Study of the weak annihilation contributions in charmless $$\varvec{B_s\rightarrow VV}$$ B s → V V decays

Abstract

In this paper, in order to probe the spectatorscattering and weak annihilation contributions in charmless B s → V V (where V stands for a light vector meson) decays, we perform the χ 2 -analyses for the endpoint parameters within the QCD factorization framework, under the constraints from the measuredB s → ρ 0 φ, φ K * 0 , φφ and K * 0K * 0 decays. The fitted results indicate that the endpoint parameters in the factorizable and nonfactorizable annihilation topologies are non-universal, which is also favored by the charmless B → P P and PV (where P stands for a light pseudo-scalar meson) decays observed in previous work. Moreover, the abnormal polarization fractions f L ,⊥ (B s → K * 0K * 0 ) = (20.1±7.0)%, (58.4±8.5)% measured by the LHCb collaboration can be reconciled through the weak annihilation corrections. However, the branching ratio ofB s → φ K * 0 decay exhibits a tension between the data and theoretical result, which dominates the contributions to χ 2 min in the fits. Using the fitted endpoint parameters, we update the theoretical results for the charmless B s → V V decays, which will be further tested by the LHCb and Belle-II experiments in the near future.

Time-reversal asymmetries and angular distributions in Λb → ΛV

“…On the other hand, once the NF contributions are considered, the arguments would not hold. In the B meson decays with b → s transitions, we know that the NF contributions are mainly found in the negative helicities [56][57][58][59][60][61], which lead to the so-called polarization puzzles in B 0 → K * 0 φ [26,27,62,63]. In analogy, we assume that the NF effects attribute solely to b + in the b → s transitions of Λ b decays.…”

Four-body decays B(s) → (Kπ)S/P(Kπ)S/P in the perturbative QCD approach

“…One can see from table 3 that various predictions for f 0 (B 0 s → K * 0K * 0 ) lie in the range 0.343 to 0.636, considerably larger than the data. The QCDF evaluation gives a low longitudinal polarization fraction f 0 (B 0 s → K * 0K * 0 ) = (27.7 +8.2+9.5 −6.7−18.9 )% [125] by including weak annihilation corrections with the best-fit endpoint parameters. This abnormal longitudinal polarization fraction seems to be reconciled, but an obvious tension between the data and the prediction for the branching ratio B(B s → φK * ) is invoked accordingly.…”

Generation of exchange magnons in thin ferromagnetic films by ultrashort acoustic pulses

“…By adding the damping term and the explicit expression for A (n) 32 from Eq. (27) we arrive at the most important analytical equation in this paper:…”

“…The discovery of ultrafast laser-induced demagnetization in ferromagnetic nickel in 1996 [1] opened new booming field of femtosecond laser manipulation of magnetization [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Depending on a mechanism, magnetization dynamics induced by a femtosecond laser pulse can be sorted into the following categories: (i) thermal effects [3,13], (ii) magnetooptical effects [22], (iii) magnetoacoustic effects [15,18,19,[23][24][25][26][27] and (iv) spin transfer torque [28][29][30][31]. Despite of the facts that the spin transfer torque is an efficient mechanism to drive coherent magnetization dynamics in ferromagnet through ultrashort pulses of spinpolarized electrons propagating in noble metals for several tens of nanometers before they lose their spin polarization [32], acoustic pulses can propagate over much larger distances before they vanish.…”

“…Picosecond acoustic pulses generated by femtosecond laser excitations [25,[33][34][35] can drive the small-angle precession of ferromagnetic resonance (FMR) in various ferromagnetic samples [15,19,23,24]. Experimental configurations using fs-laser excited periodic acoustic transients [21,26,27] can be used to resonantly enhance the amplitude of FMR precession angle. Previous experimental work on ultrafast magnetoacoustics by Kim and co-workers [20,21] demonstrated the possibility to control the ferromagnetic resonance (FMR) [36] by a series of ultrashort, picosecond acoustic pulses.…”