Moriond QCD 2001 Gianluca Cavoto - Roma 1

Charmless Hadronic B Decays at BaBar

XXXVI Rencontres de Moriond

March 17th-24th, 2001

Gianluca CavotoUniversità 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 (h+h-) (h+) (h+)

Data from 1999-2000 run• 20.7 fb-1 on-resonance

N((4S)) = 22.74 ±0.36 million

• 2.6 fb-1 off-resonance

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Physics Target B mesons : dominant decay : b c (Vcb) Charmless decays:

Direct CP search Time-dependent CP asymmetry

sin(2), 0 sin(2) Theoretical model validation

penguin diagrams

Cabibbo-suppressed tree

diagrams

Vtb

Vtd,s

VubVud,s

ud

u

u

u

d

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BaBar detectorDIRC (PID)

144 fused silica bars11000 PMs

1.5T solenoid

EMC6580 CsI(Tl) crystals

Drift Chamber40 axial/stereo layers

Instrumented Flux Returniron / RPCs (muon / neutral hadrons)

Silicon Vertex Tracker 5 double sided layers

e+

(3.1GeV)

e- (9GeV)

SVT: z resolution ~70 micronsTracking: (pT)/pT = 0.13% pT 0.45%

DIRC: K- separation > 3.4 for P<3.5GeVEMC: E/E = 1.33%E-1/4 2.1%

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DIRCherenkov

C measurement

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

Pion-Kaon separation at high momenta

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B Candidate selection

2*2beamES

*BpEm

*beam

* EEE B

Initial state kinematic constraint:

energy substitued (constrained) mass

Fully reconstructed decaysEfficiency (with daughter BF)

00,h+0,h+0,h+h: 10-45% ,3-

20%

K0 as KS to +-

K+K-

K*+ K+0,KS +

mES

signalsideband

energy difference

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Composite particles

mass KS mass

Additional cuts:KS :decay time significance : photon cos(*, cluster lateral shape

4.3 MeV

loose Kaon PID requirementson daugheters

mass

8.5 MeV

< E > ~ 3 GeV

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Background suppression

Background dominated by continuum quark-antiquark production (u,d,s,c)

cos(Th) = cosine of angle between thrust axes of B

and rest of the event Fisher discriminant:

Linear combination of event-shape variables

cos Th

Fisher signal

signal

background

background

Loose Cut on cos(Th) to suppress bkg

hh E sideband (dots) continuum hh MC (histo)

(dots) B- D0 (histo)hh MC

Jet-like topology

Moriond QCD 2001 9

Likelihood fit analysis Use an extended global likelihood fit

to extract different signal yields (NS) in each topology

mES, E, Fisher(cosTh), ( mass),

C

Independent control sample to study Probability Density Function for both BKG and SIG Gaussian 2.6 MeV

ARGUS function

B- Do- h+h- E sideband

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Why critical?:

Separate channels with same decay topology

Use as control sample: D*+ D0

C - C (K) distribution for true aon

Critical Kaon ID

PDF in momentum bins

C

p

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Systematic Uncertainties

Vary PDF parameters alternative PDF

Variation in yield

Other systematics (% variation on BF):

track finding efficiency: 1.2% per track

(S ) efficiency 5(4)% B meson counting 1.6%

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B0

2 charged particles in the final state

cut-based analysisdistributions for consistency check

K

KK

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B+ B0

KS

KS

KS to

ML fit results

Cut based analysis cross-checks

KS

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B+

BB background investigated:

ML fit allows for component

< 9.0 (UL 90%CL)

Max likelihood fit projection

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Max likelihood fit projection

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Summary 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 ( )