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arXiv 0705.4008hep-ex
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B0 -> D*- l+ nu_l衰变的形状因子和CKM矩阵元|V_cb|的确定

Determination of the Form Factors for the Decay B0 -> D*- l+ nu_l and of the CKM Matrix Element |V_cb|

The BABAR Collaboration, B. Aubert

摘要:

我们提出了Cabibbo-Kobayashi-Maskawa矩阵元的组合测量|V_{cb}|在重夸克有效理论的框架下,充分描述了B 0-> D*- l+ nu_l衰变的形状因子的参数rho^2、R_1(1)和R_2(1)。用BaBar探测器记录了52,800个B_0 → D ~(*-1)+ nu_1衰变样品,其结果为:ρ_2 =1.157 ± 0.094 ± 0.027,R_1(1)=1.327 ± 0.131 ± 0.043,R_2(1)=0.859 ± 0.077 ± 0.021,和F(1)|V_cb| =(34.7+-0.4+-1.0 x10 ^-3.第一个误差是统计误差,第二个误差是系统误差。将这些测量结果与之前的形状因子的BaBar测量结果相结合,我们改进了结果的统计精度,ρ 2 =1.191+-0.048+-0.028,R1(1)=1.429+-0.061+-0.044,R2(1)=0.827+-0.038+-0.022,和F(1)|V_cb| =(34.4+-0.3+-1.1 x10 ^-3.通过对轴向形状因子$\mathcal{F}(1)$的晶格计算,我们得出了|V_cb| =(37.4+-0.3+-1.2+1.2-1.4)x10^-3,其中第三个误差是由于F(1)的不确定性。我们还提出了一个专门的分支分数的测量,B =(4.69+-0.04+-0.34)%。

英文摘要:

We present a combined measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_{cb}| and of the parameters rho^2, R_1(1), and R_2(1), which fully characterize the form factors for the B0 -> D*- l+ nu_l decay in the framework of heavy-quark effective theory. The results, based on a selected sample of about 52,800 B0 -> D*- l+ nu_l decays, recorded by the BaBar detector, are rho2=1.157+-0.094+-0.027, R_1(1)=1.327+-0.131+-0.043, R_2(1)=0.859+-0.077+-0.021, and F(1)|V_cb|=(34.7+-0.4+-1.0)x10^-3. The first error is the statistical and the second is the systematic uncertainty. Combining these measurements with the previous BaBar measurement of the form factors, which employs a different fit technique on a partial sample of the data, we improve the statistical precision of the result, rho2=1.191+-0.048+-0.028, R_1(1)=1.429+-0.061+-0.044, R_2(1)=0.827+-0.038+-0.022, and F(1)|V_cb| = (34.4+-0.3+-1.1)x10^-3. Using lattice calculations for the axial form factor $\mathcal{F}(1)$, we extract |V_cb| =(37.4+-0.3+-1.2+1.2-1.4)x10^-3, where the third error is due to the uncertainty in F(1). We also present a measurement of the exclusive branching fraction, B = (4.69+-0.04+-0.34)%.

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