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Status of the LHCb Experiment

2010 年 4 月 17. Status of the LHCb Experiment. 杨振伟 Tsinghua Group on LHCb. 高能物理大会. ➢ Success running in 2009 @ 2.36 TeV ➢ Beam energy Ramping to 3.5 TeV last week ➢ first collision @ 7 TeV on March 30st ➢ Physical running in May. The LHCb Collaboration. ~800 物理学家 54 研究机构

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Status of the LHCb Experiment

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  1. 2010年4月17 Status of the LHCb Experiment 杨振伟 Tsinghua Group on LHCb 高能物理大会

  2. ➢ Success running in 2009 @ 2.36 TeV ➢ Beam energy Ramping to 3.5 TeV last week ➢ first collision @ 7 TeV on March 30st ➢ Physical running in May

  3. The LHCb Collaboration • ~800 物理学家 • 54 研究机构 • 15 国家 • 北美1个（美国） • 亚洲1个（中国） • 南美1个（巴西） • 主要目标：CP破坏和新物理的研究。 • 2008诺贝尔奖(Kobayashi & Maskawa), “for the discovery of the origin of the broken symmetry which predicts the existence of at least 3 families of quarks”

  4. LHCb上的物理 • 新物理探测1. CP破坏2. 稀有衰变…… • B物理和粲物理研究1. 瞬时J/Psi粒子产生机制2. Bc物理研究3. Lambda_b……

  5. LHCb 探测器 • 几何接受度：15—300mrad；1.9<η<4.9 （对撞机上的前向探测器） • 顶点探测器：σx,y ~10μm， σz ~60μm； σL ~250μm • 径迹系统：Dp/p = 0.35 % - 0.55%, s(m)=12-25 MeV/c2 • π/K鉴别：e(KK) ~95 %，误鉴别率~5% ，3σ内鉴别p<60GeV • μ鉴别：e(mm) = 94 %, 误鉴别率(pm) = 3 % • ECAL：s(E)/E= 10% E-1/2 1 % (E in GeV) • HCAL： s(E)/E= (69+/-5% E-1/2 (9+/-2) % (E in GeV)

  6. LHCb acceptance B - B B - B LHCb上B的产生 • bb 的产生前向-后向高度关联 • θ~15-300 mrad (4.9>η>1.9) • bb 产生截面（LHCb接受度内）：σbb ~ 230 µb • B+ (40%), B0 (40%), Bs (10%), b-baryons (10%), Bc (< 0.1%) • LHCb将亮度限定在1032 cm-2s-1量级（ATLAS/CMS在1034 cm-2s-1量级） • 保证单位截面发生一次相互作用的概率最大 • LHC早期运行即可达到的量度 • 每年~2fb-1数据 • 每年~ 1012 bb

  7. LHCb独特的接受度 • LHC/Tevatron上探测器接受度的比较

  8. 基本运行状况 • 目前运行状况良好： • 2009年底：900GeV（VeloOpen）各个子探测器状况良好V0物理研究~4.68×106重建事例 • 2010.03.30：7TeV（自4月5号，VeloClosed，所有探测器正常工作） • ~2.5×107重建事例(4.13)V0物理研究粲物理研究……

  9. VELO Vertex分辨率

  10. 初步结果：V0 900GeV 7TeV

  11. 初步结果：K*，(1020)  →KK K*→K Cut？RICH？

  12. 初步结果：→Λ

  13. 初步结果： D0

  14. 初步结果：D+, Ds, D* Ds→KK Harji et al. Δm D*(2010)→K

  15. 初步结果：J/ (data vs MC)

  16. Λ / Λbar ratio: the situation in 2009 Belyaev et al.

  17. anti-Λ Λ α=0.93+/-0.07 所用数据为VeloOpen，2010 7TeV 同时被VeloClosed的数据验证 900GeV??????

  18. 清华组目前的物理分析 • V0系统误差的研究 • J/Psi产生机制研究 • Bc物理 • Upsilon的产生 • …… • MC模拟研究已经完成，发布了3篇public notes • LHCb-PUB-2010-011, • CERN-LHCb-2008-059, CERN-LHCb-2008-077 • Conference talks

  19. J/Selection(MC) μ tracks: ● long tracks ● hits in muon detector (fun. of pT) ● Combined PID > -1 ● pT > 0.7 GeV/c ● Track quality (χ2/nDoF < 2) Reconstructed J/ψ: ● Mass window: 0.4 GeV/c2 ● vertex fit quality (χ2/nDoF <6) Event selection: ● At least one PV ● RemoveClones ➢ mass resolution (σ): 11.1±0.4 MeV/c2 ➢ S/B in 3σ range: 17.6 ±2.3 ➢ 1 pb-1 @ 7 TeV: 3.2 × 105J/ψ rec. ➢ 1 J/ψ rec. per 105 MB events

  20. Reconstructed tzdistribution ➢Prompt J/ψ ➢ J/ψ from b ➢ Tail distribution ➢ Background

  21. “Final” Results: Input:

  22. t distribution Four components to the t distribution Prompt component Gaussian J/ from b Exponential Prompt background [extract from mass sidebands] Long tail due to association of wrong primary vertex [Measure using the J/ vertex and the PV in different event]

  23. To be measured Theoretical model Acceptance • The acceptance depends on pt, and polarisation… LHCb geometry induces “fake polarisation” !

  24. Analysis Strategy • Measurement in bins of pt and   reduce model dependence on • Acceptance vs. cos at each bin estimated by MC • At each bin, perform a joint fit to (MJ/, t, cos) • So we simultaneously measure easy transformations to other ref. frames Cross Sections Polarisation

  25. Cross Section Measurement • Tests of fitting procedure on a sample corresponding to 0.145 pb-1 @ 14 TeV - Signal: inclusive J/ sample with full simulation - Background: toy Monte-Carlo reproducing behaviour on Minimum Bias sample Fit MC input values Number of prompt J/y Fraction of J/y from b

  26. Remarks on Lumi. • Integrated luminosity at LHCb may be measured by: - Beam-gas interaction in VELO - Van der Meer Scan (10% ) - Z0 and W-rapidity distribution fit (~1.6% in 100 pb-1) - Elastic di-muon production (~3% in 100 pb-1) • Or take ratios to a known process, i.e. B+ J/ K+ • Or normalized to ATLAS/CMS results at the overlap region

  27. Uncertainties • Statistical error <10% per pt and  bin with 5pb-1 at 8TeV • Need real data to understand tracking, muon PID, vertexing … i.e. acceptance vs cos could be checked by B+ J/ K+ • Error on luminosity: ~10% • Error on Br(bJ/ X): ~9% • Error on fit: possible errors from fit function etc.

  28. Bc Physics

  29. 总结 • 自2009年底开始运行， LHCb探测器已经准备就绪，各个子探测器状况良好。 • V0分析接近完成（首批900GeV和7TeV数据）数据与蒙特卡罗的对比仍在进行。 • 2010年7TeV数据粲物理分析开始其他物理准备中 • Promt J/Psi、Bc物理分析正在预备中

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