Matter-antimatter asymmetry?

The widely held expectation of equal matter and antimatter production during the Big Bang sharply contrasts with the observable Universe's current predominant composition of matter. This persistent asymmetry poses an intriguing puzzle and remains a paramount challenge in modern physics. In this study, we delve into the enigma of antimatter, focusing on the matter-antimatter asymmetry within the context of de Sitter spacetime as the classical background. De Sitter spacetime, representing a scenario where the cosmological constant governs, leading to accelerated expansion, emerges as a pivotal model essential for comprehending the dynamics of the present Universe. Our analysis, rooted in a fundamental requirement of the quantum field theory description of de Sitterian elementary systems — specifically, the analyticity requirement in the complexified de Sitter manifold, offers a novel perspective. It suggests that the matter-antimatter asymmetry is an observational anomaly discernible exclusively by local observers with causal access to a specific segment of de Sitter spacetime. In contrast to local observations, the global structure of this spacetime maintains a perfect matter-antimatter symmetry. This unconventional insight challenges established perspectives, ushering in a paradigm shift in our understanding of the observed asymmetry in the distribution of matter and antimatter throughout the Universe

Direct high-precision measurement of the mass difference of 77^{77}As-77^{77}Se related to neutrino mass determination

International audienceThe first direct determination of the ground-state-to-ground-state ${\beta^{-}}$-decay $Q$-value of $^{77}$As to $^{77}$Se was performed by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The resulting $Q$-value is 684.463(70) keV, representing a remarkable 24-fold improvement in precision compared to the value reported in the most recent Atomic Mass Evaluation (AME2020). With the significant reduction of the uncertainty of the ground-state-to-ground-state $Q$-value and knowledge of the excitation energies in $^{77}$Se from $\gamma$-ray spectroscopy, the ground-state-to-excited-state $Q$-value of the transition $^{77}$As (3/2$^{-}$, ground state) $\rightarrow$$^{77}$Se$^{*}$ (5/2$^{+}$, 680.1035(17) keV) was refined to be 4.360(70) keV. We confirm that this potential low $Q$-value ${\beta^{-}}$-decay transition for neutrino mass determination is energetically allowed at a confidence level of about 60$\sigma$. Nuclear shell-model calculations with two well-established effective Hamiltonians were used to estimate the partial half-life for the low $Q$-value transition. The half-life was found to be of the order of 10$^{9}$ years, which makes this candidate a potential source for rare-event experiments searching for the electron antineutrino mass

Towards experimental confirmation of quarkonia melting in Quark Gluon Plasma: A review of recent measurements of quarkonia production in relativistic heavy-ion collisions

Version accepted to SymmetryInternational audienceThe dissociation, or “melting”, of heavy quarkonia states due to color charge screening is a predicted signature of the Quark Gluon Plasma (QGP) formation, with a quarkonium state predicted to dissociate when the temperature of the medium is higher than the binding energy of the quarkonium state. A conclusive experimental observation of quarkonium melting coupled with a detailed theoretical understanding of the melting mechanism would enable the use of quarkonia states as temperature probes of the QGP, a long-sought goal in the field of relativistic heavy-ion collisions. However, the interpretation of quarkonia suppression measurements in heavy-ion collisions is complicated by numerous other cold nuclear matter effects which also result in the dissociation of bound quarkonia states. A comprehensive understanding of these cold nuclear matter effects is therefore needed in order to correctly interpret quarkonia production measurements in heavy ion collisions and to observe the melting of quarkonium states experimentally. In this review, recent measurements of quarkonia production in $p$A and AA collisions and their state-of-the-art theoretical interpretations will be discussed, as well as the future measurements needed to further the knowledge of cold nuclear matter effects and realize a measurement of quarkonia melting in heavy ion collisions

Search for long-lived particles decaying in the CMS muon detectors in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceA search for long-lived particles (LLPs) decaying in the CMS muon detectors is presented. A data sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$ recorded at the LHC in 2016-2018, is used. The decays of LLPs are reconstructed as high multiplicity clusters of hits in the muon detectors. In the context of twin Higgs models, the search is sensitive to LLP masses from 0.4 to 55 GeV and a broad range of LLP decay modes, including decays to hadrons, $\tau$ leptons, electrons, or photons. No excess of events above the standard model background is observed. The most stringent limits to date from LHC data are set on the branching fraction of the Higgs boson decay to a pair of LLPs with masses below 10 GeV. This search also provides the best limits for various intervals of LLP proper decay length and mass. Finally, this search sets the first limits at the LHC on a dark quantum chromodynamic sector whose particles couple to the Higgs boson through gluon, Higgs boson, photon, vector, and dark-photon portals, and is sensitive to branching fractions of the Higgs boson to dark quarks as low as 2$\times$10$^{-3}$

Beam test of n-type Silicon pad array detector at PS CERN

International audienceThis work reports the testing of a Forward Calorimeter (FoCal) prototype based on an n-type Si pad array detector at the CERN PS accelerator. The FoCal is a proposed upgrade in the ALICE detector operating within the pseudorapidity range of 3.2 < $\mathrm{\eta}$ < 5.8. It aims to measure direct photons, neutral hadrons, vector mesons, and jets for the study of gluon saturation effects in the unexplored region of low momentum fraction x ($\mathrm{\sim10^{-5} - 10^{-6}}$). The prototype is a $\mathrm{8\times9}$ n-type Si pad array detector with each pad occupying one cm$^2$ area, fabricated on a 6-in, 325~$\mathrm{\pm 10 \thinspace \mu}$m thick, and high-resistivity ($\sim$7 k$\Omega \thinspace$ cm) Si wafer which is readout using HGCROCv2 chip. The detector is tested using pion beams of energy 10~GeV and electron beams of energy 1-5~GeV. The measurements of the Minimum Ionizing Particle (MIP) response of pions and the shower profiles of electrons are reported

Impact of the Magnetic Horizon on the Interpretation of the Pierre Auger Observatory Spectrum and Composition Data

International audienceThe flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood of order $B_{\rm rms}\simeq (50-100)\,{\rm nG}\,(20\rm{Mpc}/{d_{\rm s})( 100\,\rm{kpc}/L_{\rm coh}})^{1/2}$, with $d_{\rm s}$ the typical intersource separation and $L_{\rm coh}$ the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., $\propto E^{-2}$. An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6~EeV

Scission Deformation of the <math display="inline"><mrow><mrow><mmultiscripts><mrow><mi>Cd</mi></mrow><mprescripts/><none/><mrow><mn>120</mn></mrow></mmultiscripts></mrow><mo>/</mo><mrow><mmultiscripts><mrow><mi>Sn</mi></mrow><mprescripts/><none/><mrow><mn>132</mn></mrow></mmultiscripts></mrow></mrow></math> Neutronless Fragmentation in <math display="inline"><mrow><mmultiscripts><mrow><mi>Cf</mi></mrow><mprescripts/><none/><mrow><mn>252</mn></mrow></mmultiscripts><mo stretchy="false">(</mo><mi>sf</mi><mo stretchy="false">)</mo></mrow></math>

International audienceWe report on a study of the radiative decay of fission fragments populated via neutronless fission of Cf252(sf). Applying the double-energy method a perfect mass identification is achieved for these rare events. In the specific case of the Cd120/Sn132 cold fragmentation, we find that Sn132 is produced in its ground state. We can therefore directly measure the excitation energy of the complementary fragment, Cd120. The reproduction of the γ-ray spectrum, measured in coincidence with the neutronless fission events, is sensitive to the angular momentum distribution of the studied primary fragment. The latter estimated using a time-dependent collective Hamiltonian model, allows us to constrain for the first time the deformation (β2≃0.4) of the studied fission fragment at scission. The present work demonstrates the high potential of the understudied neutronless fission channel for extracting detailed information on both fission fragments and process

Measurement of the <math display="inline"><mrow><mmultiscripts><mrow><mi>Ce</mi></mrow><mprescripts/><none/><mrow><mn>140</mn></mrow></mmultiscripts><mo stretchy="false">(</mo><mi mathvariant="normal">n</mi><mo>,</mo><mi>γ</mi><mo stretchy="false">)</mo></mrow></math> Cross Section at n_TOF and Its Astrophysical Implications for the Chemical Evolution of the Universe

International audienceCe140(n,γ) is a key reaction for slow neutron-capture (s-process) nucleosynthesis due to being a bottleneck in the reaction flow. For this reason, it was measured with high accuracy (uncertainty ≈5%) at the n_TOF facility, with an unprecedented combination of a high purity sample and low neutron-sensitivity detectors. The measured Maxwellian averaged cross section is up to 40% higher than previously accepted values. Stellar model calculations indicate a reduction around 20% of the s-process contribution to the Galactic cerium abundance and smaller sizeable differences for most of the heavier elements. No variations are found in the nucleosynthesis from massive stars

Formats de précision réduite et d'exposant réduit pour l'accélération du produit Matrice-Vecteur en précision adaptative

Mixed precision algorithms aim at taking advantage of the performance of low precisions while maintaining the accuracy of high precision. In particular adaptive precision algorithms dynamically adapt at runtime the precisions used for different variables or operations. For example Graillat et al (2023) have proposed an adaptive precision sparse matrix--vector product (SpMV) which stores the matrix elements in a precision inversely proportional to their magnitude. In theory, this algorithm can therefore make use of a large number of different precisions, but the practical results previously obtained only achieved high performance using natively supported double and single precisions. In this work we combine this algorithm with an efficient memory accessor for custom reduced precision formats (Mukunoki et al. 2016). This allows us to experiment with a large set of different precision formats with fine variations of the number of bits dedicated to the significand. Moreover we also explore the possibility to reduce the number of bits dedicated to the exponent using the fact that the elements that share the same precision format are of similar magnitude. We experimentally evaluate the performance of using four or seven different custom formats using reduced precision and possibly reduced exponent, and demonstrate their effectiveness compared with the existing version only using double and single precisions

Skewness and kurtosis of mean transverse momentum fluctuations at the LHC energies

International audienceThe first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions