Yields and polarizations of prompt $jpsi$ and $psits$ production in hadronic collisions

We give predictions of $jpsi$ and $psits$ yields and polarizations in prompt production at hadron colliders based on non-relativistic QCD factorization formula. We calculate short-distance coefficients of all important color-octet intermediate channels as well as color-singlet channels up to $mathcal{O}(alpha_S^4)$, i.e. next-to-leading order in $alpha_S$. For prompt $jpsi$ production, we also take into account feeddown contributions from $chi_{cJ}$(J=0,1,2) and $psits$ decays. Color-singlet long-distance matrix elements (LDMEs) are estimated by using potential model, and color-octet LDMEs are extracted by fitting the Tevatron yield data only. The predictions are satisfactory for both yields and polarizations of prompt $jpsi$ and prompt $psits$ production at the Tevatron and the LHC. In particular, we find our predictions for polarizations of prompt $jpsi$ production have only a little difference from our previous predictions for polarizations of direct $jpsi$ production.

$Upsilon(nS)$ and $chi_b(nP)$ production at hadron colliders in nonrelativistic QCD

$Upsilon(nS)$ and $chi_b(nP)$ (n=1,2,3) production at the LHC is studied at next-to-leading order in $alpha_s$ in nonrelativistic QCD. Feeddown contributions from higher $chi_b$ and $Upsilon$ states are all considered for lower $Upsilon$ cross sections and polarizations. The long distance matrix elements (LDMEs) are extracted from the yield data, and then used to make predictions for the $Upsilon(nS)$ polarizations, which are found to be consistent with the measured polarization data within errors. In particular, the $Upsilon(3S)$ polarization puzzle can be understood by a large feeddown contribution from $chi_b(3P)$ states. Our results may provide a good description for both cross sections and polarizations of prompt $Upsilon(nS)$ and $chi_b(nP)$ production at the LHC.

The Wolf-Rayet features and mass-metallicity relation of long-duration gamma-ray burst host galaxies

Aims. We have gathered optical spectra of 8 long-duration GRB host galaxies selected from the archival data of VLT/FORS2. We investigated whether or not Wolf-Rayet (WR) stars can be detected in these GRB host galaxies. We also tried to estimate the physical properties of GRB host galaxies, such as metallicity. Methods. We identified the WR features in these spectra by fitting the WR bumps and WR emission lines in blue and red bumps. We also identified the subtypes of the WR stars, and estimated the numbers of stars in each subtype, then calculated the WR/O star ratios. The (O/H) abundances of GRB hosts were estimated from both the electron temperature (Te) and the metallicity-sensitive strong-line ratio (R23), for which we have broken the R23 degeneracy. We compared the environments of long-duration GRB host galaxies with those of other galaxies in terms of their luminosity (stellar mass)-metallicity relations (LZ, MZ). Results. We detected the presence of WR stars in 5 GRB host galaxies having spectra with relatively high signal-to-noise ratios (S/N). In the comparison of LZ, MZ relations, it shows that GRB hosts have lower metallicities than other samples with comparable luminosity and stellar mass. The presence of WR stars and the observed high WR/O star ratio, together with low metallicity, support the core-collapsar model and implie the first stage of star formation in the hosted regions of GRBs.