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Exploring CP Violation in the Standard Model and Beyond

This presentation delves into the intricacies of CP violation in B physics, highlighting its significance in explaining the matter-dominated universe. The discussion encompasses an introduction to CP violation, its discovery, and the pivotal role of the CKM matrix in the Standard Model. It reviews measurements and experiments that probe these phenomena, including the unitarity triangle and new physics implications. Key findings from leading experiments like BaBar and Belle are summarized, emphasizing the ongoing quest for understanding fundamental physics beyond the Standard Model.

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Exploring CP Violation in the Standard Model and Beyond

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  1. Palm tree and CKM Beauty in the Standard Model and Beyond Gabriella Sciolla (MIT) Beauty in the Standard Model and Beyond CIPANP 2006 - Puerto Rico - May 30 - June 3, 2006

  2. Palm tree and CKM Beauty in the Standard Model and Beyond Gabriella Sciolla (MIT) Beauty in the Standard Model and Beyond CIPANP 2006 - Puerto Rico - May 30 - June 3, 2006

  3. Outline • The beauty of B physics • CP violation in the B system and the Unitarity Triangle • Standard Model measurements • Sensitivity to New Physics • Measurements of CP violation in B decays • The experiments • Measurement of the angles and sides of the Unitarity Triangle • What have we learned? • Summary and conclusion Beauty in the Standard Model and Beyond

  4. CP violation • What is CP? • Why is CP violation interesting? • Crucial ingredient to explain the matter-dominated universe • A. Sakharov (1967) • CP violation is expected in the Standard Model • Until recently, one of the least tested aspect of the theory • Many new sources of CP violation Beyond the Standard Model • Sensitive to New Physics CP = C × P C: Charge Conjugation Particle  Anti-particle P: Parity Inverts space coordinates Beauty in the Standard Model and Beyond

  5. W- c b CP violation in the Standard Model • Discovered by Fitch and Cronin in 1964 in KL decays • Introduced in Standard Model in 1973 by Kobayashi and Maskawa • In KM mechanism, CP violation originates from a complex phase in the quark mixing matrix (CKM matrix) First goal of CP violation studies: Precise determination of the parameters r and h A,l (Cabibbo angle): very well measured r,h: poorly known until recently Beauty in the Standard Model and Beyond

  6. Pros and Cons of CKM Pros: • Elegant and simple explanation of CPV in SM • It is very predictive: only one CPV phase • It accommodates all experimental results • Indirect CP violation in Kpp and KLpln • Direct CP violation in Kpp • CP violation in the B system Cons:  nB/ng predicted by CKM « observed value • …by orders of magnitude!  New sources of CPV must exist besides CKM! . CP violation as a probe for New Physics: Measure CP violation in channels theoretically well understood and look for deviations w.r.t. SM expectations Beauty in the Standard Model and Beyond

  7. (r,h) a g b (0,0) (1,0) The Unitarity Triangle Unitarity of CKM implies: V†V = 1  6 unitarity conditions Of particular interest: All sides are ~ O(1)  possible to measure both sides and angles! • CP asymmetries in B meson decays measure a, b and g • Sides from semileptonic B decays, B mixing, rare B decays Beauty in the Standard Model and Beyond

  8. (r,h) a g b (0,0) (1,0) Standard Model or New Physics? Two ways of looking for New Physics: • Compare measurement of sides and angles • 2 measurements define the apex; >2 test Standard Model • All pieces of the puzzle must fit: inconsistencies mean New Physics • Measure same quantity in channels with different sensitivity to NP • E.g.: measure b in modes mediated by different decay diagrams Precision and redundancy are essential! Beauty in the Standard Model and Beyond

  9. The experiments: B factories • BaBar (SLAC) and Belle (KEK) • e+e- asymmetric collisions • .  U(4S) resonance • Advantages of the B factories • No need for bb trigger • Very clean environment: • High luminosity • Peak luminosity > 1034 cm-2s-1 • Integrated luminosity • 350/600 fb-1 (BaBar/Belle) 350/600 fb-1 (BaBar/Belle) Beauty in the Standard Model and Beyond

  10. The experiments: Tevatron experiments • CDF and D0 at Fermilab • . • Challenges of the Tevatran • Special trigger necessary for B events • High multiplicity events • Advantages of the Tevatron • Large number of B produced • L~1032 cm-2s-1 but high x-sections • Integrated luminosity: >1 fb-1 • All b hadrons are produced • BS , Lb , BC ,… Complementary to B factories Beauty in the Standard Model and Beyond

  11. a The angle b g b b The measurements Beauty in the Standard Model and Beyond

  12. e+ Flavor tagging Q=(30.5  0.5)% BfCPexclusive reconstruction Dz~bgc Dt Precise Dt determination How to measure the CP asymmetry . e- B0 e- U(4S) m+ B0 p+ p- m- Beauty in the Standard Model and Beyond

  13. CP violation at the B factories (hf) mixing decay • When only one diagram contributes to the final state, |l|=1 ACP(t) = ± Iml sin(Dmt) (CP violation in interference between mixing and decays in B0 ) Beauty in the Standard Model and Beyond

  14. h a g b r CP violation in B0 decays: sin2b For some modes, Iml is directly and simply related to the angles of the Unitarity Triangle. Example: B0J/YKS: the “golden mode” • Theoretically clean • Experimentally clean • Relatively large BF (~10-4) ACP(t) = sin2b sinDmt Beauty in the Standard Model and Beyond

  15. sin(2b) = 0.685 ± 0.032 WA EPS 2005 The golden mode for sin2b:sin2b in B0 J/y KS Belle 386 fb-1 B0J/y KS(p+p-) Belle 386 fb-1 Dt[ps] Belle 386 fb-1 mES[GeV/c2] sin(2b)= 0.652 ± 0.039± 0.020 Beauty in the Standard Model and Beyond Dt[ps]

  16. 95% CL from sides Unitarity Triangle constraints sin2b vs indirect UT constraints: very good agreement! • New Physics does not show up in the golden mode SM reference • Compare with sin2b in independent modes with different sensitivity to NP h r CKM mechanism is the dominant source of CPV at low energies Beauty in the Standard Model and Beyond

  17. NP SM The key to New Physics: The Penguin Modes Decays dominated by gluonic penguin diagrams • The typical example: B0fKS • No tree level contributions: theoretically clean • SM predicts: ACP(t) = sin2b sin(Dmt) • Impact of New Physics could be significant • New particles could participate in the loop  new CPV phases • Low branching fractions (10-5) • Measure ACP in as many bsqq penguins as possible! • φ K0, K+ K− KS,η′ KS, KS π0, KS KS KS, ω KS,f0(980) KS Beauty in the Standard Model and Beyond

  18. The golden penguin: B0fK0 B0fKS Belle 386 fb-1 N(fKs)=180 ± 16 Belle 386 fb-1 Belle 386 fb-1 B0fKL Belle 386 fb-1 Beauty in the Standard Model and Beyond

  19. The silver penguin: B0h’KS Larger BF ~ 6 x 10-5 but theoretically slightly less clean than fKS BaBar 210 fb-1 BaBar 210 fb-1 Sη′Ks = 0.30± 0.14±0.02 Cη′Ks = −0.21±0.10±0.02 BaBar 210 fb-1 Beauty in the Standard Model and Beyond

  20. “sin2b” in penguins J/yKS BaBar + Belle average • A trend is visible • although each measurement is compatible with J/YKS… • Most significant shift in h’KS • ~2.1s • Naïve average: 0.50±0.06 • ~2.5s Penguin modes Golden mode … statistical errors still large… Beauty in the Standard Model and Beyond

  21. a The angle a g a b The measurements Beauty in the Standard Model and Beyond

  22. Tree Penguin sin2a in B0r+r- • Tree diagram dominates • Relatively large Branching Fraction • B(B0 → r+r-) = (25.2 ± 3.7 )×10-6 • Penguin contribution small • B(B0 → r0r0) < 1.1×10-6 (90%C.L.) • Vector-vector final state: is CP defined? • In principle admixture of CP+ and CP- eigentastes… ACP(t) = sin2a sinDmt Beauty in the Standard Model and Beyond

  23. BaBar 210 fb-1 Is CP defined in B0r+r-? • Vector-vector final state • 3 possible L states • Measure fraction of longitudinal polarization in angular analysis ~ 100% longitudinally polarized  CP even eigenstate Beauty in the Standard Model and Beyond

  24. CP asymmetry in B0→ r+r- BaBar 210 fb-1 BaBar 210 fb-1 BaBar 210 fb-1 Beauty in the Standard Model and Beyond

  25. Average of BaBar and Belle r cfr: CKM fit Combined constraints on a Beauty in the Standard Model and Beyond

  26. a The angle g g g b The measurements Beauty in the Standard Model and Beyond

  27. The angle g • . Cabibbo allowed Cabibbo and color suppressed NB: only tree diagrams: 100% Standard Model Beauty in the Standard Model and Beyond

  28. Currently most sensitive g from B → DK • GWL (Gronau, Wyler, London) • D  CP eigenstate • Theoretically clean • Small interference: needs more data • ADS (Atwood, Dunietz, Soni) • is doubly Cabibbo suppressed • Larger interference • Needs more data • Dalitz method (Giri, Grossman, Soffer, Zupan) • Exploits interference pattern in Dalitz plot in DKSp+p- • Combines many modes  statistical advantage • Small systematics due to Dalitz model D0KSp+p- Beauty in the Standard Model and Beyond See talk by M. Verderi

  29. Summary of g measurements • Direct measurement on g: • BaBar + Belle, all methods combined • Indirect constraints: UTFit Beauty in the Standard Model and Beyond

  30. a g b The left side: Rb NB: b is the best measured quantity in the Unitarity Triangle  precise measurement of Rb is needed for accurate tests of SM Beauty in the Standard Model and Beyond

  31. l n Hadron level Semileptonic B Decays n • Sensitive to hadronic effects • Theory error not negligible • Prob(bc)/Prob(bu)~50 • Vcbprecisely measured (2%) • Vub is the challenge Parton level l Beauty in the Standard Model and Beyond

  32. Inclusive B  Xu l n Exclusive B  p l n Two approaches to Vub Inclusive B  Xuln • Hadronic final state is not specified • bc l n background is suppressed using kinematical variables • Partial rate is measured  theoretical uncertainties ~5% l- l- l Exclusive B  p ln • Better S/B but lower branching fraction (10-4) • Needs form factor calculation from Lattice QCD  uncertainty of ~ 12% Beauty in the Standard Model and Beyond

  33. |Vub| from Inclusive B Xu l n Close collaboration between theorists and experimentalists led to c.f.r.: precision on b: 5.5% Precision on Vub: 7.4% World Average 4.45  0.33 c2/dof = 5.5/6 Beauty in the Standard Model and Beyond

  34. a g b The last side of the triangle: Rt Beauty in the Standard Model and Beyond

  35. The measurement of Rt • Bs/Bd oscillations • Theory error <5% • Dmd is precisely measured • But Bs mixing is very hard… a g b Beauty in the Standard Model and Beyond

  36. History of BS mixing • 6 experiments, > 10 years of work • Then early this Spring… • D0: double sided limit on DmS • CDF: first observation of BS mixing Dec 2005 Beauty in the Standard Model and Beyond

  37. Flavor tagging QSST~4% QOST~1% Time reconstruction s(ct)~26-70 mm Reconstruction of BS decay in hadronic or SL modes BS mixing at the Tevatron • . • . • . • . Talk on Fri by Matthew Jones Beauty in the Standard Model and Beyond

  38. BsμDs: 5601±102 D0 result • . • . • . • . 17 < Dms < 21 ps-1 @ 90% CL assuming Gaussian errors Most probable value of Dms = 19 ps-1 Beauty in the Standard Model and Beyond

  39. CDF result 3,700 events • Probability of random fluctuation: ~0.5% Beauty in the Standard Model and Beyond

  40. Impact of DmS on Unitarity Triangle Beauty in the Standard Model and Beyond

  41. Conclusion • Standard Model: precision • Tremendous improvement in r and h • Precision ~ 0.05 • First quantitative test of CPV in SM • CKM is the dominant source of CPV • New Physics: redundancy • Sides vs angles in agreement with SM • First signs of NP in sin2b in penguins? • More statistics will help: • Analyzed: ~500 fb-1 • Available: ~1 ab-1 • By 2008: > 2 ab-1 . CP-conserving measurements BaBar+Belle CP-violating measurements Beauty in the Standard Model and Beyond

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