recent results on charm decays

WIN02 Jan 24, 2002 Richard Kass

Recent Results on Charm Decays

• Lifetimes– mesons– baryons

• “Wrong” sign D0 decays– Mixing– Doubly suppressed cabibbo decays

• CP violation searches• Semileptonic charm decay• Summary/Outlook

Results from: BABAR BELLE CLEO FOCUS SELEX


Charm Particle LifetimesLifetime is a defining property of a “particle”.

necessary to convert BR’s to decay rates theoretical comparisonsWeak interaction lifetime modified by strong interaction effects non-perturbative QCD

Charmed mesons and baryons provide a rich testing ground:3 mesons (D+, D0, Ds)

4 baryons (c, c+, c

0, c)

doubly charmed baryons

spectator color suppressedinternal spectator

exchange annihilation

Interference effects are important:

0DDcc

Pattern of lifetimes “predicted” but not exact lifetime values


D0

K

Beampipe

Colliding Beam Fixed target

Silicondetectors

Silicondetectors

Better acceptance for short lifetimes Better L/ separationCleaner environment Large data samples

Neither actually “see” the decay as in emulsion and/or bubble chamber

Unbinned ML fit Binned ML fit1d or 2d vertex 3d vertex

Colliding Beam vs Fixed Target


Charmed meson lifetimes

D0K+-

signal

D0K+-

sideband

Fixed target: exponential decay

Colliding beam: exponential decay smeared by resolution


400

405

410

415

420

425

E691

E687

CLE

OII

E791

SELE

X

BEL

LE

BA

BA

R

D0 li

fetim

e (f

s)

460

470

480

490

500

510

520

E691

E687

CLE

OII

E791

SELE

X

BEL

LE

FOC

US

Ds

lifet

ime

(fs)

Annihilation and exchange diagramsare important for mesons.

Expect <1.07 without annihilationand exchange.Bigi & Uraltsev, Z.Phys. C.62, 623, 1994

1000

1020

1040

1060

1080

1100

E691 E687 CLEOII BELLE

D+ li

fetim

e (f

s)Lifetime results for Charmed Mesons

preliminary

PDG2001

02.020.1/:2001PDG 0 DDs

01.002.017.1/:BELLE 0 DDs


Charmed Baryon LifetimesBaryon lifetimes not measured as precisely as mesons: 5-30% vs 1-2%Baryon lifetimes shorter than mesons (e.g. c= 60 fs vs D0= 410 fs )Baryon cross sections are low samples smaller than mesonsLifetime calculations more complicated than mesons

New results for c+, c

+, c0

preliminary

c+

160

170

180

190

200

210

220

230

E691

NA

32

E687

NA

14

E687

CLE

OII.

V

SELE

X

FOC

US

c+

lifet

ime

(ps)

PDG2001

preliminarynot in PDG2001


Recent c+ lifetime Results

150

200

250

300

350

400

450

500

550

SPEC

85

SPEC

87

AC

CM

E687

CLE

OII.

V

FOC

US

c+

lifet

ime

(ps)

PDG2001

not in PDG2001

=5034718fs

c+

c+

c+

c+p

c+

25018

58132


Charmed Baryons LifetimesPreliminary c

0 result from FOCUS:

=109+10 fs (PDG2001: =98+23 fs)Based on a total of 13719 events (c

0, )-9 -15

Comments: Measured lifetime ratio for c

+ / c+ larger than theory:

3.08.2:V.CLEOII

c

c

1.01.2:FOCUS

c

c

Theory ranges from: 1.3 Blok and Shifman, proceedings of 3rd workshop on physics of a tau charm factory, (1993) 1.2-1.7 Guberina and Melic, Eur. Phys. J. C2, 697 (1998)

At some point in the future lifetime analyses may have to correct for:c

0c contamination of c

sample c

0c contamination of c

in sample Doubly charmed baryons

Cabibbo suppressed s uinstead of c s

NoCalculationsavailable


Why is D0-D0 mixing interesting?-

Only meson system where mixing has not been observedOnly meson system where mixing is generated by down quarksMixing in D sector expected to be small in Standard Model

doubly Cabibbo Suppressed (DCS)vanishes the limit of SU(3) flavor symmetry

If D mixing is large:M: large flavor SU(3) breaking ?: new physics ?

D mixing only involves the first two generations:CPV >> 10-3 New Physics

Can make measurements to look for mixing !


D mixing Phenomenology

0000 DqDpDDqDpD LH

Usual definitions:

)(21

LH

)(21

LH

LH mmm

)( LH

mx

2

y

Phases: is the strong phase between Cabibbo allowed and doubly Cabibbo suppressed amplitudes is the CP violating phase in mixing (very small in SM)

CP Violation: CPV in mixing due to |p/q|1 CPV in interference between decay with and without mixing sin 0 Assume no direct CPV


Ways to Observe D mixingMeasure lifetime difference between CP+ and/or CP- statesand with flavor specific (CP mixed) states.

CP+: D0K+K-, +-

CP-: D0Ks00, Ks

0

Mixed: D0K-+ Gives info on y:

sin2

1|)|/|(|cos2

xpqyyCPCP

CPCPCP

1

KKD

KDCPy

Requires good time (vertex) resolution

ycpy if no CPV

Measure “Wrong” sign Decays.hadronic decays: D0K+- semi-leptonic decays: D0K+l-v-

Don’t have tomeasure timedependence


“Wrong” sign D0 decaysThese decays can originate from:a) Double Cabibbo suppression (DCS) (hadronic decays only)

b) Mixing

Usual assumptions: CP conserved |p/q|=1 |x|, |y|, RDCS<<1

.,,,|||| 0

2

0

0etcX

DHXKDHXKRDCS

tDCSDCSWS etyxRtxyRR ])(

4))(sincos([ 2

22

=strong phase differencebetween CF and DCS decays

Wrong sign rate (RWS) has interesting time dependence due to mixing+decay:

tDCSDCSWS etyxRtyRR

])(

4)([ 2

22Convenient to rotate away : x=xcos+ysin, y=ycos-xsin

NO DCS for semi-leptonic decays:t

WS etyxR 222 ))((


Some Recent ycp Lifetime Results

FOCUS: PLB485, 62 (2000)

CLEO: sub. PRD

BABAR: preliminaryycp =-1.0

ycp =3.4

KK: ycp =-1.9 : ycp = 0.5

Not a full blown lifetime analysisLooking for lifetime differences


Recent Mixing Results via ycp

experiment ycp comments

FOCUS 3.4 Fixed target, K+K-

E791 0.8 Fixed target, K+K-

CLEO -1.2

e+e-, K+K-,+-

BELLE -0.5 e+e-, K+K-

BABAR -1.0

e+e-, K+K-

+0.7-0.8

yyKKD

KDCP

1

-4

-2

0

2

4

FOCUS E791 CLEO BELLE BABAR

y cp (%

)

preliminary


Mixing Limits using “wrong” sign and ycp measurements CLEO’sTime dependence of (D0K+- )/ (D0K-+)

tDCSDCSWS etyxRtyRR

])(

4)([ 2

22

Semi-leptonic (D0K+l-v)/ (D0K-l+v) limit:(D0K+l-v)/ (D0K-l+v)<0.5%@ 90%CL

ycp measurements (FOCUS, E791)

Published Data


Mixing Limits using “wrong” sign and ycp measurementsWhat will this plot look like in the near future?New results expected soon from CLEO, FOCUS, BABAR, BELLE

average ycp

FOCUS preliminary K

FOCUS, CLEOSL sensitivity


“Wrong” sign D0 Decay ratesImproved measurements of (D0K+- )/ (D0K-+):

CLEO II 0.77 0.25 0.25

ALEPH

E791 0.68

CLEO II.V 0.33

FOCUS 0.40

BABAR 0.38

BELLE 0.30

D0 K+-D*+ D0+

pre l

imin

ary

RWS=(D0K+- )/ (D0K-+) (%)

0

0.5

1

1.5

2

CLE

O II

ALE

PH

E791

CLE

O II

.V

FOC

US

BA

BA

R

BEL

LE

RW

S

preliminary10X data soon


More “wrong” sign D0 Decay ratesCLEO II.V result for D0 K+-+-

[0.41+0.12-0.11

(stat) 0.04(sys)] (1.070.10)(phase space)(%)

RWS=0.25 +0.36-0.34

(stat) 0.03 (sys) (%) (phase space=1)

CLEO II.V result consistent with previous E791 result:

9fb-1 of dataused in analysis

But cannot tell if this result is from DSC or mixing since:

54 14 WS eventsfrom 2D binnedML fit

)()(

0

0

KDKDRWS

)(5.0) 22 xyRyRR DCSDCSWS

Only other WS D0 result: CLEO’s %07.043.0)()( 11.0

10.000

00

KDKDRWS


D0K00 and K00 Preliminary result from BELLE

L S

Interference between the Cabibbo allowed decay D0K00

and the DCS decay D0K00 can lead to a rate difference betweenD0KL0 and KS0.

-

Expect a 5% (tan2c) asymmetry in:

)()()()(

000000

000000

LS

LS

KDKDKDKDA

The magnitude and sign of A provides info the strong phase difference ()between D0K+- and D0K-+ .

Experimentally very challenging !Difficult to reconstruct KL’s in an e+e- experiment

BELLE calibrates KL efficiency using D0K*-+ , with K*-KL- .


D0K00 and K00 L S

D0KS0D0KL0

D0K*-+ KS-+ D0K*-+ KL-+

05.005.006.0)()()()(

000000

000000

LS

LS

KDKDKDKDA

Using 23 fb-1 of data BELLE measures:

First reconstructionof D’s using KL’s!


CP Violation in D0 Decay

Look for particle anti-particle rate differences

)()()()(

00

00

fDfDfDfDACP

Use D* tag to distinguish D0 from D0.

)()()()(

**

**

fDfDfDfDACP

Measure:

Where f is: K+K-, +-, Ks, Ks0, 00, and KsKs

CPV expected to be small in the charm sectorSM predictions O(0.1%)CPV > 1% evidence for non-SM processes


CP Violation in D0 Decay

-20

-15

-10

-5

0

5

10

15

20

E691

E687

CLE

OII

E791

FOC

US

CLE

OII.

V

Acp

(KK

) (%

)

-10

-5

0

5

10

E791 FOCUS CLEOII.V

Acp

(

%)

K+K- + -

CLEO also has the following results:ACP(Ks)=-2.89.4%

ACP(Ks0)=0.11.3%ACP(00)=0.14.8%ACP(KsKs)=2319%

No evidence for CP violation in D0 decay

CLEO “wrong” sign D0K+- analysis yields: ACP(K+-)=219 1.0 %

-20No mixing in fit


CP Violation in D+ Decay

Look for direct CP violation, no mixing.Not much new since 2000All results are from fixed target experiments.

)()()()(

fDfDfDfDACP

For charged D’s measure the following:

-15

-10

-5

0

5

10

15

A CP (%

)

FOC

US

E791

E791

E791

E791

E691

E691

E691

K+K- K K*0 +-

No evidencefor CPV


CLEO Measurement of B(D+K*0l+l)This decay is sensitive to P V form factorThese form factors are related to ff’s in bulv and bsll. Can help reduce uncertainty in extraction of |Vub|CLEO Method:Use D* tag, reconstruct using jet direction for D direction 2-fold ambiguity, choose solution closest to m=MD*-MD=140.6 MeV fit K* mass in bins for m then fit resulting m with K*+data to extract signal

Re=0.74 0.04 0.06R=0.72 0.104 0.06R=0.73 0.04 0.05PDG: B(D+K-++) =(9.0 0.6)%BRe =(6.7 0.4 0.5 0.4)%BR=(6.5 0.9 0.5 0.4)% BR =(6.6 0.4 0.5 0.4)%

)()( 0*

KDBlKDBRl

preliminary


CLEO’s form factor ratio measurement in ce+Motivation: Alternative method for extracting |Vub| and |Vcb|

Same set of form factors in both decays: f1(q2), f2(q2)

Korner&Kramer predict: R= f2(q2)/f1(q2)=-0.25 (PL B275,495 (1992))

222222

2max2 )/1(

)/1()()( *max* ss

DD

ii mq

mqqfqf

Extract R using ML fit to 3 variables: t=(q/qmax)2

cosW= angle between e and W in cm of W cos= angle between p and in cm of Preliminary Result: R= -0.310.060.06

Improvement over previous CLEO result: R= -0.250.140.08, (PRL 75,624 (1995))

Consistent with Korner&Kramer

right signe+, e- wrong sign

e-, e+


c0e+

Search for c0e+ by comparing “right” (e+) sign and

“wrong” sign (e-) event yields.preliminary

(e+) (e-)

B(c0e+ )(e+e- c X)=42.214.111.9 fb

10X smallerthan ARGUS result520230130 fb

Probability of background fluctuation < 9x10-4

First observation of baryon decay with no u or d in parent particle


Charm Review SummaryLifetimes: mesons: lifetimes measured to 1- 2%

baryons: lifetimes measured ~2 - 30%theory may need a tune up: /|exp>2 vs /|th< 1.7 +

c c+c c

D Mixing: Exciting times aheadnew results expected from BELLE & BABAR soon

CP Violation: Keep looking !

Semileptonic Decays: Progress measuring rates and form factors

“The future of charm physics lies ahead of us !” Yogi Berra? George W.?

b-factories are charm factories tooCLEO-c

recent results on charm decays

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