1,402 research outputs found
Exploring the N\ensuremath{\Lambda}\textendash{}N\ensuremath{\Sigma} coupled system with high precision correlation techniques at the LHC
No full textThe interaction of and hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel
dynamics. Due to the small mass difference of the N and N systems, the sizable coupling strength of
the N ↔ N processes constitutes a crucial element in the determination of the N interaction. In
this letter we present the most precise measurements on the interaction of p pairs, from zero relative
momentum up to the opening of the N channel. The correlation function in the relative momentum
space for p ⊕ p pairs measured in high-multiplicity triggered pp collisions at √s = 13 TeV at the
LHC is reported. The opening of the inelastic N channels is visible in the extracted correlation function
as a cusp-like structure occurring at relative momentum k∗ = 289 MeV/c. This represents the first direct
experimental observation of the N ↔ N coupled channel in the p system. The correlation function
is compared with recent chiral effective field theory calculations, based on different strengths of the
N ↔ N transition potential. A weaker coupling, as possibly supported by the present measurement,
would require a more repulsive three-body NN interaction for a proper description of the in-medium
properties, which has implications on the nuclear equation of state and for the presence of hyperons
inside neutron stars
Aerobic oxidation of hydrocarbons using N-hydroxyphthalimide (NHPI) catalysts for cetane enhancement
No full textGasoline compression ignition (GCI) utilizes gasoline-like fuels in low temperature compression ignition (CI) engines. As a result, thermal efficiency is increased compared to that of a conventional spark ignition (SI) engine, while NOx and soot tailpipe emissions are reduced compared to those from a diesel engine. This combustion strategy requires gasoline fuel with a moderate ignition delay for cold start and high load demand conditions. This work proposes an approach to control the ignition characteristics of gasoline to widen GCI engine operation conditions. Aerobic oxidation of gasoline using N-hydroxyphthalimide (NHPI) catalyst has been suggested as an effective method to produce high cetane components, such as hydroperoxide. NHPI catalyzed oxidation reactions of toluene and market gasoline were studied at different reaction conditions using an autoclave batch reactor. The produced hydroperoxide (HP) was quantified by titration using triphenylphosphine (Ph3P) followed by Gas Chromatography (GC) analysis. In addition, an ignition quality tester (IQT) was used to estimate the derived cetane number (DCN) of the oxygenated product. The gasoline cetane number was enhanced by nine digits using gaseous oxygen at moderate conditions (10 bar, 110 °C for 3 h). Aerobic oxidation of gasoline using NHPI catalyst was found to be a promising approach to control the ignition characteristics of fuel and hence an enabler of the GCI engine concept.We gratefully acknowledge the High-Through Put Research Lab team in the R&D Chemical division in Saudi Aramco for their extensive support in the analysis of the samples, Anaam Shaikh Ali for conducting the TGA analysis, the Clean Combustion Research Center (CCRC) at King Abdullah University of Science and Technology (KAUST) for the IQT analysis, and Philip Embleton for providing language help. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors
Preparation and Characterization of Some Chelate Complexe with New bi-dentate (N,O)bis-Schiff base Ligand
No full text In this research newchelation complexes were prepared for Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) ions with new bis schiff base ligand [2-(-((4-(-1-(2-phenylhydrazono)ethyl)phenyl)imino)methyl)phenol](M-Sal). The new ligand chracterized depends on (Uv-Vis, IR) spectroscopies, 1H-NMR andMass spectra. The results of flame atomic absorption indicate that (Metal:Ligand) portions were (1:1) for Cr(III), Ni(II) and Cu(II) complexes and were (1:2) for Mn(II) and Co(II) complexes. The geometries of prepared complexes suggested according to the results of Uv-Vis and IR spectroscopies, magnetic susceptibility, molar conductance and flame atomic absorptionwhich were squar plannar for Ni(II)and Cu(II) complexes while the rest complexes have the octahedral geometry
Constraining the K ̄ N coupled channel dynamics using femtoscopic correlations at the LHC
No full textThe interaction of K−with protons is characterised by the presence of several coupled channels, systems like K 0 n and π with a similar mass and the same
quantum numbers as the K−p state. The strengths of these
couplings to the K−p system are of crucial importance for
the understanding of the nature of the (1405) resonance
and of the attractive K−p strong interaction. In this arti-
cle, we present measurements of the K−p correlation func-
tions in relative momentum space obtained in pp collisions at
√s = 13 TeV, in p–Pb collisions at √sNN = 5.02 TeV, and
(semi)peripheral Pb–Pb collisions at √sNN = 5.02 TeV. The
emitting source size, composed of a core radius anchored to
the K+p correlation and of a resonance halo specific to each
particle pair, varies between 1 and 2 fm in these collision sys-
tems. The strength and the effects of the K 0 n and π inelas-
tic channels on the measured K−p correlation function are
investigated in the different colliding systems by comparing
the data with state-of-the-art models of chiral potentials. A
novel approach to determine the conversion weights ω, nec-
essary to quantify the amount of produced inelastic channels
in the correlation function, is presented. In this method, parti-
cle yields are estimated from thermal model predictions, and
their kinematic distribution from blast-wave fits to measured
data. The comparison of chiral potentials to the measured
K−p interaction indicates that, while the π –K−p dynam-
ics is well reproduced by the model, the coupling to the K 0 n
channel in the model is currently underestimate
Femtoscopic study of the proton-proton and proton-deuteron systems in heavy-ion collisions at the LHC
No full textThis 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
Femtoscopic study of the proton-proton and proton-deuteron systems in heavy-ion collisions at the LHC
No full textThis 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
Photoproduction of K+K- Pairs in Ultraperipheral Collisions
No full textKþK− pairs may be produced in photonuclear collisions, either from the decays of photoproduced
φð1020Þ mesons or directly as nonresonant KþK− pairs. Measurements of KþK− photoproduction probe the
couplings between the φð1020Þ and charged kaons with photons and nuclear targets. The kaon-proton
scattering occurs at energies far above those available elsewhere. We present the first measurement of
coherent photoproduction of KþK− pairs on lead ions in ultraperipheral collisions using the ALICE detector,
including the first investigation of direct KþK− production. There is significant KþK− production at low
transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range 1.1 <
M KK < 1.4 GeV=c2 above the φð1020Þ resonance, for rapidity jy KK j < 0.8 and p T;KK < 0.1 GeV=c, the
measured coherent photoproduction cross section is dσ=dy 1⁄4 3.37 0.61ðstatÞ 0.15ðsystÞ mb. The
center-of-mass energy per nucleon of the photon-nucleus (Pb) system WγPb;n ranges from 33 to 188 GeV, far
higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for
φð1020Þ photoproduction alone. The mass spectrum is fit to a cocktail consisting of φð1020Þ decays, direct
KþK− photoproduction, and interference between the two. The confidence regions for the amplitude and
relative phase angle for direct KþK− photoproduction are presente
First measurements of N-subjettiness in central Pb-Pb collisions at sNN−−−√ = 2.76 TeV
No full textThe ALICE Collaboration reports the first fully-corrected measurements of the N-subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of s = 7 TeV and sNN = 2.76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ2/τ1, which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate of two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of R = 0.4 and charged jet transverse momentum of 40 ≤ pT,jet ≤ 60 GeV/c, which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ2/τ1 observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of τ2/τ1, together with the splitting aperture angle ∆R, are also performed in pp collisions at s = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at s = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ2/τ1 are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions. [Figure not available: see fulltext.
Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb–Pb collisions at √sNN = 5.02 TeV
No full textThe first measurement of the e+e− pair production at low lepton pair transverse momentum (p T,ee) and low invariant mass (m ee) in non-central Pb–Pb collisions at sNN = 5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|η e | < 0.8) as a function of invariant mass (0.4 ≤ m ee < 2.7 GeV/c 2) in the 50–70% and 70–90% centrality classes for p T,ee < 0.1 GeV/c, and as a function of p T,ee in three m ee intervals in the most peripheral Pb–Pb collisions. Below a p T,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The m ee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the p T,ee spectra. The measured 〈pT,ee2〉 of the excess p T,ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region. [Figure not available: see fulltext.]
Charged-particle production as a function of the relative transverse activity classifier in pp, p–Pb, and Pb–Pb collisions at the LHC
No full textAbstract Measurements of charged-particle production in pp, p–Pb, and Pb–Pb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum p T trig in the range 8 < p T trig < 15 GeV/c. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier, R T = N ch T / N ch T , is used to group events according to their UE activity, where N ch T is the charged-particle multiplicity per event in the transverse region and N ch T is the mean value over the whole analysed sample. The energy dependence of the R T distributions in pp collisions at s = 2.76, 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particle p T spectra as a function of R T in the three azimuthal regions in pp, p–Pb, and Pb–Pb collisions at s NN = 5.02 TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and p–Pb)
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