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Amir Farbin University of Maryland (BaBar Collaboration)

Measurement of Time-dependent CP Asymmetries & New Physics Searches with Rare B Meson Decays (B 0  p + p - & B 0 K s p 0 ). Amir Farbin University of Maryland (BaBar Collaboration). Outline. Some B physics background/notation

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Amir Farbin University of Maryland (BaBar Collaboration)

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  1. Measurement of Time-dependent CP Asymmetries & New Physics Searches with Rare B Meson Decays(B0p+p- & B0Ksp0) Amir Farbin University of Maryland (BaBar Collaboration)

  2. Outline • Some B physics background/notation • Describe 2 time-dependent measurements in 2-body charmless B decays in the context of how they test the SM • Method 1- CKM consistency tests. • B0p+p- measures a (one ingredient) • first t-d measurement in rare mode- First measured for LP01. I’ll present LP03 results. • Method 2- Search for new physics effects. • B0Ksp0 sensitive to SUSY, ED, etc… • thought unmeasureable • Presented at LP03 • Since the 2 analyses are very similar, I’ll describe most of the details when describing B0p+p-. • Give some idea of future prospects.

  3. CP Observing CP Violation • CPV is elusive- 36 years between discoveries in K’s and B’s • Interference effect. 3 observable types of CPV: • 1.CPV in Decay (Direct) • Requires contributions from at least 2 amplitudes with: • DifferentCP-even phases • DifferentCP-odd phases 2.CPV in Mixing • 3.CPV in Interference between Mixing and Decay • In decays of neutral mesons to a CP eigenstate mixing decay

  4. Flavor Changing Interactions in SM • The CKM Matrix: • Unitary • 4Free parameters: • 3 Real • 1 Imaginary • CPV w/ >2 Generations Connect:up quarks,down quarks, and W-bosons Only CPV in SM (quarks) Cabbibo-Kobayashi-Maskawa Matrix u u CP W+ W- Vud V*ud d d

  5. * VtdVtb * VudVub * VcdVcb The CKM Matrix (Notation) Wolfenstein Parameterization 3 real parameters: A, l, r Unitarity = |Vus|  0.2200  0.0025 A = |Vcb| / 2  0.83  0.05 (,) not well known 1 complex phase: h VudV*ub + VcdV*cb + VtdV*tb =0 Relate angles to decays of B’s to CP Eigenstates a Represented as triangle b g

  6. Testing CKM Check that CP violation in the quark sector is fully encapsulated by the CKM matrix: • Constraints in the r-h plane: • Using indirect measurements: • sin 2b=0.727±0.036 • B meson system B0J/y K0decays: • sin 2b=0.739±0.048 Method 1 •  First triumph of B factories: CKM phase dominant source of CPV • Lots of effort into improving the inputs. 32 CL range: • Check the unitarity of CKM matrix: Independently measure Unitarity Triangle angles a, b, g and test closure: a+b+g=180. (New physics test) •  Hampered by experimental (low statistics) and theoretical (hadronic uncertainties) difficulties. A. Hocker, et al. • If no inconsistency is found  precise measurements of fundamental SM parameters Time dependent analysis of B0p+p- is sensitive to the angle a.

  7. Measuring Angles with B0’s Look at interference between decay and mixing. Measure the time-dependent decay asymmetry Oscillate w/ mixing freq mixing Amplitudes: Decay amplitude ratio Tree

  8. B0p+p- Decays (Not so simple) Mode Tree Amplitude (T) Hadronic Penguin Amplitude (P) • In the case of B0J/y Ks Tree/Penguin carry same phase  Measure sin 2b • Br(B0K+p-) >> Br(B0p+p-)  Penguin contributions may be large • But for B0p+p- Tree/Penguin may contribute w/ different phases “a Effective”

  9. PEP-II accelerator schematic and tunnel view SLAC’s Asymmetric B Factory • Total: • Lint=113 fb-1 • 121M B’s (used here) Record: L=6.696x1033 cm-2 s-1 ILER=1750 mA, IHER=1070 mA, 939 bunches (1x1033 cm-2 s-1 ~ 1 B pair/s) Delivered Recorded 9 GeV e- 3.1 GeV e+

  10. The BaBar Detector • Electromagnetic Calorimeter • 6580 CsI(Tl) Crystals • sE/E= 3.0% • sf=sq=3.9 mrad 1.5 T solenoid • Cerenkov Detector (DIRC) • Radiator 144 quarks bars • Image Ring on 896 PMTs • sqc = 2.5 mrad/trk e+ (3.1 GeV) e-(9 GeV) • Drift Chamber • 80:20 He:C4H10 • 7104 Hexagonal Cells • 40 layers (24 stereo) • s=0.1-0.4 mm • Tracking • spt= 0.13% pt + 0.45% • sd0= 23 mm • sf0= 0.43 mrad • sz0= 29 mm • stan l= 0.53 x10-3 • Instrumented Flux Return • 19/18 Layers of RPC (Barrel/EndCaps) • 20-38 mm segmented (z-f or x-y) • 2-10 cm Iron in between • em =60% w/ < 2.5% p mis-id • Silicon Vertex Tracker • Double sided strip detectors (z-f) • 5 layers, 340 wafers • s=15-40 mm 9 meters

  11. B0p+p-, Ksp0 Decays • Two-body decay: two back-to-back 2.6 GeV/c particles in CM Hardest particles from any B decay  No B bkgs • Effects PID & resolution of kin vars • Rare Decays: Branch fractions ~ 10-6 - 10-5 (~ 1-10 events/fb-1) •  Maximize efficiency: loose selection + global likelihood fit. • Large background from • (~1100/325 Event/fb-1 before/after selections) •  Use multivariate techniques to discriminate against background. • B0p+p-: must separate Bp+p-,K+p-,K-p+,K+K- • BaBar’s Ring Imaging Cherenkov detector (DIRC). • B0Ksp0: No tracks from B decay vertex •  Use extra constraints to determine decay point along beam.

  12. The Observables • Kinematics • Event shape • Particle ID • B Decay points • B Flavor

  13. Kinematics Nearly orthogonal • Dominated by tracking resolution • Unique for every decay • Assume pp shift for Kp and KK • Resolution dominated by the small spread in beam energy (10.58/2 GeV) • Insensitive to reconstructed mode (DE)  26 MeV s(mES)  2.6 MeV/c2 Kp KK pp Signal B0Ksp0 B0Ksp0 Tail from EMC leakage Background Tail from EMC leakage Background (All distributions are normalized to the same area)

  14. Background Suppression Axis of “Rest Event” Axis of “Rest Event” All background from where picked 1 track from each fragmenting quark “Jets” Candidate Angle btw candidate and “Rest of Event” axes. (cos qs) Background Signal Background Optimized linear combination of event shape variables (Fisher Discriminant) Signal Cut

  15. Particle Identification (DIRC) • DIRC c resolution and K- separation measured in data  D*+ D0+ (K-+)+ decays >9s s(qc)  2.2 mrad K/p Separation 2.5s Momentum range of 2-body B Decays at BaBar

  16. z B0 B0 Coherent BB pair Measuring Time-dependent CPV Time/flavor-structure of the U(4s) system: p- bgU(4S) = 0.55 Fully Reconst.ed  Know Vertex p+ K- m- Inclusively Reconst. the Vertex and Flavor Dt @Dz/gbc

  17. Measuring of decay time difference Dt K0 Tag B sz ~ 180 mm g p- U(4s) Dz p+ bg = 0.55 CP B sz ~ 45 mm Dt @Dz/gbc • B lifetime ~ 1.54 ps •  <|Dz|> ~ 260 mm • Inclusively reconstruct BTag vertex • Background has “no” lifetime Background  Average Dz resolution: 190 mm Signal

  18. u K- l- n W- c b D, D* d d B0 B0 d d Separating B0 and B0 mesons (B Flavor Tagging) • Exploit correlation between b-quark flavor & charges of final decay products • 7 algorithms look for 4 signatures 1. Lepton 2. Kaon W+ W- s b c u PID Kin & PID • Overall Q ~ 28% (Errors on S & C ~ w/ 1/Q) Tagging e~70% 4. Hard Pion 3. Soft Pion Kin

  19. Extracting Spp & Cpp B0h+h’- candidates Measure: Spp & Cpp Signal Dt & Tagging params Maximum Likelihood Fit • Possible due to the inclusion of flavor sample • Smaller/simpler systematic errors. Bkg mES, DE, F, Dt, & Tagging params candidates Signal/Background Yields • Possible due to the inclusion of large side-bands. • Provides more accurate/simplified parameterization of the background • Smaller/simpler systematic errors • Params of: • Sig mES, DE, F from MC/data • qc from D* • Allows measuring the branching fractions for Bpp,Kp,KK & the direct CP asym in BKK

  20. Some Validations • Blind analysis  don’t look at the answer until ready • Extensive Monte Carlo tests including specialized Toy MC • Large number of BKp in sample  measure • tB=1.602± 0.058 ps (World Avg: 1.542 ± 0.016 ps) • Dmd=0.472 ± 0.036 ps-1 (World Avg: 0.489 ± 0.008 ps-1) • SKp=0.02 ± 0.15, CKp=0.09 ± 0.11 (Expect SKp=CKp=0)  We can properly measure to time/flavor dependent quantities in the Bhh sample. Likelihood selected sample of signal BKp candidates

  21. B0p+p-Results Likelihood selected sample of Bpp candidates B0 Tags Background B0 Tags B0K+p-

  22. Extracting a from Spp & Cpp Belle winter 03 (78 fb-1): Average: BaBar summer 03 (113 fb-1): • CKM fit using other measurements • SU(2)- Isospin symmetry & Bpp • SU(3)- Flavor symmetry & B0K+p- • SU(3)- Flavor symmetry & B+K0p+ • QCD Factorization • Consistent w/ SM • Note current experimental accuracy A. Hocker, et al.

  23. Comment on “Isospin” Analysis Use SU(2) isospin symmetry to relate the rates of •  Provides only theoretically clean method of obtaining a from aEff (with 4-fold ambiguity) • B0p0p0 recently observed by BaBar w/ large branching fraction: 2.1 ± 0.6 ± 0.3 x 10-6 • Quinn-Grossman bound: •  Not very useful: |a-aEff|<48o @ 90% CL • Even with flavor tagged rates might need 10 ab-1 • New hope: B0r+r- • ~100% longitudinally polarized  CP even. • Similar stat error on Srr & Crr • B(B0r0r0) is very small |a-aEff|<14.7o

  24. Testing CKM (cont’d) g Search for new physics: Study decays whose leading contributions are from loop diagrams and may therefore deviate from SM prediction due to new physics. Method 2 a. Branching fractions: Ex: bsg b. Direct CP violation: Ex: BK*g c. Time-dependent CP violation: Compare sin 2b from bsuu, bsdd, bsss to bscc(ie BJ/yKs) or • Current Status: • 4 measurements • Large Statistical Errors • Deviation in B0fKs??? 2.1s 3.5s B0Ksp0 is the most recent addition to these modes.

  25. B0 Ksp0 Decays B0 Ksp0 is a penguin dominated decay to a CP eigenstate: Cabbibo & Color Suppressed • A time-dependent analysis:P measures sin 2b • Maximal deviation in SM from sin 2b due to dynamical enhancement : 0.17<SKsp0-sin 2b<0.18 • Usual arguments of sensitivity to new physics in loop diagrams applies Grossman, Ligeti, Nir, Quinn (hep-ph/0303171) Gronau, Grossman, Rosner (hep-ph/0310020)

  26. Reconstructing the B0 Ksp0 Vertex y y z x p+ p- p0 Ks ~30 mm ~4 mm Beam ~200 mm p+ Constrain in x-y to beam-spot p- Ks Only have vtx info here e+ e- Beam p0 “Beam Constrained (BC) Vertexing” Btag- Standard Method • Method works: • Small beam size • Good beam spot reco. • Dt dominated by tag side • Same principle for Btag vtx where there’s only 1 trk Inflated Beam

  27. Properties of BC vertexing • Resolution on z-position depends on number of SVT layers traversed by pions form Ks • Belle has 3 (now 4) SVD layers  problem? Ks x-y decay lengthdistribution Insufficient SVT hits for trk matching ~50% res. difference SVT layers f cos q • Ks flight direction Expected dependence (assuming perfect resolution but finite beam size)

  28. BC vs Nominal Vertexing RMS of (Dtmeas- Dttrue) vs. sDt Mean of (Dtmeas- Dttrue) vs. sDt Class I Class II • Unique to BC Vertexing: • Only vtx ~65% of decays (mode dependent) • 2 Classes of events w/ different avg resolutions • Common to BC & Nominal Vertexing: • Dependence of Dt resolution on estimated error sDt  essential ingredient of resolution function • We have no large sample of BC vertexed events. •  Use same resolution function for nominal & BC vertexed samples. • Use MC to estimate systematic for this choice.

  29. Extracting S & C Class I + II + III + IV events Measure: S & C Loose selection  high efficiency Bkg mES, DE, F, Dt, & Tagging params Maximum Likelihood Fit Signal/Background Yields • Use Dt for events in class I and II (~ 65% of events)  Gives S (& C) • Use tagging for all tagged events  Gives C • Params of: • Sig mES, DE, F from MC/data • Sig Dt & Tagging params from Bflav

  30. Validations • Since this is a “new” technique  some validation. • Control samples: • B0 J/yKs: “Remove” J/y from B vtx by blowing up its vtx parameters (Mangling) • Compare nominal/BC vertex event by event • Compare data/MC • Compare sin 2b • DSJ/yKs(nominal-BC)=-0.027 ± 0.064 • DCJ/yKs(nominal-BC)=-0.034 ±0.026 • B+ Ksp+: “Remove” p+ from B vtx by blowing up trk parameters. • Same kinematics as our decay • Similar backgrounds • “Null test”: • SKsp+= 0.18±0.19 • CKsp+= 0.06±0.11

  31. B0Ksp0 Results Consistent w/ B0J/yKs Ns=122±16 B0 Tags Background B0 Tags

  32. Beyond SM Prospects in B Physics • Questions: • What is the likelihood of seeing new physics? • What can we learn from an “observation”? • How do we relate measurements from different channels? (ie how do we understand current measurements?) Theorist: (example) ÖÖ =Large SUSY contributuions Ö = Non-negligable deviation from SM Goto, Okada, Shimizu, Shindou, Tanaka (hep-ph/0306093) • Pessimistic: • There are enough SUSY parameters/SUSY breaking models to accommodate any scenario… including no signature in B physics. • Each measurement probes a different aspect of new physics. • Example: B0fKs could be the only New Physics signature. • Optimistic: • Multiple SUSY signatures in B physics. • Time-dependent asymmetries are more sensitive probes than BRs and direct CPV. • B factories will (at least) tighten new physics limits.  Important to check all experimentally accessible decays

  33. g New Possibility: B0K*g, K*Ksp0 • bsg decay: B0K*g, K*Ksp0 CP Eigenstate- 11% B0K*g, K*K+p- Self-tagging- 89% • B0Ksp0 final state with extra photon  Use BC vertexing • The dominant SM amplitude gives opposite photon helicities for • New physics enhance SK*g up to 50% of sin 2b • Related to B0fKs. New physics should be apparent in both!  Expect: Helicity Flip Suppressed by ms/mb mixing David Atwood, Michael Gronau, Amarjit Soni (1997) (hep-ph/9704272)

  34. Experimental Prospects Estimated maximal deviation from sin 2b • Summary • It is possible to “observe” new physics in most modes, if the deviation from SM is large. • Considering the current BaBar’s measured values it’s more difficult! • Many more modes to come soon…

  35. Summary • The angle a: • Though the B0p+p-was the “golden-mode” for a and the first time-dependent analysis in a rare B decay, the large B0p0p0 branching fraction makes extraction of a in the near future unlikely. • B0r+r- is promising… a with 10o uncertainty in the next few years? • New physics: • Belle’s B0fKs has everyone excited now. • We’ll know in 1-2 years if it is real. • The B0Ksp0 measurement has opened the door to previously inaccessible analyses. • B0K*g is promising. • Many more time-dependent analyses ahead.

  36. Backup Slides

  37. Branching Fraction Results • Likelihood projections: • Remove 1 variable from fit • Cut on probabilities used in fit

  38. Looking for NP with time-dependent CPV g CKM Suppressed Decays which are dominated by penguin AND are sensitive to sin 2b (since b is well-known) : or Tree amplitudes are generally CKM suppressed indication of new physics? When is Very conservative estimate… Dynamical enhancement can make |xf| >> 0  Use SU(3) and branching fractions to bound |xf| Grossman, Ligeti, Nir, Quinn (hep-ph/0303171) Gronau, Grossman, Rosner (hep-ph/0310020)

  39. Dt Resolution Bottom Line Dt resolution vs. cos qKs B0J/yKs (mangled) < B0Ksp0 = B+Ksp+ (mangled) < B0J/yKs (Nominal) Worse Dt Resolution Best Class I + Class II Events

  40. B0fK0 CP= -1 (Ks), +1 (KL) Stefan Spanier Mahalaxmi Krishnamurthy Diagrams Stats • Theory • Insufficient experimental data to bound xfKs • Must use B+fK+ and “cancellation assumptions” to relate fK+  fK0 (Not solid) • |xfKs|~ |xfK+|< 0.25 • BaBar/Belle status/plans • Belle has submitted a PRL • BaBar: KL’s were not included in LP03 result, but will be in upcoming PRL • Ksp0p0 will be added next • Summer 2004 Update Comments Need: Branching fractions for: B0AA’, A={w,h,h’,f,p0,r0,K0,K*0} Used:Branching fractions for: B+VP+, V={f, K*0}, P={K+,p+} Ks Only: sS(200/fb)=0.32, sS(500/fb)=0.21 Ks + KL:sS(200/fb)=0.26, sS(500/fb)=0.16

  41. B0K+K-Ks Isospin analysis: 100% CP Even CP= Mixed Denis Dujmic (Example) Diagram Stats BLIND Requires Isospin or Helicity=Dalitz analysis to determine CP content • Theory • Requires Isospin or Helicity=Dalitz analysis to determine CP content • Use U(2)  |xKKK|< 0.14 • BaBar/Belle status/plans • Belle has submitted a PRL while BaBar hasn’t presented yet. • Denis: “If I don’t hear from the Review Committee, I’ll unblind next week.” • BaBar plans for Helicity analysis for winter. • Belle is also working on Dalitz analysis. (suggested by speaker on Tuesday) • Comments • Use: Branching fractions for: B0h+h-h’+, h={p,K} • Note: BaBar isospin analysis uses Belle’s K+KsKs • Helicity analysis reduces uncertainty on CP content by factor 2 sS(200/fb)=0.19, sS(500/fb)=0.12

  42. CP= -1 Frederic Blanc, Fernando Palombo, Paul Bloom, Bill Ford, Mirna van Hoek, Jim Smith, Alfio Lazzaro B0h’Ks Diagrams Stats • Theory • For B0h‘Ks:|xh;K|< 0.36 • Bound on B+h‘K+ is better (more accurate BR measurements): |xh;K|~|xh;K+|< 0.09 • BaBar/Belle status/plans • Belle has submitted a PRL • BaBar: • Run 1-3 update by winter • Run 1-4 update by summer • Comments • Use: Ratios of branching fractions: B0AA’, A={h,h’,p0} (13 modes) sS(200/fb)=0.22, sS(500/fb)=0.14

  43. CP= -1 AF, Wouter Hulsbergen, Dmytro Kovalskyi, Maurizio Pierini B0p0Ks Diagram Stats • Experiment • Expected to be impossible (no track from B vertex) • New Beam-Constrained Vertexing technique Good Vertex ~ 65% of events • Technique validated on B0J/yKs • BaBar/Belle status/plans • BaBar: Reworking systematics now • PRL Draft by end of October • Update summer 2004 • Belle: Surprised at LP03. • Likely to have difficulty since their SVD has only 3 (now 4) layers • Theory • Cleaner than other modes: |xpK|< 0.13 • M. Gronau, Y. Grossman, J. L. Rosner (hep-ph/0310020) • Comments • Use: B0p0 p0 and B0K+K- only • Better B0K+K- UL would help sS(200/fb)=0.32, sS(500/fb)=0.21

  44. CP= -1 B0K*0g (K*0Ksp0) AF, Wouter Hulsbergen, Dmytro Kovalskyi, Maurizio Pierini Diagram Stats • Experiment • Apply same technique as B0p0Ks • BaBar/Belle status/plans • BaBar: Planning measurement for winter 2004. • Belle: Obviously is aware of the prospect • Likely to have difficulty since their SVD has only 3 (now 4) layers • Theory • The dominant SM amplitude gives opposite photon helicities • Expect: • New physics enhance S up to 50% David Atwood, Michael Gronau, Amarjit Soni (1997) (hep-ph/9704272) sS(200/fb)=0.53, sS(500/fb)=0.34

  45. B0Ks Ks Ks CP=+1 Steve Wagner Diagram Stats Not enough info to estimate errors BLIND • Experiment • UsingB0p0Ks technique will allow vertexing candidates with only 1 Ks decaying before 4th SVT layer • BaBar/Belle status/plans • BaBar: ? • Belle: ? sS(200/fb)= ?, sS(500/fb)= ?

  46. Ingredients for Measuring CPV w/ B’s (4S) In order to measure: 1. Produce many B mesons 2. B lifetime is small Provide a boost to measure B decay time  Asymmetric B Factory 3. B CP eigenstates are rare Efficient Reconstruction of fCP  Detector w/ PID & Vertexing 4. Determine Dt & B0/anti-B0

  47. Quartz bar Active Detector Surface Particle Cherenkov light Particle Identification (B0p+p-)(Detector of Internally Reflected Cherenkov Light) • Measure Angle of Cherenkov Cone in quartz • Transmitted by internal reflection • Detected by PMTs

  48. Interpreting the Results • Recall that • If decay dominated by tree amplitude (T) then • But expect large penguin contribution (P) to decay so d is relative strong phase between P and T

  49. CP Violation and the Universe The Big Bang Strings Cosmology Supersymmetry/ Extra-Dimensions Inflation Predicts more CPV Standard Model (Current Theory) Baryogenesis (Sakharov Conditions) Necessary ingredient 1 Param CP Violation = Matter/Anti-matter asymmetry Seen on both sides Observe: All matter Particle Physics Astronomy Observe: K’s & B’s Science of the smallest scale Science of the largest scales

  50. Assessing Dt and b-flavor Tagging • Need to measure the Dt resolution • Need to measure the b-flavor “mis-tag” rates, efficiencies, etc… • Use “self-tagging” B0 decays… • Know the flavor of the fully reco’d B  check determination of the flavor of BTagEx: B0  D- p+  (K- p+p-)p+ 50 times largerthan signal Add tagging effect (lot more stuff) Mistag

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