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Studying charm hadronisation into baryons with azimuthal correlations of with charged particles in pp collisions at TeV
No full textInternational audienceThe distribution of angular correlations between prompt charm hadrons and primary charged particles in pp collisions is sensitive to the charm-quark hadronisation process. In this letter, charm-baryon correlations are measured for the first time by studying the azimuthal-angle difference between charged particles and prompt baryons produced in pp collisions at a centre-of-mass energy TeV, with the ALICE detector. baryons are reconstructed at midrapidity ( GeV/ and pseudorapidity . For GeV/, the comparison with published measurements of D-meson and charged-particle correlations in the same collision system hints at a larger number of low-momentum particles associated with -baryon triggers than with D-meson triggers, both in the collinear and opposite directions with respect to the trigger particle. These differences can be quantified by the comparison of the properties of the near- and away-side correlation peaks, and are not reproduced by predictions of various Monte Carlo event generators, generally underpredicting the associated particle yields at GeV/. This tension between -baryon and D-meson associated peak yields could suggest a modified fragmentation of the charm quark, or a different hadronisation process, when a charm baryon is produced in the final state
Light neutral-meson production in pp collisions at = 13 TeV
No full textInternational audienceThe momentum-differential invariant cross sections of and mesons are reported for pp collisions at = 13 TeV at midrapidity (). The measurement is performed in a broad transverse-momentum range of GeV/ and GeV/ for the and , respectively, extending the coverage of previous measurements. Transverse-mass-scaling violation of up to 60% at low transverse momentum has been observed, agreeing with measurements at lower collision energies. Transverse Bjorken () scaling of the cross sections at LHC energies is fulfilled with a power-law exponent of = 5.010.05, consistent with values obtained for charged pions at similar collision energies. The data is compared to predictions from next-to-leading order perturbative QCD calculations, where the spectrum is best described using the CT18 parton distribution function and the NNFF1.0 or BDSS fragmentation function. Expectations from PYTHIA8 and EPOS LHC overestimate the spectrum for the and are not able to describe the shape and magnitude of the spectrum. The charged-particle multiplicity dependent and spectra show the expected hardening with increasing multiplicity. This is demonstrated across a broad transverse-momentum range and up to events with a charged-particle multiplicity exceeding five times the mean value in minimum bias collisions. The absolute magnitude of the ratio shows a dependence on the charged-particle multiplicity for GeV/, qualitatively described by PYTHIA8 and EPOS LHC due to a rising contribution from feed-down of heavier particles to the spectrum
Measurements of differential two-particle number and transverse momentum correlation functions in pp collisions at = 13 TeV
No full textInternational audienceDifferential two-particle normalized cumulants () and transverse momentum correlations () are measured as a function of the relative pseudorapidity and azimuthal angle difference of charged particle pairs in minimum bias pp collisions at = 13 TeV. The measurements use charged hadrons in the pseudorapidity region of and the transverse momentum range 0.2 2.0 in order to focus on soft multiparticle interactions and to complement prior measurements of these correlation functions in p-Pb and Pb-Pb collisions. The correlation functions are reported for both unlike-sign and like-sign pairs and their charge-independent and charge-dependent combinations. Both the and measured in pp collisions exhibit features qualitatively similar to those observed in p-Pb and Pb-Pb collisions. The and root mean square widths of the near-side peak of the correlation functions are evaluated and compared with those observed in p-Pb and Pb-Pb collisions and show smooth evolution with the multiplicity of charged particles produced in the collision. The comparison of the measured correlation functions with predictions from PYTHIA8 shows that this model qualitatively captures their basic structure and characteristics but feature important differences. In addition, the is used to determine the charge balance function of hadrons produced within the detector acceptance of the measurements. The integral of the balance function is found to be compatible with those reported by a previous measurement in Pb-Pb collisions. These results, which are sensitive to the interplay between the underlying event and mini-jets in pp collisions, establish a baseline for heavy-ion collisions
Proton emission in ultraperipheral Pb-Pb collisions at TeV
No full textInternational audienceThe first measurements of proton emission accompanied by neutron emission in the electromagnetic dissociation (EMD) of Pb nuclei in the ALICE experiment at the LHC are presented. The EMD protons and neutrons emitted at very forward rapidities are detected by the proton and neutron Zero Degree Calorimeters of the ALICE experiment. The emission cross sections of zero, one, two, and three protons accompanied by at least one neutron were measured in ultraperipheral Pb-Pb collisions at a center-of-mass energy per nucleon pair ~TeV. These 0p, 1p, 2p, and 3p cross sections are described by the RELDIS model, and according to this model, they are associated with the production of various isotopes of Pb, Tl, Hg, and Au in the EMD of Pb. The cross sections of the emission of a single proton accompanied by the emission of one, two, or three neutrons in EMD were also measured. The data are significantly overestimated by the RELDIS model, which predicts that the (1p,1n), (1p,2n), and (1p,3n) cross sections are very similar to the cross sections for the production of the thallium isotopes Tl
A Cosmological Solution to the Doublet-Triplet Splitting Problem
No full textInternational audienceWe propose a model that provides a simultaneous solution to the doublet-triplet splitting problem of grand unified theories, the electroweak hierarchy problem and the strong CP problem. The mechanism is based on the dynamics of two axion-like particles that would crunch the universe at the time of the QCD phase transition if triplets were light or had a VEV or if doublets were heavy or did not have a VEV. The only trace left at low energies are these two axion-like particles. They are weakly coupled to the Standard Model and could be detected at upcoming axion experiments or by a combination of neutron EDM measurements and the astrophysical detection of fuzzy dark matter
Enhanced strain-hardening in newly designed Co-free austenitic high entropy alloys with an optimised nitrogen solubility
No full textInternational audienceThe effect of nitrogen on the microstructure and mechanical behavior of several Co-free high entropy alloys (HEAs) from the CrFeMnNi family was studied. Alloy design approach, based on thermodynamic computations, was implemented to obtain alloys with a high chromium content, a high nitrogen solubility as well as good austenite stability. An optimisation was made to meet selected criteria which led to three compositions with different nickel contents (Cr20Fe40Mn15Ni25, Cr20Fe44Mn15Ni21, and Cr20Fe47Mn15Ni18) optimised for, respectively, 0.4, 0.5 and 0.6 wt% N. Such optimised alloys were elaborated and compared with another Co-free HEA (Cr14Fe46Mn17Ni23) doped with 0.11–0.29 wt% N. It was shown that up to 0.56 wt% N could be dissolved in the matrixes in agreement with their computed high nitrogen solubility. The differences in chemical composition between the four studied matrixes did not lead to any change in behavior in presence of nitrogen: the lattice parameter expansion and mechanical resistances (yield strength and tensile strength) evolve linearly with nitrogen addition, up to at least 0.56 wt%. Especially, a significant effect of nitrogen content on strain-hardening was observed and was attributed to the formation of nanotwins in nitrogen-rich alloys
Primordial black holes and their gravitational-wave signatures
No full textInternational audienceIn the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers observed in gravitational wave detectors and an important component of the dark matter in the Universe. Significant progress has been achieved both on the theory side and from the point of view of observations, including new models and more accurate calculations of PBH formation, evolution, clustering, merger rates, as well as new astrophysical and cosmological probes. In this work, we review, analyse and combine the latest developments in order to perform end-to-end calculations of the various gravitational wave signatures of PBHs. Different ways to distinguish PBHs from stellar black holes are emphasized. Finally, we discuss their detectability with LISA, the first planned gravitational-wave observatory in space
Acoustic Positioning for Deep Sea Neutrino Telescopes with a System of Piezo Sensors Integrated into Glass Spheres
No full textInternational audiencePosition calibration in the deep sea is typically done by means of acoustic multilateration using three or more acoustic emitters installed at known positions. Rather than using hydrophones as receivers that are exposed to the ambient pressure, the sound signals can be coupled to piezo ceramics glued to the inside of existing containers for electronics or measuring instruments of a deep sea infrastructure. The ANTARES neutrino telescope operated from 2006 until 2022 in the Mediterranean Sea at a depth exceeding 2000m. It comprised nearly 900 glass spheres with 432mm diameter and 15mm thickness, equipped with photomultiplier tubes to detect Cherenkov light from tracks of charged elementary particles. In an experimental setup within ANTARES, piezo sensors have been glued to the inside of such - otherwise empty - glass spheres. These sensors recorded signals from acoustic emitters with frequencies from 46545 to 60235Hz. Two waves propagating through the glass sphere are found as a result of the excitation by the waves in the water. These can be qualitatively associated with symmetric and asymmetric Lamb-like waves of zeroth order: a fast (early) one with mm/s and a slow (late) one with mm/s. Taking these findings into account improves the accuracy of the position calibration. The results can be transferred to the KM3NeT neutrino telescope, currently under construction at multiple sites in the Mediterranean Sea, for which the concept of piezo sensors glued to the inside of glass spheres has been adapted for monitoring the positions of the photomultiplier tubes
Helicity-dependent parton distribution functions at next-to-next-to-leading order accuracy from inclusive and semi-inclusive deep-inelastic scattering data
No full textInternational audienceWe present MAPPDFpol1.0, a new determination of the helicity-dependent parton distribution functions (PDFs) of the proton from a set of longitudinally polarised inclusive and semi-inclusive deep-inelastic scattering data. The determination includes, for the first time, next-to-next-to-leading order QCD corrections to both processes, and is carried out in a framework that combines a neural-network parametrisation of PDFs with a Monte Carlo representation of their uncertainties. We discuss the quality of the determination, in particular its dependence on higher-order corrections, on the choice of data set, and on theoretical constraints
A novel strategy to prove chiral symmetry breaking in QCD-like theories
No full textInternational audienceWe demonstrate that chiral symmetry breaking occurs in the confining phase of QCD-like theories with colors and flavors. Our proof is based on a novel strategy, called `downlifting', by which solutions of the 't Hooft anomaly matching and persistent mass conditions for a theory with flavors are constructed from those of a theory with flavors, while is fixed. By induction, chiral symmetry breaking is proven for any , where is the smallest prime factor of . The proof can be extended to under the additional assumption on the absence of phase transitions when quark masses are sent to infinity. Our results do not rely on ad-hoc assumptions on the spectrum of massless bound states