Evidence for an exotic S=-2, Q=-2 baryon resonance in proton-proton collisions at the CERN SPS

Results of resonance searches in the Xi - pi -, Xi - pi +, Xi -bar+ pi -, and Xi -bar+ pi + invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi - pi - baryon resonance with mass of 1.862±0.002 GeV/c2 and width below the detector resolution of about 0.018 GeV/c2. The significance is estimated to be above 4.2 sigma . This state is a candidate for the hypothetical exotic Xi --3/2 baryon with S=-2, I=3 / 2, and a quark content of (dsdsu-bar). At the same mass, a peak is observed in the Xi - pi + spectrum which is a candidate for the Xi 03/2 member of this isospin quartet with a quark content of (dsusd-bar). The corresponding antibaryon spectra also show enhancements at the same invariant mass

Light-Front Approach for Heavy Pentaquark Transitions

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.

H- and D-related mid-infrared absorption bands in Ga(1-y)In(y)As(1-x)N(x) epitaxial layers

Epitaxially grown ternary and quaternary layers of GaAs based dilute nitrides have been exposed to H+ and D+ ion bombardment to investigate the interaction between hydrogen (deuterium) and nitrogen. Low-temperature Fourier transform infrared absorption measurements reveal the formation of N-H (N-D) complexes by the appearance of high-frequency absorption bands in the mid-infrared due to vibrational modes of H(D). In thin layers, the transformation of isolated substitutional nitrogen, N-As, into complexes involving H (D) is complete, in thick (500-1000 nm) layers only partial. Analyses for the band intensities dependent on variations of the sample structure and parameters during ion irradiation challenge the model of a unique defect associated with the observed vibrational modes. A new model is proposed based to two different N-H (N-D) centers, each involving one H (D) atom

Correlation of band formation and local vibrational mode structure in Ga(0.95)Al(0.05)As(1-x)N(x) with 0<= x <= 0.03

We present comprehensive optical studies of a series of as-grown and hydrogenated Ga(0.95)Al(0.05)As(1-x)N(x) epitaxial layers with various amounts x of substitutional nitrogen. Photomodulated and contactless electromodulated spectroscopies were performed to gain information about the influence of N incorporation on the band structure. The results are interpreted in terms of the band-anticrossing model and compared to corresponding GaAs:N data. The local vibrational properties of the N atoms studied by Raman and Fourier-transform infrared absorption were found to depend strongly on the Ga/Al nearest-neighbour configurations of N. Correlations between local N environments and global band structure properties are confirmed by comparing results obtained before and after hydrogenation of the samples

Charakterisierung von semiisolierenden GaAs-Substraten fuer IS-Anwendungen Schlussbericht

SIGLEAvailable from TIB Hannover: FR 5421 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Atomistische Ursachen des Wafer-Verzuges Schlussbericht

With 52 refs., 5 tabs., 54 figs.Copy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman