2001 Vol. 25, No. 12
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Abstract:
The observed cross sections of processes e+e－→e+e－,μ+μ－,π+π－J/ψ and hadrons at 24 energy points in the vicinity of ψ(2S) resonance have been measured by BES(Beijing Spectrometer). The resonance cross sections for above four final states take the Breit-Wigner forms. By combining the cross sections of resonance part,continuum(QED or QCD) part and their interferences together with radiative corrections,and then convoluted with the energy spread of BEPC(Beijing Electron and Positron Collider),the χ2 fit of these 4 observed cross sections with the assumption of e-μ-τ universality gives the decay widths and branching ratios of ψ(2S):Γt,Γμ,Γh,Γπ+π－J/ψ,Bμ,Bh,Bπ+π-J/ψ. This article mainly describes the methods for calculating the intregral luminosity and for determining the fitting errors of ψ(2S) decay widths and branching ratios in this scan experiment. The intregral luminosity for each energy point is calculated by using the data of e+e－ final state and the iteration method with assumption of lepton universality,that is Be=Bμ . The errors of decay widths and branching ratios are determined by Monte Carlo sampling method.
The observed cross sections of processes e+e－→e+e－,μ+μ－,π+π－J/ψ and hadrons at 24 energy points in the vicinity of ψ(2S) resonance have been measured by BES(Beijing Spectrometer). The resonance cross sections for above four final states take the Breit-Wigner forms. By combining the cross sections of resonance part,continuum(QED or QCD) part and their interferences together with radiative corrections,and then convoluted with the energy spread of BEPC(Beijing Electron and Positron Collider),the χ2 fit of these 4 observed cross sections with the assumption of e-μ-τ universality gives the decay widths and branching ratios of ψ(2S):Γt,Γμ,Γh,Γπ+π－J/ψ,Bμ,Bh,Bπ+π-J/ψ. This article mainly describes the methods for calculating the intregral luminosity and for determining the fitting errors of ψ(2S) decay widths and branching ratios in this scan experiment. The intregral luminosity for each energy point is calculated by using the data of e+e－ final state and the iteration method with assumption of lepton universality,that is Be=Bμ . The errors of decay widths and branching ratios are determined by Monte Carlo sampling method.
Abstract:
In the framework of the topcolor-assisted multiscale technicolor(TOPCMTC)models,we discuss the s-channel resonance production of the lightest neutral technipion P0 at the First Muon Collider(FMC). Our calculation results show that the effective cross section is quite large and at least larger than that of the standard model Higgs boson h0 by one order of magnitude. Thus,the FMC provides an opportunity for detecting the technipions and testing technicolor theory.
In the framework of the topcolor-assisted multiscale technicolor(TOPCMTC)models,we discuss the s-channel resonance production of the lightest neutral technipion P0 at the First Muon Collider(FMC). Our calculation results show that the effective cross section is quite large and at least larger than that of the standard model Higgs boson h0 by one order of magnitude. Thus,the FMC provides an opportunity for detecting the technipions and testing technicolor theory.
Abstract:
Using the parton distribution functions of Fe given by the extended x-rescaling model,the influence of heavy qarkonium production mechanism to associate J/ψ and γ production in high energy proton-iron collisions is discnssed. The results show that the contribution of the color-octet states should not be ignored. Furthermore,we predict the differential cross section of associate J/ψ and γ. Comparing our theoretical results with the future experiment data,the heavy quarkonium production mechanism can be examined.
Using the parton distribution functions of Fe given by the extended x-rescaling model,the influence of heavy qarkonium production mechanism to associate J/ψ and γ production in high energy proton-iron collisions is discnssed. The results show that the contribution of the color-octet states should not be ignored. Furthermore,we predict the differential cross section of associate J/ψ and γ. Comparing our theoretical results with the future experiment data,the heavy quarkonium production mechanism can be examined.
Abstract:
The SU(2)L×SU(2)R σ-model was extended to a SU(2)L×SU(2)R×U(1)σ-model with electromagnetic interaction. The chiral SU(2)L×SU(2)R×U(1)σ-model with both dynamical breaking and vacuum spontaneous symmetry breaking is investigated by means of the Consistent Equation. It is obtained that when considering dynamical breaking and vacuum spontaneous symmetry breaking and electromagnetic interaction in different cases, σ, π and nucleon have different mass amendments, and the concrete representation forms depending on dynamical symmetry breaking in different ways are abtained for the mass generation of σ, π and nucleon. The equivalences of fundamental scalar fields and composed scalar fields are proved. This paper gives a base of constructing the unified weak-electromagnetic model based on dynamical breaking and vacuum spontaneous symmetry breaking.
The SU(2)L×SU(2)R σ-model was extended to a SU(2)L×SU(2)R×U(1)σ-model with electromagnetic interaction. The chiral SU(2)L×SU(2)R×U(1)σ-model with both dynamical breaking and vacuum spontaneous symmetry breaking is investigated by means of the Consistent Equation. It is obtained that when considering dynamical breaking and vacuum spontaneous symmetry breaking and electromagnetic interaction in different cases, σ, π and nucleon have different mass amendments, and the concrete representation forms depending on dynamical symmetry breaking in different ways are abtained for the mass generation of σ, π and nucleon. The equivalences of fundamental scalar fields and composed scalar fields are proved. This paper gives a base of constructing the unified weak-electromagnetic model based on dynamical breaking and vacuum spontaneous symmetry breaking.
Abstract:
The higher-order powers of squeezing properties of light field for odd and even two-parameter deformed-coherent states have been studied, and the numerical method is used to investigate the influence of the two parameters (q and s) on the properties. The results show that the odd and the even qs-deformed coherent states can exhibit odd number powers of squeezing but no even number powers of squeezing effects. These properties are different from those of the states of the conventional no-deformed light field. These effects can be shown in a number of intervals alternately when r2, which reflects the intensity of the light field in two-parameter deformed coherent state, is changed. When the two parameters q and s are taken certain values and r2 is taken value in a certain interval, the larger of parameter q which deviated from 1 and the smaller of parameter s, the intervals of the unusual properties become larger. The relevant results of the even and odd q-coherent states are contained in more general conclusion of this paper as special case.
The higher-order powers of squeezing properties of light field for odd and even two-parameter deformed-coherent states have been studied, and the numerical method is used to investigate the influence of the two parameters (q and s) on the properties. The results show that the odd and the even qs-deformed coherent states can exhibit odd number powers of squeezing but no even number powers of squeezing effects. These properties are different from those of the states of the conventional no-deformed light field. These effects can be shown in a number of intervals alternately when r2, which reflects the intensity of the light field in two-parameter deformed coherent state, is changed. When the two parameters q and s are taken certain values and r2 is taken value in a certain interval, the larger of parameter q which deviated from 1 and the smaller of parameter s, the intervals of the unusual properties become larger. The relevant results of the even and odd q-coherent states are contained in more general conclusion of this paper as special case.
Abstract:
Intermediate energy radioactive ion beams of 8B and 9C were produced with 75MeV/u 12C beam on 9Be target. Total reaction cross sections σ R for 8B and 9C on silicon target were measured by the transmission method at the second focus of RIBLL. If the two nuclei are treated as normal nuclei, the values of the total cross sectious calculated by Glauber Model are much lower than the experimental ones. Assuming additional tails for the nuclear density distribution of 8B and 9C, the calculated values reproduce the experimental data very well. The experimental results combined with Glauber theory analysis show that 8B and 9C may be of a halo structure.
Intermediate energy radioactive ion beams of 8B and 9C were produced with 75MeV/u 12C beam on 9Be target. Total reaction cross sections σ R for 8B and 9C on silicon target were measured by the transmission method at the second focus of RIBLL. If the two nuclei are treated as normal nuclei, the values of the total cross sectious calculated by Glauber Model are much lower than the experimental ones. Assuming additional tails for the nuclear density distribution of 8B and 9C, the calculated values reproduce the experimental data very well. The experimental results combined with Glauber theory analysis show that 8B and 9C may be of a halo structure.
Abstract:
A new model, based on unified Hauser-Feshbach and exciton model, for neutron induced light nucleus reaction has been developed. In case of E n≤20MeV, the total cross section, non-elastic cross section, elastic angular distribution, and the energy-angular spectra of outgoing neutrons in n+11B reaction have been calculated. Especially the double-differential cross section of outgoing neutrons particles of the 11B(n,xn) reaction are calculation. Because of strong recoil effect in light nucleus reactions, the energy balance is strictly takeninto account. In case of 11B, it has more reaction channels and complex reaction mechanism, and the two-body separations are also included in the calculation. This new model describes these characters of 11B very well. From the comparison between calculated results and experimental data, one can see that this model works well in calculation both for cross section and for energy-angular distributions of outgoing neutrons.
A new model, based on unified Hauser-Feshbach and exciton model, for neutron induced light nucleus reaction has been developed. In case of E n≤20MeV, the total cross section, non-elastic cross section, elastic angular distribution, and the energy-angular spectra of outgoing neutrons in n+11B reaction have been calculated. Especially the double-differential cross section of outgoing neutrons particles of the 11B(n,xn) reaction are calculation. Because of strong recoil effect in light nucleus reactions, the energy balance is strictly takeninto account. In case of 11B, it has more reaction channels and complex reaction mechanism, and the two-body separations are also included in the calculation. This new model describes these characters of 11B very well. From the comparison between calculated results and experimental data, one can see that this model works well in calculation both for cross section and for energy-angular distributions of outgoing neutrons.
Abstract:
The couplings of ΔπN and πNN are calculated by employing the relativistic quark model incorporated with pion meson cloud. Our results indicate the important role of the pion meson cloud on Δ(1232) resonance. Therefore, the pion meson cloud should be considered in the low energy region.
The couplings of ΔπN and πNN are calculated by employing the relativistic quark model incorporated with pion meson cloud. Our results indicate the important role of the pion meson cloud on Δ(1232) resonance. Therefore, the pion meson cloud should be considered in the low energy region.
Abstract:
The directed and elliptic flow in collisions of 40Ca+40Ca at energies from 30MeV/nucleon to 150MeV/nucleon is well studied in an isospin-dependent quantum molecule dynamics model (IQMD). With increasing incident energy, the directed flow rises from the negative to the positive and the elliptic flow shows decrease with increasing incident energy. The directed flow and the elliptic flow are sensible of the impact parameter and incident energy but they are not very sensible of systematic energy. The directed flow and the elliptic flow are also not very sensible of the EOS because of the combined systematic mass. Systematic studies of the cluster mass dependence are also carefully performed and the elliptic flow of heavy cluster mass is larger than that of light cluster mass. The difference of elliptic flow between the heavy cluster mass and the light one will be not very obvious with increasing incident energy because of large number of light cluster mass.
The directed and elliptic flow in collisions of 40Ca+40Ca at energies from 30MeV/nucleon to 150MeV/nucleon is well studied in an isospin-dependent quantum molecule dynamics model (IQMD). With increasing incident energy, the directed flow rises from the negative to the positive and the elliptic flow shows decrease with increasing incident energy. The directed flow and the elliptic flow are sensible of the impact parameter and incident energy but they are not very sensible of systematic energy. The directed flow and the elliptic flow are also not very sensible of the EOS because of the combined systematic mass. Systematic studies of the cluster mass dependence are also carefully performed and the elliptic flow of heavy cluster mass is larger than that of light cluster mass. The difference of elliptic flow between the heavy cluster mass and the light one will be not very obvious with increasing incident energy because of large number of light cluster mass.
Abstract:
The recent development of superdeformed identical bands are briefly reviewed. Some typical superdeformed bands are analyzed by the formula of Bohr-Mottelson's I(I+1) expansion. The results show that the dynamic moments of inertia J(2) of so-called two identical bands are very similar, but kinetic moments of inertia J (1) and bandhead moments of inertia J0 aren't equal. Signature partner bands are almost identical. Their J0,J(1),J(2) are almost identical respectively. Bohr-Mottelson Model is still one model which successfully explains the formation of identical bands.
The recent development of superdeformed identical bands are briefly reviewed. Some typical superdeformed bands are analyzed by the formula of Bohr-Mottelson's I(I+1) expansion. The results show that the dynamic moments of inertia J(2) of so-called two identical bands are very similar, but kinetic moments of inertia J (1) and bandhead moments of inertia J0 aren't equal. Signature partner bands are almost identical. Their J0,J(1),J(2) are almost identical respectively. Bohr-Mottelson Model is still one model which successfully explains the formation of identical bands.
Abstract:
We argue that effective pion mass in nuclear matter obtained from chiral effective lagrangians is unique and does not depend on off-mass-shell extensions of the pion fields as e. g. the PCAC choice. How chiral perturbation theory can be applied to the analysis of s-wave pion propagation is discussed. We consider tree level lagrangians throughout, working to O(Q 2). We illustrate the results for homogeneous, isotropic, isospin symmetric and spin-unpolarized nuclear matter, and evaluate nucleon operators in the mean field approximation, such that the corresponding results hold modulo nuclear correlation corrections. The effective pion mass in isospin symmetric nuclear matter is predicted to increase slightly with increasing nuclear density, whereas the effective time-like pion decay constant and the magnitude of the density-dependent quark condensate decrease appreciably. We work out the in-medium pion mass, the effective pion decay constant, the in-medium quark condensate, the Gell-Mann-Oakes-Renner relation and the PCAC relation in nuclear matter. The in-medium GMOR relation as well as other in-medium identities are studied in addition. Finally, we discuss how the new developments about non-relativistic chiral lagrangians and generalizations to four-quark condensates constrain the structure of the in-medium chiral lagrangians, sevral constraints on effecttive lagrangians for the description of the pion propagation in isospin symmetric, isotropic and homogenous nuclear matter.
We argue that effective pion mass in nuclear matter obtained from chiral effective lagrangians is unique and does not depend on off-mass-shell extensions of the pion fields as e. g. the PCAC choice. How chiral perturbation theory can be applied to the analysis of s-wave pion propagation is discussed. We consider tree level lagrangians throughout, working to O(Q 2). We illustrate the results for homogeneous, isotropic, isospin symmetric and spin-unpolarized nuclear matter, and evaluate nucleon operators in the mean field approximation, such that the corresponding results hold modulo nuclear correlation corrections. The effective pion mass in isospin symmetric nuclear matter is predicted to increase slightly with increasing nuclear density, whereas the effective time-like pion decay constant and the magnitude of the density-dependent quark condensate decrease appreciably. We work out the in-medium pion mass, the effective pion decay constant, the in-medium quark condensate, the Gell-Mann-Oakes-Renner relation and the PCAC relation in nuclear matter. The in-medium GMOR relation as well as other in-medium identities are studied in addition. Finally, we discuss how the new developments about non-relativistic chiral lagrangians and generalizations to four-quark condensates constrain the structure of the in-medium chiral lagrangians, sevral constraints on effecttive lagrangians for the description of the pion propagation in isospin symmetric, isotropic and homogenous nuclear matter.
Abstract:
The total reaction cross sections of some halo nucleis on the stable nucleus have been calculated by using improved Glauber theory, which includes quantum correction, Coulomb correction and isospin effects of nucleon-nucleon collision under the assumption of the effective nuclear density distribution. The effects of halo structure on the total reaction cross section of the halo nucleus on the stable nucleus have been investigated. It is found that one can get a satisfactory agreement between the calculation results and the experimental data after considering the halo structure of halo nuclei, such as 11Be,14Be and 11Li, which means the different mean fields for the halo nuclei and stable nuclei. Meanwhile it is clear that the medium correction for nucleon-nucleon collision has little effect on the total reaction cross sections induced by halo nuclei due to the very weak binding and quite thin density, which is quite different from the reactions induced by stable nuclei with salient medium corrections.
And then according to experimental total reaction cross section of halo nucleus on stable nucleus we have gotten the density distributions of halo nuclei 11Be,14Be and 11Li with a long tail of halo neutron distribution and root mean square (RMS) radii of them. It is obvious that the large RMS radii and extended density distribution in comparison with their neighborhood nuclei demonstrate that 11Be,14Be and 11Li are typical halo nuclei.
The total reaction cross sections of some halo nucleis on the stable nucleus have been calculated by using improved Glauber theory, which includes quantum correction, Coulomb correction and isospin effects of nucleon-nucleon collision under the assumption of the effective nuclear density distribution. The effects of halo structure on the total reaction cross section of the halo nucleus on the stable nucleus have been investigated. It is found that one can get a satisfactory agreement between the calculation results and the experimental data after considering the halo structure of halo nuclei, such as 11Be,14Be and 11Li, which means the different mean fields for the halo nuclei and stable nuclei. Meanwhile it is clear that the medium correction for nucleon-nucleon collision has little effect on the total reaction cross sections induced by halo nuclei due to the very weak binding and quite thin density, which is quite different from the reactions induced by stable nuclei with salient medium corrections.
And then according to experimental total reaction cross section of halo nucleus on stable nucleus we have gotten the density distributions of halo nuclei 11Be,14Be and 11Li with a long tail of halo neutron distribution and root mean square (RMS) radii of them. It is obvious that the large RMS radii and extended density distribution in comparison with their neighborhood nuclei demonstrate that 11Be,14Be and 11Li are typical halo nuclei.
Abstract:
With GEANT3 frame, we simulate the lead-scintillating fiber type barrel shower counter (BSC) of BESⅢ. The structure of BSC in the simulation is analogous to Φ Factory's, and it's thinkness is 14.4X 0. The simulations show that the shower time information read-out is necessary for improving the Z spatial resolution, the π0 invariant mass resolution and for rejecting fake photons. Also, the energy resolution σ E/E(6%/E), the relation of angle resolution σ with readout granularity and the relations of mass resolution of π0 σ m/m with light yield, attenuation length, readout granularity are given, where m is the invariant mass of π0 reconstructed by two photons.
With GEANT3 frame, we simulate the lead-scintillating fiber type barrel shower counter (BSC) of BESⅢ. The structure of BSC in the simulation is analogous to Φ Factory's, and it's thinkness is 14.4X 0. The simulations show that the shower time information read-out is necessary for improving the Z spatial resolution, the π0 invariant mass resolution and for rejecting fake photons. Also, the energy resolution σ E/E(6%/E), the relation of angle resolution σ with readout granularity and the relations of mass resolution of π0 σ m/m with light yield, attenuation length, readout granularity are given, where m is the invariant mass of π0 reconstructed by two photons.
Abstract:
An analysis of the electromagnetic field in 2D uniform and axis-symmetric structures based on FEM (Finite Element Method) is presented in this paper. The equation of FEM is derived based on the Maxwell equations and variational theory. The resulting tridiagonal matrix in FEM equation is optimized to reduce band-width of the matrix and the calculation time. Subspace method is applied to solve the eigenvalue equation where the matrices are sparse and make the solver run faster. The number of eigenvalue and eigenvector can be selected by the user which makes the solver-more efficient. Irregular triangle element is used for meshing to describe the structure geometry with good approximation and improve the accuracy of the solution. Numerical results for rectangle waveguide, pill-box cavity and disc-loaded structure show that our finite element method has high accuracy, good convergence and fast running speed. Comparing with SUPERFISH program, the FEM method is advantageous in both accuracy and speed. The accuracy of our FEM is almost the same as the variational method which is used as a basic method in many fields. All strategy used here can be applied to the 3-dimension structure and other eigenvalue problems.
An analysis of the electromagnetic field in 2D uniform and axis-symmetric structures based on FEM (Finite Element Method) is presented in this paper. The equation of FEM is derived based on the Maxwell equations and variational theory. The resulting tridiagonal matrix in FEM equation is optimized to reduce band-width of the matrix and the calculation time. Subspace method is applied to solve the eigenvalue equation where the matrices are sparse and make the solver run faster. The number of eigenvalue and eigenvector can be selected by the user which makes the solver-more efficient. Irregular triangle element is used for meshing to describe the structure geometry with good approximation and improve the accuracy of the solution. Numerical results for rectangle waveguide, pill-box cavity and disc-loaded structure show that our finite element method has high accuracy, good convergence and fast running speed. Comparing with SUPERFISH program, the FEM method is advantageous in both accuracy and speed. The accuracy of our FEM is almost the same as the variational method which is used as a basic method in many fields. All strategy used here can be applied to the 3-dimension structure and other eigenvalue problems.
Abstract:
Study on the section-division of superconducting proton linac is carried out in detail. Firstly, the principles of the section-division, the determination of the cell number of the superconducting cavity and the value of the geometric βG are introduced and discussed. Secondly, the advantages and the shortcomings of the symmetric division and non-symmetric division are examined, respectively. At last, an example for the section-division of a superconducting proton linac with an energy range from 100MeV to 1GeV is given for both cases of symmetric and non-symmetric divisions.
Study on the section-division of superconducting proton linac is carried out in detail. Firstly, the principles of the section-division, the determination of the cell number of the superconducting cavity and the value of the geometric βG are introduced and discussed. Secondly, the advantages and the shortcomings of the symmetric division and non-symmetric division are examined, respectively. At last, an example for the section-division of a superconducting proton linac with an energy range from 100MeV to 1GeV is given for both cases of symmetric and non-symmetric divisions.
Abstract:
Synchrotron radiation X-ray reflection method is used to study the depth distribution of Ge atoms in Si crystals caused by surface segregation during the MBE growth. The distribution of Ge atoms in Si crystal is found to have asymmetric exponential shape by simulating the experimental reflectivity based on X-ray reflection theory and Parratt method. The distribution decay lengths forward and backward along the growth direction are obtained as 8A and 3A, respectively, and do not change with different thicknesses of the Ge layers. The influences on X-ray reflectivity of different parameters, such as the thickness of the Si cap layer, the decay length, the surface roughness, and the thickness of SiO2 over the surface are discussed briefly.
Synchrotron radiation X-ray reflection method is used to study the depth distribution of Ge atoms in Si crystals caused by surface segregation during the MBE growth. The distribution of Ge atoms in Si crystal is found to have asymmetric exponential shape by simulating the experimental reflectivity based on X-ray reflection theory and Parratt method. The distribution decay lengths forward and backward along the growth direction are obtained as 8A and 3A, respectively, and do not change with different thicknesses of the Ge layers. The influences on X-ray reflectivity of different parameters, such as the thickness of the Si cap layer, the decay length, the surface roughness, and the thickness of SiO2 over the surface are discussed briefly.
Abstract:
N-type crystalline Si (100) implanted with 5keV B ions was subsequently irradiated with MeV Si, O and F ions. The B atom profiles were measured by means of secondary ion mass spectrometer after the treatment of rapid thermal annealing. The results show that the transient enhanced diffusion of B atoms is effectively limited by the post-implantation of high energy ions at high dose. At the same irradiation conditions, it is found that the existence of a SiO2 layer in the near surface of Si is even more effective in suppressing the transient enhanced diffusion of the doped B atoms. The results are qualitatively discussed in combination with the analyses of RBS/c measurements and calculation of the DICADA code.
N-type crystalline Si (100) implanted with 5keV B ions was subsequently irradiated with MeV Si, O and F ions. The B atom profiles were measured by means of secondary ion mass spectrometer after the treatment of rapid thermal annealing. The results show that the transient enhanced diffusion of B atoms is effectively limited by the post-implantation of high energy ions at high dose. At the same irradiation conditions, it is found that the existence of a SiO2 layer in the near surface of Si is even more effective in suppressing the transient enhanced diffusion of the doped B atoms. The results are qualitatively discussed in combination with the analyses of RBS/c measurements and calculation of the DICADA code.
Abstract:
A flowing gas proportional counter (FGPC) as the detector for astronomical observation in soft X-ray (0.2-3.5keV) range is calibrated on the 3W1B beamline at Beijing Synchrotron Radiation Facility (BSRF). The dead time, counting rate plateau curves, X-ray energy linearity, energy resolution and window transparency of the FGPC have been measured. By means of a calibrated photodiode (AXUV 100G IRD USA, calibrated in NIST) as a standard detector, the efficiency of the FGPC as function of photons energy has been obtained with an uncertainty between 10%-18%.
A flowing gas proportional counter (FGPC) as the detector for astronomical observation in soft X-ray (0.2-3.5keV) range is calibrated on the 3W1B beamline at Beijing Synchrotron Radiation Facility (BSRF). The dead time, counting rate plateau curves, X-ray energy linearity, energy resolution and window transparency of the FGPC have been measured. By means of a calibrated photodiode (AXUV 100G IRD USA, calibrated in NIST) as a standard detector, the efficiency of the FGPC as function of photons energy has been obtained with an uncertainty between 10%-18%.
Abstract:
Using the dynamical transport approach RQMD with a correlation afterburner,the behavior of two-pion HBT parameters is studied for Au+Au collisions at RHIC energy s=200GeV/u. We find that the HBT size parameters do reflect the source geometry at freeze-out for both central and non-central collisions. The transverse momentum dependence of HBT size parameters is insensitive to the pressure developed during the early stage of the collisions,rather,it is sensitive to the degree of spacemomentum correlation.
Using the dynamical transport approach RQMD with a correlation afterburner,the behavior of two-pion HBT parameters is studied for Au+Au collisions at RHIC energy s=200GeV/u. We find that the HBT size parameters do reflect the source geometry at freeze-out for both central and non-central collisions. The transverse momentum dependence of HBT size parameters is insensitive to the pressure developed during the early stage of the collisions,rather,it is sensitive to the degree of spacemomentum correlation.
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