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Form Factors and Absolute BRs for D 0 p n / K nPowerPoint Presentation

Form Factors and Absolute BRs for D 0 p n / K n

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e-

e+

8GeV

3.5GeV

= 0.425

bg

Form Factors and Absolute BRs

for D0p n / Kn

Belle in a nutshell

q²

- 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

Why are semileptonic decays interesting?

q²

- 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)

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

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°

B±

MC

MC

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

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

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

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

Form Factors – q² distribution

D0 Ken

D0 pen

signal

q²

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

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)

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)

for D0p n / Kn

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

preprint hep-ex/0604049, submitted to PRL

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

- 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

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

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

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

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

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

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

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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