1. Quantum-correlated D-decays at CLEO-c
HEP 2009
16-22 July 2009, Krakow, Poland
Quantum-correlated D-decays at CLEO-c
Stefania Ricciardi (RAL)
for the CLEO Collaboration
- Content -
First measurement of the strong-phase difference DdD between D0 and D0 decays to KSp+p-
Preliminary results on DdD between D0 and D0 to KSK+K-
Including their impact on the CKM angle g (f3)

2. Quantum-correlation at CLEO-c
818 pb-1 accumulated in
e+e- →y(3770)
Just above open-charm threshold
Coherent decay of
y(3770) → D0D0
 Reconstructing one D decay in a CP eigenstate (CP-tag) allows one to infer CP of the other D (decay mode of interest)
CP(signal) = -1 x CP(tag)
e.g., decay mode of interest is
D0 → KSp+p- (mixed CP)
CP(KSpp vs CP-even tag) = -1
CP(KSpp vs CP-odd tag) = +1
KSpp vs
CP+
Ksr
KSpp vs
CP-
Coherence in CLEO-c data:
CP+ and CP-
show different resonant structures
EPS HEP 2009
Stefania Ricciardi

3. Cleo-c clean environment
 useful kinematic constraints, e.g.:
Mbc  excellent signal purity
KSpp
Mbc = (E2beam-pD2)
M2missing for
reconstruction of KL
KSpp vs K-p+
Threshold running advantages:
very clean environment
no fragmentation particles
efficient reconstruction of both D decays
KLpp
EPS HEP 2009
Stefania Ricciardi

4. DdD from quantum-correlated data: the principle
D0 → K+ e- ne
D0 → KS p+ p-
DCP+ → K+ K-
DCP- → KS p+ p-
Y(3770)
Y(3770)
Flavour tagged
|D0|2 or |D0|2
CP-tagged
|D0|2 + |D0|2 ±2|D0||D0| cos(DdD)
cos(DdD) from CP-tagged decays without model assumptions on the intermediate resonances
In addition, mixed CP-tagged decays, sensitive to both cos(DdD) and sin(DdD)
EPS HEP 2009
Stefania Ricciardi

5. Crucial role of DdD in the measurement of the CKM-angle gB-
D0K-
D0K-
B± decay rates
depend on the
relative phase differences
between the two interfering amplitudes,
therefore on and on
(KSpp)K-
Unbinned fit used to extract g, rB and dB from B→D(Ksh+h-)K distributions in the D Dalitz plane. Relies on a model of the D-decay amplitude
Model introduces a systematic uncertainty of
BaBar [PRD 78(2008)034023]: KSππ ~7º
Belle [ArXiv: [hep-ex]]: KSππ ~9º
BaBar [PRD 78(2008)034023]: KSππ + KSKK ~5º
Model Systematic
hard to quantify
Will limit LHCb and
future B-experiments
EPS HEP 2009
Stefania Ricciardi

6. Model-independent method
Discrete measurements of DdD in Dalitz plane bins are sufficient to extract g
in a model-independent way [GGSZ, PRD 68(2003)054018]
Ti = i |AD(x,y)|2 dxdy
from flavour specific D decays
ci and si are weighted averages of cosine and sine of DdD in bin I (flavour-amplitude weighted)
These coefficients are simple functions of
CP, mixed-CP, and flavour-tagged D→Kshh decay yields in bin i (and –i)
EPS HEP 2009
Stefania Ricciardi

7. DdD between D0 and D0 decays to K0p+p-
ArXiv: [hep-ex] accepted by PRD

8. D0→KSp+p-: DdD binning Bins of equal size in DdD
give best sensitivity for g
Bin boundaries assume a D0 decay model (BaBar isobar model, PRL 95 (2005)121802)
..but NO model error!
[Bondar & Poluektov, EPJ C 55(2008) 51; EPJ C47 (2006) 347]
No bias in g extraction with binned method and phase binning.
Limited model accuracy may affect the g statistical precision only
Phase binning of the D0→ Kspp plane
EPS HEP 2009
Stefania Ricciardi

9. KSp+p- and KLp+p- Data Samples (Cleo-c, 818 pb-1)
Both KSpp and KLpp are used in the measurement to reduce statistical error
Data yields:
~ 20,000 Flavour-tags → Ti
~1, CP-tags → ci
~1, KSp+p → ci and si
Signal to background
~10 to ~100 depending on mode
EPS HEP 2009
Stefania Ricciardi

10. KSp+p- and KLp+p- vs CP-tags
Kshh vs CP ~ KLhh vs CP
O(tan2qc) corrections to approximate equality
introduce a small model systematic error
EPS HEP 2009
Stefania Ricciardi

11. Broad agreement between
Results on ci and si
Two sets of coefficients extracted
ci, si for KSpp
ci,’ si’ for KLpp
Broad agreement between
measured values
and predicted values
from BaBar model
Central values ± stat.±syst. ± (KLpp Kspp syst)
Separate systematic uncertainty to account for KLpp Kspp model difference (model predicted differences
Dci = ci’-ci and Dsi=si’-si
used as constraint in the simultaneous fit)
Statistic uncertainty dominant
EPS HEP 2009
Stefania Ricciardi

12. Impact on CKM angle g Impact estimated with toy MC study
Large sample of B+→D(KSp+p-)K+ data generated with
g = 60 °
dB =130°
rB =0.1
~1.7° residual error on g due to finite knowledge of ci and si
[Instead of model error (~7°-9°)]
G.Wilkinson, Charm09
Extrapolated total error for
B+→D(KSp+p-)K+ at LHCb
After 10 fb-1, if rB=0.1
Unbinned fit with model assumptions:
8.5° (systematic dominated)
Binned fit with Cleo-c input:
6° (statistics dominated)
EPS HEP 2009
Stefania Ricciardi

13. DdD between D0 and D0 decays to K0K+K-
Preliminary Results (new)

14. ΔδD (K0K+K-) binning
ΔδD bins boundaries defined using the BaBar model for D0→KSK+K- decay amplitude
Simpler resonant structure than D0 → Ksp+p- predicted, but branching fraction ~1/6
BaBar model
[PRD 78, (2008)]
EPS HEP 2009
Stefania Ricciardi

15. ΔδD (K0K+K-) binning
ΔδD bins boundaries defined using the BaBar model of D→KSK+K- decay amplitude
Toy MC predicts good sensitivity to g for 3 bins
[PRD 78, (2008)]
BaBar model 1 2 3
C.M.Thomas’ courtesy
EPS HEP 2009
Stefania Ricciardi

16. KsK+K- and KLK+K- data samples
Tag Modes
KSKK
KLKK
K+K- , π+π, KSπ0π0 
KSπ0, KSη(γγ), KSη(π+π-π0), KSω(π+π-π0), KSη’(π+π-η)
KLπ0, KLη(γγ), KLη(π+π-π0), KLω(π+π-π0), KLη’(π+π-η)
KLπ0π0
Total CP ± tags 96
123
KSππ
KLππ
Total Mixed CP tags (K0hh)
200
126
KSKK vs KLKK 10
K0KK vs Flavour
497
887
Many different CP- and CP+
tagging decay modes
reconstructed in order to
mitigate statistics limitations
Raw data yields:
~ CP/CP-mixed tags
~1,400 Flavour tags
Background/Signal
5-10% for KSKK
~30% for KLKK
EPS HEP 2009
Stefania Ricciardi

17. KSK+K- vs flavour-tags (Cleo-c, 818 pb-1)
Flavour tags: K+π- and K+π-π0
EPS HEP 2009
Stefania Ricciardi

18. K0K+K- vs CP-tags (Cleo-c, 818 pb-1)
Ksf
KsKK
CP tag -
CP tag -
CP tag +
KLf
KLKK
EPS HEP 2009
Stefania Ricciardi

19. ci and si (KSK+K-) preliminary results and impact on g
+ Cleo-c preliminary
(statistical error only)
Model predictions
[BaBar, PRD 78, (2008)]
Good agreement of measured values with BaBar model predictions
Errors bigger than KSpp due to smaller yields, especially in third (red) bin
~5-6° projected uncertainty on g
from B→ D0(KSKK)K±
due to Cleo-c statistical uncertainty
RMS =5.5°
Preliminary
EPS HEP 2009
Stefania Ricciardi

20. KS,LK+K- all results: ci, si and ci’,si’
+ Cleo-c preliminary
(statistical error only)
Model predictions
[BaBar, PRD 78, (2008)]
KSK+K-
KLK+K-
No significant difference between the two sets of measurements
Good agreement with predictions overall - KSKK and KLKK model predictions differ visibly only in bin 3 where yields are small, but measured difference not significant
EPS HEP 2009
Stefania Ricciardi

21. Conclusions Charming quantum-correlation effects in Cleo-c data
y(3770) coherent decay exploited to measure DdD in
8 bins of the D0 →KS,Lp+p- Dalitz planes (PRD to appear soon)
and
3 bins of the D0 → KS,LK+K- Dalitz planes (preliminary)
Other DdD measurements by Cleo-c (not presented here)
D0→K-p+ [PRL (2008), PRD 78, (2008)]
D0→K-p+p0, D0→K-p+p-p+ (coherence factor and average DdD)
[arXiv: [hep-ex]]
Crucial role of DdD in the precision of the extraction of CKM-angle g, especially important for future measurements at LHCb and super-B
Fine example of synergy between charm and B-physics programme
and of global science in the collaboration among different experiments
Many thanks to BaBar, Belle and LHCb collaborators for sharing Dalitz plot bitmaps, expertise and fruitful discussions
EPS HEP 2009
Stefania Ricciardi

22. Additional material

23. From yields to ci(`) and si(`)
Observables
Normalisations
Mi = Number of KShh vs CPtag in bin i
Mij = KShh in bin i vs Kshh in bin j
Mi =KLhh vs CPtag in bin i
Mij = KShh in bin i vs KLhh in bin j
Ki = ADTi number of flavour-tagged decays in bin i
EPS HEP 2009
Stefania Ricciardi

24. KLhh vs KShh and Residual Model Uncertainty
DCS
Correction to approximate equality between KSpp and KSKK
Minus sign introduce a 180 degrees shift for all DCS resonances
CP eigenstate resonances acquire a factor  -2reid [r = tan2(qc)]
Residual model dependence due to uncertainty on this small correction small effect
EPS HEP 2009
Stefania Ricciardi

25. KLpp ci’ –ci Measured and predicted (from D0-decay model) difference
in the range , depending on bin
EPS HEP 2009
Stefania Ricciardi

26. EPS HEP 2009
Stefania Ricciardi