The Spin Physics Detector, a universal facility for studying the nucleon spin structure and other spin-related phenomena with polarized proton and deuteron beams, is proposed to be placed in one of the two interaction points of the NICA collider that is under construction at the Joint Institute for Nuclear Research (Dubna, Russia). At the heart of the project there is huge experience with polarized beams at JINR. The main objective of the proposed experiment is the comprehensive study of the unpolarized and polarized gluon content of the nucleon. Spin measurements at the Spin Physics Detector at the NICA collider have bright perspectives to make a unique contribution and challenge our understanding of the spin structure of the nucleon. In this document the Conceptual Design of the Spin Physics Detector is presented.

The secondary proton polarization and differential cross sections of the ($$p,p^{\prime}$$) inelastic reaction on nuclei $${}^{9}$$Be and $${}^{90}$$Zr at the initial proton energy of 1 GeV were measured over a wide range of the scattered proton momenta at a laboratory angle of $$\Theta=21^{\circ}$$. Scattered protons were detected by means of the magnetic spectrometer equipped with a polarimeter based on multiwire proportional chambers and carbon analyzer. A structure in the polarization and cross section data, related probably to the quasielastic scattering off nucleon correlations in the $${}^{9}$$Be and $${}^{90}$$Zr nuclei, was observed as earlier in the same data for the $${}^{12}$$C, $${}^{28}$$Si, $${}^{40}$$Ca and $${}^{56}$$Fe nuclei. A difference in the momentum distributions of the scattering cross section ratios for the $${}^{90}$$Zr and $${}^{12}$$C nuclei and for the $${}^{90}$$Zr and $${}^{9}$$Be nuclei was observed.

A comparative μSR study of ceramic samples of the EuMn 2 O 5 and Eu 0.8 Ce 0.2 Mn 2 O 5 multiferroics is performed in the temperature range from 15 to 300 K. It is found that the Ce doping of the EuMn 2 O 5 sample slightly reduces the temperature of the magnetic phase transition from T N = 45 K for the EuMn 2 O 5 sample to T N = 42.5 K for the Eu 0.8 Ce 0.2 Mn 2 O 5 sample. Below the temperature T N for both samples, there are two types of localization of a thermalized muon with different temperature dependences of the precession frequency of the magnetic moment of the muon in an internal magnetic field. The higher frequency in both samples refers to the initial antiferromagnetic matrix. The behavior of this frequency in Eu 0.8 Ce 0.2 Mn 2 O 5 follows the Curie–Weiss law with the exponent β = 0.29 ± 0.02, which differs from the value β = 0.39 standard for 3D Heisenberg magnetics and is observed in EuMn 2 O 5 , because of the strong frustration of the doped sample. The temperature-independent low frequency is due to the presence of Mn 3+ –Mn 4+ ferromagnetic pairs located along the b axis of the antiferromagnetic matrix and in the regions of phase separation, which contain such ion pairs and e g electrons recharging them. In both samples, polarization losses are the same (about 20%) and are associated with the formation of Mn 4+ –Mn 4+ + Mu complexes near Mn 3+ –Mn 4+ ferromagnetic pairs. In the temperature interval from 25 to 45 K, the separation of the Eu 0.8 Ce 0.2 Mn 2 O 5 structure into two fractions where the relaxation rates of polarization of muons differ by an order of magnitude is revealed. This effect is due to a change in the state of regions of phase separation (1D superlattices) at the indicated temperatures. Such effect in EuMn 2 O 5 is significantly weaker.

The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related pp-> d pi^+ reaction, though the present results cover also the small-angle region, which was largely absent from these data.

The present paper is devoted to studying the multiferroics HoMnO 3 , YMnO 3 , EuMn 2 O 5 , and GdMn 2 O 5 by means of the µSR-method. Determination of the dynamic relaxation parameter 7n and the distribution of the local magnetic fields results in a clear phase diagram.

The deuteron breakup reaction pd -> {pp}(s)n, where {pp}(s) is a fast proton pair emitted in forward direction with small excitation energy E-pp < 3 MeV, has been studied at proton beam energies of 0.5-2.0 GeV using the ANKE spectrometer at COSY-Julich. The differential c. m. cross sections are measured in complete kinematics and provide angular distributions of the neutron emission angle in the range theta(n) = 168 degrees-180 degrees, the dependence on beam energy at theta(n) = 180 degrees, angular distributions of the direction of the proton in the pp rest frame, and distributions of the excitation energy Epp of the proton pair. The obtained data are analyzed on the basis of theoretical models previously developed for the pd -> dp process in a similar kinematics and properly modified for the diproton channel in pd -> {pp}(s)n. It is shown that the measured observables are highly sensitive to the short-range part of the nucleon-nucleon interaction.

1. Investigation of the magnetic properties of homogeneous copper-manganese alloys. In this work, the magnetic properties of homogeneous copper-manganese alloys Cu1-xMnx were studiedby the muon spin relaxation technique on the synchrocyclotron at the PNPI RAS [1]. Samples were homogenized by quenching in water after their heat treatment in a muffle furnase at a temperature of 1100 K for 100 h. In our experiments, we measured the time distributions of positrons Ne(t) that were formed as a result of the decay μ→e+ e μ ν ν + (the muon lifetime is τμ≈2.19711·10 s) and emitted in the direction of the initial muon polarization (polarized muon beams were used) in a time window Δt~4.5·τμ after each muon was stopped in the sample, as well as the integrated yields of these positrons [2]. The time distributions were approximated by the function Ne(t) = N0 · [1 + a0 · G(t)] · exp (-t /τμ), (1) where the normalization constant N0 and the maximum asymmetry a0 characterize the experimental conditions specific for each sample and do not depend on the muon depolarization. The muon spin relaxation function G(t) determined from the time distribution Ne(t) reflects the effect of local magnetic fields on the muon spin at the site of its stopping. In particular, we have G(t)=1 in the absence of depolarization and G(t)=0 for nonpolarized muons. Figure 1 present the normalized integrated yields of positrons for samples with different concentrations of magnetic atoms Ne(norm)=((ne/n0)−1)/a0. This integrated yield does not depend on the sample geometry, parameters of the muon spin relaxation setup, and muon beam polarization and provides general model-independent information on muon depolarization under local magnetic fields. The parameters n0 and a0 were determined at a temperature considerably higher than the temperature of the transition to the magnetically ordered phase. Specifically, the normalized integrated yield Ne(norm) measured for the Cu0.2Mn0.8 sample at temperatures T>330 K in zero magnetic field tends to unity. This circumstance suggests the absence of muon depolarization in the far paramagnetic range, in which the frequency of oscillations of electronic moments is too high (~10 Hz) for their magnetic field to change substantially the muon polarization. The paramagnetic state is also indicated by the complete depolarization of muons in a relatively weak transverse external magnetic field of ~580 Oe. In the temperature range 320−290 K, the normalized integrated yield Ne(norm) changes drastically and then reaches a value of ~1/3. This suggests that the sample transforms into a magnetically ordered state with an isotropic (on a local, cluster, or domain level) orientation of static internal local magnetic field. This behavior is in good agreement with the phase diagram previously proposed in [А. Banerjеe, A.K. Majumdar. PRB, 46 (14), pp. 8958–8973, (1992)], according to which the antiferromagnetic transition at TN~300 K occurs in a homogeneous alloy with the concentration x=0.8. The normalized integrated yield Ne(norm) equal to 1/3 is retained to T≈200 K. With a further decrease in the temperature, the normalized integrated yield Ne(norm) decreases sharply almost to zero. This indicates that in the given temperature range; there arises a strong dynamic depolarization of muons. The temperature dependence of the normalized integrated yield Ne(norm) in the range 200–20 K is characteristic of frustrated magnets, which undergo transition to a low-temperature spin-glass state through an intermediate magnetically ordered phase with a long-range order. In this case, the dynamic polarization is associated with the transformation of the magnetic structure in the transition range [3]. 0 50 100 150 200 250 300 350 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 C u 1-x Mn x

The magnetically ordered and paramagnetic states of erbium at temperatures T < T, and T > TN, where TN = 84.4 K is the NCel temperature, have been studied by the muon method. A large crystalline specimen of erbium was used with preferred orientation of the hexagonal c axes of the individual single crystals. The correlation functions GII (T ) and G, ( T ) which describe the fluctuations of the longitudinal and transverse (relative to the c axis) components of the internal magnetic field acting on a muon at T > TN were measured. The G, ( T ) dependence was also measured at T < T,. It is shown that for T > TN the correlator G, is constant over the whole temperature range investigated, TN < T 5 300K, while GII increases to a limited extent as T+TN. The limited range of the GII (T ) dependence as T+TN is regarded as an indication that a weak first-order phase transition takes place in erbium at T, = 84.4 K.

A ferrofluid based on Fe 3 O 4 nanoparticles dispersed in heavy water D 2 O is studied using the μSR method. The experiment has been carried out at temperatures 26–300 K. It is found that the diamagnetic (muon) fraction is formed in the ferrofluid in about the same amount as in D 2 O, but the muon-spin relaxation rate in the ferrofluid is much higher than in D 2 O. A significant shift of the muon-spin precession frequency in the ferrofluid is observed. It is shown that the shift of the muon precession frequency as a function of the external magnetic field is described by the Langevin function typical of paramagnetic magnetization. The mean magnetic field in the medium due to magnetic-nanoparticle polarization in an external field is experimentally determined. The nanoparticle sizes are estimated.

The magnetic characteristics of homogeneous copper—manganese alloys Cu1 − x Mn x are studied by the muon spin relaxation technique for the first time. It is revealed that the specific magnetic phase, which is most likely characterized by a fast spin dynamics and the absence of long-range order, is formed in alloys with concentrations 0.2 < x < 0.7 in the temperature range 10–330 K. The complete magnetic phase diagram is constructed.

The Pd1−x Fe x )0.95Mn0.05 alloy with random competing interaction was studied by measuring the muon spin relaxation in an external transverse magnetic field and in a zero magnetic field. Using the measured temperature dependence of the dynamic relaxation rate λ and the characteristics of the distribution of local static fields, the phase states of the sample under study are refined. In particular, it is shown that the ferromagnetic and spin-glass states coexist simultaneously in the sample below 25 K. Combined studies of the sample using the μSR and neutron depolarization methods made it possible to determine the size of magnetic inhomogeneities to be 2–6 μm in the temperature range 5–40 K.

The μSR setup for investigating the distribution of magnetic fields in solids using the muon spin rotation (μSR) method is described. The setup is characterized by a high degree of homogeneity of the magnetic field at the site of the sample under investigation, compensation of scattered magnetic fields to a level of −10−2 G, and a time resolution of 2.5 ns (the full width at half-maximum). The setup is suitable for μSR measurements on samples in the temperature range of 5–300 K with a precision of ±0.1 K.

The magnetic properties of multiferroics HoMnO3 and YMnO3 have been investigated using the muon (μSR) method. Analysis of the dependence of the dynamical relaxation rate λ and characteristics of the distribution of local static fields makes it possible to more precisely determine the phase states of the samples under investigation.