Recent Results in Heavy Flavour Physics from OPAL: Charm Counting in Beauty Decays
This presentation by David Waller from Carleton University, part of the OPAL Collaboration at the EPS Conference HEP2003, discusses recent findings in heavy flavour physics, focusing on the counting of charm quarks in beauty decays. Key topics include the motivation and methodology used in the study, detailed analyses of Z0 data, semileptonic decays of b-hadrons to orbitally excited D mesons, and reconciliation of inclusive and exclusive semileptonic branching ratios. Results align with theoretical predictions and past measurements, addressing critical aspects of charm counting.
Recent Results in Heavy Flavour Physics from OPAL: Charm Counting in Beauty Decays
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Presentation Transcript
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 • Object, motivation • Method • Results • Charm counting in beauty decays • Object, motivation • Method • Results • Conclusions Analysesof Z0 data! EPS Conference D. Waller/Carleton U.
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. Semileptonic decay of b hadrons to orbitally excited D mesons Object Motivation EPS Conference D. Waller/Carleton U.
3 mm 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**0D*+**- D0+slow K-+(+ -) • Background cuts to remove fake **- ( from fragmentation) • main background from decays plus fake **- • ANN (p, pT, d0/σd0) to select **- EPS Conference D. Waller/Carleton U.
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. EPS Conference D. Waller/Carleton U.
Results for EPS Conference D. Waller/Carleton U.
Use PDG values 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 ncto theoretical prediction: nc= 1.20 ± 0.06 (Neubert & Sachrajda) EPS Conference D. Waller/Carleton U.
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 EPS Conference D. Waller/Carleton U.
Hatched = 2 charm Green = 1 charm Red = 0 charm, charmonium, bckgd 1 and 2 charm PDFs for –ln(PJ) for different track multiplicities (TM) Charm counting in b decays:Probability Density Functions and Fits EPS Conference D. Waller/Carleton U.
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. +7.2 - 4.6 EPS Conference D. Waller/Carleton U.
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): Conclusion • Results of these recent OPAL charm counting and analyses consistent with previous measurements and theoretical predictions. EPS Conference D. Waller/Carleton U.
Key variables EPS Conference D. Waller/Carleton U.
Cross check of results • angle between **- and slow in rest frame of D*+. sidebands peak Signal peaks at higher |cos()| while background is flat. EPS Conference D. Waller/Carleton U.
Extra slide: charm counting EPS Conference D. Waller/Carleton U.
