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Dmytro Kovalskyi University of Maryland, College Park BaBar Collaboration

Search for physics beyond the Standard Model using measurements of CP violating asymmetries in rare B decays: B 0 K S  0 and B 0 K S  0 . Dmytro Kovalskyi University of Maryland, College Park BaBar Collaboration. Motivation for New Physics Searches. Gravitational Lensing.

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Dmytro Kovalskyi University of Maryland, College Park BaBar Collaboration

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  1. Search for physics beyond the Standard Model using measurements of CP violating asymmetries in rare B decays: B0KS0 and B0KS0 Dmytro Kovalskyi University of Maryland, College Park BaBar Collaboration BaBar Collaboration

  2. Motivation for New Physics Searches Gravitational Lensing Galactic Halo Accelerating Universe Microwave background SM s W b t s b SUSY Dark Matter and Energy are the strongest evidences of new physics New Physics in the Loop Correction toSM predictions BaBar Collaboration

  3. CP violation in SM t c u d s b CP violation in the Standard Model is allowed due to a single phase present in the quark flavor mixing matrix called Cabibbo-Kobayashi-Maskawa matrix. CP violating phases =0.22 – Cabibbo angle Direct CP violation A A2 A2 A A1 A1 BaBar Collaboration

  4. Time-dependent CP violation FinalState Time-dependent CP asymmetry – interference effect between decay amplitudes with and without mixing. BCP BCP – fully reconstructed (vertex, kinematics etc) Btag Btag – partially reconstructed, (vertex and flavor)  = 0.56 - boost B=1.5ps, m=0.502 ps-1 BaBar Collaboration

  5. New Physics in the loop Constrained using approximate QCD symmetries like isospin, flavor SU(3), heavy quarks, which relate nonperturbative contributions in different decays In beyond-the-Standard Model scenarios, FCNC processes are sensitive to new particles with masses up to O(1TeV), such as the Higgses, charginos, stops and neutralinos in supersymmetric theories. • Inclusive measurements: BR(B→XS) = 3.3±0.4x10-4Direct CP: ACP = -0.08 ±0.11 • Effects suppressed in the SM: Direct CP, isospin, time-dependant CP violation BaBar Collaboration

  6. 3.7s from s-penguin to sin2b (cc) Averages for sin2b and s-penguin modes • In order to clear up the situation we need: • More data • Precise measurements of CP violation in exclusive decays • Improved theoretical calculations BaBar Collaboration

  7. B-Factory at SLAC Record: L=9.2x1033 cm-2 s-1 ILER=2450 mA, IHER=1550 mA, 1588 bunches (1x1033 cm-2 s-1 ~ 1 B pair/s) 232M B pairs PEP-II accelerator schematic and tunnel view 9 GeV e- 3.1 GeV e+ BaBar Collaboration

  8. BaBar Detector Electromagnetic CalorimeterE/E = 3.0%, , = 4 mrad 1.5 T solenoid e+ (3.1 GeV) Cerenkov Detector(DIRC)c = 2.5 mrad e-(9 GeV) Drift Chamberpt/p = 0.5% Instrumented Flux Returnmuon and KL detector Silicon Vertex Tracker z=65m, d0=55m BaBar Collaboration

  9. New Method of Vertex Reconstruction + A method is more important than a discovery, since the right method will lead to new and even more important discoveries.(Landau) KS B0KS0, B0K*, B0KSKSKS - BCP Perspective: B0KS, B0KS00 … 0 Btag BaBar Collaboration

  10. B Flavor Tagging Leptons Kaons l-  s W- W- b c b c s BaBar Collaboration

  11. Motivation for B0KS0 • In the Standard Model the loop diagram represents a dominant amplitude. The CP asymmetry is expected to be: |S|=sin2=0.726 • Tree diagram is both CKM and color-suppressed. • Upper bound on S in SM is 0.2 (model independent using SU(3) symmetry - M.Gronau,Y.Grossman, J.Rosner,Phys. Lett. B 579,331-2004) and 0.1 in model dependent QCD calculations (A.Buras et al, Nucl. Phys. B697 133(2004); M.Ciuchini et al, hep-ph/0407073; J.Charles et al, hep-ph/0406184) BaBar Collaboration

  12. Event Reconstruction I (kinematics) There are many ways to select two variables that represent known 4-momentums of the CM and reconstrustructed B and make use of invariant mass constraint for both Bs. mES and E (BKS0 ) mES E mB and mmiss (BKS0 ) BaBar Collaboration

  13. udsc background has jet-like topology, whereas bb is more spherically symmetric Event Reconstruction II (background) Signal Background BaBar Collaboration

  14. The Maximum Likelihood Fit • The fit is an extended maximum likelihood fit based on RooFit package. • In case of BKS0 we use mES and E instead of mrec and mmiss; mass pdf of KS0 in K* region; B background yield as an additional component. • All continuum background parameters are floated in the nominal fit. • Fit was validated based on: • significant number of toy Monte Carlo experiments • fit to Monte Carlo samples • embedded toy MC – fully simulated signal MC events mixed with toy MC background BaBar Collaboration

  15. s-Plot Technique s-Plot – background-subtracted distribution, based on a set of observables (their PDFs and yield covariance matrix), which are not correlated with the plotting parameter. (M.Pivk, F. Le DiberderarXiv:physics/0402083) Set of discriminating observables(pdfs) signal hypothesis s-Weight calculator background hypothesis Cut on some observables Input from all observables s-Plot Projection BaBar Collaboration

  16. B0KS0 Fit Results BKS0 BaBar Collaboration

  17. B0KS0 Fit Results Standard Model Physical boundary Dominant systematic effects: pdf parameterization/model, tagging efficiency and signal dilution, vertex tracker alignment, beam constraint vertexing BaBar Collaboration

  18. Motivation for B0KS0 L W sR b t Helicity Flip Suppressed by ~ ms/mb mixing • In Standard Model the photon is circularly polarized => roughly equal mix of CP-even and CP-odd final states. • New physics can affect the photon polarization and lead to significant CP-even and CP-odd decay rate asymmetry (Left-Right Symmetric Models, SUSY) • Use the time-dependent CP asymmetry measurement to probe the photon polarization (D.Atwood, M.Gronau, A.Soni - hep-ph/9704272) • No tree contribution to the amplitude – sensitive to new physics. If there is new physics contribution in bs one might see it in this decay as well. • Standard Model prediction may vary with photon energy and it might depend on resonance structure of the decay. • The s-quark hardronization effects introduce some theoretical uncertainty at the level of 0.1 (B.Grinstein, Y.Grossman, Z.Ligeti, D.Pirjol hep-ph/0412019) BaBar Collaboration

  19. B0KS0Analysis Strategy • We consider two types of events corresponding to two KS0 mass ranges: [0.8;1.0] GeV and [1.1;1.8] GeV, and measure the CP asymmetries for each region separately. • For B0  K* decays, use K* mass in the fit and the K* helicity angle in the event selection. • Proper MC simulation of bs and fragmentation corrections based on the bs semi-inclusive measurement. bs semi-inclusive B0  KS0 (resonances) BaBar Collaboration

  20. Analysis Challenges • B vertex reconstruction using only KS flight direction. • B-background due to bs and generic decays. Main source – low momentum 0s. • Lack of information about high mass spectrum. Use recent BaBar results Data & signal MC B+B- generic MC BaBar Collaboration

  21. BB background evaluation • Tight cut on 0 energy (E>0.59 GeV) significantly suppresses peaking BB background. Challenge: distinguish BB from continuum background • Fragmentation corrections for 2 and 3 body hardronic states (semi-inclusive bs) • Extracted BB background yield is consistent with expectation for B0KS0, whereas in B0  K* the yield is lower. We fix it to expected value for systematics evaluation • Scan region for S : [-0.45:0.45] (B0  K*), [-0.45,0.45] (B0KS0) • Scan region for C : [-0.4:0.4] (B0  K*), [-0.6,0.6] (B0KS0) BaBar Collaboration

  22. s-Plots E mES BK*  E mES BKS0  BaBar Collaboration

  23. KS0 mass spectrum mX s-Plot overlaid with expected rate for K*(892) and K*2(1430) (no fit performed) Mass resolution, [GeV] BaBar Collaboration

  24. Results Taking into account fit range difference for K* and assuming that the reconstruction efficiency doesn’t depend on mass, we should expect: ~ 91± 18 non-kstar decays according to the Belle’s result. BKS0  BK*  Standard Model Physical boundary BaBar Collaboration

  25. Conclusion • New method of vertex reconstruction allows new class of measurements to be performed at B-factories. • Both BKS0 and BKS0 measurements are consistent with the Standard Model expectations. • The analyses are statistically limited and new data can significantly improve constraints on new physics effects. • Averages for sin2 and s-penguin modes show evidence of some discrepancy at the level of 3.7 sigma. By 2006 BaBar is committed to double the data set, which will help to clear up the situation. • By the time when LHC is turned on, B-factories can provide many new interesting results. BaBar Collaboration

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