Charmless hadronic b decays at babar
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Charmless Hadronic B Decays at BaBar. XXXVI Rencontres de Moriond March 17 th -24 th , 2001 Gianluca Cavoto Università di Roma La Sapienza & INFN on behalf of BaBar Collaboration. Charmless Decays. Preliminary Branching Fraction measurements

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Charmless Hadronic B Decays at BaBar

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Charmless hadronic b decays at babar

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


Charmless decays

Charmless Decays

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


Physics target

Physics Target

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


Babar detector

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%

Gianluca Cavoto - Roma


Dirc herenkov

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, 25-50 p.e./particle,

10 mrad single photon resolution

Gianluca Cavoto - Roma


B candidate selection

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

Gianluca Cavoto - Roma

unknown polarization in fK*+

select


Composite particles

Composite particles

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


Background suppression

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)

Gianluca Cavoto - Roma


Likelihood fit analysis

Likelihood fit analysis

  • Use an extendedglobal 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


    Charmless hadronic b decays at babar

    Critical Kaon ID

    • 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

    Gianluca Cavoto - Roma


    Systematic uncertainties

    Systematic Uncertainties

    • 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


    B 0 p p k p k k

    B0p+p-, K+p-, K+K-

    cut-based analysis

    distributions for consistency check

    • 2 charged particles in the final state

    Gianluca Cavoto - Roma


    B k 0 p k 0 k b 0 k 0 p 0

    B+K0p+, K0 K+B0K0p0

    KSp+

    KSp0

    KSK+

    Cut based analysis cross-checks

    KS to p+p-

    ML fit results

    Gianluca Cavoto - Roma


    B p 0 p p 0 k

    B+p0p+, p0 K+

    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


    Charmless hadronic b decays at babar

    B fK(*)

    Max likelihood fit projection

    fK0

    fK*+(K+p0)

    fK*+(K0p+)

    fK-

    Gianluca Cavoto - Roma


    Summary

    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 ( p+p-)

    Gianluca Cavoto - Roma


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