ATLAS 实验最新结果 刘衍文 中国科学技术大学 1 中国物理学会 2014 年秋季会议, 哈尔滨, 2014 年 9 月 13 日

2 日内瓦湖 Large Hadron ColliderLarge Hadron Collider 机场 CMS ATLAS LHCb ALICE 大型强子对撞机（ LHC ） 位于欧洲核子研究中心（ CERN ） 周长 27km ，跨越瑞士法国国境，总投资 40 亿美元 世界能量最高最大的加速器，设计质心系能量 14TeV(14x10 12 eV) m LHC time line : 1992 : expressions of interest : LHC TDR published : first pp collisons at CME=900 GeV : first pp collisions at CME=7 TeV 2011: CMS and ATLAS recorded ~5/fb of data 2012: CMS and ATLAS ~20/fb at CME=8 TeV 2

Inner detector (B=2 T) Si pixels and strips Transition Radiation Detector (e/  separation)  /p T ~ 0.05% p T (GeV)  0.1%; |  | < 2.5, B=2 T(central solenoid) Hadron Calorimeter Fe/scintillator (central), Cu/W-LAr (fwd)  /E ~ 50%/√E(GeV)  3% |  |<3 Muon spectrometer air-core toroids, MDT+RPC+TGC+CSC  /p T ~ 2-7 % |  | < 2.7, |  |<2.5 ( precision phys.) EM Calorimetry Pb-LAr  /E ~ 10%/√E(GeV)  1% |  |<3.2, |  | < 2.5 (fine granularity) Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Channels: ~ 10 8 L cable : ~ 3000 km Cost: 541M CHF 3

ATLAS 中国组 ATLAS Chinese Cluster (ACC) 五个单位组成（按英文字母排序） : Institute of High Energy Physics ( 高能所 ) （金山（万人、杰青）、欧阳群、庄胥爱（百人）、方亚泉（青千）、朱宏 博（百人）、单连友、娄辛丑（千人）） Nanjing University ( 南大 ) （陈申见、祁鸣） Shandong University ( 山大 ) （张学尧、马连良（青千）、冯存峰、祝成光） Shanghai Jiaotong University （上海交大） （杨海军（青千）、李亮（青千）） University of Science and Technology of China ( 科大 ) （赵政国（院士、千人）、韩良（杰青、百人）、蒋一、刘衍文、刘建北 （青千）、彭海平（优青、百人）、朱莹春、刘明辉） + 30 students and postdocs （科大学生约占一半） 4

5 大型强子对撞机 LHC 主要物理目标： 寻找 Higgs 粒子，理解对称性自发破缺机制以及质量的起源 寻找 TeV 能区 ( 其他 ) 可能的新现象 精确检验标准模型

LHC run - 1 Circumference ~ 26.7 km  Successful LHC run in  Similar for ATLAS & CMS: ~ 5 fb -1 7 TeV data ~ 20 fb -1 8 TeV data -> most results shown used full 8 TeV data, few with half 8 TeV data  Peak luminosity at 2012:  7.7 * cm -2 s -1  ~ 8TeV (Run 2: expect 2*10 34 cm -2 s -1 )  Data quality (2012):  93.7% good for physics ~ 5 fb -1 7 TeV data ~ 20 fb -1 8 TeV data 6

A Z ->  event with 20 pile-up vertices 7

2013 combination(bosonic decay channels ) 8 Phys. Lett. B 726(2013)88-119

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Mass measurement with  and ZZ* 10 Tension of ~2 standard deviations  ZZ* Combined: Difference in 4e and 4  indicative

Couplings with H->  11 arXiv: v1 Currently still dominated by statistical uncertainties. Systematical uncertainties dominated by theory.

Differential cross sections! 12 Jet pT > 30 GeV Jet pT > 50 GeV arXiv: v2 Shape satisfactorily described by theory. Overall normalization offset.

Other bumps ? 13 ATLAS-CONF Sliding signal mass windows, side-band interpolation for background estimation “Rediscovered” both the Z and Higgs bumps.

Couplings with H->ZZ*->4-lepton 14 arXiv: v1 BDT to categorize VBF signal BDT to suppress non-resonant ZZ production

Higgs->  15 Signal significance= 4.1 standard deviations Extensive usage of Boosted Decision Tree ATLAS-CONF

Higgs->  /bb 16 arXiv: v1 ATLAS-CONF VH ATLAS-CONF ttH

Electroweak SUSY production 17

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W + W - production 19 Uncertainty for the combined cross section: 7.5% Level of excess: 2.1 standard deviations. ATLAS-CONF pb 1.4 pb 4.1 pb

“Explanations” of the excess: resummation of jet veto 20 arXiv: v2 ATLAS signal simulation: qq (POWHE+PYTHIA) gg (GG2WWW +HERWIG) Invited authors to Standard Model Plenary meeting for discussions on August 14, 2014 Requested authors to check pT veto -> infinity, expect convergence with fixed order calculation

pT(WW) resummation 21 arXiv: Also presented at the same SM Plenary meeting pT(WW) correlates with jets transverse momentum -> jet veto efficiency : demonstrated an effect of a few percent Request: 1. adopt established tunes for PS 2.  2 resummation, and threshold resummation?

Same sign WW 22 arXiv: v1 Signal significance : 3.4 s.d

Summary Higgs Run 1 results mostly finalized. No other new phenomena observed …. Some 2 sigma excess W + W - production, under discussion. Looking forward to Run 2 data ! 23