ωω: J. Albert Caltech March 24, 2006

Transcription

1 ωω: Search for B 0 ωφ and B 0 ωω Are CP and polarization in loops consistent Are CP and polarization in loops consistent with the Standard Model? with the Standard Model? March 24, 2006 J. Albert Caltech

2 Hints of new physics? Anomalies in charmless decays with loops: Low value of longitudinallypolarized fraction in φk*. Unexpectedly low values of CP asymmetries. Potential signs of new physics in loops? ωω J. Albert 2

3 B 0 Some Background: The Unitarity Triangle The constraint that the CKM matrix is unitary results in three equations (in the C plane) that must be satisfied: (a) (b) Measurements sensitive to the lengths of the sides of the triangles indicate that (a) and (b) (sensitive to CPV in the K and B s systems respectively) are nearly degenerate. Only the 3 rd triangle (c) (corresponding to decays in the B system) should have large CP violating effects. These 2 decays: c J/ψ b d c s K 0 s K 0 d No significant phase in decay!! (c) Mixing: B 0 B 0 = 2β!! ωω J. Albert 3

4 Polarization: Experimental Technique For B 0 φω and B 0 ωω: For pure loop diagrams, f L 1 (due to helicity flip suppression ). ωω J. Albert 4

5 How can we tell if the SM is in trouble? SU(3) relations can be used to establish the maximum deviation one would expect from purely standard model effects. Separation of SM effects from new physics ones, eg. hep-ph/ : Relations such as establish the maximum departure in terms of BFs of related modes. ωω J. Albert 5

6 Decays related to φk* by SU(3) 1) B 0 ρ 0 ρ 0 2) B 0 φφ 3) B 0 ρ 0 ω recent Babar limits: x ) B 0 ρ 0 φ 5) B 0 φω 6) B 0 ωω Never been measured! Old CLEO limit (13 x 10-6 ) ωω J. Albert 6

7 B 0 φω and B 0 ωω At leading order, φω is pure penguin and ωω is a penguin-tree combination. Predicted branching fractions are small. Both decays are predicted to have BFs < 2 x 10-7 (Ali, Kramer, & Lu, 1998; Chen et al, 1999). Limits on BFs can provide a constraint on amplitudes of φk*; helicity amplitude measurements, nor even significant signal peaks, required. ωω J. Albert 7

8 Data and MC Samples Use runs 1-4 dataset: = 205 fb -1 of data. Generic MC: Signal MC: Use InclOmega skim for both modes. In addition, for φω, the InclPhi tagbit is required to be set true. ωω J. Albert 8

9 Reconstruction of B 0 φω and B 0 ωω Reconstruct the decays ω π + π - π 0 and φ K + K -. Resonances reconstructed as follows: Charged tracks taken from the GoodTracksLoose list. Kaon candidates must additionally satisfy the tight SMS kaon selector, and must not satisfy the VeryTight criteria of the electron Micro selector or the proton LH selector. Photons are taken from the GoodPhotonsLoose list, and must have E lab > 50 MeV. Two photons are combined to form a π 0 candidate, which must satisfy 120 < mγγ < 150 MeV. Two oppositely charged tracks and a π 0 are combined to form an ω π + π - π 0 candidate, which must satisfy 735 < m πππ < 825 MeV. Two oppositely charged kaons are combined to form a φ K + K - candidate, which must satisfy 1009 < m K+K- < 1029 MeV. ωω J. Albert 9

10 Event pre-selection After combining selected ω and φ candidates to form B 0 φω and B 0 ωω candidates, the resulting B 0 candidates are characterized by the standard variables: For a candidate to be selected, it must satisfy E < 200 MeV and 5.21 < m ES < 5.29 GeV. In addition, in order to help reject continuum background, the event shape must satisfy 1) cos θ < 0.8 and 2) -4 < F < 5, where F is a Fisher discriminant described later. When there are > 1 B 0 candidates in an event, select the best candidate based on a χ 2 constructed from the reconstructed resonance masses: B 0 φω B 0 ωω Avg = Avg. = ωω J. Albert 10

11 Efficiency Raw efficiency = (number of selected events)/(number of generated events) in a given decay mode. Must be corrected for differences btw. data and MC in tracking efficiency, neutrals (i.e. ) efficiency, and PID (i.e. kaon) efficiency. Corrections are performed using standard recipes. A flat correction is taken for tracking efficiency. The π 0 efficiency correction is the average value of 96.83% per π 0. PID corrections are done at the candidate reconstruction stage; kaon selection in MC is adjusted to match the data efficiency. There are systematics from each of these corrections (discussed later on). Efficiency must also be corrected for the branching fractions of ω π + π - π 0 and φ K + K -. ωω J. Albert 11

12 Peaking background studies A few modes contribute non-negligibly to peaking background. For B 0 φω(examples): Upsilon(4S) _ anti-b anti-b0 _ D* Sigma anti-p- _ rho D+ _ D0 pi+ _ Lambda0 gamma _ pi- pi+ deuteron deuteron p+ p+ _ pi0 pi- _ phi pi+ _ pi0 pi+ K- _ n0 pi0 _ K- K+ Upsilon(4S) _ anti-b anti-b0 _ D* omega eta pi- _ f_ omega _ D+ pi0 _ pi0 pi+ pi- _ gamma gamma _ K- K+ _ pi0 pi+ pi- _ a_ anti-k0 _ rho0 pi+ _ K_L0 _ pi- pi+ _ n0 For B 0 ωω: Upsilon(4S) _ B anti-b0 _ eta anti-d D_s* rho- _ rho omega pi- _ pi0 pi0 pi0 _ K*0 pi- pi+ _ D_s+ gamma _ pi0 pi- _ pi0 pi+ _ pi0 pi+ pi- _ pi- K+ _ rho eta _ pi0 pi+ _ gamma gamma ωω J. Albert 12

13 Maximum likelihood fit We use an unbinned maximum likelihood in the 7 variables The likelihood is defined as where n j are the free parameters of the fit, i.e. the number of events for each hypothesis (signal, combinatoric background, and peaking background), and P j (x i ) are the probabilities for each hypothesis evaluated from the vector of 7 observables x i, for each of the N total events. ωω J. Albert 13

14 PDFs: m ES The probabilities P i for each hypothesis are the products of the PDFs for each of the observables, except in the case of the two helicities, which are correlated with each other and also (via f L ) with the efficiency. For m ES, the signal is modeled by a double Gaussian. The peaking background is modeled by a Crystal Ball function. The combinatoric background is an Argus function, which is fitted to the data in sidebands of E ( E > 100 MeV). ωω J. Albert 14

15 PDFs: E In the case of E, the signal PDF is modeled by a double Gaussian, as is the peaking background. The combinatoric background is modeled by a second-degree polynomial, which is fitted to the on-peak data m ES sideband (m ES < 5.27 GeV). ωω J. Albert 15

16 PDFs: φ and ω masses For both the φ and ω masses, the signal PDF is parameterized by a double Gaussian distribution, as is the peaking background, and the combinatoric background is parameterized by a double gaussian (with the same parameters as for signal) plus a 2 nd order polynomial. Considering moving to PDFs using the mass pull distributions rather than the masses themselves. ωω J. Albert 16

17 PDFs: φ and ω helicities The φ and ω helicities are parameterized as follows: where ωω J. Albert 17

18 PDFs: Fisher discriminant The Fisher discriminant contains information from four variables: the angles between the beam axis and 1) the B momentum and 2) the B thrust axis, and 3) the zeroth and 4) second angular moments L 0,2 of the total energy flow about the B thrust axis, where where θ i is the angle with respect to the B thrust axis of track or neutral cluster i, and the sum excludes the B candidate. The shape, in the case of each of the 3 hypotheses, is parameterized by a bifurcated Gaussian distribution. ωω J. Albert 18

19 Results (I) ωω J. Albert 19

20 Results (II) Polarization vs. BF contours Log Likelihood vs. BF ωω J. Albert 20

21 Conclusion B 0 φω and B 0 ωω had been previously unmeasured, and can constrain the polarization of φk* in the context of the Standard Model. Results: B(B 0 φω) < 1.2 x 10-6 at 90% C.L. B(B 0 ωω) = x 10-6 (< 4.0 x 10-6 at 90% C.L.) +1.3 Central value of ωω is larger than expected (but uncertainties still large ). Results presented at Moriond QCD (last week), will be uploaded to hep-ex and submitted to PRD (rapid communications) next week. ωω J. Albert 21