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Photon Polarization in B→Kππγ Decay: Analysis Strategy and Prospects

This paper explores the analysis strategy and prospects for measuring the photon polarization in the B→Kππγ decay using the angular distribution of Kππ. The study also discusses the available MC samples and the ongoing selection process. The goal is to provide results by summer.

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Photon Polarization in B→Kππγ Decay: Analysis Strategy and Prospects

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

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

  3. Motivation (II) PRD 78, 071102(R) (2008) • Two ways to test photon polarization: 1) Since B→XγLandB→XγRdon’t interfere, testpolarizationindirectly 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 Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  4. Method of Gronau et al • Is Kres spin || pphotonor –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 cosθ→sensitive! 1+→ cos θ 2+→ cos θ cos 2θ Kres spin • γ spin proj ↔ Kres spin proj θ normal to plane Kππ plane photon φ E.g. Kres→K*0π0 or K*+π–→ K+π–π0 Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  5. Kππspectrum • 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 Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  6. Kππspectrum (II) • Belle: BF(B+→K1(1270)+γ = (4.3 ± 0.9 ± 0.9)x10-5) PRL94:111802,2005 • Also: (arXiv:0806.1980, 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) Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  7. 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 Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

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

  9. 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) Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  10. 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) Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  11. Summary and prospects • Measure photon polarization inB→Kππγfrom angular distributionofKππ • Just finished ntuple reconstruction code • Now looking at selection… • Have started coding signal model in Laura++ • Aiming for results in summer Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  12. BACK UP SLIDES Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  13. The BaBar experiment • Asymmetric energies: boost βγ = 0.56 • √s = 10.58 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 Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  14. 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 Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

  15. “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 constantm212, m22 3 or m213 Overlap → interference →sensitive to relative phase Observe intensity |A|2, with A ~ Σ ci BWi (Isobar) cicharacterize model so |A|2 ~ck* cl BWk* BWl k, l > 1 lift degeneracies Ideal to measure phases! Pablo del Amo Sanchez, LPNHE - IN2P3 - CNRS

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