分类： 物理学 >> 核物理学 提交时间： 2016-08-26
摘要： Measurements of strange hadron (K0s, Lambda + anti-Lambda, and Xi+ + Xi-) transverse momentum spectra in pp, pPb, and PbPb collisions are presented over a wide range of rapidity and event charged-particle multiplicity. The data were collected with the CMS detector at the CERN LHC in pp collisions at sqrt(s) = 7 TeV, pPb collisions at sqrt(s[NN]) = 5.02 TeV, and PbPb collisions at sqrt(s[NN]) = 2.76 TeV. The average transverse kinetic energy is found to increase with multiplicity, at a faster rate for heavier strange particle species in all systems. At similar multiplicities, the difference in average transverse kinetic energy between different particle species is observed to be larger for pp and pPb events than for PbPb events. In pPb collisions, the average transverse kinetic energy is found to be slightly larger in the Pb-going direction than in the p-going direction for events with large multiplicity. The spectra are compared to models motivated by hydrodynamics.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-05-30
摘要： Relativistic isobar (^{96}_{44}Ru+^{96}_{44}Ru and ^{96}_{40}Zr+^{96}_{40}Zr) collisions have revealed intricate differences in their nuclear size and shape, inspiring unconventional studies of nuclear structure using relativistic heavy ion collisions. In this study, we investigate the relative differences in the mean multiplicity (R_{ langle N_{ rm ch} rangle}) and the second- (R_{ epsilon_{2}}) and third-order eccentricity (R_{ epsilon_{3}}) between isobar collisions using Optical and Monte Carlo Glauber models. It is found that initial fluctuations and nuclear deformations have negligible effects on R_{ langle N_{ rm ch} rangle} in most central collisions, while both are important for the R_{ epsilon_{2}} and R_{ epsilon_{3}}, the degree of which is sensitive to the underlying nucleonic or sub-nucleonic degree of freedom. These features, compared to real data, may probe the particle production mechanism and the physics underlying nuclear structure.
分类： 物理学 >> 核物理学 提交时间： 2016-08-22
摘要： The polarizations of the Y(1S), Y(2S), and Y(3S) mesons are measured as a function of the charged particle multiplicity in proton-proton collisions at sqrt(s) = 7 TeV. The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The results are extracted from the dimuon decay angular distributions, in two ranges of Y(nS) transverse momentum (10-15 and 15-35 GeV), and in the rapidity interval abs(y)<1.2. The results do not show significant changes from low- to high-multiplicity pp collisions, although large uncertainties preclude definite statements in the Y(2S) and Y(3S) cases.
分类： 物理学 >> 核物理学 提交时间： 2016-08-18
摘要： Charged-particle distributions are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 μb−1, recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on the charged-particle multiplicity are presented. The measurements are performed with charged particles with transverse momentum greater than 500 MeV and absolute pseudorapidity less than 2.5, in events with at least one charged particle satisfying these kinematic requirements. Additional measurements in a reduced phase space with absolute pseudorapidity less than 0.8 are also presented, in order to compare with other experiments. The results are corrected for detector effects, presented as particle-level distributions and are compared to the predictions of various Monte Carlo event generators.
分类： 物理学 >> 核物理学 提交时间： 2025-01-24
摘要： The sign of higher order multiplicity fluctuations is a very important quantity in exploring the QCD phase transition. It is found that the kurtosis of net-baryon is typically negative in the simulations of the dynamics of conserved net-baryon density near the QCD critical point. This paper considers the effects of finite size on the multiplicity fluctuations with equilibrium critical fluctuations. It is found that the multiplicity fluctuations (or magnitude of correlation function D_{ij}) are dramatically suppressed with decreasing system size when the size of the system is small comparing correlation length, which is the so-called acceptance dependence. Consequently, the small correlation function of the small system size results in the magnitude of the negative contribution (\sim D^4_{ij}) in the four-point correlation function dominates over the one of positive term (\sim D^5_{ij}), and this finite size effects induces a dip structure near the QCD critical point.
分类： 物理学 >> 核物理学 提交时间： 2025-01-08
摘要： The sign of higher order multiplicity fluctuations is a very important quantity in exploring the QCD phase transition. It is found that the kurtosis of net-baryon is typically negative in the simulations of the dynamics of conserved net-baryon density near the QCD critical point. This paper considers the effects of finite size on the multiplicity fluctuations with equilibrium critical fluctuations. It is found that the multiplicity fluctuations (or magnitude of correlation function D_{ij}) are dramatically suppressed with decreasing system size when the size of the system is small comparing correlation length, which is the so-called acceptance dependence. Consequently, the small correlation function of the small system size results in the magnitude of the negative contribution (\sim D^4_{ij}) in the four-point correlation function dominates over the one of positive term (\sim D^5_{ij}), and this finite size effects induces a dip structure near the QCD critical point.
分类： 物理学 >> 核物理学 提交时间： 2024-05-17
Yan Zhang
Hao-Ran Zhang
Ren-Bo Wang
Ming-Yu Li
Rui Chen
Hai-Tao Wang
Xiang-Ting Meng
Shu-Min Zhou
Bin Tang
摘要： A passive neutron multiplicity measurement device, FH-NCM/S1, based on field-programmable gate arrays(FPGAs), is developed specifically for measuring the mass of plutonium-240 (240Pu) in mixed oxide fuel. FHNCM/S1 adopts an integrated approach, combining the shift-register analysis mode with the pulse-positiontimestamp mode using an FPGA. The optimal effective length of the 3He neutron detector was determined tobe 30 cm, and the thickness of the graphite reflector was ascertained to be 15 cm through MCNP simulations.After fabricating the device, calibration measurements were performed using a 252Cf neutron source; a detectionefficiency of 43.07% and detector die-away time of 55.79 μs were observed. Nine samples of plutoniumoxide were measured under identical conditions using the FH-NCM/S1 in shift-register analysis mode and aplutonium-waste multiplicity counter. The obtained double rates underwent corrections for detection efficiency(ε) and double gate fraction (f d), resulting in corrected double rates (Dc), which were used to validate the accuracyof the shift-register analysis mode. Furthermore, the device exhibited fluctuations in the measurementresults, and within a single 20-s measurement, these fluctuations remained below 10%. After 30 cycles, therelative error in the mass of 240Pu was less than 5%. Finally, correlation calculations confirmed the robustconsistency of both measurement modes. This study holds specific significance for the subsequent design anddevelopment of neutron multiplicity devices.
分类： 物理学 >> 核物理学 提交时间： 2016-09-09
摘要： The paper presents studies of Bose-Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range pT> 100 MeV and |η|< 2.5 in proton--proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 μb−1, 190 μb−1 and 12.4 nb−1 for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Passive neutron multiplicity counting is widely used as a nondestructive assay technique to quantify mass of plutonium material. One goal of this technique is to achieve good precision in a short measurement time. In this paper, we describe a procedure to derive mass assay variance for multiplicity counting based on the three-parameter model, and analytical equations are established using the measured neutron multiplicity distribution. Monte Carlo simulations are performed to evaluate precision versus plutonium mass under a fixed measurement time with the equations. Experimental data of seven weapons-grade plutonium samples are presented to test the expected performance. This variance analysis has been used for the counter design and optimal gate-width setting at Institute of Nuclear Physics and Chemistry.
分类： 物理学 >> 核物理学 提交时间： 2025-03-04
Zhang, Mr. Haoran
Zhang, Prof. Yan
Liu, Mr. Chi
Hu, Mr. Wenxing
Hu, Mr. Xuandi
Ou, Mr. Xianpei
Qu, Dr. Jin-Hui
Wang, Dr. Ren-Bo
Tang, Prof. Bin
摘要： Ensuring the safeguards and monitoring of enriched uranium is crucial for preventing its illegal theft, destruction, or transfer under arms control. Non-destructive analysis techniques for uranium quantification play a vital role in this effort. The Am-Li source is widely used as an excitation source in Active Uranium Non-destructive Analysis Techniques. However, as acquiring Am-Li becomes increasingly challenging, controllable accelerator-based neutron sources have emerged as a promising alternative due to their superior energy monochromaticity, controlled yield, and on-demand operational capabilities. This study develops an optimized neutron multiplicity measurement system based on a D-D neutron generator, using metallic uranium samples with varying 235U content. Key parameters, including the distance between the neutron generator and a two-layer 3He detector array, 3He tube length, and the material and thickness of the reflector, were optimized via Monte Carlo simulations. The detection efficiency and neutron decay time of the optimized system were evaluated, followed by experimental validation through the quantification of uranium samples with different 235U enrichments and masses. The results indicate that for highly enriched uranium (235U enrichment >50%), the M-C coupling curve yielded a measurement relative deviation of less than 10%, while for other enrichment levels, deviations remained within 100 g. Furthermore, by analyzing fission neutron detection efficiency (εf) and spatial fission rate variations within the sample chamber, a correction factor (k) was introduced using partial least squares regression to account for sample geometry, density, and 235U abundance, reducing the average relative deviation from 20.67% to 8.18%. This research provides a foundation for further development and experimental validation of neutron multiplicity measurement devices utilizing D-D neutron generators.
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