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Measurements of Radiative Penguin B Decays at BaBar

TM. Measurements of Radiative Penguin B Decays at BaBar. All results preliminary unless explicitly indicated. Jeffrey Berryhill University of California, Santa Barbara For the BaBar Collaboration. 32 nd International Conference on High Energy Physics August 17, 2004.

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Measurements of Radiative Penguin B Decays at BaBar

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  1. TM Measurements of Radiative Penguin B Decays at BaBar All results preliminary unless explicitly indicated Jeffrey Berryhill University of California, Santa Barbara For the BaBar Collaboration 32nd International Conference on High Energy Physics August 17, 2004

  2. Radiative Penguin Decays and New Physics Radiative penguin decays: b → sg and b → dg FCNC transitions SM leading order = one EW loop Vts, Vtd dependent • FCNCs probe a high virtual energy scale comparable to high-energy colliders • Radiative FCNCs have precise SM predictions: • BF(b→sg)TH = 3.57 ± 0.30 x 10-4 (SM NLO) • BF(b→sg)EXP = 3.54 ± 0.30 x 10-4 (HFAG) • Decay rate agreement highly constrains new physics at the electroweak scale! • Further tests presented here: • Exclusive b→sg decay rates • b→sg CP asymmetries • b→dg penguins Multiple new BF(b→sg) measurements coming soon from BaBar Jeffrey Berryhill (UCSB)

  3. Measuring Exclusive Radiative Penguin Decays Small rates (BF < 10-4) on top of large backgrounds Common strategy : select photon + hadrons with strict particle ID cut when possible on meson masses reduce continuum background with multivariate methods extract signal with multi-dimensional maximum likelihood fit Ex: signal fit for B → K*0g, K*0→ K+p- Best kinematic constraints from B candidate momentum and energy, compared with Ebeam: 583±30 events * denotes CM frame For signal, mES ≈ mB, s(mES) ≈ 3 MeV DE* ≈ 0, s(DE*) ≈ 50 MeV Jeffrey Berryhill (UCSB)

  4. BK* g Branching Fractions: Summary • BaBar preliminary measurements on 82 fb-1 • Becoming systematics limited • Exp. vs. theory: data more accurate • than form factor predictions! Jeffrey Berryhill (UCSB)

  5. Direct CP Asymmetry: b →sg andBK* g Sum of 12 exclusive, self-tagging B→Xsg final states Xs = K/Ks + 1-3 pions Eg* > 2.14 GeV b→sg b→sg < 1% in the SM, could receive ~10% contributions from new EW physics Either inclusive or exclusive decays could reveal new physics B or K charge tags the flavor of the b quark with ~1-2% asymmetry systematic b →sgACP = (N – N)/(N + N) = 0.025 ± 0.050 ± 0.015 PRL 93 (2004) 021804, hep-ex/0403035 Asymmetries also measured precisely in exclusive K*g decays: B →K*g ACP = -0.013 ± 0.036 ± 0.010 submitted to PRL, hep-ex/0407003 D0- = G(K*0 g) – G(K*-g) = 0.050 ± 0.045 ± 0.028 ± 0.024 G(K*0g) + G(K*-g) preliminary Jeffrey Berryhill (UCSB)

  6. bsg Asymmetries: Summary • BaBar measurements on 82 fb-1 • K*g, K2*g preliminary; Xsg published • CP asymmetries consistent with SM (0.4%) at the ~5% level • K*gisospin asymmetry D0- consistent with C7 < 0 • Statistics limited up to ~1 ab-1 sgn D0- = -sgn C7 Can we exclude C7 > 0 ? Jeffrey Berryhill (UCSB)

  7. Time-Dependent CP Asymmetry in B →K*g(113 fb-1) As in B0→J/y KS, interference between mixed and non-mixed decay to same final state required for CPV. In the SM, mixed decay to K*g requires wrong photon helicity, thus CPV is suppressed: In SM: C = -ACP ≈ -1% S ≈ 2(ms/mb)sin 2b ≈ 4% Measuring Dt of K*(→KSp0) g events requires novel beam-constrained vertexing techinque: Vertex signal B with intersection of KS trajectory and beam-line Usable resolution for KS decaying inside the silicon tracker Validated withB0→J/y KS events Jeffrey Berryhill (UCSB)

  8. Time-Dependent CP Asymmetry in B →K*g(113 fb-1) Likelihood fit of three components (qq, BB, K*g) to 5D data (mES,DE,Fisher,mK*,Dt) K*g signal = 105 ± 14 events S = +0.25 ± 0.63 ± 0.14 C = -0.57 ± 0.32 ± 0.09 submitted to PRL, hep-ex/0405082 Consistent with SM For C fixed to 0, S = 0.25 ± 0.65 ± 0.14 preliminary First ever measurement of time-dependent CP asymmetries in radiative penguins! Jeffrey Berryhill (UCSB)

  9. Search for B → rg, wg (191 fb-1) NEW! Simplest and most “common” b → dg exclusive decays are rg and wg: B+→ r+ g, r+→ p+ p0 BF ≈ BF K*g x |Vtd/Vts|2 ≈ 1.6 x 10-6 B0→ r0 g, r0→ p+ p- BF ≈ ½ BF r+g B0→ w g, w → p+ p- p0 BF ≈ ½ BF r+g Previous BaBar limit: BF r+g < 1.9 x 10-6 90% CL (78 fb-1) Preliminary Belle evidence (3.5s): BF r+g = 1.8 ± 0.6 ± 0.1 x 10-6 (140 fb-1) Comparable to rarest B decays measured! Ratio of exclusive b → dg and b → sg decay rates measures |Vtd/Vts| via Ali et al. hep-ph/0405075 DR weak annhilation correction z2 SU(3) symmetry breaking of exclusive form factors Jeffrey Berryhill (UCSB)

  10. Continuum Background Suppression • e+e-→ qq continuum events are • the dominant background • Combine properties discriminating • B →g + X from continuum • into a single-output neural net: • Event shape variables: spherical B vs. • jet-like continuum • B flavor tagging variables: kaons and • leptons in the rest of the event • B candidate vertex separation from • rest of the event • Neural net trained on simulated signal • and continuum samples e = 76% cut Neural net distribution for both signal and background described well by simulation Jeffrey Berryhill (UCSB)

  11. B Background Suppression Large (40 x signal) K* g background reduced by strict p+ PID requirements (track dE/dx, DIRC qc , DIRC Ng ) K+ misid 1-2% for most of acceptance DE provides additional separation of K*g from rg B decays to rp0, rh, wp0, wh suppressed by cut on helicity angle Combine helicity angle, B production angle, Dalitz angle (w only) into B Fisher discriminant for additional background separation in signal fit cut Jeffrey Berryhill (UCSB)

  12. Signal Fit: K*g Control Sample K*g + background Validate fit procedure on data with K*g sample (r0g candidates with no PID requirement) Unbinned extended ML fit of three background components (qq, Xsg, r0(p0/h)) and K*g component to 4D data (mES,DE,NN,Fisher) qq, Xsg, K*g yield are free parameters Large K*g signal yield consistent with BaBar BF measurement preliminary DE shifted background Jeffrey Berryhill (UCSB)

  13. Signal Fit: B+→ r+g r+g + background N(signal) = 26 ± 15 ± 2 significance = 1.9 s e = 13.2 ± 1.4 % BF = (0.9 ± 0.6 ± 0.1) x10-6 BF < 1.8 x10-6 90% CL preliminary background Fit of four backgrounds (qq, Xsg, r+(p0/h), K*g) and r+g signal qq, Xsg, r+g yield are free parameters Jeffrey Berryhill (UCSB)

  14. Signal Fit: B0→ r0g small peaking background +7.2 +1.7 - 5.4 - 1.6 N(signal) = 0.3 significance = 0.0 s e = 15.8 ± 1.9 % BF = (0.0 ± 0.2 ± 0.1) x10-6 BF < 0.4 x10-6 90% CL preliminary Fit of four backgrounds (qq, Xsg, r0(p0/h), K*g) and r0g signal qq, Xsg, r0g yield are free parameters Jeffrey Berryhill (UCSB)

  15. Signal Fit: B0→ w g +5.7 +1.3 - 4.5 – 1.9 N(signal) = 8.3 significance = 1.5 s e = 8.6 ± 0.9 % BF = (0.5 ± 0.3 ± 0.1) x10-6 BF < 1.0 x10-6 90% CL preliminary Fit of two backgrounds (qq, w(p0/h)) and wg signal qq, wg yield are free parameters Jeffrey Berryhill (UCSB)

  16. Combined Fit: B → r, w g Simultaneous fit to all three samples with the constraint Combined BF(r,wg) ≡ BF(r+g) = 2(t+/t0) BF(r0g) = 2(t+/t0) BF(wg) BF = (0.6 ± 0.3 ± 0.1) x10-6 significance = 2.1s BF < 1.2 x10-6 90% CL preliminary Jeffrey Berryhill (UCSB)

  17. bdg Branching Fractions: Summary Comparison of measurements with predictions for individual modes and combined BF central value 90% C.L. upper limit Belle BF vs. BaBar BF 2.0s difference Jeffrey Berryhill (UCSB)

  18. CKM matrix constraint BaBar BF ratio upper limit < 0.030→|Vtd/Vts| < 0.19 (90% CL) Ali et al. hep-ph/0405075 no theory error Penguins are starting to provide meaningful CKM constraint (z2,DR) = (0.85,0.10) rg 95% C.L. allowed Jeffrey Berryhill (UCSB)

  19. CKM matrix constraint BaBar BF ratio upper limit < 0.030→|Vtd/Vts| < 0.19 (90% CL) Ali et al. hep-ph/0405075 weak annhilation correction DR = 0.1 ± 0.1 SU(3) breaking of form factors z2= 0.85 ± 0.10 w/ theory error no theory error Penguins are starting to provide meaningful CKM constraint Reduction of theory errors necessary to be competitive with Bd,Bs mixing (z2,DR) = (0.75,0.00) (z2,DR) = (0.85,0.10) rg 95% C.L. allowed Jeffrey Berryhill (UCSB)

  20. Summary • Decay rate measurements ofb→ sg penguins are well into the precision era. • CP asymmetries ofb→ sg penguins are statistics limited and will continue to test • the SM • ACP in B → XsgPRL 93 (2004) 021804, hep-ex/0403035 • BF, ACP, and Isospin asymmetry in B→ K*gsubmitted to PRL, hep-ex/0407003 • time-dependent CPV in B0 → K*0 gsubmitted to PRL, hep-ex/0405082 b→ dg penguinsare only now beginning to reveal themselves in B-factory data. • They could also uncover new physics, or measure the poorly known |Vtd|. • BaBar finds no evidence for B → rg in 211 million BB events • submitted to PRL, hep-ex/0408034 • BF(B → r,w g) < 1.2 X 10-6 |Vtd/Vts| < 0.19 (90% CL) First measurement! Jeffrey Berryhill (UCSB)

  21. TM Backup Slides

  22. B → K*g (82 fb-1): Signal fits Jeffrey Berryhill (UCSB)

  23. B → K*g (82 fb-1): K*g lineshape K* lineshape for events with: mES > 5.27 GeV/c2 -0.2 GeV < DE < 0.1 GeV Background subtracted with shape from mES sideband Fit to relativistic Breit-Wigner with PDG G(K*), mK* Jeffrey Berryhill (UCSB)

  24. Time-Dependent CP Asymmetry in B →K*g Z resolution vs. KS decay radius Projection of fit with likelihood cut Jeffrey Berryhill (UCSB)

  25. B → rg: Neural net performance Jeffrey Berryhill (UCSB)

  26. B → rg: K*g Control Sample r0g, no PID r+g, no PID Jeffrey Berryhill (UCSB)

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