1. Plans for B→Kππ γ Pablo del Amo Sanchez & Eli Ben-Haïm
LPNHE (Univ. Paris VI et VII) – IN2P3 – CNRS

2. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Motivation
Radiative modes B→Xsγ due to b→sγ loop amplitude
Photon polarization probes V-A structure in the loop:
b(b) decays in left-handed (right-handed) photon up to ~ms/mb≈ 2%
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

3. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Motivation (II)
PRD 78, (R) (2008)
Two ways to test photon polarization:
1) Since B→XγL and B→XγR don’t interfere,
test polarization indirectly in
time-dependent asymmetries, e.g.
S(B0→KS0π0γ) = –0.03±0.29±0.03
→Poor vertexing + low stats…
2) Alternative method: infer photon
polarization from angular distribution
of resonance Kres→3body in B→Kresγ
(Gronau, Grossman, Pirjol & Ryd,
PRL88:051802,2002 & PRD66:054008,2002)
KS0π0γ
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

4. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Method of Gronau et al
γ spin proj ↔ Kres spin proj
Kres spin
Is Kres spin || pphoton or –pphoton?
Distribution of events in θ depends on spin, parity of Kres:
1+ → 1+cos2 θ
1– → sin2 θ
2+ → cos2 θ+cos2 2θ
…all in cos2 θ → no sensitivity
Interference in Kres→3body
gives terms in cos θ → sensitive!
1+ → cos θ
2+ → cos θ cos 2θ θ
normal to plane
Kππ plane
photon φ
E.g. Kres→K*0π0 or K*+π–→ K+π–π0
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

5. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Kππ spectrum
BaBar: inclusive BFs and background-substracted plots (211/fb):
ns=899±38
eff ~ 13%
ns=572±31
eff ~ 6%
ns=176±20
eff ~ 4%
PRL98:211804,2007
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

6. Kππ spectrum (II) Belle: BF(B+→K1(1270)+γ = (4.3 ± 0.9 ± 0.9)x10-5)
PRL94:111802,2005
Also: (arXiv: , Nishida at CKM2008)
Prominent axial vector K1(1270)
Significant axial vector K1(1400)
Small, well known contribution of tensor K2(1430)
Possible vector K*(1680)
…all decaying via several 2-body resonance modes → method of Gronau et al possible?
(Non-K* region cut away)
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

7. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Analysis strategy
Rich spectrum of J≥1 Kππ resonances, all decaying via several different 2-body resonance modes
→ method of Gronau et al possible?
Analysis possibilities:
Model all degrees of freedom: θ, resonances in mij2 (↔  »Dalitz»)
→ Most sensitive to polarization; complex!
Model only θ
→ Far simpler; is it sensitive enough?
Decide by studying sensitivity with MC
→ Problem: subtle interference effects not in EvtGen
→ Have started to modify Laura++ to model them
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

8. Analysis strategy (II)
Tentative strategy:
1) Extract Kππ resonant content from mKππ 1D fit
2) Quantify sensitivity and decide fit vars (θ vs θ+mij2)
3) If using mij2, test fit on / extract Kres decay model from
control sample J/ψKππ
4) Fit B→Kππγ data!
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

9. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Selection
SimpleComposition + BtaTupleMaker in R24 used for ntuple prod
Selection ongoing, heavily based on previous BaBar B→Kππγ analysis:
0.7 < mKππ < 1.8 GeV
High energy photon: -0.74<cosθγ<0.93, distance to any other EMC cluster > 25cm, 2nd moment < 0.002, EMC status = 0, π0 and η veto
KS0 from KsDefault,
cosθflight > 0.995, cτKs > 5 σcτ
PID on K+, π+
π0 from pi0Loose
Neural Network (cos θBmom,
cos θthrust, L2, L0, Tag04)
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

10. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Available MC samples
None of the available samples contains right angular distributions
→ Reweight MC using self-coded Laura++ model
Available SP modes:
B0/+→K1(1270)0/+γ (SP-1452 & 1453)
B0/+→K1(1400)0/+γ (SP-1454 & 1455)
B0/+→K2*(1430)0/+γ (SP-1765 & 1766)
B0/+→K*(1410)0/+γ (SP-1970 & 1971)
B0/+→K*(1680)0/+γ (SP-1972 & 1973)
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

11. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
Summary and prospects
Measure photon polarization in B→Kππγ from angular distribution of Kππ
Just finished ntuple reconstruction code
Now looking at selection…
Have started coding signal model in Laura++
Aiming for results in summer
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

12. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
BACK UP SLIDES
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

13. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
The BaBar experiment
Asymmetric energies:
boost βγ = 0.56
√s = GeV
= m(Υ(4S)) ≈ 2 m(B0)
so e+e–→Υ(4S)→BB
SVT: 100µm resolution
in Δz ~ βγcτ = 250 µm
SVT: good eff
for low pt tracks
PID from DIRC essential for tagging
Belle experiment similar
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

14. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
The BaBar experiment
Υ(4S) data taking ended Dec 2007: ~ 465 M BB
Have recorded ~ 30/fb on
Υ(3S) and ~ 15/fb on Υ(2S)
Routinely collect data 40 MeV below Υ(4S) peak for background characterization
Finished running
on 8th April
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

15. Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS
“Dalitz” analysis
2 degrees of freedom in B→P1P2P3, usually m2P1P2 and m2P1P3:
3 daughters x 3 p comp – 4 (E, p conservation) - 3 Euler angles
Resonances, bands of
constant m212, m22 3 or m213
Overlap → interference
→sensitive to relative phase
Observe intensity |A|2,
with A ~ Σ ci BWi (Isobar)
ci characterize model
so |A|2 ~ck* cl BWk* BWl
k, l > 1 lift degeneracies
Ideal to measure phases!
Réunion BaBar France, Octobre 2008
Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS