Study of the decays at Wasa-at-COSY. Elisabetta Prencipe on behalf of the Wasa Collaboration MesonNet Workshop, 17th -19th June 2013, Praha

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1 Study of the decays at Wasa-at-COSY on behalf of the Wasa Collaboration MesonNet Workshop, 17th -19th June 2013, Praha

2 Outline Introduction The Wasa-at-COSY detector decays in the pd reaction e+e e+e e+e e+e decays in the pp reaction e+e 2

3 Introduction The study of light mesons provides an ideal laboratory for: high precision measurements rare process search test symmetry and symmetry breaking High statistics of light mesons in many experiments CMD/SND, Novosibirsk CLEO, Cornell CLAS, JLab BES III. Beijing WASA-at-COSY, Jülich Crystal Ball, Mainz KLOE, Frascati 3

4 The COSY facility WASA-at-COSY 4

5 The detector Wasa-at-COSY Target: fixed hydrogen/deuterium pellet target Forward detector: measurement of recoil particles Central detector: measurement of charged and neutral decay products PID from deposit of energy in different detector layers Tracking: drift chamber 5

6 Wasa-at-COSY The reactions under study here are: pd 3He k = 1.0 GeV pp pp k = 1.4 GeV inclusive pd 3 x 107 mesons tagged 10 /s produced exclusive pp 5 x 108 mesons produced 100 /s produced The missing mass is used to identify mesons 6 MesonNet,

7 Which decays and why PDG See the poster session: D. Lersch, Lersch this evening 7

8 and e e + The decays and e+e are closely related 2 anomalous contributions to the decay amplitudes: Triangle anomaly Box anomaly Strong contribution from the triangle diagram via -coupling vector meson dominance Information extracted from: inv. Mass (E angular distribution. 8

9 : results (I) PLB 707 (2012) PLB 718 (2013) p-wave With a model independent parameterization s = inv. mass of Stollenwerk et all., PLB 707 (2012), 184 9

10 : results (II) The measurement from CLEO is ~3 lower than the PDG average global fit [PRL 99 (2007) ] The CLEO measurement was confirmed by KLOE [ PLB 718 (2013), ] D. Coderre The WASA-at-COSY measurement: (98002±382) reconstructed events in pd BR extracted: work in progress... (need to finalize systematic effects) Analysis in pp data in progress: x10 higher statistics available 10

11 e e + Possible interference between the M1 transition (CP conserving) and E1 transition (CP violating) in the decay e+e : polarization of a real photon is possible, but not yet measured e+e : we can measure the asymmetry in the decay plane e Theoretical upper limit: ~1% Experimental value: (-0.6± 2.5 ±1.8)% [PLB 675 (2009), ] 11

12 e e : results + D. Coderre 10-2 (263±24) reconstructed events BR in agreement with other experiments A limited by statistical error in pd data: analysis in progress with pp data 12

13 e e and e e e e The interest in the decay e+e is to extract the form factor: it is useful to describe the coupling of the virtual photon to the vector meson We can compare the e+e invariant mass spectrum with the QED prediction: The interest in the double Dalitz decay e+e e+e is: - precise determination of BF - double form factor 13

14 e e : Branching Ratio + D. Coderre Full range (16637±117) reconstructed events in pd data PID to reduce bkg from pions Eliminated background from conversion e+e in the beam pipe BR evaluated, not yet released Analysis in pp in progress... 14

15 e e Form Factor + M. Hodana M. Hodana Preliminary results from pd data sample 15

16 e e e e : Branching Ratio + + Very limited from the statistics in pd data: (54 ±13) reconstructed events In the new analysis the kinematic fit is used lower background Consistent with previous result Improvement expected with pp data to extract the double form factor 16

17 e e : Branching Ratio + Very rare decay: theoretically BF ~ 10-8 Sensitive to non-standard model process Discrepancy found between theory and experimental result for the channel e+e [PRD 75 (2007) ] What about the meson? Analysis on 2 weeks data from pp pp Consistent with HADES [Eur J.P. A 48 (2012) 64] Additional 15 weeks of data collected at WASA 17

18 Summary and conclusions Wasa-at-COSY has high statistics in pd and pp datasets to analyze decays The study of the decays is useful for: precise measurement of the BR form factor box anomaly C and CP violation eventually new physics beyond the Standard Model Preliminary results of several decay modes today were presented, using the pd dataset: the Wasa Collaboration will soon provide BR measurements. Improvements are expected when the pp dataset is used for these analyses work in progress: a statistics x10 is available with the pp dataset Stay tuned! 18

19 THANK YOU! 19

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