Searches for single-spin asymmetry in the inclusive production of neutral pions in the central region at a proton beam energy of 70 GeV

Results are presented that were obtained by measuring single-spin asymmetry in the inclusive production of neutral pions in the reaction p+p ↑→ π ⁰+X at x _F≈0. A beam of 70-GeV protons was extracted directly from the vacuum chamber of the accelerator by means of a bent single crystal. For transverse momenta in the range 1.0<p _T<3.0 GeV/c, the single-spin asymmetry independently measured by two detectors is zero within the errors. This result is in agreement with Fermilab data obtained at 200 GeV, but it is at odds with CERN data measured at 24 GeV.     

Manifestations of Surface States in the Longitudinal Magnetoresistance of an Array of Bi Nanowires

The longitudinal magnetoresistance of the array of parallel-oriented bismuth nanowires each 100 nm in diameter grown by electrochemical deposition in nanopores of an Al₂O₃ membrane has been studied in magnetic fields up to 14 T and at temperatures down to 0.3 K. The resistance increases with the field and reaches a broad maximum in fields about 10 T. An anomalous increase in the resistance in weak fields is qualitatively consistent with the suppression of the antilocalization correction to the resistance, and the maximum is qualitatively associated with the classical size effect. Near the maximum at temperatures below 0.8 K, manifestations of reproducible magneto-oscillations of the resistance, which are periodic in field, have been detected. The period of these oscillations is close to a value corresponding to the passage of the flux quantum hc/e through the section of a nanowire. The Fourier analysis also confirms that the oscillations are periodic. This result is similar to the manifestation the Aharonov–Bohm effect caused by conducting surface states of Dirac fermions occupying L-valleys of bismuth.     

Production of High-Transverse-Momentum Deuterons and Tritons at an Angle of 40 $${{}^{\circ}}$$ in Proton–Nucleus Interactions at a Beam Energy of 50 GeV

Physics of Atomic Nuclei - Data on the production of positively charged particles emitted at an angle of 40 $${}^{\circ}$$ (in the laboratory frame) with transverse momenta of up to 2.7 GeV $$/c$$...     

Knockout of deuterons and tritons with large transverse momenta in <Emphasis Type="Italic">pA</Emphasis> collisions involving 50-GeV protons

Formation of the d and t cumulative light nuclear fragments emitted from the nucleus with large transverse momenta at an angle of 35° in the laboratory frame is investigated. The data on collisions of 50-GeV protons with the C, Al, Cu, and W nuclei are collected using the extracted proton beam of the IHEP accelerator and the SPIN detector. The results indicate that the dominant contribution to formation of nuclear fragments comes from the local process of direct knockout from the nucleus.     

Role of anion ordering in the coexistence of spin-density-wave and superconductivity in (TMTSF)2ClO4

Using various transport and magnetotransport probes, we study the coexistence of spin-density wave and superconductor states in (TMTSF)₂ClO₄ at various degrees of ClO₄ anions ordering. In the two-phase complex state when both superconductivity and spin-density wave are observed in transport, we find prehistory effects, enhancement of the superconducting critical field, and strong spatial anisotropy of the superconducting state. These features are inconsistent with the conventional model of structural inhomogeneities produced by anion ordering transition. We reveal instead that superconductor and spin-density wave regions overlap on the temperature—dimerization gap V phase diagram, where V is varied by anion ordering. The effect of anion ordering on (TMTSF)₂ClO₄ properties is thus analogous to that of pressure on (TMTSF)₂X (X = PF₆ or AsF₆), thereby unifying general picture of the coexistence of superconductivity and spin-density wave in these compounds.     

Magnetotransport in thin epitaxial Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> films

The magnetoconductivity of thin Bi₂Se₃ films covered by a protective Se layer and grown at (111) BaF₂ substrates is studied. It is shown that the negative magnetoconductivity observed at low magnetic fields and caused by the effect of weak antilocalization, as well as the Shubnikov?de Haas oscillations at higher fields, is determined only by the magnetic field component perpendicular to the film plane. The obtained experimental results can be reasonably interpreted under the assumption that the studied films exhibit two-dimensional topologically protected electron states. Moreover, the contribution of these states to the total conductivity turns out to be the dominant one.     

Analyzing Power in the Reaction p + p └ → π 0 + X in the polarized-target fragmentation region at an energy of 50 GeV

The results obtained by measuring, at the U-70 accelerator in Protvino, the single-spin asymmetry A _N in the reaction p + p _└ → π⁰ + X at a beam energy of 50 GeV in the Feynman variable range of ?0.6 < x _F < ?0.1 are presented. The asymmetry A _N is close to zero at small |x _F | and grows in magnitude with |x _F |, reaching 6.4% in the region of |x _F | > 0.25. The results of these measurements agree with data of the E704 experiment on the asymmetry of π ₀ mesons at the Fermi National Accelerator Laboratory in the region of polarized-beam fragmentation and with the results of measurements in the region of polarized-target fragmentation that were performed in Protvino by using a 40-GeV π ^?-meson beam and a 70-GeV proton beam.     

Single-spin asymmetry of inclusive neutral-pion production in pp ↑ interactions at 70 GeV in the region −0.4 < x F < −0.1

For the kinematical region specified by the inequalities ?0.4 < x _F < ?0.1 and 0.9 < p _T < 2.5 GeV/c, the results are presented that were obtained by experimentally determining the single-spin asymmetry of inclusive neutral-pion production in the reaction p + p _↑ → π ⁰ + X at 70 GeV. According to these results, the asymmetry is close to zero in the region ?0.2 < x _F < ?0.1 and grows in magnitude with decreasing x _F, amounting to (?10.6 ± 3.2)% for ?0.4 <x _F < ?0.2.     

Metal-insulator transition in a HgTe quantum well under hydrostatic pressure

The 2D semimetal in a 20 nm (100) HgTe quantum well is characterized by a comparatively low overlap between the conduction and the valence bands induced by lattice mismatch. In the present paper we report the results of transport measurements in this quantum well under hydrostatic pressure of 14.4 kbar. By applying pressure we have further reduced the band overlap, thereby creating favorable conditions for the formation of the excitonic insulator state. As a result, we observed that the metallic-like temperature dependence of the conductivity at lowering temperature sharply changes to the activated behavior, signaling the onset of an excitonic insulator regime.