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Alex Smith – University of Minnesota Determination of |V cb | Using Moments of Inclusive B Decay Spectra BEACH04 Conference June 28-July 3, 2004 Chicago,

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Presentation on theme: "Alex Smith – University of Minnesota Determination of |V cb | Using Moments of Inclusive B Decay Spectra BEACH04 Conference June 28-July 3, 2004 Chicago,"— Presentation transcript:

1 Alex Smith – University of Minnesota Determination of |V cb | Using Moments of Inclusive B Decay Spectra BEACH04 Conference June 28-July 3, 2004 Chicago, IL Alex Smith University of Minnesota  Introduction  Hadron Mass Moments in B  X c l  Lepton Energy Moments in B  X c l  Photon Energy Moments in B  X s  decays  Combined Fit to Determine |V cb | and HQET parameters  Summary

2 Alex Smith – University of Minnesota Measuring |V cb | |V cb | is a fundamental parameter of the Standard Model Inclusive semileptonic b  c transitions provide a good laboratory in which to measure |V cb | –Exclusive semileptonic modes suffer large theoretical uncertainties –Purely hadronic final states too complicated –Weak b  cl process still obscured by strong interactions Strong interactions of inclusive semileptonic decays described by –Perturbative QCD Short-distance effects –Heavy Quark Effective Theory/Operator Product Expansion Non-perturbative long-distance effects

3 Alex Smith – University of Minnesota Heavy Quark Effective Theory Semileptonic rate expressed as a double expansion in  s and 1/m b –Use “kinetic mass” formulation of Uraltsev, et al (hep-ph/0401063)

4 Alex Smith – University of Minnesota Moments of Observable Spectra Moment of distribution defined in usual way: A commom set of HQET parameters appear in expressions for –Lepton energy moments in B  X c l –Hadronic mass-squared moments in B  X c l –q 2 moments in B  X c l –Photon energy moments in B  X s  –Semileptonic width Simultaneously fit these measurements to determine HQET parameters eg., lepton energy moment:

5 Alex Smith – University of Minnesota The CLEO II Detector CESR symmetric e + e - collider –Energy near  (4S) Most relevant features of detector: –Hermeticity of detector  neutrino reconstruction –Excellent shower resolution of CsI calorimeter  photons, electrons –Good charged particle resolution and dE/dx of drift chamber  leptons

6 Alex Smith – University of Minnesota Hadronic Mass and q 2 Moments in B  X c l Hadronic Mass and q 2 Moments in B  X c l Infer hadronic mass Reconstruct neutrino Identify lepton B XW l  Wl q MXMX ElEl E Neutrino reconstruction technique hep-ex/0403052

7 Alex Smith – University of Minnesota Hadronic Mass and q 2 Moments in B  X c l Hadronic Mass and q 2 Moments in B  X c l Infer hadronic mass Reconstruct neutrino Identify lepton B XW l  Wl q MXMX ElEl E Neutrino reconstruction technique

8 Alex Smith – University of Minnesota Hadronic Mass and q 2 Moments in B  X c l Hadronic Mass and q 2 Moments in B  X c l Selection criteria applied to suppress continuum and enhance neutrino reconstruction Fit differential decay rate in three dimensions: –q 2 –M X 2 –cos  Wl Fit Components and models: –B  Dl HQET+measured FF’s –B  D * l  HQET+measured FF’s –B  D ** l  ISGW2 –B  (X c ) non-res l  Goity-Roberts –B  X u l  ISGW2+NR –Secondary leptons CLEO MC –Continuum and fakes data Note: histograms normalized to same area Fit Components

9 Alex Smith – University of Minnesota Hadronic Mass and q 2 Moments in B  X c l Hadronic Mass and q 2 Moments in B  X c l Fit projections –Fit provides reasonable description of the data Branching fractions of individual modes are very model-dependent Inclusive differential decay rate much less model-dependent q2q2 MX2MX2 cos  Wl |p l | E

10 Alex Smith – University of Minnesota Hadronic Mass and q 2 Moments in B  X c l Hadronic Mass and q 2 Moments in B  X c l Results are consistent with previous CLEO measurements Uncertainties and results comparable to BaBar measurements q 2 moments expected to be somewhat complementary to M X moments –Only measured by CLEO hep-ex/0403052

11 Alex Smith – University of Minnesota Lepton Energy Moments in B  X c l Lepton Energy Moments in B  X c l Di-lepton event sample Use one lepton as the “tag”: –p l > 1.4 GeV/c, e or  –~97% of sample is primary B  Xl –Lepton charge tags flavor of parent B meson Look for signal electron in “tagged” events –p e > 0.6 GeV/c –Correct for backgrounds and efficiencies –Use charge and kinematic correlations to separate the spectra from primary and secondary leptons Primary leptons are the signal Monte Carlo simulation of electron daughters from B decay hep-ex/0403053

12 Alex Smith – University of Minnesota Lepton Energy Moments in B  X c l Lepton Energy Moments in B  X c l Unmixed B 0 Mixed B 0 Primary Events Opposite B Secondaries Same B Secondaries

13 Alex Smith – University of Minnesota Lepton Energy Moments in B  X c l Lepton Energy Moments in B  X c l Unmixed B 0 Mixed B 0 Primary Events Opposite B Secondaries Same B Secondaries Easily vetoed with kinematic cut X25 rejection 66% efficient

14 Alex Smith – University of Minnesota Lepton Energy Moments in B  X c l Lepton Energy Moments in B  X c l Subtract backgrounds Correct for efficiencies Algebraically solve for primary spectrum

15 Alex Smith – University of Minnesota Lepton Energy Moments in B  X c l Lepton Energy Moments in B  X c l Correct for –EW radiation –B boost Results consistent with previous CLEO measurements Systematics-limited--- Uncertainty on moments comparable to BaBar Integrate measured spectrum hep-ex/0403053

16 Alex Smith – University of Minnesota Photon Energy Moments in B  X s  Large photon background from continuum processes –  0 and  veto –Suppress using neural network Several different inputs related to event shape –Pseudo-reconstruction K s 0 or K +/- 1-4 pions, at most one  0 –Large subtraction necessary hep-ex/0108032

17 Alex Smith – University of Minnesota Photon Energy Moments in B  X s  b  s  measurement is key to extracting HQET parameters –Sensitive to m b Mean energy (1 st moment) roughly equal to m b /2 –Independent of m c New analysis in progress –Previous analysis optimized for branching fraction measurement –New analysis of old data optimized for extraction of spectrum –New results soon

18 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | Measurements included in fit: –1 st and 2 nd photon energy moments : E  > 2.0 GeV –1 st and 2 nd lepton energy moments : E e > 0.7, 1.2, 1.5 GeV –1 st and 2 nd hadronic mass moments : E e > 1.0, 1.5 GeV –1 st q 2 moment : E e > 1.0, 1.5 GeV Chi-squared fit including full correlation matrix of measurements Uses O(1/m 3 ) formulation and code from Uraltsev and Gambino (hep-ph/0401063) –Includes perturbative corrections to account for lepton/photon energy cuts Will also use approach of Bauer, Ligeti, et al before finalizing results (hep-ph/0210027)

19 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | CLEO data (GeV/c 2 ) (GeV 2 )

20 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | 1 st and 2 nd Lepton Energy Moments CLEO data (GeV/c 2 ) (GeV 2 )

21 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | 1 st and 2 nd Photon Energy Moments CLEO data (GeV/c 2 ) (GeV 2 )

22 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | 1 st and 2 nd Hadronic Mass Moments CLEO data (GeV/c 2 ) (GeV 2 )

23 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | 1 st q 2 Moments CLEO data (GeV/c 2 ) (GeV 2 )

24 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | Only CLEO has measured photon energy, q 2, hadronic mass, and lepton energy in a single experiment –A solution consistent with all measurements is found –Without B  X s  m b and m c almost completely correlated in fit –Most of the sensitivity to m b comes from B  X s  measurement First moment  mean photon energy  m b /2 (approx.) Other measurements primarily constrain m b -Cm c, C~0.6 –q 2 moment gives some complementary information Nearly independent of   2

25 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | CLEO data (GeV/c 2 )

26 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | 1 st Lepton Energy Moment 2 nd Lepton Energy Moment 1 st Photon Energy Moment 2 nd Photon Energy Moment

27 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | 2 nd Hadronic Mass Moment 1 st Hadronic Mass Moment 1 st q 2 Moment

28 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | measurement key

29 Alex Smith – University of Minnesota Combined Fit to Determine |V cb | Measurement of |V cb | and HQET parameters, including m b (  ), m c (  ),    (  ) at  =1 GeV Expect to reduce experimental errors significantly with additional measurements Theory errors under study and not shown or included in fit –Expected to be >= experimental errors

30 Alex Smith – University of Minnesota Summary Potential to significantly improve measurement of |V cb | –Experimental errors expected to be less than 2% –Theoretical errors expected to be comparable to experimental errors –Theoretical models will benefit from experimental constraints on higher order parameters Many improvements to analysis in progress: –3 rd lepton energy moments– work in progress –Include more 1 st and 2 nd lepton energy moment measurements in fit –2 nd q 2 moments – should have corrections soon Complementary sensitivity to parameters –Improved B  X s  moments – soon Critical constraint on m b –Include theoretical uncertainties in fit– almost ready CLEO has measured several different moments in a single experiment –Complementary to and of comparable precision to public BaBar measurements


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