Recent b physics results from OPAL

David Waller, Carleton University for the OPAL Collaboration

EPS Conference HEP2003 Heavy Flavour Physics Session

Aachen, Germany 17 July 2003

July 17, 2003 EPS Conference D. Waller/Carleton U. 2

Outline•

– Object, motivation– Method– Results

• Charm counting in beauty decays– Object, motivation– Method– Results

• Conclusions

X)D b( *0*Br

Analyses of Z0 data!

July 17, 2003 EPS Conference D. Waller/Carleton U. 3

Semileptonic decay of b hadrons to orbitally excited D mesons

• Measure • D**0 are L=1 orbitally excited

charm mesons.– Measure narrow Jq= 3/2

states (D10, D2

*0).

– Wide Jq= 1/2 states not visible with statistics.

• Reconcile difference between measured inclusive and exclusive semileptonic branching ratios.

• Reduce uncertainty in |Vcb|.• Test HQET predictions.

X)D b( *0*Br

Object Motivation

July 17, 2003 EPS Conference D. Waller/Carleton U. 4

Semi-leptonic decay of b hadrons to orbitally excited D mesons: Method

• Identify high p lepton (,e)– high efficiency and purity for

p> 3 GeV/c, pe> 2 GeV/c• Exclusively reconstruct D**0

D**0 D*+ **- D0 +

slow

K-+(+ -)• Background cuts to remove

fake **- ( from fragmentation)– main background from

decays plus fake **-

– ANN (p, pT, d0/σd0) to select **-

XD b *0

3 mm

July 17, 2003 EPS Conference D. Waller/Carleton U. 5

D**0 – D*+ mass difference

Combine D0→ K and K3 channels to reduce uncertainty due to background.

Unbinned ML fit to determine number ofD1 and D2

* events (B.-W. Gaussian).

Number of wrong sign and right sign background events fit simultaneously.

July 17, 2003 EPS Conference D. Waller/Carleton U. 6

Results for X)D b( *0*

Br

3-

-*01

-01

10syst))(39.00.79(stat)(2.64

)πDD(X) DB()B(b

BrBrBr

C.L.) %95(101.4

)πDD(X) DB()B(b3-

-**02

-*02

BrBrBr

July 17, 2003 EPS Conference D. Waller/Carleton U. 7

Charm counting in b decays: Object and Motivation

• Object:(1) measure with inclusive method. (2) use to calculate average

number of c plus anti-c quarks per b quark decay, nc.

• Motivation: compare experimental value of nc to theoretical prediction:

nc = 1.20 ± 0.06 (Neubert & Sachrajda)

X)DD b( BrX)DD b( Br

charm) no b( - X))( b( X)DDb(1 BrccBrBrnc

Use PDG values

July 17, 2003 EPS Conference D. Waller/Carleton U. 8

Charm counting in b decays: Inclusive method

• Differentiate b→1 charm from b→2 charm using topology.

• Impact parameter significance, S (=d0/σd0), of tracks from D decay greater than S of tracks from b decay.

• In b→2 charm most tracks from D decay.

• Combine S of tracks in jet into single joint probability variable: PJ

July 17, 2003 EPS Conference D. Waller/Carleton U. 9

Charm counting in b decays:Probability Density Functions and Fits

1 and 2 charm PDFs for –ln(PJ)for different track multiplicities (TM)

Hatched = 2 charmGreen = 1 charmRed = 0 charm, charmonium, bckgd

July 17, 2003 EPS Conference D. Waller/Carleton U. 10

Charm Counting in b decays: Results

• measured for each year separately.• Results for each year combined → consistent.

• Two dominant systematics from physics modelling: – charged particle multiplicity in fragmentation (±6.2%)– neutral K and multiplicities in D decays ( %)

• combined with and to yield nc. 11.0

10.012.1 cn

X)DD b( Br

X)DD b( Br)X)cc( b( Br

charm) no b( Br

)phys((det)3.2(stat) 10.0 X)DD b( 4.100.9

2.42.9-

Br

+7.2- 4.6

July 17, 2003 EPS Conference D. Waller/Carleton U. 11

Conclusion• Results of these recent OPAL charm counting and

analyses consistent with previous measurements and theoretical predictions.

this result:pink band

X)D b( *0*Br

01D

Semileptonic B decays to narrow L=1 D mesons

This result: 3-

-*01

-01

10syst))(39.00.79(stat)(2.64

)πDD(X) DB()B(b

BrBrBr

ALEPH (1997):

3-

-*01

-01

-

10syst))(52.00.85(stat)(3.73

)πDD() DB(

BrBr

3-

-*01

-01

10syst))(29.00.38(stat)(1.68

)πDD(X) DB(

BrBr

CLEO (1998):

*02D

This result:CL) (95% 104.1

)πDD(X) DB()B(b3-

-**02

-*02

BrBrBr

ALEPH (1997):

CL) (90% 106.1

)πDD() DB(3-

-**02

-*02

-

BrBr

CL) %95( 1029.1

)πDD(X) DB(3-

-**02

-*02

BrBr

CLEO (1998):

July 17, 2003 EPS Conference D. Waller/Carleton U. 12

Key variables

July 17, 2003 EPS Conference D. Waller/Carleton U. 13

Cross check of results

angle between **- and slow

in rest frame of D*+.

Signal peaks at higher |cos()|while background is flat.

peak sidebands

July 17, 2003 EPS Conference D. Waller/Carleton U. 14

Extra slide: charm counting