2006 Vol. 30, No. 8
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We calculate the effective mass terms of the tritium beta decay (〈m〉e) and the neutrinoless double beta decay (〈m〉ee) in the minimal seesaw model with two heavy right-handed Majorana neutrinos. By using current neutrino oscillation data, we obtain the ranges of 〈m〉e and 〈m〉ee for two possible patterns of the neutrino mass spectrum: (1) 0.00424eV≤〈m〉e≤0.0116eV and 0.00031eV≤〈m〉ee≤0.0052eV for the normal neutrino mass hierarchy; (2) 0.0398eV≤〈m〉e≤0.0571eV and 0.0090eV≤〈m〉ee≤0.0571eV for the inverted neutrino mass hierarchy. The sensitivity of 〈m〉ee on the smallest neutrino mixing angle and the Majorana CP-violating phase is also discussed.
The energy loss of the quark in the nuclear matter can be well described by the nuclear dependence in the high energy nuclear Drell-Yan process. In terms of the parametrization of the quark energy loss given in the literature and the nuclear parton distribution extracted from the experimental data of the deep inelastic scattering between lepton and nucleus only, the cross section ratios of lepton pair production in the nuclear Drell-Yan process induced by a proton of 800GeV bombarding on various nuclear targets at E772-FNAL are analyzed. It is shown that our results with the energy loss effect are in good agreement with the E772-FNAL data. Therefore, in order to extract the parton distribution functions in nucleus from the experimental data of the Drell-Yan process reliably, the energy loss effect should be taken into account.
To experimentally study the charmonium ψ′cascade radiative decay, ψ′→γ′χcJ→γ′γJ/ψ, a generator which describes correctly all angular distributions is a necessity. We can determine the photon multipolarities (or equivalently the helicity couplings) by analyzing the angular correlations. In this work, a generator with fulls description of angular distributions for such process will be introduced, as well as the measurement method of multipolarities will be discussed, which can be implemented at BESⅢ/BEPCⅡ or CLEOc.
Based on the branching ratios of ψ(2S)→VP given by the BES collaboration, we make a new analysis to study the mixing of pseudoscalars. The mixing angle of η and ηp, θp is determined to be (－7.54±1.52)° which is consistent with the value obtained from quadratic Gell-Mann-Okubo formula. From this work we also know that the strength of DOZI to SOZI is about 14% in ψ(2S)→VP, and the phase angle of electromagnetic amplitude to strong amplitude is (156±89)°.
The exclusive decays of χc0 into multi-body BBMM(B:baryon,M:meson)are investigated based on the SU(3) symmetry. The transitional amplitudes of χc0→BBMM are given in terms of the isospin coupling constant. Based on these amplitudes, it is found that N* resonances make a relatively large contribution to the χc0→NNππ, which might serve as a channel to study N* resonance in data analysis.
The photon attenuation effects are different, when the photons with different energy pass through the attenuators with different thickness and material. Using the above attenuators and the thermoluminescent probes, the degrader detector was designed for detecting the gamma spectrum of the fast reactor. Meanwhile the unfolding Program is programmed for the continuous spectrum in GRAVEL algorithm, and this program is proved reliable by experimental results. Finally, the photon spectrum of the fast reactor is given.
High-spin structures in 146Ce nucleus have been re-investigated by measuring the prompt γ rays from spontaneous fission of 252Cf. The previously reported level scheme of 146Ce has been updated. The octupole deformed collective bands have been extended up to higher spin states. A possible quasi-γ band structure was examined and reconstructed according to our data analysis. In addition, the reflection asymmetric shell model was applied to describe the octupole deformed bands in 146Ce, and the calculated results are in good agreement with the experimental data at lower spins.
The ground state properties of the Pb isotopic are studied by using the axially deformed relativistic mean field (RMF) calculation with the parameter set TM1. The pairing correlation is treated by the BCS method and the isospin dependent pairing force is used. The ‘blocking’method is used to deal with unpaired nucleons. The theoretical results show that the relativistic mean field theory with non-linear self-interactions of mesons provides a good description of the binding energy and neutron separation energy. The present paper focus on the physical mechanism of the Pb isotope shifts.
The triaxial deformed Relativistic Mean Field (RMF) model including the time-odd component is developed. The magnetic potential and baryon current in 41Ca and their influence on the magnetic moment, single particle level splitting for time reversal states and other properties are investigated in triaxial deformed RMF model with the spatial-component of vector meson fields by using PK1 effective interaction, which includes the self-coupling of σ and ω meson fields as well as the microscopic correction for the center of mass.
Variational method and TDA approximation was applied to construct the SD pairs in the SD-pair shell model (SDPSM). The results show that this new method seems better than the surface δ-interaction in determining the pair structure of the SDPSM in the description of collectivity of low-lying spectra of nuclei.
A comparative analysis for dissipation behaviors of nucleus 110,112In formed in 130MeV 3He+natAg reactions and 111In populated via 84Kr on 27Al collisions at 890 and 714MeV suggests that nuclear dissipation strength may have an angular momentum dependence besides the known deformation and/or temperature dependence.
To meet the physics requirement, the time resolution of TOF (Time-of-flight) detector of the BESⅢ (Beijing Spectrometer Ⅲ) is required to be less than 90ps (rms), and the FEE (front end electronic) must contribute less than 25ps. This paper describes the prototype design of BESⅢ's TOF readout system (including time and amplitude measurement circuits).Preliminary results for prototypes of TOF front end electronics are given.
GEM gas detector is a type of Micro-pattern gas detectors, which has a wide potential in particle physics experiment and lower energy X-ray imaging system. In this paper a tri-GEM gas detector was developed, and the gas gain, energy resolution and charge transfer efficiency of the tri-GEM detector were studied with source of 55Fe. The results of the test indicate that more than 105 effective gain and about 24% energy resolution of 5.9keV X ray of the tri-GEM detector can be reached. The results also show that when the electric field in transfer region is more than 3kV/(cm.atm), the best energy resolution of the tri-GEM detector can be obtained.
In the case of a small size detector lying inside a bulk of medium, there are two problems in the correction factors calculation of the detectors. One is that the detector is too small for the particles to arrive at and collide in; the other is that the ratio of two quantities is not accurate enough. The method discussed in this paper, which combines correlated sampling with modified particle collision auto-importance sampling, and has been realized on the MCNP-4C platform, can solve these two problems. Besides, other 3 variance reduction techniques are also combined with correlated sampling respectively to calculate a simple calculating model of the correction factors of detectors. The results prove that, although all the variance reduction techniques combined with correlated sampling can improve the calculating efficiency, the method combining the modified particle collision auto-importance sampling with the correlated sampling is the most efficient one.
Characteristics of time of flight counter wrapped with five reflective materials: tyvek, teflon, millipore, ESR and Al film is studied by test beam at BEPC linear accelerator. It includes three aspects: the time resolution, the attenuation length and the effective speed of light. Al film wrapping can give the best time resolution of 95.6±2ps. ESR wrapping can give the biggest amplitude and longest attenuation length. The effective speed of light in the scintillator bar with these 5 different reflective materials is basically the same.
Phase detection performs a crucial role in the phase control loop of RF signals in accelerators. This paper presents two methods that apply I/Q technique to phase detection of RF signals. The content includes the study of arithmetic and the setup of systems. The methods are as follows: 1. adopting I/Q demodulator, AD card and the technique of digital processing to detect the phase; 2. direct digital I/Q method. In the former, feasible calibration arithmetic against the inherent error of I/Q demodulators is suggested. In the latter, I and Q signals are generated by modulating the LO signal with a step of(2π/N). The phase detection error is below 0.5° by using either of them.
The electron beam measurement system for Dragon-I must work synchronously with the beam production and transportation accurately in order to obtain correct data．The synchronization with about 1ns is important．The output waveform of Blumlein lines in pulsed-power system is of amplitude of about 250kV and 20ns active edge time(following edge)．The electron beam will hit the conversion target in about 145ns later steadily and the jitter time is about 1—2ns．The synchronization precision with the same level of the jitter time will be reached if the sharp following edge of waveform is selected to be the time base．The synchronization trigger signal for measurement system can be obtained by the way of differentiating the following edge and the accuracy of about ns can also be reached with suitable circuit parameters．The optical fiber is also adopted to remove the interference on the measurement system from the high voltage system．This kind of burst trigger mode overcomes many disadvantages such as low accuracy, long delay time, large jitter in normal trigger mode and can provide the trigger time accurately．It can meet the need to measure the electron beam parameters at any required time．
In order to reduce the influence of the stray electric field of the buncher in the axial injection system of SFC and to improve the injection efficiency of SFC, the existing buncher electrode is investigated and a new electrode is designed. The influences of the electric field to the beams for the both cases are simulated. The simulation results show that the bunching efficiency is improved from 55% to 74% with the new electrode. At the same time, the influence of the space charge is computed and according to the results, the location of the buncher is readjusted too.
The paper describes the ultraviolet light beam profile and emittance measurement system for HLS (Hefei Light Source). The system is based on the optical measurement, composed by two functional blocks: optical imaging and image acquisition. The optical imaging system is to form the 1:1 image of the ultraviolet part of SR on the surface of the CCD. The image acquisition system receives NTSC signal from the CCD camera which acquires the image of the ultraviolet part of SR, the signal is processed by a LabVIEW program to obtain the beam information of beam profile size, emittance and coupling between vertical and horizontal directions. Some measured results are also given.
Based on several facts of CSRm, such as the layout of the ring, the lattice parameters, exiting Schottky noise diagnosis equipment and fund, the primary stochastic cooling design of CSRm has been carried out. The optimum cooling time and the optimum cooling bandwidth are obtained through simulation using the cooling function. The results indicate that the stochastic cooling is quite a powerful cooling method for CSRm. The comparison of the cooling effects of stochastic cooling and electron cooling in CSR are also presented. We can conclude that the combination of the two cooling methods on CSRm will improve the beam cooling rate and quality beam greatly.
The simulation result of thermal distortion of DCM crystal indirectly cooled by liquid nitrogen(LN2) at Shanghai synchrotron radiation facility (SSRF) has been reported. The source is U27 undulator. The maximum of power density at 24m is 60W/mm2. We give the correlation of the slope error of crystal surface vs. Bragg angle, the convection film coefficient, the bulk temperature of LN2 and total power absorbed by the first crystal, respectively. The slope error is less than 3 arcsec when the Bragg angle is less than 30°, the thickness of crystal is larger than 30mm, the current of storage ring is up to 400mA and cooled by 78K LN2.
In single photon emission computed tomography (SPECT), accurately modeling of the physics of SPECT imaging process is essential to degrading factor compensation and image quality enhancement. In this paper, an analytical SPECT modeling method is proposed based on the theory of the Boltzmann transport equation and its Neumann series solution. The analytical model was numerically evaluated using high dimensional integration algorithm based on number theory. SPECT projection images for both uniform cylinder phantom with point source and NCAT phantom were calculated and compared with those which were generated by conventional Monte-Carlo modeling methods. Results show that the analytical modeling method demonstrates improved performance in computation accuracy and speed relative to the Monte-Carlo method, as well as the advantage that the computational results of the analytical method are free from statistical noise. Therefore, we conclude that the analytical method is more appropriate for modeling the SPECT imaging process than Monte-Carlo modeling methods.
In a traditional cone-beam CT system, the cost of product and computation is very high. In this paper, we propose a transversely truncated cone-beam X-ray CT system with a reduced size detector positioned off-center, in which X-ray beams only cover half of the object. The reduced detector size cuts the cost and the X-ray dose of the CT system. The existing CT reconstruction algorithms are not directly applicable in this new CT system. Hence, we develop a BPF-type direct backprojection algorithm. Different from the traditional rebinning methods, our algorithm directly backprojects the pretreated projection data without rebinning. This makes the algorithm compact and computationally more efficient. Finally, some numerical simulations and practical experiments are done to validate the proposed algorithm.
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