Hot Topics from BABAR

Christos Touramanis

FPCP 2006, April 9, Vancouver, Canada

C. Touramanis - FPCP 2006 2

Contents

Recent BABAR results:

• B→ρ+ρ0

• B→a1+π-

• T, CP, and CPT studies in B mixing with dileptons• FCNC search in charm decays• Flavor-tagged charm in B decays

C. Touramanis - FPCP 2006 3

Motivation: member of the B→ρρ isospin family: current most sensitive probe of the UT angle α

Data sample: 232M B-pairs

Previous results: (from <100M B-pairs)

0B ρ ρ± ±→

( )3.8 66.77.1 10

0.95 0.11 0.020.00 0.22

Belle, PRL 91, 221801 (2003)

31.7

0.03

STAT SYST

L STAT SYST

CP STAT SYST

BF

fA

+ −−= ±

= ± ±= ± ±

( )5.7 65.4

0.030.07

BA

5.

BAR, PRL 91, 1718

8 10

0.97 0.040.19 0.23 0.0

02 (200

22

3)

.5

3

STAT SYST

L STAT SYST

CP STAT SYST

BF

fA

+ −−

+−

= ±

= ±

= − ± ±

( ) 617.2BABAR

2.prelimina

5 2.8 1r

0y

STAT SYSTBF −= ± ±

C. Touramanis - FPCP 2006 4

Helicity basis (λ=0,+1,-1):the λ=0 state is a CP-even mixture of S and D waves (longitudinal polarization)

is the fraction of longitudinal component

0B ρ ρ± ±→

Longitudinal dominance in all observed modesIsospin analysis (ignoring EW penguins)Penguin pollution smaller than 2-pion systemBest reach in UT angle α

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Improved analysis, main features:• PID: proton, electron, kaon veto• D0 mass veto• Efficiency: 8.4% (long. pol.), 18.6% (transv.

pol.)• Extended likelihood fit using:

– mES, ∆E– Rho masses and decay angles θ– Neural Net (8 variables, B versus continuum)

• Event categories:– Signal, reconstructed correctly– Signal, self-crossfeed– B backgrounds: 16 types– Continuum

• Fitted sample: 65,500 events• Signal yield: 334±46 events

0B ρ ρ± ±→

ESm

E∆

Likelihood-enhanced plots~1/3 of signal

~0.8% of background

( ) 62.5 2.8 100.96 0.04 0.05

0.10 0.1

1

4 0.

7

09

.2 STAT SYST

L STAT SYST

CP STAT SYST

BFf

A

−= ± ±

= ± ±

= − ± ±

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Motivation:• test of factorization• poor knowledge of a1 parameters• possibly UT angle α in futureData sample: 218M B-pairs

Prediction (BSW): few times 10-5

Previous limits: few times 10-4 (CLEO, DELPHI)

01 (1260)B a π±→ ∓

( )0 61 1

hep-ex/060305016.6

9.( (1260) ) ( (1260) ) 1.9 1.5 10

significance

BABAR preliminary ( )

: 2 STAT SYSTBF B a BF a π

σπ π π± ± ± ± −→ × → = ± ±∓ ∓

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01 (1260)B a π±→ ∓

• PID: proton, electron, kaon veto• Vertex fit cut (at 0.01 probability)• Efficiency: 11.7%• Extended likelihood fit:

– mES, ∆E– resonance mass (relativistic B-W, mass-dependent width)– Fisher (B versus continuum)– Angular variable to distinguish from spin-2 a2(1320) and spin-0

π(1300) – no significant yield found– No separation of (ππ)ρπ and (ππ)σπ – dominated by ρπ

• Fitted sample: 35,285 events• Signal yield: 421±48 events

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01 (1260)B a π±→ ∓

a1(1260) mass:

( )

( )( ) 2

2

2

2

PDG mean 1230 40

width 250 600Our 1229 21result mean

393 62width

MeV c

MeV c

MeV c

MeV c

= ±

=

±=

±

−

=

( )0 61 1 16.6

9( (1260) ) ( (1260) ) 1.9 1.5 10

significance .2: STAT SYSTBF B a BF a π π π

σπ± ± ± ± −→ × → = ± ±∓ ∓

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Dileptons: T, CP, CPTPhysical Bd states:

|q/p|≠1 violates CP and T in mixingz≠0 violates CP and CPT in mixing

Time-independent asymmetryProbes CP,T violation in mixing|q/p| small (~10-3) in SM

Time-dependent asymmetryProbes CP,CPT violation in mixingSensitive to Imz, ∆ΓxRez

(hep-ex/0603054)

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Dileptons: T, CP, CPT

b c s

− +DirectLepton

CascadeLepton

Semileptonic decays: lepton sign determines B flavour at decay timeNeed to take into account:• Cascade leptons• Charm flight• All possible combinations

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Dileptons: T, CP, CPT

• Data sample: 232M B-pairs• Event selection:

– Fox-Wolfram moments, invariant mass, aplanarity, track multiplicity

– Tight lepton PID– Photon conversion and charmonium veto

• Event types in fit:– Signal (both leptons, 81% of B pair events)– Direct – cascade leptons from the two B mesons (9%)– Direct – cascade leptons from the same B meson (4%)– b→ τ→(e or µ) (3%)– Charmonium leptons (3%)

C. Touramanis - FPCP 2006 12

Dileptons: T, CP, CPTResults:

70%

cor

rela

tion

Ext

ensi

ve u

se o

f re

al d

ata

cont

rol s

ampl

es

C. Touramanis - FPCP 2006 13

Search for FCNC in charm decays

• FCNC: rare decays, ideal for NP searches• So far big activity in b→sll, b→sγ, s→dll, s→dνν

• FCNC in c→ull strongly suppressed by GIM cancellations• SM expectations for D→Xul+l- at ~10-8

• Intermediate resonances expected at ~10-6

• Need to veto resonances in l+l- invariant mass• Example:

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Search for FCNC in charm decays• Data sample: 288fb-1

• Channels investigated: D+, DS+, Λc

+ to (π, K, p)(ee, µµ, eµ)• Event selection:

– Tight lepton PID– Track counting, event shape: Bhabha, ISR, two-photon rejection– Lepton vertex and total energy, momentum: B decays rejection– Photon conversion veto

• Normalization modes:– Known D decays used for normalization– Cancellation of many non-PID systematic errors

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Search for FCNC in charm decaysFit results and upper limits

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Flavor tagged charm production in B decays

• Charm hadrons decay to D, DS, ΛC

• Full reconstruction of one B in the event and the charm hadron on the other side allows flavor-specific charm counting

• First results published in PRD 70, 091106(R)• Improved analysis using 231M B-pairs

• b→cW*- : dominant, correlated cproduction, rate close to 100%

• W- decays: anti-correlated cproduction, lower rate

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Flavor tagged charm production in B decaysFully reconstructed B candidates in B→D(*)(π,ρ,a1)

B+ 0B

Number of B extracted from fitsSmall neutral (charged) cross-feed estimated from MC (~3%)

200,359±705 110,735±424

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Flavor tagged charm production in B decaysCharm counting in 2-d likelihood fit (mES, charmed hadron mass)

B−

2

All disctributions:Charmed Hadron Mass ( c )GeV

NEW

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Flavor tagged charm production in B decaysResults: B branching fractions

B− 0B

: charmedhadron

C

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SummaryNew BABAR results presented for:

• B→ρ+ρ0 (improved precision)

• B→α1+π- (first observation)

• T, CP, and CPT studies in B mixing with dileptons(improved precision and new measurements)

• FCNC search in charm decays (first BABAR results; best limits in 15 channels)

• Flavor-tagged charm in B decays (new results, improved precision)

( ) 62.5 2.8 1.2 017 STAT SYST−± ±

( )0 61 1 16.( (1260) ) ( (1260) ) 1.9 5 06 1. 1STAT SYSTBF B a BF aπ π π π± ± ± ± −→ × → = ± ±∓ ∓