B Meson Semileptonic Form Factors from Unquenched Lattice QCD

Abstract

The semileptonic process, B --> πl ν, is studied via full QCD Lattice simulations. We use unquenched gauge configurations generated by the MILC collaboration. These include the effect of vacuum polarization from three quark flavors: the $s$ quark and two very light flavors ($u/d$) of variable mass allowing extrapolations to the physical chiral limit. We employ Nonrelativistic QCD to simulate the $b$ quark and a highly improved staggered quark action for the light sea and valence quarks. We calculate the form factors $f_{+}(q^2)$ and $f_0(q^2)$ in the chiral limit for the range 16 GeV${}^2\le q^2<q_{max}^2$ and obtain ${\int }_{16Ge{V}^2}^{q_{max}^2}[d\hat{I}“/d{q}^2]d{q}^2/|v_{ub}{|}^2=1.46(35)p{s}^{-1}$. Combining this with a preliminary average by the Heavy Flavor Averaging Group (HFAG'05) of recent branching fraction data for exclusive B semileptonic decays from the BaBar, Belle and CLEO collaborations, leads to $|V_{ub}|=4.22(30)(51)\times 10^{-3}$. PLEASE NOTE APPENDIX B with an ERRATUM, to appear in Physical Review D, to the published version of this e-print (Phys.Rev.D 73, 074502 (2006)). Results for the form factor $f_{+}(q^2)$ in the chiral limit have changed significantly. The last two sentences in this abstract should now read; "We calculate the form factor $f_{+}(q^2)$ and $f_0(q^2)$ in the chiral limit for the range 16 Gev${}^2\le q^2<q_{max}^2$ and obtain ${\int }_{16Ge{V}^2}^{q_{max}^2}[d\hat{I}“/d{q}^2]d{q}^2/|V_{ub}{|}^2=2.07(57)p{s}^{-1}$. Combining this with a preliminary average by the Heavy Flavor Averagibg Group (HFAG'05) of recent branching fraction data for exclusive B semileptonic decays from the BaBar, Belle and CLEO collaborations, leads to $|V_{ub}|=3.55(25)(50)\times 10^{-3}$."

15 pages, 14 figures. This replacement includes the original version of the e-print, as published in Phys.Rev.D{\bf 73}, 074502 (2006), and additionally a new Appendix B with an ERRATUM to appear in Physicsl Review D. Results for the form factor $f_{+}(q^2)$ in the chiral limit have changed considerably