陳國(guó)明

摘 要：去年在歐洲核子中心大型強(qiáng)子對(duì)撞機(jī)上的CMS實(shí)驗(yàn)和ATLAS實(shí)驗(yàn)同時(shí)發(fā)現(xiàn)了質(zhì)量為125 GeV的新粒子，今年，也即2013年，CMS實(shí)驗(yàn)研究該粒子的性質(zhì)，看到該粒子的衰變方式，信號(hào)強(qiáng)度，與其他粒子的相互作用強(qiáng)度以及自旋宇稱都與理論預(yù)言的希格斯粒子一致，盡管目前還不能100%的確定，人們基本上相信該粒子就是上述理論家所預(yù)言的希格斯粒子。因此，做出預(yù)言的理論家獲得今年的諾貝爾物理學(xué)獎(jiǎng)。在希格斯粒子的發(fā)現(xiàn)以及性質(zhì)測(cè)量中，我方做出了重要貢獻(xiàn)。CMS實(shí)驗(yàn)是從雙光子和4輕子這兩個(gè)衰變道找到希格斯粒子的。CMS中國(guó)組參加了雙光子道的分析。希格斯到雙光子的產(chǎn)率很低，而本底的產(chǎn)率則要高12個(gè)量級(jí)，這好比在一大堆的沙子中找一顆金沙子，非常難。如何有效排除本底是成功的關(guān)鍵，中國(guó)組提出了最有效排除本底的辦法，被CMS合作組采用。因此，在雙光子道，我方解決了一個(gè)最關(guān)鍵的問(wèn)題。在性質(zhì)測(cè)量中，我方同時(shí)參加了雙光子和4輕子這兩個(gè)衰變道的分析。CMS利用H→雙伽瑪衰變道測(cè)量Higgs粒子的質(zhì)量以及產(chǎn)生截面與理論預(yù)測(cè)之比，結(jié)果與標(biāo)準(zhǔn)模型在誤差范圍內(nèi)一致。我方的主要貢獻(xiàn)在于提供了多變量識(shí)別光子的方法，提供了信號(hào)與本底的干涉效應(yīng)對(duì)信號(hào)強(qiáng)度的修正因子和光子能量的標(biāo)定。CMS同時(shí)利用4輕子道測(cè)量Higgs粒子的質(zhì)量，衰變寬度和自旋宇稱，結(jié)果與標(biāo)準(zhǔn)模型預(yù)言一致。我們的主要貢獻(xiàn)是負(fù)責(zé)了分析方案的設(shè)計(jì)、施行，代碼的編寫、調(diào)試等，我方在CMS的分析中對(duì)統(tǒng)計(jì)分析以及統(tǒng)計(jì)模型的建立做出了重要貢獻(xiàn)。

關(guān)鍵詞：大型強(qiáng)子對(duì)撞機(jī) CMS 希格斯粒子

The Progress Report of CMS Physics Research in 2013

Chen Guoming

（Institute of High Energy Physics， Chinese Academy of Sciences）

Abstract：IHEP CMS group made a good contribution for both discovery and property measurement. At CMS， Higgs boson was discovered from two gamma and four lepton channel. IHEP group participated the two gamma channel analysis. As the production rate of Higgs to two gamma is very low， while the background rate is 12 magnitudes higher. To find Higgs in this channel is just like to dig out gold sand in a heap of normal sand. To reject the background effectively is the key for success. IHEP group provided the best method to reject background， 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 was measured 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， the mass， production rate， couplings， spin and parity was measured. And the results all agree with the Standard Model prediction. IHEP group provided the statistical model， analysis scheme， and performed code development and debug. Mingshui Chen from our group is the convener of CMS Higgs combination and property measurement， and plays a key role in the Higgs property measurement. Now all the particles predicted were found， the Standard Model gained a great success. But it can not explain what is dark matter， nor dark energy， and has no idea for the asymmetry between mass and anti-mass. People believe it is only an effective theory under a certain energy scale. Something beyond must exist， and we are going to find it. CMS IHEP group tried to do it through two ways， one is to search for new physics directly， the other is to check the Standard Model predictions， any violation could hint to a new physics. In the new particle search， we see an evidence of a new resonance at 17.6 GeV through double J/psi decay. It is not approved by CMS， and we are still working on it. For the Standard Model examining， we measured the two gamma final state differential production rate， and the results agree with the Standard Model prediction.

Key Words：LHC； CMS； Higgs Boson