Transcript PPT-Version

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
Outline
• Br (b  D**0  X)
– Object, motivation
– Method
– Results
• Charm counting in beauty decays
– Object, motivation
– Method
– Results
• Conclusions
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Analyses of
Z0 data!
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Semileptonic decay of b hadrons
to orbitally excited D mesons
Object
Motivation
• Measure Br (b  D   X)
• 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.
**0
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• Reconcile difference
between measured
inclusive and exclusive
semileptonic branching
ratios.
• Reduce uncertainty in |Vcb|.
• Test HQET predictions.
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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*+ **D0 +slow
K-+(+ -)
• Background cuts to remove
fake **- ( from fragmentation)
D**0
– main background from
b  D*0  X decays
plus fake **– ANN (p, pT, d0/σd0) to
select **July 17, 2003
EPS Conference
3 mm
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D**0 – D*+ mass difference
Combine D0→ K and K3 channels to
reduce uncertainty due to background.
Unbinned ML fit to determine number of
D1 and D2* events (B.-W.  Gaussian).
Number of wrong sign and right sign
background events fit simultaneously.
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Results for
Br (b  D   X)
**0
Br (b  B)  Br ( B  D10 - X)  Br (D10  D* π - )
 (2.64  0.79(stat)  0.39(syst)) 10-3
*0
* Br (b  B)  Br ( B  D*0


X)

Br
(
D

D
π)
2
2
 1.4 10-3 (95% C.L.)
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Charm counting in b decays:
Object and Motivation
• Object:(1) measure Br (b  DDX) with inclusive method.
(2) use Br (b  DDX) to calculate average
number of c plus anti-c quarks per b quark
decay, nc.
nc  1  Br (b  DDX) Br (b  (cc )X) - Br (b  no charm)
Use PDG values
• Motivation: compare experimental value of nc to
theoretical prediction:
nc = 1.20 ± 0.06 (Neubert & Sachrajda)
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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
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Charm counting in b decays:
Probability Density Functions and Fits
1 and 2 charm PDFs for –ln(PJ)
for different track multiplicities (TM)
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Hatched = 2 charm
Green = 1 charm
Red = 0 charm, charmonium, bckgd
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Charm Counting in b decays:
Results
• Br (b  DDX)
measured for each year separately.
• Results for each year combined → consistent.
2.4
.4
Br (b  DDX)  10.0  3.2(stat) -2.9
(det) 10
9.0 (phys )
• Two dominant systematics from physics modelling:
– charged particle multiplicity in fragmentation (±6.2%)
– neutral K and  multiplicities in D decays ( +7.2
%)
- 4.6
•
Br (b  DDX) combined with Br (b  no charm) and
Br (b  (cc)X) to yield nc.
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nc  1.12 00..11
10
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Conclusion
• Results of these recent OPAL charm counting and Br (b  D**0  X)
analyses consistent with previous measurements and theoretical
predictions.
Semileptonic B decays to narrow L=1 D mesons
This result:
ALEPH (1997):
CLEO (1998):
This result:
this result:
pink band
ALEPH (1997):
CLEO (1998):
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Br (b  B)  Br ( B  D10 - X)  Br (D10  D* π - )
 (2.64  0.79(stat)  0.39(syst)) 10-3
Br ( B  D10 - X)  Br (D10  D* π - )
 (1.68  0.38(stat)  0.29(syst)) 10-3
D10
Br (B-  D10 - )  Br (D10  D* π - )
 (3.73  0.85(stat)  0.52(syst)) 10-3
*0
* Br (b  B)  Br ( B  D*0
2   X)  Br (D 2  D π )
 1.4 10-3 (95% CL)
*0
* Br ( B  D*0
2   X)  Br (D 2  D π )
D *0
2
 1.29 10 (95% CL)
-3
*0
* Br (B-  D*0
2   )  Br (D 2  D π )
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 1.6 10-3 (90% CL)
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Key variables
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Cross check of results
 angle between **- and slow
in rest frame of D*+.
peak
sidebands
Signal peaks at higher |cos()|
while background is flat.
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Extra slide: charm counting
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