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The Radiative Pion Decay Anomalie Revisited

The Radiative Pion Decay Anomalie Revisited. (by the PIBETA Collaboration). Motivated by results obtained by the ISTRA (1990) [1] and PIBETA (2001) [2] collaborations which both found deviations from the SM-description. [1] V.N. Bolotov et al., Phys. Lett. B 243 (1990), 308.

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The Radiative Pion Decay Anomalie Revisited

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  1. The Radiative PionDecay Anomalie Revisited (by the PIBETA Collaboration) W. Bertl (LTP / PSI)

  2. Motivated by results obtained by the ISTRA (1990) [1] and PIBETA (2001) [2] collaborations which both found deviations from the SM-description. [1] V.N. Bolotov et al., Phys. Lett. B 243 (1990), 308. [2] E. Frlez et al., Phys. Rev. Lett. 93 (2004), 181804 Motivation to measure p+ e++n+g • Determine weak form factors of the Pion • Testing the Standard Model • CVC hypothesis • Search for scalar and tensor currents W. Bertl (LTP / PSI)

  3. The Decay Rate Amplitude Inner Bremsstrahlung Amplitude + Structure-dependent Amplitude Radiation from strong interaction states Parametrize by form factors FV and FA Axial vector current → pure QED FV (q): from CVC: FA (q): model dependent calculation q~0 for regions A and B but not for C W. Bertl (LTP / PSI)

  4. Collaboration University of Virginia USA K.A.Assamagan, M. Bychkov, E.Frlež,J.E.Koglin, W.Li,R.C.Minehart,D.Počanić, P.L.Slocum, L.C.Smith, W.A.Stephens, B.Vandevender, Y.Wang, K.O.H.Ziock, Paul-Scherrer Institut CH W.Bertl, Ch.Brönnimann,J.F.Crawford, M.Daum, Th.Flügel, R.Frosch, Z.Hochman, R.Horisberger, B.Krause,H.Obermeier, D.Renker, S.Ritt, R.Schnyder, H.P.Wirtz, …and Hallendienst, Elektronic divisions, workshops and and and… Inst. for Nuclear Studies, Swierk, PL T.Kozlowski, Arizona State University, Tempe, USA D.W.Lawrence, B.G.Ritchie, Joint Inst. of Nuclear Research, Dubna, RU V.A.Baranov,V.A.Kalinnikov, V.V. Karpukhin, N.V.Khomutov,A.S.Korenchenko, S.M.Korenchenko, N.P.Kravchuk, N.A.Kuchinsky, A.M.Rozhdestvensky,V.V.Sidorkin, E.P.Velicheva, Inst. for High Energy Physics, Tbilisi, GUS D.Mzhavia, Z.Tsamalaidze, Rudjer Bošković Institute, Zagreb, HR I.Supek University of Virginia USA O.A. Rondon-Aramayo Joint Inst. of Nuclear Research, Dubna, RU Y. Bystritsky, A. Moisenko, E.P. Velicheva, V. Volnykh Rudjer Bošković Institute, Zagreb, HR M. Korolija, D. Mekterovic University of Zurich, CH P. Robmann, T. Sakhelashvili, S. Scheu, U. Straumann, A. van der Schaaf, University of Sofia, BL M.V. Chizhov (theoretical support) up to 2001 up to 2004 spokesperson graduate student technician W. Bertl (LTP / PSI)

  5. the differential decay rate can be written: The Decay Rate • Kinematics: Range of x: 1-y < x < 1 Range of y: 0 < y < 1 W. Bertl (LTP / PSI)

  6. g e+ ne y C SD- A SD+ ne g Qeg = 0º e+ Qeg = 0º g g ne ne e+ e+ B x x Kinematics Qeg = 180º Qeg = 180º x W. Bertl (LTP / PSI)

  7. The PIBETADetector E.Frlez et al., NIM A526, 300 (2004) W. Bertl (LTP / PSI)

  8. The PIBETA Detector W. Bertl (LTP / PSI)

  9. 1Supercluster 2-arm Trigger (T2) : 1 SC and 5 not adjacent SC’s 1-arm Trigger (T1) : any SC Threshold: high = 51.7 MeV (just at Michel edge) low = 4.5 MeV Prescaling: T2HH = 1, T2HL = 1, T2LL = 16, T1H = 1, T1L = 512, Beam: prompt/non promp events Random trigger Cosmic Trigger Trigger 240 CsI –Crystals grouped to 60 clusters Out of 60 clusters 10 Superclusters were formed (SC) Those 10 Supercluster provide the Triggerinput: W. Bertl (LTP / PSI)

  10. GpenThis measurement: (1.2450.010)10-4Set 1 (1.2370.010)10-4Set 2 Best measurements: (1.2350.005)10-4Czapek et al. ‘93 (1.22650.0034(stat) 0.0044(sys))10-4 Britton et al. ‘92 Theory: (1.23520.0005)10-4Marciano et al. ‘93 (1.23560.0001)10-4Decker et al. ‘95 Normalization: p+ e++n Decay Energy subtraction and background calibration by 2 indep. Methods (a)ADC, b) TDC) Agreement better than 1% Corrected for radiative corrections W. Bertl (LTP / PSI)

  11. Analysis p+ e++n+g Decay Only events from 1-arm-high trigger used Basic procedures same as for pen events Eetotal = EeCsI + Eetarget + EePV Egtotal = EgCsI W. Bertl (LTP / PSI)

  12. Yield: (Corrected for gate fraction) pb-Bckgrd: (Error 5%) 171.59 4 404.8 ± 85.45 10 314.1 ± 157.8 172.04 165.15 13 365.5 ± 155.0 p+ e++n+g: Background m-decays rejected by kinematics, lifetime W. Bertl (LTP / PSI)

  13. A 1% change ! p+ e++n+g: Energy Calibration a) From p+e++n decay b) DL  l1-l2 (Is sensitive to asymmetries in energy calibration for e and g ) W. Bertl (LTP / PSI)

  14. p+ e++n+g: Some Distributions Region B W. Bertl (LTP / PSI)

  15. p+ e++n+g: Results Global Fit: 3 different studies: Fit variables: • “classical”: 3 regions, E>20MeV • Extended regions, E>15MeV • More (=8) regions Form factor ratio a q dependence ( ) FV W. Bertl (LTP / PSI)

  16. p+ e++n+g: Resulting Bran. Ratios 3 Regions, Threshold 20 MeV PRELIMINARY! 3 Regions, Threshold 15 MeV 8 Regions, Threshold 15 MeV W. Bertl (LTP / PSI)

  17. PIBETA Results: Form Factor Ratio g THEORY; Scheck ‘73 Holstein ‘86 Bijnens ‘97 Geng ‘04 0.468 ± 0.0118 This experiment PRELIMINARY! W. Bertl (LTP / PSI)

  18. FV from previous experiments: Egli ‘86 0.014 ± 0.009 Bolotov ‘90 Main Result: • FA = 0.0118 ± 0.0003 • Fv = 0.0262 ± 0.0015 • a = 0.241 ± 0.093 PRELIMINARY! First time measured From theory: 0.0263 ± 0.0009 CVC Vaks ‘58 0.0270 – 0.0273 cPT Geng ‘04 W. Bertl (LTP / PSI)

  19. Radiative Muon Decay Goal: - Used as control measurement - determination of (SM: =0) 400 000 mmeasured in region Eg > 10 MeV; qeg > 30o BR = (4.40 ± 0.09)x10-3 BRtheor = 4.30x10-3 or This is about as good as the result of Eichenberger et al. ‘84 W. Bertl (LTP / PSI)

  20. Conclusion • First analysis of 2004 data finished • Second analysis in good progress • FA from 1999-2001 data confirmed • FV precision 6 fold increased • q-dependence first measured • Tentativ tensor form factor consistent with zero (SM prediction) W. Bertl (LTP / PSI)

  21. Outlook • We investigate data of 1999-2001 to understand the cause of the discrepancy in region B. • Once discrepancy is understood those data will be combined with 2004 data tripling the statistics to ~60000 events in a broad kinematic region. (pre-PIBETA aera: 1200 events) W. Bertl (LTP / PSI)

  22. bad c2 ! Results (p→eng) (2001-3) The resulting g: (assuming CVC determines FV) Region A: sensitive to SD+ → measure (1+g)2→ |g| only g = 0.480 → FA = 0.0124(4) Regions B, C: also dependent on SD- → measure (1-g)2 → sign! g = 0.443 → FA = 0.0115(4) published: E. Frlez et al., Phys. Rev. Lett. 93 (2004) 181804 W. Bertl (LTP / PSI)

  23. PIBETA: practically all pion and muon decaysmeasured at once. Simultaneous precise matching of all kinematical variable spectra to the MC prediction in all decay processes withoutseparate adjustments Expression for decay rate becomes more complicated. Effect only -1.0%, -1.4% and -3.3% for regions A,B and C resp. ISTRA A Tensor Form Factor ? • Fact: An FT ≠ 0 is incompatible with the Standard Model • We could not find an exp. Explanation (e.g. X-checks with ) • Radiative corrections recalculated (Kuraev, Bystritsky, Velicheva : hep-ph 0310275) • A similar effect seen by the ISTRA group V.N. Bolotov et al., Phys.Lett. B243, 308 (1990) A.A. Poblaguev proposed FT = -0.0056(17) Phys.Lett. B286, 169 (1992) and revised it to FT = -0.0115(33) Phys.Rev. D68, 054020 (2003) (based on all available data sets) ? • Fiction: • P. Herczeg could not rule out FT on basis of all existent b-decay data (=Leptoquarks) • M.V. Chizhov proposed a new intermediate chiral boson with anomalous interaction with matter • M.D.Scadron et al. propose a non-CVC FV (linear sigma model) Phys. Rev. D49, 247 (1994) Mod.Phys.Lett. A8, 2753 (1993) hep-ph 0307100 and hep-ph 0310203 Nucl. Phys. A724, 391 (2003) How: W. Bertl (LTP / PSI)

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