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Charmless Hadronic B Decays at BaBar

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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

Gianluca Cavoto - Roma

PreliminaryBranchingFraction 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 1999-2000 run
- 20.7 fb-1 on-resonance
- N((4S)) = 22.74 ±0.36 million

- 2.6fb-1 off-resonance

Gianluca Cavoto - Roma

d

u

- 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

Vtd,s

u

u

Vub

Vtb

Vud,s

d

u

Cabibbo-suppressed tree diagrams

penguin diagrams

Gianluca Cavoto - Roma

u

p+, K+

Vtb

Vtd,s

d,s

b

W

d,s

p+, K+

W

Vub

Vud,s

u

b

u

t

u

p-

B0

d

d

p-

d

d

Cabibbo-suppressed tree diagrams

penguin diagrams

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%

Gianluca Cavoto - Roma

qC measurement

Pion-Kaon separation

at high momenta

Detector of Internally Reflected Cherenkov light.

144 fused silica bars (1.7 cm thick)

11000 PMTs, 25-50 p.e./particle,

10 mrad single photon resolution

Gianluca Cavoto - Roma

- Initial state kinematic constraint:

K0 as KS to p+p-

fK+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

Gianluca Cavoto - Roma

unknown polarization in fK*+

select

s=4.3 MeV

< E > ~ 3 GeV

s=8.5 MeV

loose Kaon PID

requirements

onf/K* daugheters

f mass

KS mass

p0 mass

Additional cuts:

KS:decay time significance

p0: photoncos(q*),

cluster lateral shape

Gianluca Cavoto - Roma

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)

Gianluca Cavoto - Roma

- Use an extendedglobal likelihood fit to extract different signal yields (NS) in each topology

- 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

Critical Kaon ID

- Why critical?:

PDF in momentum bins

qC

p

qC - qC (K) distribution

for true Kaon

Gianluca Cavoto - Roma

- Vary PDF parameters
- alternative PDF

- Other systematics (% variation on BF):
- track finding efficiency: 1.2% per track
- p0 (KS ) efficiency 5(4)%
- B meson counting 1.6%

Variation in yield

Gianluca Cavoto - Roma

cut-based analysis

distributions for consistency check

- 2 charged particles in the final state

Gianluca Cavoto - Roma

KSp+

KSp0

KSK+

Cut based analysis cross-checks

KS to p+p-

ML fit results

Gianluca Cavoto - Roma

Max likelihood fit projection

p0 p+

BB background investigated:

ML fit allows for rp component

< 9.0(UL 90%CL)

p0 K+

Gianluca Cavoto - Roma

Max likelihood fit projection

fK0

fK*+(K+p0)

fK*+(K0p+)

fK-

Gianluca Cavoto - Roma

- 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-)

Gianluca Cavoto - Roma