The BaBar experiment

BaBar的主要目标是利用B介子研究弱相互作用的性质。到目前为止，BaBar最令人兴奋的结果是第一次观察到，在B介子的衰变中，电荷共轭宇称（CP）对称性--它将物质与反物质联系起来--被破坏了。 特别是，BaBar测得sin 2 β为0.710 +/- 0.039，其中β是酉三角形的三个角之一，表示CKM矩阵，表征弱相互作用。 Vu B，CKM矩阵的确定三角形的一条边的长度的元素，也在包含和排除B衰减中以增加的精度被测量。总的来说，BaBar的物理程序包括一组广泛的测量，以确定幺正三角形的所有边和角度，并具有足够的精度来过度约束标准模型的基础参数。它还包括对新物理的各种各样的搜索，包括B和τ的罕见或禁止衰变，以及意想不到的CP破坏。这个程序已经产生了第一个有趣的暗示物理超越标准模型。使用包含有重虚粒子的高阶环的衰变模式--所谓的“企鹅”衰变--测量sin 2 β产生的值与在粲偶素模式下测量的值相差2.6个标准差。人们预计，目前尚不清楚的重粒子会造成这种差异。这些企鹅模式都是罕见的，要确定这种观察到的差异是统计波动还是新物理学的标志，需要大量增加数据。 在2006年的夏季和秋季，提供BaBar光束的PEP-II e+e对撞机将进行升级，以达到所需的更高亮度。BaBar正在同时升级其μ子系统，以确保我们能够充分利用额外的数据。从现在到2008年9月完成数据采集，我们预计BaBar数据集的大小将增加2.5倍。

The primary goal of BaBar is to study the nature of the weak interaction using B mesons. The most exciting result from BaBar so far is the first observation that the Charge Conjugation - Parity (CP) symmetry - which relates matter to antimatter - is violated in the decay of B mesons.  In particular, BaBar has measured sin 2 beta to be 0.710 +/- 0.039, where beta is one of the three angles of the Unitarity Triangle, a representation of the CKM matrix that characterizes the weak interaction.   Vub, an element of the CKM matrix that determines the length of one of the sides of the Triangle is also being measured with increasing precision in both inclusive and exclusive B decays. Overall, BaBar's physics program includes a broad set of measurements to determine all sides and angles of the Unitarity Triangle with sufficient precision to overconstrain the underlying parameters of the Standard Model. It also includes a wide variety of searches for new physics, including rare or forbidden decays of the B and tau, and unexpected CP violation.This program has already produced the first intriguing hint of physics beyond the Standard Model. Measurements of sin 2 beta using decay modes involving higher order loops with heavy virtual particles - so called "penguin" decays - produce a value that differs by 2.6 standard deviations from the value measured in charmonium modes. Heavy, as yet unknown, particles would be expected to cause such a difference. These penguin modes are all rare, and establishing whether this observed difference is a statistical fluctuation or a sign of new physics will require a substantial increase in data.  In the summer and fall of 2006, the PEP-II e+e- collider that provides BaBar's beams will undergo upgrades to achieve the needed higher luminosity. BaBar is simultaneously upgrading its muon system to ensure that we can fully utilize the additional data. We expect to increase the size of the BaBar dataset by a factor of 2.5 from now until the completion of data taking in September 2008.