production are reported. The baryon-to-meson ratio increases toward low $p_T$ up to a value of approximately 0.3. The measurements are compared with various models that take different hadronization mechanisms into consideration. The results provide stringent constraints to these theoretical calculations and additional evidence that different processes are involved in charm hadronization in electron-positron (e$^+$e$^-$) and hadronic collisions

Multiharmonic Correlations of Different Flow Amplitudes in Pb-Pb Collisions at sNN=2.76\sqrt{s_{_{NN}}}=2.76 TeV

The event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions, using higher-order symmetric cumulants. We find that different three-harmonic correlations develop during the collective evolution of the medium when compared to correlations that exist in the initial state. These new results cannot be interpreted in terms of previous lower-order flow measurements since contributions from two-harmonic correlations are explicitly removed in the new observables. A comparison to Monte Carlo simulations provides new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions

Pseudorapidity distributions of charged particles as a function of mid- and forward rapidity multiplicities in pp collisions at s\sqrt{s} = 5.02, 7 and 13 TeV

The multiplicity dependence of the pseudorapidity density of charged particles in proton–proton (pp) collisions at centre-of-mass energies $\sqrt{s}~=~5.02$, 7 and 13 TeV measured by ALICE is reported. The analysis relies on track segments measured in the midrapidity range ($|\eta | < 1.5$). Results are presented for inelastic events having at least one charged particle produced in the pseudorapidity interval $|\eta |<1$. The multiplicity dependence of the pseudorapidity density of charged particles is measured with mid- and forward rapidity multiplicity estimators, the latter being less affected by autocorrelations. A detailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented. The results can be used to constrain models for particle production as a function of multiplicity in pp collisions

Measurement of the low-energy antideuteron inelastic cross section

In this Letter, we report the first measurement of the inelastic cross section for antideuteron-nucleus interactions at low particle momenta, covering a range of 0.3 ≤ p < 4 GeV/c. The measurement is carried out using p-Pb collisions at a center-of-mass energy per nucleon–nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.02 TeV, recorded with the ALICE detector at the CERN LHC and utilizing the detector material as an absorber for antideuterons and antiprotons. The extracted raw primary antiparticle-to-particle ratios are compared to the results from detailed ALICE simulations based on the geant4 toolkit for the propagation of (anti)particles through the detector material. The analysis of the raw primary (anti)proton spectra serves as a benchmark for this study, since their hadronic interaction cross sections are well constrained experimentally. The first measurement of the inelastic cross section for antideuteron-nucleus interactions averaged over the ALICE detector material with atomic mass numbers ⟨A⟩ = 17.4 and 31.8 is obtained. The measured inelastic cross section points to a possible excess with respect to the Glauber model parametrization used in geant4 in the lowest momentum interval of 0.3 ≤ p < 0.47 GeV/c up to a factor 2.1. This result is relevant for the understanding of antimatter propagation and the contributions to antinuclei production from cosmic ray interactions within the interstellar medium. In addition, the momentum range covered by this measurement is of particular importance to evaluate signal predictions for indirect dark-matter searches

Jet fragmentation transverse momentum distributions in pp and p-Pb collisions at s \sqrt{s} , sNN \sqrt{s_{\mathrm{NN}}} = 5.02 TeV

Jet fragmentation transverse momentum (j$_{T}$) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti-k$_{T}$ algorithm with resolution parameter R = 0.4 in the pseudorapidity range |η| < 0.25. The j$_{T}$ values are calculated for charged particles inside a fixed cone with a radius R = 0.4 around the reconstructed jet axis. The measured j$_{T}$ distributions are compared with a variety of parton-shower models. Herwig and Pythia 8 based models describe the data well for the higher j$_{T}$ region, while they underestimate the lower j$_{T}$ region. The j$_{T}$ distributions are further characterised by fitting them with a function composed of an inverse gamma function for higher j$_{T}$ values (called the “wide component”), related to the perturbative component of the fragmentation process, and with a Gaussian for lower j$_{T}$ values (called the “narrow component”), predominantly connected to the hadronisation process. The width of the Gaussian has only a weak dependence on jet transverse momentum, while that of the inverse gamma function increases with increasing jet transverse momentum. For the narrow component, the measured trends are successfully described by all models except for Herwig. For the wide component, Herwig and PYTHIA 8 based models slightly underestimate the data for the higher jet transverse momentum region. These measurements set constraints on models of jet fragmentation and hadronisation

Measurements of the groomed and ungroomed jet angularities in pp collisions at s \sqrt{s} = 5.02 TeV

International audienceThe jet angularities are a class of jet substructure observables which characterize the angular and momentum distribution of particles within jets. These observables are sensitive to momentum scales ranging from perturbative hard scatterings to nonperturbative fragmentation into final-state hadrons. We report measurements of several groomed and ungroomed jet angularities in pp collisions at $\sqrt{s}$ = 5.02 TeV with the ALICE detector. Jets are reconstructed using charged particle tracks at midrapidity (|η| < 0.9). The anti-k$_{T}$ algorithm is used with jet resolution parameters R = 0.2 and R = 0.4 for several transverse momentum {p}_{\mathrm{T}}^{\mathrm{ch}} ^{jet} intervals in the 20–100 GeV/c range. Using the jet grooming algorithm Soft Drop, the sensitivity to softer, wide-angle processes, as well as the underlying event, can be reduced in a way which is well-controlled in theoretical calculations. We report the ungroomed jet angularities, λ$_{α}$, and groomed jet angularities, λ$_{α,g}$, to investigate the interplay between perturbative and nonperturbative effects at low jet momenta. Various angular exponent parameters α = 1, 1.5, 2, and 3 are used to systematically vary the sensitivity of the observable to collinear and soft radiation. Results are compared to analytical predictions at next-to-leading-logarithmic accuracy, which provide a generally good description of the data in the perturbative regime but exhibit discrepancies in the nonperturbative regime. Moreover, these measurements serve as a baseline for future ones in heavy-ion collisions by providing new insight into the interplay between perturbative and nonperturbative effects in the angular and momentum substructure of jets. They supply crucial guidance on the selection of jet resolution parameter, jet transverse momentum, and angular scaling variable for jet quenching studies.[graphic not available: see fulltext

Experimental Evidence for an Attractive p-ϕ\phi Interaction

This Letter presents the first experimental evidence of the attractive strong interaction between a proton and a ϕ meson. The result is obtained from two-particle correlations of combined $p$-ϕ⊕ $\bar{p}$-ϕ pairs measured in high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV by the ALICE Collaboration. The spin-averaged scattering length and effective range of the p-ϕ interaction are extracted from the fully corrected correlation function employing the Lednický-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the p-ϕ interaction. These data demonstrate that the interaction is dominated by elastic p-ϕ scattering. Furthermore, an analysis employing phenomenological Gaussian- and Yukawa-type potentials is conducted. Under the assumption of the latter, the N-ϕ coupling constant is found to be $g_{N-ϕ}$ = 0.14 ± 0.03(stat) ± 0.02(syst). This work provides valuable experimental input to accomplish a self-consistent description of the N-ϕ interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium