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Inclusive | V ub |Measurements From Babar

Inclusive | V ub |Measurements From Babar. Roberto Sacco. IoP HEPP Conference, Dublin, 22 March 2005. q 2 =M lep 2. u. The Method. Semileptonic decays b → u ℓ n Look at inclusive kinematic quantities Assume parton-hadron duality Measure Br ( B → X u ℓ n ).

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Inclusive | V ub |Measurements From Babar

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  1. Inclusive |Vub|Measurements From Babar Roberto Sacco IoP HEPP Conference, Dublin, 22 March 2005

  2. q2=Mlep2 u The Method Semileptonic decays b → uℓn Look at inclusive kinematic quantities Assume parton-hadron duality Measure Br (B→Xuℓn) OPE relates total rate toVub, total uncertainty ~5% Need to reduce b→cℓn background Exploit mu<<mc: select c-forbidden regions of phase space Eℓ mX q2 …or a combination R. Sacco - IoP HEPP Conference – 22 March 2005 Models needed to compute acceptance This is where most of the theory uncertainty is located mX

  3. efficiency purity Experimental Techniques Untagged: electron near kinematic endpoint Untagged: n reco from missing momentum Hadronic tag: recoil of fully reconstr. B → D(*)X Apply cuts Get partial branching ratio: dBr (b→uℓn)= Nsel-Nbkg/e Compute full branching ratio: Br (b→uℓn)= dBr (b→uℓn) /fu fu ∫∫∫ H(q2,Eℓ,mX)  F(k,l1SF, LSF) parton level Shape Function Use OPE to determine Vub: R. Sacco - IoP HEPP Conference – 22 March 2005

  4. Belle 1st and 2nd moment of SF determined The Shape Function (SF) b-quark motion within the B k=“reduced” b momentum l1<Ekinb>, L mb Assumption: universal function for all b→ light quark transitions (L.O.) Get Λ and l1 from b → sg decays F(k+) Detailed shape, and especially the low tail, are not constrained Rough features (mean Λ, r.m.s. l1) are known R. Sacco - IoP HEPP Conference – 22 March 2005

  5. BELLE CLEO OPE Babar OPE CLEO Our default Acceptance Calculations DeFazio-Neubert (DFN ), triple differential decay rate (Ee,MX,q2) computed to O(aS,mb-2) convoluted with shape function. MX vs q2 approach by Bauer, Ligeti and Luke. (BLL ). OPE calculation in region of phase space where SF effects are small. Theoretical uncertainties on non-perturbative effects evaluated using lSF an LSF ellipse from bsg from Belle. Tried also CLEObsgand bcℓnmoments from BaBar R. Sacco - IoP HEPP Conference – 22 March 2005

  6. Data (continuum sub) MC for BB background PRELIMINARY Data (eff. corrected) MC Endpoint Analysis One high energy electron (2.0GeV<Ee<2.6GeV) (larger acceptance smaller theory errors) hep-ex/0408075 Cuts on missing momentum and event shape 80 fb-1 Continuum bkg using off-peak data and on-peak for Eℓ >2.8 GeV BB bkg fitting Eℓ spectrum (Den,D*en, D**en,D(*)pen, Xuen and non semilept. components) R. Sacco - IoP HEPP Conference – 22 March 2005

  7. Endpoint: Results and Outlook dBr 2.0-2.6GeV = (5.31 ± 0.32stat ± 0.49syst)10-4 Main experimental systematics: signal modeling (~8%), event selection efficiency (~6%), D(*,**)en description (~3%) fu= 0.246 ± 0.031 Br (B → Xuℓn) = (2.16 ± 0.24exp ± 0.27fu) 10-3 Vub= (4.40 ± 0.24exp± 0.28fu± 0.21OPE) 10-3 dVub/Vub= 5.5%exp 6.3%fu 4.8%OPE = 9.7% Small (3%) statistical error, already on current data sample (250 fb-1) Possible improvement in experimental systematic error: ~5% ondBr → 2.5% onVub→tot. exp. error 3% R. Sacco - IoP HEPP Conference – 22 March 2005 near future

  8. q2-Eℓ with neutrino reconstruction Use pν = pmiss in addition to pe Calculate q2 Acceptance ~25% less than cut on Ee alone, but S/N=1/2 is much better q2 (GeV^2) Accepted region Select high energy electron (p* > 2 GeV/c) b cℓn background separated by: bcℓνallowed R. Sacco - IoP HEPP Conference – 22 March 2005 Ee (GeV)

  9. q2-Eℓ : analysis strategy Check efficiency and shape modeling by using a pure B0D*+ℓn(X) control sample Extract BR by requiring Eℓ >2GeVand sh<3.5 GeV2/c4 Subtract BB background normalized by sideband (sh>4.25 GeV2/c4) extract signal R. Sacco - IoP HEPP Conference – 22 March 2005 normalise background hep-ex/0408045 80 fb-1

  10. q2-Eℓ : results and outlook dBr Ee>2GeV, shmax<3.5GeV2= (4.46 ± 0.42stat ± 0.83syst)10-4 Main experimental systematics: neutrals (6%), KL (7%), stability tests (12%), background modeling (7%). Signal modeling ~5%. fu= 0.163 ± 0.010 Br (B → Xuℓn) = (2.76 ± 0.560.60exp ± 0.200.16fu) 10-3 Vub= (4.99 ± 0.49exp± 0.16fu± 0.22OPE) 10-3 dVub/Vub= (4.7stat 9.3exp sys  3.2fu 4.8OPE )% = 11.9% Statistical error on 250 (500) fb-1: 2.7% (1.9%) Experimental systematic error can be improved ~6-8% ondBr →3-4% onVub →total experimental error 6%(80 fb-1) 5%(250 fb-1)4%(500 fb-1) R. Sacco - IoP HEPP Conference – 22 March 2005 near future

  11. Recoil Analyses Fully reconstruct the tag side more then 1000 modes, 0.4% efficiency In the recoil side: PB,sig = -PB,tag look for single ℓ with E>1GeV missing P in the acceptance charge correlation, charge conservation veto K±, Ks Fully reconstructed B hadrons reconstruct u-jet: MX > 1.7 GeV q2 = (PB,sig- PX)2> 8 GeV2 v R. Sacco - IoP HEPP Conference – 22 March 2005 Fit MX vs. q2: dBr (MX<1.7, q2>8) lepton acceptances by DFN and BLL unfold detector effects X

  12. BABAR BABAR MX Analysis 80 fb-1 Simple fit inMXshows clear b→ uℓvsignal (S/N ~ 2/1 forMX< 1.55 GeV) Br (B → Xuℓn) = (3.04 ± 0.35stat ± 0.34exp ± 0.24fu) 10-3 Vub= (5.22 ± 0.30stat± 0.31exp sys ± 0.21fu ± 0.25OPE) 10-3 dVub/Vub= (5.7stat 5.9exp sys  4.0fu 4.8OPE )% = 10.3% Statistical error on250 (500)fb-1:3.2% (2.3%) Experimental Systematics: 4% (?) R. Sacco - IoP HEPP Conference – 22 March 2005 hep-ex/0408068 near future

  13. MX-q2 Analysis 80 fb-1 2D fit to measuredBrin {MX<1.7 GeV, q2>8 GeV2} hep-ex/0408068 dBr weakly dependent on shape function Pure OPE calculation can be applied (BLL, hep-ph/0111387) fu=0.325 ± 0.061 DFN:fu=0.300 ± 0.026 NB: BLL includes OPE errors dBr mX<1.7 GeV, q2>8 GeV2= (8.96 ± 1.43stat ± 1.44exp) 10-4 Vub= (4.98 ± 0.40stat± 0.39exp sys ± 0.47fu+OPE) 10-3 (BLL) Vub= (5.18 ± 0.41stat± 0.40exp sys ± 0.250.20fu ± 0.25OPE) 10-3 (DFN) R. Sacco - IoP HEPP Conference – 22 March 2005

  14. MX-q2: results and outlook dBr mX<1.7 GeV, q2>8 GeV2 = (8.96 ± 1.43stat ± 1.44syst)10-4 Main experimental systematics: detector systematics (10%), stability tests (7%), background modeling (7%), MC stats (5%). Signal modeling ~1.5%. Br (B → Xuℓn) = (2.98 ± 0.67exp ± 0.25fu) 10-3 Vub= (5.18 ± 0.57exp± 0.250.20fu± 0.25OPE) 10-3 dVub/Vub= (8.0stat 8.0exp sys  4.3fu 4.8OPE )% = 13% Statistical error on 250 (500) fb-1 : 4.5% (3.2%) Experimental systematic error can be improved ~8-10% ondBr →4-5% onVub → total experimental error 9%(80 fb-1) 7%(250 fb-1)6%(500 fb-1) near future R. Sacco - IoP HEPP Conference – 22 March 2005

  15. Conclusions Three different approaches to measure |Vub| inclusively at BaBar Experimental systematics can be improved for all of them: Better understanding of detector effects (neutrals, KL) More refined systematic studies Better knowledge of B SL decays and form factors Larger datasets: Marginal for untagged analyses Very important for recoil analyses and unfolding More studies under way New theoretical framework Sub-leading shape functions and O(as2) corrections R. Sacco - IoP HEPP Conference – 22 March 2005 Use bcℓnmoments to extract SF parameters

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