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Understanding CP Violation in Bs at the Tevatron

Explore the history, measurements, and analysis of CP violation in Bs meson decays at the Tevatron collider, examining the transversity angles and flavor tagging techniques used. Understand the complex nature of these decays and the implications for particle physics.

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Understanding CP Violation in Bs at the Tevatron

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  1. CP Violation in Bs → J/yjat the Tevatron Karen Gibson

  2. History

  3. of Run II In the beginning, measurement of DGs ^ CDF measures DGs/Gs= 0.65 +0.25 – 0.33 ps-1  Dms ~ 125 ps-1 Released in 2004, 270 pb-1 Phys. Rev. Lett. 94, 101803 (2005) Beauty 2009

  4. At that time, life was simpler… Didn’t know Dms no need for flavor tagging! Beauty 2009

  5. Definition of Transversity Angles J/yrest frame jrest frame VV final state defines 3D coordinate system

  6. Check angular fit with B0 J/yK*0 Beauty 2009

  7. D0 measurement soon follows… Measure DGs/Gs= 0.24 +0.28 – 0.38 ps-1 Released in 2005, 450 pb-1 Phys. Rev. Lett. 95, 171801 (2005) Beauty 2009

  8. D0 includes fit to CP phase bs Likelihood more complicated… Previously ignored these, 2bs ~ 0 in SM • d║ = arg(A║(0) A0*(0)) • d  = arg(A  (0) A0*(0)) Beauty 2009

  9. Released in Jul. 2006, 1.1 fb-1 Phys. Rev. Lett. 98, 121801 (2007) js = –0.79 ± 0.56 • Dotted line indicates 39% CL Note: js-2bs“experimentally” No flavor tagging  four-fold ambiguity in determination of phase js t (Bs0) = 1.52 ± 0.08 (stat) +0.01 -0.03 (syst) ps DG= 0.17 ± 0.09 (stat) ± 0.02 (syst) ps-1 Beauty 2009

  10. CDF finds that things are not so simple • Can reliably quote some point estimates with 2bs fixed to standard model prediction • Mean lifetime, DG, |A0(0)|2, |A║(0)|2, |A(0)|2 • When 2bs floats freely in fit, see significant biases and non-Gaussian errors in pseudo-experiments at low statistics

  11. Quote confidence regions, rather than point estimates, when bs floats freely For bs fixed to 0, find: t (Bs0) = 1.52 ± 0.04 (stat) ± 0.02(syst) ps DG= 0.076 +0.059-0.063 (stat) ± 0.006 (syst) ps-1 Released in Aug. 2007, 1.7 fb-1 Phys. Rev. Lett. 100, 121803 (2008) Beauty 2009

  12. Meanwhile, everything changes! CDF observes Bs mixing in 2006  measures Dms & validates calibration of SST Dms [ps-1] Dms = 17.77 ± 0.10 (stat) ± 0.07(sys) Beauty 2009

  13. Tevatron Flavor Tagging • b quarks generally produced in pairs at Tevatron • Tag either b quark which produces J/yj, or other b quark Same side Opposite side

  14. Tagged CP measurements now possible Time dependence on DG, Dms, 2bs CP asymmetry h = +1 Bs0,h = -1Bs0 Dependence on cos(Dmst) Beauty 2009

  15. For comparison, without flavor tagging… CP asymmetry h = +1 Bs0,h = -1Bs0 Beauty 2009

  16. Two exact symmetries are present in Bs0 J/yj untagged analysis: • 2bs – 2bs, d d + p • DG –DG, 2bs 2bs + p • Gives four equivalent solutions in bs and DG! • With flavor tagging, only one exact symmetry is present: • 2bs p – 2bs • DG –DG • d║ 2p – d║ • d p – d • Leads to two equivalent solutions in bs and DG! Beauty 2009

  17. Reduce number of solutions in DG-bs CDF observes 1.5s deviation from SM bs Released in Dec. 2007, 1.35 fb-1 Phys. Rev. Lett. 100, 161802 (2008) Beauty 2009

  18. Approximate symmetry also present… For low statistics, likelihood profile is not parabolic  cannot reliably separate the two minima! N(Bs) ~ 2000 Choose one solution by restricting d║ [0,p) Beauty 2009

  19. D0 also includes flavor tagging Constrain strong phases d║and d┴within p/5 of the values measured in B0 J/yK*0 N(Bs) ~ 2000 Released in Feb. 2008, 2.8 fb-1 Phys. Rev. Lett. 101, 241801 (2008) Beauty 2009

  20. Present

  21. Current CDF result Updated for ICHEP 08 http://www-cdf.fnal.gov/physics/new/bottom/080724.blessed-tagged_BsJPsiPhi_update_prelim/ Yield increased from N(Bs0) ~ 2000 (1.35 fb-1) to N(Bs0) ~ 3200 (2.8 fb-1) For bs fixed to 0 (& no flavor tagging), find: t (Bs0) = 1.53 ± 0.04 (stat) ± 0.01(syst) ps DG= 0.02± 0.05 (stat) ± 0.01 (syst) ps-1 Beauty 2009

  22. Observe deviation from SM bs of 1.8s Beauty 2009

  23. Transversity angles  not efficiency subtracted! Beauty 2009

  24. Present CDF result doesn’t fully utilize data • No particle ID in Neural Network selection • No SSKT after 1.3 fb-1 Beauty 2009

  25. Current D0 result D0 released constraint on strong phases d║, d┴, added systematic uncertainties to Dms Released in May 2009 http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/B/B58/B58.pdf Beauty 2009

  26. D0 has also measured DG w/o tagging For bs fixed to 0, find: t (Bs0) = 1.48 ± 0.06 ps DG= 0.08 +0.07–0.08 ps-1 Released in Sept. 2008, 2.8 fb-1 Phys. Rev. Lett. 102, 032001 (2009) Beauty 2009

  27. Combination of CDF & D0 results Combined likelihood finds 2.1s deviation from SM Combination including other measurements of DG, e.g. asl, will be shown in Iain Bertram’s talk Updated for EPS 2009 http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/B/B59/B59.pdf http://www-cdf.fnal.gov/physics/new/bottom/090721.blessed-betas_combination2.8/ Beauty 2009

  28. Deviation from Gaussian regime Beauty 2009

  29. Future

  30. Available data D0 has collected 6.1 fb-1 of data CDF has collected ~5.8 fb-1 Beauty 2009

  31. Tevatron plans for next results • Update measurement to full data available through summer shutdown • >5 fb-1 of data good for B physics per experiment • Use particle ID and full tagging (both OS and SS) (CDF) Beauty 2009

  32. Non-resonant K+K- under j mass Both CDF and D0 plan to make statement about S-wave contamination in m(K+K-) • LHCb just released study on the effect of neglecting the possible S-wave contribution • see talk by Olivier Leroy for details Released in Aug. 2009 arXiv:0908.3627 Beauty 2009

  33. Simultaneous minimization of CDF & D0 data • Idea is to combine CDF and D0 datasets before minimizing • Most powerful method of combining datasets • Could minimize data as usual or use Markov chain Monte Carlo to combine the datasets • Different interpretations (frequentist vs. Bayesian) • Have already set up technical framework to combine the two datasets • In the process of confirming individual expts’ results • Plan to use new combination method for 5 fb-1 results Beauty 2009

  34. Stay tuned to Tevatron for future results! Beauty 2009

  35. Back-up

  36. Tagged Likelihood Bs0: Time dependence in T, U, V Bs0: + - Beauty 2009

  37. Deviation from Gaussian regime Beauty 2009

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