大型强子对撞机CMS、ATLAS和ALICE实验物理研究2013年度报告

The 2013 Annual Report of the CMS、ATLAS and ALICE Physics Study at LHC Experiment

该研究分为3个研究组,分别按照任务书2013年度计划和要求展开研究,具体研究内容如下:(1)CMS研究组。1Higgs粒子确认及其性质研究:用2012全年数据测量H->YY的截面,并与标准模型预言相比较。在测量方法上将使用2D拟合提高灵敏度。2新物理寻找:寻找W->tb。与费米实验室合作完成,我方将负责t->wb,W->enu部分。开展SUSY粒子寻找,Top粒子产生和衰变中的新物理研究。(2)ATLAS研究组。1ATLAS实验中Higgs粒子的寻找:VBF Higgs衰变到双光子道研究;H->γγ中Higgs微分产生截面测量;H->WW*物理分析。2ATLAS实验中超对称物理研究:di-tau末态弱相互作用SUSY粒子寻找;强相互作用SUSY粒子的寻找。3top夸克物理研究:单top夸克伴随W玻色子产生过程寻找;单top夸克模拟;Track MET重建研究;top衰变中的W自旋分布测量。(3)ALICE研究组。1围绕夸克物质硬探针信号,通过观测质子-质子碰撞、质子-核碰撞和核-核碰撞中的中性粒子产生、粒子关联、重夸克和W玻色子的muon谱,以及部分子函数矩分布,检验QCD预言,建立核-核碰撞粒子谱压低参考标准,研究冷核效应影响,观测部分子在密度物质中的能量损失效应,研究夸克物质性质。2围绕夸克物质集体运动,通过观测高能核-核碰撞中phi粒子和多奇异重子的椭圆流、重夸克衰变muon粒子的椭圆流,研究夸克物质的热化程度和集体运动行为,研究夸克物质体系部分子自由度行为。

IHEP CMS group made a good contribution for both discovery and property measurement. As the production rate of Higgs to twogamma is very low, while the background rate is 12 magnitudes higher. To find Higgs in this channel is just like to dig out gold sandin a heap of normal sand. To reject the background effectively is the key for success. IHEP group provided the best method to rejectbackground, and method was accepted by CMS. So we solved a key problem in the two gamma channel. When measuring the property,IHEP group participated both two gamma and 4 lepton channel analyses. In the two gamma channel, the mass and production rate wasmeasured and the results are consistent with the Standard Model prediction. For the analysis we provided gamma identification method,a production rate scale factor from the interference of signal and background and gamma energy calibration. In the 4 lepton channel, themass, production rate, couplings, spin and parity was measured. And the results all agree with the Standard Model prediction. Now allthe particles predicted were found, the Standard Model gained a great success. But it can not explain what is dark matter, nor darkenergy, and has no idea for the asymmetry between mass and anti-mass. People believe it is only an effective theory under a certainenergy scale. Something beyond must exist, and we are going to find it. CMS IHEP group tried to do it through two ways, one is tosearch for new physics directly, the other is to check the Standard Model predictions, any violation could hint to a new physics. ATLASChinese Cluster (ACC) made leading contributions in many important physics topics, including study of Higgs particle, searches of SUSYparticle and study of top quark physics. In the VBF Higgs production studies, ACC firstly applied MVA technique, which significantlyimprove the sensitivity of the analysis so that we observed the first evidence of VBF Higgs boson production in ATLAS experment. ACCfirtly performed the analysis to search for SUSY particles in the di-tau final states which is sensitive to the stau particle searches,we also deeply involved in the SUSY search with one soft lepton final state. We played leading role in the above two SUSY analyses.ACC members are the editors of physics papers of the above Higgs and SUSY papers. ACC also made major contributions to the H->WWdecays and top phsycis studies, including the single top production and top spin correlation measurements.