Physics of Atomic Nuclei最新文献

The SND@LHC (Scattering and Neutrino Detector at the Large Hadron Collider) experiment studies processes involving neutrinos generated at the LHC in the pseudorapidity range of (7.2<eta<8.6). The detector includes a target having a mass of 830 kg and consisting of tungsten plates interspersed with emulsion and electronic detectors, which is followed downstream by a hadronic calorimeter and a muon-detecting system. The detector structure provides a unique possibility for studying charm production in the pseudorapidity region inaccessible to other experiments at the LHC. The modern state of the experiment and its prospects for the near future are described in the present study.

The near detector ND280 is an essential part of the T2K experiment. Its data are used to tune the parameters of the cross-section and flux models, thereby reducing systematic uncertainties and enhancing the precision of neutrino oscillation measurements. ND280 is a complex apparatus consisting of several subdetectors. The structure leads to various sources of systematic uncertainties related to the simulation and tracking of neutrino interaction products. This paper presents the methods used to estimate the systematic errors and to propagate them through the stages towards the final oscillation analysis.

A hypothetical particle known as the axion holds the potential to resolve both the cosmic dark matter riddle and particle physics’ long-standing, strong CP dilemma. An unusually strong 21-cm absorption feature associated with the initial star formation era, i.e., the dark ages, may be due to ultralight axion dark matter (({sim}10^{-22}) eV) at this time. The radio wave observation’s 21-cm absorption signal can be explained as either anomalous baryon cooling or anomalous cosmic microwave background photon heating. Shortly after the axions or axion-like particles (ALPs) thermalize among themselves and form a Bose–Einstein condensate, the cold dark matter ALPs make thermal contact with baryons, cooling them. ALPs are thought to be the source of some new evidence for dark matter, as the baryon temperature at cosmic dawn was lower than predicted based on presumptions. The detection of baryon acoustic oscillations is found to be consistent with baryon cooling by dark matter ALPs. Simultaneously, under the influence of the primordial black hole and/or intergalactic magnetic fields, the dark radiation composed of ALPs can resonantly transform into photons, significantly heating up the radiation in the frequency range relevant to the 21-cm tests. When examining the 21-cm cosmology at redshifts (z) between 200 and 20, we see that, when taking into account both heating and cooling options at the same time, heating eliminated the theoretical excess number of neutrino species, (Delta N_{text{eff}}), from the cooling effect.

Superfluid He-4 is a promising tool for neutrino and dark matter detection. The low-energy neutrino interaction with superfluid He-4 proceeds through coherent elastic neutrino–atom scattering (CE(nu)AS), which has not yet been observed. The first experimental study of CE(nu)AS is under preparation in Sarov using a tritium neutrino source and a superfluid He-4 detector. This will allow testing the neutrino physics of the Standard Model and beyond at unprecedentedly low energies. We develop a theoretical approach for studying neutrino interaction with a superfluid He-4, taking into account single quasiparticle (phonon and roton) production in the target upon tritium neutrino scattering. We show that such collective effects significantly affect the neutrino scattering cross section at energy transfers of the order of 1 meV and less.

The results of measurements of charge losses at registration of xenon ions (({}^{132})Xe) with the energies of 44.5, 81.5 and 165 MeV in the detectors based on silicon carbide (SiC) and silicon (Si) are presented. The measured values of the amplitude defect for SiC and Si detectors are 43 and 21(%) of the true ({}^{132})Xe ion energy, respectively. The reason is the incomplete collection of charge carriers due to their recombination in a dense track of the heavy ion being detected.

The NOvA experiment is a long-baseline neutrino experiment designed to study the oscillation behavior of neutrinos and antineutrinos, utilizing Fermilab’s Megawatt-capable NuMI neutrino beam. Over the past 10 years, NOvA has collected data from two functionally identical tracking calorimeter detectors, which are situated off the NuMI beam axis and separated by 810 km. The construction of the experiment enables observation of muon (anti)neutrino disappearance and electron (anti)neutrino appearance. Consequently, precision measurements of oscillation parameters, including the mass splitting (Delta m_{32}^{2}) and its sign, the mixing angle (theta_{23}), and the phase of (CP)-symmetry violation, can be obtained. This paper presents an overview of the NOvA experiment and its latest results.

The angular-correlation function for a final particle (y) and a photon is used to analyze gamma radiation that deexcites the nucleus produced in a nuclear reaction. The experimentally measured and calculated angular distributions of gamma radiation accompanying the deexcitation of ({}^{12})C((2^{+})) nuclei in reactions of inelastic deuteron and neutron scattering are compared. In the inelastic scattering of 15.3-MeV deuterons, this analysis was performed with the aid of the experimental and calculated values that we determined earlier for the spin-tensor components (A_{k0}(theta_{d})) of the ({}^{12})C((2^{+})) density matrix. In the inelastic scattering of 14.1-MeV neutrons, the experimental angular distribution of photons that was obtained by the TANGRA Collaboration is contrasted against its counterpart calculated on the basis of the spin-tensor components (A_{k0}(theta_{n})) determined by means of the coupled-channel method. The normalized angular distributions of photons agree with the experimental ones both in deuteron and in neutron scattering. It is shown that the anisotropy of gamma radiation in inelastic neutron scattering is greater by a factor of about 1.5 than that in inelastic deuteron scattering.

The DANSS experiment at Kalininskaya NPP is running for already 8 years since April 2016. The largest in the world in the single experiment statistics of 8.5 million inverse beta-decay events is already collected. The data sample covers 4 full cycles of the industrial power reactor. DANSS experimental program includes both a search for physics beyond the Standard Model, like sterile neutrinos or large extra dimensions, and applied studies connected to reactor monitoring using electron antineutrino flux. The model independent exclusion area in the sterile neutrino parameter space for (3+1) hypothesis extends till (sin^{2}2theta=0.004) for (Delta m^{2}=0.9) eV({}^{2}), where sensitivity of the experiment is the best. Our data show presence of antineutrinos with energies above 10 MeV in the reactor spectrum with significance of 6.8(sigma). Along with ongoing statistics collection DANSS is preparing for an upgrade, which shall significantly improve its energy resolution and also increase the fiducial volume. The article covers recent analysis results and the upgrade status.

Parameterizations of signals from the towers of the electromagnetic calorimeter of the MPD/NICA detector, aimed at an estimation of the time resolution of the calorimeter, are considered. Optimal parameters of the timing are determined within the constant fraction method. In test measurements with cosmic rays, a time resolution of 1.3–0.8 ns was obtained depending on the signal amplitude. These results show the possibility of relative calibration of the time parameters of calorimeter towers using cosmic rays.

The DANSS detector is placed under the reactor core of Kalinin NPP (at distances 10.9–12.9 m) and collects up to 5000 antineutrino events daily. One of the main goals of the experiment is to scrutinize the sterile neutrino hypothesis. A large fraction of allowed parameter space was excluded by DANSS: for some values of (Delta m^{2}), the exclusion goes down to (sin^{2}(2theta)<0.01), which had become the best in the world. In addition, the combination of a favorable detector placement near the reactor and large acquired statistics allows us to investigate other scenarios of electron antineutrino disappearance. This paper reports preliminary results on probing the Large Extra Dimensions (LED) hypothesis in the simplest approach of only one additional dimension. This theory describes particle oscillations to hidden, finite-size dimensions and provides sensitivity to neutrino masses. The report covers MC generation for different LED parameters, the study of the experiment sensitivity for oscillation to LED, and the investigation of exclusion areas in the parameter space in the coordinates of (a) and (m_{0})—the size of a hidden large extra dimension and a mass of the lightest neutrino.