Effects of stitching on delamination of satin weave carbon-epoxy laminates under mode I, mode II and mixed-mode I/II loadings

The objective of the present study is to characterize the effect of modified chain stitching on the delamination growth under mixed-mode I/II loading conditions. Delamination toughness under mode I is experimentally determined, for unstitched and stitched laminates, by using untabbed and tabbed double cantilever beam (TDCB) tests. The effect of the reinforcing tabs on mode I toughness is investigated. Stitching improves the energy release rate (ERR) up to 4 times in mode I. Mode II delamination toughness is evaluated in end-notched flexure (ENF) tests. Different geometries of stitched specimens are tested. Crack propagation occurs without any failure of stitching yarns. The final crack length attains the mid-span or it stops before and the specimen breaks in bending. The ERR is initially low and gradually increases with crack length to very high values. The mixedmode delamination behaviour is investigated using a mixed-mode bending (MMB) test. For unstitched specimens, a simple mixed-mode criterion is identified. For stitched specimens, stitching yarns do not break during 25% of mode I ratio tests and the ERR increase is relatively small compared to unstitched values. For 70% and 50% of mode I ratios, failures of yarns are observed during crack propagation and tests are able to capture correctly the effect of the stitching: it clearly improves the ERR for these two mixed modes, as much as threefold

Improved Measurements of Partial Rate Asymmetry in B -> h h Decays

We report improved measurements of the partial rate asymmetry (Acp) in B -> h h decays with 140fb^-1 of data collected with the Belle detector at the KEKB e+e- collider. Here h stands for a charged or neutral pion or kaon and in total five decay modes are included: K-+ pi+-, K0s pi-+, K-+ pi0, pi-+ pi0 and K0s pi0. The flavor of the last decay mode is determined from the accompanying B meson. Using a data sample 4.7 times larger than that of our previous measurement, we find Acp(K-+ pi+-) -0.088+-0.035+-0.013, 2.4 sigma from zero. Results for other decay modes are also presented.Comment: 9 pages, 1 figur

Studies of the Decay B+- -> D_CP K+-

We report studies of the decay B+- -> D_CP K+-, where D_CP denotes neutral D mesons that decay to CP eigenstates. The analysis is based on a 29.1/fb data sample of collected at the \Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e+ e- storage ring. Ratios of branching fractions of Cabibbo-suppressed to Cabibbo-favored processes involving D_CP are determined to be B(B- -> D_1 K-)/B(B- -> D_1 pi-)=0.125 +- 0.036 +- 0.010 and B(B- -> D_2 K-)/B(B- -> D_2 pi-)=0.119 +- 0.028 +- 0.006, where indices 1 and 2 represent the CP=+1 and CP=-1 eigenstates of the D0 - anti D0 system, respectively. We also extract the partial rate asymmetries for B+- -> D_CP K+-, finding A_1 = 0.29 +- 0.26 +- 0.05 and A_2 = -0.22 +- 0.24 +- 0.04.Comment: 10 pages, 2 figures, submitted to Physical Review Letter

Search for CP violation in the decay B0->D*+-D-+

We report a search for CP-violating asymmetry in B0 -> D*+- D-+ decays. The analysis employs two methods of B0 reconstruction: full and partial. In the full reconstruction method all daughter particles of the B0 are required to be detected; the partial reconstruction technique requires a fully reconstructed D- and only a slow pion from the D*+ -> D0 pi_slow+ decay. From a fit to the distribution of the time interval corresponding to the distance between two B meson decay points we calculate the CP-violating parameters and find the significance of nonzero CP asymmetry to be 2.7 standard deviations.Comment: 4 pages, 3 figure

Observation of Ds+K- and evidence for D-s(+)pi(-) final states in neutral B decays

We report the first observation of a B meson decay that is not accessible by a direct spectator process. The channel (B) over bar (0)-->Ds+K- is found in a sample of 85x10(6) B (B) over bar events, collected with the Belle detector at KEKB, with a branching fraction B((B) over bar (0)-->Ds+K-)=(4.6(-1.1)(+1.2)+/-1.3)x10(-5). We also obtain evidence for the B-0-->D(s)(+)pi(-) decay with branching fraction B(B-0-->D(s)(+)pi(-))=(2.4(-0.8)(+1.0)+/-0.7)x10(-5). This value may be used to extract a model-dependent value of \V-ub\

Measurements of B decays to two kaons

We report measurements of B meson decays to two kaons using 253 fb(-1) of data collected with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We find evidence for signals in B+->(K) over bar K-0(+) and B-0-> K-0(K) over bar (0) with significances of 3.0 sigma and 3.5 sigma, respectively. (Charge-conjugate modes are included.) The corresponding branching fractions are measured to be B(B+->(K) over bar K-0(+))=(1.0 +/- 0.4 +/- 0.1)x10(-6) and B(B-0-> K-0(K) over bar (0))=(0.8 +/- 0.3 +/- 0.1)x10(-6). These decay modes are examples of hadronic b -> d transitions. No signal is observed in the decay B-0-> K+K-, and we set an upper limit of 3.7x10(-7) at 90% confidence level

Measurement of polarization and triple-product correlations in B -> phi K-* decays

We present measurements of decay amplitudes and triple-product correlations in B ->phi K-* decays based on 253 fb(-1) of data recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) storage ring. The decay amplitudes for the three different helicity states are determined from the angular distributions of final-state particles. The longitudinal polarization amplitudes are found to be 0.45 +/- 0.05 +/- 0.02 for B-0->phi K-*0 and 0.52 +/- 0.08 +/- 0.03 for B+->phi K*+ decays. CP- and T-odd CP-violating triple-product asymmetries are measured to be consistent with zero

Measurement of forward-backward asymmetry and wilson coefficients in B -> K(*)l(+)l(-)

We report the first measurement of the forward-backward asymmetry and the ratios of Wilson coefficients A(9)/A(7) and A(10)/A(7) in B -> K(*)l(+)l(-), where l represents an electron or a muon. We find evidence for the forward-backward asymmetry with a significance of 3.4 sigma. The results are obtained from a data sample containing 386x10(6) (B) over bar pairs that were collected on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider

Evidence for direct CP violation in B-0 -> K+pi(-) decays

We report evidence for direct CP violation in the decay B-0-->K(+)pi(-) with 253 fb(-1) of data collected with the Belle detector at the KEKB e(+)e(-) collider. Using 275x10(6) B(B) over bar pairs we observe a B-->K(+/-)pi(-/+) signal with 2140+/-53 events. The measured CP violating asymmetry is A(CP)(K(+)pi(-))=-0.101+/-0.025(stat)+/-0.005(syst), corresponding to a significance of 3.9sigma including systematics. We also search for CP violation in the decays B+-->K(+)pi(0) and B+-->pi(+)pi(0). The measured CP violating asymmetries are A(CP)(K(+)pi(0))=0.04+/-0.05(stat)+/-0.02(syst) and A(CP)(pi(+)pi(0))=-0.02+/-0.10(stat)+/-0.01(syst), corresponding to the intervals -0.05< A(CP)(K(+)pi(0))<0.13 and -0.18< A(CP)(pi(+)pi(0))<0.14 at 90% confidence level