1 / 16

Inclusive b → u ℓ v and b → s g Spectrum

Inclusive b → u ℓ v and b → s g Spectrum. Masahiro Morii Harvard University B A B AR Collaboration SLAC/INT Workshop on Flavor Physics and QCD May 11–14, 2005. Experimental Program. Inclusive rate G u = G ( B → X u ℓv )  | V ub | 2

wes
Download Presentation

Inclusive b → u ℓ v and b → s g Spectrum

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Inclusive b→ uℓv andb → sg Spectrum Masahiro Morii Harvard University BABAR Collaboration SLAC/INT Workshop on Flavor Physics and QCD May 11–14, 2005

  2. Experimental Program • Inclusive rate Gu=G(B→Xuℓv)  |Vub|2 • Total rate not measurable due to b →c background • Measure partial rate in the “charm-free” regions of phase space • Expect theory to calculate • Inputs required for the shape function (SF) • Eg spectrum in b →sg • Eℓand mX spectra in b →cℓv • SF errors considered “experimental” • Theoretical errors include: • Perturbative • Sub-leading SF • Weak annihilation (WA) b → sg b → cℓv Shape Function Partial Gu |Vub| M. Morii, Harvard

  3. Measurements of b → sg • Egspectrum depends on the shape function • Measure Egmoments (1st, 2nd, 3rd)  fit with theory, or • Fit the spectrum itself with theory • Is there a preference? • Two types of measurements: • Inclusive measurement detects only the photon • Poor S/B ratio forces tight selection cuts • Efficiency depends strongly on Eg • Sum-of-exclusive measurement reconstructsa large number of exclusive decay channels and add them up • Better S/B ratio • Efficiency depends on the s-quark fragmentation model M. Morii, Harvard

  4. Inclusive b → sg • Inclusive Eg spectrum can be measured above ~1.9 GeV Belle Belle, efficiency-corrected BABAR, partial BF M. Morii, Harvard

  5. Sum of Exclusive B→ Xsg • BABAR uses 38 channels: (K± or KS) plus ≤4 pions, etc. • Data sample is 80 fb-1 • Measure Eg spectrum and thefirst three truncated moments • Table of values in R. Mommsen’stalk at Moriond Electroweak BABAR preliminary Eg cut (GeV) M. Morii, Harvard

  6. Shape Function Parameters • Fit the Eg spectrum from the BABARS(excl.) measurement with • Kinetic scheme by Benson, Bigi, Uraltsev (Nucl.Phys.B710:371,2005) • Shape-function scheme by Neubert (Eur.Phys.J.C40:165,2004) • b → sg and b → cℓv agree, and have comparable precision • Final results based on the moments in the works • |Vub| results in this talk use the SF parameters from b → cℓv • Caveat: Error on L is 80 MeV (BABAR) vs. 70 MeV (Belle) Preliminary BABAR PRL 93:011803,2004 Neubert PLB612:13,2005 M. Morii, Harvard

  7. Measurements of b→ uℓv • Three degrees of freedom in B→Xuℓv • Lepton energyEℓ: Easy to measure • Hadronic system mass mX : Efficient for b →c rejection • Lepton-neutrino mass squared q2 : Mild dependence on the SF • Sample selection technique determines the available variable(s) • Inclusive lepton sample  Eℓ • Lepton + missing momentum  Eℓ and q2 • Recoil of reconstructed B Eℓ, mX, and q2 • Experiments measure partial branching fraction DB • Translation to |Vub| requires tB and • BABAR/Belle use Bosch, Lange, Neubert, Paz (NPB699:335,2004) for the latter Efficiency Purity M. Morii, Harvard

  8. Lepton Endpoint • Experiments push the Eℓ cut as low as possible • Better efficiency • Weaker SF dependence • Smaller WA error • S/B < 1/10  Background modeling! • Pushing below 1.9 GeV difficult • Hit poorly-understood B→ D**ℓv Belle on-peak off-peak on – off M. Morii, Harvard

  9. Lepton + Neutrino • Find lepton with Eℓ > 1.9 GeV and assume pv = pmiss of the event • Now we have Eℓ and q2 • Define charm-free space by calculating • rejects the charm background • Actual cut is shmax < 3.5 GeV2 • Signal/background = 1/2 • Final result will have smaller experimental errors Maximum hadronicmass squared + correction for B motion in the c.m.s. M. Morii, Harvard

  10. Recoil B Analysis • Reconstruct one B completely in B→ D(*) + hadrons • Efficiency ~0.2%/B • Recoilgives a clean and unbiased sample of B • Charge and 4-momentum known • Find a lepton in the recoil B and require • Charge conservation • Missing mass = 0 • Veto against K (likely from D) • We get complete event kinematics • Leave Eℓ cut loose (>1 GeV) • Use mX and/or q2 to select signal Fully reconstructedB hadrons v lepton X Recoil B M. Morii, Harvard

  11. mX and q2 Spectra • Experiments plan to measure the mX and q2 spectra in b→ uℓv • Potential goal: determine the SF parameters with b→ uℓv • What else can we learn? No q2 cut mX < 1.7 GeV BABAR, corrected for efficiency and resolution Belle, background-subtracted distributions M. Morii, Harvard

  12. mX vs. q2 • Select mX < 1.7 GeV and q2 > 8 GeV2 • Proposed by Bauer, Ligeti, Luke (PRD64:113004, 2001) • Reminder: SF errors differ because the error on L is different b→ uℓv outside the signal region signal background M. Morii, Harvard

  13. P+ Variable • Define P+ = EX – PX and cut at P+ < 0.66 GeV • Proposed by Bosch, Lange, Neubert, Paz (PRL93:221801,2004) Belle Note small theoretical error M. Morii, Harvard

  14. Inclusive |Vub| in May 2005 • Experimental errors 8–11%  5% if combined • Shape-function errors 7–12%  8% on average • Theoretical errors 3–5%  4% on average • We have determined |Vub| to 5%exp 8%SF 4%theo  10% • We said this last summer – Do we believe it now? M. Morii, Harvard

  15. Inclusive |Vub| at Moriond 2007 • Experimental error (5%) in |Vub| will shrink with the statistics • Even syst. errors improve with larger control samples • 500 fb-1/expt. by summer 2006  2.5%? • Largest uncertainty (8%) comes from the shape function • Will improve as soon as we start using the new b→ sg results • BABARS(excl.) result alone can halve the error on L • 2 expts. × 2 methods × more data  3%? • Theory error (4%) will be the largest error (again) • We’d better be darn sure about them • We’d better have a strategy to shrink them M. Morii, Harvard

  16. Questions + Remark • How robust are the current theory errors? • BABAR/Belle rely on calculation by one group • Error estimates come from Lange, Neubert, Paz, hep-ph/0504071 • We’d love to have an independent calculation or two • Sub-leading SF error small (0.5% for mX-q2)  Do we all agree? • P+ cut has small theo. error (3%)  Will another group confirm? • What can we do to shrink the theory errors? • Leading error is perturbative  Any hope for improvement? • We will pursue B+-B0 difference  Precision unknown yet • Experimental handles on sub-leading SFs? • |Vub| will be determined to a 5% precision in 2 years if the theory error becomes 3%, and we believe it M. Morii, Harvard

More Related