Gluon polarization and the proton spin
1 August 2014
The proton spin is determined by spins of the constituent quarks and gluons and their orbital angular momenta. The earlier experiments on deeply inelastic lepton-proton scattering showed that the quark spins only explain about a quarter of the proton spin magnitude. The forerunning data also pointed out that even if nonzero, the gluon polarization in the proton (the averaged resultant value of their spins) is insignificant, that is, the contribution of gluon spins to the total proton spin is small. However, D. de Florian (the University of Buenos Aires, Argentina) with colleagues used the large statistical array of data on Relativistic Heavy Ion Collider – RHIC (Brookhaven National Laboratory, USA) and applied the new modified method of analysis to obtain the evidence of the fact that gluons in the proton composition still have the general nonzero polarization and hence make a considerable contribution to the total proton spin, the contribution of quark and gluon orbital momenta to the proton spin being less than was believed earlier.
Source: Phys. Rev. Lett. 113 012001 (2014)
Triangular symmetry D3h in the 12C nucleus
1 August 2014
D.J. Marin-Lambarri (Birmingham University, Great Britain) with colleagues have found that nucleons in the 12C nucleus are concentrated in three clusters (α-particles) arranged as vertices of an equilateral triangle. Clusterization of nucleons in nuclei in α-particles consisting of two protons and two neutrons is in some cases energetically more advantageous than a uniform distribution. The described experiment investigated collisions of a beam of α-particles from a cyclotron with a carbon target. The momentum and energy distribution of α-particles produced in the reaction 12C(4He,3α)4He and registered by silicon strip-detectors made it possible to determine the character of nucleon distribution in 12C nuclei. A new energy state of the nucleus was revealed for an energy of 22.4(0.2) MeV with spin-parity Jπ = 5- which corresponds to the ground rotational state of the equilateral triangular configuration with the symmetry group D3h. Such symmetry was earlier known in triatomic molecules H+3, but for the nucleus it was observed for the first time. For 12C it was theoretically predicted by R. Bijker and F. Iachello. The understanding of the 12C nucleus structure is also important for clarification of the properties of the Hoyle energy level at 7.654 MeV which plays a significant role for nucleosynthesis in stars. The authors believe that the Hoyle level may be the state 0+ of the 12C nucleus in triangular configuration D3h.
Source: Phys. Rev. Lett. 113 012502 (2014)
Mutual information in quantum measurement
1 August 2014
J.V. Koski (Aalto University, Finland) with colleagues experimentally confirmed validity of the generalized Bochkov – Kuzovlev and Jarzynski (BKJ) relation which allows for the contribution of mutual information. The quantity referred to as mutual information is expressed in terms of the correlations between the real state of a thermodynamic system and the records in the memory cells of the device used to measure this state. Thus, mutual information characterizes precision of measurements. According to the generalized BKJ relation, mutual information affects the thermodynamic properties of the system being measured. A one-electron box was used in the experiment which was made of two microscopic conductors separated by a thin insulator at a temperature of 100 mK. The state of the box was registered using a one-electron transistor. When electrons were tunneling through the insulator, the energy of the capacitor made of conductors changed, which affected the magnitude of the alternating current running through the device. Thereby, the presence or absence of an electron in the box influenced the thermodynamic properties of the system via the capacitor energy. The noises that lowered the measurement precision but were needed for verification of the generalized BKJ relation were artificially introduced in the experiment. The experiments carried out at the available level of accuracy validated the generalized state of BKJ and demonstrated for the first time the role of feedback through mutual information in the fluctuation theorem and in thermodynamics of irreversible processes. The Jarzynski equation derived in 1997 is a particular case of the Bochkov – Kuzovlev relations which they put forward in 1977-1983, see
Phys. Usp. 54 625 (2011), Phys. Usp. 56 590 (2013) A generalization of BKJ relations with allowance for mutual information was proposed by T. Sagawa and M. Ueda in their papers of 2010-2012 (see Phys. Rev. Lett. 104 090602 (2010); Phys. Rev. E85 021104 (2012)).
Source: Phys. Rev. Lett. 113 030601 (2014)
1 August 2014
Researchers from Brown University (USA), Shanxi University, and Tsinghua University (China) were the first to reveal nearly ball-shaped (but with bulges and edges) B40 molecules resembling the known fullerene molecules C60. Boron B40 is called “borospherene”. The possibility of the existence of B40 molecules and their spectral properties were earlier predicted by a complicated computer simulation. In the experiment, boron was evaporated, using laser, from a solid sample and was then cooled in a helium stream. This process yielded boron atom clusters which were separated according to their masses. These clusters were examined by photoelectron spectroscopy methods, i.e., measured were the energy spectra of electrons appearing in photoelectron emission under the effect of second laser radiation. The clusters had two different modifications, which had been predicted theoretically, with a flattened and approximately spherical shape. B36molecules, which had already been observed before, were formed of the flattened clusters. On their surface, spherical B40 have a rather complicated arrangement of boron atoms in the form of several rings and triangles.
Supervoid as the cause of the Cold Spot in relic radiation
1 August 2014
Several regions with a lowered temperature are observed in relic (cosmic microwave) radiation. Their origin has not yet been fully clarified, but these features are most probably due to the rare large perturbations of matter density. The orbital telescope WMAP revealed what is probably the most extensive of such regions referred to as a “Cold Spot”, and then this result was confirmed by the Planck telescope. I. Szapudi and his colleagues were the first to reveal with good precision the relation between the Cold Spot and the supervoid which is the region of the Universe with a lowered concentration of galaxies. The search for the void in the direction of the Cold spot was undertaken earlier, but the results were contradictory, namely, the very weak indications of the presence of a void (L. Rudnick, S. Brown, and L.R. Williams, 2007) were not endorsed in other studies. The gravitational potential of voids must lead to the occurrence of cold spots in relic radiation via the mechanism of the Sachs – Wolfe integral effect or owing to the nonlinear density evolution in later epochs (Rees – Sciama mechanism). According to calculations the latter effect makes the basic contribution to the Cold Spot formation. The data from WISE-2MASS, Pan-STARRS1, and GAMMA galaxy catalogues were used in the work, and a giant (probably the largest ever known) supervoid with R≈ 270 Mpc was revealed with the center in the red shift z = 0.22 ± 0.01 and the density by nearly 13% lower than the mean matter density in the Universe. This supervoid exactly corresponds to the position of the Cold spot. Since such a supervoid is a rare formation (fluctuations ≥3.5 σ are needed), the probability of its random projection to a cold spot in relic radiation is low. This identification suggests that other extended regions in relic radiation can be associated with large-scale structures in the Universe.
Source: arXiv:1406.3622 [astro-ph.CO]
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
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