ATLAS - 中国科学技术大学

Report
https://twiki.cern.ch/twiki/bin/view/AtlasPublic
ATLAS实验最新结果
刘衍文
中国科学技术大学
中国物理学会2014年秋季会议, 哈尔滨, 2014年9月13日
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•Large
Hadron Collider
大型强子对撞机(LHC)
位于欧洲核子研究中心(CERN)
日内瓦湖
•CMS
LHC time line :
1992 : expressions of interest
1995.10 : LHC TDR published
2009.11: first pp collisons at CME=900 GeV
2010.2: first pp collisions at CME=7 TeV
m
2011: CMS and ATLAS recorded ~5/fb of data
2012: CMS and ATLAS ~20/fb at CME=8 TeV
•ALICE
•LHCb
•ATLAS
• 周长27km,跨越瑞士法国国境,总投资40亿美元
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• 世界能量最高最大的加速器,设计质心系能量14TeV(14x1012eV)
2
Muon spectrometer
• air-core toroids,
MDT+RPC+TGC+CSC
• s/pT ~ 2-7 %
• |h| < 2.7, |h|<2.5 ( precision
phys.)
Inner detector (B=2 T)
• Si pixels and strips
• Transition Radiation Detector
(e/ separation)
• s/pT ~ 0.05% pT(GeV)0.1%;
• |h| < 2.5, B=2 T(central solenoid)
EM Calorimetry
• Pb-LAr
• s/E ~ 10%/√E(GeV)1%
• |h|<3.2, |h| < 2.5 (fine granularity)
Length: ~ 46 m
Radius : ~ 12 m
Weight : ~ 7000 tons
Channels: ~ 108
Lcable: ~ 3000 km
Cost: 541M CHF
Hadron Calorimeter
• Fe/scintillator (central), Cu/W-LAr (fwd)
• s/E ~ 50%/√E(GeV)3%
• |h|<3
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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)
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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
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Delivered Luminosity [fb-1]
LHC run - 1
 Successful LHC run in
2010-2012
35 ATLAS Online Luminosity
30
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2010 pp s = 7 TeV
2011 pp s = 7 TeV
2012 pp s = 8 TeV
~ 5 fb-1 7 TeV data
~ 20 fb-1 8 TeV data
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15
10
 Similar for ATLAS & CMS:
~ 5 fb-1 7 TeV data
~ 20 fb-1 8 TeV data
5
0
Ja n
Apr
Jul
Oc t
Month in Year
-> most results shown used full 8
TeV data, few with half 8 TeV
data
 Peak luminosity at 2012:
 7.7 * 1033 cm-2s-1
 <μ> ~ 21 @ 8TeV
(Run 2: expect 2*1034 cm-2 s-1 )
 Data quality (2012):

Circumference ~ 26.7 km
93.7% good for physics
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A Z ->  event with
20 pile-up vertices
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Phys. Lett. B 726(2013)88-119
2013 combination(bosonic decay channels )
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Tension of ~2 standard deviations
Mass measurement with  and ZZ*

ZZ*
Combined:
Difference in 4e and 4 indicative
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arXiv:1408.7084v1
Couplings with H->
Currently still dominated by statistical
uncertainties.
Systematical uncertainties dominated
by theory.
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arXiv:1407.4222v2
Differential cross sections!
Jet pT > 30 GeV
Jet pT > 50 GeV
Shape satisfactorily described by theory.
Overall normalization offset.
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ATLAS-CONF-2014-031
Other bumps ?
Sliding signal mass windows, side-band interpolation for
background estimation
“Rediscovered” both the Z and Higgs bumps.
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arXiv:1408.5191v1
Couplings with H->ZZ*->4-lepton
BDT to categorize VBF signal
BDT to suppress non-resonant ZZ production
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ATLAS-CONF-2013-108
Higgs-> 
Signal significance= 4.1 standard deviations
Extensive usage of Boosted Decision Tree
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Higgs->/bb
ATLAS-CONF-213-079
VH
arXiv:1406.7663v1
ATLAS-CONF-2014-011
ttH
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Electroweak
SUSY production
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ATLAS-CONF-2014-033
+
WW
production
Uncertainty for the combined cross section: 7.5%
Level of excess: 2.1 standard deviations.
53.2 pb
1.4 pb
4.1 pb
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arXiv:1407.4537v2
Invited authors to Standard Model Plenary meeting for discussions
on August 14, 2014
“Explanations” of the excess: resummation of jet veto
ATLAS signal simulation: qq (POWHE+PYTHIA)
gg (GG2WWW +HERWIG)
Requested authors to check pTveto -> infinity, expect convergence with fixed
order calculation
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pT(WW) resummation
arXiv:1407.4481
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?
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arXiv:1405.6241v1
Same sign WW
Signal significance :
3.4 s.d
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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 !
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