4/17/2005 FOCUS / Doris Kim 1

Doris Y. KimUniversity of IllinoisUrbana-Champaign

Content ( hep-ex/0410037,

PLB 607 (2005) 233 )

• Part I: Theories of charm semileptonic decays.

• Part II: Reconstructing D0 K + and +

• Part III: q2 dependence, f+(q2)

a. Deconvolution approach: Non-parametric analysis.

b. Parametric fit.

• Part VII: Summary

Measurements of q2 Dependence of D0 K + and + Form Factors.

APS Meeting April 17, 2005

Tampa, FL

4/17/2005 FOCUS / Doris Kim 2

I: Charm semileptonic decay as tests of LQCDThe decay rates are computed from first principles (Feynman diagrams) using CKM matrix elements.

Charm SL decays provide a high quality lattice calibration, which is crucial in reducing systematic errors in the Unitarity Triangle. The techniques validated by charm decays can be applied to beauty decays.

The hadronic complications are contained in the form factors, which can be calculated via non-perturbative Lattice QCD, HQET or quark models.

(*)KD

c W l

q

qcqV

etc.

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The lattice community is actively fixing the situation and calculating f+ as a function of q2.

hep-ph/0408306PRL 94 (2005) 011601

Theories of D Pseudoscalar l decays

22 3

2 3

22 2

2(

4( ) )

F cq P

lf q O mG V Pd D P

dq

But a major disconnection exists between experiment and theory. In the past, theories worked best where experiments worked worst.

0 0.5 1 1.5 2 2.5 3

3P

2q

cleanest theory

highest rate

D l

is the easiest point for LQCD calculation.

c

q

2max

2 qq

s

q

l

lattice daughtera P at rest in D frame

Simple kinematics Easy to extract form factors.

4/17/2005 FOCUS / Doris Kim 4

Until quite recently, one required a specific parameterized form to bridge the gap between a theory and an experiment, since neither an experiment nor a theory had clean f+(q2) information. Now we have enough data, hence,

What do we measure?

2 2pole

1

1 /f

q m

2expf q (old) ISGW1

• Method I: f+(q2) shape obtained non-parametrically by deconvolution.

• Method II: Or fit f+(q2) using specific forms.

(old) pole

* *

2 2 2 2

D D

1

(1 / )(1 / )f

q m q m

modified pole

f+(q2) parameterization

ISGW2 Updated version.

Spin 1 D*S

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• A good muon candidate.

• Cerenkov ID for K/ candidates.

• Good CL’s for D production/decay vertices, and L/ > 5 between two vertices.

• D* tag required, and wrong sign soft subtraction

II. Reconstructing D0 K + and +Selection

~

cutrs-ws

MC ws

12,840 K +

Neutrino Reconstruction

• K rest frame

• The D and D* mass constraints the neutrino lies on a cone around the soft pion.

• Pick the that points the D closest to the primary vertex.

* 0D D

K

m K m K

/GeV

/c2

4/17/2005 FOCUS / Doris Kim 6

III.a q2 dependence: Deconvolution approach.

2genq2

genq2genq

2genq 2

genq

2recq 2

recq2recq

2recq

2recq

1 2 2 2 3 21 1 1 2 1 3

1

2 21

122 2 2 3 2

2 1 2 2 2 3

1 2 2 2 3 23 1 3 2

22

33 3

2

2 23

1/ / /

/ / /

/ / /

G G GM M M

G G GM M M

G G GM M M

N f N f N f f qM

M f qN f N f N f

N f N f N f M f q

We actually use a 10 10 matrix

A deconvolution matrix is constructed from the number of events generated in the i-th q2 bin that end up reconstructed in the j-th q2 bin. This matrix is then used to correct data for resolution and efficiency.

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Correcting for charm backgrounds inD0 K +

The background only affects the highest q2 bins.

After subtracting known charm backgrounds, f+(q2) is an excellent match to a pole form with mpole= 1.91 0.04 0.05 GeV/c2 or = 0.32 (CL 87%, 82%).

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

after subtraction pole=1.9 before subtraction

2f q

2 2 4 (GeV / )q c

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III.b Parameterized f+(q2) for D0 K + / +

6574 K + events

288 + events

• 2-dim fit: cos l, q2

• Signal ~ MC with reweighted intensity.

• Backgrounds are floated within known uncertainties.

D0W

rest frame

l

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Comparing to Lattice Gauge Result

2f q

K +

21.93 0.05 0.0: 3 / ,poleK m GeV c 0.28 0.08 0.07 1.51.41.(0) / 7 0.3(0)f f

0.30 20.15: 1.91 0.07 /pole GeV cm

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Other q2 information in D0 K l /l

lpole mass is l

Kl

It disfavors ISGW2 form by ~4.2form factor f+(q²)

single-pole model

single-pole model

Based on 820 events

q² / GeV²

Kl

l

Cleo 2004 lpole mass is

Preliminary study

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Fo

cus 05

MK

3

E691

Cleo

91

Cleo

93

E687 tag

E687 in

c

Cleo

041.4

1.6

1.8

2.0

2.2

2.4

2.6

po

le m

ass

Summary of D0 K l l Results

Clearly the data does not favor the simple Ds* pole

2

1.91 0.04

/GeV c

Kl

32

2

2

2

2 324( )

F cq PG V Pd D P

dqf q

New world average for K l

2 2pole

(0)

1 /

ff

q m

New world average for l 0.10 20.071.88 /GeV c

4/17/2005 FOCUS / Doris Kim 12

Question slides