2004 Vol. 28, No. 7
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This paper discusses the method of searching for TeV gamma ray point sources and estimates the significance of statistical differences between on-source and off-source observations by using student variable t.Based on Bayes theorem,the number of observed signals, and the detection efficiency via Monte Carlo simulation,the differential energy spectrum of TeV gamma ray from Crab Nebula are calculated.
In the context of the littlest Higgs (LH) model, we consider the Higgs strahlung process e+e-→ZH. We find that the correction effects on the process mainly come from the heavy photon A′. If we take the mixing angle c in the range of 0.85—1, the contributions of the heavy gauge boson Z′ can not be neglected. In most of the parameter space, the deviation of the total production cross section σ tot from its SM value is larger than 5%, which may be observable in the future high energy e+e- collider (LC) experiments. The future LC experiments could test the LH model by measuring the cross section of the process e+e-→ZH.
Based on the closed time path formalism, a deduced Feynman rule for directly calculating the retarded and advanced Green functions is given. This Feynman rule is used to calculate the two-point self-energy and three-point vertex correction in φ3 theory. The generalized fluctuation-dissipation theorem for three-point nonlinear response function is verified.
The quantal symmetry property in the CP1 non-linear sigma model with Maxwell-Chern-Simons (MCS) term in (2+1) dimensions is studied. In the Coulomb gauge, the system is quantized in the Faddeev-Senjanovic (FS) path-integral formalism. Based on the quantal symmetries of a constrained Hamiltonian system, the fractional spin at the quantum level of this system is presented.
High-spin states in doubly odd 170Re have been populated and investigated using 142Nd (32S,1p3nγ)170reaction at 166MeV bombarding energy. X-γ and γ-γ-t coincidence measurements have been carried out in the experiment. Based on the coincidence relationships, a rotational band in 170has been identified for the first time, extending the high-spin studies of A≈160 odd-odd nuclei to the currently lightest rhenium isotope. The band has been assigned to be built on the πh11/2⊙υi13/2 configuration according to their rotational properties in quasiparticle alignment, signature splitting, level spacing systematics, as well as the existing knowledge in neighboring nuclei. Low-spin signature inversion has been suggested for the πh11/2⊙υi13/2 band in 170.
At Large Hadron-Hadron Collider(LHC), the structure of nucleon at much small x region can be revealed. With the high twist modified AP evolution equation (MDAP equation), the saturation problem of partons at LHC energies is analyzed. It is found that the parton distribution will not be saturated in this region, instead, due to the high twist effects, the parton distribution is obviously suppressed and partial saturation appears. With the MDAP equation, parton distributions at LHC energies are calculated.
For investigating physical mechanism of the quark distributions due to the nuclear environment under the non-constant K condition the nuclear medium effect on the distribution functions of the sea and valence quarks R Av(x2) RAs(x2) is computed by considering QCD non-perturbation effect in the DIS process and energy loss effect in the nuclear Drell-Yan process. Calculated results show that non-perturbative terms or energy loss effect terms have a tiny influence on the nuclear medium effect on the sea quark distribution in the small x2 region, while a strong influence on the valence quark's. However in the large x2 region, the non-perturbative or energy loss effects obviously affect the nuclear medium effect on the sea quark distribution.
The level structure of 76—84Kr isotopes is discussed within the framework of Interacting Boson Model (IBM-2). One-phonon mixed symmetry states J+2+ and two-phonon mixed symmetry states J +1+,2+ and 3+ have been identified by analyzing the wave function and M1 transitions. Special attention is paid to the occurrence of 0+2 which is not reproduced well by other calculations. The study of the influence of the [d+d] Lπ·[d+d] Lυ interactions on the nuclear structure of these nuclei are undertaken. The calculated results are compared with available experimental data; the results are in general good agreement.
Based on an improved quantum molecular dynamics model the static and dynamic potential in the entrance channel of synthesis of superheavy nuclei are studied. The dependence of the static potential (and driving potential) on mass-asymmetry is obtained. From this study we find out that the mass-symmetric system seems to be difficult to fuse and the fusing system with the largest driving potential could be the optimal choice of the projectile-target combination. By comparing the static potential barrier with the dynamic one we find that the latter one is lower than former one obviously, and that the dynamical potential barrier is entrance energy dependent. The maximum and minimum of dynamic potential barriers approach to the diabatic (sudden approximation) and the adiabatic static potential barriers, respectively.
A prototype with 28 modules of 168-channel multi-gap resistive plate chamber (MRPC) time-of-flight system for the STAR experiment at RHIC was built, and its 12 modules (72 readout channels) equipped with read out electronics were tested for 10 weeks at the AGS, BNL from February 2002. The working gas mixtures have significant influence on the performance of MRPC. Several gas mixtures such as 90% C2H2F4+5%iso-C4H10+5%SF6,95.3%C2H2F4+4.7%iso-C4H10 and 100% C2H2F4 were tested. The results on detection efficiency, time resolution and streamer probability are presented.
In the analysis of Beijing Spectrometer (BES) data, the dE/dx and TOF information have been used in the particle identification. When combining the dE/dx and TOF information to do the particle identification, the χ2 of dE/dx and TOF are usually added with equal weight. But the particle identification capability of dE/dx and TOF is different in different momentum region. In this paper, we give the weights of dE/dx and TOF in different momentum region and form a new variable which uses different weights for dE/dx and TOF informations to do the particle identification.
A new type combination PIN detector was developed and studied using γ and 14MeV neutron radiations generated by Dense Plasma Focus device. The study shows that the detector is insensitive to γ radiation, and the sensitivity to neutron depends on the converter target of neutron radiation. The signal to noise of the detector is 30∶1, it is a new type pulse neutron detector in the neutron and γ mixture radiations.
We describe a track finding method based on the Combinatorial Hough Transform (CHT) in the large drift chambers of the L3+C experiment at CERN. With the feature of near parallelism of muons in cosmic multi-muon events, the dominant direction can be estimated from the histogram of directions of segments. Then the CHT in finding the whole track can be greatly optimized. The cross octant reconstruction program can efficiently reconstruct cosmic muon events with multiplicity up to 50.
Detailed studies and discussions on the determination of coupling gap and designing of the dipole mode stabilizer rods in an RFQ with intense beams have been done. By taking use of the existent cold model of one section RFQ, measurements of the eigenfrequencies of the eigen quadrupole and dipole modes, tuning and measurement of the RF field distribution and experiments of the dipole mode stabilizer rods are carried out. By making comparison between the results from the experiments and from simulations, the reliability and creditability of the code used in designing the RFQ cavity is proved. In the same time, a brief discussion on the design of RFQ with stabilization is given.
The formulae of 3rd order quadrupole aberrations are derived with Lie-algebraic map. It is the field extension along the axis that dominates the aberrations. For fixed focal length, the aberrations are small if the quadrupole length is long enough or its aperture is large enough. When the length is comparable to the aperture, the quadrupole with soft edge carries relatively small aberrations.
A full-dimension oxygen-free-copper technological cavity was developed for the study on the design and the technological process of a high-current proton RFQ. The physical and mechanical design, machining and brazing technological studies, and RF performance measurements and tuning were introduced. An ideal field distribution could be reached by tuning cavity, whose consistence and smoothness of the field distributions in the four quadrants meet the demands of use. Its dipole components are small enough, too.
Betatron stochastic cooling will be built to cool hot beams in very short time on HIRFL-CSRm during its stripping injection. Here the transverse cooling is described and simulated. The cooling time and the beam distribution are obtained. The power-limited cooling system, which performance is limited by available output power, is contrasted with non-power-limited system and the upgrading is also mentioned. All these are useful for analysis of experimental data and for design of the cooling system and running, i.e., optimization of the system passband specification of accuracy of the signal’s transmission, etc.
DC-SC photoinjector is a new injector based on the laser-driven photocathode. It is designed to produce the electron beam with high average current required by high average power FEL experiments. For this projector, Cs2Te and Cs3Sb photocathodes are fabricated in a self-designed preparation chamber, which is bakable and the vacuum can reach values of 10－6Pa. Cs2Te is excited by 266nm UV laser, and its quantum efficiency(QE) is above 2.5% for more than 50 hours, and the QE of Cs3Sb at 532nm is about 2% and stable for only several hours in vacuum. They can provide enough electrons for our electron gun. Because of its stability, Cs2Te is adopted in the test facility of the DC-SC photoinjector.
In this paper, we present a general theory of the double-undulator free-electron laser, in which an additional undulator with period close to the beam electron betatron oscillation period in the main undulator is introduced. A set of self-consistent equations is developed to describe the evolution of the optical wave in this device. The basic nonlinear equations are analyzed in the low-gain regime, the high-gain regime, and the saturation regime, respectively. By properly selecting parameters of the additional undulator, we may enhance the gain or efficiency of the free-electron laser.
Strong electronic excitation effect of C60 films induced by 2.0 GeV 136Xe and 2.7GeV 238U ions was investigated by means of Fourier transform infrared (FTIR), Raman Scattering and X-ray diffraction (XRD) spectroscopies. A new peak located at 670 cm－1, which corresponds to an unknown structure, was observed in the FTIR spectra of C60 films irradiated for the first time. The variation in intensity of 670 cm－1 peak with electronic energy loss and irradiation dose were studied. The analysis results indicated that electronic energy transfer dominates the damage process of C60 films. The partial recovery of the damage in irradiated C60 films at middle electronic energy loss is attributed to an annealing effect of the strong electronic excitation. The ion velocity also plays a role in the process of the damage creation.
A new type of coherent THz light source is building in SINAP. It will use the femto-second electron beam passing through a variable elliptically polarized undulator to produce the high bright THz radiation with various linear, elliptical or circular polarization. The paper describes the computation methods and the simulation results of the flux density, spectrum, polarization and coherence for this kind of radiation. For the electron beam with the energy 20MeV, the emmitance 1 5πmm·mrad, the beam length 200fs and the electric charge 50pC, the THz radiation with the horizontal linear polarization or the circular polarization of the maximum flux density of 2×10 9 photons/mm 2/0 1%bw can be obtained at the distance 1m from the center of the undulator with 0 6m length.
For cancer therapy using heavy-ion beams at HIRFL, a simple Positron Emission Tomography(PET) imaging system was made using two position sensitive BGO scintillator detectors. The object images and γ ray energy spectra were measured for the PET. The energy resolution for the 511keV full energy peak is 18.6% and its countiong fraction is 52 4%. Monte Carlo calculations were performed for the PET imaging system by using GEANT3 code. The object images and γ ray energy spectra are in good agreement with the experimental data. In order to develop a PET imaging system with high efficiency, good resolution and low cost, the PET imaging system was optimized.
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