CMS Bc 模拟重建和分析

1. CMS Bc 模拟重建和分析 陈 国 明

2. CMS Experiment 2007年夏 Large Hadron Collider CMS

3. At 1034 Bunch cross: every 25ns 23 inelastic events per bunch cross Pile Up 16μm 77mm At 1033 : 2.3 events /cross

4. Minimum bias events the average charge multiplicity: 30 for |η|<2.5, pT>150MeV

5. CMS Experiment

6. CMS Experiment η=2.5 z y x Cross-sectional view of CMS

7. Transverse slice through CMS detector Click on a particle type to visualise that particle in CMS Press “escape” to exit

8. 高能所： 端盖μ子 探测器的 1/3 磁铁支架 地板 北大： 部分RPC CMS 5M CHF 2500万人民币

9. ATLAS 高能所： 桶部和端盖交接 处的μ子探测器 部分桶部μ子探测器 山东大学： 端盖μ子触发器的1/6 中国科技大学： 端盖μ子触发电子学 南京大学： 前后向吸收体 1.5M CHF 750万人民币

10. 取得了入场券 • 我国在硬件上的投了资, 取得了数据分析的入场券。 • 与投资多的国家有平等的机会，分析所有数据。

11. 数据分析是挑战 • 数据量大 • 本底高 • 探测器庞大, 软件环境复杂 • 竞争激烈：30 多个国家，200多个大学和研究所， 2000多科学家

12. 国内LHC物理分析的现状 从2000年开始连续3次向基金委申请面上项目, 用作CMS 的MC 研究, 未批准. 2004年设立重点基金, 并批准135万支持CMS和ATLAS的MC模拟. 2005—2008 4年 CMS 高能所 30 万 Bc HVV CMS 北大 35 万 大横动量J/Ψ ATLAS 高能所 30 万 Htt ATLAS 山大 30 万 tt 公用 10 万

13. 计算设施初步计划 在高能所为CMS 和 ATLAS各建一个Tier2 计算设施， 需经费 2000万 但还没有落实

14. IHEP CMS物理分析设想 选取 2l+X sample 头三年, 亮度≈1033, 轻子触发横动量: single electron >29GeV double electron >17GeV single muon >19GeV double muon >7GeV 合计 事例率: 60Hz 每年: RECO 75TB, AOD 25TB, 共100TB 往后,亮度1034 ,轻子触发横动量提高

15. 刻度 根据人力情况选做部分子探测器的刻度: • MUCH μ+μ-对, J/Ψ, Z0峰, MUCH 径迹与TRACKER径迹的对比 • TRACKER e+e-对, μ+μ-对, J/Ψ, Z0峰, MUCH 径迹与TRACKER径迹的对比 • ECAL e+e-对, J/Ψ, Z0峰, 能量动量对比

16. 亮度测量 通过Drell-Yan e+e-,μ+μ-的角分布测量亮度 目前，理论计算的误差 2%

17. 物理研究 • J/Ψ→μ+μ-,Υ→μ+μ-横动量分布 • Bc→J/Ψlν, J/Ψπ J/Ψ→μ+μ- ,e+e- • Blind search e+e- , μ+μ- , e+μ- , e-μ+ 共振态 • Stau 寻找 • HWW coupling l+l+ missing ET • l-l- , l+l+ , without missing ET majorana ν • Higgs search H →ZZ →l+l- jj

18. CMS Bc goals and channels Mass , life time and relative branching ratio 1. Bc→J/Ψlν(J/Ψ→l+l-) 2. Bc→J/Ψπ(J/Ψ→l+ l-)

19. Bc Meson (Experiment) Experimental observation (CDF & D0 , Tevatron) 1998 2004 2005 Recent results on Bc meson

20. LHC (14TeV) p p Production of Bc at LHC

21. CMS Experiment Adavantage • LHC : PP Energy 14TeV The production cross section of Bc meson will be ~ 10 bigger than that at Tevatron. • The CMS detector has the similar structure as CDF, and has larger detector cover region than CDF. CMS :eta~(-2.5,2.5) CDF:eta~(-1,1) (RUN I) eta~(-1.5,1.5) (RUN II) (Muon system) • The CMS detector has a better identified ability to muons ,this is more useful for the channels which include muon/muons in the final state. And better vertexing.

22. Our MC goals • Studying the feasibility of research of Bc meson at the CMS • Studying the events select strategy of the Bc reconstruction • Estimating the number of Bc events available at the CMS • Studying the system error Preparing for the near future experiment!

23. List of CMS Software

24. The Installation of CMS Software The CMS software was downloaded and installed in our home machine successfully. ORCA_8_1_3 OSCAR_3_2_4 (2004,10) ORCA_8_6_1 OSCAR_3_6_3 (2004,12) ORCA_8_7_3 OSCAR_3_7_0 (2005,4) The version of the CMS software are being used in our home machines are OSCAR_3_7_0ORCA_8_7_3 Newest: OSCAR_3_9_8 ORCA_8_13_1 need new framework .

25. Display of Bc events Bc→J/ψµν (J/ψ→µµ)

26. Display of Bc events Bc→J/ψµν (J/ψ→µµ)

27. The CMS Analysis chain HEPEVTNtuple MC generator ORCA OSCAR OSCAR 1)digitization 2)reconstruction 3)analysis SimReader RecReader RecReader Ntuplesignal POOLSimHits/signal ROOTTree POOL Digis DST Ntupleminbias POOLSimHits/minbias “data summary tape” User

28. MC generator Bc production: C.H. Chang X.G. Wu ITP Beijing Bc decay and interface with OSCAR: G.M. Chen S.H. Zhang IHEP Beijing A.A. Belkov S. Shulga JINR Dubna (Russia)

29. MC generator comparision of Pt distributions of Bc meson PYTHIA~ 1event/2 min. BCVEGPY~ 102 events/ min.

30. Single lepton reconstruction efficiency The reconstructed efficiency of single muon/electron V.S. The Pt cut of the single muon/electron In order to get the reconstructed muon or electron as efficiency as enough,we require in the generator level: For µ : Pt >= 4.0GeV |Eta|<=2.2 For e : Pt >= 4.0GeV |Eta|<=2.2

31. Generator Bc is generated with (pT≥10GeV,|eta|≤2) The production cross section is σ=10.6nb (including 11S0 ,13S0)

32. Generator Level Muon pT Cut Efficiency Bc→J/ψµν (J/ψ→µµ) |η|≤ 2.2

33. Generator (Ntuple) Simulation (OSCAR) Reconstruction (ORCA) Event Select Analysis Results

34. J/Ψ Selection Bc→J/Ψ+ lν (or π) J/Ψ→l+l- 2 leptons Pt ≥ 4.0 GeV 2 leptons share the same vertex 2 leptons have different charge 2 leptons’ invariant mass around the J/Ψ

35. Selection of the Lepton from Bc Bc→J/Ψ+ lν J/Ψ→l+l- Be identified as a muon or a electron Pt ≥ 4.0 GeV come from the same vertex (J/Ψvertex)

36. Bc SignalReconstructed Results J/ψ µ Mass (GeV/c2) M(µ+µ-) (GeV/c2) Bc→J/ψµν (J/ψ →µµ)

37. Bc SignalReconstructed Results µ from Bc directly 1/Ptrec – 1/Ptgene (GeV-1) Bc→J/ψµν (J/ψ →µµ)

38. Bc→J/ψπEvents Selection Study (1). J/Ψ Selection is as before. (2). for pion, we required: Be not identified as a lepton Pt ≥ 2 GeV Share the same vertex with 2 leptons (J/Ψ vertex)

39. Bc Signal Reconstructed Results M(µ+µ-) (GeV/c2) J/ψ π Mass (GeV/c2) Bc→J/ψ π (J/ψ →µµ)

40. Bc SignalReconstructed Results Bc π from Bc 1/Ptrec – 1/Ptgen (GeV-1) 1/Ptrec – 1/Ptgen (GeV-1) Bc→J/ψπ (J/ψ →µµ)

41. CERN INFN IHEP,BEIJING Backgrounds Study We don’t have enough computing power A series of Datasets of backgrounds we need are stored in CERN, CNAF, etc. LHC Computing Grid

42. __________

43. Backgrounds Study The backgrounds which have been transmitted and studied by now includes: _

44. Backgrounds Study Number of Events in the integrated Luminosity of 10 fb-1 _

45. Backgrounds Study Bc signal After event select and CMS HLT, the effect of background B0s→ J/ψΦ(J/ψ→µµ) to the Bc channel Bc→J/ψπ(J/ψ→µµ)

46. Backgrounds Study After event select and CMS HLT, in the integrated Luminosity of 10 fb-1 , the background B0s→ J/ψΦ(J/ψ→µµ) V.S. Bc signal Bc→J/ψπ(J/ψ→µµ)

47. Summary (I) 1. Preliminary Events Select (for the search of Bc at the CMS experiment) 1. Bc→J/Ψlν(J/Ψ→l+l-) • Pt (lepton) ≥ 4.0GeV. • 3 leptons shared the same vertex. • The invariant mass of a pair of leptons (l+l-) which have different charges is around J/ψ. e.g. |M(µ+µ-) – M(J/ψ)|≤ 0.2GeV • For the uncertainty of the losing of neutrino, we take the range[3.0GeV,7.0GeV] as our signal region of J/ψl. • For CMS HLT, required: Single µ: Pt≥ 19GeV Double µ: Pt ≥ 7GeV • Single e: Pt≥ 29GeV Double e: Pt ≥ 17GeV 2. Bc→J/Ψπ(J/Ψ→l+ l-) • 2 leptons (from J/ψ) • Pt (lepton) ≥4.0GeV ,share the same vertex, have different charge • Invariant mass of the 2 leptons is around J/ψ • Pion selection • The particle is not identified as a lepton • Pt ≥ 2.0GeV , shares the same vertex of J/ψ • Pion candidate is isolated in the cone • 3) For CMS HLT.

48. Summary (II) 2. Number of Bc events available at the CMS experiment (S-wave)

49. Summary (III) 3. Bc study in CMS After our analysis of Bc signals and background ,for the channels Bc→J/Ψlν(J/Ψ→l+l-) , it’s believed we can distinguish the signals from the backgrounds efficiently. For the channels Bc→J/Ψπ(J/Ψ→l+ l-) ,we still need more detailed analysis of the properties of the π in order to distinguish the signals and backgrounds more efficiently. In a word, It’s believe that studying the Bc meson at the CMS experiment is very optimistic.

50. To do list • More backgrounds research: prompt J/Ψ etc. for Bc→J/Ψπ(J/Ψ→l+ l-) ,the more important background is B±→J/ΨK± ,now we have been starting to simulate this channel. • Research the Bc signals and backgrounds carefully, find out a better selection to distinguish the Bc signals from backgrounds . • Mass and lifetime fitting, error estimation.