ATLAS实验上ZZ双玻色子产生的物理研究

发布时间：2017-09-24 05:32

  本文关键词：ATLAS实验上ZZ双玻色子产生的物理研究

  更多相关文章： 粒子物理 ATLAS实验 ZZ 标准模型 Higgs粒子 新物理

【摘要】：在大型强子对撞机LHC上的质子-质子对撞中,有多种物理机制可以产生ZZ双玻色子末态。利用Z玻色子的轻子衰变(Z→ll)和中微子衰变(Z→vv),即双轻子和丢失横动量的实验末态,本论文研究了ATLAS实验上在质心系对撞能量为8TeV下采集的ZZ事例,总积分亮度为20.3fb-1。 首先,利用ZZ→llvv衰变道,我们测量了标准模型下ZZ产生的反应截面。这一产生过程在粒子物理标准模型下可以进行精确的理论计算,通过实验测量,我们可以与标准模型的预言相比较,验证理论计算。实验测得的8TeV能量下ZZ产生的总截面为σZZtot=8.84-0.88+1.04(stat.)-0.85+0.87(syst.)-0.28+0.33(lumi.)pb；而在NLO精度下的理论预言结果为6.58-0.28+0.30pb；两者相差为1.8个标准差。在最新的NNLO QCD修正下,理论计算结果为7.74-0.31+0.35pb,与我们的测量结果符合的更好。我们还进一步利用实验数据寻找了三玻色子异常耦合对ZZ产生的可能贡献。由于在实验上没有观察到与标准模型预言的明显偏差,我们给出了异常耦合参数的上限值。与ATLAS先前发表的实验结果相比,我们获得了对异常耦合最严格的限制。 2012年在LHC上发现的希格斯(Higgs)粒子被发现同样具有离壳效应(off-shell),这一效应在Higgs质量高于2倍于Z玻色子质量(2mz)的范围内可以被观察到,并对ZZ事例的产生增加额外的贡献。因此H*→ZZ衰变提供了一个独特的机制来测量Higgs粒子的离壳耦合强度。利用ZZ→llvv末态,在95%的置信水平下,Higgs离壳信号强度的上限被确定为在9.6-12.4的范围内,预期的上限区间为8.8-13.3。进一步与ZZ→4l及WW→evμv衰变道的实验结果相结合,我们观察到(预期)的约束范围为5.1-8.6(6.7-11.0)。在每种情况下,上限范围是通过改变未知gg→ZZ和gg→WW本底的高阶QCD修正因子与已知的gg→H→ZZ和gg→H→WW信号的高阶QCD修正因子之间的比值来确定的,并且这一比值的变化区间为0.2-2。假设相关的Higgs的耦合是独立于Higgs生产的能标,与在壳(on-shell)测量的耦合强度相结合,我们可以进一步限制Higgs粒子的总的质量宽度ΓH。在95%的置信水平下,我们获得的观察(预期)的ΓH/THSM范围是4.5-7.5(6.5-11.2)。假定未知的gg→VV本底的高阶QCD修正因子与信号的相同,这一结果可以转化成Higgs总宽度在95%的置信水平下的上限,即观察(预期)结果为22.7(33.0)MeV。 最后,基于H→ZZ→llvv衰变,我们寻找了质量在240和1000GeV之间的新的Higgs粒子。实验数据与本底假设相符合,我们设定了在双Higgs二重态模型(2HDM)中的额外Higgs粒子产生的截面的上限。在这一模型中,tanβ的很大一部分范围被排除了,并且排除范围取决于cos(β-α)；对于cos(β-α)=±0.1,tanβ1的区域,在95%的置信水平下,Higgs质量在250-350GeV区间内被排除了。我们还提供了独立于任何物理模型的关于Higgs产生截面与H→ZZ分支比的乘积的上限。在胶子-胶子融合(ggG)反应道下,对于一个质量为400GeV的Higgs粒子,σggF×BΥH→ZZ在95%的置信水平下的上限为227fb,预期的上限为209fb。在矢量玻色子融合(VBF)反应道下,σggF×BΥH→ZZ在95%的置信水平下的上限为248fb,预期的上限为136fb。
【关键词】：粒子物理 ATLAS实验 ZZ 标准模型 Higgs粒子 新物理
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O572.214
【目录】：

• 摘要6-8
• 英文摘要8-10
• acknowledgements10-13
• 致谢13-15
• Contents15-20
• 附件20-21
• 1 Introduction21-25
• 2 Theory25-55
• 2.1 The Standard Model of Particle Physics25-31
• 2.1.1 Elementary particles26-27
• 2.1.2 Electroweak theory27-29
• 2.1.3 Electroweak symmetry breaking and the Higgs mechanism29-31
• 2.2 Beyond the Standard Model31-34
• 2.3 Dark Matter34-38
• 2.3.1 Dark matter particle candidates34-35
• 2.3.2 Effective field theories35
• 2.3.3 Higgs portal35-37
• 2.3.4 Dark matter detections37-38
• 2.4 Phenomenology for the Large Hadron Collider38-44
• 2.4.1 Hadronic collision39-42
• 2.4.2 Monte Carlo event generators42-44
• 2.5 Diboson physics at the LHC44-47
• 2.5.1 Diboson production44
• 2.5.2 Anomalous triple gauge couplings44-47
• 2.6 Higgs physics at the LHC47-54
• 2.6.1 Higgs production at LHC47-48
• 2.6.2 Higgs decays48-50
• 2.6.3 BSM Higgs benchmark models50-54
• 2.7 Physics with ZZ production54-55
• 3 The Large Hadron Collider and the ATLAS Experiment55-73
• 3.1 The Large Hadron Collider55-59
• 3.1.1 Design parameters and machine layout55-58
• 3.1.2 Operation and performance58-59
• 3.2 The ATLAS Experiment59-73
• 3.2.1 Overview59-62
• 3.2.2 Physics requirements62-63
• 3.2.3 Inner Detector63-65
• 3.2.4 Calorimeters65-68
• 3.2.5 Muon Spectrometer68-70
• 3.2.6 Trigger70-73
• 4 The ATLAS Detector Simulation and Event Reconstruction73-105
• 4.1 Event Simulation73-77
• 4.1.1 Simulation framework73-75
• 4.1.2 Fast simulation75-77
• 4.2 Event Reconstruction77-105
• 4.2.1 Track77-80
• 4.2.2 Primary vertex80-81
• 4.2.3 Electron81-91
• 4.2.4 Muon91-96
• 4.2.5 Jet96-101
• 4.2.6 Missing Transverse Energy101-105
• 5 Measurement of the SM ZZ Production Cross Section105-215
• 5.1 Introduction105-111
• 5.1.1 Theory and Experimental status107-108
• 5.1.2 Analysis Overview108-111
• 5.2 Theoretical calculations and uncertainties111-120
• 5.2.1 Cross Section Definitions111-112
• 5.2.2 Cross Section Prediction112-120
• 5.3 Data and MC Samples120-122
• 5.3.1 Data Samples120
• 5.3.2 Signal MC modeling120
• 5.3.3 Background MC modeling120-122
• 5.4 Trigger122-123
• 5.5 Physics Object Selection123-129
• 5.5.1 Electrons123-125
• 5.5.2 Muons125-127
• 5.5.3 Jets127
• 5.5.4 Missing Transverse Momentum127
• 5.5.5 Primary Vertex and Pileup Reweighting127-128
• 5.5.6 Object Overlap Removal128-129
• 5.6 Event Selection129-136
• 5.6.1 Preselection129-130
• 5.6.2 l+l-vv Selection130-131
• 5.6.3 Signal cut flow131-136
• 5.7 Backgrounds136-160
• 5.7.1 W Z background136-140
• 5.7.2 tt,tW,WW and ττ background140-145
• 5.7.3 Z background145-151
• 5.7.4 Data-driven estimate of W and multijet background151-158
• 5.7.5 The other backgrounds158-160
• 5.8 Systematic Uncertainties160-171
• 5.8.1 Electrons160-161
• 5.8.2 Muons161-162
• 5.8.3 Jets162-164
• 5.8.4 Missing transverse energy164
• 5.8.5 Luminosity and pileup164
• 5.8.6 Theoretical uncertainties164-169
• 5.8.7 Summary of systematic uncertainties169-171
• 5.9 Selection Results171-177
• 5.9.1 Final Numbers of Observed and Expected Events171
• 5.9.2 Kinematic Distributions171-177
• 5.10 Cross Section Extraction177-184
• 5.10.1 Efficiency Correction Factor and Acceptance177-179
• 5.10.2 Cross Section Extraction Procedure179-181
• 5.10.3 Cross Section Results181-184
• 5.11 Extraction of the Anomalous Triple Gauge Couplings(aTGC)184-201
• 5.11.1 Introduction184-185
• 5.11.2 MC samples and Observables Sensitive to aTGC's185-187
• 5.11.3 TGC Parametrization and Matrix-element Reweighting187-191
• 5.11.4 TGC Limits Setting191-194
• 5.11.5 Binning Optimization194-196
• 5.11.6 Results196-201
• 5.12 Conclusions201-203
• 5.13 Appendix203-215
• 5.13.1 Background mc samples203-204
• 5.13.2 Performance packages204
• 5.13.3 Jet veto acceptance204-215
• 6 Measurement of the Off-shell Higgs Signal Strength215-287
• 6.1 Introduction215-217
• 6.2 Analysis idea and theoretical considerations217-220
• 6.3 Simulation220-244
• 6.3.1 Simulation and corrections to the gg→VV→4f processes220-230
• 6.3.2 Simulation and corrections to the qq→VV→4f background230-237
• 6.3.3 Correlations between gg→VV→4f and qq→VV→4f237-238
• 6.3.4 Simulation of VV final states in electroweak production modes238-242
• 6.3.5 Dependence of the off-shell signal and the background interference on the signal strength242-244
• 6.4 Analysis strategy in the ZZ→2l2v channel244-251
• 6.4.1 Physics Object Selection244-248
• 6.4.2 Cut Optimization248-251
• 6.5 Background estimation251-262
• 6.5.1 ZZ and WZ Backgrounds251-253
• 6.5.2 WW,tt,Wt,and Z→ττ Backgrounds253-256
• 6.5.3 Z→ee,μμ Backgrounds256-261
• 6.5.4 W+jets and Multijet Backgrounds261-262
• 6.6 Systematic uncertainties262-269
• 6.6.1 Experimental Uncertainties262-263
• 6.6.2 Theoretical Uncertainties263-269
• 6.7 Event Selection Results269-271
• 6.8 Extraction of off-shell couplings and Higgs total width271-280
• 6.8.1 Extraction of off-shell couplings in H~*-→ZZ→llvv271-272
• 6.8.2 Combination with H~*→ZZ→llll and H~*→WW→lvlv Channel272-275
• 6.8.3 Constrains on the Higgs Total Width275-280
• 6.9 Summary280-281
• 6.10 Appendix281-287
• 6.10.1 Additional study of theoretical uncertainties281-287
• 7 Search for Heavy Higgs Bosons287-381
• 7.1 Introduction287-289
• 7.2 Data and Monte Carlo Samples289-291
• 7.2.1 Data sample289
• 7.2.2 Signal samples289
• 7.2.3 SM Higgs samples289-290
• 7.2.4 Other Background Samples290-291
• 7.3 Selection of Physics Objects291-292
• 7.4 Event Selection292-303
• 7.4.1 Trigger292
• 7.4.2 Event Preselection292-295
• 7.4.3 H→ZZ→llvv Selection295-303
• 7.5 Backgrounds303-333
• 7.5.1 Di-boson background303-304
• 7.5.1.1 ZZ background303
• 7.5.1.2 WZ background303-304
• 7.5.2 Z background304-314
• 7.5.3 Wand multijet backgrounds314-326
• 7.5.4 WW,tt,Wt and Z→ττ326-331
• 7.5.5 Other backgrounds331
• 7.5.6 Summary331-333
• 7.6 Systematic Uncertainties333-337
• 7.6.1 Experimental systematic uncertainties333-335
• 7.6.2 Theoretical uncertainties335-337
• 7.7 Results337-340
• 7.8 Statistical interpretation340-358
• 7.8.1 Likelihood definition340-341
• 7.8.2 Fit inputs341
• 7.8.3 Statistical uncertainties341
• 7.8.4 Pruning of the Systematic Uncertainties341-342
• 7.8.5 Nuisance parameter pulls and constraints342
• 7.8.6 Nuisance parameter correlations342-345
• 7.8.7 Nuisance parameter ranking345
• 7.8.8 Postfit plots345-358
• 7.9 Exclusion Limits358-364
• 7.9.1 Exclusion limits on narrow-width Higgs358-359
• 7.9.2 Esclusion limits on 2HDM359-364
• 7.10 Conclusion364-365
• 7.11 Appendix365-381
• 7.11.1 MC samples for the Higgs signal365
• 7.11.2 Expected Higgs signal yields365
• 7.11.3 Signal acceptance uncert ainty365-373
• 7.11.4 WZ Theory Uncertainties373-376
• 7.11.5 Pruning of systematics and MC statistical uncertainties376-380
• 7.11.6 2HDM Interpretation380-381
• 8 Summary381-383
• 9 The Expected Sensitivity for Run 2383-393
• 9.1 Introduction383-385
• 9.2 Expected Sensitivity for Invisible Higgs Search385-387
• 9.3 Expected Sensitivity for Higgs Off-shell Signal Strength Measurement387
• 9.4 Expected Sensitivity for Heavy Higgs Search387-391
• 9.5 Summary391-393
• Bibliography393-413

【共引文献】

中国期刊全文数据库 前10条

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2 郭奉坤;Ulf-G.Mei?ner;王伟;;Production of Charged Heavy Quarkonium-Like States at the LHC and Tevatron[J];Communications in Theoretical Physics;2014年03期

3 王青;;2013年诺贝尔物理学奖介绍:规范粒子质量的起源[J];物理与工程;2014年01期

4 刘星;曹学香;李公平;魏龙;，

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