Semileptonic Charm Decays

Will E. Johns (for the FOCUS Collaboration)

Vanderbilt University,BEACH 2004, July 1

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Subjects Covered

Data from 96-97 run of FOCUS

Over 1,000,000Reco’d. Charm

-Vertex Resolution-Particle ID-Mass Resolution

VeryGood

Lots ofPubs

Semileptonic Charm Decays

022

222

2

cossin4

sin})cos1()cos1{(

coscos

V

V

Vdd

d

(D decay, No form factors, V decays to spin 0 particles)

Neutrino is left handed

Prefers W spin along muon,e

V products spinless

Prefer LZ=0

Form Factors

Scalar Resonance? CP?

More than just CKM measurement tools…

FOCUS saw discrepancies in the data

2

20

2

2

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5

)(sincos2

)()cos1(sin

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coscos

0*

0*

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qHB

qHBe

qHBe

ddddqdm

d

KV

Ki

V

Ki

V

Vk

Phys.Lett.B535:43-51, 2002hep-ex/0203031

0*KD

Yield 31,254

DataMC

Focus “K*” signal

matches model

-15% F-B asymmetry!

FOCUS added a term, things got better

2

20

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2

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5

)()(cossin2

)(sin)cos1(

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coscos

0*

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qHAeB

qHBe

qHBe

ddddqdm

d

iKV

Ki

V

Ki

V

Vk

L=0 ansatz

Signal Events weightedby avg(cosV):

No added term

FOCUS Semileptonic cuts description ),( KDLook for N bodies with a muon

L/ – Lp

s ISO1 – CL DK’s in prim

DCL – CL of DK vertex

MuCL – CL for Muon ID Cuts on P( for ’s

Cerenkov for ’s and K’s (from ~ 4-60 GeV/c)

Vertexing cuts:

ISO2 – No Xtra trks in DK OOM – No DK’s in stuff

Particle ID cuts: TRKFITcl – Muon P consistency

MISIDMCS Radius, Decay Prob

(Ask me offline for all the detailed cut values!)

FOCUS Form Factors

and ,parameters waveS and)0(

)0(

)0(

)0( Fit to

)/1.2(,/1

)0()()/5.2(,

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Ar

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qAmM

KMqAmMqmM

qmqH

mqHqVmM

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v

VV

AA

ii

KD

DKDKD

K

tKD

DKD

Tried in fit,no sensitivity (E791?)

(common – vary generated parameters in Montecarloby using agreement with reconstructed distributions and data)

Pioneered by D.M. Schmidt for E691 K*ev analysis: NIM A 328 (1993)

0*

KD

2max

2V /in 3 and in 3 ,cosin 5 ,cosin bins 5 qq

Kmin 4 and in 3 ,cosin 3 ,cosin bins 3 V

S-wave termBreaks symmetry

S-wave term andr’s essentially decouple

FOCUS Form Factors 0*

KDCuts similar to previous, some change to get uniform acceptance, one extra

Cut on q2 < 0.2 GeV2/c2

r’s are flat, feeling mμ? Goodness of fit issue

Right sign – Wrong sign

Charm Background

Systematic ChecksS-wave – varied cuts35 fits – Sample VarianceForm Factor (3 sources)1) Varied Cuts2) Split sample

3) Vary MC input Charm Backgrounds

)/9.0(2,, cGeVKD mDDP

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Phys.Lett.B544:89-96, 2002hep-ex/0207049

Very Clean Data

0*

KDForm Factors Comparison

S-Wave effects apparent only with high statistics

Lattice Gauge!

Experiment Models

A more detailed look at the K line shapeTake advantage of the very clean signal

Previous best K* parametersLass (1988) K scattering

Spectra is complicated

Mass range limit in fitMore Blatt-Weisskopf radius info away from pole

FOCUS sees S-wave effects primarily Below K*

Using LASS parametersfor ER model of

Constant

FOCUS PRELIMINARY

K* MassK* WidthBL-WK radius#K* eventsScalar Fraction

Mass and WidthDon’t change

-Careful studies of resolution effects too

FOCUS PRELIMINARY200051.0

00022.0*

200015.000016.0*

/00081.004751.0

/00030.089463.0

cGeV

cGeVM

K

K

Systematics by varying cuts,

background contribution, shapes

FOCUS Form Factors SD

- Event by Event version of discrete transform method

)()(

284.0202.0713.02

0148.0250.0549.1

sysstat

r

rV

- No evidence for S - wave

Phys.Lett.B586:183-190, 2004hep-ex/0401001

- Backgrounds higher (cut on M

Ds form factor enigma

Theoretically the Dslform factor should be within 10% of D+ K*l The rV values were consistent but r2 for Dslwas 2 higher than D+ K*l

E7

91

CL

EO

E6

53

E6

87

BK

S

LM

MS

ISG

W2

0

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1.5

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R2

circa 1999

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cus

E79

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EO

E65

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E68

7 BK

S

LM

MS

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6 7 8 9

RV

But the (2004) FOCUS measurement has consistent r2 values as well!

Ds versus D+ K*l

Backgrounds Make a difference! 0D

Biggest Players:Signal, ~400 events (red and dots)Combinatoric Background,~750 events (pink hatch)Muon Misid, ~300 events(faint black histogram)

A peek at:

Search for Cabibbo Suppressed Ds semileptonic decay

c

ss

d

W

u u

K

cdV

Cabibbo suppressed SL Decay

*K

sD

Would be a discovery!

A Cabibbo favored SL decay

s

sc

s

W

csV

u u

K

K sD

Easy to see and study

Right SignWrong Sign

MK (GeV/c2)

DsK*decay is a small WS background component in our previous D+K*work

Note kaon and muon have same sign

K+ K- mass in KK events K mass in K events

What’s this?

Preliminary results of the search

dataMC

After lots of cuts

In the loosely cut sample, the MC was a poor match to the observed WS Kspectrum. Large non-charm contribution?

With tight cuts, the MC matched the data away from the K* peak. We saw a excess in K* yield in data over MC

*

12.9 3.3 ??? %s

s

D K

D

We compared the WS K spectrum to a MC that incorporated all known charm decay and normalize the MC to the D+K*yield observed in the data

If this K* excess were interpreted as DsK*, we would obtain...

MK (GeV/c2) MK (GeV/c2)

This BR is very consistent with (10 ±1.3)% predicted by R.J. Oakes et al. (1997) (hep-ph/9708277)

FOCUS BR Measurements

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Includes S-wave interference

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offraction a as expressed

:errors Systematic

stat

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Phys.Lett.B540:25-32, 2002hep-ex/0206013

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BR Comparisons to Exp. & Models

focu

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e68

7

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0.4

0.6

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0.540 0.040

BR relative to are consistent

K

*l /K

E691

E653

Focus

Argus

Omega

Cleo 1

Cleo 2

Cleo 2

E687

0.3

0.4

0.5

0.6

0.7

0.8

0.9

muons electrons

0.620.02

BR relative to K …not so good

What about

0

0*

KD

KD?

-Could resolve lepton ID issues- Topological trouble though > need an extra particle for K*-Most Experiments measure ~0.5 (E687 too!) (some use rates though…compare D+ D0)

10

0*

KD

KDBut CLEO2 Reported )( 0 KDBUsing the

From the PDG

nsDD eKeK /)7.925()()( 00

But using PDG values we also find: Isospin Violation?

0

0*

KD

KDFOCUS

In the FOCUS silicon

)(&)( 0*0 KKKS

Reconstruct both

Drawback: Only about 10% of Ks>+-

Decays occur in the FOCUS silicon

Find Background Dominated by D>KsX

FOCUS is world’s best

0

0*

KD

KD

034.0045.0625.00

KD

KD

nsDD KK /)1111()()( 00

Correct for S-Wave:

hep-ex/0406060Submitted to PLB

030.0043.0594.00

0*

KD

KD

Measure:

Use Focus K* and PDG Kcompare to D0: Isospin OK again

11.072.00

0

KD

eKD?=1.03=? 07.012.1

0

0

KD

eKDLong standing “difference” for D0 is in “wrong” direction

Other Exp’s Models

Comparison to other Experiments and Theory

Focus measurementssuggest little “missing”Semileptonic rate

%9.12.17)( anythingeDPDG

%9.12

))2/3((6.14.1

0

eKKD

Sum of PDG CA e modes

Focus ’s as e’s

%2.19.14

))03.1()05.1(( 0

KKD

Hard to believe PDG forPS electron is correct

Preview of other FOCUS analysis

)( 00SKD 0D KD0

-Plot of pseudo D*-D mass difference-Will repeat Vector analysis (tough to see S-wave)-measure q2 shape and BR for and K (expect BR/BR<10%)

Conclusions:

• Resolved some outstanding enigmas ( ff’s, V/PS Ratio, PDG rates)

• Raised some new ones (low q2 in K*, proper S-wave description

• We’ve gotten a lot of physics out of the careful analysis of the Vector decays (S-wave, B(K*,f), M(K*), r’s, W(K*), CS(K*)…

• Looking at new things