M. S. Gill

Measurement of the branching fraction of Υ(4S)→B0B̄0

We report the first measurement of the branching fraction f00 for Υ(4S)→B0B 0. The data sample consists of 81.7  fb-1 collected at the Υ(4S) resonance with the BABAR detector at the SLAC PEP-II asymmetric-energy e+e- storage ring. Using partial reconstruction of the decay B 0→D*+l-ν l in which only the charged lepton and the soft pion from the decay D*+→D0π+ are reconstructed, we obtain f00=0.487±0.010(stat)±0.008(syst). Our result does not depend on the branching fractions of B 0→D*+l-ν l and D*+→D0π+ decays, on the ratio of the charged and neutral B meson lifetimes, nor on the assumption of isospin symmetry.

Measurements of CP-Violating Asymmetries in B0→ K s 0π0 Decays

We present a measurement of the time-dependent CP-violating (CPV) asymmetries in B0-->K(0)(S)pi(0) decays based on 124x10(6) Upsilon(4S)-->BB decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. In a sample containing 122+/-16 signal decays, we obtain the magnitudes of the direct CPV asymmetry CK(0)(S)(pi(0))=0.40(+0.27)(-0.28)+/-0.09 and of the CPV asymmetry in the interference between mixing and decay SK(0)(S)(pi(0))=0.48(+0.38)(-0.47)+/-0.06 where the first error is statistical and the second systematic.

Measurement of the B+/B0 production ratio from the Υ(4S) meson using B+→J/ψK+ and B0→J/ψKS0 decays

We report a measurement of the production ratio of charged and neutral B mesons from Υ(4S) decays based on the ratio of efficiency-corrected yields for the charmonium modes J/ψK+ and J/ψKs0 with 81.9 fb-1 of data collected with the BABAR detector on the Υ(4S) resonance at 10.580 GeV. We find a value of 1.006±0.036(stat)±0.031(syst) for the ratio R+/0=Γ(Υ(4S)→B+B-)/Γ(Υ(4S)→B0B0).

Search for factorization-suppressed B→χcK(*) decays

We search for the factorization-suppressed decays B→χc0K(*) and B→χc2K(*), with χc0 and χc2 decaying into J/ψγ, using a sample of 124×106 BB events collected with the BABAR detector at the PEP-II storage ring of the Stanford Linear Accelerator Center. We find no significant signal and set upper bounds for the branching fractions.

Improved measurement of the Cabibbo-Kobayashi-Maskawa angle α using B0(B̄)→ρ+ρ- decays

We present results from an analysis of B(0)B(0)--> rho(+)rho(-) using 232 x 10(6) Gamma (4S) --> BB decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We measure the longitudinal polarization fraction f(L) = 0.978 +/- 0.014(stat) + 0.021 / -0.029(syst) and the CP-violating parameters S(L)= -0.33 +/- 0.24(stat) + 0.08 / -0.14(syst) and C(L)= -0.03 +/- 0.18(stat) +/- 0.09(syst). Using an isospin analysis of B --> rhorho decays, we determine the unitarity triangle parameter alpha. The solution compatible with the standard model is alpha = (100 +/- 13) degrees.

Search for decays of B0→e+e-, B0→μ+μ-, B0→e± μ

We present a search for the decays B0->e+e-, B0->mu+mu-, and B0->e+- mu-+ in data collected at the Y(4S) resonance with the Babar detector at the SLAC B Factory. Using a data set of 111 fb^-1, we find no evidence for a signal in any of the three channels investigated and set the following branching fraction upper limits at the 90% confidence level: B(B0->e+e-) mu+mu-) e+-mu-+) < 18 x 10^-8.

Measurement of the B̄ 0 → D * + ℓ - ν̄ ℓ decay rate and |V cb |

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V(cb)vertical bar based on a sample of about 53 700 (B) over bar (0) -> D*(+)l(-)(nu) over bar (l) decays observed by the BABAR detector. We obtain the branching fraction averaged over l = e, mu, B((B) over bar (0) -> D*(+)l(-)(nu) over bar (l)) = (4.90 +/- 0.07(stat.)(-0.35)(+0.36)(syst.))%. We measure the differential decay rate as a function of iv, the relativistic boost gamma of the D*+ in the Wo rest frame. By extrapolating d Gamma/dw to the kinematic limit w -> 1, we extract the product of vertical bar V(cb)vertical bar and the axial form factor A(1)(w = 1). We combine this measurement with a lattice QCD calculation of A(1)(w = 1) to determine vertical bar V(cb)vertical bar = (38.7 +/- 0.3(stat.) +/- 1.7(syst.)(-1.3)(+1.5)(theory)) x 10(-3).We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V{sub cb}| based on a sample of about 53 700 B{sup 0}{yields}D*{sup +}l{sup -}{nu}{sub l} decays observed by the BABAR detector. We obtain the branching fraction averaged over l=e,{mu}, B(B{sup 0}{yields}D*{sup +}l{sup -}{nu}{sub l})=(4.90{+-}0.07(stat.){sub -0.35}{sup +0.36}(syst.))%. We measure the differential decay rate as a function of w, the relativistic boost {gamma} of the D*{sup +} in the B{sup 0} rest frame. By extrapolating d{gamma}/dw to the kinematic limit w{yields}1, we extract the product of |V{sub cb}| and the axial form factor A{sub 1}(w=1). We combine this measurement with a lattice QCD calculation of A{sub 1}(w=1) to determine |V{sub cb}|=(38.7{+-}0.3(stat.){+-}1.7(syst.){sub -1.3}{sup +1.5}(theory))x10{sup -3}.We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| based on a sample of about 53 700 B 0→D*+l-ν l decays observed by the BABAR detector. We obtain the branching fraction averaged over l=e,μ, B(B 0→D*+l-ν l)=(4.90±0.07(stat.)-0.35+0.36(syst.))%. We measure the differential decay rate as a function of w, the relativistic boost γ of the D*+ in the B 0 rest frame. By extrapolating dΓ/dw to the kinematic limit w→1, we extract the product of |Vcb| and the axial form factor A1(w=1). We combine this measurement with a lattice QCD calculation of A1(w=1) to determine |Vcb|=(38.7±0.3(stat.)±1.7(syst.)-1.3+1.5(theory))×10-3.

Measurement of the B0 → φ K*0 decay amplitudes

With a sample of about 227x10(6) BB pairs recorded with the BABAR detector we perform a full angular analysis of the decay B0-->phiK(*0)(892). We make novel measurements of five parameters sensitive to CP violation. We also measure the branching fraction to be (9.2+/-0.9+/-0.5)x10(-6) and determine the fractions of longitudinal and parity-odd transverse contributions as f(L)=0.52+/-0.05+/-0.02 and f( perpendicular)=0.22+/-0.05+/-0.02. The phases of the parity-even and parity-odd transverse amplitudes relative to the longitudinal amplitude are found to be phi( parallel)=2.34(+0.23)(-0.20)+/-0.05 rad and phi( perpendicular)=2.47+/-0.25+/-0.05 rad. We also observe the decay B0-->phiK(*0)(1430).

Search for the decay B0→pp̄

We present the result of a search for the charmless two-body baryonic decay B-0-->p(p) over bar in a sample of 88 million Y(4S)-->B(B) over bar decays collected by the BABAR detector at the SLAC PEP-II asymmetric-energy B Factory. We use Cherenkov radiation to identify protons cleanly, and determine the signal yield with a maximum-likelihood fit technique using kinematic and topological information. We find no evidence for a signal and place a 90% confidence-level upper limit of B(B-0--> )<2.7x10(-7).We present the result of a search for the charmless two-body baryonic decay B^0 ->ppbar in a sample of 88 million Y(4S) ->BBbar decays collected by the BaBar detector at the SLAC PEP-II asymmetric-energy

Observation of the decay B0 → ρ+ ρ- and measurement of the branching fraction and polarization

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