Search for production of invisible final states in single-photon decays of Υ(1S)

We search for single-photon decays of the Υ(1S) resonance, Υ → γ + invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson A?, or a pair of dark matter particles, χχ. Both A? and χ are assumed to have zero spin. We tag Υ(1S) decays with a dipion transition Υ(2S) → π?π?Υ(1S) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range m(A?) ≤ 9.2 GeV and m(χ) ≤ 4.5 GeV in the sample of 98 × 10? Υ(2S) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.     

Slow magnetic order-order transition in the spin chain antiferromagnet Ca3Co2O6

Using powder neutron diffraction, we have discovered an unusual magnetic order-order transition in the Ising spin chain compound Ca3Co2O6. On lowering the temperature, an antiferromagnetic phase with a propagation vector k=(0.5,-0.5,1) emerges from a higher temperature spin density wave structure with k=(0,0,1.01). This transition occurs over an unprecedented time scale of several hours and is never complete.     

Induction of superconductivity in pulsed laser ablated La2CuO4 thin films by post-deposition fluorination

Pulsed laser ablation has been used to fabricate La₂CuO₄ thin films. Superconducting properties have been successfully induced in the films by an ex-situ, post-ablation annealing process in F₂ gas resulting in a T_c (onset) of 36 K. The presence of two slightly different c-axis expanded phases in the X-ray diffraction data of the fluorinated films implies a degree of inhomogeneity in F₂ uptake. Critical current densities (J_c) and the irreversibility line have been established from hysteresis cycles. A J_c of 10⁶ A cm⁻² for a typical film was observed at 10 K in zero field.     

The use of PDE centres in the local RBF Hermitian method for 3D convective-diffusion problems

In this work an extension is proposed to the Local Hermitian Interpolation (LHI) method; a meshless numerical method based on interpolation with small and heavily overlapping radial basis function (RBF) systems. This extension to the LHI method uses interpolation functions which themselves satisfy the partial differential equation (PDE) to be solved. In this way, a much improved reconstruction of partial derivatives can be obtained, resulting in significantly improved accuracy in many cases.     

Evidence for charged B meson decays to a1+/-(1260)pi0 and a1(0)(1260)pi+/-

We present measurements of the branching fractions for the decays B;{+/-}-->a_{1};{+/-}(1260)pi;{0} and B;{+/-}-->a_{1};{0}(1260)pi;{+/-} from a data sample of 232x10;{6} BB[over ] pairs produced in e;{+}e;{-} annihilation through the Upsilon(4S) resonance. We measure the branching fraction B(B;{+/-}-->a_{1};{+/-}(1260)pi;{0})xB(a_{1};{+/-}(1260)-->pi;{-}pi;{+}pi;{+/-})=(13.2+/-2.7+/-2.1)x10;{-6} with a significance of 4.2sigma, and the branching fraction B(B;{+/-}-->a_{1};{0}(1260)pi;{+/-})xB(a_{1};{0}(1260)-->pi;{-}pi;{+}pi;{0})=(20.4+/-4.7+/-3.4)x10;{-6} with a significance of 3.8sigma, where the first error quoted is statistical and the second is systematic.     

Improved measurement of CP violation in neutral B decays to cc[over]s

We present updated measurements of time-dependent CP asymmetries in fully-reconstructed neutral B decays to several CP eigenstates containing a charmonium meson. The measurements use a data sample of (383+/-4)x10(6) Upsilon(4S)-->BB[over] decays collected with the BABAR detector at the PEP-II B factory. We determine sin2beta = 0.714+/-0.032(stat)+/-0.018(syst) and |lambda|=0.952+/-0.022(stat)+/-0.017(syst).     

Measurements of CP-violating asymmetries in B0-->a1+/-(1260)pi-/+ decays

We present measurements of CP-violating asymmetries in the decay B(0)-->a(1)(+/-)(1260)pi(-/+) with a(1)(+/-)(1260)-->pi(-/+)pi(+/-)pi(+/-). The data sample corresponds to 384x10(6) BB[over ] pairs collected with the BABAR detector at the PEP-II asymmetric B factory at SLAC. We measure the CP-violating asymmetry A(CP)(a(1)pi)=-0.07+/-0.07+/-0.02, the mixing-induced CP violation parameter S(a(1)pi)=0.37+/-0.21+/-0.07, the direct CP violation parameter C(a(1)pi)=-0.10+/-0.15+/-0.09, and the parameters DeltaC(a(1)pi)=0.26+/-0.15+/-0.07 and DeltaS(a(1)pi)=-0.14+/-0.21+/-0.06. From these measured quantities we determine the angle alpha(eff)=78.6 degrees +/-7.3 degrees.     

Measurement of cos2beta in B;{0}-->D;{(*)}h;{0} decays with a time-dependent Dalitz plot analysis of D-->K_{s};{0}pi;{+}pi;{-}

We study the time-dependent Dalitz plot of D-->K_{S};{0}pi;{+}pi;{-} in B;{0}-->D;{(*)}h;{0} decays, where h;{0} is a pi;{0}, eta, eta;{'}, or omega meson and D;{*}-->Dpi;{0}, using a data sample of 383x10;{6} Upsilon(4S)-->BB[over ] decays collected with the BABAR detector. We determine cos2beta=0.42+/-0.49+/-0.09+/-0.13, sin2beta=0.29+/-0.34+/-0.03+/-0.05, and |lambda|=1.01+/-0.08+/-0.02, where the first error is statistical, the second is the experimental systematic uncertainty, and the third, where given, is the Dalitz model uncertainty. Assuming the world average value for sin2beta and |lambda|=1, cos2beta>0 is preferred over cos2beta<0 at 86% confidence level.     

Search for the rare decay B-->pil+ l-

We have performed a search for the flavor-changing neutral-current decays B-->pil+ l-, where l+ l- is either e+ e- or mu+ mu-, using a sample of 230 x 10(6) Upsilon(4S)-->BB decays collected with the BABAR detector. We observe no evidence of a signal and measure the upper limit on the isospin-averaged branching fraction to be B(B-->pil+ l-)<9.1 x 10(-8) at 90% confidence level. We also search for the lepton-flavor-violating decays B-->pie+/- mu-/+ and measure an upper limit on the isospin-averaged branching fraction of B(B-->pie+/- mu-/+)<9.2 x 10(-8) at 90% confidence level.     

Measurement of the CP asymmetry and branching fraction of B0-->rho0K0

We present a measurement of the branching fraction and time-dependent CP asymmetry of B(0)-->rho0K0. The results are obtained from a data sample of 227x10(6) Upsilon(4S)-->BB decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at Stanford Linear Accelerator Center. From a time-dependent maximum likelihood fit yielding 111+/-19 signal events, we find B(B(0)-->rho0K0)=(4.9+/-0.8+/-0.9)x10(-6), where the first error is statistical and the second systematic. We report the measurement of the CP parameters S(rho)(0)K(0)S=0.20+/-0.52+/-0.24 and C(rho)(0)K(0)S=0.64+/-0.41+/-0.20.