Measurements for Muon g-2 Hadronic Vacuum Polarization

目前测量的介子反常磁矩a_u=(g-2)/2与理论预测相差约3.5个标准差。如果在更高的意义上得到证实，这将是新物理学的明确标志，并将给该领域带来革命性的变化。新的费米实验室g-2实验将显著改进测量，但必须与之比较的标准模型理论误差主要取决于强子真空极化(HVP)校正的确定。如果要在这一差异上取得进展，就需要同时改进对HVP贡献的确定。由于相应的能量标度太低，不适合应用微扰QCD，解决这一问题最可靠的方法是测量从阈值到约3GeV的过程e+e--&gt；强子，并用它通过色散关系计算HVP的贡献。到目前为止，这个过程的主要通道是e+e--&gt；pi+pi-。这是一种使用初始态辐射(ISR)方法来精确测量e+e-&gt；pi+pi-/e+e-&gt；u+mU-从阈值到3-5GeV能量的横截面比率的建议：即，测量e+e--&gt；和e+e--&gt；伽马-mU+mU-，其中伽马是在与光束成大角度时被探测和精确测量的ISR光子。BABAR使用其前半部分数据(232/FB)公布了这一比率，这笔赠款将用于分析和出版BABAR数据集的后半部分(245/FB)。巴布尔数据集的后半部分使用了不同的Muon探测器系统，因此，相对于现有出版物的收益不仅是统计上的独立，而且是很大程度上不同的系统不确定性，因为Muon系统被用来将探测器中的Muon和介子完全分开。这一新的计量方法将大大改进对卫生价值贡献的确定。该提案将支持一名正在测量e+e--&gt；u+u--的现有研究生和一名博士后，该博士后将致力于在BABA数据集的后半部分完成e+e--&gt；Gamma pi+pi-/e+e--&gt；伽马u+Mu分析并与以前的BABA结果相结合。它包括对一些旅行支持的请求。这次旅行将使申请者、学生和博士后能够参加BABAR会议和几个会议。旅行支持也将使申请人能够履行其作为BABA代言人的职责。

Current measurements and theoretical predictions of the muon anomalous magnetic moment, a_mu = (g-2)/2, are in disagreement by approximately 3.5 standard deviations. If verified at higher significance, this would be a clear signature of new physics and revolutionize the field. The new Fermilab g-2 experiment will improve the measurement significantly, but the Standard Model theoretical error, to which it must be compared, is dominated by the determination of the hadronic vacuum polarization (HVP) correction. Simultaneous improvements to the determination of the HVP contribution are required if there is to be progress on this discrepancy. Because the relevant energy scale is too low for applying perturbative QCD, the most reliable method for attacking this problem is to measure the process e+e- -> hadrons from threshold to approximately 3GeV and use that to calculate the HVP contributions though a dispersion relation. By far the dominant channel for this process is e+e- -> pi+ pi-. This is a proposal to make a precision measurement of the ratios of the cross section for e+e- -> pi+ pi- / e+e- -> mu+mu- from threshold to an energy of 3-5GeV using the initiate-state radiation (ISR) method: i.e. the measurement of e+e- -> gamma pi+pi- and e+e- -> gamma mu+mu- where the gamma is an ISR photon detected and precisely measured at large angles to the beam. BaBar published on this ratio using the first half of its data (232/fb) and this grant will fund the analysis and publication of the second half of the BaBar dataset (245/fb). The second half of the BaBar dataset uses a different muon detector system and therefore the gain over the existing publication is not only statistical independence, but a largely different systematic uncertainty, since the muon system is used to cleanly separate muons from pions in the detector. This new measurement will provide a substantial improvement on the determination of the HVP contribution. The proposal will support an existing graduate student who is measuring e+e- -> mu+mu-, and a postdoc who will be dedicated to completion to publication of the e+e- -> gamma pi+ pi- / e+e- -> gamma mu+mu analysis in the second half of the BaBar dataset and a combination with the previous BaBar result. It includes a request for some travel support. The travel will enable the applicant, student and postdoc to attend BaBar meetings and a few conferences. The travel support will also enable the applicant to fulfill his responsibilities as BaBar Spokesperson.