Measurement of electric polarizabilities of 3He and 4He

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1 Measurement of electric polarizabilities of 3He and 4He
范功涛1 徐望1 潘强岩1 罗文1 杨利峰1 李永江1 蔡晓鹭1 徐本基1 林承键2 贾会明2 徐新星2 吴振东2 杨峰2 张焕乔2 1中科院上海应用物理研究所 2中国原子能科学研究院 PART Ⅰ Background & Motivation PART II Experimental details PART III Data analysis PART IV Extract α by Fresco PART V Summary 第十三届全国核结构研讨会暨第九次全国“核结构与量子力学”专题讨论会 2010/07/26

2 I Background & Motivation
1.1 物质极化的物理图象 原子的极化: 分子的极化: 极化率 (polarizability) 描述了原子或分子，因感受到外电场的作用，而改变其正常子云形狀的程度。 P= αE α为电极化率，E 是外电场，P为感应电偶极矩。 原子核的极化: 核子的极化: Company Logo

3 处在重核的库仑场中的轻核极化的物理过程 原子核在强外电场中同样也会被极化，感应产生的感应电偶极矩为P= αE。
如果处在重核的库仑场中，产生的极化势为： 炮弹的电极化率=0 炮弹的电极化率=αP 炮弹的电极化率=0 Rmin E~2*10-21N/m 4He 208Pb 靶核的电激化率=αT 靶核的电激化率=0 靶核的电激化率=0 Company Logo

4 1.2 理论上研究核子或核电磁极化率的现状 A Company Logo

5 Total potential between two nucleus is given:
1.3 Experimental methods To measure electric and magnetic polarizability of nucleon through Compton quasielastic scattering of gamma from a nucleon. To measure electric polarizability of light nucleus through elastic scattering of the nucleus from a heavy and spherical nucleus (e.g. Pb). or elastic scattering of a heavy and spherical nucleus (e.g. Pb) from the nucleus. Total potential between two nucleus is given: we have measured the cross section ratio Company Logo

6 Elastic scattering Compton scattering PRC, 64（2001） 025203
Company Logo PRC 78, (R) (2008)

7 1.4 实验上研究核子或核电磁极化率的现状 A Company Logo

8 电极化率（α）和磁极化率（β）是用于描述处于外加电场、磁场中的原子核&核子的基本物理量[1]；
实验上测量电磁极化率的意义 电极化率（α）和磁极化率（β）是用于描述处于外加电场、磁场中的原子核&核子的基本物理量[1]； 精确测量原子核&核子的电磁极化率可以用于检验关于基本夸克和胶子以及一些 核子的机制计算与模型（例如手征微扰理论等）[1][2]； 精确测量原子核&核子的电磁极化率可以为理解更复杂系统提供根据[1]； 精确测量原子核&核子的电磁极化率可以用于修正原子能级的精确计算[3]； [1] B.E.MacGibbon et.al Phys. Rev. C 52(1995)2097 [2] J.Schmiedmayer et.al Phys. Rev. Lett 66(1991)1015 [3] K.Pachucki et.al Phys. Rev. A 75(2007)032521 Company Logo

9 1.5 为什么测量3He和4He的电极化率？ 4He 电极化率数据 3He 电极化率数据 www.themegallery.com
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10 测量3He和4He的电极化率的意义 ♣ 3He 4He 是连接少体系统和更复杂系统的中介[1]；
♣ 解决用不同的方法（Elastic scattering and Compton scattering）测量的3He电极 化率 数据不一致的问题； ♣ 第一次用弹散的方法得到4He的电极化率； ♣ 国内少有的高精度（R(E)的精度为0.1%）核物理实验； ♣ 对3He，4He分别用了两个靶（208Pb和144Sm）保证了测量的可靠性; ♣ 为以后在ＳＬＥＧＳ上用Compton scattering测量他核或核子的电磁极化率打下基础。 [1] Doron Gazit et.al Phys. Rev. Lett 96(2006)112301 [2] K.Pachucki et.al Phys. Rev. A 75(2007)032521 Company Logo

11 At low energy, the effects of strong interactions between the two nuclei can be neglected. The cross-section therefore is approximately given by the Rutherford formula, while other deviations may arise from several sources. One of the most important of these deviations is due to electric polarization of each nucleus. Therefore, total potential between two nucleus is given: Vtotal = Vcoul +Vpol+……, where . So we will measure the cross section ratio between one energy point and the referenced energy point: . What we have measured Company Logo

12 II Experimental details
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13 What we have measured Company Logo

14 Calibration +144Sm at 18MeV Left60o Company Logo

15 III Data analysis 3.1 Check our data by a simple cut method
preliminary results Company Logo

16 3.2 Signal overlap and overflow correction
3He+208Pb at 8MeV Left60o 1300 2600 Ncre=T*V*Ns T: gate width V: signal rate Ns: signal counts Company Logo

17 3.3 High-energy tails of the scattering peak correction
3He+208Pb at 16MeV Left60o A simple method for this correction (1) Get the length of the “tail” : mean*2=2572 (2) Get the mean counts per channel : M， M=848/300=2.83 (3) Extract the correction: Ncre=（mean*2-n）*M=（ ）*2.83=1619 Ncre’=1952 Company Logo

18 3.4 Low-energy tails of the scattering peak correction
4He+208Pb at 6MeV Left60o A simple method for this correction C谱 延伸部分 比较 通过调节延长时起始点的位置，比较“延长”部分加上C谱的计数和实际谱的计数。 并作Χ2。以此确定延长时起始点的位置。 Company Logo

19 3.5 Check the corrections by R(60o/30o) and R(140o/165o)
4He+208Pb Company Logo

20 3.6 Other corrections we will consider
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21 IV Extract the polarizabilitis by Fresco
4.1 About Fresco Company Logo

22 4.2 Simulate the possible situation of our experiment
The situation we considered ： A: Axes of the detectors deviated 5o B: Beam pass though the collision point but deviated 5o C: Beam deviated collision point 1mm D: Detectors deviated 2.5o Total deviation ： Company Logo

23 4.3 Target polarization effect and other effect we should consider
A: Inelastic scattering B: Existence of nuclear reactions C: Several other effects includes atomic screening, vacuum polarization and relativistic corrections Company Logo

24 4.4 Try to extract the polarizability by Fresco
preliminary results preliminary results preliminary results preliminary results Company Logo

25 Some improvement should be considered
数据分析方面: A: 扣除12C 衬底的影响； B: 靶内能损的影响； C: RUN by RUN 检查cut； D: 做相应的模拟； E: 等等; 理论方面: A: 仔细检查修改后的Fresco程序； B: 研究其他反应道的影响，如散射过程中208Pb被激发到 3-态； 3He+208Pb-> d+209Bi 等； C: 研究其他效应的影响，如：atomic screening, vacuum polarization and relativistic corrections； D: 独立用ECIS 提取电极化率以检查用Fresco提取的结果; E: 等等. Company Logo

26 V Summary In this work, using the method-the light nucleus scattered by the heavy nucleus at energies below the Coulomb barrier, we precisely and systematically measured the electric polarizabilities of 3He and 4He in Aug.2008 and Sep.2008 on HI-13 tandem accelerator in China Institute of Atomic Energy. We hope we can solve the problem of inconsistency among the results of the 3He’s electric polarizability and extract the 4He’s electric polarizability by our experiment. Detail analyses are still in progress. Company Logo

27 I would like to thank Prof Wang Xu, Dr Wen Luo, Prof Qiang-yan Pan, Dr
Yong-jiang Li and other fellows of our group for their help during the data analysis. I also would like to thank Prof Cheng-jian Lin, Prof Huan-qiao Zhang, Xin-xing Xu, Huimin Jia, Fei Jia and Feng Yang of China Institute of Atomic Energy for their help during the experiment. Thank you！ Company Logo