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Searches for New Physics in Rare B Decays at BaBar

This paper discusses the search for new physics in rare B decays at BaBar, focusing on decays with no tree-level Standard Model contribution. The analyses use the BaBar detector and dataset, exploiting its good energy resolution and charged K/π separation. Results for b→sγ and B→K(*)ll decays are presented, as well as measurements of exclusive B→η(')Kγ decays and their CP asymmetries. The analysis of B→K(*)ll decays is also discussed, including measurements of angular variables and forward-backward asymmetries.

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Searches for New Physics in Rare B Decays at BaBar

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  1. Searches for New Physics in Rare B Decays at BaBar • b→s inclusive/exclusive • B → Kll and B → K*ll • B→ and B→ Jonathan Hollar University of Wisconsin - Madison For the BaBar collaboration Pheno ‘06 Symposium

  2. Searching for New Physics in B Decays At tree-level, Standard Model usually dominates  focus on decays with no tree-level SM contribution • Rare flavor-changing neutral currents proceeding through loop/box “penguin” diagrams • Virtualt, W appear in the loop indirect probes of much higher energy scales New Physics can enter at leading order! Pheno 2006 Symposium

  3. BaBar detector & dataset Need large data samples to study rare decays • >350 fb-1 (~370 million B-pairs) delivered by PEPII • Analyses shown here use 80 – 210 fb-1 samples B→K(*)ll, B→, B→(‘)K, B→ b→s Analyses exploit BaBar’s: • Good neutral energy resolution • Charged K/ separation, lepton ID • Low multiplicity environment, coherent production of B-pairs Pheno 2006 Symposium

  4. Short-distance /perturbative Long-distance /non-perturbative b → s • Rate depends on the C7 “Wilson coefficient” in the Operator Product Expansion • New physics can alter magnitude/sign of C7 • Also sensitive to non-SM right-handed currents Experimentally: large backgrounds of photons from light quarks (continuum), initial state radiation, 0 from B decays Analyses can be done: • Inclusively: theoretically clean, more difficult experimentally • Exclusively: easier experimentally, more theoretical uncertainties (form factors) Pheno 2006 Symposium

  5. Total Continuum Signal B Bkg. Inclusive b → s analyses E > 1.9 GeV Sum-of-exclusive Fully reconstruct the B in 38 distinct final states (~60% of total): • K+n (n < 5), also states w. an  or 1-3 kaons • Neural network to reject background • Extract yield from fit to energy substituted mass: Phys. Rev. Lett 93, 021804 (2004) Phys. Rev. D 72, 052004 (2005) Fully Inclusive E > 1.9 GeV Use only the  Lepton “tag” from the other B to reduce backgrounds Subtract remaining backgrounds Pheno 2006 Symposium

  6. b → s results B(B → s) = (3.55  0.26)x 10-4Exp. world avg. B(B → s) = (3.61 +0.37-0.49) x 10-4 SM (NLO) (HFAG extrapolation to E > 1.6 GeV) Outstanding agreement between experiment and SM • Strong constraints on many New Physics scenarios Coming improvements • More data (experiment) • NNLO calculation (theory) Example: mSUGRA A0 = -2 2 > 0 tan() = 30 m0 Allowed Excluded by b → s stau LSP Direct searches/ theoretically inaccessible m1/2 Djouadi, Drees, and Kneur JHEP 0603:033, 2006 Pheno 2006 Symposium

  7. b → s asymmetries CP, isospin asymmetries are complementary probes of New Physics Null tests of SM predictions, e.g. ACP(B → Xs) ~ 10-4 ACP(B → (Xs + Xd)) ~ 10-9 New Physics could lead to asymmetries of order 10-2 – 10-1 Results are all consistent with the SM • CP asymmetries measured with precision of 5-10% Pheno 2006 Symposium

  8. Exclusive B → (')K K+ BF Results (x 10-6) B(B+ → K+) = 10.0  1.3  0.5 B(B0 → K0) = 11.3 +2.8-2.6  0.6 B(B+ → ′K+) < 4.2 B(B0 → ′K0) < 6.6 Improved measurement of K - First 5 observation of neutral mode First search for ′K - No signal observed (suppressed relative to K) First measurement of direct CP asymmetry in K mode – consistent with 0, SM Submitted to PRL (hep-ex/0603054) ACP(B → K+) = -0.086  0.120  0.010 Pheno 2006 Symposium

  9. ? B → K(*)ll Three diagrams (at least) at leading order •  penguin, Z penguin, W-box C7 (EM), C9(vector), C10(axial vector) Wilson coefficients • Magnitude of C7 fixed by b → s, sign not yet determined • Magnitude and sign of C9,C10 weakly constrained • Additional operators/Ci also possible: scalar/Higgs penguins, etc. 3-body decays  disentangle magnitude and sign of different operators B(B → Kll) = (0.34  0.07  0.02) x 10-6 B(B → K*ll) = (0.78  0.18  0.11) x 10-6 Pheno 2006 Symposium

  10. Lepton decay angle cos(*) B l+ * l- Angular variables Forward-backward asymmetric in K*llvs. q2 • ~sign of Wilsoncoefficients Forward-backward symmetric in Kll • If no new scalar operators -C7(SM) SM -C9C10(SM) -C9C10(SM) and -C7(SM) Predictions using NNLO Wilson coefficients + LCSR form factors Kaon decay angle cos(K) gives longitudinal K* polarization • Sensitive to sign(C7) or new right-handed currents at low q2 Pheno 2006 Symposium

  11. B → K(*)ll Analysis and B → Kll Results Fits to cos(*), cos(K) to extract AFB, K* polarization in 2 bins of q2 • Background angular distributions modeled from sideband control samples • Correct for angular efficiency/acceptance • Procedure validated on J/K(*), ’K(*)control samples FB asymmetry, scalar contribution in B+ → K+ll is consistent with 0, SM Total AFB(B+ → K+ll) = 0.15 +0.21-0.23  0.08 FS (B+ → K+ll) = 0.81 +0.58-0.61  0.46 Signal Bkg. Pheno 2006 Symposium

  12. SM -C7(SM) -C9C10(SM) B → K*ll Results SM • First measurement of K* polarization in this mode • Consistent with SM • With more data, can determine sign of C7 • High q2 AFB agrees with SM, excludes wrong sign C9C10 at >3 (agrees with Belle results) • Low q2 limit is consistent with SM at 2% (2.05 ) Phys. Rev. D 73 092001 (2006) Pheno 2006 Symposium

  13. l or hadrons D(*)0 Tag B e- e+  Signal B Bkg. Signal Rare B decays with ’s New Physics could couple strongly to heavy/3rd generation leptons • Higgs, leptoquarks, etc. Extremely challenging analyses • The  decays, with undetectable neutrinos in the final state Reconstruct the other (“Tag”) B as B→ D(*) + hadrons or B→ D(*)l • Anything left is (ideally) from the other B • Partially reconstruct  candidates in several decay modes (typically 30-50% of the total rate) • True signal has little residual energy (“Eextra” or “Eres”) in the calorimeter Pheno 2006 Symposium

  14. W+(H+) Decay modes B →  B →  Leading order loop/box diagrams • SM B(B → ) ~ 1 x 10-7 • No previous experimental results for this mode Hadronic tag analysis (210 fb-1) • Neural network to suppress remaining backgrounds W annihilation diagram in SM • SM B(B → ) ~ 1.6 x 10-4 • Sensitive to charged Higgs at tree level Two statistically independent analyses • Semileptonic tag (211 fb-1) • Hadronic tag (82 fb-1) + Pheno 2006 Symposium

  15. Combined constraint M(H+) Excluded by s Excluded by  tan  B →  results No signals observed  set upper limits from combined hadronic/semileptonic tag analyses Limits within a factor ~2 of SM prediction Constraints on charged Higgs mass/tan in Type II 2HDM • Complementary to limits from b→s at high tan B(B → ) < 2.6 x 10-4 (90% CL) Phys. Rev. D 73, 057101 (2006) Update: Evidence for B →  reported by Belle at FPCP 2006 (414 fb-1): B(B → ) = (1.06+0.34-0.28+0.18-0.16)x 10-4 Pheno 2006 Symposium

  16. Expected bkg. Signal region B →  results No evidence of signal: N (expected background) = 281  40 N (observed) = 263  19 B(B → ) < 3.4 x 10-3 (90% CL) First ever limits on this decay mode! New limits on 3rd generation leptoquark masses/couplings Submitted to PRL (hep-ex/0511015) Pheno 2006 Symposium

  17. Conclusions Rare Bdecays are an excellent place to find/constrain New Physics b → s rates, CP asymmetries are now precision measurements • Strong constraints on many models AFB(B → K*ll) disfavors new physics with wrong sign C9C10 • Determination of sign of C7 with more data B →  approaching SM sensitivity (evidence from Belle) First limits on B →  Analyses shown here use only 8 - 20% of the final BaBar dataset Most measurements are statistics limited – stay tuned for new results! Pheno 2006 Symposium

  18. Extra Slides Pheno 2006 Symposium

  19. b → s spectrum/moments b → s photon spectrum, moments not sensitive to new physics(2-body decay) • Can study parameters of the Heavy Quark Expansion (HQE) • Determination of mb to < 1% From combination of b → s (BaBar, Belle + CLEO) with b → cl (BaBar): Pheno 2006 Symposium

  20. More B → K(*)ll ACP(K+ll) = -0.07  0.22  0.02 ACP(K*ll) = 0.03  0.23  0.03 ACP(SM) ~ 0 Muon/electron ratios RK= 1.06  0.48  0.08 RK* = 1.40  0.78  0.10 RK(SM) = 1.0000  0.0001 Improved limits on LFV modes B(B→Ke) < 3.8 x 10-8 (90% CL) B(B→K*e) < 51 x 10-8 (90% CL) All results are consistent with SM predictions Pheno 2006 Symposium

  21. Belle B → K(*)ll • Analysis based on 414 fb-1 • Fit directly for Wilson coefficients from q2, cos(*) • Fix C7 to +/- SM value • Wrong-sign C9C10 excluded at 98.2% CL • Consistent with SM or wrong-sign C7 Integrated discrete asymmetry AFB (K*ll) = 0.50  0.15  0.02 AFB (Kll) = 0.10  0.14  0.01 Pheno 2006 Symposium

  22. B → (/) If no new physics in loops, ratio (B→(/))/(B→K*) gives ratio of CKM matrix elements Vtd/Vts BaBar 192 fb-1 result: B(B → ()) = (0.6  0.3 0.1) x 10-6 (2.1 significance) |Vtd/Vts| < 0.19 (90% CL) Combined BaBar/Belle constraint from 0 mode (UTfit) If SM, should be consistent with values extracted from Bs mixing (CDF/D0) Pheno 2006 Symposium

  23. B →  in the SM B →  depends onB-meson decay constant fB and CKM element Vub If no new physics, rate can constrain Vub OR assume Vub and extract fBfor comparison with lattice QCD prediction Combined BaBar/Belle constraint (UTfit) fB = 0.180  0.031 GeVExperiment fB = 0.192  0.026  0.009 GeVLattice QCD Pheno 2006 Symposium

  24. B →  Leptoquark limits BF is enhanced by 3133, suppressed by 1/m(LQ)4 Grossman, Ligeti, and Nardi Phys. Rev. D 55, 2768 (1997) Pheno 2006 Symposium

  25. Even more rare leptonic decays Pheno 2006 Symposium

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