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V ub measurements with the BaBar detector

V ub measurements with the BaBar detector. Daniele del Re University of California San Diego (on behalf of the BaBar collaboration). Exclusive b ul n measurements: B 0  p + l n on recoil of Partial tags B ( p,r,w,h,h ’,a 0 )l n on recoil of Breco tags. Outline:

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V ub measurements with the BaBar detector

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  1. Vub measurements with the BaBar detector Daniele del Re University of California San Diego (on behalf of the BaBar collaboration) • Exclusive buln measurements: • B0p+lnon recoil of Partial tags • B(p,r,w,h,h’,a0)lnon recoil • of Breco tags • Outline: • Inclusive buln measurements: • Endpoint • n reconstruction • mX on recoil of Breco tags • mX vs q2 on recoil of Breco tags

  2. buln decays and Vub l Vub n b u B0,± p,r... q q Charmless semileptonic B decays, BXuln, allow for the measurement of |Vub| Experimentally challenging, because • BXcln background (50 times higher) • Tight cuts are needed and signal is analyzed in limited region of phase space • extrapolation introduces uncertainties I will present two approaches: • Inclusive:look at kinematic quantities inclusively, use duality assumption and study buln. Once total B(buln) is obtained |Vub| can be extracted with small uncertainties. • Exclusive:study exclusive decays, use form factor to extract branching ratio and |Vub| Daniele del Re (UCSD) - ICHEP 04

  3. Three Experimental Techniques Fully Had. Reco Partial Reco p+ l+ n n p- p- D0 D0 Untagged h+ h- Y(4S) g g Three ways of studying BXuln decays in BaBar: Method signal recoil Xu l n (nh,mg) Xu ln psoft l(D0nX) Xu ln D(*) X efficiency purity No recoil and n reco from miss. momentum Untagged Recoil of partially reconstructed D* Partial Tags Recoil of fully recon. BD(*)X Breco Tags p+ n l- Reco’ed Missed (or not all used) Daniele del Re (UCSD) - ICHEP 04

  4. Inclusive: Endpoint and n Reco Untagged Endpoint: • one high energy electron (2.0GeV<Ee<2.6GeV) • cut on the missing momentum ( )and event shape cuts • Continuum bkg using off-peak data and on-peak for El>2.8GeV. • BBbar bkg fitting El spectrum (Den, D*en, D**en, D(*)pen, Xuen and non semileptoniccomponents) n Reconstruction: • Same approach as in the endpoint method (same p*>2GeV/c) but it selects a refined subset of events (much better S/B) • bcln background separated by: where Y(4S) rest frame. Less sensitive to non perturbative parameters than mX. Signal box: sh<3.5 GeV2/c4 • efficiency and shape modeling checked using pure BD0ln(X) control sample Daniele del Re (UCSD) - ICHEP 04

  5. Inclusive: Endpoint and n Reco n reco Untagged Endpoint 80fb-1 Data (continuum sub) MC for BB background Data (eff. corrected) MC Daniele del Re (UCSD) - ICHEP 04

  6. Inclusive: mX vs. q2 Breco Tags Extension of the already published result (PRL92,071802). • Recoil selection and reconstruction ofXsystem: One and only one lepton with p*> 1 GeV/c Correlation between lepton charge and Breco flavor Cut on the missing mass: Mmiss2 < 0.5GeV2, charge conservation: Qtot=0 Partially reconstructed neutrino to reject B0 D*l nevents kinematic fit (2-C): improve hadronic mass resolution Kaon veto • Systematics due to lepton ID and tag normalization reduced by measuring a ratio of BRs • mX <1.7GeV and q2>8GeV2 using the approach by Bauer et al. Dependence on shape function parameters is much reduced This approach and sample have been also used to unfold the mX spectrum. Daniele del Re (UCSD) - ICHEP 04

  7. Inclusive: mX vs. q2 Breco Tags 80fb-1 Unfolded mX spectrum and cumulative distribution for buln decays Stability of |Vub| as a function of the q2 cut BLL=Bauer et al. DFN=De Fazio,Neubert (using BLL) Daniele del Re (UCSD) - ICHEP 04

  8. Exclusive Decays on Recoil Partial Tags • Semil Tags (B0D*ln): measurement in bins of q2(0-8-16GeV2/c4) Signal yields are extracted by fitting Mn2(n mass squared): • Breco Tags (BD(*)X):9 B  Xuln modes: Xu=p+,p0,r+,r0 ,w,h,h’,a00, a0+ Approach similar to the inclusive analysis but resonances are exclusively and fully reconstructed on recoil. Breco Tags (upper limits for h,h’,a00, a0+, results in backup slides) 80fb-1 Partial Tags Breco Tags Breco Tags q2 < 8GeV2/c4 Daniele del Re (UCSD) - ICHEP 04

  9. Conclusions SF param. from BELLE bsg We measured |Vub| with different experimental inclusive techniques: • Dominant error from modellization of non-perturbative effects (Shape Function, SF). Fitted on bsg events; two fits available not yet combined: CLEO(2001), Belle(2004) • We measured the unfolded mX distribution. In future buln decays can be used to put constraints on SF parameters. SF param. from CLEO bsg Daniele del Re (UCSD) - ICHEP 04

  10. Vub measurements with BaBar Untagged inclusive Untagged inclusive Breco Tags inclusive Breco Tags inclusive Partial Tags exclusive Breco Tags Daniele del Re (UCSD) - ICHEP 04

  11. BACKUP SLIDES Daniele del Re (UCSD) - ICHEP 04

  12. Incl. Decays: Theory and Uncertainties Relevant issues • hadronization effects and Fermi motion (b quark mass) • non-perturbative parametrizations (Shape Function, SF) affected by large uncertainties. Two approaches to extract |Vub| and estimate theo. systematics: • DeFazio-Neubert paper (DFN ), tri-differential parametrization (Ee,mX,q2) to extrapolate. |Vub| extracted by • q2 vs mX approach by Bauer et al. (BLL ). partial BR with q2 vs mX cut. |Vub| is extracted using Dependence on SF (here in G) is much reduced. Theo. uncertainties on non-perturbative effects are evaluated using lSF and LSF ellipse from bsg from CLEO. Belle ellipse as an alternative. BELLE OPE Our default CLEO Alternative Daniele del Re (UCSD) - ICHEP 04

  13. Excl. Decays: Theory and Uncertainties • primary challenge is calculation of the form factors (containing hadronization effects and non-pert. contributions) • Large uncertainties both extrapolation to full phase space and determination of |Vub| • different theoretical models predict different q2 distributions. • discriminate among models by a precise measurement of differential BRs. The differential branching ratio can be related to |Vub| by the following relation The bigger the integrated region the smaller the uncertainty on |Vub| Brln Daniele del Re (UCSD) - ICHEP 04

  14. Inclusive: Endpoint Method Untagged • one high energy electron (p*>1.1GeV) • cut on the missing momentum ( )and event shape cuts • Continuum bkg using off-peak data and on-peak for El>2.8GeV. • BBbar bkg fitting El spectrum (Den, D*en, D**en, D(*)pen, Xuen and non semileptoniccomponents) • For 2.0GeV<El<2.6GeV we obtain (using DFN): Results are stable by applying tighter cuts on El. Main exp. systematics from signal modeling (~2-8%) and event selection efficiency (~6%), and D(*,**)en description (~3%) 80fb-1 Daniele del Re (UCSD) - ICHEP 04

  15. Inclusive: n Reconstruction Method Untagged Same approach as in the endpoint method but it select a refined subset of events (much better S/B) : • one high energy electron (p*>2GeV/c) is identified • visible 4-momentum by using charged tracks (with particle ID) and energy deposits in the calorimeter • missing momentum defined as and used to estimate neutrino • cuts on the missing momentum and on the event shape. • bcln background separated by: where Y(4S) rest frame. Less sensitiveSF parameters than mX • efficiency and shape modeling checked using a pure B0D*+ln(X) control sample Data-MC agreement for pmiss Daniele del Re (UCSD) - ICHEP 04

  16. Inclusive: n Reconstruction Method Untagged • BR extracted by applying the following cuts El>2GeVand sh<3.5 GeV2/c4 • The region sh>4.25 GeV2/c4 is used to normalize the MC bkg to the data • De Fazio-Neubert parametrization to extrapolate to full phase space Results: Main experimental systematics are from: Neutrals (~6%), KL (~7%), BXcln modeling: (7%), stability in scans (~12%) 80fb-1 Daniele del Re (UCSD) - ICHEP 04

  17. Inclusive: mX vs. q2 Breco Tags For Breco tags the reconstructed modes are(~1000 modes): B  D(*)p, D(*)p p 0, D(*)3p, etc... The eff. is ~0.4% corresponding to ~4000 B/fb-1 (~2500 B/fb-1 B+ and B ~1500 B/fb-1 B0) The sample has low purity but it improves a lot once cuts on recoil are applied. Recoil selection and reconstruction ofX system: One and only one lepton with p*> 1 GeV/c Correlation between lepton charge and Breco flavor Cut on the missing mass: Mmiss2 < 0.5GeV2, charge conservation: Qtot=0 Partially reconstructed neutrino to reject B0 D*l nevents kinematic fit (2-C): improve hadronic mass resolution SeparateBXuln in signal enriched and depleted based on veto on K± and KS Systematics reduced by measuring Daniele del Re (UCSD) - ICHEP 04

  18. Inclusive: mX and mX vs. q2 Breco Tags Daniele del Re (UCSD) - ICHEP 04

  19. Inclusive: Unfold Had. Mass Spectrum Breco Tags mX spectrum can be converted in a universal variable by unfolding detector and selection effects. relationship between measured and true spectra is: where is the detector response matrix, in general is non-invertible. Unfolding method is based on procedure specified in hep-ph/9509307. Systematics effects are properly taken into account. First and second moment of the buln mX distribution are extacted: 80fb-1 Daniele del Re (UCSD) - ICHEP 04

  20. Comparison Using Belle’s (mb,a) Ellipse Daniele del Re (UCSD) - ICHEP 04

  21. Exclusive: B0 p+l-n Partial Tags Partially reco’ed sample is selected by following variables combined in a likelihood ratio: • Some preselection cuts on shape and multiplicity • lepton mom. (p*>1.3GeV) • soft pion mom. (50MeV<pp <200MeV) • lepton-p Vtx probability Signal yield is extracted via Mn2(mis. mass squared). D* is assumed to be collinear with the soft p Then: Additional cuts to: • remove b-bbar background (like the charge correlation of the two reconstructed leptons and quantities related to the remainder of the event) • remove continuum background (like the invariant mass and the opening angle of the two electrons) Right sign wrong sign Daniele del Re (UCSD) - ICHEP 04

  22. Exclusive: B0 p+l-n Partial Tags • Measurement is performed in bins of q2 • Three bins: (q2 < 8GeV2 ; 8GeV2 < q2 <16GeV2 ; q2 >16GeV2) • Signal yields are extracted by fitting Mn2(neutrino mass squared in B0 pln). We obtain: Main experimental systematics are due to detector (~8%), background composition (~10%) and shape of BBbar background (~15%) 80fb-1 Daniele del Re (UCSD) - ICHEP 04

  23. Exclusive: B (p,r,w,h,a0) ln Breco Tags 9 B  Xuln modes are studied: Xu=p+,p0,r+,r0 ,w,h,h’,a00, a0+ Resonances are exclusively reconstructed on the recoil. Similar cuts as for the inclusive mX analysis, such as p*>1GeV and miss. mass squared of the event. Further per mode cuts to reject bc and crossfeed background are used 80fb-1 Daniele del Re (UCSD) - ICHEP 04

  24. Exclusive: B (p,r,w,h,a0) ln Breco Tags Similar approach to the inclusive analysis but resonances are exclusively and fully reconstructed on recoil. We measure: These two results make use of: Systematics are dominated by MC statistics. Large systematics due to non-resonant contribution in B  rln. Theoretical systematics are small (~ 4-7%) 80fb-1 Daniele del Re (UCSD) - ICHEP 04

  25. Results (80fb-1) B±p0ln B0rln B±r0ln B0wln Daniele del Re (UCSD) - ICHEP 04

  26. Results (80fb-1) B±hln B±h’ln B±a00l n B0a0l n Daniele del Re (UCSD) - ICHEP 04

  27. Vub measurements with BaBar Untagged inclusive Untagged inclusive Breco Tags inclusive Breco Tags inclusive Partial Tags exclusive Breco Tags Daniele del Re (UCSD) - ICHEP 04

  28. Vub measurements Daniele del Re (UCSD) - ICHEP 04

  29. Conclusions for Exclusive Decays We also developed novel methods to measure EXCL. CHARMLESS decays: • Breco tags: • Semil tags: AVERAGE Daniele del Re (UCSD) - ICHEP 04

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