2000 Vol. 24, No. 8
TeV gamma rays will be attenuated or absorbed due to the interaction with soft photons in intergalactic space. The spectra of Mrk421 and Mrk501 during their flaring have been observed by ACTs. Using the data obtained with Tibet Ⅱ/HD AS array from October of 1995 to Augest of 1997,the preliminary results of energy density of intergalactic infrared radiation field are presented in this paper. Analysis shows that no statistically significant absorption evidence of high energy gamma rays is found up to around 30 TeV.
It is shown that the magnetic monopole and the electric monopole can be generated on an unified model based on the Hopf bundle (S3=S2×S1) with the structure group U(1). The connection on the base manifold S2 is divided into two types,the type of electric monopole and the type of magnetic monopole. The magnetic charge obeys the quantized condition,and the electric monopole is the solution where the magnetic quantum number n=0. The electric monopole and the magnetic monopole have the theoretical identity. They are two different states of one physical object. The time coordinate is introduced by the homotopic shift,and the electric monopole appears in an active model in the Minkowski space. The theory is Lorentz invariant.
The O(αs) correction to the inclusive decay of b→X sγ is calculated in the technicolor model with scalars. We find that the deviation of the decay width from the standard model prediction can be reduced by as much as 50% when ALEPH experimental value is used. In particular,the CLEO measurement which corresponds to the 33% reduction gives more stringent constraint on the parameter space in the technicolor with scalars model than B-B mixing. The model predictions can be observable in the forthcoming few years with upgraded CLEO detector and B-factories.
130Pm and 128 Pr were produced by irradiation of 96Ru with 171MeV 36Ar beam,and a He-jet recoil tape transport system transported radioactivities to shielded reigon. Based on X-γ-t and γ-γ-t coincidence measurements ,the (EC+β+)decay scheme of 130Pm was proposed for the first time and the (EC+β+)decay scheme of 128Pr was revised.
The angular distributions for elatic scattering of the two systems,16O+94Zr at energies 52,57,59,62,72,82 and 92 MeV and 16O+116Sn at energies 57,59,62,67,72,82 and 92 MeV have been measured.The scattered ions were datected by the Beijing Q3D magnetic spectrometer and its heavy ion focal plane detector.The optical model analysis of the data was made with the Coupled Channels code ECIS, and the optical potential parameters have been obtained by fitting the data.Within the limited data,the phenomenon of the ‘threshold anomaly’is observed.
One of our recent works demonstrates that the previous quark mass scaling should be modified, which has significantly changed the density behavior of the sound velocity in strange quark matter. In the present study, we provide a selfconsistent thermodynamic treatment to determine the parmeter in the mass formula, and prove that, under the new quark mass scaling, proper negative charges can still lower the critical density, and thus be favorable to the searches for strangelets in heavy ion experiments. Naturally, too much negative charges can still make it impossible to maintain flavor equilibrium.
By using the alpha cluster structure model of hypernuclei and the phenomenological interaction potential between Λ hyperon and α-particle, the Λ seperate energy of the hypernucleus 13ΛC is calculated. A good agreement with the experimental data is achieved. Based on this the Λ-seperate energy of the hypernucleus 17ΛO is predicted. It is consistent with the empirical value of 17ΛO and advantages over the existing theoretical calculation made up-to-date.
The Λ multiplicity and Λ/p ratio are studied by hadron transportation-string fragmentation model in relativistic heavy ion collisions. Firstly, the dependence of Λ multiplicity and Λ/p ratio on the system size and the collision centrality is studied. It shows that the Λ and p multiplicities go up as the increase of system size and the increase of collision centrality. However, their ratio keeps almost a constant. The effect of Λ annihilation cross section to Λ multiplicity and Λ/p ratio is also studied. It is found that this effect is weak: Λ multiplicity and Λ/p ratio have a little amount of increase by the decrease of Λ annihilation cross section. Even the cross section is down to zero, Λ/p ratio is only 1.2 in 200A GeV AuAu head on collision. The Λ/p ratio is obtained to be 0.28 in pp collision, lying in the range of experimental data:0.2—0.3. It is also obtained that the ratio in AA collisions is 3—5 times of that in pp collision.
The ground-state properties of Pr isotopic chain have been studied in the framework of the relativistic mean field(RMF) theory. The pairing correlation is treated by BCS method and the isospin dependent pairing forces have been used. The ‘blocking’ method is used to deal with the unpaired nucleon and the axially symmetric deformation is assumed. The theoretical results show that the RMF theory with non-linear meson self interactions provides a good description of the binding energy, the deformation of nuclei, the density distributions of neutrons and protons, the isotope shifts and so on over a large isospin range of Pr isotopes. The theoretical results are in good agreement with those obtained from the Finite Range Droplet Model. The domain of the validity of the BCS approximation is checked, and the extent and the origin of the BCS failure are studied.
The reactions for intermediate energy protons bombarding 208Pb have been analyzed by the quantum molecular dynamics model (QMD). It is found that the whole reaction process can be divided into three stages, i.e. the direct, the cascade and the evaporation stage. The time scale of the change of reaction mechanism in the process of reaction is investigated. The corresponding time scales of the direct, the cascade and the evaporation stage are about<30 fm/c, 30—100fm/c and >100fm/c, respectively. The calculation results of the double differential cross sections for reaction 208Pb (p, xn) can reproduce the experimental results reasonably well.
The beam dynamics of longitudinal coupled bunch instability with unequal spaced bunches is studied by means of Vlasov equation method in this paper. Our formula will be the same as Samson’s when bunches equally spaced and populated, and for the unequal spaced bunches, our calculation agrees well with experimental results of BEPC.
The emission character and discharge character of a purchased LaMo cathode material applied in high current ion source are measured. It is found that the LaMo cathode is an efficient heat cathode emitter. When used in high current ion source, the cathode arc is in normal operation and the lifetime of cathode is longer than that of LaB6. From the practical use of this cathode, the LaMo cathode is indecd a new kind applicable cathode of high current ion source.
The betatron and synchrotron tunes are measured frequently during the period of the machine operation and machine studies. The tune measurement system of the BEPC storage ring includes a spectrum analyzer, two sets of the stripline, two voltage amplifiers and a beam oscillation detector. This paper gives the detailed description of the upgraded tune measurement system in the BEPC storage ring.
The concept of moving spin of the relativistic particle is further discussed in the quantum field theory. Two new operators, field quanta spin and moving spin of quantum field system, are introduced. We show that, in virtue of these two operators, some problem in the quantum field theory concerned spin can be neatly settled.
A general formalism is given for the collective motion in a system with general multipolar-deformations, which is treated as vibrations in body-fixed frame and rotation of whole system about the axes of Lab-system, as well as the coupling between vibrations and rotation. 18 various body-fixed frames are defined for octupole deformed system, which shows they can be put into 9 various classifies and the determinants of metric matrix in the body-fixed frames defined by the variables a30,a31,a32,b31and a30,a31,b31,b32are 9a2 32 and 9b2 32, which are the simplest.
The influence of multiplicity distribution (fluctuation of multiplicity in the event space) on the erraticity behaviour in high energy collisions is investigated via Monte Carlo simulation and compared with the experimental results from NA27 data. It is shown that, the erraticity phenomenon is insensitive to the multiplicity fluctuation. When the average multiplicity is low this phenomenon is dominated by the statistical fluctuations, also in the case of multiplicities fluctuating from event to event.
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