1. 硕转博答辩 Student ID：SA17004015 Name：刘明依 E-mail：nh196245@mail.ustc.edu.cn
Supervisor：赵政国、吴雨生

2. Outline Resume Scholastic record Research progress Research statement
1. Overview
2. My work & objectives
3. Cross-section calculation at LO and NLO
4. Acceptance factor calculation and theory uncertainty for 4 lepton channel
5. Summary
Research statement
2018/4/28
Mingyi.Liu

3. Resume Education Sept. 2010-Jun. 2013 :
Shiyan High School, Shenyang, Liaoning Province, China
Sept Jun :
Department of Modern Physics, University of Science and Technology of China (USTC), Hefei, Anhui, China.
Major: Experimental high energy physics; Weighted average：86.9/100
Feb.2017-Aug :
CERN, visiting scholar. Undergraduate thesis: ATLAS - VBSZZ (13 TeV)
Sept :
Major: Experimental high energy physics; Weighted average：90/100
Reward
2012: Second Prize in Physics Contest of National Middle School students.
2012: Second Prize in Mathematics Contest of National Middle School students.
2014, 2015, 2016: USTC Excellent Student Scholarship
2018/4/28
Mingyi.Liu

4. Scholastic record SA17004015 刘明依 FL05301 研究生综合英语 通过 2 40 外语系
学年第一学期
公共必修课
PS05101a
自然辩证法概论 1 18
燕京晶
PS05102a
中国特色社会主义理论与实践研究 36
吴神贵
PS06101a
中国马克思主义与当代 徐飞
PH05101
高等量子力学 97 4 80
张仁友
基础课
PH14203
粒子物理(I)
杨为民
专业课
PH24211
粒子探测技术 91
刘建北等
PH14205
高等统计物理 88 陈志
PH14202
量子场论（I） 85
高道能
PH14201
物理学中的群论 79
朱界杰
2018/4/28
Mingyi.Liu

5. Vector Boson Scattering ZZ production with the ATLAS detector at the LHC
13 TeV
EWK ZZjj (non-VBS)
EWK ZZjj (VBS)
QCD ZZjj
Motivation
The scattering of two weak bosons is closely linked to the mechanism of electroweak symmetry breaking.
The observation of weak gauge boson scattering is a good opportunity to gain information on quartic gauge couplings of massive weak bosons and to compare to the Standard Model prediction.
First VBS ZZ+2jets measurement with ATLAS data.
Objective
Measure the ZZ+2jets cross section (EWK and QCD)
Evidence on EWK VBS ZZ+2jets
aQGC limits settings
Plan
Combine 4l and 2l2v
Dataset
13TeV( )
Try to achieve 3 sigma
2018/4/28
Mingyi.Liu

6. Overview Fiducial phase space Total phase space
For electron pt > 5GeV && |η| < 2.47
For muon pt > 5GeV && |η| < 2.7
two pairs of well-paired leptons
|Ml1l2-MZ|+|Ml3l4-MZ|->min
pt > 20,20,10,7GeV
Z mass window [60,120] GeV
mll > 10GeV (SFOC)
△Rll>0.2 for any two leptons in the truth quad
AntiKt4TruthJets ηj1*ηj2<0
For |η| < pt > 30GeV
For 2.4 < |η| < pt > 40GeV
mjj > 200 GeV
|ηj1 – ηj2| > 2
For leptons pt > 5GeV && |η| < 2.7
two pairs of well-paired leptons
|Ml1l2-MZ|+|Ml3l4-MZ|->min
Z mass window [60,120] GeV
mll > 10GeV (SFOC)
AntiKt4TruthJets ηj1*ηj2<0
For jets |η| < 5 pt > 20GeV
mjj > 200 GeV
These are for the 4 lepton channel
2018/4/28
Mingyi.Liu

7. Overview Currently we haven’t looked at data in the signal region yet
A BDT has been trained on top of the SR
The sensitivity has been enhanced
For the signal region, defined similar to P6 fiducial region.
Control region to study QCD ZZjj background
2018/4/28
Mingyi.Liu

8. My work & Objectives
Generate the EW sample(signal) with Madgraph5+Pythia8 under Athena framework and standalone Madgraph5; compare the private sample with the official sample and with the Sherpa2.1 sample Undergraduate thesis
Determine the k-factor of EWK 4 lepton channel, for which I calculated the production cross section using generator VBFNLO (V2.7.1).
Study the fiducial region and total phase space to calculate the A factor and C factor of 4 lepton channel.
Study of theoretical uncertainty on A factors
2018/4/28
Mingyi.Liu

9. Cross-section calculation at LO and NLO
Cross-section comparison (LO) K-factor (VBFNLO 2.7.1)
Process
Madgraph5 cross-section
VBFNLO cross-section
p p>2Z2j>4e2j fb fb
p p>2Z2j>4m2j
p p>2Z2j>4l2j fb fb
process
Cross-section(LO)
Cross-section(NLO)
K-factor
p p>2Z2j>4e2j fb fb
p p>2Z2j>4m2j
p p>2Z2j>4l2j fb fb
K factor of the 4 lepton process is very close to 1, which means the contribution from NLO is quite small.
For leading order of EWK process, final results do not depend on the choice of renormalization scale. (M. Peskin: Chap 12.2)
So the theoretical unc. caused by ren scale is insignificant.
2018/4/28
Mingyi.Liu

10. A factor & its theoretical uncertainty
A factor: A= 𝑊𝑒𝑖𝑔ℎ𝑡𝑒𝑑 𝑒𝑣𝑒𝑛𝑡 𝑛𝑢𝑚𝑏𝑒𝑟 𝑓𝑖𝑑𝑢𝑐𝑖𝑎𝑙 𝑟𝑒𝑔𝑖𝑜𝑛 𝑊𝑒𝑖𝑔ℎ𝑡𝑒𝑑 𝑒𝑣𝑒𝑛𝑡 𝑛𝑢𝑚𝑏𝑒𝑟 𝑡𝑜𝑡𝑎𝑙 𝑝ℎ𝑎𝑠𝑒 𝑠𝑝𝑎𝑐𝑒 theoretical uncertainty
Reweight to get A factors of different weights, compare with the nominal one:
Statistical uncertainty 𝑆𝑡𝑎.𝑈𝑛𝑐= 1−𝐴 𝐴/𝑁 A means the nominal a factor, N is the event number at total phase space
Theoretical uncertainty
1. PDF uncertainty: The standard variance of the A factor calculated by different PDF weights.
2. Scale uncertainty: Sorting the A factors of different Scale weights, get Amax and Amin, upper/lower unc. = |Amax/min – A|
3. Theoretical uncertainty: 𝑇ℎ𝑒𝑜.𝑈𝑛𝑐= (𝑃𝐷𝐹.𝑈𝑛𝑐) 2 + (𝑆𝑐𝑎𝑙𝑒.𝑈𝑛𝑐) 2
About the sample
Official sample:
mc15_13TeV MGPy8EvtGen_A14_NNPDF23LO_VBFH125_sbi_4l_m4l130_EW6
Self-generated sample:
PDF uncertainty
Ren/Fac scales
Different weights
NNPDF30_lo_as_0118(LO)
Scale factor: 0.5, 1, 2
Nominal scale: geometric mean of M2+PT2 of each particle
2018/4/3
Mingyi.Liu

11. Self-generated sample (σ=0.639fb) Official sample (σ=0.636fb)
Research Progress
A factor & its theoretical uncertainty Theo. Unc. of Yield at Fiducial phase-space
Generator level
X-section (fb)
Total phase space
Fiducial phase space
Event number
Official sample
0.636
0.330
0.232
290000
Private sample
0.639
0.333
0.233
99993
A factor
Sta. unc.
PDF unc.
Up/Low QCD unc.
Up/Low unc.
0.699
0.002
0.003
0.004/0.004
0.005/0.005
~ 1%
Self-generated sample (σ=0.639fb)
Official sample (σ=0.636fb)
Yield of nominal weight (L=80fb-1)
18.64
18.56
Yield
Sta. Unc.
PDF. Unc.
Scale Unc. (up)
Scale Unc. (low)
Unc. (up)
Unc(low)
18.64
0.16
1.16
1.12
1.00
1.60
1.52
The whole Uncertainty for the yield ~ 8%
2018/4/28
Mingyi.Liu

12. Distribution & its theoretical uncertainty
Bin-by-bin symmetrized
2018/4/28
Mingyi.Liu

13. Distribution & its theoretical uncertainty
2018/4/28
Mingyi.Liu

14. Summary
QCD ZZjj prediction agrees with data well in the control region. For signal prediction needs BDT to reduce the signal-background ratio
NLO K-factor for the EWK ZZjj production is very close to 1
Theoretical uncertainty of A factor and yield has been done. Unfortunately, uncertainties go larger in the high mJJ or large |dEtaJJ| region, needs to calculate the uncertainty caused by Parton shower.
2018/4/28
Mingyi.Liu

15. Research Statement Next step in current study:
Uncertainty caused by parton shower; Theoretical uncertainty of 2l2v channel
For future:
Attend the CSC joint project to BNL
A further and more precise study about VBSZZ by using Run3 data
ATLAS upgrade/Certificate
Searching for dark photon by using data from LHC
2018/4/28
Mingyi.Liu

16. Thanks
2018/4/28
Mingyi.Liu

17. Backup
2018/4/28
Mingyi.Liu

18. Generator parameter settings
2018/4/28
Mingyi.Liu