Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal

Research and development of a CBM-RICH prototype

We have developed a gaseous Ring Imaging CHerenkov detector prototype (PNU-RICH2) of the CBM-RICH detector. This prototype has the same radiator length as the planned CBM-RICH detector. The PNU-RICH2 includes a spherical concave mirror and 2 types of Multi-anode PMTs. The PNU-RICH2 detector has tested at the PAL-TEST LINAC with 60MeV electron beam. A detector performance from the beam test will be presented and discussed in comparison with simulation results

Research and development of a CBM-RICH prototype

We have developed a gaseous Ring Imaging CHerenkov detector prototype (PNU-RICH2) of the CBM-RICH detector. This prototype has the same radiator length as the planned CBM-RICH detector. The PNU-RICH2 includes a spherical concave mirror and 2 types of Multi-anode PMTs. The PNU-RICH2 detector has tested at the PAL-TEST LINAC with 60MeV electron beam. A detector performance from the beam test will be presented and discussed in comparison with simulation results

Colloidal synthesis and thermoelectric properties of La-doped SrTiO3 nanoparticles

We describe n-type nanostructured bulk thermoelectric La-doped SrTiO3 materials produced by spark plasma sintering of chemically synthesized colloidal nanocrystals. The La doping levels could be readily controlled from 3 to 9.0 at% by varying the experimental conditions. We found that nanoscale interfaces were preserved even after the sintering process, and the thermoelectric properties of the nanostructured bulk La-doped SrTiO3 were characterized. An enhanced thermoelectric efficiency was observed and attributed to the large decrease in thermal conductivity obtained with no significant change in the Seebeck coefficient or electrical conductivity. The nanostructured bulk of the La-doped SrTiO3 exhibited a maximum ZT of similar to 0.37 at 973 K at 9.0 at% La doping, which is one of the highest values reported for doped SrTiO3. Furthermore, the materials showed high thermal stability, which is important for practical high-temperature thermoelectric applications. This report demonstrates the high potential for low-cost thermoelectric energy production using highly stable and inexpensive oxide materials.close97

n-Type Nanostructured Thermoelectric Materials Prepared from Chemically Synthesized Ultrathin Bi₂Te₃ Nanoplates

We herein report on the large-scale synthesis of ultrathin Bi₂Te₃ nanoplates and subsequent spark plasma sintering to fabricate n-type nanostructured bulk thermoelectric materials. Bi₂Te₃ nanoplates were synthesized by the reaction between bismuth thiolate and tri-n-octylphosphine telluride in oleylamine. The thickness of the nanoplates was ∼1 nm, which corresponds to a single layer in Bi₂Te₃ crystals. Bi₂Te₃ nanostructured bulk materials were prepared by sintering of surfactant-removed Bi₂Te₃ nanoplates using spark plasma sintering. We found that the grain size and density were strongly dependent on the sintering temperature, and we investigated the effect of the sintering temperature on the thermoelectric properties of the Bi₂Te₃ nanostructured bulk materials. The electrical conductivities increased with an increase in the sintering temperature, owing to the decreased interface density arising from the grain growth and densification. The Seebeck coefficients roughly decreased with an increase in the sintering temperature. Interestingly, the electron concentrations and mobilities strongly depended on the sintering temperature, suggesting the potential barrier scattering at interfaces and the doping effect of defects and organic residues. The thermal conductivities also increased with an increase in the sintering temperature because of grain growth and densification. The maximum thermoelectric figure-of-merit, ZT, is 0.62 at 400 K, which is one of the highest among the reported values of n-type nanostructured materials based on chemically synthesized nanoparticles. This increase in ZT shows the possibility of the preparation of highly efficient thermoelectric materials by chemical synthesis

n-Type Nanostructured Thermoelectric Materials Prepared from Chemically Synthesized Ultrathin Bi2Te3 Nanoplates

We herein report on the large-scale synthesis of ultrathin Bi 2Te 3 nanoplates and subsequent spark plasma sintering to fabricate n-type nanostructured bulk thermoelectric materials. Bi 2Te 3 nanoplates were synthesized by the reaction between bismuth thiolate and tri-n-octylphosphine telluride in oleylamine. The thickness of the nanoplates was ???1 nm, which corresponds to a single layer in Bi 2Te 3 crystals. Bi 2Te 3 nanostructured bulk materials were prepared by sintering of surfactant-removed Bi 2Te 3 nanoplates using spark plasma sintering. We found that the grain size and density were strongly dependent on the sintering temperature, and we investigated the effect of the sintering temperature on the thermoelectric properties of the Bi 2Te 3 nanostructured bulk materials. The electrical conductivities increased with an increase in the sintering temperature, owing to the decreased interface density arising from the grain growth and densification. The Seebeck coefficients roughly decreased with an increase in the sintering temperature. Interestingly, the electron concentrations and mobilities strongly depended on the sintering temperature, suggesting the potential barrier scattering at interfaces and the doping effect of defects and organic residues. The thermal conductivities also increased with an increase in the sintering temperature because of grain growth and densification. The maximum thermoelectric figure-of-merit, ZT, is 0.62 at 400 K, which is one of the highest among the reported values of n-type nanostructured materials based on chemically synthesized nanoparticles. This increase in ZT shows the possibility of the preparation of highly efficient thermoelectric materials by chemical synthesis.close5