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Semileptonic and EW Penguin Decay Results from BaBar John J. Walsh INFN-Pisa BaBar Collaboration XXXXth Rencontres de Moriond QCD and Hadronic Interactions.

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Presentation on theme: "Semileptonic and EW Penguin Decay Results from BaBar John J. Walsh INFN-Pisa BaBar Collaboration XXXXth Rencontres de Moriond QCD and Hadronic Interactions."— Presentation transcript:

1 Semileptonic and EW Penguin Decay Results from BaBar John J. Walsh INFN-Pisa BaBar Collaboration XXXXth Rencontres de Moriond QCD and Hadronic Interactions La Thuile, Italy March 12-March 19, 2005 I) Exclusive charmless SL decays –Tagged analysis: B 0    l + and B +    l + –Untagged analysis: B 0       l + –Motivations: extract Vub (CKM) Form Factor calculations (QCD) II) B  X s  decays –Fully inclusive analysis –Sum of exclusive states analysis –Motivations: search for New Physics (NP) photon spectrum in b  s  decays is used to determine Heavy Quark parameters m b and   2 (QCD) All results presented here are preliminary!

2 Walsh - Moriond QCD Exclusive B   l decays |V ub | determines one side of the Unitarity Triangle –Precise measurments of |V ub | and sin2  constrain the U.T. Error on |V ub | dominated by theory: –Inclusive analyses – prediction of spectra: theory error ~ 10-15% of |V ub |, need Shape Function from B  X s  –Exclusive decays – theory must predict form factors – uncertainty hard to quantify This talk  focus on new results from BaBar on exclusive decays B   (  )l : 2 types of analyses –Tagged analysis, using B  D(*)l of “other” B to tag event  reduced BG levels –Untagged analysis, emphasis on neutrino reconstruction  higher statistics

3 Walsh - Moriond QCD Form Factors B   l Calculations: –Light-Cone Sum Rules Ball/Zwicky (hep- ph/ ) quote % uncertainty at q 2 =0 Range of validity: q 2 < 14 GeV 2 –Lattice QCD Unquenched calculations from HPQCD (hep- lat/ ) and FNAL (hep-lat/ ) quote 11% uncertainty at high q 2 Valid above ~ 15 GeV 2 –ISGW2 quark model HPQCD’04 Ball’04 FNAL’04 ISGW2

4 Walsh - Moriond QCD Exclusive B   l decays: tagged analysis Use B  D (*) l decays of opposite B to “tag” event –consider only products of “recoil”  reduce combinatorial background Use doubly-tagged B  D (*) l events to check tagging efficiency Measure  B(B 0   - l + ) in bins of q 2 BF for B +   0 l + l l D (*) v v  signal B tag B Discriminating Variables B 0   - l + angle between the B momentum and the plane defined by the D(*)l and  l momenta: cos 2  B –<~ 1 for signal events –flat distribution for BG B +   0 l + angle between B and  0 l system: cos  B-  l –Signal region: −1.1 < cos  B-  l < 1.0 –BG much broader

5 Walsh - Moriond QCD Results: Tagged Analyses on-peak data signal MC B   lv MC b  ¨ ulv MC B 0 B 0 MC B + B − MC off-peak data 232 million BB pairs 88 million BB pairs B 0   - l + B +   0 l + Branching Fraction Results in 3 bins of q 2

6 Walsh - Moriond QCD B   (  )l : untagged analysis Reconstruct neutrino from full event + ensure good reconstruction quality Fit signal and background in  E, m ES, and q 2 neutrino momentum scaled so  E=0  improved q 2 resolution q 2 resolution

7 Walsh - Moriond QCD B   (  )l : Signal Extraction Data Signal MC Comb. Sig. Crossfeed b  cl qq B   l B   l 83 million BB pairs B A B A R preliminary Branching Fraction Results

8 Walsh - Moriond QCD Form Factor Fits & |V ub | The  l untagged sample begins to distinguish among FF calculations: ISGW II is disfavored: Prob(  2 ) = 3% Other calculations tested are compatible with data Untagged  l  l B A B A R preliminary Tagged Extraction of |V ub | (stat  syst  FF shape  FF norm ) uses LQCD- FNAL FF calculation

9 Walsh - Moriond QCD B  X s  Measurements Sensitive to New Physics –New heavy particles (Higgs, Susy) can participate in loop process Hadronic Effects –Photon Spectrum can be used to measure Heavy Quark parameters measure BR and moments as function of min E  cut largest uncertainty in |Vub| from inclusive b  ul decays due to b quark motion: can measure it with b  s  Two main experimental techniques: –fully inclusive –sum of exclusive modes b motion E min

10 Walsh - Moriond QCD Sum of Exclusive Modes Sum of 38 modes: Kn , n=1-4, plus modes with  and 3 kaon modes Kinematic constraints of fully- reconstructed B meson effectively reduces background Photon energy measured directly in B rest frame  superior resolution Primary systematic from missing modes (fragmentation) b  s  Experimental Issues Fully Inclusive Reconstruct high-energy photon ( GeV) Suppress huge background with lepton tagging Main systematic from subtraction of BB background Subtract b  d  (~4%) B+B+ B+B+ B-B- B-B- e or   XcXc XsXs B+B+ B+B+ B-B- B-B-  X K , K s , etc

11 Walsh - Moriond QCD Fully Inclusive b  s  Continuum Background - –Lepton tagging –Event-shape cuts –Remaining removed using off-peak data subtraction BB Background – –80% from  0,  decays –explicit  0 /  vetoes –Remaining subtracted using MC simulation – with corrections based on  0,  control sample Background-subtracted Event Yield 89 million BB pairs Event yield in range 2.0 – 2.7 GeV: – Signal: 992  79 stat  53 BBsyst – BB BG: 675  53 stat+syst –Cont. BG: 442  59

12 Walsh - Moriond QCD Inclusive b  s  Partial BFs, 1 st Moments E minFirst Energy Moment: (GeV) ± ± ± ± ± ± ± ± ± ± ± ± E rangePartial BF (×10 -4 ) 1.9 to ± 0.29 ± 0.34 ± to ± 0.27 ± 0.29 ± to ± 0.24 ± 0.25 ± to ± 0.21 ± 0.20 ± 0.13 First step towards determination of HQ parameters, Shape Function Coming soon: 2 nd moment measurement Further interaction with theory community to extract HQ parameters ( ± stat ± syst ± model ) B A B A R preliminary Photon Energy Spectrum efficiency corrected

13 Walsh - Moriond QCD b  s  Sum of Exclusive States Reconstruct 38 exclusive states containing K’s,  ’s,  ’s, etc.  missing fraction is fcn of M Xs Usual B decay kinematic variables to extract signal:  E and m ES Very good photon energy resolution: note the K*  peak Energy-substituted Mass Photon Energy Spectrum 89 million BB pairs B A B A R preliminary

14 Walsh - Moriond QCD b  s  (Semi-inclusive):  BF and Spectrum Moments Total BF for E  >1.6 GeV, use average of Kinetic and Shape Fcn scheme results Good agreement with inclusive analysis ( ± stat ± syst ± model ) World Average (HFAG, August 2004) Values of moments  (For reference, do not try to read)

15 Walsh - Moriond QCD OPE theory errors not included b  s  (Semi-inclusive):  Results on Heavy Quark Parameters Heavy Quark parameters related to b-quark mass and its Fermi momentum inside the B-hadron: Results derived for two different theoretical schemes: –Kinetic Scheme (Benson, Bigi, Uraltsev: hep-ph/ ) –Shape Fcn Scheme (Neubert: hep-ph/ ) B A B A R preliminary Kinetic ShapeFcn Scheme Kinetic scheme results can be compared with inclusive SL result from BaBar: PRL 93, (2004) ( ± stat ± syst ± model )

16 Walsh - Moriond QCD Summary Preliminary results from BaBar on semileptonic and EW penguin decays Exclusive analyses of B   (  )l using tagged and untagged samples: –Determination of |V ub | –BF measurements as function of q 2 –Begin to test Form Factor calculations The process b  s  studied with 2 experimental techniques: –fully inclusive: partial branching fractions and first moment as a function of E min  towards HQ parameters –semi-inclusive: BF and moments (1-3)  determination of m b and   2 –Will give significant improvement in determination of |V ub | from inclusive SL measurements

17 Walsh - Moriond QCD Backup slides


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