Search for B to K Nu Nubar Decays with a Semileptonic Tag
Author | : |
Publisher | : |
Total Pages | : 145 |
Release | : 2010 |
ISBN-10 | : OCLC:958229917 |
ISBN-13 | : |
Rating | : 4/5 (17 Downloads) |
Book excerpt: Flavor-changing neutral-current transitions such as b 2!s[nu]$\bar{v}$ are absent at tree level in the Standard Model and can only occur via loop diagrams. Several new physics models may enhance the rate of these transitions. This document presents searches for the exclusive decays B+ u 2!K+[nu]$\bar{v}$ and B0 d 2!K0S [nu]$\bar{v}$, which have a predicted theoretical branching fraction of (3.8+1.2 -0.6) × 10-6. The presence of two neutrinos in the final state makes recognition of the signal challenging, so the full reconstruction of one B meson in the semileptonic decay channel B 2!D(*)l[nu] is used to facilitate the search for the signal in the recoiling B. This analysis uses approximately 420 fb-1 or 460 million B$\bar{B}$ pairs collected over runs 1-6 with the BABAR detector at the PEP-II B factory. This analysis finds 90% confidence level upper limits on the branching fractions of 1.3×10-5 for B+ u 2!K+[nu]$\bar{v}$, 5.6×10-5 for B0 d 2!K0[nu]$\bar{v}$, and the first upper limits on the partial branching fractions for B+ u 2!K+[nu]$\bar{v}$ of 3.1 × 10-5 for K+ CMS momentum 1.5 GeV/c and of 0.89 × 10-5 for K+ CMS momentum 1.5 GeV/c. These results improve upon the previous best upper limits, which came from the Belle experiment, of 1.4 × 10-5 for B+ u 2!K+[nu]$\bar{v}$ and 16 × 10-5 for B0 d 2!K0[nu]$\bar{v}$. They also rule out a new physics model of scalar dark matter for scalar particle masses below 1.7 GeV/c2.