We present new results on charmonium-like states from the BaBar experiment located at the PEP-II asymmetric energy e+e− collider at the SLAC National Accelerator Laboratory.
The J/ψ meson has negative G parity so that, in the limit of isospin conservation, its decay into π+π− should be purely electromagnetic. However, the measured branching fraction B(J/ψ→π+π−) exceeds ...by more than 4.5 standard deviations the expectation computed according to BABAR data on the e+e−→π+π− cross section. The possibility that the two-gluon plus one-photon decay mechanism is not suppressed by G-parity conservation is discussed, even by considering other multipion decay channels. As also obtained by phenomenological computation, such a decay mechanism could be responsible for the observed discrepancy. Finally, we notice that the BESIII experiment, having the potential to perform an accurate measurement of the e+e−→π+π− cross section in the J/ψ mass energy region, can definitely prove or disprove this strong G-parity-violating mechanism by confirming or confuting the BABAR data.
The design of the Forward Tracker for the Forward Spectrometer of the PANDA experiment is described. The tracker consists of 6 tracking stations, each comprising 4 planar double layers of straw tube ...detectors, and has a total material budget of only 2% X0. The straws are made self-supporting by a 1 bar over-pressure of the working gas mixture (Ar/CO2). This allows to use lightweight and compact rectangular support frames for the double layers and to split the frames into pairs of C-shaped half-frames for an easier installation on the beam line.
The identification of charged particles based on energy losses in straw tube detectors has been simulated. The response of a new front-end chip developed for the PANDA straw tube tracker was ...implemented in the simulations and corrections for track distance to sense wire were included. Separation power for p−K, p−π and K−π pairs obtained using the time-over-threshold technique was compared with the one based on the measurement of collected charge.
A cylindrical GEM detector is under development, to serve as an upgraded inner tracker at the BESIII spectrometer. It will consist of three layers of cylindrically-shaped triple GEMs surrounding the ...interaction point. The experiment is taking data at the e+e− collider BEPCII in Beijing (China) and the GEM tracker will be installed in 2018. Tests on the performances of triple GEMs in strong magnetic field have been run by means of the muon beam available in the H4 line of SPS (CERN) with both planar chambers and the first cylindrical prototype. Efficiencies and resolutions have been evaluated using different gains, gas mixtures, with and without magnetic field. The obtained efficiency is 97–98% on single coordinate view, in many operational arrangements. The spatial resolution for planar GEMs has been evaluated with two different algorithms for the position determination: the charge centroid and the micro time projection chamber (μ-TPC) methods. The two modes are complementary and are able to cope with the asymmetry of the electron avalanche when running in magnetic field, and with non-orthogonal incident tracks. With the charge centroid, a resolution lower than 100μm has been reached without magnetic field and lower than 200μm with a magnetic field up to 1 T. The μ-TPC mode showed to be able to improve those results. In the first beam test with the cylindrical prototype, the detector had a very good stability under different voltage configurations and particle intensities. The resolution evaluation is in progress.
To assess the value of 3-Tesla (3-T) MR imaging (MRI) in the evaluation of the course of the intracranial and extra-cranial tracts of the facial nerve.
83 patients were studied by MRI in order to ...detect the course of facial nerve; a total of 166 facial nerves were examined. T2-weighted 3D Fast imaging employing steady-state acquisition (FIESTA) and T1-weighted Fast spoiled gradient recalled echo (fast SPRG) sequences were used. Two radiologists (reader A and B), independently, evaluated the course of the tracts of the facial nerve according to a qualitative scale (excellent, good, fair, poor). The Intraclass Correlation Coefficient (ICC) and Pearson correlation coefficient were used to assess the intra-observer and interobserver variability in the nerve course evaluation.
Reader A evaluated 35 facial nerves as excellent, 94 as good, 33 as fair and 4 as poor. Reader B rated 31 facial nerves excellent, 89 good, 43 fair and 3 poor. The intraobserver variability was ICC = 0.919 in reader A and ICC = 0.842 in reader B. The interobserver variability (Pearson correlation coefficient) was 0.713 (p ≤ 0.01).
According to the preliminary results of our study the use of 3-T MRI with FIESTA and fast SPGR sequences may allow the study of the course of the facial nerve and its branches. The knowledge of the course and of the anatomic relationships of these nerve bundles with surrounding structures, as well as of the anatomical variants, provide useful informations for a prompt neurosurgery and maxillofacial surgical planning.
Gas detector development is one of the pillars of the research in fundamental physics. Since several years, a new concept of detectors, called Micro Pattern Gas Detector (MPGD), allowed to overcome ...several problems related to other types of commonly used detectors, like drift chamber and micro strips detectors, reducing the rate of discharges and providing better radiation tolerance. Among the most used MPGDs are the Gas Electron Multipliers (GEMs). Invented by Sauli in 1997, nowadays GEMs have become an important reality for particle detectors in high energy physics. Commonly deployed as fast timing detectors and triggers, their fast response, high rate capability and high radiation hardness make them also suitable as tracking detectors. The readout scheme is one of the most important features in tracking technology. Analog readout based on the calculation of the center of gravity technique allows to overcome the limit imposed by digital pads, whose spatial resolution is limited by the pitch dimensions. However, the presence of high external magnetic fields can distort the electronic cloud and affect the performance. The development of the micro-TPC reconstruction method brings GEM detectors into a new prospective, improving significantly the spatial resolutionin presence of high magnetic fields. This innovative technique allows to reconstruct the 3-dimensional particle position, as Time Projection Chamber, but within a drift gap of a few millimeters. In these report, the charge centroid and micro-TPC methods are described in details. We discuss the results of several test beams performed with planar chambers in magnetic field. These results are one of the first developments of micro-TPC technique for GEM detectors, which allows to reach unprecedented performance in a high magnetic field of 1 T.
A new inner tracker based on a cylindrical gas electron-multiplier detector is under development to replace the current inner drift chamber of the BES III spectrometer. The BES III experiment is ...carried out at the BEPC II e
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collider in Beijing at center-of-mass energies in the tau-charm region with a design luminosity of 1.0
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. The new inner tracker consists of three cylindrical layers of triple GEM surrounding the interaction point, covering 93% of solid angle. To fulfill physics requirements, a spatial resolution of 130 μm must be achieved. Both planar and cylindrical prototypes have been built and tested. A custom ASIC using UMC 110-nm technology has been designed to provide charge and time measurements—the first prototype is in testing. Notable and innovative aspects of the new inner tracker and the performance of the detector prototypes and readout ASIC are reported here.
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