EuFe2_2As2_2 under high pressure: an antiferromagnetic bulk superconductor

We report the ac magnetic susceptibility $\chi_{ac}$ and resistivity $\rho$ measurements of EuFe$_2$As$_2$ under high pressure $P$. By observing nearly 100% superconducting shielding and zero resistivity at $P$ = 28 kbar, we establish that $P$-induced superconductivity occurs at $T_c \sim$~30 K in EuFe$_2$As$_2$. $\rho$ shows an anomalous nearly linear temperature dependence from room temperature down to $T_c$ at the same $P$. $\chi_{ac}$ indicates that an antiferromagnetic order of Eu$^{2+}$ moments with $T_N \sim$~20 K persists in the superconducting phase. The temperature dependence of the upper critical field is also determined.Comment: To appear in J. Phys. Soc. Jpn., Vol. 78 No.

The BaBar detector: Upgrades, operation and performance

Contains fulltext : 121729.pdf (preprint version ) (Open Access

Measurements of CP-Violating Asymmetries in the Decay B^{0}→K^{+}K^{-}K^{0}

We analyze the decay B0→K+K-K0 using 383×106 BB̅ events collected by the BABAR detector at SLAC to extract CP violation parameter values over the Dalitz plot. Combining all K+K-K0 events, we find ACP=-0.015±0.077±0.053 and βeff=0.352±0.076±0.026  rad, corresponding to a CP violation significance of 4.8σ. A second solution near π/2-βeff is disfavored with a significance of 4.5σ. We also report ACP and βeff separately for decays to ϕ(1020)K0, f0(980)K0, and K+K-K0 with mK+K->1.1  GeV/c2

Measurement of the time-dependent CP asymmetry in B0→DCP(*)h0 decays

We report a measurement of the time-dependent CP-asymmetry parameters S and C in color-suppressed B-0 -> D((*)0)h(0) decays, where h(0) is a pi(0), eta, or omega meson, and the decays to one of the CP eigenstates K+K-, K-S(0)pi(0), or K-S(0)omega. The data sample consists of 383x10(6) Upsilon(4S)-> B (B) over bar decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The results are S=-0.56 +/- 0.23 +/- 0.05 and C=-0.23 +/- 0.16 +/- 0.04, where the first error is statistical and the second is systematic

Branching fraction measurements of B+→ρ+γ, B0→ρ0γ, and B0→ωγ

We present a study of the decays B+->rho(+)gamma, B-0 ->rho(0)gamma, and B-0 ->omega gamma. The analysis is based on data containing 347x10(6) B (B) over bar events recorded with the BABAR detector at the PEP-II asymmetric B factory. We measure the branching fractions B(B+->rho(+)gamma)=(1.10(-0.33)(+0.37)+/- 0.09)x10(-6) and B(B-0 ->rho(0)gamma)=(0.79(-0.20)(+0.22)+/- 0.06)x10(-6), and set a 90% C.L. upper limit B(B-0 ->omega gamma)(rho/omega)gamma)=(1.25(-0.24)(+0.25)+/- 0.09)x10(-6), from which we determine vertical bar V-td/V-ts vertical bar=0.200(-0.020)(+0.021)+/- 0.015, where the first uncertainty is experimental and the second is theoretical

Measurement of cos2β in B0→D(*)h0 decays with a time-dependent Dalitz plot analysis of D→Ks0π+π-

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-* -> D pi(0), using a data sample of 383 x 10(6) Upsilon(4S) -> B (B) over bar decays collected with the BABAR detector. We determine cos2 beta = 0.42 +/- 0.49 +/- 0.09 +/- 0.13, sin2 beta = 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 sin2 beta and |lambda| = 1, cos2 beta > 0 is preferred over cos2 beta < 0 at 86% confidence level

Search for the decay B+-> K+tau(-/+)mu(+/-)

We present a search for the lepton flavor violating decay B+-> K+tau(-/+)mu(+/-) using 383x10(6) B (B) over bar events collected by the BABAR experiment. The branching fraction for this decay can be substantially enhanced in new physics models. The kinematics of the tau from the signal B decay are inferred from the K+, mu, and other B in the event, which is fully reconstructed in one of a variety of hadronic decay modes, allowing the signal B candidate to be fully reconstructed. We observe no excess of events over the expected background and set a limit of B(B+-> K+tau mu)< 7.7x10(-5) at 90% confidence level, where the branching fraction is for the sum of the K+tau(-)mu(+) and K+tau(+)mu(-) final states. We use this result to improve a model-independent bound on the energy scale of flavor-changing new physics

The e(+)e(-)-> 2(pi(+)pi(-))pi(0), 2(pi(+)pi(-))eta, K+K-pi(+)pi(-)pi(0) and K+K-pi(+)pi(-)eta cross sections measured with initial-state radiation

We study the processes e(+)e(-)-> 2(pi(+)pi(-))pi(0)gamma, 2(pi(+)pi(-))eta gamma, K+K-pi(+)pi(-)pi(0)gamma and K+K-pi(+)pi(-)eta gamma with the hard photon radiated from the initial state. About 20 000, 4300, 5500, and 375 fully reconstructed events, respectively, are selected from 232 fb(-1) of BABAR data. The invariant mass of the hadronic final state defines the effective e(+)e(-) center-of-mass energy, so that the obtained cross sections from the threshold to about 5 GeV can be compared with corresponding direct e(+)e(-) measurements, currently available only for the eta pi(+)pi(-) and omega pi(+)pi(-) submodes of the e(+)e(-)-> 2(pi(+)pi(-))pi(0) channel. Studying the structure of these events, we find contributions from a number of intermediate states, and we extract their cross sections where possible. In particular, we isolate the contribution from e(+)e(-)->omega(782)pi(+)pi(-) and study the omega(1420) and omega(1650) resonances. In the charmonium region, we observe the J/psi in all these final states and several intermediate states, as well as the psi(2S) in some modes, and we measure the corresponding branching fractions

Amplitude analysis of the decay D0→K-K+π0

Using 385 fb(-1) of e(+)e(-) collisions, we study the amplitudes of the singly Cabibbo-suppressed decay D-0 -> K-K+pi(0). We measure the strong phase difference between the (D) over bar (0) and D-0 decays to K-*(892)K-+(-) to be -35.5 degrees +/- 1.9 degrees(stat)+/- 2.2 degrees(syst), and their amplitude ratio to be 0.599 +/- 0.013(stat)+/- 0.011(syst). We observe contributions from the K pi and K-K+ scalar and vector amplitudes, and analyze their angular moments. We find no evidence for charged kappa, nor for higher spin states. We also perform a partial-wave analysis of the K-K+ system in a limited mass range