A model for the B±→π−π+π± decay amplitude is proposed to study the large CP violation observed at the high mass region of the Dalitz plane. A short distance b→u amplitude with the weak phase γ is ...considered together with the contribution of a hadronic charm loop and a s-wave DD¯→ππ rescattering. In the model, the χc0 appears as a narrow resonant state of the DD¯ system below threshold. It is introduced in an unitary two channel S-matrix model of the coupled DD¯ and ππ channels, where the χc0 complex pole in DD¯ channel shows its signature in the off-diagonal matrix element and in the associated DD¯→ππ transition amplitude. The strong phase of the resulting decay amplitude has a sharp sign change at the DD¯ threshold, changing the sign of the CP asymmetry, as it is observed in the data. We conclude that the hadronic charm loop and rescattering mechanism are relevant to the broadening of the CP asymmetry around the χc0 resonance in the ππ channel. This novel mechanism provides a possible interpretation for the CP asymmetry challenging experimental result presented by the LHCb collaboration for the B±→π−π+π± decay in the high mass region.
We propose a theoretical framework to understand the observable global charge-parity (CP) violation in charmless three-body B± decays. The decay amplitudes consider the effects of the ππ→KK ...rescattering treated within a CPT invariant framework together with the U-spin symmetry relation, s↔d, which results π↔K in the final state. This approach applied to a two-channel model provides the magnitudes and signs of the ratios of the global CP asymmetries for B±→K±π+π−, B±→K±K+K−, B±→π±K+K−, and B±→π±π+π− decays, qualitatively consistent with those obtained from the available experimental data. In addition, by considering the neutral channels, we predict the ratios for the global CP asymmetries for these decays.
Following the experimental results from LHCb on the rare decay Bc+→K−K+π+, we investigate the possibility where this process is dominated by a double charm rescattering. The Bc decay to double charm ...channels have a weak topology that is favored in comparison with the direct production of K−K+π+ in the final state, suppressed by quark annihilation. The decay amplitude for Bc+→K−K+π+ with Bc decaying first to double charm channels is described by charm hadronic triangle loops, which reach the final state of interest after DD¯→KK¯ or D+Ds−→π+K− transitions. We show that these processes give rise to non-resonant amplitudes with a clear signature in the Dalitz plot. In a near future, the new data from LHCb run II will be able to confirme if the main hypotheses of this work is correct and the dominant mechanism to produce K+K+π− from the decay of Bc+ is through charm rescattering.
Charm penguin diagrams are known to be the main contribution to charmless B decay process with strangeness variation equal to minus one, which is the case of B±→K±K+K− decay. The large phase space ...available in this and other B three-body decays allows non trivial final state interactions with all sort of rescattering processes and also access high momentum transfers in the central region of the Dalitz plane. In this work we investigate the charm Penguin contribution to B±→K±K+K−, described by a hadronic triangle loop in nonperturbative regions of the phase space, and by a partonic loop at the quasi perturbative region. These nonresonant amplitudes should have a particular structure in the Dalitz plane and their contributions to the final decay amplitude can be confirmed by a data amplitude analysis in this channel. In particular, the hadronic amplitude has a changing sign in the phase at DD¯ threshold which can result in a change of sign for the CP asymmetry.
Charge parity asymmetry in charmless B meson decays is a key issue to be understood. Many theoretical calculations have been performed using short distance factorization approaches which, in general, ...do not take into account the CPT invariance constraint. For each channel with CP violation there is an equal amount of CP asymmetry in another channel or other channels, with an opposite sign. This happens if these channels are coupled through final state interactions. In the specific process B→PV, involving one pseudoscalar and one vector particle in the final state, we argue that the CP asymmetry, inherent from a short distance mechanism, could be suppressed due to the CPT constraint. In this case, we propose a sensitive and practical experimental method to identify even a small CP asymmetry, which provides the values for ACP without the need for an amplitude analysis. This method, if applied directly to data, will enable one to extract the CP asymmetry information in a model independent way and check to which extent the suggested suppression due to the CPT constraint is verified.
Up to now, the theory for analysis of continuous spindle speed variation in milling processes was developed for sinusoidal variation only, and for average tooth passing frequency an exact multiple of ...speed variation frequency. This paper presents the general theory for analysis in the frequency domain and for any speed variation strategy. Results are compared with those obtained by semidiscretization and time integration, as well as with those obtained by experiments. The discrepancies of the results obtained by the different approaches are discussed, and the analysis of the evolution of the stability along the speed variation period is proposed.
Chatter vibration problems arise during machining. This paper aims to produce a strategy that can detect the emergence of chatter so that subsequently, in accordance with the lobe on the stability ...diagram where the process is located, the proper strategy may be determined, either by taking the machine to a stable spindle speed or causing continuous variation in spindle speed. The effectiveness of this strategy is contrasted for a number of different cases, using both simulation and experimental testing. The context targeted by the strategy is a high-speed mill roughing operation for cases of vibration arising on the headstock/cutting tool unit, when high material removal rates (MRR) must be maintained. Industrial implementation of the strategy and the chatter detection and diagnosis algorithm is carried out using a portable digital assistant (PDA).
The continuous rotation speed variation is demonstrated to be an efficient method to avoid regenerative chatter in different machining processes. This paper presents a time-domain dynamic model for ...throughfeed centerless grinding process that can predict chatter by means of part roundness error evolution. Continuous workpiece speed variation (CWSV) has been implemented in this model to analyze the influence of this disturbing method on the dynamic instability. Experimental results have validated the model and verified the effectiveness of CWSV for chatter avoidance and surface finish and dimensional tolerances improvement. It has been demonstrated that the selection of the optimal variation parameters is an important factor not only for chatter avoidance, but also for the stability of surface finish and dimensional tolerances since workpiece speed variation has a direct influence on throughfeed rate and grinding forces.
► A time-domain dynamic model for throughfeed centerless grinding is developed. ► CWSV decreases chatter amplitude and improves workpiece roundness and roughness. ► CWSV has a direct influence on throughfeed rate, forces and workpiece tolerances. ► It is necessary to select optimal combinations of variation amplitude and frequency. ► There is a trend towards selection of low frequencies and large amplitudes.
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