B Lifetimes at BABAR
Paris Group
April 13, 1999
[Introduction , Status
, 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.
[Introduction , Status
, Motivations , Samples,
Methods
, Outlook ]
April 13, 1999 Jacques Chauveau
Paris group: H. Briand,
J. Chauveau, C. de la Vaissiere, F. Martinez-Vidal, J. Stark