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e -. e +. 8GeV. 3.5GeV. = 0.425. bg. Form Factors and Absolute BRs for D 0  p  n / K  n. Belle in a nutshell. q². located at KEK / Japan KEKB Collider B-Factory at (4s) resonance peak luminosity 16.270 1/nb/s

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slide1

e-

e+

8GeV

3.5GeV

= 0.425

bg

Form Factors and Absolute BRs

for D0p n / Kn

Belle in a nutshell

  • located at KEK / Japan
  • KEKB Collider
  • B-Factory at (4s) resonance
  • peak luminosity 16.270 1/nb/s
  • integrated luminosity 600 1/fb(as of June 2006; 280 1/fb used in this analysis)
  • main physics goal: observation of CPV in B meson Decays

Laurenz Widhalm

HEPHY Vienna

Belle Collaboration

KEK 高エネルギ

slide2

Why are semileptonic decays interesting?

  • single form factor fD(q2)
  • calcuable in LQCD, but
  • needs checking from data
  • D-System ideal for experimental input
  • results can be applied in B-physics (extraction of CKM parameters)
slide3

K

p

recoil

p

D*-

K

recoil

pslow

D0

„inverse“ fit

recoil

K/p+

e/µ-

n

p

p

Method of Reconstruction (Event Topology)

additional primary mesons

IP

3.5 GeV

e+

e-

8 GeV

D*

g

p

mass-constrained vertex fits

D

  • note:
  • all possible combinations tried in parallel
  • cuts after complete reconstruction
  • equal weight for remaining combinations
  •  no event loss due to particle exchanges!

Ktag

p

signal side

tag side

slide4

D0 Signal and Background*

* from decays without a D0 , or combinatorial background

  • cuts
  • all mass-constr. fits CL >0.1%(released on D0 fit for righthand plot)
  • same charge Ktag/pslow

control region

signal region

same sign

Ktag/pslow

s=0.0006 GeV!

signal D0 invariant mass

opposite sign

Ktag/pslow

note: data used for bkg subtraction,

MC shown only for comparison

data (normalized)

B0

charm (D°)

MC

MC

charm, no D°

uds

MC

MC

wrong sign D°

MC

MC

slide5

D0  K/plnSignal and Background

  • additional cuts
  • same charge pslow / lepton
  • extra g energy < 700 MeV
  • no excess charge
  • En > 100 MeV

recoil neutrino mass

D0 Kln

  • Backgroundsources
  • fake D0
  • other semileptonic channels
  • hadronic channels

mn² / GeV²

D0 pln

signal region

note high resolution

s(m²n)=0.016 GeV²

slide6

hadronic background

same sign

µ/pslow

opposite sign

µ/pslow

signal region

D0  K/plnSignal and Backgrounds (for pmn)*

semileptonic background

control region for K*/r bkg measurement

signal region

recoil neutrino mass for D0 pln

note: data used for bkg subtraction,

crosschecked by MC

bkg from misidentified kaons

fake-D0 bkg

data

data

bkg from Kmn

bkg from misidentified pions

data

data

* smaller background for pen and Kln handled likewise

bkg from K*/rmn

MC

data

slide7

Summary of Signal / Background Decomposition

D0 Ken

D0 pen

remaining signal

data

fake-D0 bkg

data

D0 Kmn

D0 pmn

hadronic bkg

data

Kln bkg

data

K*/rln bkg

MC

mn² / GeV²

* error dominated by MC stats ** error dominated by fit errors & bias special bkg sample

slide8

Absolute Branching Ratios

  • ratio to total number of recoil D0 tags
  • efficiency correction
  • corrected for bias due to differences data/MC
  • (1.9%±3.9%)
slide9

Form Factors – q² distribution

D0 Ken

D0 pen

signal

non-D bkg

hadronic bkg

semileptonic bkg

s(q²) = 0.0145 GeV²/c²

(width of red line)

 no unfolding necessary!

D0 Kmn

D0 pmn

background shapes from data

slide10

f+(q²)= 1-q²/m²

  •  f+(0)

m......pole mass

= m D*s 2.11 GeV (Kln)

= m D*  2.01 GeV (pln)

Form Factors - Theory

  • in principle, two form factors f+(q²) and f-(q²)
  • kinematically only f+(q²) relevant, f-(q²) suppressed by ml²
  • three differentmodels that are frequently discussed in literature:

simple pole

modified pole

f+(q²)= (1-q²/m²) (1-aq²/m²)

 0.50 (Kln)

atheor.

G. Armoros, S. Noguera,

J. Portoles,

Eur. Ph. J. C27, 243 (2003)

 0.44 (pln)

ISGW2

f+(q²)= (1-a(q²-q²max))²

N. Isgur and D. Scora,

Phys. Lett. B 592 1(2004)

slide11

Form Factors – Comparison with Models

modified pole model

D0 Kln

lattice calculation

ISGW2 model

fit results

simple pole

D0 pln

modified pole

(poles fixed at theo. values)

slide12

Form Factors and Absolute BRs

for D0p n / Kn

Summary & Conclusion

  • events searched in e+e-D(*)D*cX (X=np/K)
  • new full-reconstruction-recoil method: 56k D0 in 282 fb-1 of BELLE data
  • high resolution neutrino s(m²n)=0.016 GeV²
  • background <5%(<27%) for K/p
  • absolute BRs of better accuracy than previous experiments, in good agreement with recent CLEO measurements
  • good agreement with relative measurements done by BES and FOCUS
  • high q² resolution, no unfolding necessary
  • absolute multi-bin measurement of f+(q²)
  • measured form factorin good agreement with theoretical predictions and other experiments
  • competitative with recent CLEO-c measurements

Laurenz.Widhalm@oeaw.ac.at

preprint hep-ex/0604049, submitted to PRL

slide14

K

p

p

K

p

e/µ

p

p

Method of Reconstruction (Event Topology)

  • tag side:
  • reconstruction & fit of D0,± Kp, K2p, K3p
  • reconstruction & fit of D*0,± Dp, Dg
  • use either D or D* as primary meson
  • signal side:
  • reconstruction & fit of inclusive D*0,± via recoil from e+e-  D(*) D*np/K
  • reconstruction & fit of inclusive D0 via recoil from D*  Dp
  • reconstruction & fit of neutrino via recoil from D  mpn

additional primary mesons

e+

e-

( )

D*

D*

D

g

p

p

D

n

p

K

tag

signal

slide15

D*-sig

m/GeV

D*+tag

D0sig

D*0 tag

m/GeV

m/GeV

Method of Reconstruction (Event Topology)

slide16

stable particle selection:

  • gammas:
    • p > 40 MeV
  • charged tracks (general):
    • p > 100 MeV
    • trk_fit.nhits(3) > 0
    • dr < 2 cm, dz < 4 cm
  • electron:
    • p > 500 MeV
    • eid.prob(3,-1,5) > 0.9
  • muon:
    • p > 500 MeV
    • prerejection != 1
    • Muon_likelihood > 0.9
  • kaon / pion:
    • atc_pid (3,1,5,3,2)
    • prob*(1-prob_e-prob_mu) > 0.5
    • for meson in hlnu: > 0.9

List of Cuts

  • unstable particle selection:
  • pi0:
    • PDG mass ± 10 MeV
    • fit CL > 0.1
  • K0:
    • only via decay pi+pi-
    • PDG mass ± 25 MeV
  • D_tag:
    • channels Knpi, n=1-3
    • PDG mass ± 20 MeV
  • D*_tag:
    • channel Dpi, Dg
    • PDG mass ± 5 MeV
    • mass/vertex fit CL > 0
  • D*_signal:
    • via recoil from D*_tag+n pi/K, n=0-5
    • mass/vertex fit CL > 0.001
  • D_signal:
    • via recoil from D*_signal  Dpi
    • mass/vertex fit CL > 0.001
  • n:
    • via recoil from D_signal  hlnu
    • |m²| < 0.05 GeV²
    • mass/vertex fit CL > 0
  • additional Klnu / pilnu cuts:
  • E_leftover < 700 MeV, no leftover charge
  • E_nu > 100 MeV
  • right charges of slow pions & lepton
slide17

Bias by mass-constrained Fits on Background?

no real D0

with real D0

after fit of D*

before fit of D*

D0 invariant mass

  • very sharp mass peak after fit
  • no bias on background

slide18

D0 Signal and Background*

* from decays without a D0 , or combinatorial background

  • cuts
  • confidence level of all mass-constrained vertex fits >0.1%(released on D0 fit for righthand plot)
  • right charge correlation between slow pion and tag side kaon (right sign, RS)

control region

same sign

Ktag/pslow

signal D0 invariant mass

  • procedure to measure background:
  • select wrong charge correlation data (WS) to get shape of background
  • correct for small WS signal component
  • normalize to RS data in region 1.84-1.85 GeV

signal region

opposite sign

Ktag/pslow

B0 MC

data (normalized)

charm MC

charm, no D°

uds MC

wrong sign true D°

B± MC

slide19

Measurement of Semileptonic Background (for pln)*

  • procedure to measure background:
  • 1. crosstalk from Kln:
  • prepare special background sample, with K intentionally misidentified as p
  • normalize to standard Kln sample
  • then reweight the sample using known** efficiencies / fake rates (in p,)
  • 2. background from vector mesons:
  • get shapes for K*ln and rlnfrom MC (simulated ratio K*/r from PDG)
  • normalize to data in region m²n > 0.3 GeV²

recoil neutrino mass

control region for K*/r bkg measurement

D0 pln

signal region

data

non-D° bkg (measured as described previously)

* background for Kln is very small, and is handled the same way

** measured independently in data

measured bkg from Kln

measured bkg from K*ln

measured bkg from rln

slide20

Measurement of Hadronic Background (for pmn)*

  • procedure to measure background:
  • prepare special background samples, with K(p) intentionally misidentifiedas m(subtract fake D0 background in these samples with the method described above)
  • separate into same sign (SS) and opposite sign (OS) samples, with respect to the charges of the lepton and the slow pion
  • semileptonic channels are highly suppressed in OS  clean sample of hadronic background
  • perform a 2-parameter fit in the standard OS sample, using the shapes from the OS background samples for K and p, to measure the effective fake rates
  • then apply these fake rates in the background SS sample to obtain the backgrounds in the signal sample

same sign SS

signal: D*  D0p+

 p-m+n

SS

both signs

D*  D0p+

 p-p+p0/K0

p-m± n

opposite sign OS

D*  D0p+

 K-p+p0

p+m-n

SS

OS

OS

D*  D0p+

 K-p+p0/K0

p-m+ n

* significant background only for this channel; other channels are handled likewise

slide21

use result of fit here

fit in this sample

Fit ofHadronic Background (for pmn)*

D0 pmn

comparison with MC

MC true composition

SS

green = particle seen in recoil mass

D0 p-p+p0

D0 K0p-p+

D0 K-p+p0

OS

signal region

bkg from misidentified kaons

bkg from Kmn

bkg from misidentified pions

bkg from K*/rmn

* background for pen and Kln are much smaller

remaining events in signal region

fake-D0 bkg

slide22

Measured Absolute Form Factors as function of q²

D0 Ken

D0 pen

D0 pmn

D0 Kmn

  • extracted by dividing q² distribution by kinematical factor
  • no unfolding necessary due to very good q² resolution
slide23

Kmn

Ken

f+ kinematical factor

f+ kinematical factor

f- kinematical factor

f- kinematical factor

f+(q²)= 1-q²/m²

q² / GeV²

q² / GeV²

  •  f+(0)

m......pole mass

pen

pmn

f+ kinematical factor

f+ kinematical factor

= mass D*s 2.11 GeV (Kln)

= mass D*  2.01 GeV (pln)

f- kinematical factor

f- kinematical factor

Form Factor Theory

  • in principle, two form factors f+(q²) and f-(q²)
  • kinematically only f+(q²) relevant, f-(q²) suppressed by ml²
  • applying certain boundary conditions, theory* suggests model-independently a pole-structure for the form factor:

* G. Amoros et al., hep-ph/0109169

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