课程文献中心 更多>>

关键词： QCD因子化   D 介子   光前夸克模型   湮灭  

摘要： 在考虑幂次压低且不忽略c 夸克和D 介子质量的条件下,采用光前夸克模型结果作为输入,在 QCD因子化(QCDF)框架下给出了B0(s)→D+(s)K-和B0(s)→D+(s)π-中旁观者和湮灭图的贡献大小.旨在解释这两个衰变道中理论预言与实验测量存在 4σ～5σ偏差的问题.研究结果表明,旁观者和湮灭图贡献对这一偏差有一定的改善,但理论与实验之间的偏差仍然比较明显.

摘要： The predictions of the Standard Model (SM) of particle physics have been probed with remarkable accuracy, so far. The Large Hadron Collider (LHC) at CERN has significantly contributed to this quest. A remarkable achievement of the ATLAS and CMS experiments at the LHC was the discovery of the Higgs boson in 2012, the last missing piece of the SM. With the increasing amount of proton-proton collisions delivered by the LHC, more precise measurements of the Higgs boson are now possible, while rare processes are accessible as well. A property of the Higgs boson that is of particular importance is its coupling to the top quark, which is expected to be the strongest in the SM due to the high mass of the top quark. Therefore, its precise measurement is a stringent test of the SM. A direct measurement of the top-quark Yukawa coupling can be assessed through the Higgs-boson production in association with a pair of top quarks (ttH). This thesis presents the measurement of the ttH process with a subsequent Higgs-boson decay to a pair of b-quarks (H -> bb), the decay mode with the largest branching ratio. The measurement is performed with data collected by the ATLAS detector, corresponding to an integrated luminosity of 139 fb^-1 at a center-of-mass energy of 13 TeV. Events with one or two charged leptons from the tt decay in the final state are considered to the measurement. The main challenge of the ttH(H -> bb) channel emerges from the large SM backgrounds from the production of top-quark pairs with additional jets (tt+jets). Also the many jets coming from b-hadrons (b-jets) in the final state cause combinatorial ambiguities. Thus, the identification of such jets is decisive in order to determine the signal and reject many background processes. The ttH events are split into exclusive analysis regions, based on the number of leptons, jets, and jets tagged as b-jets, providing regions enhanced in signal, or in the main background components. Specifically in the single-lep

关键词： 埋藏史   热史   磷灰石裂变径迹   秀水盆地   松辽外围南部   油气地质调查工程  

摘要： 【研究目的】松辽外围白垩世断陷盆地群在构造-热演化史的研究方面相对薄弱，秀水盆地作为松辽外围南部潜力较大的勘探新区，对盆地的热史-埋藏史的恢复已然成为该地区油气勘探亟待解决的重要问题。【研究方法】本文通过对秀水盆地辽法地1井5件钻井岩心样品开展磷灰石裂变径迹测试分析，首次厘定了盆地经历的热史-埋藏史及烃源岩成熟演化过程。【研究结果】结果表明，秀水盆地在早白垩世晚期地层达到最大埋深，而后持续抬升剥蚀近2000m；在初始沉降期大地热流值随时间线性升高，至120 Ma左右达到最大值，约为100.5 mW/m2。而后经历了三段式降温过程，即先快速降温，再缓慢降温，最后快速降温的过程。该热流规律与邻区张强凹陷、松辽盆地相似并可对比。【结论】辽法地1井热史-埋藏史恢复结果表明，义县组三段烃源岩在90 Ma左右进入到生油窗阶段，此后由于地层的抬升降温，热成熟度末进一步演化，从而最终定型。

摘要： This thesis presents measurements of the first to fourth moments of the lepton mass squared q2=(pl + pν)2 distribution of B→Xclν decays for l=e,μ and with Xc denoting a hadronic system containing a charm quark. These results use a sample of e+e--collisions at the Υ(4S) resonance corresponding to 62.8 fb-1 of integrated luminosity and collected by the Belle II experiment in 2019 and 2020. To identify the Xc system and reconstruct q2, one of the B mesons from an Υ(4S)→BB decay is fully reconstructed in a hadronic decay mode using a multivariate B tagging algorithm. The yields of the remaining e+e-→qqcontinuum and BB background events are determined with a binned likelihood fit to the hadronic mass mX distribution. To correct the bias in the mean value of the reconstructed q2 distribution, an event-wised calibration method is applied to the reconstructed q2 values. The q2 moments are calculated as a weighted mean using the calibrated q2 values summing all selected events. In this approach, the weights denote a signal probability and effectively subtract the contribution of the remaining background events. This work reports raw and central q2 moments measured as functions of lower q2 thresholds from q2 > 1.5 GeV2 up to q2 > 8.5 GeV2, probing up to 77% of the accessible B→Xclν phase space. This is the first measurement of moments in the experimentally challenging range of q2 ∈ [1.5, 2.5] GeV. In addition, this thesis presents a first determination of |Vcb| using q2 moments of inclusive B→Xclν decays. Like the prediction of total rate, the expressions for spectral moments of inclusive semileptonic PB decays can be calculated using the heavy quark expansion and depend on a set of non-perturbative parameters which can only be determined from measurements. At higher orders in the expansion, one observes a proliferation of these parameters which further complicates their extraction. The q2 moments and the total rate are reparameterization invariant quantities and depend on a

摘要： 据日本经济新闻网2023年2月23日报道,在核聚变研究领域,中国的存在感正在提高.核聚变作为新一代能源技术,有望在21世纪40年代以后实现实用化.对重要专利的统计发现,中国排在首位,领先于美国(第二位)和日本(第四位). 报道说,从专利申请趋势可以看出,在可能从根本上解决全球变暖问题的核聚变技术领域,起步较晚的中国正在迅速赶超.中国不仅与日本、美国及一些欧洲国家一同参与了国际核聚变实验堆项目,而且在以发电实证为目的的开发计划方面走在了世界前列.

关键词： 暗物质   电磁相互作用   引力相互作用   黑洞   强相互作用   辐射电磁波   长寿命   Q&A  

摘要： Q:黑洞与暗物质之间有没有相互作用?如果有,用什么方法能够探测?A:先说一下黑洞与暗物质的性质。现在已知暗物质参与引力相互作用,不参与电磁相互作用与强相互作用,同时暗物质应该是稳定或长寿命的粒子。因为不参与电磁相互作用,暗物质不发光,不辐射电磁波。