LHCb

Abstract:

A bstract The first full angular analysis of the $$ {B}^0\to {D}^{\ast -}{D}_s^{\ast +} $$ B 0 → D ∗ − D s ∗ + decay is performed using 6 fb − 1 of pp collision data collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The $$ {D}_s^{\ast +}\to {D}_s^{+}\gamma $$ D s ∗ + → D s + γ and D * − → $$ {\overline{D}}^0{\pi}^{-} $$ D ¯ 0 π − vector meson decays are used with the subsequent $$ {D}_s^{+} $$ D s + → K + K − π + and $$ {\overline{D}}^0 $$ D ¯ 0 → K + π − decays. All helicity amplitudes and phases are measured, and the longitudinal polarisation fraction is determined to be f L = 0 . 578 ± 0 . 010 ± 0 . 011 with world-best precision, where the first uncertainty is statistical and the second is systematic. The pattern of helicity amplitude magnitudes is found to align with expectations from quark-helicity conservation in B decays. The ratio of branching fractions [ℬ( $$ {B}^0\to {D}^{\ast -}{D}_s^{\ast +} $$ B 0 → D ∗ − D s ∗ + ) × ℬ( $$ {D}_s^{\ast +}\to {D}_s^{+}\gamma $$ D s ∗ + → D s + γ )] / ℬ( B 0 → D * − $$ {D}_s^{+} $$ D s + ) is measured to be 2 . 045 ± 0 . 022 ± 0 . 071 with world-best precision. In addition, the first observation of the Cabibbo-suppressed B s → D * − $$ {D}_s^{+} $$ D s + decay is made with a significance of seven standard deviations. The branching fraction ratio ℬ( B s → D * − $$ {D}_s^{+} $$ D s + ) / ℬ( B 0 → D * − $$ {D}_s^{+} $$ D s + ) is measured to be 0 . 049 ± 0 . 006 ± 0 . 003 ± 0 . 002, where the third uncertainty is due to limited knowledge of the ratio of fragmentation fractions.

Abstract:

The first search for the doubly heavy Omega(0)(bc) baryon and a search for the Xi(0)(bc) baryon are performed using collision data collected via the experiment from 2016 to 2018 at a centre-of-mass energy of, corresponding to an integrated luminosity of 5.2 fb(-1). The baryons are reconstructed via their decays to Lambda(+)(-)(c)(pi) and Xi(+)(c)pi(-). No significant excess is found for invariant masses between 6700 and 7300 MeV/c(2), in a rapidity range from 2.0 to 4.5 and a transverse momentum range from 2 to 20 MeV/c. Upper limits are set on the ratio of the Omega(0)(bc) and Xi(0)(bc) production cross-section times the branching fraction to Lambda(+)(c)pi(-)(Xi(+)(c)pi(-)) relative to that of the Lambda(0)(b)(Xi(0)(b)) baryon, for different lifetime hypotheses, at 95% confidence level. The upper limits range from 0.5x10(-4) to 2.5x10(-4) for the Omega(0)(bc) -> Lambda(+)(c)pi(-) (Xi(0)(bc) -> Lambda(+)(c)pi(-)) decay, pending on the considered mass and lifetime of the Omega(0)(bc) (Xi(0)(bc)) baryon.