摘要
2012年,位于大型强子对撞机(Large Hadron Collider,LHC)上的CMS(Compact Muon Solenoid)探测器和ATLAS探测器分别独立地观测到了Higgs粒子,有力验证了标准模型.在标准模型中,W玻色子是传递电弱相互作用的规范矢量玻色子,通过电弱对称性自发破缺(electroweak symmetry breaking,EWSB)的Higgs机制获得基本质量及纵向极化分量;随着LHC数据的累积,在高能标下更加细致地检验和研究W规范矢量玻色子的相互作用成为可能.本文简要回顾W玻色子研究的相关内容,并重点介绍近期在大型强子对撞机CMS实验上由北京大学高能组主导完成的W玻色子相互作用的研究,包括Wγ的联合产生、Wγ的散射过程、WW散射过程(极化散射、Majorana中微子探寻)以及WWW共振态的寻找.当前,LHC已经进入三期取数阶段,相信随着亮度的持续增加,LHC上CMS实验有关W玻色子的研究会更加拓展和深入.
The Higgs boson discovery in 2012,the final piece of the Standard Model(SM)puzzle,marked a new era in particle physics.At the Large Hadron Collider(LHC),it is a hot research topic at the high-energy frontier of high-energy physics to precisely test the SM by measuring processes such as multi-bosons coupling with W or exploring new physical phenomena containing W boson beyond the Standard Model(BSM)in the Standard Model.With the accumulation of data at LHC,it becomes possible to examine and study the interaction of the W gauge vector bosons in more detail at the LHC at the frontier of high-energy physics.At CMS(compact muon solenoid),the first measurement of the associated production of a W boson and a photon process and both the electron and the muon decay modes of the W boson were used to extract the cross section by a maximum likelihood fit to the lepton-photon mass distribution.The measured cross section in a defined fiducial region isσ=15.58±0.75 pb,consistent with theoretical expectations at next-to-leading order in quantum chromodynamics.This search further studied possible new physics by the limits on the coefficients of the dimension-six operators relevant to anomalous triple gauge couplings with the effective field theory(EFT)approach at the 95%confidence level(CL),and finally gave a world’s best limit on the Cwww parameter,which provides important input information for the indirect search for new physics beyond the SM.The first observation Wγwith two jets was also performed at CMS,with observed(expected)significance 5.3(4.8)standard deviations,where the W boson decays events were selected by requiring one identified electron or muon and an imbalance in transverse momentum,and the two jets were required to have a high di-jet mass and a large separation in pseudorapidity.CMS also reported polarized same-sign W boson pairs search for the first time in the world.The longitudinally polarized vector boson scattering can verify if the Higgs boson preserves the unity and help deeply understand the electroweak symmetry breaking.The observed(expected)upper limit at 95%CL on the production cross section for longitudinally polarized same-sign WW scattering is provided to be 1.17(0.88)fb.Based on the same-sign WW scattering,CMS researchers also probed heavy Majorana neutrinos at the TeV energy scale and the dimension-five Weinberg operator for the first time at a collider,and the observed(expected)upper limit at 95%confidence level on the effectiveμμMajorana mass was reported in this study to be 10.8(12.8)GeV.For the decay of a resonance to two heavy bosons,various final states have also been searched at CMS.By studying WWW resonance,the theoretical hypothesis of WKK with mass less than 3 TeV can be excluded at 95%confidence level.The studies of the W boson at the high-energy frontier contain a wealth of content,and it is believed that W boson physics at high-energy colliders will enter an unprecedented crucial period with the high-luminosity LHC(HL-LHC)phase.
作者
关喆
彭靖
肖杰
安莹
郭启隆
钱思天
牟天钰
冒亚军
班勇
李强
Zhe Guan;Jing Peng;Jie Xiao;Ying An;Qilong Guo;Sitian Qian;Tianyu Mu;Yajun Mao;Yong Ban;Qiang Li(State Key Laboratory of Nuclear Physics and Technology,School of Physics,Peking University,Beijing 100871,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2023年第20期2634-2641,共8页
Chinese Science Bulletin
基金
国家自然科学基金(12061141002)资助
