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

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

Branching fraction and CP-violation charge asymmetry measurements for B-meson decays to ηK±, ηπ±, η′K, η′π±, ωK, and ωπ±

We present measurements of the branching fractions for B-0-meson decays to eta'K-0 and omega K-0, and of the branching fractions and CP-violation charge asymmetries for B+-meson decays to eta pi(+), eta K+, eta'pi(+), eta'K+, omega pi(+), and omega K+. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 383x10(6) B (B) over bar pairs produced in e(+)e(-) annihilation. The measurements agree with previous results; we find no evidence for direct CP violation

Production and decay of Ωc0

We present an analysis of inclusive Omega(0)(c) baryon production and decays in 230.5 fb(-1) of data recorded with the BABAR detector. Omega(0)(c) baryons are reconstructed in four final states (Omega(-)pi(+), Omega(-)pi(+)pi(0), Omega(-)pi(+)pi(+)pi(-), Xi K--(-)pi(+)pi(+)) and the corresponding ratios of branching fractions are measured. We also measure the momentum spectrum in the e(+)e(-) center-of-mass frame. From the spectrum, we observe Omega(0)(c) production from B decays and in c (c) over bar events, and extract the two rates of production

Improved limits on the lepton-flavor violating decays tau(-) -> l(-)l(+)l(-)

A search for the neutrinoless, lepton-flavor violating decay of the tau lepton into three charged leptons has been performed using 376 fb(-1) of data collected at an e(+)e(-) center-of-mass energy around 10.58 GeV with the BABAR detector at the SLAC PEP-II storage rings. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (4-8)x10(-8) at 90% confidence level

Measurements of CP-violating asymmetries in B0→a1±(1260)π∓ 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) B(b) over bar pairs collected with the BABAR detector at the PEP-II asymmetric B factory at SLAC. We measure the CP-violating asymmetry A(CP)(a1 pi)=-0.07 +/- 0.07 +/- 0.02, the mixing-induced CP violation parameter S-a1 pi=0.37 +/- 0.21 +/- 0.07, the direct CP violation parameter C-a1 pi=-0.10 +/- 0.15 +/- 0.09, and the parameters Delta C-a1 pi=0.26 +/- 0.15 +/- 0.07 and Delta S-a1 pi=-0.14 +/- 0.21 +/- 0.06. From these measured quantities we determine the angle alpha(eff)=78.6 degrees +/- 7.3 degrees

Evidence for the rare decay B+→Ds+π0

We have searched for the rare decay B+ -> D-s(+) pi(0). The analysis is based on a sample of 232 X 10(6) Y(4S) -> B (B) over bar decays collected with the BABAR detector at the SLAC PEP-II e(+)e(-) storage ring. We find 19.6 signal events, corresponding to a significance of 4.7 sigma. The extracted signal yield including statistical and systematic uncertainties is 20.1(-6.0-1.5)(+6.8+0.4) and we measure B(B+ -> D-s(+) pi(0)) = (1.5(-0.4)(+0.5) +/- 0.1 +/- 0.2) X x 10(-5), where the first uncertainty is statistical, the second is systematic, and the last is due to the uncertainty on the D-s(+) decay and its daughter decay branching fractions

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