Results of BABAR experiment
on CP violation and B physics
L.Lista
INFN Sezione di Napoli
Gr. I , 10/9/01
Luca Lista
Outline
• Experimental set-up
• CP asymmetries
 sin2b
 sin2eff
• B Mixing and lifetime
• Rare B decays
• Conclusions
(Many topics will be skipped)
Gr. I , 10/9/01
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(4S)
The PEP-II B-Factory
center of mass energy
 MU(4S) =10.58 GeV/c2
bg = 0.56
PEP-II at SLAC
Low Energy Ring
[e+, 3.1GeV]
BaBar
High Energy Ring
[e-, 9.0GeV]
Gr. I , 10/9/01
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Integrated Luminosity
32 Million Y(4S) decays recorded
• BaBar recorded:
37.7fb-1
4.05 fb-1 off peak
• Top luminosity:
• 3.4x1033 cm-2s-1
• Design:
3x1033 cm-2s-1
Gr. I , 10/9/01
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The BaBar detector
Electromagnetic
Calorimeter
6580 CsI(Tl) crystals
1.5T solenoid
e+
DIRC (PID)
144 quartz bars
11000 PMTs
Drift Chamber
40 axial stereo
layers
e-
Instrumented Flux Return
19 iron / 18-19 RPC layers
Gr. I , 10/9/01
Silicon Vertex Tracker
5 layers, 2-sided Si strips
Luca Lista
The Unitarity Triangle
d
s
u  Vud

c  Vcd


t  Vtd
Vus
Vcs
Vts
b
Vub 

Vcb 


Vtb 
• Quark mixing is described
by the CKM matrix
• Unitarity relations on matrix
elements lead to a triangle
in the complex plane
A=(,)
*
ud ub
*
cd cb
VV
VV
*
*
VudVub
 VcdVcb
 VtdVtb*  0

g
C=(0,0)
Gr. I , 10/9/01
VtdVtb*
VcdVcb*
Luca Lista
b
1
B=(1,0)
CP violation at asymmetric B factory
CP violation via mixing interference
B0
fCP
ACP (t ) 
B0
B0
b
t
W
W
t
d
0
B
b
C fCP 
B0
B0
F
S fCP 
F
t (ps)
Gr. I , 10/9/01
(B0d (t )  f CP )  (B0d (t )  f CP )
 C f CP cos(mBd t )  S f CP sin (mBd t )
d
@t=0
(B0d (t )  f CP )  (B0d (t )  f CP )
1 |  fCP |2
1 |  fCP |2
 2 Im  fCP
1 |  fCP |2
f   f
CP
CP
q A f CP
p AfCP
fCP eigenvalue
For “golden” bccs modes:
ACP (t )  CP sin 2 b sin (mBd t )
Luca Lista
 e-2ib
sin2b: Improvements w.r.t. run I
• More data!
• Added new modes
 c1KS, J/K*0
• Improved reconstruction
efficiency
 Improved tracking
 ~ +30% KS reconstruction eff.
• Improved vertex resolution
 New alignments
 More elaborated vertex algorithm
• Optimized KL selection taking into account the
background CP asymmetry
 Maximize (S+AB/ASB)2/(S+B), not S2/(S+B)
Gr. I , 10/9/01
Luca Lista
All sin2b CP modes
CP = +1
CP = -1
KL momentum not measured
E determined from B mass
and beam energy constraints
B0J/K0S
B0(2S)K0S
B0cK0S
B0J/K0L
N=129
(65% pur.)
N=724
EMC
Golden modes:
~30% higher efficiency than run 1:
KS efficiency improved
Gr. I , 10/9/01
IFR
Luca Lista
N=128
(56% pur.)
Fully reconstructed B flavor modes
• Cabibbo favored decays:
 B0D(*)p//a1
 B+ D(*)0 p+ , J/K+, (2S)K+
Gr. I , 10/9/01
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Mixing and CP asymmetry of B0/B0
B01 partially reconstructed
flavor tagged
B02 fully reconstructed
D*+ p - or J/K0S
e-e+
z
B1 = B0
CP modes: FCP(t)  e-|t|/tB ( 1  CP sin2b .sin md t )
B1 = B0
unmixed B0 B0
Flavour specific modes:
Fflav(t)  e-|t|/tB ( 1  cos md t )
mixed B0B0 or B0B0
Gr. I , 10/9/01
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Imperfect tagging and resolution
D = 1-2w = dilution, w = wrong tag fraction
R(t) = resolution function
B0
B0
Imperfect
tagging
e-|t|/tB (1 CP sin2b
 sin md t)
Imperfect
resolution
e-|t|/tB (1 CP D sin2b
sin md t)
e-|t|/tB (1 CP D sin2b
 sin md t)  R(t)
unmixed
mixed
e-|t|/tB (1 cos mdt)
Gr. I , 10/9/01
e-|t|/tB (1 D cos md t)
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e-|t|/tB (1 D cos mdt)
 R(t)
Fitting Procedure
• Unbinned maximum likelihood fit
• Mistag and resolution: empirical distribution
 fitted from data
• fixed in the fit:
md = 0.472 ps-1 (was extracted from the same fit in Run-I analysis)
tB = 1.548 ps
Parameter
Separate for Run I & II
Gr. I , 10/9/01
#
sample
sin2b
1 CP
w and w
8 Flavor
t resolution
16 Flavor, CP
Bkgd w
8 Sidebands
Bkgd t
12 Sidebands
Luca Lista
Largest correlation
With sin2b: 13%
Flavor misid. measurement
e
D=1-2w
Q=e(1-w)2
s(sin2b)  1/(Q)
Neural network mainly to
recover unidentified leptons
and use soft pions from D*
Gr. I , 10/9/01
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w
sin2b result
sin2b = 0.59 ± 0.14stat ± 0.05syst
Gr. I , 10/9/01
Luca Lista
Comparison of different samples
Submitted to
Phys. Rev. Lett.
On July 5 2001
Gr. I , 10/9/01
Luca Lista
Unitarity triangle
sin2b =
0.59 ± 0.14stat ± 0.05syst
Gr. I , 10/9/01
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1s
2s
Search for direct CP violation
• Assuming more than one amplitude dominate the
decay:
|| may be 1
ACP ( t )  C fCP cos( mBd t )  S fCP sin( mBd t )
•
C fCP 
S fCP 
Only CP = -1 used
1 |  fCP |2
1 |  fCP |2
 2 Im  fCP
1 |  fCP |2
 High purity, no assumption needed on CP of the background
||=0.93 ± 0.09 ± 0.03
 No evidence found (none expected from SM)
Gr. I , 10/9/01
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Systematic errors
• 0.03 from vertexing
• 0.03 from tagging
• 0.02 from background
Total 0.05
Gr. I , 10/9/01
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md measurement
preliminary
md =
0.519 ± 0.020stat ± 0.016syst ps-1
Run I only
Gr. I , 10/9/01
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Lifetime results
B
B0/B0
background
t (ps)
t (ps)
t0 = 1.546  0.032(stat)  0.022(syst) ps
t = 1.673  0.032(stat)  0.022(syst) ps
t0 /t = 1.082  0.026(stat)  0.011(syst)
Gr. I , 10/9/01
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common resolution
Charmless Hadronic Decays
• Physics motivations
Vud(s)
B0
b
{d
Vub W

u
d(s)
u
d
} p (K )
}p



Cabibbo suppressed tree diagram
B0
b
{d
W Vtd(s)
Vtb
t
}
}
u
p(K)
d(s)
u
p
d
Penguin diagram
Gr. I , 10/9/01
• Significant penguin
contribution
• Direct CP violation
studies
• Measurement of  from
time-dependent
asymmetry + isospin
analysis
• Possible field for new
physics…
Luca Lista
Two body Branching fractions
> 3 sigma
p (GeV/c)
Gr. I , 10/9/01
control sample:
D*pD0, D0Kp
Run I only
Luca Lista
CP violation in B0pp: sin2eff
• Neglecting penguin pollution:
  = f e-2i(bg) = f e2i  Cpp=0, Spp= sin2
Run I + II
• Considering penguin diagrams:
 ||  1
 Cpp  0, Spp= sin2eff = sin2  f (Penguin / Tree)
 Extraction of sin2 requires the
and B0p0p0
expected ~0.3
study of B0p0p0
• Fitted simultaneously with branching fractions
• Dilutions and time resolutions taken from sin2b fit
preliminary
Spp = 0.03 +0.53-0.56  0.11
C pp = 0.25 +0.45-0.47  0.14
Gr. I , 10/9/01
ACP(Kp) = -0.07  0.08  0.02
Luca Lista
Radiative Penguin: B  K*g
Signal:
• Sensitive to top quark
couplings
 CKM matrix elements
Vtd,Vts
• Sensitive to New
Physics
 SUSY, Charged Higgs
• No CP asymmetry in the
Standard Model (< 1%)
 Possible sources
beyond SM
Gr. I , 10/9/01
B0  K*0g,
K*0  K+pBackgrounds:
e+e-  qq g
e+e-  qq  X p0
Luca Lista
B0  K*0g: yield and branching ratio
B0  K*0g
K*0  K+p
• Nsignal = 139.2  13.1 events
• Br(B0  K*0g) = (43.9  4.1  2.7)  10-6
• Br(B  Kl+l-) < 0.6  10-6 (90% C.L.)
• Br(B  K*l+l-) < 25.7  10-6 (90% C.L.)
Gr. I , 10/9/01
Luca Lista
BK, BK*
• Penguin dominated
Max Lik. Fit projections
B+K+
= (7.7 +1.6-1.4  0.8)  10-6
B+ p
< 1.4  10-6 (90% C.L.)
B+ K*+
= (9.7 +4.2-3.4  1.7)  10-6
• Possible measure of sin2b:
B0 K*0
= (8.6 +2.8-2.4  1.1)  10-6
B0 K0
= (8.1 +3.1-2.5  0.8)  10-6
Gr. I , 10/9/01
Luca Lista
Quasi 2-body and 3-body decays
B+p+
B0K0
B+K+
B0K0
B+K*+
B0K*0
= ( 6.6 +2.1-1.8  0.7 )  10-6
< 12  10-6
= ( 70  8  5 )  10-6
= ( 42 +13-11  4 )  10-6
= ( 22.1 +11.1-9.2  3.3 )  10-6
= ( 19.8 +6.5-5.6  1.7 )  10-6
B0K*0 p
< 28  10-6
B+0K+
< 39  10-6
B+0p+
< 39  10-6
B+K+pp
< 54  10-6
Potential for sin2
B+p+pp
< 22  10-6
B0p
= ( 49  13 +6-5 )  10-6
First
B0a0(980)p
Br(a0 p)= ( 6.7 +3.2-2.7  1.3 )  10-6 Observation
Gr. I , 10/9/01
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Search for direct CP violation
B  K *g  ASM  ANEW ei s ei w
*
B  K g  ASM  ANEW ei s e i w
ACP 

2
*
2
2
*
2
BK g  BK g
*
BK g  BK g
*
ANEW
sin  s sin  w
ASM
Gr. I , 10/9/01
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B  D*D(*)K
• Study of the bccs transition
Color suppressed
Color allowed
• Experimental inclusive estimate from from
BDSX, (cc)X, CX, CX (ALEPH, CLEO)
 Br(bccs) ~ 15.82.8 %
• Theoretical calculation can’t determine this low value
together with inclusive s.l. branching ratio (bcW)
 Three-body B  DDK can contribute
• Study of color suppressed modes (B D*D*K)
Gr. I , 10/9/01
Luca Lista
B  D*D(*)K
• Reconstructed
decays:







D*+ D0p+
D*0 D0p0
D*0 D0g
D0 K-p+
D0 K-p+p0
D0 K-p+p-p+
D+ K-p+p+
B+ (all modes)
NS = 11715
• Br(B0 D*D0K) = (0.280.070.05)10-2
• Br(B0 D*D*0K) = (0.680.170.17)10-2
• Br(B D*D*K) = (0.340.160.11)10-2
 First observation of color suppressed
mode other than B  (charmonium)X
Gr. I , 10/9/01
Luca Lista
B0 (all modes)
NS = 18021
B D*D*K
NS = 8.23.5
Conclusions
• sin2b extracted from 37.7 millions of BB events
sin2b = 0.59 ± 0.14stat ± 0.05syst
• CP violation established at 4.1s level
• First measurement of CP violation in B0pp
• High precision measurements of mixing
parameter and lifetimes
• High precision measurements of B decays
branching fractions
 Many newly observed decays
• Most of the results are still statistically limited
Gr. I , 10/9/01
Luca Lista
Backup slides
Gr. I , 10/9/01
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J/ K* angular analysis
J/ rest frame
K* decay plane
Channels without p0
Channels with p0
• L=0,1,2 waves
• Both CP even and odd amplitudes are
present
• Measurement of sin2b is possible
from angular analysis
f ( costr, cosK*, tr ) =
f1 |A0|2 + f2 |A|||2 + f3|A|2
|A|2 = 0.1600.032  0.014
CP odd, P wave
+ f4 Im(A||* A) + f5 Re (A0* A||)
|A|||2 = 0.2430.034  0.017
CP even, S+D wave
+ f6 Im (A0* A)
|A0|2 = 0.5970.028  0.024
CP even, S+D wave
 = arg(A/A0)=0.170.16 0.07
Time dependent CP asymmetry
dilution factor:
|| = arg(A|| /A0)=2.500.20 0.08
D = 1 – 2 |A|2 = 0.680.10
Gr. I , 10/9/01
Luca Lista
B0  D*+D*
• Cabibbo suppressed decay
• A measurement in bccd of CP
violating time-dependent asymmetry can
be performed from angular analysis
 Possible penguin contamination
Tree diagram
• Measurement of sin2b independent from
B0J/K0S
 Significant deviations from B0J/K0S
measurement of sin2b may be indication
of new physics
Penguin contribution
• Branching ration measurement of B  D(*)+D(*)-:
Gr. I , 10/9/01
Luca Lista
B0  D*+D*
Signal box
(38 events)
Background sample
(6.240.49 expected in signal box)
Br(B0D*+D*-) = (8.0  1.6  1.2)10-4
Gr. I , 10/9/01
Luca Lista
Inclusive Charmonium decays
b
B0, B
W-
d, u
c
c
J/ 
J/, (2S), c
s, d
X
• Inclusive J/ branching ratio:
Br(BJ/X)
= (1.0440.013 0.028)  10-2
Br(BJ/X dir.) = (0.7890.010 0.034)  10-2
• Inclusive (2S) branching ratio:
Br(B (2S) X) = (0.2750.020 0.029) 10-2
 (2S)ll branching ratio:
(2S) 
(2S)  
ee
(7.8  0.9 
(6.7  0.8  0.7)10-3
0.8)10-3
pp)
Br((2S)  J/
assumed from PDG
p*J/ < 2 GeV/c
• Inclusive c branching ratios:
Br(B c1 X)
= ( 0.378  0.034  0.026 )  10-2
Br(B c1 X dir.)= ( 0.353  0.034  0.024 )  10-2
Br(B c2 X)
< 0.2110-2 @ 90% C.L.
= ( 0.137  0.058  0.012 )  10-2
Gr. I , 10/9/01
J/ ee
Luca Lista
Exclusive B decays
• Main motivation:
 Channels are used for CP
violation measurements
 Kinematics selection:
 Energy substituted mass
mES 
B0J/ p0
s
 pB2 ,cm
4
• Independent on particle
mass hypotheses

First observation:
B0c1 K*0
Energy difference
in the center of mass
s
E  E B 
2
Gr. I , 10/9/01
Luca Lista
J/ production in continuum
• First observation of J/ production in
continuum
  (4S) events with p*J/>2 GeV/c
 Off-resonance events
Angular distribution
1+A cos2*
• A (all E*)
= 0.25  0.19
• A (p*>3.5 GeV) l= 0.62  0.39
se e
 
 J /X
 2.52  0.21  0.21 pb
BU ( 4 S ) J /X  4.3  104 (90%C.L.)
Gr. I , 10/9/01
 Color singles prediction: s  0.8 pb
A  –0.8,
 NRQCD (c.o.) prediction: s  2.8 pb
0.6<A<1.0
Luca Lista
Branching ratios results
Mode
Br (10-4)
B0  J/ p0
0.20  0.06  0.02
B0  J/ K*0
12.4  0.5  0.9
B+  J/ K*
B+  J/ K
B0  J/ K0(KL)
13.7  0.9  1.1
10.1  0.3  0.5
6.8  0.8  0.8
B0  J/ K0(KSp0p0) 9.6  1.5  0.7
B0  J/ K0(KSp+p) 8.5  0.5  0.6
B0  J/ K0(All)
B0  c1 K*0
B0  c1 K0
B+  c1 K+
B+  (2S) K+
8.3  0.4  0.5
B0  (2S) K0
6.8  1.0  1.1
Br(B+J/p)/
Br(B+J/K ) =
(3.910.78 0.19)10-2
Gr. I , 10/9/01
4.8  1.4  0.9
5.4  1.4  1.1
7.5  0.8  0.8
6.3  0.5  0.8
Luca Lista
RUN 1:
22.7 MBB
md measurement: the di-lepton analysis
e-e+
l+or l-
Asymmetry
z
A(z)=
l+or l-
N+ –, – + – N+ +, – –
N+ –, – + + N+ +, – –
md = 0.499 ± 0.010 ± 0.012 ps-1
Gr. I , 10/9/01
Luca Lista
Semileptonic B decays
• Determine the sign of the B from a sample of
~14000 fully reconstructed B
B0D(*)p, D(*), D(*)a1, J/K*0
B D(*)0p, J/K, (2S)K
• Lepton identified in the decay of the other B
B+
B0
B( B  eX ) 
10.4  0.5  0.4
B( B  eX )

0
B( B  eX )
0.99  0.10  0.03
Mixing corrected
Gr. I , 10/9/01
Luca Lista
bsg, B0  gg
•
mES for 0.6 <mhad < 2.0 GeV
Semi-exclusive study
 Sum of exclusive modes
K+np(n=1,2,3)
B0  gg
Gr. I , 10/9/01
Branching ratio measurement
coming soon…
• Theoretical exp.: ~ 108
• Br(B0gg) < 1.7 x 10-6 90% C.L.
• PDG: Br(B0 gg) < 3.9 x 10-5 90% C.L. (L3)
Luca Lista