1. Sin(2β) measurement with b→c transitions in BaBar
Marco Bomben
Università degli Studi & INFN – Trieste
On behalf of BaBar Collaboration

2. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
Outline
Introduction
Motivations
CPV measurements at B-factories
charmoniumK0
J/Ψπ0
D(*)+D(*)-
Results
Conclusions
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

3. Outline Introduction charmoniumK0 J/Ψπ0 D(*)+D(*)- Results Conclusions
Motivations
CPV measurements at B-factories
charmoniumK0
J/Ψπ0
D(*)+D(*)-
Results
Conclusions
I will focus on these two analyses
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

4. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
Motivations
CPV has been observed first in neutral Kaon system and then in B mesons.
It can be explained in SM via quark mixing matrix (CKM)
complex phase changes sign under CP application d s b u
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb c t
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

5. Time evolution of the B0 meson
The time-dependent rate for B0 (f+) or B0 (f−) decays to a final state f is:
Δt ≡ decay time
where , , ,
aCP is the time-evolution asymmetry:
If f is a CP eigenstate, fCP, we have CP violation if λf ≠ ±1:
|q/p | ≠ 1 (CP violation in mixing, negligible in SM)
|Af /Af | ≠ 1 (direct CP violation, small in b→ccs)
Im(λf ) ≠ 0 (interference between mixing and decay)
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

6. CPV measurements at B-factories
We need to know the flavour of the B at a reference t=0.
Dz = Dt gbc
At t=0 we know this meson is B0
BCP
B 0
(4S)
bg =0.56
In this example, the tag-side meson decays first.
It decays semi-leptonically and the charge of the lepton gives the flavour of the tag-side meson :
l - = B l + = B 0.
(Kaon and pion tags also used)
tag
l - (e-, m -) vl
B 0
The two mesons oscillate coherently : at any given time, if one is a B0 the other is necessarily a B0
Dt picoseconds later, the B 0 (or perhaps it is now a B 0) decays.
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

7. Exclusive B decay reconstruction
Likelihood fits with discriminating variables:
Kinematics:
Particle ID: , K, e, , …
Event shape variables, to separate the continuum bkgd (use “off-resonance” data as control sample!!!)
Efficiency
Typically 1540%
Purity
Up to 97% (for J/KS)
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

8. Charmonium K0 modes
“Golden” modes: tree diagrams dominate; the t-quark penguin has the same weak phase as the tree, so the measured SM quantity is sin2β
SM prediction: Cf=0 →ACP(Δt) = Sf sin(ΔmΔt)
B→J/ψK0~8.5x10-4
B→ψ(2S)K0~6.2x10-4
B→χc1K0~4x10-4
B→ηcK0~1.2x10-3
Experimentally very clean!
Many accessible decay modes
with (relatively) large BFs
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

9. Charmonium K0: details (I)
BCP sample
B→J/ψK0
J/ψ → e e, μ μ
Ks0 → π π
KL0 : cluster
B→ψ(2S)K0
ψ(2S) → e e, μ μ, J/ψ γ
B→χc1K0
χc1 → J/ψ γ
B→ηcK0
ηc → K0K+ π-
Bflav sample
B→D*- π+
B→D*- ρ+
B→D*- a1+
B→D- π+
B→J/ψK*0(K*0→K+ π-)
B- sample
B-→D0 π-
B-→D*0 π-
B-→J/ψK-
B-→ψ(2S)K-
B-→χc1K-
B-→J/ψK*-(K*-→K- π0)
For tagging performance and resolution studies
Control sample
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

10. Charmonium K0: details (II)
ICHEP 06
Reference: hep-ex/
Using ~ 315 Υ(4S) KL KS
Flavor
eigenstates
K*0
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

11. Charmonium K0: results Raw CP asymmetry Mistag dilution
Final state CP eigenvalue
We determine sin2β with a simultaneous ML fit to the Δt distribution of the
tagged BCP and Bflav samples
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

12. Charmonium K0 systematics
2006
2004
Improved CP background descriptions
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

13. Charmonium K0 : world average
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

14. J/ψπ0 and Sin(2β) Potential penguin pollution
Tree amplitude:
Potential penguin pollution
b→d penguin amplitude has different weak & strong phases with respect to tree.
Adding penguins
δ≡relative strong phase between P and T.
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

15. J/ψπ0: details B→J/ψπ0 J/ψ → e e, μ μ π0 → γ γ
Data (points)
Total PDF
Signal PDF
Background PDF
Using fb-1:
1318 on-peak events
(signal efficiency is 22.0%)
BR(B→J/ψπ0) =(1.94±0.22±0.17) x 10-5
Reference: hep-ex/ , Phys.Rev. D74 (2006)
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

16. J/ψπ0: results B0→ J/ψπ0 updated(*) measurement S = -0.68 ±0.30 ±0.04
C = ±0.26 ±0.09
(*)consistent with previous results
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

17. J/ψπ0: results B0→ J/ψπ0 updated(*) measurement S = -0.68 ±0.30 ±0.04
Consistent with a SM tree-dominated amplitude
B0→ J/ψπ0 updated(*) measurement
S = ±0.30 ±0.04
C = ±0.26 ±0.09
(*)consistent with previous results
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

18. J/ψK0 and penguin contribution
Using B0→ J/ψπ0 results we can extract estimate on penguin contribution to B0→ J/ψK0
ΔS = S(J/ψK0) - sin2β = ±0.012
95% probability
M. Ciuchini, M. Pierini and L.Silvestrini,
PRL 95, (2005)
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

19. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
J/ψπ0: systematics
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

20. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
J/ψπ0: world average
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

21. Sin2β from b→c: world average
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

22. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
Conclusions
BABAR measures sin2β in charmoniumK0 modes to 5% precision
sin2β ccK0=0.710±0.034±0.019
J/Ψπ0 could give info on penguin pollution but results indicate that amplitude is tree-dominated
S=-0.68±0.30±0.04
Both measurements are still limited by statistics
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

23. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

24. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
Backup slides
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

25. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
D(*)+ D(*)- and Sin(2β)
D(*)D(*) modes: the tree diagram still dominates (but is Cabibbo-suppressed); the penguin is comparatively larger and has a different weak phase – contamination
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

26. D(*)+ D(*)- : details (I)
210.5 fb-1 of On Peak data
2 analysis:
D(*)+ D- PRL 95, (2005)
D*+ D*- PRL 95, (2005)
D*+→D0π+ , D+π0
D0 →Kπ, Kππ0, K πππ, Ksππ
D+ →K-π+π+ , Ksπ+, K+K-π+ (only D*+ D*-)
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

27. D(*)+ D(*)- : details (II)
VV decay: both CP-odd and CP-even fraction are present
Angular analysis is required
Result: fodd = 0.125±0.044±0.070
D*+D −, D*−D+, D+D−
Nsig = 391 ± 28
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

28. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
D(*)+ D(*)- : results
D*+D*-
S+=-0.75±0.25±0.03
C+=+0.06±0.17±0.03
D*+D−, D*−D+, D+D−
SDD=-0.29±0.63±0.06
CDD=+0.11±0.35±0.06
SD*+D-=-0.54±0.35±0.07
CD*+D-=+0.09±0.25±0.06
SD*-D+=-0.29±0.33±0.07
CD*-D+=+0.17±0.24±0.04
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

29. D(*)+ D(*)- : world average
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

30. D(*)+ D(*)- : systematics
The systematic uncertainties on Sf and Cf are separately evaluated for each of the decay modes. The dominant systematic uncertainty is the precision to which we are able to ascertain, using a Monte Carlo simulation, that the measurement method is unbiased (giving systematic uncertainties in the range ). Other important uncertainties are due to the amount of peaking background and its potential CP asymmetry ( ); assumptions on the Δt resolution function ( )
D*+D*-
The systematic uncertainties on C+ and S+ arise from the amount of possible backgrounds that tend to peak under the signal and their CP asymmetry, the assumed parameterization of the t resolution function,
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

31. DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste
Sin(2β) : world average
PREDICTIONS: sin 2β = ± (from UT sides) sin 2β = ± (from UT sides + εK) sin 2β = ± (all constraints) MEASUREMENT: sin 2β = ± (from b → ccs)
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

32. Resolutions Variables that reflect energy and momentum conservation:
peaking for fully reconstructed B decays, smooth for combinatorial background
resolution ~ 2.5 – 3.0 MeV
depending on presence of neutrals in the final state
resolution ~ 15 – 80 MeV
continuum background in the Grand Side Band
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

33. Tagging: efficiency and effects
The figure of merit for tagging is the
effective tagging efficiency Q ≡ Σi εi(1 − 2wi)2 = (30.4±0.3)%
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste

34. J/ψπ0: penguin contribution
M. Ciuchini, M. Pierini and L. Silvestrini, PRL 95, (2005)
Potential effect on S and C
|P2GIM-P2|=0.27± 0.27
10/31/2006
DPF06 meeting, Honolulu Hawaii Marco Bomben - Trieste