Conditional statistics of electron transport in interacting nanoscale conductors

Interactions between nanoscale semiconductor structures form the basis for charge detectors in the solid state. Recent experimental advances have demonstrated the on-chip detection of single electron transport through a quantum dot (QD). The discreteness of charge in units of e leads to intrinsic fluctuations in the electrical current, known as shot noise. To measure these single-electron fluctuations a nearby coherent conductor, called a quantum point contact (QPC), interacts with the QD and acts as a detector. An important property of the QPC charge detector is noninvasiveness: the system physically affects the detector, not visa-versa. Here we predict that even for ideal noninvasive detectors such as the QPC, when a particular detector result is observed, the system suffers an informational backaction, radically altering the statistics of transport through the QD as compared to the unconditional shot noise. We develop a theoretical model to make predictions about the joint current probability distributions and conditional transport statistics. The experimental findings reported here demonstrate the reality of informational backaction in nanoscale systems as well as a variety of new effects, such as conditional noise enhancement, which are in essentially perfect agreement with our model calculations. This type of switching telegraph process occurs abundantly in nature, indicating that these results are applicable to a wide variety of systems.Comment: 16 pages, 3 figures, to appear in Nature Physic

Evidence for the η_b(1S) Meson in Radiative Υ(2S) Decay

We have performed a search for the η_b(1S) meson in the radiative decay of the Υ(2S) resonance using a sample of 91.6 × 10^6 Υ(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E_γ = 609.3^(+4.6)_(-4.5)(stat)±1.9(syst) MeV, corresponding to an η_b(1S) mass of 9394.2^(+4.8)_(-4.9)(stat) ± 2.0(syst) MeV/c^2. The branching fraction for the decay Υ(2S) → γη_b(1S) is determined to be [3.9 ± 1.1(stat)^(+1.1)_(-0.9)(syst)] × 10^(-4). We find the ratio of branching fractions B[Υ(2S) → γη_b(1S)]/B[Υ(3S) → γη_b(1S)]= 0.82 ± 0.24(stat)^(+0.20)_(-0.19)(syst)

The role of kinetic context in apparent biased agonism at GPCRs

Biased agonism describes the ability of ligands to stabilize different conformations of a GPCR linked to distinct functional outcomes and offers the prospect of designing pathway-specific drugs that avoid on-target side effects. This mechanism is usually inferred from pharmacological data with the assumption that the confounding influences of observational (that is, assay dependent) and system (that is, cell background dependent) bias are excluded by experimental design and analysis. Here we reveal that ‘kinetic context’, as determined by ligand-binding kinetics and the temporal pattern of receptor-signalling processes, can have a profound influence on the apparent bias of a series of agonists for the dopamine D2 receptor and can even lead to reversals in the direction of bias. We propose that kinetic context must be acknowledged in the design and interpretation of studies of biased agonism

Evidence for B^+ → [overline K]^(*0)K^(*+)

We present measurements of the branching fraction and fraction of longitudinal polarization for the decay B^+ K^(*0)K^(*+) with a sample of (467±5)×10^6 BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider at the SLAC National Accelerator Laboratory. We obtain the branching fraction B(B^+ K^(*0)K^(*+))=(1.2±0.5±0.1)×10^(-6) with a significance of 3.7 standard deviations including systematic uncertainties. We measure the fraction of longitudinal polarization f_L=0.75_(-0.26)^(+0.16)±0.03. The first error quoted is statistical and the second is systematic

Measurement of B→K^*(892)γ Branching Fractions and CP and Isospin Asymmetries

We present an analysis of the decays B^0→K^(*0)(892)γ and B^+→K^(*+)(892)γ using a sample of about 383×10^6 BB̅ events collected with the BABAR detector at the PEP-II asymmetric energy B factory. We measure the branching fractions B(B^0→K^(*0)γ)=(4.47±0.10±0.16)×10^(-5) and B(B^+→K^(*+)γ)=(4.22±0.14±0.16)×10^(-5). We constrain the direct CP asymmetry to be -0.033<A(B→K^*γ)<0.028 and the isospin asymmetry to be 0.017<Δ_(0-)<0.116, where the limits are determined by the 90% confidence interval and include both the statistical and systematic uncertainties

Evidence for X(3872) → Ψ (2S)y in B^± → X(3872)K^± Decays and a Study of B → ccyK

In a search for B → ccyK decays with the BABAR detector, where cc includes J/Ψ and Ψ (2S), and K includes K^±, K^0_S , and K^*(892), we find evidence for X(3872) → J/Ψy and X(3872) → Ψ (2S) with 3:6σ and 3:5σ significance, respectively. We measure the product of branching fractions B(B^± → X(3872)K^±)B(X(3872) → J/Ψy)= [2:8 ± 0:8(stat) ± 0:1(syst)]X 10^(-6) and B(B^± → X(3872)K^±) X B(X(3872) → Ψ (2S)y) = [9:5 ± 2:7(stat) ± 0:6(syst)] X 10^(-6)

Measurements of [script B]([overline B]^0 → Λ_c^+[overline p]) and [script B](B^- → Λ_c^+[overline p]π^-) and studies of Λ_c^+π^- resonances

We present an investigation of the decays [overline B]^0 → Λ_c^+[overline p] and B^- → Λ_c^+[overline p]π^- based on 383×10^6 γ(4S) → B[overline B] decays recorded with the BABAR detector. We measure the branching fractions of these decays; their ratio is [script B](B^- → Λ_c^+[overline p]π^-)/[script B]([overline B]^0 → Λ_c^+[overline p])=15.4 ± 1.8 ± 0.3. The B^- → Λ_c^+[overline p]π^- process exhibits an enhancement at the Λ_c^+[overline p] threshold and is a laboratory for searches for excited charm baryon states. We observe the resonant decays B^- → ∑_c(2455)^0[overline p] and B^- → ∑_c(2800)^0[overline p] but see no evidence for B^- → ∑_c(2520)^0[overline p]. This is the first observation of the decay B^- → ∑_c(2800)^0[overline p]; however, the mass of the observed excited ∑_c^0 state is (2846 ± 8 ± 10) MeV/c^2, which is somewhat inconsistent with previous measurements. Finally, we examine the angular distribution of the B^- → ∑_c(2455)^0[overline p] decays and measure the spin of the ∑_c(2455)^0 baryon to be 1/2, as predicted by the quark model

Measurement of D^0-D̅ ^0 Mixing from a Time-Dependent Amplitude Analysis of D^0→K^+π^-π^0 Decays

We present evidence of D^0-D̅ ^0 mixing using a time-dependent amplitude analysis of the decay D^0→K^+π^-π^0 in a data sample of 384  fb^(-1) collected with the BABAR detector at the PEP-II e^+e^- collider at the Stanford Linear Accelerator Center. Assuming CP conservation, we measure the mixing parameters x_(Kππ)^(0′)=[2.61_(-0.68)^(+0.57)(stat)±0.39(syst)]%, y_(Kππ)^(0′)=[-0.06_(-0.64)^(+0.55)(stat)±0.34(syst)]%. This result is inconsistent with the no-mixing hypothesis with a significance of 3.2 standard deviations. We find no evidence of CP violation in mixing

Search for a Low-Mass Higgs Boson in Υ(3S)→γA^0, A^0→τ^+τ^- at BABAR

We search for a light Higgs boson A^0 in the radiative decay Υ(3S)→γA^0, A^0→τ^+τ^-, τ^+→e^+ν_eν̅ _τ, or τ^+→μ^+ν_μν̅_τ. The data sample contains 122×10^6 Υ(3S) events recorded with the BABAR detector. We find no evidence for a narrow structure in the studied τ^+τ^- invariant mass region of 4.03(1.5–16)×10^(-5) across the m_(τ+τ-) range. We also set a 90% C.L. upper limit on the τ^+τ^- decay of the η_b at B(η_b→τ^+τ^-)<8