标题： |V_{ub}/V_{cb}|（和 |V_{ub}|）在单态非轻子衰变中的测量，\bar{B}^0 --> D_s^{(*)-}(π^+,ρ^+) 和\bar{B}^0 --> D_s^{(*)-}D^{(*)+} 显示英文标题

标题： Measurement of |V_{ub}/V_{cb}| (and |V_{ub}|) in Exclusive Nonleptonic Decays, \bar{B}^0 --> D_s^{(*)-}(π^+,ρ^+) and \bar{B}^0 --> D_s^{(*)-}D^{(*)+}

摘要： 我们研究了通过在因子化假设下计算包含penguin效应的比值${\cal B}(\bar{B}^0\to D_s^{(*)-}(\pi^+,\rho^+))/{\cal B}(\bar{B}^0\to D_s^{(*)-}D^{(*)+})$来提取$|\vub/\vcb|$。 涉及$\bar{B}^0\to D_s^-D^{+}$模式的比值具有显著的penguin修正（在振幅层面为$\sim 15%$），但涉及$\bar{B}^0\to D_s^-D^{*+}$模式的比值具有相对较小的penguin修正。 另一方面，$\bar{B}^0\to D_s^-D^{+}$模式具有较小的形式因子依赖性。 因此，这些比值在测量$\vub/\vcb$时相互补充。 我们方法中强子形式因子的理论不确定性约为15%，这与从单举半轻子B介子衰变中测量的$| \vub/\vcb |$的模型依赖性不确定性约20%相当。 利用CLEO对$B\to D_s \pi$衰变的最新上限，我们的方法设定了一个上限$| \vub/\vcb | < 0.13$，这与半轻子B介子衰变的测量值非常接近。 我们还讨论了因子化假设可能的破坏。 显示英文摘要

摘要： We have studied extracting $|\vub/\vcb|$ by calculating the ratios ${\cal B}(\bar{B}^0\to D_s^{(*)-}(\pi^+,\rho^+))/{\cal B}(\bar{B}^0\to D_s^{(*)-}D^{(*)+})$ including penguin effects within the factorization assumption. The ratios involving $\bar{B}^0\to D_s^-D^{+}$ mode have considerable penguin corrections ($\sim 15%$ at the amplitude level), but those involving $\bar{B}^0\to D_s^-D^{*+}$ mode have relatively small penguin corrections. On the other hand, the $\bar{B}^0\to D_s^-D^{+}$ mode has smaller form-factor dependance. Therefore, these ratios complement each other in measuring $\vub/\vcb$. The theoretical uncertainty from the hadronic form factors in our method is at the level of 15%, which is comparable to the model-dependence uncertainty of about 20% in the measurement of $| \vub/\vcb |$ from the exclusive semileptonic B decays. Using the newest upper limit on $B\to D_s \pi$ decay from CLEO, our method sets an upper limit $| \vub/\vcb | < 0.13$ which is very close to the measured values from the semileptonic B decays. We also discuss the possible breaking of factorization assumption.