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Vub 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) Outline: Inclusive buln measurements: Endpoint n reconstruction mX on recoil of Breco tags mX vs q2 on recoil of Breco tags Exclusive buln measurements: B0p+ln on recoil of Partial tags B(p,r,w,h,h’,a0)ln on recoil of Breco tags

2 Daniele del Re (UCSD) - ICHEP 04
buln decays and Vub 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| b u q Vub n B0,± p,r... l 08/17/04 Daniele del Re (UCSD) ICHEP 04

3 Three Experimental Techniques
Three ways of studying BXuln decays in BaBar: Method signal recoil Xu l n (nh,mg) Xu l n psoft l(D0nX) Xu l n D(*) X efficiency purity Untagged No recoil and n reco from miss. momentum Partial Tags Recoil of partially reconstructed D* p- l+ n D0 Partial Reco h+ h- Untagged g Recoil of fully recon. BD(*)X Breco Tags n p- p+ D0 Fully Had. Reco p+ n Y(4S) l- Reco’ed Missed (or not all used) 08/17/04 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 semileptonic components) 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 08/17/04 Daniele del Re (UCSD) ICHEP 04

5 Inclusive: Endpoint and n Reco
Untagged Endpoint n reco 80fb-1 Data (continuum sub) MC for BB background Data (eff. corrected) MC 08/17/04 Daniele del Re (UCSD) ICHEP 04

6 Daniele del Re (UCSD) - ICHEP 04
Inclusive: mX vs. q2 Breco Tags Extension of the already published result (PRL92,071802). Recoil selection and reconstruction of X 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 n events 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. 08/17/04 Daniele del Re (UCSD) ICHEP 04

7 Daniele del Re (UCSD) - ICHEP 04
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) 08/17/04 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 08/17/04 Daniele del Re (UCSD) ICHEP 04

9 Daniele del Re (UCSD) - ICHEP 04
Conclusions 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 BELLE bsg SF param. from CLEO bsg 08/17/04 Daniele del Re (UCSD) ICHEP 04

10 Vub measurements with BaBar
method S/B Pros&Cons Vub(x10-3) Electron spectrum endpoint Ee>2.0GeV Total rate using fu from CLEO 0.050.2 High statistics Duality valid for tight Ee cuts? Bkg subtraction Ee vs q2 and neutrino reconstruction Ee>2.0GeV and sh<3.5 GeV2/c4 Total rate using DeFazio-Neubert ~0.5 Lower syst. on shape functions mX analysis (1-D) mX<1.55 GeV/c2 ~1.7 Low background High resolution Low statistics Shape func. syst. mX vs q2 analysis mX<1.7 GeV/c2 and q2 >8.0 GeV2/c4 Vub using Bauer et al. ~2 Very small syst. on SF param. Small statistics Total rate using Form Factors calc. 120 Very small bkg ~no cut on kinem Untagged inclusive Untagged inclusive Breco Tags inclusive Breco Tags inclusive Partial Tags exclusive Breco Tags 08/17/04 Daniele del Re (UCSD) ICHEP 04

11 Daniele del Re (UCSD) - ICHEP 04
BACKUP SLIDES 08/17/04 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 08/17/04 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 08/17/04 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 semileptonic components) 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 08/17/04 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 sensitive SF parameters than mX efficiency and shape modeling checked using a pure B0D*+ln(X) control sample Data-MC agreement for pmiss 08/17/04 Daniele del Re (UCSD) ICHEP 04

16 Inclusive: n Reconstruction Method
Untagged BR extracted by applying the following cuts El>2GeV and 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 08/17/04 Daniele del Re (UCSD) ICHEP 04

17 Daniele del Re (UCSD) - ICHEP 04
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 of X 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 n events kinematic fit (2-C): improve hadronic mass resolution Separate BXuln in signal enriched and depleted based on veto on K± and KS Systematics reduced by measuring 08/17/04 Daniele del Re (UCSD) ICHEP 04

18 Inclusive: mX and mX vs. q2
Breco Tags 08/17/04 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/ Systematics effects are properly taken into account. First and second moment of the buln mX distribution are extacted: 80fb-1 08/17/04 Daniele del Re (UCSD) ICHEP 04

20 Comparison Using Belle’s (mb,a) Ellipse
CLEO ellipse BELLE ellipse n reco Shift as expected. Theo. error reduced Endpoint Shift as expected. Theo. error reduced. With Belle ellipse cut variation on Ee shows results that are less consistent among them mX mX vs q2 Small change demonstrates that this method is less affected by SF params. With Belle ellipse theo. error is larger with respect to the others methods unfolding Unfolded spectrum seems to prefer Belle ellipse. Comparison with expected mX shape is better. 08/17/04 Daniele del Re (UCSD) ICHEP 04

21 Daniele del Re (UCSD) - ICHEP 04
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 08/17/04 Daniele del Re (UCSD) ICHEP 04

22 Daniele del Re (UCSD) - ICHEP 04
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 08/17/04 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 Mass(MeV) Width(MeV) Decay modes pln 139.57 - p0ln 134.98 gg rln 775 150 p0p r0ln p-p+ wln 782.6 8.5 p-p+p0 (89%) hln 547.8 gg (39.4%) pp+p0(22.6%) p0p0p0(32.5%) h´ln 957.8 r0g(29.5%) hp-p+ (44.3%) a0 ln 985 50-100 hp (~all) a00ln hp0 (~all) 80fb-1 08/17/04 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 08/17/04 Daniele del Re (UCSD) ICHEP 04

25 Daniele del Re (UCSD) - ICHEP 04
Results (80fb-1) B±p0ln B0rln B±r0ln B0wln 08/17/04 Daniele del Re (UCSD) ICHEP 04

26 Daniele del Re (UCSD) - ICHEP 04
Results (80fb-1) B±hln B±h’ln B±a00l n B0a0l n 08/17/04 Daniele del Re (UCSD) ICHEP 04

27 Vub measurements with BaBar
method S/B Results Electron spectrum endpoint Ee>2.0GeV Total rate using DeFazio-Neubert 0.11 Ee vs q2 and neutrino reconstruction Ee>2.0GeV and sh<3.5 GeV2/c4 ~0.3 mX analysis (1-D) mX<1.55 GeV/c2 ~1.7 mX vs q2 analysis mX<1.7 GeV/c2 and q2 >8.0 GeV2/c4 Total rate and Vub using Bauer et al. ~2 Total rate by using Form Factors calc. 120 Untagged inclusive Untagged inclusive Breco Tags inclusive Breco Tags inclusive Partial Tags exclusive Breco Tags 08/17/04 Daniele del Re (UCSD) ICHEP 04

28 Daniele del Re (UCSD) - ICHEP 04
Vub measurements 08/17/04 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 08/17/04 Daniele del Re (UCSD) ICHEP 04

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