Measurement of the CP violation parameter ∣η+−∣|\eta_{+−}| and the charge asymmetry in K±→3πK^{\pm} \rightarrow 3\pi decays by NA48 and NA48/2

Throughout all periods of data taking, the main goal of the NA48 experiment has been the search for CP violation (CPV) in kaon decays. The observable $\eta_{+−}$ links the parameters of indirect and direct CPV $(\eta_{+−} = \epsilon + \epsilon^{\prime})$ and is defined as the CP violating amplitude ratio of the neutral kaon decaying into two charged pions: $\eta_{+−} = A(K_{L} \rightarrow \pi^{+}\pi^{-})/A(K_{S} \rightarrow \pi^{+}\pi^{-})$. NA48 has determined $|\eta_{+−}|$ via the measurement of the ratio of decay rates $\Gamma (K_{L} \rightarrow \pi^{+}\pi^{-})/\Gamma(K_{L} \rightarrow \pi e\nu)$, denoted as $\Gamma_{K2\pi}/\Gamma_{Ke3}$, using a pure $K_{L}$ beam in 1999. From a sample of 47000 $K_{2\pi}$ and five million $K_{e3}$ decays, we obtained results for $\Gamma K_{2\pi}/\Gamma_{Ke3}$, BR$(K_{L} \rightarrow \pi^{+}\pi^{-})$ and $|\eta_{+−}|$. Complementary with $\epsilon^{0}/\epsilon$, the observable for direct CPV in the charged kaons sector is the asymmetry Ag = $(g^{+} − g^{−})/(g^{+} + g^{−})$ of the linear slope parameter $g$ in the Dalitz plot of $K^{\pm} \rightarrow 3\pi$ decays. The NA48/2 experiment used simultaneous $K^{+}/K^{−}$ beams, and from the data samples taken in 2003 and 2004, $3 \times 10^{9} K^{\pm} \rightarrow \pi^{\pm}\pi^{+}\pi^{-}$ and $9 \times 10^{7} K^{\pm} \rightarrow \pi^{\pm}\pi^{0}\pi^{0}$ were selected. The charge asymmetry parameter Ag was determined with a total uncertainty of $∼ 2 \times 10^{−4}$ for each mode, ten times more accurate than previous measurements

An Active Sensing Paradigm for Studying Human Auditory Perception

Our perception is based on active sensing, i.e., the relationship between self-motion and resulting changes to sensory inputs. Yet, traditional experimental paradigms are characterized by delayed reactions to a predetermined stimulus sequence. To increase the engagement of subjects and potentially provide richer behavioral responses, we developed Sensory Island Task for humans (SITh), a freely-moving search paradigm to study auditory perception. In SITh, subjects navigate an arena in search of an auditory target, relying solely on changes in the presented stimulus frequency, which is controlled by closed-loop position tracking. A “target frequency” was played when subjects entered a circular sub-area of the arena, the “island”, while different frequencies were presented outside the island. Island locations were randomized across trials, making stimulus frequency the only informative cue for task completion. Two versions of SITh were studied: binary discrimination, and gradual change of the stimulus frequency. The latter version allowed determining frequency discrimination thresholds based on the subjects’ report of the perceived island location (i.e., target frequency). Surprisingly, subjects exhibited similar thresholds as reported in traditional “stationary” forced-choice experiments after performing only 30 trials, highlighting the intuitive nature of SITh. Notably, subjects spontaneously employed a small variety of stereotypical search patterns, and their usage proportions varied between task versions. Moreover, frequency discrimination performance depended on the search pattern used. Overall, we demonstrate that the use of an ecologically driven paradigm is able to reproduce established findings while simultaneously providing rich behavioral data for the description of sensory ethology

Opacity calculation for target physics using the ABAKO/RAPCAL code

Radiative properties of hot dense plasmas remain a subject of current interest since they play an important role in inertial confinement fusion (ICF) research, as well as in studies on stellar physics. In particular, the understanding of ICF plasmas requires emissivities and opacities for both hydro-simulations and diagnostics. Nevertheless, the accurate calculation of these properties is still an open question and continuous efforts are being made to develop new models and numerical codes that can facilitate the evaluation of such properties. In this work the set of atomic models ABAKO/RAPCAL is presented, as well as a series of results for carbon and aluminum to show its capability for modeling the population kinetics of plasmas in both LTE and NLTE regimes. Also, the spectroscopic diagnostics of a laser-produced aluminum plasma using ABAKO/RAPCAL is discussed. Additionally, as an interesting application of these codes, fitting analytical formulas for Rosseland and Planck mean opacities for carbon plasmas are reported. These formulas are useful as input data in hydrodynamic simulation of targets where the computation task is so hard that in line computation with sophisticated opacity codes is prohibitive

The Scalar B→πB\to \pi and D→πD \to \pi Form Factors in QCD

QCD sum rules on the light-cone are derived for the sum $f^+ + f^-$ of the $B\to \pi$ and $D\to \pi$ form factors taking into account contributions up to twist four. Combining the results with the corresponding $f^+$ form factors calculated previously by the same method, we obtain the scalar form factors $f^0$. Our sum rule predictions are compared with lattice results, current-algebra constraints, and quark-model calculations. Furthermore, we calculate decay distributions and the integrated width for the semileptonic decay $B \to \pi \bar{\tau}\nu_\tau$ which is sensitive to $f^0$. Finally, the dependence of the sum rules on the heavy quark mass and the asymptotic scaling laws are discussed.Comment: 19 pages, 10 figures, Latex, epsfi

Predictions on B→πlˉνlB \to \pi \bar{l} \nu_l, D→πlˉνlD \to \pi \bar{l} \nu_l and D→KlˉνlD\to K \bar{l} \nu_l from QCD Light-Cone Sum Rules

The $f^+$ form factors of the $B\to \pi$, $D\to \pi$ and $D\to K$ transitions are calculated from QCD light-cone sum rules (LCSR) and used to predict the widths and differential distributions of the exclusive semileptonic decays $B\to \pi \bar{l}\nu_l$, $D \to\pi \bar{l}\nu_l$ and $D \to K \bar{l}\nu_l$, where $l=e,\mu$. The current theoretical uncertainties are estimated. The LCSR results are found to agree with the results of lattice QCD calculations and with experimental data on exclusive semileptonic D decays. Comparison of the LCSR prediction on $B\to \pi \bar{l} \nu_l$ with the CLEO measurement yields a value of |V_{ub}| in agreement with other determinations.Comment: 24 pages, 12 figures, Latex, epsfig, some additional remarks on the two-pole parameterization, prediction on the $B\to K$ form factor added, version to appear in Phys. Rev.

Measurement of XUV-absorption spectra of ZnS radiatively heated foils

Time-resolved absorption of zinc sulfide (ZnS) and aluminum in the XUV-range has been measured. Thin foils in conditions close to local thermodynamic equilibrium were heated by radiation from laser-irradiated gold spherical cavities. Analysis of the aluminum foil radiative hydrodynamic expansion, based on the detailed atomic calculations of its absorption spectra, showed that the cavity emitted flux that heated the absorption foils corresponds to a radiation temperature in the range 55 60 eV. Comparison of the ZnS absorption spectra with calculations based on a superconfiguration approach identified the presence of species Zn6+ - Zn8+ and S5+ - S6+. Based on the validation of the radiative source simulations, experimental spectra were then compared to calculations performed by post-processing the radiative hydrodynamic simulations of ZnS. Satisfying agreement is found when temperature gradients are accounted for

Observation of the rare decay K_S -> pi^0mu^+mu^-

A search for the decay K_S -> pi^0mu^+mu^- has been made by the NA48/1 Collaboration at the CERN SPS accelerator. The data were collected during 2002 with a high-intensity K_S beam. Six events were found with a background expectation of 0.22^+0.18_-0.11 event. Using a vector matrix element and unit form factor, the measured branching ratio is B(K_S -> pi^0mu^+mu^-)=[2.9^+1.5_-1.2(stat)+/-0.2(syst)]x10^{-9}.Comment: 19 pages, 8 figures, 4 tables. To be published in Physics Letters