Early physics with ATLAS and CMS

The status of the CMS and ATLAS experiments is given, as it is end of 2007. A quick tour of possible new physics is presented.      

Symmetry tests within the Standard Model and beyond from nuclear muon capture

Precision measurements in nuclear muon capture on the proton and ³He allow for tests of the Standard Model for the strong and electroweak interactions, complementary to those achieved in high energy experiments. The present situation and future prospects are reviewed, emphasizing where renewed efforts could prove to be rewarding in exploring ever further beyond the confines of the Standard Model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Discovery of the Higgs boson by the ATLAS and CMS experiments at the LHC

The Standard Model (SM) Higgs boson was predicted by theorists in the 1960s during the development of the electroweak theory. Prior to the startup of the CERN Large Hadron Collider (LHC), experimental searches found no evidence of the Higgs boson. In July 2012, the ATLAS and CMS experiments at the LHC reported the discovery of a new boson in their searches for the SM Higgs boson. Subsequent experimental studies have revealed the spin-0 nature of this new boson and found its couplings to SM particles consistent to those of a Higgs boson. These measurements confirmed the newly discovered boson is indeed a Higgs boson. More measurements will be performed to compare the properties of the Higgs boson with the SM predictions.     

Leading order one-loop CP and P violating effective action in the Standard Model

The fermions of the Standard Model are integrated out to obtain the effective Lagrangian in the sector violating P and CP   at zero temperature. We confirm that no contributions arise for operators of dimension six or less and show that the leading operators are of dimension eight. To assert this we explicitly compute one such non-vanishing contribution, namely, that with three Z⁰$Z^0$, two W⁺$W^{+}$ and two W⁻$W^{-}$. Terms involving just gluons and W?s are also considered, however, they turn out to vanish in the P-odd sector to eighth order. The analogous gluonic term in the CP-odd and P-even (C-odd) sector is non-vanishing and it is also computed. The expressions derived apply directly to massive Dirac neutrinos. All CP-violating results display the infrared enhancement already found at dimension six.     

无中微子双贝塔衰变与超出标准模型的新物理

作为自然界中最罕见的过程之一,无中微子双贝塔衰变是寻找超出标准模型的重要手段。文章将介绍这一过程的理论和实验研究面临的重大挑战。对这个过程的精确计算依赖于原子核多体方法,而目前的多体方法的精度还有待提高。不同多体方法得到的结果之间存在一定的差异,这些差异定性上可以通过相关模型的缺陷来解释,定量上还缺乏有效的研究。通过有限的实验可观测量来约束衰变的底层机制是理论上的一个重要挑战,目前的可观测量主要是出射电子的性质和原子核的性质,相关的研究还比较匮乏。