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From East to West, From Charmonium to CP in B Decays

From East to West, From Charmonium to CP in B Decays. A story by Yuehong Xie CERN & Tsinghua University Edinburgh, 12 June 2003. Personal. 1969 Birth in Hunan, China 1976-1988 Educated in an Chinese culture environment 1988-1995 Physics student at Nankai University, China 1995-1999

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From East to West, From Charmonium to CP in B Decays

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  1. From East to West,From Charmonium to CP in B Decays A story by Yuehong Xie CERN & Tsinghua University Edinburgh, 12 June 2003

  2. Personal • 1969 • Birth in Hunan, China • 1976-1988 • Educated in an Chinese culture environment • 1988-1995 • Physics student at Nankai University, China • 1995-1999 • PhD student at Institute of High Energy Physics (Beijing) on BES experiment • 1999.11-2001.4 • INFN Postdoctoral Fellow at Laboratori Nazionalidi di Frascation Babar • 2001.10-2002.1 • Research scientist at Institute of High Energy Physics on BES • 2002.2-present • Researcher at CERN & Tsinghua University on LHCb Y. Xie, CERN & Tsinghua Univ.

  3. PART I Long Time Ago Y. Xie, CERN & Tsinghua Univ.

  4. When I was Young … • Philosophy in Chinese stories • Matter in the world started from collision of “Yin” & “Yang” (Negative & Positive) • Matter is composed of “Yin” & “Yang” • Simple but intriguing: is it true? • Dreamed to become a physicist and learned more in school • Origin of the universe : Big Bang • Composition: atom-> nucleus … • Too complicated! • Went to university to study physics Y. Xie, CERN & Tsinghua Univ.

  5. M.S. Thesis e- Z • Calculation of with two Higgs doublets • Find Feynman rules • Derive amplitudes of 10 tree diagrams by hand • Design a tool for calculation of tree Feynman diagrams in Fortran • Evaluate possible experimental observation • What I gained? • Some understanding of theory • Interest in experiment triggered… Z b H/h e+ b Experimental signature: Z->e+e-, m+m- Two b-jets Cross section vs E c.m.s. Mass recoiling from Z Y. Xie, CERN & Tsinghua Univ.

  6. PhD on BES • BES – Beijing Electron Positron Spectrometer • 2-5GeV: J/Y, Y(2S), t, D0, D+/D-, Ds, … • My physics interest: Y(2S) decays • Search for hc(1p1) in Y(2S) ->p0 h_c(1p1) • Is there a vector glueball mixed with J/Y which is responsible for the suppressed rate of Br(Y(2S) ->rp) / Br(J/Y ->rp) ? • Also worked on reconstruction and calibration of TOF subsystem Main Objectives: t-charm physics , understanding of strong interaction, test of QCD prediction and precision of QCD calculation tools at charm energy Y. Xie, CERN & Tsinghua Univ.

  7. PhD Study – Search for hc(1p1) • hc(1p1) reported by E760 in pp ->p0 J/Y • M=3526MeV, 1+ - state expected • Need confirmation • BESI Search for Y(2S) ->p0 hc(1p1) • Upper limit of branching ratio • Limited by calorimeter resolution • MC study for future detectors • Fast Monte Carlo method • Spin-parity analysis sensitivity Will Continue with BEPCII/BESIII p0 g Y(2S) hc hc Y. Xie, CERN & Tsinghua Univ.

  8. PhD Study – Vector Glueball? Expectation based on perturbative QCD • Br(Y(2S) ->rp) / Br(J/Y ->rp) <<14% • Vector glueball “O”? • Degenerate(mixed) with J/Y. 1 state • “O”: Large component of |ggg> • J/Y: Large component of |cc> • Experimental method: • Select Y(2S) ->p+ p- r p • Fit to get likelihood for all allowed settings of “O” mass and width • Compare with no-“O” likelihood • Sorry, “O”, or I can’t see you • Physics is not so easy as I dreamed -- What is experienced in search for new things? Hope - Excitement -Frustration - New hope - Reality - Honesty Side product: PhD g c g O J/Y c g Y. Xie, CERN & Tsinghua Univ.

  9. Pleasant Stay in Rome • Mainly worked on BaBar KL reconstruction software • Reject charged residual clusters • Improve match of IFR neutral clusters with EMC • Improve composite clustering algorithm • Used in BaBar 2000-2001 run • Involved in selection of Bd->J/Y KL for sin(2b) measurement • Learned some B physics … Y. Xie, CERN & Tsinghua Univ.

  10. On Crossroad in the New Millennium … • Was going to move to SLAC to be more involved in CPV, but in life there are always things we can’t control … • Diverted to non-physics business: easy and enjoyable, but Life without challenge = Dinner without wine ! • Soon back to Institute of High Energy Physics • Worked on e+ e- ->S L p to studyproperties of excited S and L baryons • CERN opportunity to work on LHCb: why is the world not symmetric in terms of particle-antiparticle and left-right ? Y. Xie, CERN & Tsinghua Univ.

  11. Part II Footmark in LHCb Y. Xie, CERN & Tsinghua Univ.

  12. General Remark About LHCb • LHCb : the experiment on LHC dedicated to the study of CP violation in B meson decays and rare B decays • What is essential for the task? • Efficient trigger : 10MHz -> 200 Hz • Efficient particle detection/reconstruction and precise momentum/energy measurement • Efficient particle identification • Efficient B flavor tagging • Precise measurement of B flight time Y. Xie, CERN & Tsinghua Univ.

  13. Realization Trigger Velo B flight Time PID B tagging Tracking Y. Xie, CERN & Tsinghua Univ.

  14. Track Finding Algorithms (fromJeroen van Tilburg’s talk on LHC2003 Symposium, Fermilab) Finally apply clone killing algorithm. • Select the best candidate among tracks that share many hits. Velo tracks 23 Forward tracks 27 Matched tracks Seed tracks 4 VTT tracks 10 T  TT tracks 10 Y. Xie, CERN & Tsinghua Univ.

  15. Contains Detector Geometry information Material information Parameters for digitization Totally ~ 400 xml files! Used by IT Detector simulation IT Digitization Track transport in fitting My First Step: IT Geometry Description in XML Y. Xie, CERN & Tsinghua Univ.

  16. Reconstruction of Low Momentum Particles: Velo->TT (VTT) Tracking • Why are low momentum particles important: • For a complete tracking • For RICH1 pattern recognition • For B tagging with Charged Kaons • For physics analysis: slow pions in D* decays, Ks … • How ? • Look for hits in Velo and TT detectors that are compatible with being produced by the same charged particles • Tak into account the magnetic field effect: parameterization Y. Xie, CERN & Tsinghua Univ.

  17. VTT Parameterization x • Straight line extrapolation in y • Parameterize the deviation in x from straight line extrapolation as a function of 1/pxz for each layer of the TT • Given moment, can predict hit position • Given a TT cluster, can estimate pxz Dx4 z Y. Xie, CERN & Tsinghua Univ.

  18. VTT Track Finding Algorithm • Estimate moment p for a unused VELO track and each TT hit, requiring the extrapolated y is consistent with the y range of the TT hit • Find a TT pair inside a TT half-station and require dp/p<20% • Find another TT hit in a layer of the other half and require dp/p<40% wrt to the other 2 TT hits • Fast fit: find a p value to minimize c2 • Loop over all combinations and choose the best combination for the VELO trackwithsmallest c2 • Build a track with this Velo track and the selected TT measurements, and refit it with a Kalman Filter to take into account the full geometry and magnetic field information • c2 < cut Y. Xie, CERN & Tsinghua Univ.

  19. Justification … (Plots for old TT layout, not updated for latest TT) Close p estimates: coherent multiple scattering effects in RICH1 94.8% True combinations have smaller c2 96.8% 92.5% Y. Xie, CERN & Tsinghua Univ.

  20. VTT Performance Y. Xie, CERN & Tsinghua Univ.

  21. RICH1 RICH1 needs VTT Tracks • RICH1 needs all type of tracks for Cherenkov photon image pattern recognition • Number of tracks seen by RICH • Availability of VTT tracks is essential for K/pi separation of long tracks at low momentum region Busy environment Y. Xie, CERN & Tsinghua Univ.

  22. PID Improvement by VTT [ Guy Wilkinson’s talk at LHCb light meeting Tuesday 12 November 2002 ] Y. Xie, CERN & Tsinghua Univ.

  23. Kaons Tag with VTT tracks (Marta Calvi, LHCb Week, 26th February 2003 ) • 19% of sel.events have a K- from B, reconstructed as long track • 3% of sel.events have a K- from B, reconstructed as VTT track • PID of Long tracksthemselves already benefits from VTT tracks K VTT track K long track VTT helps here! Y. Xie, CERN & Tsinghua Univ.

  24. %15 of Kaons can be recuperated by using VTT tracks assuming perfect PID First attempt to include VTT tracks gives only marginal effect PID of VTT tracks themselves not optimized VTT track quality not checked before use Using VTT Tracks in Tagging Need to be exploited! Y. Xie, CERN & Tsinghua Univ.

  25. Why Use VTT Tracks in Analysis? • VTT tracks are low momentum tracks starting from Velo but not reconstructed as long tracks • ~ 10 VTT tracks/event, shouldn’t be ignored • Velo measurements as good as that of long tracks • ~15% momentum resolution. But in some channels, kinematical constrained fitting can compensate for it • Vretex constraint : Ks vertex, B vertex, … • Mass constraint: Ks mass • B0->J/y(mm) Ks(pp) is such a channel • Low momentum pions from D*->D p Y. Xie, CERN & Tsinghua Univ.

  26. VTT Tracks in Bd->J/y(mm) Ks Event topology B0 & J/Y vertex B0 m m p PV p Ks Ks vertex Y. Xie, CERN & Tsinghua Univ.

  27. VTT in Bd->J/y(mm) Ks : Selected Ks Y. Xie, CERN & Tsinghua Univ.

  28. VTT in Bd->J/y(mm) Ks : Selected B0 With J/y and Ks mass constraints Missed association? Y. Xie, CERN & Tsinghua Univ.

  29. Long-Long 775 signal Long-VTT 281 signal TTT-TTT 1842 signal Bd->J/y(mm) Ks : Official Result(Olivier Schneider,LHCb Week, 23rd May 2003 ) • KS reconstructed as long-long, long-VTT and TTT-TTT (different cuts in each case) • New selection on 49.5k signal events (before trigger) Y. Xie, CERN & Tsinghua Univ.

  30. Bd0 -> D*π Analysis D0 / p Combined Mass Study (Lisa allebone,LHCb Week, 20th May 2003) Forward and matched slow pion tracks only VTT slow pion tracks only Y. Xie, CERN & Tsinghua Univ.

  31. Look at Primary Vertices in Multiple-Interaction Events • 28% events have >1 reconstructed PVs • In such events 68% of the time the first PV is a signal PV • 9% wrong, if only use the first PV • Anyway to do better? No trigger After L0 Y. Xie, CERN & Tsinghua Univ.

  32. What to Look at? • What may be interesting to discriminate signal PV and MB PV ? • Charged multiplicity • Total pt • Largest pt • Pt dispersion Y. Xie, CERN & Tsinghua Univ.

  33. Track Multiplicity • PV with most tracks is equivalent to the first PV Signal MB No trigger e =69% Signal MB L0 trigger e =75% Y. Xie, CERN & Tsinghua Univ.

  34. Total pt Signal MB No trigger e =70% Signal MB L0 trigger e =77% Y. Xie, CERN & Tsinghua Univ.

  35. Pt Dispersion: Signal MB No trigger e =61% Signal MB L0 trigger e =63% Y. Xie, CERN & Tsinghua Univ.

  36. Correlation between Total pt and Multiplicity Average track pt Signal MB Signal MB No trigger Signal MB Signal MB L0 trigger Y. Xie, CERN & Tsinghua Univ.

  37. Suggestion to Signal PV Selection • It is dangerous to use any topological or kinematical criteria to choose PV without using B candidates! • Keep all found primary vertices • Leave the work of signal PV selection to the analysis phase • For each B candidate choose the PV with smallest impact parameter ( or its significance) Y. Xie, CERN & Tsinghua Univ.

  38. Ongoing Work: non-Velo Ks Reconstruction • Based on O.Callot’s new T->TT track finding algorithm (compared with the old algorithm used in production) • Improve the new T->TT algorithm • Identify sources of Ks background and find rejection method • Study Ks reconstruction performance • Reject Ks background Y. Xie, CERN & Tsinghua Univ.

  39. Breakdown of TTT Composition(500 J/Y Ks events, no c2 cut) • Associated tracks • Old: 2608-> 1554, 59% ( 478-> 393, 82% ks pions) • New: 2608-> 1657, 65% (478-> 405, 85% ks pions) • Ghost from seed ghosts • Old: 1716 ->780, 45% • New: 1716 ->452, 26% • Ghost from true seeds without enough TT hits • Old: 4433->1981, 45% • New: 4433->1333, 30% • Ghost from wrong TT assignment • Old: 2608->715, 27% (478->66, 14% Ks pions) • New: 2608->431, 17% (478->40, 8% Ks pions) Main source Y. Xie, CERN & Tsinghua Univ.

  40. True seeds without enough TT hits • Project the seeds to a reference plane at z=2450mm • 2cm tolerance at boundary was used to seach for TT hits – the reason ghosts survive • Explicit cut can be applied Y. Xie, CERN & Tsinghua Univ.

  41. TTT Ghost Source 1: p from Beam Pipe • Important source: -200<z<200mm Y. Xie, CERN & Tsinghua Univ.

  42. Ghost Source 2: e+/e- from Beam Pipe and Material • Important source :2500<z<3500mm Y. Xie, CERN & Tsinghua Univ.

  43. Applying the TT hole cut • Project seed to zTT=2450mm • X@zTT>40mm or y@zTT>40mm • Performance ( for unique tracks) • Ghost rate: 47% • Eff: 63% (84% for Ks pions ) • Compared with • Ghost rate: 56% • Eff: 63% (85% for Ks pions ) • Very small loss of Ks pions efficiency • Reduction of ghosts: 32% Y. Xie, CERN & Tsinghua Univ.

  44. Remove e+/e- background to Ks • Use Ecal information to reject e+/e- : c2 of ematch>20 253 with a e+/e- Y. Xie, CERN & Tsinghua Univ.

  45. Ks Reconstruction old Ks <-B True Ks old 50 78 50 new new 73 (c2 cut on TTT tracks adjusted to keep same signal Ks efficiency) Y. Xie, CERN & Tsinghua Univ.

  46. Ks Reconstruction: Summary • 20% reduction of ghost type background with new TTT • Another 34% reduction of ghost background by the TT hole cut • Ecal information remove 30% Ks background from e+/e- • To-do list • Use rich information to identify protons from L • Reject tracks from primary vertices by cut on impact parameters to all primary vertices • Test with Bd -> f Ks channel, where signal branching ratio is lower, thus more study of Ks background is needed Y. Xie, CERN & Tsinghua Univ.

  47. Road towards a LHCbee • Started as a beginner … (2002.3) • XML description of Inner Tracker geometry (2002.4-6) • C++ interface to extract IT parameters from XML description (2002.6) • Software for reconstruction of low momentum particles (VTT tracking) (2002.7-2003.2) • Talk given at LHCb Collaboration Week at Cambridge in 2002.9 and Tracking session of Collaboration Week at CERN in 2002.12 • Presented at LHCB Tracking Workshop in Zurich in 2002.10.28 • Reported at LHCb Light meeting of 2002.6.9, 2002.7.30, 2002.8.13, 2002.9.10, 2002.11.19 and 2003.2.11 Y. Xie, CERN & Tsinghua Univ.

  48. Road towards a LHCbee (cont’d) • Investigation of Primary Vertices in multiple-interaction events (2003.2) • Reported at LHCb Light meeting of 2003.2.18 • Investigation of using VTT tracks in analysis of B0 -> J/Y Kschannel (2003.3) • Reported at LHCb Light meeting of 2003.3.18 • Improving non-Velo Ks finding (since 2003.4) • Reported at LHCb Light meeting of 2003.5.27 • Oh, tracking is just as simple as walking: find the road and go ahead Our present work is essential as a first step toward our physics goals. Now it is time to think about the challenge we will face in physics analysis after 2006 ! Y. Xie, CERN & Tsinghua Univ.

  49. Part IIIFuture … Y. Xie, CERN & Tsinghua Univ.

  50. Why Study CP Violation ? • CP violation in standard model can’t explain the extreme excess of matter over anti-matter in the universe: new source of CP violation is needed • Why CP violation is only seen in EW interaction but not in strong interaction? • Is there any new source of CP violation introduced by new physics? Y. Xie, CERN & Tsinghua Univ.

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