多重库仑散射对小尺度物体缪子透射成像精度的影响

缪子透射成像方法是一种基于宇宙线缪子穿过目标物体前后的通量变化,进而获得其内部密度结构的无损探测成像方法.缪子透射成像方法假设缪子在低原子序数物质中沿直线运动,但实际上多重库仑散射作用会使缪子路径一定程度上偏离直线,有可能对成像精度造成影响.为此,本文使用Geant4软件包开展了缪子透射成像蒙特卡罗模拟,针对数米尺度多种密度结构的模型,定量分析了打开和关闭多重库仑散射物理过程时对成像精度的影响.结果表明:对于数米尺度标准岩石物质,缪子透射成像方法能够很好地恢复内部密度异常几何特征;但多重库仑散射作用对目标物体内部区域近垂向缪子通量造成的偏差可达5%,而在目标物体边界区域的偏差可达13%.因此,需要宇宙线缪子透射成像中考虑多重库仑散射作用的影响,以获得数米尺度目标物体更准确的绝对密度值成像结果.     

An Approach to Extract the Spin Transfer to ∧in Polarized Proton--Proton Collision

We introduce an approach to extract the spin transfer to A in polarized proton-proton collision, based on the relation between single spin asymmetry and the polarization of A production. With 4 × 10^6 ∧ events simulated for a PHENIX detector system, DLL = 0.1598 ± 0.0343 is retrieved by the approach and it agrees very well with the input value of 0.1429. The approach is further tested and confirmed with ‘bunch shuffling＇ method for the simulated events as well as experimental events collected at PHENIX in 2003. It is concluded that one can correctly extract the spin transfer without detailed understanding of acceptance correction even if the correction is significantly large in PHENIX experiment by using the approach described here. The method can be generally used for spin transfer study.     

在200GeV极化质子质子对撞中产生的反Lambda粒子的极化

We study the polarization of produced Λ in s=200GeV polarized proton-proton collision at RHIC/PHENIX, and also the polarization as a function of its rapidity which may be sensitivity to the quark helicity distributions of the proton and to the polarized fragmentation functions of the quark into the baryon. For polarized data collected in 2003 a very clean Λ peak in pπ⁺ invariant mass spectrum in the mid-rapidity(|η|<0.35) is obtained. In this letter, we report the calculation process of P_Λ as extracted from the data.     

地球中微子——把脉地球内部热量

 地球内部包含有巨大的热量,这些热量简称地球内热,它是驱动板块构造、地幔对流和地球自激发电机的动力,是推动整个地球发生发展和演化的原动力。在45亿~47亿年前的地球形成早期,地热促成了核、幔、壳的分异,使地球从一个太空中未曾分异的"混沌体"演变成现今所看到的多圈层的地球;在现今,地热驱动着诸如构造运动、岩浆活动、火山作用等一切内力作用,使地球发生着翻天覆地的变化。     

在200GeV极化质子质子对撞中产生的反Lambda粒子的极化

We study the polarization of produced (-Λ)in (√s)=200GeV polarized proton-proton collision at RHIC/PHENIX, and also the polarization as a function of its rapidity which may be sensitivity to the quark helicity distributions of the proton and to the polarized fragmentation functions of the quark into the baryon. For polarized data collected in 2003 a very clean (-Λ) peakin (-p)π invariant mass spectrum in the mid-rapidity(|η| ＜ 0.35) is obtained. In this letter, we report the calculation process of P(-Λ) as extracted from the data.