Joint Institute for Nuclear Research
Recent publications
The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.
An experiment on the study of the 246Fm spontaneous fission was conducted using the SHELS separator. The isotope was synthesized in the complete fusion reaction of 40Ar beam ions and 208Pb target nuclei. The neutron yields of 246Fm spontaneous fission (ν = 3.79 ± 0.30, σν2 = 2.1) were obtained using the SFiNx detector system. The multiplicity distribution of emitted prompt neutrons was restored using the Tikhonov method of statistical regularisation (ν = 3.79 ± 0.20, σ2 = 2.8). The spontaneous fission branching ratio (bSF = 0.061 ± 0.005) and the half-life (T1/2 = 1.50+0.08−0.07 s) of the isotope were determined. The experimental data were compared with scission point model predictions. An agreement was observed in the average number of neutrons per spontaneous fission process. However, the forms of the experimental and model prompt neutron multiplicity distributions differ significantly. Full text:
The authors present a concurrent Monte Carlo (MC)–molecular dynamics (MD) approach to modeling matter response to excitation of its electronic system at nanometric scales. The two methods are combined on-the-fly at each time step in one code, TREKIS-4. The MC model describes the arrival of irradiation (a photon, an electron, or a fast ion). It traces induced cascades of secondary electrons and holes, and their energy exchange with atoms due to scattering. The excited atomic system is simulated with an MD model. An efficient way is proposed to account for nonthermal effects in the electron-atom energy transfer in covalent materials via the conversion of the potential energy of the electronic ensemble into the kinetic energy of atoms. Such a combined MC–MD approach enables a time-resolved tracing of the excitation kinetics of both, the electronic and atomic systems, and their simultaneous response to a deposited dose. As a proof-of-principle, it is shown that the proposed method describes atomic dynamics after X-ray irradiation in good agreement with tight-binding MD. The model also allows gaining insights into the atomic system behavior during the energy deposition from a nonequilibrium electronic system excited by an ion impact.
Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matter–antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry ¹ . As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon–antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ ⁻ baryon and its antiparticle ² $${\bar{{\Xi }}}^{+}$$ Ξ ¯ + , has enabled a direct determination of the weak-phase difference, ( ξ P − ξ S ) = (1.2 ± 3.4 ± 0.8) × 10 ⁻² rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods ³ . Finally, we provide an independent measurement of the recently debated Λ decay parameter α Λ (refs. 4,5 ). The $${\Lambda }\bar{{\Lambda }}$$ Λ Λ ¯ asymmetry is in agreement with and compatible in precision to the most precise previous measurement ⁴ .
We have refurbished and tested a neutron array composed of 81 BC400 plastic scintillator detectors dedicated for neutron measurements in future fusion–fission experiments The Neutron Array (NA) detectors, installed at the 9 MV Tandem accelerator facility of the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), have been refurbished and the data acquisition system has been updated. We present the characteristics and performances of the NA and of the associated electronics.
Significant differences between the properties of Fe–Ga alloys (Galfenols) in their metastable and equilibrium states, as well as discrepancies between existing Fe–Ga phase diagrams and for the transition rates for the metastable to equilibrium state have been detected and discussed. In view of both the fundamental understanding and the technological importance of these alloys, the exact knowledge of the equilibrium phase diagram, metastable phases, and the transition rates between different phase states towards equilibrium are necessary and require further clarification. We have studied the influence of alloy composition, annealing temperature and annealing time (up to 1800 h) on the metastable-to-equilibrium phase transitions in binary Fe–Ga using a coherent set of complementing methods, including diffraction methods (X-ray and neutron diffraction), scanning electron microscopy, and electron backscatter diffraction. We propose several important changes to the low-temperature part of the binary Fe–Ga diagram close to the Fe-rich corner and a new method based on interdiffusion couples for varying the structure and phase states of Fe–Ga alloys.
LHC data on the correlations of the elliptic flow v 2 of particles at low and high transverse momenta p T from Pb+Pb collisions at center-of-mass energy per nucleon pair √ s NN = 5.02 TeV are analyzed in the framework of the HYDJET++model. This model includes soft and hard components which allows to describe the region of both low and high transverse momenta. The origin of v 2 values in different p T regions is investigated at different centralities. It is shown that the experimentally observed correlations between v 2 at low and high p T in peripheral lead-lead collisions is due to correlation of particles in jets.
Рассмотрена причинная пертурбативная квантовая теория поля Боголюбова с единственным уточнением: операторы рождения-уничтожения в точке, т. е. для определенного импульса, с математической точки зрения понимаются как операторы Хиды, введенные в теории, основанной на вероятностном пространстве белого шума. Остальная часть теории сохраняется полностью неизменной. Это позволяет избежать инфракрасных и ультрафиолетовых расходимостей при переходе к адиабатическому пределу для взаимодействующих полей. Приведено доказательство существования адиабатического предела взаимодействующих полей в причинной квантовой электродинамике с операторами Хиды. Этот предел существует тогда и только тогда, когда нормировка в разложении Эпштейна-Глейзера причинных распределений, применяющемся при построении оператора рассеяния, является стандартной, или естественной. Таким образом устраняется произвольность в выборе разложения, что делает теорию однозначной, при этом ее предсказательная сила значительно усиливается. В качестве примера рассмотрено экспериментально подтвержденное соотношение между зарядом и массой, которое можно доказать в рамках представленной теории.
The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research.
Herein, an investigation of a deeply subcritical uranium assembly irradiated by a high-energy deuteron beam is presented. The determination of the total number of fission events is a key task in these investigations. Thus, this study is focused on the investigation of the number of fission events induced by deuterons, neutrons, and protons inside the deuteron beam volume. To measure the number of fission products in uranium activation detectors, germanium gamma detectors have been used. Furthermore, the total number of fission events has been measured by applying Solid State Nuclear Track Detectors (SSNTDs). The new method for determining the number of fissions using activation detectors is compared with the SSNTD and Monte Carlo (MC) methods. The method estimates the total number of fission events and agrees with the results obtained using the SSNTD and MC methods. The experiments were conducted at JINR, Dubna, Russia.
A bstract A search for decays of pair-produced neutral long-lived particles (LLPs) is presented using 139 fb − 1 of proton-proton collision data collected by the ATLAS detector at the LHC in 2015–2018 at a centre-of-mass energy of 13 TeV. Dedicated techniques were developed for the reconstruction of displaced jets produced by LLPs decaying hadronically in the ATLAS hadronic calorimeter. Two search regions are defined for different LLP kinematic regimes. The observed numbers of events are consistent with the expected background, and limits for several benchmark signals are determined. For a SM Higgs boson with a mass of 125 GeV, branching ratios above 10% are excluded at 95% confidence level for values of c times LLP mean proper lifetime in the range between 20 mm and 10 m depending on the model. Upper limits are also set on the cross-section times branching ratio for scalars with a mass of 60 GeV and for masses between 200 GeV and 1 TeV.
A bstract A measurement of inclusive, prompt, and non-prompt J/ ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV is presented. The inclusive J/ ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum p T = 0. The inclusive J/ ψ nuclear modification factor R pPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/ ψ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced J/ ψ on a statistical basis for p T larger than 1.0 GeV/ c . These results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity $$ \mathcal{L} $$ L int = 292 ± 11 μ b − 1 , which is six times larger than the previous publications. The total uncertainty on the p T -integrated inclusive J/ ψ and non-prompt J/ ψ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and R pPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ ψ production cross section, the $$ \mathrm{b}\overline{\mathrm{b}} $$ b b ¯ production cross section at midrapidity, $$ {\mathrm{d}\sigma}_{\mathrm{b}\overline{\mathrm{b}}} $$ d σ b b ¯ / d y , and the total cross section extrapolated over full phase space, $$ {\sigma}_{\mathrm{b}\overline{\mathrm{b}}} $$ σ b b ¯ , are derived.
Commercially available and administered to the patients ethosuximide is a racemic mixture of two enantiomers, each of them exist in different conformations. The presence of the species mentioned are proven by the title experimental methods aided by DFT model calculations. Results of the latter are matched against spectroscopic data by the clustering window analysis. One type of hydrogen bonds exist in the solid forms of ethosuximide N-H⋯O, leading to the polymorphic variety of the substance studied.
A bstract The production of J/ ψ is measured as a function of charged-particle multiplicity at forward rapidity in proton-proton (pp) collisions at center-of-mass energies $$ \sqrt{s} $$ s = 5.02 and 13 TeV. The J/ ψ mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5 < y < 4.0), whereas the charged-particle multiplicity density (d N ch / d η ) is measured at midrapidity ( |η| < 1). The production rate as a function of multiplicity is reported as the ratio of the yield in a given multiplicity interval to the multiplicity-integrated one. This observable shows a linear increase with charged-particle multiplicity normalized to the corresponding average value for inelastic events (d N ch /d η /〈d N ch /d η 〉), at both the colliding energies. Measurements are compared with available ALICE results at midrapidity and theoretical model calculations. First measurement of the mean transverse momentum (〈 p T 〉) of J/ ψ in pp collisions exhibits an increasing trend as a function of d N ch /d η /〈d N ch /d η 〉 showing a saturation towards high charged-particle multiplicities.
The multiplicity dependence of jet production in pp collisions at the centre-of-mass energy of $$\sqrt{s} = 13\ {\mathrm {TeV}}$$ s = 13 TeV is studied for the first time. Jets are reconstructed from charged particles using the anti- $$k_\mathrm {T}$$ k T algorithm with resolution parameters R varying from 0.2 to 0.7. The jets are measured in the pseudorapidity range $$|\eta _{\mathrm{jet}}|< 0.9-R$$ | η jet | < 0.9 - R and in the transverse momentum range $$5<p_\mathrm {T,jet}^{\mathrm{ch}}<140\ {\mathrm {GeV}}/c$$ 5 < p T , jet ch < 140 GeV / c . The multiplicity intervals are categorised by the ALICE forward detector V0. The $$p_{\mathrm T}$$ p T differential cross section of charged-particle jets are compared to leading order (LO) and next-to-leading order (NLO) perturbative quantum chromodynamics (pQCD) calculations. It is found that the data are better described by the NLO calculation, although the NLO prediction overestimates the jet cross section below $$20\ {\mathrm {GeV}}/c$$ 20 GeV / c . The cross section ratios for different R are also measured and compared to model calculations. These measurements provide insights into the angular dependence of jet fragmentation. The jet yield increases with increasing self-normalised charged-particle multiplicity. This increase shows only a weak dependence on jet transverse momentum and resolution parameter at the highest multiplicity. While such behaviour is qualitatively described by the present version of PYTHIA, quantitative description may require implementing new mechanisms for multi-particle production in hadronic collisions.
The DANSS detector (Alekseev et al. in JINST 11:P11011, 2016) is located directly below a commercial reactor core at the Kalinin Nuclear Power Plant. Such a position provides an overburden about 50 m.w.e. in vertical direction. In terms of the cosmic rays it occupies an intermediate position between surface and underground detectors. The sensitive volume of the detector is a cubic meter of plastic scintillator with fine segmentation and combined PMT and SiPM readout, surrounded by multilayer passive and active shielding. The detector can reconstruct muon tracks passing through its sensitive volume. The main physics goal of the DANSS experiment implies the antineutrino spectra measurements at various distances from the source. This is achieved by means of a lifting platform so that the data is taken in three positions – 10.9, 11.9 and 12.9 meters from the reactor core. The muon data were collected for nearly four calendar years. The overburden parameters ⟨Ethrcosθ⟩ and ⟨Ethr⟩, as well as the temperature and barometric correlation coefficients are evaluated separately for the three detector positions and, in each position, in three ranges of the zenith angle – for nearly vertical muons with cosθ>0.9, for nearly horizontal muons with cosθ<0.36, and for the whole upper hemisphere.
The effect of a high magnetic field (HMF) on phase transition and microstructure formation in Fe-Ga alloys with a Ga concentration of about 25 at.% has been investigated using experimental research and ab initio modeling. We found that the HMF of 25 T significantly accelerates the D03 to L12 transformation in the hyperstoichiometric Fe-27%Ga alloy upon isothermal annealing at 475 °C. At the same time, the field has little effect on the transformation in the hypostoichiometric Fe-24%Ga alloy. We have found that HMF does affect the kinetics of the transformation rather than the energy of the phases. We have shown that the effect of HMF is mainly associated with the ferromagnetic ordering of magnetic moments, which leads to lattice instability of the D03 phase and enhancement of the D03 → L12 transition due to the initiation of the barrierless mechanism.
We present results of analysis of KS0-meson spectra in Au+Au collisions obtained by the STAR Collaboration in the first phase of the Beam Energy Scan program at RHIC using the z-scaling approach. The analyzed data on inclusive cross sections were measured over a wide range of collision energy sNN=7.7−200 GeV and transverse momentum of produced particles for different centralities in the rapidity range |y|<0.5. A scaling behavior of the spectra in z-presentation is observed. The concept of the z-scaling is based on fundamental principles of self-similarity, locality, and fractality of hadron interactions at a constituent level. Structure of the colliding nuclei and fragmentation process in final state are described by fractal dimensions δA and ϵAA, respectively. Produced medium is characterized by a “specific heat” cAA. Onset of constant δA, smooth increase of ϵAA and anomalous behavior of cAA with collision energy in the scaling regime are observed. The self-similarity of fractal structure of nuclei and fragmentation processes with KS0 probe is demonstrated. The energy loss as a function of the collision energy, centrality and transverse momentum of the inclusive particle is estimated. An anomaly in the entropy behavior of system configurations in the region sNN∼30−40 GeV at low pT in the central collisions is found. A possible signature of phase transition indicated by the peculiarities of specific heat and entropy as ingredients of the z-scaling of KS0-meson production is discussed.
We present Raman spectroscopy and quantum chemical computational study for model phospholipid membrane molecule dipalmitoylphosphatidylcholine (DPPC) mixed with cholesterol or melatonin at various concentrations. Utilizing a confocal Raman microspectroscopy setup, we capture a DPPC conformation state by evaluating the number of trans/gauche bonds using I1064/I1090 and I1128/I1090 vibrational modes intensity ratios. We show that the cholesterol increases the number of trans bonds in DPPC hydrocarbon chains, i.e. causes membrane ordering, while melatonin addition introduces gauche conformers, generating disorder. It is noticed that the I1128/I1090 intensity ratio is more suitable parameter for the characterization of DPPC hydrocarbon chains structural properties compared with I1064/I1090. We thus clarify our experimental observations by performing careful density functional theory (DFT) calculations of Raman spectra for DPPC tails, containing up to three gauche bonds at different chain positions. The obtained results demonstrate strong interconnection between 1064 and 1090 cm‐1 vibrational modes originated from their complex splitting and shifting along with continuous Raman activity redistribution upon various gauche bonds introduction, while it is not the case for 1128 cm‐1 and 1090 cm‐1 modes pair.
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1,129 members
Vadim A. Naumov
  • Bogoliubov Laboratory of Theoretical Physics
Alexander Bakulev
  • Bogoliubov Laboratory of Theoretical Physics
Krassimira Petrova Marinova
  • Laboratory of Nuclear Reactions
Jordan Brankov
  • Bogoliubov Laboratory of Theoretical Physics
Wael M. Badawy
  • Group of Neutron Activation Analysis
Dubna, Russia
Head of institution
V.A. Matveev
+749621 65059