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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
C. Touramanis - FPCP 2006 5
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
−= ± ±
= ± ±
= − ± ±
C. Touramanis - FPCP 2006 6
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± ± ± ± −→ × → = ± ±∓ ∓
C. Touramanis - FPCP 2006 7
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
C. Touramanis - FPCP 2006 8
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± ± ± ± −→ × → = ± ±∓ ∓
C. Touramanis - FPCP 2006 9
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)
C. Touramanis - FPCP 2006 10
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
C. Touramanis - FPCP 2006 11
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:
C. Touramanis - FPCP 2006 14
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
C. Touramanis - FPCP 2006 15
Search for FCNC in charm decaysFit results and upper limits
C. Touramanis - FPCP 2006 16
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
C. Touramanis - FPCP 2006 17
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
C. Touramanis - FPCP 2006 18
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
C. Touramanis - FPCP 2006 19
Flavor tagged charm production in B decaysResults: B branching fractions
B− 0B
: charmedhadron
C
C. Touramanis - FPCP 2006 20
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± ± ± ± −→ × → = ± ±∓ ∓
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