Oct., 2006 1

Overview of the CLEO experiment D and DS leptonic decays to and :

Measurements of absolute branching fractions Measurements of absolute decay constants

Comparison with theory (LQCD)

Victor Pavlunin on behalf of

the CLEO collaborationDPF-2006

Oct., 2006 2

The CLEO detector

The CLEO detector was developed for B physics at the Y(4S). CLEO-III configuration:

B-field: 1.5 T Gas (drift chamber): He and C3H8

Tracking: 93% of 4, P/P0.6% for a 1.0 GeV track Hadron particle ID: RICH (80% of 4) and dE/dx E/M crystal calorimeter: 93% of 4π, E/E 2.0%

(4.0)% for a 1.0 GeV (100 MeV) photon Muon prop. chambers at 3, 5 and 7 I .

Transition from CLEO III to CLEO-c:

B-field: 1.5 T 1.0 T Silicon vertex detector low mass stereo drift

chamber

Advantages of running at the (3770) for charm physics:

Pure DD, no additional particles [DD at (3770)] = 6.4 nb [(cc) at Y(4S) ~1.3 nb] Low mulitplicity, high tagging efficiency (>20%)

An event taken at the

Y(4S)

KDKD

DDee

,

,)3770(

6-layer all-stereo

Oct., 2006 3

The main task of the CLEO-c open charm program:

Calibrate and Validate Lattice QCD

Help heavy flavor physics constrain the CKM matrix now: Precision tests of the Standard Model or Discovery of new physics beyond the SM in b or c quark decays

Difficulty: hadronic uncertainties complicate the interpretation of exp. results:

Help LHC search for and interpret new physics if new physics is strongly coupled in the future

Why a Charm Factory?

Reduce theory error on B form factors and B decay constants using tested

LQCD

Oct., 2006 4

Leptonic decays (D+ and Ds):

Semileptonic decays (D e, D Ke ):

Combination of leptonic and semileptonic decays:

Examples of LQCD tests and their impact

Bd Bd2*2 || tbtdB VVfRate

d

2)(

2 ||)( scdD VfRate

s

LQCDExperimentKnown to 1% from

the CKM unitarity

Lattice predicts fB/fD and

fB/fBs with small errors

precise fD gives precise fB

and |Vtd|; fD/fDs checks fB/fBs and allows precise |Vtd|/|Vts|

|VCKM|2

|fD|2

D

|f(q2)|2

|VCKM|2

D )(

,)(22

222

)(

eMqwhereqfVRate scd

Test LCQD calculations of f+

(q2) in the D system and apply them to the B system for |Vub| and |Vcb|

The topic of the next CLEO talk

222 /)()(/)( DfqfDeD Test LQCD with no errors from CKM couplings

)(K

The main topic of this talk

Oct., 2006 5

CLEO-c Data SamplesResults presented in this talk were obtained using the

following data samples:

(3770): total luminosity = ~ 280 pb 1

ECM = 4170 MeV: total luminosity = ~ 200 pb1

CLEO scanned ECM = 3.97 – 4.26 GeV:

Optimal energy for Ds physics:

ECM = 4.170 GeV

Dominant production mechanism:

[Additional 120 pb-1 at ECM = 4170 MeV already collected: to be analyzed]

*SS DDee

*SS DD

SS DD**SS DD

DATA

Preliminary

Oct., 2006 6

D(s) Leptonic Decays

cdV

Df

222

2222 ||)1(

8

1)( cd

D

lDlDF V

M

mMmfGlD

Standard Model predicts: D decays: Ds decays:

Use Vcd and Vcs to extract fD and fDs, and compare them to theory

7.2:0.1:103.2)(:)(:)( 5 e

7.9:0.1:105.2)(:)(:)( 5 e

Oct., 2006 7

D+ and D+ at the (3770)

References:PRL 95, 25801 (2005)PRD 73, 112005 (2006)

Oct., 2006 8

Tagging at the (3770) The (3770) is about 40 MeV above the DD pair threshold (

)

Variables used in the tag reconstruction:

Leptonic decays are identified using missing mass squared:

DD PP

22candidatebeambc PEM

beamcandidate EEE

Tagging creates a beam of D mesons with known momentum

222 )()( ppEEMM tagbeam

Oct., 2006 9

D Tags

][22 GeVPEM candidatebeambc

DATA (280/pb) All 6 modes

Cut on E and fit MBC:

Total number of tags: [158.4 0.5 (stat)]103

][22 GeVPEM candidatebeambc

K 0 K

SK SK

0 SK KK

DATA (280/pb)

Oct., 2006 10

][)()( 2222 GeVppEEMM tagbeam

D

0KD

D+ + and e+ Full event reconstruction:

require a tag, require a muon cand. (ECC

track < 300 MeV),

veto events with extra tracks and energy clusters > 250 MeV.

Results: 50 D+ candidates Estimated bckg: 2.8 events

The same analysis is repeated for D+ e+. No signal candidates are seen:

410)](1.0)(7.04.4[)( syststatDB

MeVsyststatfD

)](3)(17223[

)%90(104.2)( 5 CLateDB

DATA

Oct., 2006 11

Case I: ECCtrack

< 300 MeV

Case II: ECCtrack

> 300 MeV

Sign. Candidates: 12Est. Background: 6.1

Sign. Candidates: 8Est. Background: 5.0

D+ + Reconstruct D++ with ++ [B(++ ) ~11%]; the same

technique but two ’s complicate the analysis:

Consider two cases: Case I: ECC

track < 300 MeV ( and )

Case II: ECCtrack > 300 MeV (mostly )

No significant signal

)(: DMC

Broad MM2

)%90(101.2)( 3 CLatDB )]%90(10)2.01.1()(:[ 3 CLatDBSM

DATA

DATA

Oct., 2006 12

DS and DS at ECM = 4170 MeV

References:CLEO CONF 06-17hep-ex/0610026

Oct., 2006 13

][)( GeVDM S

KKKKS

0** KK

DS Tags (1)

Recall at ECM = 4170 MeV:

DS* decays to DS via emission of ~150 MeV

photon ~95% of the time significant smearing of MBC

Tag modes used in the analysis:Yields from M(Ds)

Total number of tags from M(Ds): [19.2 0.3 (stat)]103

*SS DDee

DATA (200/pb)

Oct., 2006 14

DS Tags (2)

To fully reconstruct the event, the photon must be detected. The missing mass squared can be used to obtain the number of tags:

22

2*

)()( ppEEEMM

SS DDCM

All 8 Modes DATA

][ 22* GeVMMTotal number of tags in the signal

region of MM*2: [11.9 0.4 (stat) 0.5

(syst)]103

Oct., 2006 15

Electron Sample

ECCtrack < 300MeV

64 events

24 events

12 events

Case I:

Case IIECC

track > 300MeV

Case III

Mostly DS +

Mostly DS +

Signal region

region

A

region

B

DATA

DATA

DS + and +(+) (1)

Full event reconstruction: Require a tag and a from DS

*, Require one additional track, Veto events with ECC > 300 MeV

or extra tracks.

Use MM2 to separate +, +(+) and background:

Consider three cases: Case I: ECC

track < 300 MeV (accept 99% of muons and 60% of pions) Case II: ECC

track > 300 MeV (accept 1% of muons and 40% of pions) Case III: require an electron

[Kinematical constraints are used to improve resolution and remove multiple combinations]

22)(

2 )()( pppEEEEMMSS DDCM

Oct., 2006 16

100 events

Sum of Case I and Case II

K0+

signal line shape

Consistency Check

Note the scale limits: 0.20 and 0.80 GeV2

MM2 MM2

MC MC+ +

DATA

DS + and +(+) (2)

Oct., 2006 17

Electron Sample

ECCtrack < 300MeV

64 events

24 events

12 events

Case I:

Case IIECC

track > 300MeV

Case III

Mostly DS +

Mostly DS +

Signal region

region

A

region

B

DATA

DATA

DS + and +(+) (3)

DS + (Case I, Reg.A) 64 signal candidates, 2.0 bkg

events:

DS + (Case I,Reg.B+Case II)

36 signal candidates, 4.8 bkg events:

Use the SM B(+)/B(+) to average results above:

DS e+ (Case III): No signal candidates:

)]%(03.0)(09.066.0[)( syststatDB S

)]%(3.0)(4.11.7[)( syststatDB S

)]%(03.0)(08.066.0[)( syststatDB S )%]19.061.0()(:06[ SDBPDG

4101.3)( eDB S

)%]5.14.6()(:06[ SDBPDG

MeVsyststatfSD )](7)(16282[

Preliminary

Oct., 2006 18

DS +(e+ )

Complimentary analysis: DS

+ with +e+ .

B(DS+)B(+e+)~1.3% is large [cf. B(DS

+→Xe+)~8%] Analysis Technique:

Find e+ and DS tag ( from DS

* is not reconstructed, same tag modes)

Veto events with extra tracks Extra energy in CC < 400 MeV

Results:

400 MeV

Xe+

)]%(5.0)(8.03.6[)( syststatDB S )%]5.14.6()(:06[ SDBPDG

MeVsyststatfSD )](12)(17278[

Preliminary

Oct., 2006 19

Comparison with theorySummary of CLEO-c results:

Unquenched LQCD [PRL 95, 122002 (2005)]

MeVsyststatfD

)](3)(17223[

MeVsyststatfSD )](6)(12280[ [Weighted average; syst. errors

are mostly uncorrelated]

11.026.1 D

D

f

fS

MeVsyststatfD

)](17)(3201[

MeVsyststatfSD )](16)(3249[

07.024.1 D

D

f

fS

CLEO-c: statistically limited

LQCD: systematically limited

An example of theor. preditions:

Preliminary

Oct., 2006 20

Conclusions An important task of CLEO-c is to calibrate and validate LQCD.

Charm leptonic decays provide particularly stringent tests.

Current precision of CLEO-c and LQCD results is comparable. CLEO-c results are statistically limited; LQCD results are limited by systematic uncertainties.

Expect a three fold increase in the size of CLEO-c data sample and a complete suite of leptonic and semileptonic measurements in the next few years.

On a longer time scale, BES III (China) should be able to improve CLEO-c results and further constrain the theory.

Oct., 2006 21

Additional Slides

Oct., 2006 22

)3770(

Data taking started in the fall of 2003

Note

: Log

Scale

Over 20 years operated at the Y(4S)

~16 fb-1 at the Y(4S)

CESR and CLEO

The CLEO experiment is located at the Cornell Electron Storage Ring (CESR), a symmetric e+e-

collider that operated in the region of the Upsilon resonances for over 20 years:

Max inst luminosity achieved: 1.31033 cm-2s-1

Total integrated luminosity at the Y(4S): 16 fb-1

Lots of important discoveries, e.g., Y(nS), bs, buW.

In 2003, CLEO started running at the (3770), ~40 MeV above DD production threshold, and slightly higher energies for DS studies.

Transition from CESR to CESR-c:

12 wigglers are installed to increase synchrotron radiation/beam cooling

Max luminosity achieved: ~71031 cm-2s-1

Oct., 2006 23

The main task of the CLEO-c open charm program: Calibrate and Validate Lattice QCD

Help heavy flavor physics constrain the CKM matrix now: Precision tests of the Standard Model or Discovery of new physics beyond the SM in b or c quark decays

Difficulty: hadronic uncertainties complicate interpretation of exp. results

Help LHC search for and interpret new physics (future)

Why a Charm Factory?

Reduce theory error on B

form factors and B decay constants

using tested LQCD

A realistic example using recent CKM status (new Bs mixing results are not included):

200 fb-1

at Babar/Belle 500 fb-1 at Babar/Belle

Oct., 2006 24

Why now?

C. Davies opened her talk in Lisbon at EPS-2005: “There has been a revolution in LQCD…”

BEFOREquenched

NOWunquenchedPRL 92, 022001 (2004)

LQCD demonstrated that it can reproduce a wide range of mass differences and decay constants in unquenched calculations. These were postdictions.

Testable predictions are now being made for:

Decay constants fD and fB; D and B Semileptonic form factors

.exp

LQCD

.exp

LQCDCLEO-c can test fD and D semileptonic form factors

Oct., 2006 25

Tagging at the (3770)

The (3770) is about 40 MeV above the DD pair threshold ( )

One of the two D’s is reconstructed in a hadronic “tag” mode (e.g., K+ - ). Two key variables:

From the remaining tracks and showers the semileptonic decay is reconstructed (e.g., Ke+)

U Emiss |Pmiss| is used to identify signal, where Emiss and Pmiss are the missing energy and momentum approximating the neutrino E and P. The signal peaks at zero in U.

Full event reconstruction allows to measure any kinematic variable with no ambiguities and with high precision

DD PP

22candidatebeambc PEM

beamcandidate EEE

K-

-

e+

K+

(3770)D0 D0

D0K+-, D0K-e+

Oct., 2006 26

DS Tags at 4170

MC:DS

][GeVM BC

*SS DDee