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

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

Resume Education Sept. 2010-Jun. 2013 : Shiyan High School, Shenyang, Liaoning Province, China Sept. 2013-Jun. 2017 : 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. 2017 : CERN, visiting scholar. Undergraduate thesis: ATLAS - VBSZZ (13 TeV) Sept. 2017- : 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

Scholastic record SA17004015 刘明依 FL05301 研究生综合英语 通过 2 40 外语系 2017-2018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

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(2015+2016+2017) Try to achieve 3 sigma 2018/4/28 Mingyi.Liu

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| < 2.4 pt > 30GeV For 2.4 < |η| < 4.5 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

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

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

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 0.155 +- 0.001 fb 0.155 +- 0.0001 fb p p>2Z2j>4m2j p p>2Z2j>4l2j 0.618 +- 0.001 fb 0.621 +- 0.0004 fb process Cross-section(LO) Cross-section(NLO) K-factor p p>2Z2j>4e2j 0.155 +- 0.0001 fb 0.154 +- 0.0001 fb 0.994 +- 0.001 p p>2Z2j>4m2j p p>2Z2j>4l2j 0.621 +- 0.001 fb 0.604 +- 0.007 fb 0.973 +- 0.011 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

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.345071.MGPy8EvtGen_A14_NNPDF23LO_VBFH125_sbi_4l_m4l130_EW6 Self-generated sample: https://indico.cern.ch/event/709245/contributions/2931541/attachments/1615309/2566840/A_factor_uncertainty.pdf 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

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

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

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

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

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

Thanks 2018/4/28 Mingyi.Liu

Backup 2018/4/28 Mingyi.Liu

Generator parameter settings 2018/4/28 Mingyi.Liu