Engineering semiconductor devices requires an understanding of charge carrier mobility. Typically mobilities are estimated using measurements of the Hall effect and electrical resistivity. Such measurements are routinely performed at room temperature and below in materials with mobilities greater than 1cm 2 /Vs. With the availability of combined Seebeck coefficient and electrical resistivity measurement systems, it is now easy to measure the weighted mobility (electron mobility weighted by the density of electronic states). Here we introduce a simple method to calculate the weighted mobility from combined Seebeck coefficient and electrical resistivity measurements that gives good results at room temperature and above, and for mobilities as low as 10 −3 cm 2 /Vs.

A sample of 1.69 × 10 7 fully reconstructed π 0 → γ e + e − decay candidates collected by the NA48/2 experiment at CERN in 2003-2004 is analyzed to search for the dark photon (A) production in the π 0 → γ A decay followed by the prompt A → e + e − decay. No signal is observed, and an exclusion region in the plane of the dark photon mass m A and mixing parameter ε 2 is established. The obtained upper limits on ε 2 are more stringent than the previous limits in the mass range 9 MeV/c 2 < m A < 70 MeV/c 2. The NA48/2 sensitivity to the dark photon production in the K ± → π ± A decay is also evaluated. 0. Introduction Kaons are a source of tagged neutral pion decays, and high intensity kaon experiments provide opportunities for precision π 0 decay measurements. The NA48/2 experiment at the CERN SPS collected a large sample of charged kaon (K ±) decays in flight, corresponding to about 2 × 10 11 K ± decays in the fiducial decay volume. This letter reports the search for a hypothetical dark pho-ton (DP, denoted A) using a large sample of tagged π 0 mesons from identified K ± → π ± π 0 and K ± → π 0 μ ± ν decays. In a rather general set of hidden sector models with an extra U (1) gauge symmetry [1], the interaction of the DP with the visible sector proceeds through kinetic mixing with the Standard Model (SM) hypercharge. Such scenarios with GeV-scale dark matter provide possible explanations to the observed rise in the cosmic-ray positron fraction with energy and the muon gyromag-netic ratio (g − 2) measurement [2]. The DP is characterized by two a priori unknown parameters, the mass m A and the mixing parameter ε 2. Its possible production in the π 0 decay and its subsequent decay proceed via the chain π 0 → γ A , A → e + e −. The expected branching fraction of the above π 0 decay is [3] B(π 0 → γ A) = 2ε 2 1 − m 2 A m 2 π 0 3 B(π 0 → γ γ), (1) which is kinematically suppressed as m A approaches m π 0. In the DP mass range 2m e < m A < m π 0 accessible in pion decays, the only allowed tree-level decay into SM fermions is A → e + e − , while the loop-induced SM decays (A → 3γ , A → ν ¯ ν) are highly suppressed. Therefore, for a DP decaying only into SM particles, B(A → e + e −) ≈ 1, and the expected total decay width is [3] A ≈ (A → e + e −) = 1 3 αε 2 m A 1 − 4m 2 e m 2 A 1 + 2m 2 e m 2 A. (2) It follows that, for 2m e m A < m π 0 , the DP mean proper lifetime τ A satisfies the relation cτ A = ¯ hc/ / A ≈ 0.8 μm × 10 −6 ε 2 × 100 MeV/c 2 m A. (3) This analysis is performed assuming that the DP decays at the production point (prompt decay), which is valid for sufficiently large values of m A and ε 2 , as quantified in Section 5. In this case, the DP production and decay signature is identical to that of the Dalitz decay π 0 D → e + e − γ , which therefore represents an irreducible but well controlled background and determines the sensitivity. The NA48/2 experiment provides pure π 0 D decay samples through the reconstruction of K ± → π ± π 0 and K ± → π 0 μ ± ν decays (denoted K 2π and K μ3). Additionally, the K ± → π ±...

We report results from the analysis of the K ± → π + π − e ± ν (K e4 ) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in [2003][2004]. The hadronic form factors in the S-and P-wave and their variation with energy are obtained. The phase difference between the S-and P-wave states of the ππ system is accurately measured and allows a precise determination of a 0 0 and a 2 0 , the I = 0 and I = 2 S-wave ππ scattering lengths: a 0 0 = 0.2220 ± 0.0128 stat ± 0.0050 syst ± 0.0037 th , a 2 0 = −0.0432 ± 0.0086 stat ± 0.0034 syst ± 0.0028 th . Combination of this result with the other NA48/2 measurement obtained in the study of K ± → π 0 π 0 π ± decays brings an improved determination of a 0 0 and the first precise experimental measurement of a 2 0 , providing a stringent test of Chiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based on analyticity and chiral symmetry, even more precise values are obtained: a 0 0 = 0.2196 ± 0.0028 stat ± 0.0020 syst and a 2 0 = −0.0444 ± 0.0007 stat ± 0.0005 syst ± 0.0008 ChPT .

n-Type conduction in a Mg3Sb1.5Bi0.5 system is achieved with La-doping at cation sites with a peak zT > 1.