s=630GeV pp碰撞中微喷注的新分析

根据喷注判定的圆锥法来判断喷注,重新分析了UA1-1985年的s=630GeV非单衍pp碰撞实验数据. 分析发现对事件样本,单事件平均横动量p_t与多重数n是正关联的,而对喷注事件子样本则是负关联的;分析了微喷注产生的关联和退关联,表明微喷注产生来源于非软过程和高阶效应;并首次从实验上观测到微喷注间存在大快度间隔内无粒子的事例,分析了微喷注产生时存在大快度gap的迹象.     

高能强子–强子碰撞中硬软过程的比较分析

根据QCD中“圆锥定义”来确定喷注,对高能强子-强子碰撞中的硬、软过程作细致的分析.用Pythia产生蒙特卡罗模拟样本,得到的喷注赝快度分布在中心区有平台,喷注内部的粒子密度和横能密度,随离喷注轴的距离指数地下降,比较发现对整个事件样本,单事件平均横动量或最大横动量与多重数是正关联的,而对喷注事件它们是负关联的.引入两个物理量来描述喷注事件的硬、软程度.发现它们与单事件平均横动量是正关联的,而与多重数是负关联的.表明用单事件平均横动量比用多重数能更好地描述喷注事件的硬软程度.     

高能强子–强子碰撞中喷注性质的蒙特卡洛研究

在喷注“圆锥判定法”的基础上,对高能强子–强子碰撞中产生的喷注(微喷注)的性质进行了蒙特卡洛研究.采用以喷注动量为z轴的“喷注坐标系”,给出了表征喷注性质的各物理量在新坐标系中的分布情况.结果表明,圆锥判定法能够作为一种有效手段来对高能强子–强子碰撞和相对论重离子碰撞中发生的硬和半硬过程开展实验研究.由有喷注事件和无喷注事件的多重数分布可以看到,E_t=2GeV是用圆锥法确定喷注的合理的横能截断值.     

高能强子–强子碰撞喷注内部动力学起伏的自仿射分析

对CERN-SppS对撞机能区的质子–反质子碰撞事件中产生的喷注(微喷注)内部的动力学起伏进行了自仿射分析.按圆锥法判定由蒙特卡洛事件产生器产生的事件样本中的喷注(微喷注).通过一维阶乘矩的研究得到自仿射的赫斯特指数.按照所得到的赫斯特指数进行三维自仿射分析,在双对数图上得到较好的直线.从而进一步证明,喷注内部的动力学起伏近似地和SPS静止靶强子–强子碰撞中的动力学起伏一样,呈现为纵–横各向异性,而在横平面内各向同性.     

高能强子–强子碰撞中喷注的产生与演化过程的动力学起伏

用蒙特卡洛方法对630GeV/c质子–反质子碰撞中的无偏样本、喷注事件样本和喷注内样本中的动力学起伏进行了研究.结果表明,喷注事件样本和电子–正电子对撞的全事件样本相似,近似地有各向同性的动力学起伏,而喷注内样本则和电子–正电子对撞的喷注一样,有类似于强子–强子碰撞软过程的各向异性动力学起伏.这表明,强子–强子碰撞中喷注的产生和演化分别和电子–正电子碰撞中喷注的产生和演化有类似的动力学性质.     

e+e－湮灭成两喷注中的末态强子快度分布和BB关联

本文在文献[1]给出的模型中,进一步赋给夸克简单的四动量分布,通过Monte-Carlo计算,不但得到了与实验符合得很好的轻夸克喷注事例末态强子快度分布等,还给出了与实验基本一致的末态重子之间的快度和角度关联.     

Z0能区正负电子湮没强子多重数分布的近泊松形式与肩状结构

对Z⁰能区91.2GeV正负电子湮没产生强子末态的事例,分别针对全喷注和双喷注在不同快度窗口的单、双半球空间内进行多重数分布的泊松拟合.根据/D参量及拟合度得到近泊松形式,与有关理论模型进行了比较,并讨论了与KNO无标度性的关系.分析了偏离泊松形式的有关参数与非独立粒子发射及关联强度之间的联系.利用JADE喷注分析法讨论了中心快度区的“肩状结构”.     

高能强子–强子碰撞中喷注内部动力学起伏的蒙特卡洛研究

用蒙特卡洛方法对CERN-SppS对撞机质子–反质子对撞中由圆锥法判定的(微)喷注内部的动力学起伏进行了研究.结果表明,喷注内部的动力学起伏近似地和SpS静止靶强子–强子碰撞中的动力学起伏一样,呈现为纵–横各向异性,而在横向平面内各向同性的特征.     

夸克喷注与胶子喷注角分布特性的研究

用蒙特卡洛模拟Jetset 7.4产生质心能量为91.2GeV的正负电子对撞事件. 在引入喷注的圆锥角后, 对不同味的夸克喷注和由不同味夸克发射的胶子产生的喷注的角分布特性进行了仔细研究. 结果发现, 在相同的能量下, 胶子喷注的角分布范围比夸克喷注的角分布范围要明显宽一些. 在带电粒子数、横动量相同的条件下, 胶子喷注的平均圆锥角比夸克喷注的平均圆锥角大很多. 喷注的平均圆锥角随带电多重数以及喷注的横动量的分布都呈线性正关联. 由不同味的夸克发射的胶子产生的喷注的圆锥角分布特性相同；而不同味的夸克喷注的圆锥角分布存在明显的差异.     

夸克胶子喷注的人工神经网络识别研究

为了将人工神经网络用于高能物理中对喷注的分类识别,用从高能正负电子对撞的蒙特卡洛模拟中得到的不对称三喷注事件中的夸克喷注和胶子喷注的平均多重数、平均横动量和两类喷注所对的夹角的平均值作为输入BP神经网络的3个特征参量,对2?.5—2?2?.5GeV能区的8个能量间隔进行等精度的训练.用训练好的神经网络模型对不对称三喷注事件中的夸克喷注和胶子喷注样本进行检验判定,并对混合喷注样本进行分类识别.所得结果表明,有望将人工神经网络用于高能正负电子对撞产生的喷注的分类分析.     

On high energy leptoproduction

The particle distributions and the event structures in high energy leptoproduction are considered in a model where perturbative QCD is used to compute the cross sections to order α _s and the Lund jet model is used for the soft hadronization process. Since complete events are generated by a Monte Carlo program not only single-particle spectra can be studied but also various correlations, thus making a more detailed comparison between theory and experiment possible. The model is found to be in agreement with data from the European Muon Collaboration. We indicate how a one-particle trigger can be used to study an enriched sample of two forward jet events, and exhibit a useful experimental test for the existence of such events with the properties predicted by perturbative QCD. We also indicate how to gain further information on the confinement and soft fragmentation mechanisms.     

Comparison of the Hard and Soft Processes in High Energy Hadron-Hadron Colisions

Using the“con ealgorithm”in QCD to identify jet,the hard and soft processes in high energy hadroncic olisions are analysed indetail.A Monte Carlo simulation event sample is produced by PYTHIA.The resultant pseudorapidity distribution of jets has a plateau in the central region.The particle and transverse energy density in jets decreases exponentially with the increase of the distance from particles to jet axis.Through comparisons,we find the event average transverse momentum or maximum transverse momentum is positively correlated with multiplicity for the whole event sample,and negatively correlated with multiplicity for jet event subsample.Two ratio variables well describe the hardness of jet events,and they are positively correlated with the event average transverse momentum and negatively correlated with multiplicity,which confirms the event average transverse momentum is a better characteristic quantity to describe the hardness of jet events than multiplicity.     

Hadronic Interactions in the Energy Region of Future Hadron Colliders,Dual Topological Unitarization of Hard and Soft Hadronic Cross Sections

The dual topological unitarization of hard and soft hadronic collisions is formulated as a Monte Carlo event generator for events containing both the soft (low p ?) and hard (jets, minijets) component of hadron production. The parameters of the model are determined from fits to the energy dependence of the total and inelastic hadron cross-sections and from the predictions of the QCD-parton model for the perturbative hard constituent scattering cross sections. The predictions of the model for TeV colliders are presented. Interesting changes of the produced multiparticle system are found when selecting classes of events with and without hard jets or minijets.     

Exploiting non-leptonic decays in top searches

We show that a massive use of statistical event correlations, learned by means of Monte Carlo event generators, makes it feasible to employ a pure jet signature in top quark searches. A relevant ingredient for that is also the less diffuse angular distribution of energy deposition and of particles in top events, which are dominated by quark jets. On the other, hand, we show that the utilization of mass cuts on jet combinations to identify top non-leptonic decays meets severe limitations already at the parton level, largely because of QCD radiation.     

Minijet activity in high ET jet events at the tevatron

Gluon bremsstrahlung in scattering events with high transverse momentum jets is expected to increase markedly with the hardness (∑E_T) of the primary event. Within perturbative QCD we estimate a probability of order unity to see additional minijets with E_T 15 GeV in “dijet” events with ∑E_T > 400 GeV. The veto of such minijets is a promising background rejection tool for the Higgs search at the LHC.     

Jet fragmentation function moments in heavy ion collisions

The nature of a jet’s fragmentation in heavy-ion collisions has the potential to cast light on the mechanism of jet quenching. However, the presence of the huge underlying event complicates the reconstruction of the jet fragmentation function as a function of the momentum fraction z of hadrons in the jet. Here we propose the use of moments of the fragmentation function. These quantities appear to be as sensitive to quenching modifications as the fragmentation function directly in z. We show that they are amenable to background subtraction using the same jet-area-based techniques proposed in the past for jet p _t ’s. Furthermore, complications due to correlations between background-fluctuation contributions to the jet’s p _t and to its particle content are easily corrected for.     

Transverse-energy correlations and jet shape in collisions of ultrarelativistic nuclei

Measurement of angular correlations between energy fluxes is one of the promising methods for analyzing the structure of events in ultrarelativistic heavy-ion collisions. The possibility of diagnosing the rescattering and the energy loss of hard partons in dense QCD matter is studied here on the basis of an analysis of the transverse-energy correlation function. It is shown that, if events are chosen for an analysis in a special way (that is, if at least one jet is required to have a transverse energy above some threshold) and if the procedure of background subtraction is applied in each event, the energy correlation function is sensitive to the parton energy loss and the angular spectrum of gluons emitted in a medium. The transverse-energy correlation function calculated for all events reflects the global structure of the transverse energy flux: it is independent of the azimuthal anisotropy of the energy flux for central collisions and is sensitive to the azimuthal anisotropy of the energy flux, reproducing all of its Fourier harmonics for noncentral collisions, but the coefficients of these harmonics are squared. A special correlation function in the vicinity of the maximum energy deposition in each event makes it possible to study changes in the jet shape. Within the conventional scenario of the scattering of hard jet partons on accompanying medium constituents, the correlation function is independent of the rapidity position of the jet axis and becomes much broader (symmetrically in the rapidity and azimuthal angle) than in proton-proton collisions. In the case of scattering on slow medium constituents, the broadening of the correlation function depends on the rapidity position of the jet axis and, in relation to the preceding scenario, increases sizably for jets of rather high rapidity.     

Identification of exotic jet topologies via three-particle correlations in PHENIX

Modifications of jet properties resulting from the coupling of jets to the strongly interacting matter produced in RHIC collisions are of great current interest. In recent work, the PHENIX collaboration has applied a novel technique to the analysis of two-particle azimuthal correlations which extinguishes the harmonic part of the underlying event revealing the true jet shape. Recent extensions of the method to three-particle correlations allow for a more revealing study of jet topologies in Au+Au collisions at (√s _NN=200 GeV).