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Why charmless sl. Decays? Analysis Techniques Overview of BaBar results (3 new results in 2005)

Jochen Dingfelder , SLAC SLAC Experimental Seminar, June 9 th 2005. Why charmless sl. Decays? Analysis Techniques Overview of BaBar results (3 new results in 2005) Form Factors Vub Prospects for 500 fb-1. |V ub |/|V cb | band ( ±2 σ ) σ =12%. Why Charmless Semileptonic B Decays ?.

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Why charmless sl. Decays? Analysis Techniques Overview of BaBar results (3 new results in 2005)

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  1. Jochen Dingfelder , SLAC SLAC Experimental Seminar, June 9th 2005 Why charmless sl. Decays? Analysis Techniques Overview of BaBar results (3 new results in 2005) Form Factors Vub Prospects for 500 fb-1

  2. |Vub|/|Vcb| band (±2σ) σ=12% Why Charmless Semileptonic B Decays ? • Study b  u transitions Goal: Precise determination of |Vub| • Test CKM description of quark coupling and CP violation • Complementary constraint of UT to angle measurements; • try to reach similar precision as sin2b. s(|Vcb|) ≈ 2% s(|Vub|) ≈ 12%

  3. Why Charmless Semileptonic B Decays ? • Study b  u transitions Goal: Precise determination of |Vub| • Test CKM description of quark coupling and CP violation • Complementary constraint of UT to angle measurements; • try to reach similar precision as sin2b. Constraints w/o angles s(|Vcb|) ≈ 2% s(|Vub|) ≈ 12% |Vub|/|Vcb| band (±2σ) σ=12%

  4. u/d u/d Xu= p, r, ... B0,± b u l Vub n Why Charmless Semileptonic B Decays ? • Vub is best measured in charmless semileptonic decays B  Xuln • Factorization of leptonic and hadronic currents • Learn about electroweak interaction (coupling) • Learn about strong interaction study structure of B meson •  allows tests of e.g. Lattice QCD • So far B pln and rln have been measured (CLEO, Belle, BaBar (rln) ). • Also wln (Belle) and hln (CLEO) have been seen. • Will present preliminary BABAR results from 2004-05 (82 fb-1 or 211 fb-1)

  5. Semileptonic B decays : The “Big Picture” |Vub|2 / |Vcb|2 ≈ 1 / 50 • Exclusive Decays • Low signal rate, better bkg reduction and kinematic constraints • Need Form FactorsF(q2) to describe the hadronization process u  p, r, … • Measurement as function of q2 • Inclusive Decays • Large signal rate, high b cln bkg • “Easy” to calculate (OPE/HQE) • Need Shape Function (b-quark motion inside B meson) . Constrain SF param. mb, mp2 with b  sg or b  cln.

  6. CsI (Tl) BaBar DIRC e+ (3.1 GeV) • 5-layer SVT tracker • 40-layer Drift CHamber dE/dx • Novel RICH based on total internal reflection (DIRC) • CsI(Tl) crystal calorimeter (e±, γ) • RPC and LST chambers in flux return for muon ID e- (9 GeV) IFR SVT DCH How Do We Detect These Decays ? B  Xu l+n (l = e,m) • Good e,m ID(p*l>1GeV)and hadron ID • (e.g. p/K separation  reject kaon tracks) • Reliable track and g reco. (DCH,EMC) • Angular coverage ≈ 92% of 4πin CMS • (challenge forνreco)  p’s , g’s

  7. CsI (Tl) BaBar DIRC e+ (3.1 GeV) • 5-layer SVT tracker • 40-layer Drift CHamber dE/dx • Novel RICH based on total internal reflection (DIRC) • CsI(Tl) crystal calorimeter (e±, γ) • RPC and LST chambers in flux return for muon ID e- (9 GeV) IFR SVT DCH How Do We Detect These Decays ? B  Xu l+n (l = e,m) • Good e,m ID(p*l>1GeV)and hadron ID • (e.g. p/K separation  reject kaon tracks) • Reliable track and g reco. (DCH,EMC) • Angular coverage ≈ 92% of 4πin CMS • (challenge forνreco)  p’s , g’s

  8. CsI (Tl) BaBar DIRC e+ (3.1 GeV) • 5-layer SVT tracker • 40-layer Drift CHamber dE/dx • Novel RICH based on total internal reflection (DIRC) • CsI(Tl) crystal calorimeter (e±, γ) • RPC and LST chambers in flux return for muon ID e- (9 GeV) IFR SVT DCH How Do We Detect These Decays ? B  Xu l+n (l = e,m) • Good e,m ID(p*l>1GeV)and hadron ID • (e.g. p/K separation  reject kaon tracks) • Reliable track and g reco. (DCH,EMC) • Angular coverage ≈ 92% of 4πin CMS • (challenge forνreco)  p’s , g’s

  9. CsI (Tl) BaBar DIRC e+ (3.1 GeV) • 5-layer SVT tracker • 40-layer Drift CHamber dE/dx • Novel RICH based on total internal reflection (DIRC) • CsI(Tl) crystal calorimeter (e±, γ) • RPC and LST chambers in flux return for muon ID e- (9 GeV) IFR SVT DCH How Do We Detect These Decays ? B  Xu l+n (l = e,m) • Good e,m ID(p*l>1GeV)and hadron ID • (e.g. p/K separation  reject kaon tracks) • Reliable track and g reco. (DCH,EMC) • Angular coverage ≈ 92% of 4πin CMS • (challenge forνreco)  p’s , g’s DIRC p/K separation

  10. CsI (Tl) BaBar DIRC e+ (3.1 GeV) • 5-layer SVT tracker • 40-layer Drift CHamber dE/dx • Novel RICH based on total internal reflection (DIRC) • CsI(Tl) crystal calorimeter (e±, γ) • RPC and LST chambers in flux return for muon ID e- (9 GeV) IFR SVT DCH How Do We Detect These Decays ? B  Xu l+n (l = e,m) • Good e,m ID(p*l>1GeV)and hadron ID • (e.g. p/K separation  reject kaon tracks) • Reliable track and g reco. (DCH,EMC) • Angular coverage ≈ 92% of 4πin CMS • (challenge forνreco)  p’s , g’s EMC

  11. D* D0 p+ p+ p+ n p+ Y(4S) Y(4S) Y(4S) n n n l- l- l- p- l- Tagging Methods Hadronic Tag: Fully reconstruct hadronic decay of one B: B D(*) + (p+,p0,K+,K0) ≈ 1000 modes  know kinematics of other B Semileptonic Tag: Reconstruct B  D(*) l n and study recoil - Full reconstruction of D(*) - Partial reconstruction of D* (only l, psoft) Two n tag-B kinematics incomplete No Tag: High statistics High backgrounds and cross-feed  Fully reconstruct signal side (n reco.)

  12. Tagging Methods: Event Yields • Advantages of Tagging: • Determine tag-Bcharge, flavor, momentumconstraints for signal B • Separating the two B decays  reducecombinatorics / cross-feed • Reduce non-BB(continuum) background looser cutsfull phase space • BUT: Significantly lower signal rates ! × 4 ×10 for pln ×1/3 ×1/3

  13. Hadronic Tags

  14. M2miss p+ln b  cln Hadronic Tags: B p (r, w, h,...) l n • Tag side: fully reco. B  PB sig = -PB tag • Signal side: Plep > 1 GeV • n fully constrained : M2miss < 0.5 GeV2 • Pro: Clean sample, almost bkg free • Loose cuts  keep full phase space • Con:Very low signal rate ! Variety of signal modes studied ! 82 fb-1

  15. 82 fb-1 Plus competitive limits for h, a0,a + Systematics dominated by MC statistics Hadronic Tags: B p (r, w, h,...) l n

  16. Semileptonic Tag

  17. Semileptonic Tag Method • Reconstruct B D(*)ln and study semileptonic recoil • Tagging efficiency measured with “Double Tags” (two D(*)ln) D(*)ln decays Correct sl. decay  |cosqBY| < 1, bkg broader ( tag side: cosqBY, signal side: cosqB,pl) cos2fB < 1 for signal, bkg flat

  18. B+p0ln with SL Tag : Signal Extraction • Cut-and-count analysis in cosqB,pl and mD • Signal region: -1.1 < cosqB,pl < 1.0 • Subtract mD sidebands remove cominatoric background • Subtract other background using MC normalized in -20 < cosqBpl < -1.5 82 fb-1 45 p0ln

  19. 14 p+ln 26 p+ln 21 p+ln 211 fb-1 Mainly B0B0 bkg ≈ 30% rln X-feed B0 p+ln with SL Tag : Signal Extraction Extract signal yields by binned c2 fit to cos2fBin3 bins of q2 : q2 = (pB – pp)2 , s(q2) ≈ 0.7 GeV2 Fit parameters = signal and background normalizations

  20. Partial SL (D*ln) Tag: B p+l n • Tag only l+ and p-soft from D*-D0p-soft •  D* momentum pD* = f (psoft) • Tag side n mass:Mn2 = (pB - pD* - pl)2 • Signal side: Look for l- p+hard • Check consistency of remaining particles (X) with D0 decay (multivariate discriminator) • Signal yieldfromfit to signal side mn2 MX pln BB bkg B(B0->p-l+n) = (1.46 ± 0.27 ±0.34 ±0.03FF) × 10-4 q2<8 8<q2<16 q2>16 82 fb-1

  21. No Tag

  22. u/d u/d Xu= p/r B0,± Y = p/r + l b u l n • Harsh suppression of b  cln background • e+e- qq background Untagged B pln, B  rln : Analysis Strategy • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Select signal decay candidates: • Y = hadron (p/r) + lepton (e/m) • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0)

  23. u/d u/d Xu= p/r B0,± Y = p/r + l b u l n • Harsh suppression of b  cln background • e+e- qq background Untagged B pln, B  rln : Analysis Strategy • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Select signal decay candidates: • Y = hadron (p/r) + lepton (e/m) • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0)

  24. u/d u/d Xu= p/r B0,± Y = p/r + l b u l n • Harsh suppression of b  cln background • e+e- qq background Untagged B pln, B  rln : Analysis Strategy • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Select signal decay candidates: • Y = hadron (p/r) + lepton (e/m) • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0)

  25. pmiss resolution s = 70 MeV Landau: 280 MeV Tail due to losses |pmiss| - |pn|(GeV) Neutrino Reconstruction Neutrino “Quality Cuts”: • Net charge: |SQ| ≤ 1, qmiss > 0.6 rad  limit losses due to acceptance • Missing mass: |M2miss/2Emiss| < 0.4 GeV2 B0 pln MC no add. KL, n add. KL add. n M2miss/2Emiss (GeV)

  26. pmiss resolution s = 70 MeV Landau: 280 MeV Tail due to losses |pmiss| - |pn|(GeV) Neutrino Reconstruction Neutrino “Quality Cuts”: • Net charge: |SQ| ≤ 1, qmiss > 0.6 rad  limit losses due to acceptance • Missing mass: |M2miss/2Emiss| < 0.4 GeV2 B0 pln MC no add. KL, n add. KL add. n Scale neutrino momentum, so that DE=0  Improves q2 resolution M2miss/2Emiss (GeV) w/o DE=0

  27. u/d u/d Xu= p/r B0,± Y = p/r + l b u l n • Harsh suppression of b  cln background • e+e- qq background Untagged B pln, B  rln : Analysis Strategy • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Select signal decay candidates: • Y = hadron (p/r) + lepton (e/m) • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0)

  28. Background Suppression Continuum Suppression: Off-res. data statistics low Need to rely on MC Minimize impact of continuum bkg L2 =Spi*cos2qi *< 1.5 GeV  Suppress 80% b  c l n b  c l n Suppression: Need to suppress large charm bkg in rln channel kinem. cuts on p*l ,p*h (for pln we can keep nearly whole phase space) L2 Signal (p) qq cosqthr cosqthr p*h Signal (r) b cln b  c l n p*l p*l Selection efficiencies: ≈ 3% for pln, ≈ 1% for rln

  29. u/d u/d Xu= p/r B0,± Y = p/r + l b u l n • Harsh suppression of b  cln background • e+e- qq background Untagged B pln, B  rln : Analysis Strategy • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Select signal decay candidates: • Y = hadron (p/r) + lepton (e/m) Before we fit the signal, we should check that selection / n reconstruction really work! • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0)

  30. “Proof of Principle”: B  D*ln Control Sample • Select high statistics and high purity control sample • Perform same selection as for b  uln signal (except b  cln suppression) • Cross-check MC modeling of signal decays • Study modeling ofdominant charm background component (D*) • Two modes for B  D*-l+n D0p-l+n: D0 K+p- , D0 K+p- p0 . K+p-p0 K+p-p0 K+p-p0 Signal other D* D/D** q2 (GeV2) M2miss/2Emiss (GeV) DE (GeV) Efficiencies of cuts agree between data and MC within a few %.

  31. u/d u/d Xu= p/r B0,± Y = p/r + l b u l n • Harsh suppression of b  cln background • e+e- qq background Untagged B pln, B  rln : Analysis Strategy • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Select signal decay candidates: • Y = hadron (p/r) + lepton (e/m) • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0)

  32. Fine binning in Signal Region Coarse binning in Sideband Region B pln pln rX-feed Xu fixed cln qq fixed Fit in DE-mES and q2 • Binned max.-likelihood fit, including MC statistics (Barlow & Beeston) • Fit all signal modes simultaneously • Float p±, p0, r±, r0in each q2 bin • 5 (3) q2 bins for pln (rln) • Use isospin relations: • G(B0 p-l+n) = 2G(B+ p0l+n) • G(B0 r-l+n) = 2 G(B+ r0l+n) • One free parameter for b  cln • Total: 9 free parameters

  33. 5 bins for pln 3 bins for rln Results for pln : Fitted DE and mES 76 fb-1 Sum of 396 p+ln, 137 p0ln

  34. 5 bins for pln 3 bins for rln Results for rln : Fitted DE and mES 76 fb-1 Sum of 95 r+ln, 98 r0ln

  35. B p ln Form Factors • Light-Cone Sum Rules : • Valid for q2 < 14 GeV2 • Ball/Zwicky quote 10-13% error at q2=0 • Lattice QCD : • Unquenched calculations by HPQCD, FNAL • Valid for q2 > 15 GeV2 • 11-13% error at high q2 • Useparametrizations(e.g. Becirevic-Kaidalov)to extrapolate to full q2 range • Quark models: ISGW II (no error quoted) Theo. FF uncertainties enter twice: (1) FFshape acceptance (2) FF normalization extraction of Vub

  36. ISGW II LCSR LQCD BK-Fit to BABAR data B pln a = 0.60 ± 0.15 Fitting the Form-Factor Shape Fit Becirevic-Kaidalov (BK) Parametrization to data: f(0) = norm. factor,a = shape parameter Result of BK-Fit consistent with unquenched LQCD: HPQCD’04 : a = 0.42 ± 0.07 , FNAL’04 : a = 0.62 ± 0.05

  37. Measured q2 Distribution pln • Recent LQCD and LCSR calculations agree • well with BABAR B plndata • ISGW II shows marginal agreement P*p Improved Data-MC agreement in kinematic distributions, e.g., hadron momentum. ISGW II BK Fit

  38. Current Measurements of B pln as Function of q2 M. Morii hep-ex/0505070 More data will help!

  39. d=1 68% CL Limits Experiment HPQCD FNAL a=0 Constraining Form-Factor Parametrizations • Form factor contains soft-overlap (z) and hard-scattering (H) contributions: • BK param. is approximation that neglects H •  study more general parametrization: • with B Hard gluon p u b • Richard Hill, hep-ph/0505129 : • d < 1  limits hard scattering • contribution • Simple Pole Model (only B* pole) • ruled out with 99.99% CL • Single Pole Model not ruled out • (a ∞, d1, a(1-d) fixed )

  40. rln B rln Form Factors • For vector mesons we need 3 FFs, e.g. A1,A2,V  much more difficult ! Ball & Zwicky ‘04 04 • Good agreement with all FF calculations • Statistical and systematic errors still too large to measure three FFs

  41. Theory Uncertainty: Dependence on FF shape “Do we have a model-independent BF measurement?” Effect of pln FF on BF small. Some effect of X-feed from rln Acceptance effect due to harsh kinem. cuts for rln

  42. Experimental Systematic Uncertainties

  43. Detector effects: Track, Photon, KLefficiencies and resolutions (losses, g bkg, …) Experimental Systematic Uncertainties

  44. Detector effects: Track, Photon, KLefficiencies and resolutions (losses, g bkg, …) All D* D D** Experimental Systematic Uncertainties Relative contributions to charm bkg have large uncertainties: B D, D*, D**, … BF

  45. Detector effects: Track, Photon, KLefficiencies and resolutions (losses, g bkg, …) All B uln Hybrid D* D D** M(Xu) Experimental Systematic Uncertainties Relative contributions to charm bkg have large uncertainties: B D, D*, D**, … BF

  46. Detector effects: Track, Photon, KLefficiencies and resolutions (losses, g bkg, …) All D* D D** Experimental Systematic Uncertainties Comparison off-resonance data with continuum MC. Mainly low q2 (secondary leptons) Relative contributions to charm bkg have large uncertainties: B -> D, D*, D**, … BFs B uln Hybrid M(Xu)

  47. Branching Fraction Measurements B pln B rln BABAR CLEO

  48. Consistency Check : Isospin Symmetry Measure B0, B+ separately:  Test isospin constraint Consistent with 2 within stat. error

  49. ub

  50. No FF norm. uncertainty available Extraction of Vub Extraction of |Vub| relies on FF norm. in distinct q2 regions LCSR q2 <15 GeV2, LQCD q2 > 15 GeV2or Extrapolation to whole q2 range Theory error dominates: 11-13% in restricted q2 ranges 15-17% for whole q2 range BABAR’s choice 7% exp. 4%6%

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