2,230 research outputs found
Pulsar timing analysis in the presence of correlated noise
Pulsar timing observations are usually analysed with least-square-fitting
procedures under the assumption that the timing residuals are uncorrelated
(statistically "white"). Pulsar observers are well aware that this assumption
often breaks down and causes severe errors in estimating the parameters of the
timing model and their uncertainties. Ad hoc methods for minimizing these
errors have been developed, but we show that they are far from optimal.
Compensation for temporal correlation can be done optimally if the covariance
matrix of the residuals is known using a linear transformation that whitens
both the residuals and the timing model. We adopt a transformation based on the
Cholesky decomposition of the covariance matrix, but the transformation is not
unique. We show how to estimate the covariance matrix with sufficient accuracy
to optimize the pulsar timing analysis. We also show how to apply this
procedure to estimate the spectrum of any time series with a steep red
power-law spectrum, including those with irregular sampling and variable error
bars, which are otherwise very difficult to analyse.Comment: Accepted by MNRA
Obesity: A Biobehavioral Point of View
Excerpt: If you ask an overweight person, âWhy are you fat?â, you will, almost invariably, get the answer, âBecause 1 eat too much.â You will get this answer in spite of the fact that of thirteen studies, six find no significant differences in the caloric intake of obese versus nonobese subjects, five report that the obese eat significantly less than the nonobese, and only two report that they eat significantly more
Search for a CP-odd light Higgs boson in J/Ï âÎłA<sup>0</sup>
Using J/Ï radiative decays from 9.0 billion J/Ï events collected by the BESIII detector, we search for di-muon decays of a CP-odd light Higgs boson (A0), predicted by many new physics models beyond the Standard Model, including the next-to-minimal supersymmetric Standard Model. No evidence for the CP-odd light Higgs production is found, and we set 90% confidence level upper limits on the product branching fraction B(J/ÏâÎłA0)ĂB(A0âÎŒ+ÎŒ-) in the range of (1.2-778.0)Ă10-9 for 0.212â€mA0â€3.0 GeV/c2. The new measurement is a 6-7 times improvement over our previous measurement, and is also slightly better than the BABAR measurement in the low-mass region for tanÎČ=1
Overconstrained estimates of neutrinoless double beta decay within the QRPA
Estimates of nuclear matrix elements for neutrinoless double beta decay
(0nu2beta) based on the quasiparticle random phase approximations (QRPA) are
affected by theoretical uncertainties, which can be substantially reduced by
fixing the unknown strength parameter g_pp of the residual particle-particle
interaction through one experimental constraint - most notably through the
two-neutrino double beta decay (2nu2beta) lifetime. However, it has been noted
that the g_pp adjustment via 2\nu2\beta data may bring QRPA models in
disagreement with independent data on electron capture (EC) and single beta
decay (beta^-) lifetimes. Actually, in two nuclei of interest for 0nu2beta
decay (Mo-100 and Cd-116), for which all such data are available, we show that
the disagreement vanishes, provided that the axial vector coupling g_A is
treated as a free parameter, with allowance for g_A<1 (``strong quenching'').
Three independent lifetime data (2nu2beta, EC, \beta^-) are then accurately
reproduced by means of two free parameters (g_pp, g_A), resulting in an
overconstrained parameter space. In addition, the sign of the 2nu2beta matrix
element M^2nu is unambiguously selected (M^2nu>0) by the combination of all
data. We discuss quantitatively, in each of the two nuclei, these
phenomenological constraints and their consequences for QRPA estimates of the
0nu2beta matrix elements and of their uncertainties.Comment: Revised version (27 pages, including 10 figures), focussed on Mo-100
and Cd-116. To appear in J. Phys. G: Nucl. Phys. (2008
New insight into the low-energy He spectrum
The spectrum of He was studied by means of the He(,)He
reaction at a lab energy of 25 MeV/n and small center of mass (c.m.) angles.
Energy and angular correlations were obtained for the He decay products by
complete kinematical reconstruction. The data do not show narrow states at
1.3 and 2.4 MeV reported before for He. The lowest resonant
state of He is found at about 2 MeV with a width of 2 MeV and is
identified as . The observed angular correlation pattern is uniquely
explained by the interference of the resonance with a virtual state
(limit on the scattering length is obtained as fm), and with
the resonance at energy MeV.Comment: 5 pages, 4 figures, 2 table
Investigation of the 6He cluster structures
The 4He+2n and t+t clustering of the 6He ground state were investigated by
means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment
was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled
to the MUST array. Experimental data for the transfer reaction were analyzed by
a DWBA calculation including the two neutrons and the triton transfer. The
couplings to the 6He --> 4He + 2n breakup channels were taken into account with
a polarization potential deduced from a coupled-discretized-continuum channels
analysis of the 6He+1H elastic scattering measured at the same time. The
influence on the calculations of the 4He+t exit potential and of the triton
sequential transfer is discussed. The final calculation gives a spectroscopic
factor close to one for the 4He+2n configuration as expected. The spectroscopic
factor obtained for the t+t configuration is much smaller than the theoretical
predictions.Comment: 10 pages, 11 figures, accepted in PR
Study of the decay D<sup>+</sup> â K<sup>â</sup>(892)<sup>+</sup>K<sup>0</sup><sub>S</sub> in D<sup>+</sup> â K<sup>+</sup>K<sup>0</sup><sub>S</sub>Ï<sup>0</sup>
Based on an e+eâ collision data sample corresponding to an integrated luminosity of 2.93ââfbâ1 collected with the BESIII detector at âs=3.773ââGeV, the first amplitude analysis of the singly Cabibbo-suppressed decay D+âK+K0SÏ0 is performed. From the amplitude analysis, the Kâ(892)+K0S component is found to be dominant with a fraction of (57.1±2.6±4.2)%, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction B(D+âK+K0SÏ0) measured by BESIII, we obtain B(D+âKâ(892)+K0S)=(8.69±0.40±0.64±0.51)Ă10â3, where the third uncertainty is due to the branching fraction B(D+âK+K0SÏ0). The precision of this result is significantly improved compared to the previous measurement. This result also differs from most of theoretical predictions by about 4Ï, which may help to improve the understanding of the dynamics behind
Study of the decay D<sup>+</sup><sub>s</sub> â Ï<sup>+</sup>Ï<sup>+</sup>Ï<sup>â</sup>η and observation of the W-annihilation decay D<sup>+</sup><sub>s </sub>â a<sub>0</sub>(980)<sup>+</sup>Ï<sup>0</sup>
The decay D+sâÏ+Ï+Ïâη is observed for the first time, using e+eâ collision data corresponding to an integrated luminosity of 6.32ââfbâ1, collected by the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV. The absolute branching fraction for this decay is measured to be B(D+sâÏ+Ï+Ïâη)=(3.12±0.13stat±0.09syst)%. The first amplitude analysis of this decay reveals the substructures in D+sâÏ+Ï+Ïâη and determines the relative fractions and the phases among these substructures. The dominant intermediate process is D+sâa1(1260)+η,a1(1260)+âÏ(770)0Ï+ with a branching fraction of (1.73±0.14stat±0.08syst)%. We also observe the W-annihilation process D+sâa0(980)+Ï(770)0, a0(980)+âÏ+η with a branching fraction of (0.21±0.08stat±0.05syst)%, which is larger than the branching fractions of other measured pure W-annihilation decays by 1 order of magnitude
Long-Time Asymptotics of Perturbed Finite-Gap Korteweg-de Vries Solutions
We apply the method of nonlinear steepest descent to compute the long-time
asymptotics of solutions of the Korteweg--de Vries equation which are decaying
perturbations of a quasi-periodic finite-gap background solution. We compute a
nonlinear dispersion relation and show that the plane splits into
soliton regions which are interlaced by oscillatory regions, where
is the number of spectral gaps.
In the soliton regions the solution is asymptotically given by a number of
solitons travelling on top of finite-gap solutions which are in the same
isospectral class as the background solution. In the oscillatory region the
solution can be described by a modulated finite-gap solution plus a decaying
dispersive tail. The modulation is given by phase transition on the isospectral
torus and is, together with the dispersive tail, explicitly characterized in
terms of Abelian integrals on the underlying hyperelliptic curve.Comment: 45 pages. arXiv admin note: substantial text overlap with
arXiv:0705.034
Observation of Ï(3686) â Î(1530)<sup>0</sup>ÎÂŻ(1530)<sup>0</sup> and Î(1530)<sup>0</sup>ÎÂŻ<sup>0</sup>
Using (448.1±2.9)Ă106 Ï(3686) events collected with the BESIII detector and a single-baryon tagging technique, we present the first observation of the decays Ï(3686)âÎ(1530)0ÎÂŻ(1530)0 and Î(1530)0ÎÂŻ0. The branching fractions are measured to be B(Ï(3686)âÎ(1530)0ÎÂŻ(1530)0)=(6.77±0.14±0.39)Ă10-5 and B(Ï(3686)âÎ(1530)0ÎÂŻ0)=(0.53±0.04±0.03)Ă10-5. Here, the first and second uncertainties are statistical and systematic, respectively. In addition, the parameter associated with the angular distribution for the decay Ï(3686)âÎ(1530)0ÎÂŻ(1530)0 is determined to be α=0.32±0.19±0.07, in agreement with theoretical predictions within one standard deviation
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