分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: The cross section for the process e+e− ! π+π−J/ψ is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb−1 of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (4222.0 ± 3.1±1.4) MeV/c2 and a width of (44.1±4.3±2.0) MeV, while the second one has a mass of (4320.0±10.4± 7.0) MeV/c2 and a width of (101.4+25.3−19.7 ± 10.2) MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y (4260) resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in e+e− ! π+π−J/ψ for the first time. The statistical significance of this resonance is estimated to be larger than 7.6σ.The mass and width of the second resonance agree with the Y (4360) resonance reported by the BABAR and Belle experiments within errors. Finally, the Y (4008) resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: The Circular Electron Positron Collider (CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. Using Monte Carlo samples of 5 ab−1 at 250 GeV center-of-mass energy, the benchmark luminosity of CEPC Higgs runs, model independent (MI) analyses on Higgsstrahlung (ZH) cross section σZH and Higgs mass mH are performed with ZH events where the Z boson decays into a pair of muons. The relative precision of σZH could reach 0.92\% and the mH could be measured to an accuracy of 6.5 MeV. Using information from Higgs decay final states, the backgrounds could be further reduced, leading to a mass precision of 5.4 MeV. The impacts of tracker size are investigated and parameterized for these measurements. Using similar analysis technology, we analyzed the capability of CEPC in measuring the Higgs invisible decay. Using ZH (Z→μ+μ−) events at 5 ab−1, the upper limit of invisible decay cross section beyond the standard model (SM) σBSMZH,H→inv can be determined to be 2.0 fb at 95\% confidence level.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: Based on e+e− annihilation data samples collected with the BESIII detector at the BEPCII collider at 13 center of mass energies from 4.008 to 4.600 GeV, measurements of the Born cross section of e+e− → pp¯π0 are performed. No significant resonant structure is observed in the measured energy-dependent cross section. The upper limit on the Born cross section of e+e− → Y (4260) → pp¯π0 at the 90% C.L. is determined to be 0.01 pb.
分类: 物理学 >> 核物理学 提交时间: 2016-09-12
摘要: The cross-section for the production of a single top quark in association with a W boson in proton--proton collisions at s√=8 TeV is measured. The dataset corresponds to an integrated luminosity of 20.3 fb−1, collected by the ATLAS detector in 2012 at the Large Hadron Collider at CERN. Events containing two leptons and one central b-jet are selected. The Wt signal is separated from the backgrounds using boosted decision trees, each of which combines a number of discriminating variables into one classifier. Production of Wt events is observed with a significance of 7.7σ. The cross-section is extracted in a profile likelihood fit to the classifier output distributions. The Wt cross-section, inclusive of decay modes, is measured to be 23.0±1.3(stat.)+3.2−3.5(syst.)±1.1(lumi.) pb. The measured cross-section is used to extract a value for the CKM matrix element |Vtb| of 1.01±0.10 and a lower limit of 0.80 at the 95\% confidence level. The cross-section for the production of a top quark and a W boson is also measured in a fiducial acceptance requiring two leptons with pT>25 GeV and |η|20 GeV and |η|20 GeV, including both Wt and top-quark pair events as signal. The measured value of the fiducial cross-section is 0.85±0.01(stat.)+0.06−0.07(syst.)±0.03(lumi.) pb.
分类: 物理学 >> 核物理学 提交时间: 2016-09-10
摘要: We present an extraction of azimuthal correlations between two pairs of charged pions detected in opposite jets from electron-positron annihilation. These correlations may arise from the dependence of the di-pion fragmentation on the polarization of the parent quark in the process e+e−→qq¯. Due to the correlation of the quark polarizations, the cross-section of di-pion pair production, in which the pion pairs are detected in opposite jets in a dijet event, exhibits a modulation in the azimuthal angles of the planes containing the hadron pairs with respect to the production plane. The measurement of this modulation allows access to combinations of fragmentation functions that are sensitive to the quark's transverse polarization and helicity. Within our uncertainties we do not observe a significant signal from the previously unmeasured helicity dependent fragmentation function G⊥1. This measurement uses a dataset of 938~fb−1 collected by the Belle experiment at or near s√≈10.58 GeV.
分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-04-29
摘要: One-neutron stripping process between 6Li and 209Bi was studied at 28, 30, and 34 MeV using the in-beam γ-ray spectroscopy method. The γ-γ coincident analysis clearly identified two γ-rays feeding the ground and long-lived isomeric states, which were employed to determine the cross section. The one-neutron stripping cross sections were similar to the cross sections of complete fusion in the 6Li+209Bi system, but the one-neutron stripping cross sections decreased more gradually at the sub-barrier region. A coupled-reaction-channel calculation was performed to study the detailed reaction mechanism of the one-neutron stripping process in 6Li. The calculations indicated that the first excited state of 5Li is critical in the actual one-neutron transfer mechanism, and the valence proton of 209Bi can be excited to the low-lying excited state in (6Li, 5Li) reaction, unlike in the (d,p) reaction.
分类: 物理学 >> 核物理学 提交时间: 2023-10-09
摘要: Photonuclear reactions using a laser Compton scattering (LCS) gamma source provide a new method forproducing radioisotopes for medical applications. Compared with the conventional method, this method has theadvantages of a high specific activity and less heat. Initiated by the Shanghai Laser Electron Gamma Source(SLEGS), we conducted a survey of potential photonuclear reactions, (, n), (, p), and (, ) whose cross#2;sections can be measured at SLEGS by summarizing the experimental progress. In general, the data are rareand occasionally inconsistent. Therefore, theoretical calculations are often used to evaluate the production ofmedical radioisotopes. Subsequently, we verified the model uncertainties of the widely used reaction codeTALYS-1.96, using the experimental data of the 100Mo(, n) 99Mo, 65Cu(, n) 64Cu, and 68Zn(, p) 67Cu reac#2;tions.
分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The nuclear dynamical deformation, the fusion probability and the evaporation residue (ER) cross sections for the synthesis of superheavy nuclei are studied with the di-nuclear system model and the related dynamical potential energy surface. The intrinsic energy and the maximum dynamical deformations for 48Ca+248Cm are calculated. The effect of dynamical deformation on the potential energy surface and fusion is investigated. It is found that the dynamical deformation influences the potential energy surface and fusion probability significantly. The dependence of the fusion probability on the angular momentum is investigated. The ER cross sections for some superheavy nuclei in 48Ca induced reactions are calculated and it is found that the theoretical results are in good agreement with the experimental results.
分类: 物理学 >> 核物理学 提交时间: 2023-07-12
摘要: The 232Th(n,f) cross-section is very important in basic nuclear physics and applications based on the Th/U fuel cycle. Using the time-of-flight method and a multi-cell fast fission ionization chamber, a novel measurement of the 232Th(n,f) cross-section relative to 235U in the 1200 MeV range was performed at the China Spallation Neutron Source Back-n white neutron source (Back-n). The fission event-neutron energy spectra of 232Th and 235U fission cells were measured in the single-bunch mode. Corrected 232Th/235U fission cross-section ratios were obtained, and the measurement uncertainties were 2.53.7% for energies in the 220 MeV range and 3.66.2% for energies in the 20200 MeV range. The 232Th(n,f) cross-section was obtained by introducing the standard cross-section of 235U(n,f). The results were compared with those of previous theoretical calculations, measurements, and evaluations. The measured 232Th fission cross-section agreed with the main evaluation results in terms of the experimental uncertainty, and 232Th fission resonances were observed in the 13 MeV range. The present results provide 232Th(n,f) cross-section data for the evaluation and design of Th/U cycle nuclear systems.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: We report a measurement of differential cross section of π0 pair production in single-tag two-photon collisions. These results are obtained with 759fb−1 of the data collected with the Belle detector at the KEKB asymmetric energy e+e−collider. The cross section is measured for Q2 up to 30 GeV2, where Q2 is the negative of the invariant mass squared of the tagged virtual photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and |cosθ∗| < 1.0 for the total energy and pion scattering angle, respectively. The transition form factor of the f0(980) and that of the f2(1270)with the helicity-0,-1, and -2 components separately are measured for the first time and are compared with theoretical calculations.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: The cross sections of the Higgs production and the corresponding backgrounds of e+e− annihilations at the CEPC (Circular Electron and Positron Collider) are calculated by a Monte-Carlo method, and the beamstruhlung effect at the CEPC is carefully investigated. The potential for new physics beyond the Standard Model at the CEPC is discussed.
分类: 物理学 >> 核物理学 提交时间: 2016-09-09
摘要: Various differential cross-sections are measured in top-quark pair (tt¯) events produced in proton-proton collisions at a centre-of-mass energy of s√=7 TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of 4.6 fb−1. The differential cross-sections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a top-quark proxyreferred to as the pseudo-top-quark as well as the pseudo-top-quark pair system. The dependence of the measurement on theoretical models is minimal. The measurements are performed on tt¯ events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a b-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the W boson produced by the top-quark decay in events with a single charged lepton. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.
分类: 物理学 >> 核物理学 提交时间: 2016-08-29
摘要: This paper describes a measurement of the inclusive top quark pair production cross-section (σtt¯) with a data sample of 3.2 fb−1 of proton--proton collisions at a centre-of-mass energy of s√=13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron--muon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously σtt¯ and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be: σtt¯= 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented.
分类: 物理学 >> 核物理学 提交时间: 2023-09-13
摘要: The total absolute cross sections of single- and double-electron capture (SEC and DEC) in the collisions of He2+ with He and Ne8+ with O2, N2, and CH4 were studied in the energy ranges 3.5 to 50 keV/u and 2.8 to 40 keV/u, respectively. Through a deep analysis of the experimental systematic uncertainties in the measurement procedure and data evaluation, the error in the experimental results of the SEC cross sections is less than 9%. Within the uncertainties, the present results of the He2+ -He collision show good consistency with previous measurements, validating the experimental system and paving the way for precise measurements of EC cross sections for a variety of ions and neutral gases. The present measurements allow for a test of EC theory and provide crucial EC cross section data for the establishment of plasma models in fusion research and astrophysical X-ray studies.
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: With a Geant4 software package based on the Monte Carlo method, a multi-cell 4 detection system is designed, which consists of 40 Gadolinium-loaded liquid scintillation detectors. These detectors, associated with a fission chamber in its geometrical center, constitute a platform. This platform is mainly used for the measurement of a fissionable nucleus (n, 2n) reaction cross section. In order to properly determine the experimental set-up, we carry out a systematic numerical simulation using our model which is established by the Geant4 software package. This work provides rich and valuable reference data for experiments on the fissionable nucleus (n, 2n) cross section measurement in the future.
分类: 物理学 >> 核物理学 提交时间: 2016-09-12
摘要: The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for tt¯events in the lepton+jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum for values above 300 GeV. The hadronically decaying top quark is reconstructed as an anti-kt jet with radius parameter R=1.0 and identified with jet substructure techniques. The observed yield is corrected for detector effects to obtain a cross-section at particle level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of a majority of next-to-leading-order and leading-order matrix-element Monte Carlo generators are found to agree with the measured cross-sections.
分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-04-11
摘要: Aluminum is the primary structural material in nuclear engineering, and its cross-section induced by 14 MeV neutrons is of great significance. To address the issue of insufficient accuracy for the 27Al(n,2n)26Al reaction cross-section, the activation method and accelerator mass spectrometry (AMS) technique were used to determine the 27Al(n,2n)26Al cross-section, which could be used as a D-T plasma ion temperature monitor in fusion reactors. At the China Academy of Engineering Physics (CAEP), neutron activation was performed using a K-400 neutron generator produced by the T(d,n)4He reaction. The 26Al/27Al isotope ratios were measured using the newly installed GYIG 1 MV AMS at the Institute of Geochemistry, Chinese Academy of Sciences. The neutron flux was monitored by measuring the activity of 92mNb produced by the 93Nb(n,2n)92mNb reaction. The measured results were compared with available data in the experimental nuclear reaction database, and the measured values showed a reasonable degree of consistency with partially available literature data. Thenewly acquired cross-sectional data at 12 neutron energy points through systematic measurements clarified the divergence, which has two different growth trends from the existing experimental values. The obtained results are also compared with the corresponding evaluated database, and the newly calculated excitation functions with TALYS-1.95 and EMPIRE-3.2 codes, the agreement with CENDL-3.2, TENDL-2021 and EMPIRE-3.2 results are generally acceptable. A substantial improvement in the knowledge of the 27Al(n,2n)26Al reaction excitation function was obtained in the present work, which will lay the foundation for the diagnosis of the fusion ion temperature, testing of the nuclear physics model, and evaluation of nuclear data, etc.
分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The influence of the -decay radionuclide layer (the energy of -particles are 5.45 MeV) on the radar cross section (RCS) of sphere objects was calculated under different radioactivities, frequencies, and sphere radii. When the sphere radius is smaller than 50 cm, the tendency of the electron densities of the plasma slab is to ascend first and then descend, and the typical maximum electron densities with a radioactivity of 10 Ci/cm2 raises from 7.021010 to 1.761011 when the sphere radii increases from 10 to 300 cm. The average data of a normalized RCS of a sphere with radius of 12.5 cm, which is coated with a radionuclide layer with different radioactivities are -0.35, -0.50, -0.79 and -1.13 dB when the radioactivity is, per-mode=symbol 1, 2, 5 and 10 Ci/cm2, respectively.
分类: 核科学技术 >> 裂变堆工程技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Neutron spectrum should be measured before test samples are irradiated. Neutron spectrum in an irradiation chamber of a research reactor was measured by using activation method when the reactor is in normal operation under 2 MW. Sixteen kinds of non-fission foils (19 reaction channels) were selected, of which 10 were sensitive to thermal and intermediate energy regions, while the others were of different threshold energy and sensitive to fast energy regions. By measuring the foil radioactivity, the neutron spectrum was unfolded with the iterative methods SAND-II and MSIT. Finally, shielding corrections of group cross-section and main factors affecting the calculation accuracy were studied and the uncertainty of solution was analyzed using the Monte Carlo method in the process of SAND-II.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: The effects of absolute energy calibration on BESIII physics are discussed in detail, which mainly involve the effects on τ mass measurement, cross section scan measurement, and generic error determination in other measurements.