Syntheses, crystal structures, and vibrational spectroscopic properties of MgCN2, SrCN2, and BaCN2

The alkaline-earth metal cyanamides MgCN* SrCN* and BaCN2 were prepared by the reaction of melamine with the metal nitrides (M&N2, Sr-jN, Ba3N2 ) at temperatures between 740 e C and 850 °C. MgCN2 was structurally characterized by X-ray analysis using powder methods (R3m, Ζ - 3 , a=327.34(1) pm, c-1412.82(5) pm). The crystal structures of SrCN2 and BaCN2 were determined from X-ray single crystal data (SrCN2 : Pnma, Ζ-A, 0-1241.0(2) pm, 6-396.3(2) pm, c-538.9(2) pm, BaCN2 : R3c, Z=18, e-1528.2(2) pm, c-70l.3(2) pm). All compounds consist of the respective cations and CN2 2~-anions with an increasing degree of distortion of the coordination polyhedra with increasing radii of the cations. The structural features are correlated with vibrational spectroscopic data

Numerical Results for the Ground-State Interface in a Random Medium

The problem of determining the ground state of a $d$-dimensional interface embedded in a $(d+1)$-dimensional random medium is treated numerically. Using a minimum-cut algorithm, the exact ground states can be found for a number of problems for which other numerical methods are inexact and slow. In particular, results are presented for the roughness exponents and ground-state energy fluctuations in a random bond Ising model. It is found that the roughness exponent $\zeta = 0.41 \pm 0.01, 0.22 \pm 0.01$, with the related energy exponent being $\theta = 0.84 \pm 0.03, 1.45 \pm 0.04$, in $d = 2, 3$, respectively. These results are compared with previous analytical and numerical estimates.Comment: 10 pages, REVTEX3.0; 3 ps files (separate:tar/gzip/uuencoded) for figure

QCD Studies at LEP I

The high hadronic event statistics collected at the Z energy (LEP I) allowed a good understanding of the QCD dynamics. The coupling constant $\alpha_s$ has been measured with several methods giving a global average $\alpha_s(M_Z) = 0.122 \pm 0.004$. The flavour independence of $\alpha_s$ has been tested obtaining $\alpha_s^b/\alpha_s^{udsc} = 0.997 \pm 0.023$. Quark-gluon jet differencies has been observed among which $_{gluon}/_{quark} = 1.234 \pm 0.027$. A big role has been plaied by the silicon vertex detectors.Comment: 1 uuencoded PostScript file. Invited talk at Les Rencontres de Physique de la Vall\'ee d'Aoste, La Thuile, March 3-9, 199

The Quark Model and bb Baryons

The recent observation at the Tevatron of $\Sigma_b^{\pm}$ ($uub$ and $ddb$) baryons within 2 MeV of the predicted $\Sigma_b - \Lambda_b$ splitting and of $\Xi_b^-$ $(dsb)$ baryons at the Tevatron within a few MeV of predictions has provided strong confirmation for a theoretical approach based on modeling the color hyperfine interaction. The prediction of $M(\Xi^-_b) = 5790$ to 5800 MeV is reviewed and similar methods used to predict the masses of the excited states $\Xi_b^\prime$ and $\Xi_b^*$. The main source of uncertainty is the method used to estimate the mass difference $m_b - m_c$ from known hadrons. We verify that corrections due to the details of the interquark potential and to $\Xi_b$--$\Xi_b^\prime$ mixing are small. For S-wave $qqb$ states we predict $M(\Omega_b) = 6052.1 \pm 5.6$ MeV, $M(\Omega^*_b) = 6082.8 \pm 5.6$ MeV, and $M(\Xi_b^0) = 5786.7 \pm 3.0$ MeV. For states with one unit of orbital angular momentum between the $b$ quark and the two light quarks we predict $M(\Lambda_{b[1/2]}) = 5929 \pm 2$ MeV, $M(\Lambda_{b[3/2]}) = 5940 \pm 2$ MeV, $M(\Xi_{b[1/2]}) = 6106 \pm 4$ MeV, and $M(\Xi_{b[3/2]}) = 6115 \pm 4$ MeV. Results are compared with those of other recent approaches.Comment: 20 pages, 1 figure, to be published in Annals of Physics. Eq. (58) correcte

Melem (2,5,8-Triamino-tri-s-triazine), an Important Intermediate during Condensation of Melamine Rings to Graphitic Carbon Nitride: Synthesis, Structure Determination by X-ray Powder Diffractometry, Solid-State NMR, and Theoretical Studies

Single-phase melem (2,5,8-triamino-tri-s-triazine) C6N7(NH2)3 was obtained as a crystalline powder by thermal treatment of different less condensed C−N−H compounds (e.g., melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4[N(CN)2], or cyanamide H2CN2, respectively) at temperatures up to 450°C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu Kα1:  P21/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, β = 99.912(2)°, and Z = 4). In the solid, melem consists of nearly planar C6N7(NH2)3 molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed 13C and 15N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state was performed employing density functional methods utilizing LDA and GGA. A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem. According to temperature-dependent X-ray powder diffractometry investigations above 560°C, melem transforms into a graphite-like C−N material

Measuring Semileptonic Asymmetries in LHCb

The $C\!P$-violating flavour-specific asymmetry in neutral $b$ mesons provides a method for testing the Standard Model. The measurements from the D0 experiment yield values of this asymmetry that disagree with the Standard Model at a level of 3.6 $\sigma$. This contribution discusses the latest LHCb measurements in this sector both from $B^0$ mesons ($a_{\mathrm{sl}}^d$) and $B^0_s$ mesons ($a_{\mathrm{sl}}^s$). Using their 2011 dataset, corresponding to an integrated luminosity of 1.0 $\mathrm{fb}^{-1}$ obtained in 2011, LHCb measured a value of $a_{\mathrm{sl}}^s = (-0.06 \pm 0.50_{\text{stat}} \pm 0.36_{\text{syst}}) \%$. Combining the 2011 and 2012 datasets, with an integrated luminosity of 3 $\mathrm{fb}^{-1}$, LHCb measured $a_{\mathrm{sl}}^d = (-0.02 \pm 0.19_{\text{stat}} \pm 0.30_{\text{syst}}) \%$. These are the most precise measurements of the parameters $a_{\mathrm{sl}}^s$ and $a_{\mathrm{sl}}^d$ to date. Plans for an updated result for $a_{\mathrm{sl}}^s$ using the full 3 $\mathrm{fb}^{-1}$ dataset are discussed. This will include new methods to determine detection asymmetries which are the dominating systematic uncertainty of the 2011 measurement.Comment: Proceedings of the workshop "Flavorful Ways to New Physics", 28-31 October 2014, Freudenstadt, German