6,608 research outputs found
Constraints on the parameters of the CKM matrix by End 1998
A review of the current status of the Cabibbo-Kobayashi-Maskawa matrix (CKM)
is presented. This paper is an update of the results published in [1]. The
experimental constraints imposed by the measurements of \epsilon_K,
V_{ub}/V_{cb}, \Delta m_d and from the limit on \Delta m_d are used. Values of
the constraints and of the parameters entering into the constraints, which
restrict the range of the \bar{\rho} and \bar{\eta} parameters, include recent
measurements presented at 1998 Summer Conferences and progress obtained by
lattice QCD collaborations. The results are: \bar{\rho}=0.202
^{+0.053}_{-0.059},\bar{\eta}=0.340 \pm 0.035, from which the angles \alpha,
\beta and \gamma of the unitarity triangle are inferred : \sin 2 \alpha = -0.26
^{+ 0.29}_{-0.28} ,\sin 2 \beta = 0.725 ^{+0.050}_{-0.060} ,\gamma=
(59.5^{+8.5}_{-7.5})^{\circ}. Without using the constraint from \epsilon_K,
\sin 2 \beta has been obtained: \sin 2 \beta = 0.72 ^{+0.07}_{-0.11}. Several
external measurements or theoretical inputs have been removed, in turn, from
the constraints and their respective probability density functions have been
obtained. Central values and uncertainties on these quantities have been
compared with actual measurements or theoretical evaluations. In this way it is
possible to quantify the importance of the different measurements and the
coherence of the Standard Model scenario for CP violation. An important result
is that \Delta m_s is expected to be between [12.0-17.6] ps^{-1} with 68% C.L.
and <20 ps^{-1} at 95% C.L. Finally relations between the CKM parameters and
the quark masses are examined within a given model.Comment: 26 page
Sub-millimeter nuclear medical imaging with high sensitivity in positron emission tomography using beta-gamma coincidences
We present a nuclear medical imaging technique, employing triple-gamma
trajectory intersections from beta^+ - gamma coincidences, able to reach
sub-millimeter spatial resolution in 3 dimensions with a reduced requirement of
reconstructed intersections per voxel compared to a conventional PET
reconstruction analysis. This '-PET' technique draws on specific beta^+
- decaying isotopes, simultaneously emitting an additional photon. Exploiting
the triple coincidence between the positron annihilation and the third photon,
it is possible to separate the reconstructed 'true' events from background. In
order to characterize this technique, Monte-Carlo simulations and image
reconstructions have been performed. The achievable spatial resolution has been
found to reach ca. 0.4 mm (FWHM) in each direction for the visualization of a
22Na point source. Only 40 intersections are sufficient for a reliable
sub-millimeter image reconstruction of a point source embedded in a scattering
volume of water inside a voxel volume of about 1 mm^3 ('high-resolution mode').
Moreover, starting with an injected activity of 400 MBq for ^76Br, the same
number of only about 40 reconstructed intersections are needed in case of a
larger voxel volume of 2 x 2 x 3~mm^3 ('high-sensitivity mode'). Requiring such
a low number of reconstructed events significantly reduces the required
acquisition time for image reconstruction (in the above case to about 140 s)
and thus may open up the perspective for a quasi real-time imaging.Comment: 17 pages, 5 figutes, 3 table
A detector of small harmonic displacements based on two coupled microwave cavities
The design and test of a detector of small harmonic displacements is
presented. The detector is based on the principle of the parametric conversion
of power between the resonant modes of two superconducting coupled microwave
cavities. The work is based on the original ideas of Bernard, Pegoraro, Picasso
and Radicati, who, in 1978, suggested that superconducting coupled cavities
could be used as sensitive detectors of gravitational waves, and on the work of
Reece, Reiner and Melissinos, who, {in 1984}, built a detector of this kind.
They showed that an harmonic modulation of the cavity length l produced an
energy transfer between two modes of the cavity, provided that the frequency of
the modulation was equal to the frequency difference of the two modes. They
achieved a sensitivity to fractional deformations of dl/l~10^{-17} Hz^{-1/2}.
We repeated the Reece, Reiner and Melissinos experiment, and with an improved
experimental configuration and better cavity quality, increased the sensitivity
to dl/l~10^{-20} Hz^{-1/2}. In this paper the basic principles of the device
are discussed and the experimental technique is explained in detail. Possible
future developments, aiming at gravitational waves detection, are also
outlined.Comment: 28 pages, 12 eps figures, ReVteX. \tightenlines command added to
reduce number of pages. The following article has been accepted by Review of
Scientific Instruments. After it is published, it will be found at
http://link.aip.org/link/?rs
2000 CKM-Triangle Analysis A Critical Review with Updated Experimental Inputs and Theoretical Parameters
Within the Standard Model, a review of the current determination of the sides
and angles of the CKM unitarity triangle is presented, using experimental
constraints from the measurements of |\epsilon_K|, |V_{ub}/V_{cb}|, \Delta m_d
and from the limit on \Delta m_s, available in September 2000. Results from the
experimental search for {B}^0_s-\bar{B}^0_s oscillations are introduced in the
present analysis using the likelihood. Special attention is devoted to the
determination of the theoretical uncertainties. The purpose of the analysis is
to infer regions where the parameters of interest lie with given probabilities.
The BaBar "95 %, C.L. scanning" method is also commented.Comment: 44 pages (revised version
Constraints on the parameters of the matrix at the end of 1997
A review of the current status of the Cabibbo-Kobayashi-Maskawa matrix V_CKM
is presented. This paper contains an update of the results published in
hep-ph/9711261. Values of the parameters entering into the constraints, which
restrict the range for rho and eta parameters, include recent measurements
given at 1997 Summer Conferences and progress obtained by lattice QCD
collaborations.Experimental constraints imposed by the measurements of
epsilon_k,V_ub/V_cb, Delta m_d and by the limit on Delta m_s, are compatible
and do not show evidence for New Physics inside measurements errors. Values for
the angles alpha, beta and gamma of the C.K.M. triangle have been also
obtained: rho=0.156 +- 0.090, eta=0.328 +- 0.054 sin 2alpha = -0.10+-0.40, sin
2beta = 0.68 +- 0.10, gamma= 64+-12 Angles theta,theta_u,theta_d and phi
proposed in the parametrisation (Phys. Lett. B5353 (1995) 114.) of the C.K.M.
matrix have been also determined. Finally, as there are more constraints than
the fitted rho and eta parameters, several external measurements or theoretical
inputs have been removed, in turn, from the constraints and their respective
values have been fitted simultaneously with rho and eta.Central values and
uncertainties on these quantities have been compared with actual measurements
or theoretical evaluations. In this way it is possible to quantify the
importance of the different measurements and the coherence of the Standard
Model scenario for CP violation.Comment: 29 page
Stem Cell Therapy in Ocular Pathologies in the Past 20 Years
Stem cell therapies are successfully used in various fields of medicine. This new approach of research is also expanding in ophthalmology. Huge investments, resources and important clinical trials have been performed in stem cell research and in potential therapies. In recent years, great strides have been made in genetic research, which permitted and enhanced the differentiation of stem cells. Moreover, the possibility of exploiting stem cells from other districts (such as adipose, dental pulp, bone marrow stem cells, etc.) for the treatment of ophthalmic diseases, renders this topic fascinating. Furthermore, great strides have been made in biomedical engineering, which have proposed new materials and threedimensional structures useful for cell therapy of the eye. The encouraging results obtained on clinical trials conducted on animals have given a significant boost in the creation of study protocols also in humans. Results are limited to date, but clinical trials continue to evolve. Our attention is centered on the literature reported over the past 20 years, considering animal (the most represented in literature) and human clinical trials, which are limiting. The aim of our review is to present a brief overview of the main types of treatments based on stem cells in the field of ophthalmic pathologies
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