We present evidence for the flavor-changing neutral current decay B→K*ℓ+ℓ- and a measurement of the branching fraction for the related process B→Kℓ+ℓ-, where ℓ+ℓ- is either an e+e- or a μ+μ- pair. These decays are highly suppressed in the standard model, and they are sensitive to contributions from new particles in the intermediate state. The data sample comprises 123×106 Υ(4S)→BB̅ decays collected with the BABAR detector at the SLAC PEP-II e+e- storage ring. Averaging over K(*) isospin and lepton flavor, we obtain the branching fractions B(B→Kℓ+ℓ-)=(0.65-0.13+0.14±0.04)×10-6 and B(B→K*ℓ+ℓ-)=(0.88-0.29+0.33±0.10)×10-6, where the uncertainties are statistical and systematic, respectively. The significance of the B→Kℓ+ℓ- signal is over 8σ, while for B→K*ℓ+ℓ- it is 3.3σ.
Evidence for the Rare Decay B→K*ℓ+ℓ- and Measurement of the B→Kℓ+ℓ- Branching Fraction
CONTRI, ROBERTO;LO VETERE, MAURIZIO;MONGE, MARIA ROBERTA;PATRIGNANI, CLAUDIA;ROBUTTI, ENRICO;SANTRONI, ALBERTO;TOSI, SILVANO;
2003-01-01
Abstract
We present evidence for the flavor-changing neutral current decay B→K*ℓ+ℓ- and a measurement of the branching fraction for the related process B→Kℓ+ℓ-, where ℓ+ℓ- is either an e+e- or a μ+μ- pair. These decays are highly suppressed in the standard model, and they are sensitive to contributions from new particles in the intermediate state. The data sample comprises 123×106 Υ(4S)→BB̅ decays collected with the BABAR detector at the SLAC PEP-II e+e- storage ring. Averaging over K(*) isospin and lepton flavor, we obtain the branching fractions B(B→Kℓ+ℓ-)=(0.65-0.13+0.14±0.04)×10-6 and B(B→K*ℓ+ℓ-)=(0.88-0.29+0.33±0.10)×10-6, where the uncertainties are statistical and systematic, respectively. The significance of the B→Kℓ+ℓ- signal is over 8σ, while for B→K*ℓ+ℓ- it is 3.3σ.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.