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1.
One of the NA61/SHINE experiment??s goals is to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. This is to be achieved by performing a two-dimensional phase diagram (T-?? B ) scan??measuring hadron production in collisions of various beam particles and targets at various beam energies. NA61/SHINE also collects data for the T2K experiment, which are just about to be published.  相似文献   

2.
Theoretical calculations locate the critical point (CP) of strongly interacting matter at energies accessible at the CERN SPS. Event-by-event transverse momentum and multiplicity fluctuations are considered as one of the most important tools to search for the CP. Pilot studies of the energy dependence and the system size dependence of both p T and multiplicity fluctuations were performed by the NA49 experiment. The NA61/SHINE ion program is a continuation of these efforts. After briefly recalling the essential NA49 results on fluctuations we will discuss the technical methods (removing Non-Target interactions) which we plan to apply for future transverse momentum and multiplicity fluctuation analyses.  相似文献   

3.
CERN experiment NA44 measures pion and kaon distributions at p T = 0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at low p T relative to p+Be, but less than observed at target rapidity. The low p T behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.  相似文献   

4.
The NA35 experiment used several independent methods to determine the strange particle production in p+S and S+A collisions. The different techniques show consistent results. Strangeness conservation in full phase space is used as an additional check of the consistency of the data. On the base of the analysis in full phase space it could be shown that strangeness conservation is fullfilled. The NA35K S 0 in S+S and S+Ag are consistent with the NA44 results forK + andK ?. The results of the NA36 collaboration for S+Pb collisions were extrapolated to full phase space. The comparison with the NA35 results shows more than two times lower yields. The ratio of Λ to $\bar \Lambda $ at midrapidity of NA36 is inconsistent with the high baryon density determind by NA35. The strange particle production is compared to the abundance of non strange particles, especially negatively charged pions which are measured in full phase space in the same experiment. A clear enhanced strange hadron production relative to σ? is observed in S+Ag collisions compared to p+S reactions at the same energy. TheK S 0 multiplicity in full phase space per negative hadron (h ?) in S+S, S+Ag and Pb+Pb is enhanced by about a factor 1.6 compared to N+N and p+S collisions. The NA36 result for theK S 0 multiplicity perh ? in S+Pb is below the N+N value.  相似文献   

5.
Two experimental programs are aiming to study nuclear collisions in the energy regime in order to explore an essential part of the phase diagram of strongly interacting matter. The programs are motivated by observations that indicate a phase transition to take place in this energy domain: the onset of deconfinement. The STAR collaboration proposes an energy scan in the Relativistic Heavy Ion Collider (RHIC) at BNL. The ongoing program of the NA61/SHINE experiment consists of a two-dimensional energy-system size scan in nuclear and elementary collisions. The goal of both programs is to study the properties of the onset of deconfinement and to eventually discover the conjectured critical point of strongly interacting matter. A comparison of the strengths and limitations reveals the complementarity of the two programs.  相似文献   

6.
CERN experiment NA44 measures pion and kaon distributions atpT=0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at lowpT relative to p+Be, but less than observed at target rapidity. The lowpT behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.  相似文献   

7.
Ultrasonic sound velocity measurements have been carried out in order to determine the adiabatic compressibility and elastic moduli of the pseudobinary HoxTb1?xCo2 Laves phase compounds. The anomalies, associated with the Curie temperatures and the presence of various spin reorientations, allowed the determination of the spin orientation diagram of the system. The similarity of this spin orientation diagram with that previously established of the HoxTb1?xFe2 system strongly supports the single rare earth ion model for the magnetic anisotropy behavior of the compounds studied. Measurements carried out in an external magnetic field revealed the presence of a significant ΔE effect.  相似文献   

8.
Tunneling experiments on Be films condensed onto helium cooled substrates show that these films are homogeneously disordered with a uniform transition temperatureT c when Ge is codeposited, whereas thick films of pure Be do not grow homogeneously. For films of Be+10 at.% Ge a ratio 2Δ/k B T c =3.7 is found. Phonon induced structure in the tunneling density of states is not observed. The metastable phase obtained by quench-condensation is considered to be a disordered high-temperature phase of Be which transforms to the room temperature phase at about 60 K.  相似文献   

9.
In the framework of the Landau theory of phase transitions, the influence of the magnetoelastic interaction on structural transitions in cubic ferromagnetics with a positive first magnetic anisotropy constant is analyzed. It is shown that structural transitions are not accompanied by a reorientation of magnetization in this case. The phase diagrams of such ferromagnetics either contain a termination point of the structural transition or a critical point in which the first-order transition is replaced by a second-order one. Magnetoelastic interaction also leads to the appearance of an interval of the ferromagnetic parameters in which a coupled first-order structural-magnetic transition exists. The phase T?x diagram for Heusler Ni2+x Mn1?x Ga alloys is calculated, which is in good agreement with the experimental phase diagram of these alloys.  相似文献   

10.
A review of the current experimental situation on the search for a critical point in the QCD phase diagram and the onset of deconfinement is given. Ongoing (STAR, NA61), as well as previous (NA49) experiments are presented. Their main results up-to-now are summarized and their findings are put into a general context. The future experimental program (CBM at FAIR, MPD at NICA) is discussed as well.  相似文献   

11.
We report on the magnetostriction of hexagonal HoMnO3 and YMnO3 single crystals in a wide range of applied magnetic fields (up to H = 14 T) at all possible combinations of the mutual orientations of magnetic field H and magnetostriction ΔL/L. The measured ΔL/L(H, T) data agree well with the magnetic phase diagram of the HoMnO3 single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO3 crystal is caused by the Ho3+ ion; the magnetic moment of the Mn3+ ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO3 are consistent with the phase diagram of these compounds. For the isostructural YMnO3 single crystal with a nonmagnetic rare-earth ion, the ΔL/L(H, T) dependences are described well by a conventional quadratic law in a wide temperature range (4–100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.  相似文献   

12.
Differential cross-section excitation functions at lab scattering angles 86.9°, 120.0°, 140.0° and 160.0° were measured for 9Be(p, po)9Be, 9Be(p, p2)9Be and 9Be(p, d0)8Be at proton lab energies from 6 to 15 MeV in 100 keV steps. A broad anomaly was observed in the 9Be(p, p0)9Be excitation functions. Differential cross-section angular distributions were measured for 9Be(p, p0)9Be and 9Be(p, p2)9Be at lab energies of 13.0, 14.0, 15.0, 21.35 and 30.3 MeV and for 9Be(p, d0)8Be at 13.0, 14.0, 15.0 and 21.35 MeV. Angular distributions of polarization analysing powers for 9Be(p,p0)9Be, 9Be(p, p2)9Be and 9Be(p, d0)8Be were measured at 8.0, 11.0, 12.0, 13.0 and 15.0 MeV. A spherical optical-model (SOM) analysis of the elastic scattering angular distribution data from 13.0 to 30.3 MeV showed that an energy dependence of only VR and Ws (volume real and surface imaginary depths) is sufficient to reproduce the measurements. Coupled-channels (CC) analyses were made with a quadrupole-deformed optical-model potential and strong coupling of 32?, 52? and 72? levels of a K = 32 ground-state rotational band of 9Be. The 9Be(p, p0)9Be and 9Be(p, p2)9Be data from 13.0 to 30.3 MeV were analyzed simultaneously at each energy, varying only VR and Ws with energy, for a potential deformation of β = 1.1. Both SOM and CC analyses indicated the same energy dependence in VR, while Ws averaged 3.5 MeV lower in CC than in SOM, with both energy dependences consistent with previous analyses of nucleon scattering from 1p shell nuclei.  相似文献   

13.
A comparison with the alkali halides suggests that all the ammonium halides should occur in the NaCl centre-of-mass structure. Experimentally, at room temperature and atmospheric pressure, only NH4I crystallizes in this structure, while NH4F is found in the ZnO structure, and NH4C1 and NH4Br occur in the CsCl structure. We show that a distributed charge on the NH4+ ion can explain these structures. Taking charges of + 0.2e on each of the five atoms in NH4+, as suggested by other studies, we have recomputed the Madelung energy in the cases of interest. A full ionic theory including electrostatic, van der Waals and repulsive interactions then explains the centre-of-mass structures of all the four ammonium halides. The thermal and pressure transitions are also explained reasonably well. The calculated phase diagram of NH4F compares well with experiment. Barring the poorly understood NH4F(II) phase, which is beyond the scope of this work, the other features are in qualitative agreement. In particular, the theory correctly predicts a pressure transition at room temperature from the ZnO structure directly to the CsCl structure without an intermediate NaCl phase. A feature of our approach is that we do not need to invoke hydrogen bonding in NH4F.  相似文献   

14.
The cation valence and distribution in copper manganese spinels containing 1.0-1.6 mol copper per formula unit (CuxMn3−xO4) was resolved from their electrical conductivity and thermoelectric properties. The limit of thermal stability of the cubic spinel phase was also determined for each stoichiometry. A corrected phase diagram for the Cu-Mn-O system in air is proposed accordingly. The electronic defect structure could be described through a chemical approach, involving the competition between the redox of Cu+ and Mn4+ to Cu2+ and Mn3+ and the disproportionation of the Jahn-Teller ion Mn3+ into Mn2+ and Mn4+. Thermodynamic parameters for the redox reaction were determined from experimental data as well as calculated, confirming the validity of the modeled defect equilibria.  相似文献   

15.
The 48.7 m111m Cd activity was implanted in Zn and Be single crystals which were soldered to the cold finger of a dilution refrigerator and kept below 0.2 K during implantation. Subsequent nuclear orientation experiments allowed the determination of the quadrupole interaction frequencyv Q of the 11/2? isomeric state of111Cd in Zn and Be as ?139 (15) MHz and +43(16) MHz respectively. With these results we derive the quadrupole moment of the 5/2+ 245 keV level of111Cd including sign asQ = +0.83(13) b and the sign of the electric field gradient for Cd in Be. The half-life of111m Cd was redetermined as 48.67 (6) m.  相似文献   

16.
The phase diagram of ferromagnetic alloys Ni2+x Mn1?x Ga is reconstructed on the basis of temperature dependences of the resistance. It is seen from this diagram that for small x, structural transitions from the cubic to the tetragonal phase are preceded by structural transformations in the cubic phase. In the framework of the phenomenological Landau theory of phase transitions, phase diagrams of the structural and magnetic phase transitions in these alloys are analyzed with regard for the modulation order parameter. It is shown that premartensitic and postmartensitic phase transitions related to the appearance of the modulated structure can occur along with martensitic transformations. The strain and modulation order parameters substantially affect the magnetic phase transitions via the interaction with the magnetic order parameter.  相似文献   

17.
The Fe2+ localized magnetic excitations observed in the Co-rich antiferromagnetic phase of the randomly mixed system with competing Ising and XY spin anisotropies, Fe(1?x)CoxBr2 have been analyzed quantitatively. The calculated frequency-field diagram reproduces well the experiments. The expectation values of the Fe2+ spin components in the ground state are calculated. It is shown that even in the Co-rich antiferromagnetic phase Fe2+ spins make an angle with the c-plane of the crystal in which Co2+ spins are confined.  相似文献   

18.
X-Ray analysis was made of solid solutions and heterogeneous compositions of the general formula Mn3?xCrxOm (0?x ? 3, Δx = 0.05). Subsolidus portions of the high temperature phase equilibria diagram and the diagram of water-quenched phases of the system Mn-Cr-O in air were established in the temperature range 700–1400°C. Comparative analysis of these diagrams has revealed the mechanism of the processes occurring upon rapid cooling of the system (in water and in air in a ceramic crucible) from high temperatures to room temperature. Rapid cooling is shown to preserve the phase composition and crystal structure of nonspinel phases, but for equilibrium solid solutions with spinel or hausmannite structure, this is not always the case. Depending on the quench temperature and the solution composition the following phenomena are observed: (1) tetragonal distortion of a high temperature phase with spinel structure; (2) merging of a tetragonally distorted spinel and spinel and formation of a homogeneous phase with hausmannite structure; (3) decomposition of the homogeneous phase with spinel structure into two spinel-type phases with spinel and hausmannite structures. Possible causes of these phenomena are discussed.  相似文献   

19.
The quantum anisotropic antiferromagnetic Heisenberg model with single ion anisotropy, spin S=1 and up to the next-next-nearest neighbor coupling (the J1J2J3 model) on a square lattice, is studied using the bond-operator formalism in a mean field approximation. The quantum phase transitions at zero temperature are obtained. The model features a complex T=0 phase diagram, whose ordering vector is subject to quantum corrections with respect to the classical limit. The phase diagram shows a quantum paramagnetic phase situated among Neél, spiral and collinear states.  相似文献   

20.
This paper reports on the results of analyzing p-T and x-T phase diagrams and calorimetric properties of solid solutions in (NH4)3Ga1?x ScxF6 cryolites with scandium concentrations x=0.0, 0.1, 0.35, 0.4, 0.6, 0.8, and 1.0. The thermodynamic parameters of the phase transitions observed in the studied compounds are determined. The generalized phase diagram and successive structural transformations in a series of (NH4)3 Me 3+F6 ammonium cryolites are discussed.  相似文献   

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