The BaBar experiment

BABA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测到电荷共轭-宇称(CP)对称性--将物质与反物质联系在一起--在B介子的衰变中被破坏。尤其是，BABAR已经测量到SIN2β为0.710+/-0.039，其中β是单位三角形的三个角之一，单位三角形是表征弱相互作用的CKM矩阵的表示。在包含性和排他性B衰变中，确定三角形一侧长度的CKM矩阵的一个元素-VUB也在以越来越高的精度进行测量。总体而言，巴布尔的物理计划包括一系列广泛的测量，以确定单位三角形的所有边和角度，并具有足够的精度，以过度约束标准模型的基本参数。它还包括对新物理的各种搜索，包括B和tau的罕见或被禁止的衰变，以及意想不到的CP违反。这个程序已经产生了第一个有趣的超越标准模型的物理学提示。使用包含高阶环和重虚粒子的衰变模式--所谓的“企鹅”衰变--测量SIN2β，得到的值与用Charmonium模式测得的值相差2.6个标准差。到目前为止还不为人所知的重粒子预计会造成这样的差异。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的迹象，需要大量的数据。2006年夏秋两季，提供巴布尔光束的PEP-II e+e对撞机将进行升级，以获得所需的更高光度。巴布尔正在同步升级其Muon系统，以确保我们能够充分利用额外的数据。我们预计，从现在到2008年9月完成数据采集，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.