d 0 k/ l analysis laurenz widhalm 北京, june 5 th form factors and absolute brs for d 0 / k...

D0 K/l Analysis Laurenz Widhalm 北京 , June 5th

Form Factors and Absolute BRsfor D0 / K

KEK 高エネルギ

Belle in a nutshell

e-

8GeVe+

3.5GeV

= 0.425

• 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 WidhalmHEPHY Vienna

Belle Collaboration

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)

Why are semileptonic decays interesting?

q²


Ktag

D

mass-constrained vertex fits

e+ e-3.5 GeV 8 GeV

K

K

D0

slow

e/µ

D*-

„inverse“ fit

tag side

Method of Reconstruction (Event Topology)

D*

signal side

additional primary mesonsIP

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


D0 Signal and Background*

charm (D°)charm, no D°B±

B0

udswrong sign D°

data (normalized)

result (282 fb-1 of BELLE

data) yield

after cuts 95250

background 38789

signal

charge correlationsignal subtractionstats bkg sample

56461± 309stat

± 776syst

± 233syst

± 194syst

cuts• all mass-constr. fits CL >0.1%

(released on D0 fit for righthand plot)

• same charge Ktag/slow

* from decays without a D0 , or combinatorial background

control region

signal region

signal D0 invariant mass

opposite signKtag/slow

same signKtag/slow

MC

MC

MC

MC

MC

MC

note: data used for bkg subtraction,MC shown only for comparison

=0.0006 GeV!


D0 K/l Signal and Background

D0 l

m² / GeV²

D0 lBackground sources

1. fake D0

2. other semileptonic channels

3. hadronic channels

additional cuts• same charge slow / lepton• extra energy < 700 MeV• no excess charge• E > 100 MeV

recoil neutrino mass

signal region

note high resolution(m²)=0.016 GeV²


fake-D0 bkg

bkg from K

bkg from K*/ * smaller background for e and Klhandled likewise

data

control region for K*/ bkg measurement

signal region

recoil neutrino mass for D0 l

D0 K/l Signal and Backgrounds (for )*

bkg from misidentified kaons

bkg from misidentified pions

semileptonic background

opposite signµ/slow

same signµ/slow

signal region

hadronic background

MC

data

data data

data

note: data used for bkg subtraction,crosschecked by MC


Summary of Signal / Background Decomposition

Results (282 fb-1 of BELLE data) Ke K e

signal events 1318± 37stat ± 7syst

1249± 37stat ± 25syst

126± 12stat ± 3syst

106± 12stat ± 6syst

fake D0 bkg 12.6 ± 2.2 12.2 ± 4.8 12.3 ± 2.2 12.5 ± 4.5

semileptonic bkg* 6.7 ± 2.6 10.0 ± 2.5 11.7 ± 1.2 12.6 ± 1.9

hadronic bkg** 11.9 ± 5.6 62.1 ± 23.9 1.8 ± 0.7 9.7 ± 3.7

fake-D0 bkg

Kl bkg

D0 e

D0

l bkg

D0 e

D0 hadronic bkg

m² / GeV²

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

MC

data

data

data

data

remaining signal


Absolute Branching Ratios

BRs (%) this analysis PDG(2005)

CLEO-c (hep-ex/0505035)

K-e+ 3.45 ± 0.10stat ± 0.19syst 3.62 ± 0.16 3.44 ± 0.10stat ± 0.10syst

K-+ 3.45 ± 0.10stat ± 0.21syst 3.20 ± 0.17

-e+ 0.279 ± 0.027stat ± 0.016syst 0.311 ± 0.030 0.262 ± 0.025stat ± 0.008syst

-+ 0.231 ± 0.026stat ± 0.019syst 0.24 ± 0.04

• 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

signal

non-D bkg

hadronic bkg

semileptonic bkg

D0 e D0 e

D0 D0

q²

background shapes from data

(q²) = 0.0145 GeV²/c² (width of red line) no unfolding

necessary!


Form Factors - Theory

• in principle, two form factors f+(q²) and f-(q²)

• kinematically only f+(q²) relevant, f-(q²) suppressed by ml²• three different models that are frequently discussed in literature:

f+(q²) = 1-q²/m² f+(0)

m......pole mass = m D*s 2.11 GeV (Kl)= m D* 2.01 GeV (l)

simple pole

f+ (q²) = (1-q²/m²) (1-q²/m²)

modified pole

ISGW2

0.50 (Kl) 0.44 (l)

theor.

f+ (q²) = (1-q²-q²max))²

G. Armoros, S. Noguera,J. Portoles, Eur. Ph. J. C27, 243 (2003)

N. Isgur and D. Scora, Phys. Lett. B 592 1(2004)


Form Factors – Comparison with Models

ISGW2 modellattice calculation modified pole modelD0 l

D0 l

pole mass (GeV)

Kl 1.82 ± 0.04stat ± 0.03syst

l 1.97 ± 0.08stat ± 0.04syst

simple pole

Kl 0.52 ± 0.08stat ± 0.06syst

l 0.10 ± 0.21stat ± 0.10syst

modified pole(poles fixed at theo. values)

fit results

f+(0)

Kl 0.695 ± 0.007stat ± 0.022syst

l 0.624 ± 0.020stat ± 0.030syst


• events searched in e+e- D(*)D*cX (X=n/K)• new full-reconstruction-recoil method: 56k D0 in 282 fb-1 of BELLE data• high resolution neutrino (m²)=0.016 GeV²• background <5%(<27%) for K/• 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 factor in good agreement with theoretical predictions and other experiments• competitative with recent CLEO-c measurements

preprint hep-ex/0604049, submitted to PRL

[email protected]

Form Factors and Absolute BRsfor D0 / K Summary & Conclusion


Spares


tag side:

• reconstruction & fit of D0,± K, K2, K3• reconstruction & fit of D*0,± D, D• use either D or D* as primary meson

signal side:

• reconstruction & fit of inclusive D*0,± via recoil from e+e- D(*)

D*n/K• reconstruction & fit of inclusive D0 via recoil from D* D• reconstruction & fit of neutrino via recoil from D m

D

D*

e+ e-

D

e/µ

D*

tag signal

K

( )

K

K

additional primary mesons




m/GeV

D*+tag

D*0 tag

D*-sig

m/GeV

D0sig

m/GeV


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

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, D• 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

• :• 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

List of Cuts


Bias by mass-constrained Fits on Background?

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

no real D0

D0 invariant mass

with real D0

after fit of D*before fit of D*


D0 Signal and Background*

charm MCcharm, no D°B± MC

B0 MCuds MCwrong sign true D°

data (normalized)

result (282 fb-1 of BELLE data) yield

selected D0 events 95250

subtracted background 38789

signal 56461± 309stat ± 830syst

systematics breakdown eventscharge correlation RS/WS 776

WS signal subtraction 233

statistics of WS sample 194

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)

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

* from decays without a D0 , or combinatorial background

control region

signal region

signal D0 invariant mass

opposite signKtag/slow

same signKtag/slow


Measurement of Semileptonic Background (for l)*

procedure to measure background:

1. crosstalk from Kl:

• prepare special background sample, with K intentionally misidentified as • normalize to standard Kl sample • then reweight the sample using known** efficiencies / fake rates (in p,)

2. background from vector mesons:

• get shapes for K*l and l from MC (simulated ratio K*/ from PDG)• normalize to data in region m² > 0.3 GeV²

* background for Klis very small, and is handled the same way** measured independently in data

measured bkg from K*l

measured bkg from Kl

measured bkg from l

data

control region for K*/ bkg measurement

non-D° bkg (measured as described previously)

signal region

recoil neutrino mass

D0 l


procedure to measure background:• prepare special background samples, with K() intentionally misidentified as (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 to measure the effective fake rates• then apply these fake rates in the background SS sample to obtain the backgrounds in the signal sample

Measurement of Hadronic Background (for )*

same sign SSsignal: D* D0+

-+ both signsD* D0+

-+

-±

opposite sign OSD* D0+

K-+

+-D* D0+

K-+

-+

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

OS

SS

SS OS


Fit of Hadronic Background (for )*

bkg from misidentified kaons

bkg from misidentified pions

fake-D0 bkg

bkg from K

remaining events in signal region

bkg from K*/

D0

MC true composition

* background for e and Klare much smaller

fit in this sample

use result of fit here

OS

SS

comparison with MC

D0 K0-+D0 K-+0

D0 -+0

green = particle seen in recoil mass

signal region


Measured Absolute Form Factors as function of q²

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

D0 e

D0

D0 e

D0


Form Factor Theory

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

• 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:

f+(q²) = 1-q²/m² f+(0)

m......pole mass = mass D*s 2.11 GeV (Kl)= mass D* 2.01 GeV (l)

Ke

q² / GeV²

K

e

q² / GeV²

f+ kinematical factor

f- kinematical factor







d 0 k/ l analysis laurenz widhalm 北京, june 5 th form factors and absolute brs for d 0 / k...

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