山东大学ATLAS组工作进展

1、C. Zhu Top WG 01/06/061山东大学山东大学ATLAS组工作进展组工作进展已完成工作的总结数据分析工作进展祝成光祝成光 (山东大学山东大学)C. Zhu 01/06/0622002年至2005年, 山东大学负责为ATLAS研制 子子探测器：TGC(thin gap chamber), 400台探测器现已按时交付CERN。目前，山东大学派出一个3人小组在CERN进行TGC探测器的安装和维护 已完成工作的总结C. Zhu 01/06/063TGC探测器实验室C. Zhu 01/06/064我们所贡献的探测器质量明显好于另外两个合作单位KEK和Weizmann所研制的探测器。- A

2、TLAS子谱仪负责人G. Mikenberg教授信中称所有探测器1%的死区 （标准为20GeV34% electron-events have exactly 1 electron pt25GeVL1 trigger “EM25I “ 3 jets with highest are used to form top9.6% has exactly 4 jets (Cone0.4) pt40GeVThe fourth jet C. Zhu 01/06/0612Trigger EM25I suppress 4% of signal comparing to offline cutS/B is sl

3、ightly pessimistic because no trigger used for rome data (background)Background not perfectly represented by fit(pol3)ttbar_dilep, Singletop, and ttbar_had events are negligibleHadronic top reconstruction(1)S/B=0.45Nsig=203Com bkgdTtbar_dilepTtbar_tauTtbar_had & Singletop W4jetsCom bkgd: deltaR(

4、jjj, true_t)0.3C. Zhu 01/06/0613Method to choose 2 light jets in topjjjCompute Ea, Eb, Ec without knowing bjetCase 1( 43%), only 1 E falls in energy windowLight jets First 2 jets used to calculate this E Otherwise (57%): First light jet with smallest energy.Second light jet with higher pt in labo fr

5、ame out of the rest 2.Reconstruct W in jjj Ea( j1 + j2 jb ) Eb( jb + j1 j2 ) Ec( jb + j2 j1 )In top C.M. frame:E(q1+q2- b)= E(w- b)=37.4GeV, smeared in full simulation. only Ea is peaking around 37GeV, and most drop in window +/-15GeV. C. Zhu 01/06/0614Keeping only events within Mw peak+/-10GeV to c

6、lean the backgroundS/B increased from 0.45 to 0.71, # of signals decrease from 203 to 147Hadronic top reconstruction(2)S/B=0.71Nsig=147C. Zhu 01/06/0615(after kinematic and Mw cuts)M(l,the 4th jet)pure signal ttbar event w4jets eventOther quality cut variablesC. Zhu 01/06/0616W mass within 10GeV win

7、dow of fitted Mw AND Mlb150GeVS/B increased from 0.71 to 1.0, # of signals decrease from 147 to 136.Between +/-30GeV beside jjj peak, there are 272 events, the fourth jet are b jet in 122 events.Hadronic top reconstruction(3)S/B=1.0Nsig=136C. Zhu 01/06/0617Detector performance degradation S/B keeps

8、similar with standard cut Removing Etmiss cut doesnt include much ttbar_had events (5evts) Will include QCD backgroundMw +/- 10GeV & Mlb30GeV0.65210 Ejet*1.11.07152 Ejet*0.91.01100C. Zhu 01/06/0618Raw btag当前的工作是，我们试图尝试使用较为粗糙的btag，来检测它是否能带给我们更好的结果C. Zhu 01/06/0619使用ttbar的单轻子衰变事例37k(weighted) Jets

9、 ( pt40GeV |eta|2)efficiency and purity is : 0.631722 and 0.778004C and l jet rejection is : 3.08441 and 8.97827weight btag (IP3D+SV13 for btag)efficiency and purity is : 0.722355 and 0.921742C and l jet rejection is : 4.57797 and 74.75C. Zhu 01/06/0622Reconstruct W in jjj If there is 1 and only 1 j

10、et are b-tagged in this jjj system (49.7% of the case), then combine the other 2 jets to w. Otherwise, disgard this event (50.3% of the case)C. Zhu 01/06/0623Hadronic top reconstruction(2)S/B=0.71Nsig=147S/B=3.39Nsig=68Keeping only events within 70GeVwjj_mass90GeVFrom presentation06_06_01C. Zhu 01/06/0624(after kinematic and Mw cuts)M(l,the 4th jet)pure signal ttbar event w4jets eventOther quality cut variablesC. Zhu 01/06/062570GeVwjj_ma