6,555 research outputs found
Results on CP Violation from the NA48 experiment at CERN
In this article the current status and latest results of the NA48 experiment
at CERN are given. We present in more details the analysis performed for the
Re(e'/e) measurement with the combined statistics accumulated during the 1998
and 1999 data periods. Reviewing the NA48 rare decay program, we select to
underline the new results on the branching ratio and the A_v factor for the
decay KL->pi0gg and the KL->pi+pi-e+e- CP violating decay. This article is the
contribution to the Proceedings of the Lepton-Photon Conference held in Roma,
July 23-29 2001.Comment: 13 pages, 11 figures, contribution to the Lepton-Photon 2001
Conference Proceedings -ne
Age- and sex-related variations in platelet count in Italy: a proposal of reference ranges based on 40987 subjects' data
BACKGROUND AND OBJECTIVES: Although several studies demonstrated that platelet count is higher in women, decreases with age, and is influenced by genetic background, most clinical laboratories still use the reference interval 150-400Ă10(9) platelets/L for all subjects. The present study was to identify age- and sex-specific reference intervals for platelet count. METHODS: We analysed electronic records of subjects enrolled in three population-based studies that investigated inhabitants of seven Italian areas including six geographic isolates. After exclusion of patients with malignancies, liver diseases, or inherited thrombocytopenias, which could affect platelet count, reference intervals were estimated from 40,987 subjects with the non parametric method computing the 2.5° and 97.5° percentiles. RESULTS: Platelet count was similar in men and women until the age of 14, but subsequently women had steadily more platelets than men. The number of platelets decreases quickly in childhood, stabilizes in adulthood, and further decreases in oldness. The final result of this phenomenon is that platelet count in old age was reduced by 35% in men and by 25% in women compared with early infancy. Based on these findings, we estimated reference intervals for platelet count Ă10(9)/L in children (176-452), adult men (141-362), adult women (156-405), old men (122-350) and, old women (140-379). Moreover, we calculated an extended reference interval that takes into account the differences in platelet count observed in different geographic areas. CONCLUSIONS: The age-, sex-, and origin-related variability of platelet count is very wide, and the patient-adapted reference intervals we propose change the thresholds for diagnosing both thrombocytopenia and thrombocytosis in Italy
Double-Spin Asymmetry of J/psi Production in Polarized pp Collisions at HERA-
We calculated the color-octet contribution to the double spin asymmetry of
hadroproduction with nonzero transverse momenta at fixed target
energies GeV. It is shown that the color-octet contribution
is dominant in the asymmetries. The expected asymmetries and statistical errors
in a future option of HERA with longitudinally polarized protons at HERA- should allow one to distinguish between different parametrizations for the
polarized gluon distribution in the proton.Comment: 14 pages with 6 figures (epsfig), LaTeX; Some figures are changed and
misprint is correcte
Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence
The cross section for coherent pair production by linearly polarised photons
in the 20-170 GeV energy range was measured for photon aligned incidence on
ultra-high quality diamond and germanium crystals. The theoretical description
of coherent bremsstrahlung and coherent pair production phenomena is an area of
active theoretical debate and development. However, under our experimental
conditions, the theory predicted the combined cross section and polarisation
experimental observables very well indeed. In macroscopic terms, our experiment
measured a birefringence effect in pair production in a crystal. This study of
this effect also constituted a measurement of the energy dependent linear
polarisation of photons produced by coherent bremsstrahlung in aligned
crystals. New technologies for manipulating high energy photon beams can be
realised based on an improved understanding of QED phenomena at these energies.
In particular, this experiment demonstrates an efficient new polarimetry
technique. The pair production measurements were done using two independent
methods simultaneously. The more complex method using a magnet spectrometer
showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for
publicatio
Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons
We present the first experimental results on the use of a thick aligned Si
crystal acting as a quarter wave plate to induce a degree of circular
polarisation in a high energy linearly polarised photon beam. The linearly
polarised photon beam is produced from coherent bremsstrahlung radiation by 178
GeV unpolarised electrons incident on an aligned Si crystal, acting as a
radiator. The linear polarisation of the photon beam is characterised by
measuring the asymmetry in electron-positron pair production in a Ge crystal,
for different crystal orientations. The Ge crystal therefore acts as an
analyser. The birefringence phenomenon, which converts the linear polarisation
to circular polarisation, is observed by letting the linearly polarised photons
beam pass through a thick Si quarter wave plate crystal, and then measuring the
asymmetry in electron-positron pair production again for a selection of
relative angles between the crystallographic planes of the radiator, analyser
and quarter wave plate. The systematics of the difference between the measured
asymmetries with and without the quarter wave plate are predicted by theory to
reveal an evolution in the Stokes parameters from which the appearance of a
circularly polarised component in the photon beam can be demonstrated. The
measured magnitude of the circularly polarised component was consistent with
the theoretical predictions, and therefore is in indication of the existence of
the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for
publicatio
A precision measurement of direct CP violation in the decay of neutral kaons into two pions
The direct CP violation parameter Re(epsilon'/epsilon) has been measured from
the decay rates of neutral kaons into two pions using the NA48 detector at the
CERN SPS. The 2001 running period was devoted to collecting additional data
under varied conditions compared to earlier years (1997-99). The new data yield
the result: Re(epsilon'/epsilon) = (13.7 +/- 3.1) times 10^{-4}. Combining this
result with that published from the 1997, 98 and 99 data, an overall value of
Re(epsilon'/epsilon) = (14.7 +/- 2.2) times 10^{-4} is obtained from the NA48
experiment.Comment: 19 pages, 5 figures, to be published in Physics Letters
Results on the Coherent Interaction of High Energy Electrons and Photons in Oriented Single Crystals
The CERN-NA-59 experiment examined a wide range of electromagnetic processes
for multi-GeV electrons and photons interacting with oriented single crystals.
The various types of crystals and their orientations were used for producing
photon beams and for converting and measuring their polarisation.
The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm
thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the
String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised
photon beams.
A new crystal polarimetry technique was established for measuring the linear
polarisation of the photon beam. The polarimeter is based on the dependence of
the Coherent Pair Production (CPP) cross section in oriented single crystals on
the direction of the photon polarisation with respect to the crystal plane.
Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set
of synthetic Diamond crystals were used as analyzers of the linear
polarisation.
A birefringence phenomenon, the conversion of the linear polarisation of the
photon beam into circular polarisation, was observed. This was achieved by
letting the linearly polarised photon beam pass through a 10 cm thick Silicon
single crystal that acted as a "quarter wave plate" (QWP) as suggested by N.
Cabibbo et al.Comment: Presented at International workshop "Relativistic Channeling and
Related Coherent Phenomena", Frascati (Rome) 23-26 March 200
Systematics of Heavy Quark Production at HERA
We discuss heavy quark and quarkonium production in various kinematic regions
at the HERA ep collider. In contrast to fixed target experiments, collider
kinematics allows the possibility of detailed measurements of particle
production in the proton fragmentation region. One thus can study parton
correlations in the proton Fock states materialized by the virtual photon
probe. We discuss various configurations of inelastic electron-proton
scattering, including peripheral, diffractive, and deep inelastic processes. In
particular, we show that intrinsic heavy quark Fock states can be identified by
the observation of quarkonium production at large and a low mean
transverse momentum which is insensitive to the virtuality of the photon.Comment: 17 pages, postscript. To obtain a copy of this paper send e-mail to
[email protected]
The Soft Gluon Emission Process in the Color-Octet Model for Heavy Quarkonium Production
The Color-Octet Model has been used successfully to analyze many problems in
heavy quarkonium production. We examine some of the conceptual and practical
problems of the soft gluon emission process in the Color-Octet Model. We use a
potential model to describe the initial and final states in the soft gluon
emission process, as the emission occurs at a late stage after the production
of the heavy quark pair. It is found in this model that the soft gluon M1
transition, 1S0(8)->3S1(1), dominates over the E1 transition, 3PJ(8)->3S1(1),
for J/psi and psi' production. Such a dominance may help resolve the questions
of isotropic polarization and color-octet matrix element universality in the
Color-Octet Model.Comment: 26 pages, in LaTe
Hadroproduction and Polarization of Charmonium
In the limit of heavy quark mass, the production cross section and
polarization of quarkonia can be calculated in perturbative QCD. We study the
-averaged production of charmonium states in collisions at
fixed target energies. The data on the relative production rates of \jp and
is found to disagree with leading twist QCD. The polarization of the
\jp indicates that the discrepancy is not due to poorly known parton
distributions nor to the size of higher order effects (-factors). Rather,
the disagreement suggests important higher twist corrections, as has been
surmised earlier from the nuclear target -dependence of the production cross
section.Comment: 19 page
- âŠ