Determination of v cb using moments of inclusive b decay spectra
This presentation is the property of its rightful owner.
Sponsored Links
1 / 30

Determination of | V cb | Using Moments of Inclusive B Decay Spectra PowerPoint PPT Presentation


  • 126 Views
  • Uploaded on
  • Presentation posted in: General

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 n Lepton Energy Moments in B  X c l n Photon Energy Moments in B  X s g decays

Download Presentation

Determination of | V cb | Using Moments of Inclusive B Decay Spectra

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Determination of v cb using moments of inclusive b decay spectra

Determination of |Vcb| 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Xcln

  • Lepton Energy Moments in BXcln

  • Photon Energy Moments in BXsg decays

  • Combined Fit to Determine |Vcb| and HQET parameters

  • Summary

Alex Smith – University of Minnesota


Measuring v cb

Measuring |Vcb|

  • |Vcb| is a fundamental parameter of the Standard Model

  • Inclusive semileptonic bc transitions provide a good laboratory in which to measure |Vcb|

    • Exclusive semileptonic modes suffer large theoretical uncertainties

    • Purely hadronic final states too complicated

    • Weak bcln 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

Alex Smith – University of Minnesota


Heavy quark effective theory

Heavy Quark Effective Theory

  • Semileptonic rate expressed as a double expansion in as and 1/mb

    • Use “kinetic mass” formulation of Uraltsev, et al(hep-ph/0401063)

Alex Smith – University of Minnesota


Moments of observable spectra

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Xcln

    • Hadronic mass-squared moments in BXcln

    • q2 moments in BXcln

    • Photon energy moments in BXsg

    • Semileptonic width

  • Simultaneously fit these measurements to determine HQET parameters

eg., lepton energy moment:

Alex Smith – University of Minnesota


The cleo ii detector

The CLEO II Detector

  • CESR symmetric e+e- collider

    • Energy near U(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

Alex Smith – University of Minnesota


Hadronic mass and q 2 moments in b x c l n

l

El

qWl

X

W

MX

En

q

n

B

Hadronic Mass and q2 Moments in BXcln

  • Neutrino reconstruction technique

Identify

lepton

1

hep-ex/0403052

Infer

hadronic

mass

3

Reconstruct

neutrino

2

Alex Smith – University of Minnesota


Hadronic mass and q 2 moments in b x c l n1

l

El

qWl

X

W

MX

En

q

n

B

Hadronic Mass and q2 Moments in BXcln

  • Neutrino reconstruction technique

Identify

lepton

1

Infer

hadronic

mass

3

Reconstruct

neutrino

2

Alex Smith – University of Minnesota


Hadronic mass and q 2 moments in b x c l n2

Hadronic Mass and q2 Moments in BXcln

  • Selection criteria applied to suppress continuum and enhance neutrino reconstruction

  • Fit differential decay rate in three dimensions:

    • q2

    • MX2

    • cosqWl

  • Fit Components and models:

    • BDlnHQET+measured FF’s

    • BD*ln HQET+measured FF’s

    • BD**ln ISGW2

    • B(Xc)non-resln Goity-Roberts

    • BXuln ISGW2+NR

    • Secondary leptons CLEO MC

    • Continuum and fakes data

Fit Components

Note: histograms

normalized to same area

Alex Smith – University of Minnesota


Hadronic mass and q 2 moments in b x c l n3

Hadronic Mass and q2 Moments in BXcln

  • 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

q2

MX2

cosqWl

|pl|

En

Alex Smith – University of Minnesota


Hadronic mass and q 2 moments in b x c l n4

Hadronic Mass and q2 Moments in BXcln

  • Results are consistent with previous CLEO measurements

  • Uncertainties and results comparable to BaBar measurements

  • q2 moments expected to be somewhat complementary to MX moments

    • Only measured by CLEO

hep-ex/0403052

Alex Smith – University of Minnesota


Lepton energy moments in b x c l n

Lepton Energy Moments in BXcln

  • Di-lepton event sample

  • Use one lepton as the “tag”:

    • pl > 1.4 GeV/c, e or m

    • ~97% of sample is primaryBXln

    • Lepton charge tags flavor of parent B meson

  • Look for signal electron in “tagged” events

    • pe > 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

hep-ex/0403053

Monte Carlo simulation of electron daughters from B decay

Alex Smith – University of Minnesota


Lepton energy moments in b x c l n1

Lepton Energy Moments in BXcln

Unmixed B0Mixed B0

Primary Events

Opposite B Secondaries

Same B Secondaries

Alex Smith – University of Minnesota


Lepton energy moments in b x c l n2

Lepton Energy Moments in BXcln

Unmixed B0Mixed B0

Primary Events

Opposite B Secondaries

Same B Secondaries

Easily vetoed with kinematic cut

66% efficient

X25 rejection

Alex Smith – University of Minnesota


Lepton energy moments in b x c l n3

Subtract backgrounds

Correct for efficiencies

Algebraically solve for primary spectrum

Lepton Energy Moments in BXcln

Alex Smith – University of Minnesota


Lepton energy moments in b x c l n4

Lepton Energy Moments in BXcln

  • 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

Alex Smith – University of Minnesota


Photon energy moments in b x s g

Photon Energy Moments in BXsg

  • Large photon background from continuum processes

    • p0 and h veto

    • Suppress using neural network

      • Several different inputs related to event shape

    • Pseudo-reconstruction

      • Ks0 or K+/-

      • 1-4 pions, at most one p0

    • Large subtraction necessary

hep-ex/0108032

Alex Smith – University of Minnesota


Photon energy moments in b x s g1

Photon Energy Moments in BXsg

  • bsg measurement is key to extracting HQET parameters

    • Sensitive to mb

      • Mean energy (1st moment) roughly equal to mb/2

    • Independent of mc

  • New analysis in progress

    • Previous analysis optimized for branching fraction measurement

    • New analysis of old data optimized for extraction of spectrum

    • New results soon

Alex Smith – University of Minnesota


Combined fit to determine v cb

Measurements included in fit:

1st and 2nd photon energy moments : Eg > 2.0 GeV

1st and 2nd lepton energy moments : Ee > 0.7, 1.2, 1.5 GeV

1st and 2nd hadronic mass moments : Ee > 1.0, 1.5 GeV

1stq2 moment : Ee > 1.0, 1.5 GeV

Chi-squared fit including full correlation matrix of measurements

Uses O(1/m3) 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)

Combined Fit to Determine |Vcb|

Alex Smith – University of Minnesota


Combined fit to determine v cb1

Combined Fit to Determine |Vcb|

CLEO data

(GeV2)

Preliminary

(GeV/c2)

Alex Smith – University of Minnesota


Combined fit to determine v cb2

Combined Fit to Determine |Vcb|

CLEO data

(GeV2)

Preliminary

1st and 2nd Lepton

Energy Moments

(GeV/c2)

Alex Smith – University of Minnesota


Combined fit to determine v cb3

Combined Fit to Determine |Vcb|

CLEO data

(GeV2)

Preliminary

1st and 2nd Photon

Energy Moments

(GeV/c2)

Alex Smith – University of Minnesota


Combined fit to determine v cb4

Combined Fit to Determine |Vcb|

CLEO data

(GeV2)

Preliminary

1st and 2nd Hadronic

Mass Moments

(GeV/c2)

Alex Smith – University of Minnesota


Combined fit to determine v cb5

Combined Fit to Determine |Vcb|

CLEO data

(GeV2)

Preliminary

1stq2 Moments

(GeV/c2)

Alex Smith – University of Minnesota


Combined fit to determine v cb6

Only CLEO has measured photon energy, q2, hadronic mass, and lepton energy in a single experiment

A solution consistent with all measurements is found

Without BXsg,mb and mc almost completely correlated in fit

Most of the sensitivity to mb comes from BXsg measurement

First moment  mean photon energy  mb/2 (approx.)

Other measurements primarily constrain mb-Cmc, C~0.6

q2 moment gives some complementary information

Nearly independent of mp2

Combined Fit to Determine |Vcb|

Alex Smith – University of Minnesota


Combined fit to determine v cb7

Combined Fit to Determine |Vcb|

CLEO data

(GeV/c2)

Preliminary

(GeV/c2)

Alex Smith – University of Minnesota


Combined fit to determine v cb8

Combined Fit to Determine |Vcb|

1st Lepton Energy

Moment

Preliminary

2nd Lepton Energy

Moment

Preliminary

1st Photon Energy

Moment

2nd Photon Energy

Moment

Preliminary

Preliminary

Alex Smith – University of Minnesota


Combined fit to determine v cb9

Combined Fit to Determine |Vcb|

Preliminary

1stq2 Moment

1st Hadronic Mass

Moment

2nd Hadronic Mass

Moment

Preliminary

Preliminary

Alex Smith – University of Minnesota


Combined fit to determine v cb10

Combined Fit to Determine |Vcb|

Preliminary

measurement key

Alex Smith – University of Minnesota


Combined fit to determine v cb11

Measurement of |Vcb| and HQET parameters, including mb(m), mc(m), mp2(m) at m=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

Combined Fit to Determine |Vcb|

Preliminary

Alex Smith – University of Minnesota


Summary

Summary

  • Potential to significantly improve measurement of |Vcb|

    • 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:

    • 3rd lepton energy moments– work in progress

    • Include more 1st and 2nd lepton energy moment measurements in fit

    • 2ndq2 moments – should have corrections soon

      • Complementary sensitivity to parameters

    • Improved BXsg moments – soon

      • Critical constraint on mb

    • 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

Alex Smith – University of Minnesota


  • Login