B Lifetimes at BABAR

                                                 Paris Group        April 13, 1999
[IntroductionStatus , Motivations , Samples, Methods , Outlook ]
 
 

Introduction

  • Main focus on B reconstruction and and vertexing/composition tools which are key for CP analyses.
  • State of the art and prospects

    The latest compilation (winter 1999 conferences)  of LEP B lifetime working group gives the following
    results for charged  and  neutral B's as well as for the  ratio .

    Charged B: 1.66 +/- 0.03 ps    (1.67 +/- 0.04 in BaBar book)

    Neutral B:  1.55 +/- 0.03 ps    (1.57 +/- 0.04)

    Ratio:          1.08 +/- 0.03        (1.07 +/- 0.04)
     

  • Dominant  contributions: LEP,CDF, SLD.
  • Lowest quoted systematics +/- 0.02 (CDF J/Psi)
  • Lif. raNT COLOR="#000000">Lif. ratio inferred from Branching Ratios: 0.95 +0.15 -0.12 (PDG98)
  • Why measure the B lifetimes

  •  Test theoretical models of heavy quark decays. Needs O(1%) precision.
  •  "Calibrate" the experiment on known numbers.
  •  Provide engineering numbers for measurements at BaBar (e.g. mixing).
  • Data samples

  • For 30 fb-1 or about 30M B mesons of each charge.
  • Table below is snapshot of work in progress (Jan Stark after G.L.). See also earlier  work  by  Christian .

  •         eps(charged track)=0.85,
            eps(pi_0)=0.45,
      &nbFONT COLOR="#000000">        J/Psi decay only to mu+ mu- [eps(J/Psi)=0.7 from full vertex QA study],
            Ks only to pi+ pi-
            no penalty from combinatorics
  • Expect more details from ongoing simulations.

  •       -
    B DECAYS INTERMEDIATE STATES B0 B0 (D_sl) B+ B+(D_sl)
    HADRONIC J/Psi      1.3 k     -     3.4 k     -
    D-    33.3 k     5.9 k     -     -
    D0bar     -     -    73.1 k   18.1 k
    D*-    63.6 k   13.7 k     -     -
        -
    D*0bar     -     -    10.7 k     2.4 k
    total     98.2 k   19.6 k    87.2 k   20.5 k
    grand total    117.8 k  107.7 k
    SEMI LEPTONIC  226.   k     -  138.   k     -
    ALL  344    k  246    k

     
  • Maximum B reco efficiency about 1%
  • Maximum B reco efficiency about 1%
  • Balanced between neutral and charged B mesons, espicially for hadronic decays.
  • Semileptonic B decays dominates the total sample size (espicially for B0)
  •  Semileptonic charm decays add 20% statistics to the B->D decays sample, but it is very unclear that they can be used.
  • Methods to measure the B lifetimes

      Don't know yet how to obtain picture of correct size... Please get the .eps file here .
     
  • CP-like delta_z method.
  • sophisticated methods (only for fully hadronic modes). See BaBar note 436
  • Lrec using the beam constraint in y
  • Lrec and Lopp using the tag vertex
  • or only using one (or more) tracks from the tag vertex
  • BaBar book error estimates for 30 fb-1: 1.5% statistical, similar systematics (not really studied)
  •  Implementation using the vertexing tools
  •  impact on the Btag vertex studies for the CP analyses
  • OLOR="#FF0000">CP analyses

    "The questions"

  • Motivation: physics, reproduce known measurements, engineering numbers
  • MDC2: not done
  • PRV0: QA of vertexing/composition tools
  • First 100k events: Expect few hundred events. Understand detector. Live with background .
  • May -August run: More of the same.
  • Outlook

  •  B reconstruction scope definition
  •  Work on vertex/composition tools
  •  Precise strategy for the semileptonic decays (only delta_z,  D** complication).
  •  Note synergy of vertex/comp tools, B reconstruction and CP discovery effort.

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     [IntroductionStatus , Motivations , Samples, Methods , Outlook ]


    April 13, 1999 Jacques Chauveau


    Paris group: H. Briand, J. Chauveau, C. de la Vaissiere, F. Martinez-Vidal, J. Stark