1. Charmless Hadronic B Decays at BaBar
XXXVI Rencontres de Moriond
March 17th-24th, 2001
Gianluca Cavoto
Università di Roma La Sapienza & INFN
on behalf of BaBar Collaboration
Moriond QCD 2001
Gianluca Cavoto - Roma

2. Charmless Decays Preliminary Branching Fraction measurements
( and upper limit ) with BaBar at PEP-II
p+p-, K+p-, K+K- (h+h-)
p0 p+, p0 K+ (p0h+)
K0 p+, K0 K+ (K0h+)
K0p0
fK*+
fK+,fp+
fK0
Data from run
20.7 fb-1 on-resonance
N((4S)) = ±0.36 million
2.6 fb-1 off-resonance
Moriond QCD 2001
Gianluca Cavoto - Roma

3. Cabibbo-suppressed tree diagrams Cabibbo-suppressed tree diagrams
Physics Target
B mesons : dominant decay : b  c (Vcb)
Charmless decays:
Direct CP search
Time-dependent CP asymmetry
p+p-  sin(2a), fK0  sin(2b)
Theoretical model validation d u
Vtd,s u u
Vub
Vtb
Vud,s d u
Cabibbo-suppressed tree diagrams
penguin diagrams
Moriond QCD 2001
Gianluca Cavoto - Roma u
p+, K+
Vtb
Vtd,s b W
d,s
d,s
p+, K+ W
Vub
Vud,s u b u t p- u B0 d d p- d d
Cabibbo-suppressed tree diagrams
penguin diagrams

4. Instrumented Flux Return Silicon Vertex Tracker
BaBar detector
EMC
6580 CsI(Tl) crystals
DIRC (PID)
144 fused silica bars
11000 PMs
1.5T solenoid
Instrumented Flux Return
iron / RPCs (muon / neutral hadrons)
Drift Chamber
40 axial/stereo layers
e+ (3.1GeV)
Silicon Vertex Tracker
5 double sided layers
e- (9GeV)
SVT: z resolution ~70 microns
Tracking: (pT)/pT = 0.13%  pT  0.45%
DIRC: K- separation > 3.4 for P<3.5GeV
EMC: E/E = 1.33%E-1/4  2.1%
Moriond QCD 2001
Gianluca Cavoto - Roma

5. DIRCherenkov qC measurement Pion-Kaon separation at high momenta
Detector of Internally Reflected Cherenkov light.
144 fused silica bars (1.7 cm thick)
11000 PMTs, p.e./particle,
10 mrad single photon resolution
Moriond QCD 2001
Gianluca Cavoto - Roma

6. B Candidate selection Initial state kinematic constraint:
K0 as KS to p+p-
f  K+K-
K*+  K+p0,KS p+
energy substitued
(constrained) mass
Fully reconstructed decays
Efficiency (with daughter BF)
K0p0,h+p0,h+K0,h+h: 10-45%
fK*+,fK0,fK :3-20%
energy difference DE
signal
sideband
mES
Moriond QCD 2001
Gianluca Cavoto - Roma
unknown polarization in fK*+
select

7. Composite particles f mass s= 4.3 MeV s= 8.5 MeV loose Kaon PID
< E > ~ 3 GeV
s= 8.5 MeV
loose Kaon PID
requirements
on f/K* daugheters
f mass
KS mass
p0 mass
Additional cuts:
KS :decay time significance
p0 : photon cos(q*),
cluster lateral shape
Moriond QCD 2001
Gianluca Cavoto - Roma

8. Background suppression
Jet-like topology
Background dominated by continuum quark-antiquark production (u,d,s,c)
cos(qTh) =
cosine of angle between thrust axes of B and rest of the event
Fisher discriminant:
Linear combination of event-shape variables
cos qTh
background
Loose Cut on cos(qTh)
to suppress bkg
Fisher
signal
(dots) B-  D0p-
(histo) h+h- MC
background
signal
h+h- DE sideband (dots)
continuum h+h- MC (histo)
Moriond QCD 2001
Gianluca Cavoto - Roma

9. Likelihood fit analysis
Use an extended global likelihood fit to extract different signal yields (NS) in each topology
mES, DE, Fisher(cosqTh), (f mass), qC
Independent control sample to study Probability Density Function for both BKG and SIG
h+h- DE sideband
B-  Dop-
Gaussian
s  2.6 MeV
ARGUS function

10. Critical Kaon ID Use as control sample: D*+  D0p+  K-p+
Why critical?:
Separate channels with same decay topology
Use as control sample: D*+  D0p+  K-p+
PDF in momentum bins qC p
qC - qC (K) distribution
for true Kaon
Moriond QCD 2001
Gianluca Cavoto - Roma

11. Systematic Uncertainties
Vary PDF parameters
alternative PDF
Variation in yield
Other systematics (% variation on BF):
track finding efficiency: 1.2% per track
p0 (KS ) efficiency 5(4)%
B meson counting 1.6%
Moriond QCD 2001
Gianluca Cavoto - Roma

12. B0  p+p-, K+p-, K+K- 2 charged particles in the final state
cut-based analysis
distributions for consistency check
2 charged particles in the final state
Moriond QCD 2001
Gianluca Cavoto - Roma

13. B+ K0p+, K0 K+ B0  K0p0 KSp+ KSp0 KSK+
Cut based analysis cross-checks
KS to p+p-
ML fit results
Moriond QCD 2001
Gianluca Cavoto - Roma

14. B+ p0p+, p0 K+ p0 p+ p0 K+ Max likelihood fit projection
< 9.0 (UL 90%CL)
p0 K+
BB background investigated:
ML fit allows for rp component
Moriond QCD 2001
Gianluca Cavoto - Roma

15. B  fK(*) Max likelihood fit projection fK0 fK*+(K+p0) fK*+(K0p+) fK-
Moriond QCD 2001
Gianluca Cavoto - Roma

16. Summary Next targets : Direct CP asymmetry in these and other channels
BaBar has recorded
20.7 fb-1 last year
Expect to collect additional ~30 fb-1 in 2001
Next targets :
Direct CP asymmetry in these and other channels
Time-dependent CP asymmetry ( p+p-)
Moriond QCD 2001
Gianluca Cavoto - Roma