L.Lista INFN Sezione di Napoli

1
L.Lista INFN Sezione di Napoli
Results of BABAR experiment on CP violation and B
physics
2
Outline

• Experimental set-up
• CP asymmetries
• sin2b
• sin2?eff
• B Mixing and lifetime
• Rare B decays
• Conclusions
• (Many topics will be skipped)

?(4S)
3
The PEP-II B-Factory
4
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

5
The BaBar detector
6
The Unitarity Triangle

• Quark mixing is described by the CKM matrix

• Unitarity relations on matrix elements lead to a
  triangle in the complex plane

?
?
?
1
7
CP violation at asymmetric B factory
CP violation via mixing interference
fCP eigenvalue
? e-2ib
For golden b?ccs modes
8
sin2b Improvements w.r.t. run I

• More data!
• Added new modes
• ?c1KS, J/?K0
• 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 (SAB/ASB)2/(SB), not S2/(SB)

9
All sin2b CP modes
hCP 1
IFR
B0?J/?K0L
KL momentum not measured DE determined from B
mass and beam energy constraints
N129 (65 pur.)
hCP -1
B0?J/?K0S B0??(2S)K0S B0??cK0S
N724
EMC
N128 (56 pur.)
Golden modes 30 higher efficiency than run 1
KS efficiency improved
10
Fully reconstructed B flavor modes

• Cabibbo favored decays
• B0?D()-p/r/a1
• B? D()0 ? , J/??K, ?(2S)K

11
Mixing and CP asymmetry of B0/B0
CP modes FCP?(Dt) ? e-Dt/tB ( 1 ? hCP sin2b .
sin Dmd Dt )
Flavour specific modes
Fflav?(Dt) ? e-Dt/tB ( 1 ? cos Dmd Dt )
mixed B0B0 or B0B0
12
Imperfect tagging and resolution
D 1-2w dilution, w wrong tag fraction R(Dt)
resolution function
Imperfect tagging
Imperfect resolution
B0 B0
e-Dt/tB (1? hCP sin2b ? sin Dmd Dt)
e-Dt/tB (1? hCP D sin2b ?sin Dmd
Dt)
e-Dt/tB (1? hCP D sin2b ? sin Dmd Dt) ?
R(Dt)
unmixed mixed
e-Dt/tB (1? cos DmdDt)
e-Dt/tB (1? D cos Dmd Dt)
e-Dt/tB (1? D cos DmdDt) ? R(Dt)
13
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 sample
sin2? 1 CP
w and ?w 8 Flavor
?t resolution 16 Flavor, CP
Bkgd w 8 Sidebands
Bkgd ?t 12 Sidebands
Separate for Run I II
Largest correlation With sin2b 13
14
Flavor misid. measurement
e
w
D1-2w Qe(1-w)2 s(sin2b) ? 1/?(Q)
Neural network mainly to recover unidentified
leptons and use soft pions from D
15
sin2b result
sin2b 0.59 0.14stat 0.05syst
16
Comparison of different samples
Submitted to Phys. Rev. Lett. On July 5 2001
17
Unitarity triangle
sin2b 0.59 0.14stat 0.05syst
18
Search for direct CP violation

• Assuming more than one amplitude dominate the
  decay
• ? may be ?1
• Only ?CP -1 used
• High purity, no assumption needed on CP of the
  background
• No evidence found (none expected from SM)

?0.93 0.09 0.03
19
Systematic errors

• 0.03 from vertexing
• 0.03 from tagging
• 0.02 from background
• Total 0.05

20
Dmd measurement
preliminary
Dmd 0.519 0.020stat
0.016syst ps-1
Run I only
21
Lifetime results
B?
B0/B0
background
Dt (ps)
Dt (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)
common resolution
22
Charmless Hadronic Decays

• Physics motivations

• Significant penguin contribution
• Direct CP violation studies
• Measurement of ? from time-dependent asymmetry
  isospin analysis
• Possible field for new physics

p-(K-)
Vud(s)
d(s)
W-
Vub

b
p
u
B0
Cabibbo suppressed tree diagram
p-(K-)
Vtd(s)
W-
d(s)
Vtb
p
b

u
t
B0
Penguin diagram
23
Two body Branching fractions
control sample D??D0, D0?K-?
gt 3 sigma
Run I only
p (GeV/c)
24
CP violation in B0???- sin2aeff

• Neglecting penguin pollution
• ? ?f e-2i(???) ?f e2i? ? C??0, S?? sin2?
• Considering penguin diagrams
• ? ? 1
• C?? ? 0, S?? sin2?eff sin2? ? f (Penguin /
  Tree)
• Extraction of sin2? requires the study of B0??0?0
  and B0??0?0
• Fitted simultaneously with branching fractions
• Dilutions and time resolutions taken from sin2b
  fit

Run I II
expected 0.3
preliminary
S?? 0.03 0.53-0.56 ? 0.11 C ?? 0.25
0.45-0.47 ? 0.14
ACP(Kp-) -0.07 ? 0.08 ? 0.02
25
Radiative Penguin B ? K?
Signal B0 ? K0?, K0 ?
K?- Backgrounds ee- ? qq ? ee- ? qq ? X
?0

• Sensitive to top quark couplings
• CKM matrix elements Vtd,Vts
• Sensitive to New Physics
• SUSY, Charged Higgs
• No CP asymmetry in the Standard Model (lt 1)
• Possible sources beyond SM

26
B0 ? K0? yield and branching ratio
B0 ? K0? K0 ? Kp-

• Nsignal 139.2 ? 13.1 events
• Br(B0 ? K0?) (43.9 ? 4.1 ? 2.7) ? 10-6
• Br(B ? Kll-) lt 0.6 ? 10-6 (90 C.L.)
• Br(B ? Kll-) lt 25.7 ? 10-6 (90 C.L.)

27
B??K, B??K

• Penguin dominated

Max Lik. Fit projections

• B??K (7.7 1.6-1.4 ? 0.8) ? 10-6
• B ??p lt 1.4 ? 10-6 (90 C.L.)
• B ??K (9.7 4.2-3.4 ? 1.7) ? 10-6
• Possible measure of sin2b
• B0 ??K0 (8.6 2.8-2.4 ? 1.1) ? 10-6
• B0 ??K0 (8.1 3.1-2.5 ? 0.8) ? 10-6

28
Quasi 2-body and 3-body decays

• B??p ( 6.6 2.1-1.8 ? 0.7 ) ? 10-6
• B0??K0 lt 12 ? 10-6
• B???K ( 70 ? 8 ? 5 ) ? 10-6
• B0???K0 ( 42 13-11 ? 4 ) ? 10-6
• B??K ( 22.1 11.1-9.2 ? 3.3 ) ? 10-6
• B0??K0 ( 19.8 6.5-5.6 ? 1.7 ) ? 10-6
• B0?K0 p lt 28 ? 10-6
• B??0K lt 39 ? 10-6
• B??0p lt 39 ? 10-6
• B?Kpp- lt 54 ? 10-6
• B?ppp- lt 22 ? 10-6
• B0???p ( 49 ? 13 6-5 ) ? 10-6
• B0?a0(980)?p
• ?Br(a0 ??p) ( 6.7 3.2-2.7 ? 1.3 ) ? 10-6

Potential for sin2a
?
First Observation
?
29
Search for direct CP violation
30
B ? DD()K

• Study of the b?ccs transition
• Experimental inclusive estimate from from B?DSX,
  (cc)X, ?CX, ?CX (ALEPH, CLEO)
• Br(b?ccs) 15.8?2.8
• Theoretical calculation cant 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? DD-K)

Color allowed
Color suppressed
31
B ? DD()K

• Reconstructed decays
• D? D0p
• D0? D0p0
• D0? D0g
• D0? K-p
• D0? K-pp0
• D0? K-pp-p
• D? K-pp
• Br(B0? DD0K) (0.28?0.07?0.05)?10-2
• Br(B0? DD0K) (0.68?0.17?0.17)?10-2
• Br(B? DD-K) (0.34?0.16?0.11)?10-2
• First observation of color suppressed mode other
  than B ? (charmonium)X

B0 (all modes) NS 180?21
B (all modes)NS 117?15
B? DD-K NS 8.2?3.5
32
Conclusions

• sin2? extracted from 37.7 millions of BB events
• sin2b 0.59 0.14stat 0.05syst
• CP violation established at 4.1? level
• First measurement of CP violation in B0?????
• 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

33
Backup slides
34
J/? K angular analysis
J/? rest frame K decay plane
Channels without p0
Channels with p0

• L0,1,2 waves
• Both CP even and odd amplitudes are present
• Measurement of sin2b is possible from angular
  analysis

• f ( cos?tr, cos?K, ?tr )
• f1 A02 f2 A2 f3A?2
• f4 Im(A A?) f5 Re (A0 A)
• f6 Im (A0 A?)

A?2 0.160?0.032 ? 0.014 CP odd, P wave
A2 0.243?0.034 ? 0.017 CP even, SD wave
A02 0.597?0.028 ? 0.024 CP even, SD wave
?? arg(A?/A0)-0.17?0.16 ?0.07
? arg(A /A0)2.50?0.20 ?0.08
Time dependent CP asymmetry dilution factor D
1 2 A?2 0.68?0.10
35
B0 ? DD-

• Cabibbo suppressed decay
• A measurement in b?ccd of CP violating
  time-dependent asymmetry can be performed from
  angular analysis
• Possible penguin contamination
• Measurement of sin2b independent from B0?J/?K0S
• Significant deviations from B0?J/?K0S measurement
  of sin2b may be indication of new physics

Tree diagram
Penguin contribution

• Branching ration measurement of B ? D()D()-

36
B0 ? DD-
Br(B0?DD-) (8.0 ? 1.6 ? 1.2)?10-4
37
Inclusive Charmonium decays
c
J/?, ?(2S), ?c
b
c
W-
B0, B-
s, d
X
d,
u

• 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)?ll- branching ratio
• ?(2S) ? ee- (7.8 ? 0.9 ? 0.8)?10-3
• ?(2S) ? ??- (6.7 ? 0.8 ? 0.7)?10-3
• 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) lt 0.21?10-2 _at_ 90 C.L.
  ( 0.137 ? 0.058 ? 0.012 ) ? 10-2

Br(?(2S) ? J/?pp-) assumed from PDG
38
Exclusive B decays

• Main motivation
• Channels are used for CP violation measurements
• Kinematics selection
• Energy substituted mass
• Independent on particle mass hypotheses
• Energy difference in the center of mass

B0?J/? ?0
First observation B0??c1 K0
39
J/? production in continuum

• First observation of J/? production in continuum
• ? (4S) events with pJ/?gt2 GeV/c
• Off-resonance events

Angular distribution ?1A cos2q

• A (all E) 0.25 ? 0.19
• A (pgt3.5 GeV) l 0.62 ? 0.39

• Color singles prediction ? ? 0.8 pb A ?
  0.8,
• NRQCD (c.o.) prediction ? ? 2.8 pb 0.6ltAlt1.0

40
Branching ratios results
Mode Br (?10-4)
B0 ? J/? ?0 0.20 ? 0.06 ? 0.02
B0 ? J/? K0 12.4 ? 0.5 ? 0.9
B ? J/? K 13.7 ? 0.9 ? 1.1
B ? J/? K 10.1 ? 0.3 ? 0.5
B0 ? J/? K0 (KL) 6.8 ? 0.8 ? 0.8
B0 ? J/? K0 (KS??0?0) 9.6 ? 1.5 ? 0.7
B0 ? J/? K0 (KS???-) 8.5 ? 0.5 ? 0.6
B0 ? J/? K0 (All) 8.3 ? 0.4 ? 0.5
B0 ? ?c1 K0 4.8 ? 1.4 ? 0.9
B0 ? ?c1 K0 5.4 ? 1.4 ? 1.1
B ? ?c1 K 7.5 ? 0.8 ? 0.8
B ? ?(2S) K 6.3 ? 0.5 ? 0.8
B0 ? ?(2S) K0 6.8 ? 1.0 ? 1.1
Br(B?J/??)/ Br(B?J/?K ) (3.91?0.78 ?0.19)?10-2
RUN 1 22.7 MBB
41
Dmd measurement the di-lepton analysis
Dmd 0.499 0.010 0.012 ps-1
42
Semileptonic B decays

• Determine the sign of the B from a sample of
  14000 fully reconstructed B
• B0?D()-?, D()-?, D()-a1, J/?K0
• B- ?D()0?, J/?K, ?(2S)K
• Lepton identified in the decay of the other B

B
B0
Mixing corrected
43
b?s?, B0 ? ??
mES for 0.6 ltmhad lt 2.0 GeV

• Semi-exclusive study
• Sum of exclusive modesKnp (n1,2,3)

Branching ratio measurementcoming soon
B0 ? ??

• Theoretical exp. 10-8
• Br(B0???) lt 1.7 x 10-6 90 C.L.
• PDG Br(B0 ???) lt 3.9 x 10-5 90 C.L. (L3)