4,654 research outputs found
Bias-Free Estimation in Multicomponent Maximum Likelihood Fits with Component-Dependent Templates
The possibility of strong biases in a multicomponent Maximum Likelihood fits
with component-dependent templates has been demonstrated in some toy problems.
We discuss here in detail a problem of practical interest, particle
identification based on time-of-flight or dE/dx information. We show that large
biases can occur in estimating particle fractions in a sample if differences
between the momentum spectra of particles are ignored, and we present a more
robust fit technique, allowing bias-free estimation even when the particle
spectra in the sample are unknown.Comment: May 2006, 4 pages, 6 figures To appear in the proceedings of
PHYSTATO5: Statistical Problems in Particle Physics, Astrophysics and
Cosmology, Oxford, England, United Kingdom, 12-15 Sep 200
Neutrino optics and oscillations in gravitational fields
We study the propagation of neutrinos in gravitational fields using wave
functions that are exact to first order in the metric deviation. For
illustrative purposes, the geometrical background is represented by the
Lense-Thirring metric. We derive explicit expressions for neutrino deflection,
helicity transitions, flavor oscillations and oscillation Hamiltonian.Comment: 16 page
Flavor and CP Violation with Fourth Generations Revisited
The Standard Model predicts a very small CP violation phase %= \arg M_{12} \simeq \arg\,(V^*_{ts}V_{tb})^2B_s\bar B_s\lambda^2\eta\Phi_{B_s}\sin2\Phi_{B_s}t'\Delta m_{B_s}{\cal B}(B \to X_s\ell^+\ell^-)f_{B_s}\sin2\Phi^{\rm
SM4}_{B_s} \sim -0.33m_{b'} = 4800.06 < |V_{t'b}| < 0.13\Gamma(Z\to b\bar b)\Delta m_{D}{\cal
B}(K^+\to\pi^+\nu\bar\nu){\cal
B}(K_L\to\pi^0\nu\bar\nu)V_{t'd}$.Comment: 8 pages, 11 figure
An Unbiased 1.3 mm Emission Line Survey of the Protoplanetary Disk Orbiting LkCa 15
The outer (>30 AU) regions of the dusty circumstellar disk orbiting the ~2-5
Myr-old, actively accreting solar analog LkCa 15 are known to be chemically
rich, and the inner disk may host a young protoplanet within its central
cavity. To obtain a complete census of the brightest molecular line emission
emanating from the LkCa 15 disk over the 210-270 GHz (1.4 - 1.1 mm) range, we
have conducted an unbiased radio spectroscopic survey with the Institute de
Radioastronomie Millimetrique (IRAM) 30 meter telescope. The survey
demonstrates that, in this spectral region, the most readily detectable lines
are those of CO and its isotopologues 13CO and C18O, as well as HCO+, HCN, CN,
C2H, CS, and H2CO. All of these species had been previously detected in the
LkCa 15 disk; however, the present survey includes the first complete coverage
of the CN (2-1) and C2H (3-2) hyperfine complexes. Modeling of these emission
complexes indicates that the CN and C2H either reside in the coldest regions of
the disk or are subthermally excited, and that their abundances are enhanced
relative to molecular clouds and young stellar object environments. These
results highlight the value of unbiased single-dish line surveys in guiding
future high resolution interferometric imaging of disks.Comment: 35 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Modafinil-Induced changes in functional connectivity in the cortex and cerebellum of healthy elderly subjects
In the past few years, cognitive enhancing drugs (CEDs) have gained growing interest and the focus of investigations aimed at exploring their use to potentiate the cognitive performances of healthy individuals. Most of this exploratory CED-related research has been performed on young adults. However, CEDs may also help to maintain optimal brain functioning or compensate for subtle and or subclinical deficits associated with brain aging or early-stage dementia. In this study, we assessed effects on resting state brain activity in a group of healthy elderly subjects undergoing acute administration of modafinil, a wakefulness-promoting agent. To that aim, participants (n = 24) were investigated with resting state functional Magnetic Resonance Imaging (rs-fMRI) before and after the administration of a single dose (100 mg) of modafinil. Effects were compared to age and size-matched placebo group. Rs-fMRI effects were assessed, employing a graph-based approach and Eigenvector Centrality (EC) analysis, by taking in account topological changes occurring in functional brain networks. The main finding of the study is that modafinil promotes enhanced centrality, a measure of the importance of nodes within functional networks, of the bilateral primary visual (V1) cortex. EC analysis also revealed that modafinil-treated subjects show increased functional connectivity between the V1 and specific cerebellar (Crus I, Crus II, VIIIa lobule) and frontal (right inferior frontal sulcus and left middle frontal gyrus) regions. Present findings provide functional data supporting the hypothesis that modafinil can modulate the cortico-cerebellar connectivity of the aging brai
A Statistical Prescription to Estimate Properly Normalized Distributions of Different Particle Species
We describe a statistical method to avoid biased estimation of the content of
different particle species. We consider the case when the particle
identification information strongly depends on some kinematical variables,
whose distributions are unknown and different for each particles species. We
show that the proposed procedure provides properly normalized and completely
data-driven estimation of the unknown distributions without any a priori
assumption on their functional form. Moreover, we demonstrate that the method
can be generalized to any kinematical distribution of the particles
Study of the doubly charmed tetraquark Tcc+
Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the (DD0)-D-0 pi(+) mass spectrum just below the D*+D-0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T-cc(+), tetraquark with a quark content of cc (u) over bar(d) over bar and spin-parity quantum numbers J(P) =1(+). Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*(+) mesons is consistent with the observed D-0 pi(+) mass distribution. To analyse the mass of the resonance and its coupling to the DID system, a dedicated model is developed under the assumption of an isoscalar axial-vector T-cc(+), state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T-cc(+), state. In addition, an unexpected dependence of the production rate on track multiplicity is observed
Rigorous luminosity function determination in presence of a background: theory and application to two intermediate redshift clusters
In this paper we present a rigorous derivation of the luminosity function
(LF) in presence of a background. Our approach is free from the logical
contradictions of assigning negative values to positively defined quantities
and avoid the use of incorrect estimates for the 68 % confidence interval
(error bar). It accounts for Poisson fluctuations ignored in previous
approaches and does not requires binning of the data. The method is extensible
to more complex situations, does not require the existence of an
environment--independent LF, and clarifies issues common to field LF
derivations. We apply the method to two clusters of galaxies at intermediate
redshift (z~0.3) with among the deepest and widest K_s observations ever taken.
Finally, we point out short-comings of flip--flopping magnitudes.Comment: MNRAS, in pres
On the main stages of the history of intra-articular therapy
In this review the main stages in the history of intra-articular therapy of the rheumatic diseases are summarized. The first approach to such a local treatment has been likely performed in 1792 by the French physician Jean Gay, who injected in a swelling knee the "eau du Goulard" (Goulard's water), namely a mixture based on lead compounds. In the XIX century iodine derivatives have been mainly applied as an intra-articular treatment. In the XX century, before the wide use of intra-articular corticosteroids, chiefly due to the Joseph Lee Hollander's experiences, a variety of drugs has been employed, including cytostatics and sclerosing substances. A further important stage has been synoviorthesis, by using specific radionuclides, that would actually represent an anti-synovial treatment. In the last years a spread use of intra-articular hyaluronic acid, particularly in osteoarthritis, has been recorded, with the aim to warrant articular viscosupplementation. Future of intra-articular treatment should be represented by the biological drugs, i.e., anti-TNF, but it is still untimely to define the exact role of such a local treatment of arthritis
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