Rare Pion and Muon Decays: Summary of Results and Prospects

Transcription

1 Rare Pion and Muon Decays: Summary of Results and Prospects Dinko Počanić University of Virginia Low Energy Precision Electroweak Physics in the LHC Era Institute for Nuclear Theory, University of Washington, Seattle 21 Nov 2008 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 1 / 61

2 Outline Outline The PIBETA PEN program Pion Beta Decay: π + π 0 e + ν PIBETA Apparatus and Method Results Radiative pion decay: π eνγ Radiative muon decay: µ eν νγ The PEN Experiment: π eν SM calculations; mass limits Lepton universality New detectors Brief look at 2007 and 2008 results Summary D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 2 / 61

3 The PIBETA PEN program The PIBETA PEN Program of Measurements Perform precision checks of Standard Model and QCD predictions: 1st phase: The PIBETA experiment π + π 0 e + ν e SM checks related to CKM unitarity π + e + ν e γ(or e + e ) F A /F V, π polarizability (χpt prediction) tensor coupling besides V A (?) µ + e + ν e ν µ γ(or e + e ) departures from V A in L weak 2nd phase: The PEN experiment π + e + ν e e-µ universality pseudoscalar coupling besides V A ν sector anomalies, Majoron searches, m h+, PS l-q s, V l-q s,... D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 3 / 61

4 The PIBETA PEN program Brief review of the basics Known and Measured Pion and Muon Decays Decay BR π + µ + ν (4) (π µ2 ) µ + νγ 2.00 (25) 10 4 (π µ2γ ) e + ν (4) 10 4 (π e2 ) e + νγ 1.61 (23) 10 7 (π e2γ ) π 0 e + ν (34) 10 8 (π e3, π β ) e + νe + e 3.2 (5) 10 9 (π e2ee ) π 0 γγ (32) e + e γ (32) 10 2 e + e e + e 3.14 (30) 10 5 e + e 6.2 (5) 10 8 µ + e + ν ν 1.0 e + ν νγ (4) e + ν νe + e 3.4 (4) 10 5 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 4 / 61

5 Pion Beta Decay Pion Beta Decay: π + π 0 e + ν D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 5 / 61

6 Pion Beta Decay Motivation Quark-Lepton (Cabibbo) Universality The basic weak-interaction V-A form (e.g., µ decay): persists in hadronic weak decays M e l α ν e ū e γ α (1 γ 5 )u ν M p h α n ū p γ α (G V G A γ 5 )u n with G V,A 1. Departure from G V = 1 (plain CVC) comes from weak quark mixing (Cabibbo 1963): G V = G µ cos θ C (= G µ V ud ) cos θ C q generations lead to the CKM matrix V ud V us V ub (Kobayashi, Maskawa 1973): V cd V cs V cb V td V ts V tb CKM unitarity cond.: V ud 2 + V us 2 + V ub 2? = 1, can test the SM. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 6 / 61

7 Status of CKM unitarity Pion Beta Decay Motivation (PDG before) V us = (26) from K e3 decays. V ub = (7) from B decays. V ud from superallowed Fermi nuclear β decays 1990 Hardy reconciled Ormand & Brown s and Towner s ft values: V ud 2 + V us 2 + V ub 2 = (16), or 1 2.4σ. V ud from neutron β decay (many results; currently incompatible) Vui 2 = (28), or 1 3.0σ. [perkeo ii (2002)] V ud from pion β decay pibeta expt discussed below. 2004: V us revised upward; CKM unitarity discrepancy removed! D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 7 / 61

8 The Pion Beta Decay Pion Beta Decay Motivation π ± π 0 e ± ν: B , pure vector trans.: 0 0. Theoretical decay rate at tree level: 1 = G2 F V ud 2 ( 1 ) 3 5 f(ɛ, ) τ 0 30π 3 2M + = (22) V ud 2 (s 1 ). With radiative and loop corrections: branching ratio becomes: 1 τ = 1 (1 + δ), so that the τ 0 B(πβ) = τ + τ 0 (1 + δ) = (6) 10 8 (1 + δ) V ud 2. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 8 / 61

9 Pion Beta Decay Motivation Recent calculations of pion beta decay radiative corrections (1) In the light-front quark model W. Jaus, Phys. Rev. D 63 (2001) full RC for pion beta decay: δ = (3.230 ± 0.002) (2) In chiral perturbation theory Cirigliano, Knecht, Neufeld and Pichl, Eur. Phys. J. C 27 (2003) 255. χpt with e-m terms up to O(e 2 p 2 ) theoretical uncertainty of in extracting V ud from π e3. (3) Marciano and Sirlin further reduced theoretical uncert s in all beta decays [hep-ph/ , PRL 96, (2006)]. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov 08 9 / 61

10 Pion Beta Decay Motivation Experimental accuracy of the pion beta decay rate Best result prior to PIBETA: [McFarlane et al., PRD 32 (1985) 547.] B(π + π 0 e + ν) = (1.026 ± 0.039) 10 8, (i.e., 4 %) Accuracy: 1 % 0.5 % check CVC and rad. corrections add to SAF & n β input to V ud < 0.3 % check for failure of CKM unitarity: 4 th generation coupling m Z Λ of compositeness SUSY viol. of q-l universality signal of a smaller G F (ν osc.) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

11 Pion Beta Decay PIBETA Collaboration Experiment R (PIBETA) collaboration members: V. A. Baranov, c W. Bertl, b M. Bychkov, a Yu.M. Bystritsky, c E. Frlež, a N.V. Khomutov, c A.S. Korenchenko, c S.M. Korenchenko, c M. Korolija, f T. Kozlowski, d N.P. Kravchuk, c N.A. Kuchinsky, c D. Mzhavia, c,e D. Počanić, a P. Robmann, g O.A. Rondon-Aramayo, a A.M. Rozhdestvensky, c T. Sakhelashvili, b S. Scheu, g V.V. Sidorkin, c U. Straumann, g I. Supek, f Z. Tsamalaidze, e A. van der Schaaf, g B. A. VanDevender, a E.P. Velicheva, c V.V. Volnykh, c and Y. Wang a a Dept of Physics, Univ of Virginia, Charlottesville, VA , USA b Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland c Joint Institute for Nuclear Research, RU Dubna, Russia d Institute for Nuclear Studies, PL Swierk, Poland e IHEP, Tbilisi, State University, GUS Tbilisi, Georgia f Rudjer Bošković Institute, HR Zagreb, Croatia g Physik Institut der Universität Zürich, CH-8057 Zürich, Switzerland Web page: D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

12 Pion Beta Decay PIBETA Apparatus and Method The PIBETA/PEN Apparatus stopped π + beam active target counter 240-det. CsI(p) calo. central tracking digitized PMT signals stable temp./humidity BC π + beam AC1 AC2 AD pure CsI AT PV MWPC1 MWPC2 10 cm D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

13 Pion Beta Decay PIBETA Apparatus and Method The PIBETA/PEN Apparatus stopped π + beam active target counter 240-det. CsI(p) calo. central tracking digitized PMT signals stable temp./humidity BC π + beam AC1 AC2 AD pure CsI AT PV MWPC1 MWPC2 10 cm D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

14 Pion Beta Decay PIBETA Apparatus and Method The PIBETA/PEN Apparatus stopped π + beam active target counter 240-det. CsI(p) calo. central tracking digitized PMT signals stable temp./humidity BC π + beam AC1 AC2 AD pure CsI AT PV MWPC1 MWPC2 10 cm D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

15 Pion Beta Decay PIBETA Apparatus and Method PIBETA Detector Assembly (1998) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

16 Pion Beta Decay PIBETA Apparatus and Method PIBETA Detector on Platform (1998) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

17 Pion Beta Decay Results D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

18 Pion Beta Decay Results Number of events π + π 0 e + ν γ1 γ2 Simulation Data Opening angle Θ γ1γ2 (degr) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

19 Pion Beta Decay Results Normalizing decay: π + e + ν Number of Events Simulation Data π e ν Positron Energy (MeV) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

20 Pion Beta Decay Extracting the π eν Signal Results D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

21 Pion Beta Decay Results Summary of the main πβ uncertainties Type Quantity Value Uncertainty (%) external: π + lifetime ns 0.02 R exp π 0 γγ R exp πe internal: N tot A HT πβ /AHT πe2 (syst.) πe r πg = f πβ /f πe2 πg πg π β accid. bgd < 0.1 f CPP correction f ph correction statistical: N πβ D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

22 Pion Beta Decay Results π eν decay: SM predictions; measurements Modern theoretical calculations: B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 3629] (1) 10 4 Decker and Finkemeier, [NP B 438 (1995) 17] (1) 10 4 Cirigliano and Rosell, [PRL 99, (2007)] Experiment, world average [current PDG]: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.230 ± 0.004) 10 4 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

23 Pion Beta Decay Results π eν decay: SM predictions; measurements Modern theoretical calculations: B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 3629] (1) 10 4 Decker and Finkemeier, [NP B 438 (1995) 17] (1) 10 4 Cirigliano and Rosell, [PRL 99, (2007)] Experiment, world average [current PDG]: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.230 ± 0.004) 10 4 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

24 Pion Beta Decay Results PIBETA Result for π β Decay [PRL 93, (2004)] B exp πβ = [1.040 ± (stat) ± (syst)] 10 8, B exp πβ = [1.036 ± (stat) ± (syst) ± (π e2)] 10 8, McFarlane et al. [PRD 1985]: B = (1.026 ± 0.039) 10 8 SM Prediction (PDG, 2006): B = (90% C.L.) ( excl. rad. corr.) PDG 2008: V ud = (3) PIBETA current: V ud = (25) or V ud = (30). D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

25 Radiative pion decay π eνγ Radiative pion decay: π eνγ D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

26 Radiative pion decay Motivation and Status π + e + νγ: Standard IB and V A terms SM A tensor interaction, too? Exchange of S=0 leptoquarks P Herczeg, PRD 49 (1994) 247 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

27 Radiative pion decay The π eνγ amplitude and FF s The IB amplitude (QED): M IB = i eg F V ud f π m e ɛ µ ē 2 The structure-dependent amplitude: Motivation and Status ( kµ kq p µ pq + σ µνq ν ) (1 γ 5 ) ν. 2kq M SD = eg F V ud m π 2 ɛ ν ēγ µ (1 γ 5 )ν [F V ɛ µνστ p σ q τ + if A (g µν pq p ν q µ )]. The SM branching ratio (γ F A /F V ; x = 2E γ /m π ; y = 2E e /m π, ) dγ πe2γ dx dy = α { ( 2π Γ FV m 2 ) 2 π πe2 IB (x, y) + 2f π m e [ (1 + γ) 2 SD + (x, y) + (1 γ) 2 SD (x, y) ] ( ) FV m π [(1 } + + γ) S + int (x, y) + (1 γ) S int (x, y)]. f π D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

28 Radiative pion decay Motivation and Status Available data on Pion Form Factors F V cvc = 1 α 2 πτ π 0m π = (9). F A 10 4 reference note 106 ± 60 Bolotov et al. (1990) (F T = 56 ± 17) 135 ± 16 Bay et al. (1986) 60 ± 30 Piilonen et al. (1986) 110 ± 30 Stetz et al. (1979) 116 ± 16 world average (PDG 2004) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

29 Radiative pion decay Motivation and Status Available data on Pion Form Factors F V cvc = 1 α 2 πτ π 0m π = (9). F A 10 4 reference note 106 ± 60 Bolotov et al. (1990) (F T = 56 ± 17) 135 ± 16 Bay et al. (1986) 60 ± 30 Piilonen et al. (1986) 110 ± 30 Stetz et al. (1979) 116 ± 16 world average (PDG 2004) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

30 Radiative pion decay Motivation and Status Available data on Pion Form Factors F V cvc = 1 α 2 πτ π 0m π = (9). F A 10 4 reference note 106 ± 60 Bolotov et al. (1990) (F T = 56 ± 17) 135 ± 16 Bay et al. (1986) 60 ± 30 Piilonen et al. (1986) 110 ± 30 Stetz et al. (1979) 116 ± 16 world average (PDG 2004) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

31 Radiative pion decay PIBETA Expt. Results π + e + νγ (S/B) data set Region A: E γ, E e + > 51.7 MeV Region B: E γ > 55.6 MeV E e + > 20 MeV θ eγ > 40 Region C: E γ > 20 MeV E e + > 55.6 MeV θ eγ > 40 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

32 Radiative pion decay PIBETA Expt. Results π + e + νγ data set (timing) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

33 Radiative pion decay PIBETA Expt. Results Results of the SM fit [Phys. Rev. Lett. 93, (2004)] Best-fit π eνγ branching ratios obtained with: F V = (fixed) and F A = (4) (fit) χ 2 /d.o.f. = Radiative corrections are included in the calculations. E min e E min + γ θeγ min B exp B the no. of (MeV) (MeV) ( 10 8 ) ( 10 8 ) events (5) 2.583(1) 30.6 k (3) 14.34(1) 5.2 k (13) 37.83(1) 5.7 k D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

34 Radiative pion decay PIBETA Expt. Results Region B: global fits [F T = ( 16 ± 2) 10 4 ] projected uncertainties in 2004 run D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

35 Radiative pion decay PIBETA Expt. Results π + e + νγ (S/B) 2004 Region A: E γ, E e + > 51.7 MeV Region B: E γ > 55.6 MeV E e + > 20 MeV θ eγ > 40 Region C: E γ > 20 MeV E e + > 55.6 MeV θ eγ > 40 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

36 Radiative pion decay PIBETA Expt. Results Analysis of 2004 data [M. Bychkov, PhD thesis, 2005] Number of events Simulation Data λ=(2e e /m π )sin 2 (Θ eγ /2) Standard Model fit (V A) only. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

37 Radiative pion decay PIBETA Expt. Results region analysis [M. Bychkov, PhD thesis, 2005] Number of events y=2(e e )/m π λ=(2e e /m π )sin 2 (Θ eγ /2) x=2(e γ /m π ) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

38 Radiative pion decay PIBETA Expt. Results F A Form Factor x σ 2σ 1σ χ 2 Contours Best values of pion Form Factor Parameters: Combined analysis of and 2004 data sets [M. Bychkov, 2007] 100 F V CVC = 259 x F V Form Factor x D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

39 Radiative pion decay PIBETA Expt. Results Experimental History of Pion F A and F V THIS WORK POCANIC (2004) BOLOTOV (1990) DOMINGUEZ 2 (1988) EGLI 1 (1986) PIILONEN (1986) BAY (1986) STETZ (1978) DEPOMMIER (1963) F V = F V = F V = CVC PREDICTION (2006) THIS WORK BOLOTOV (1990) EGLI (1986) γ=f A /F V F V D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

40 Radiative pion decay PIBETA Expt. Results Summary of Pion Form Factor Results Also: F V = ± (14 ) F A = ± exp (F CVC V ) (16 ) a = ± ( ) < F T < % C.L. Derived pion polarizability and π 0 lifetime: α E = β M = (2.783 ± exp ) 10 4 fm 3 τ π 0 = (8.5 ± 1.1) s PDG: 8.4(6) B πe2γ (E γ > 10 MeV, θ eγ > 40 ) = 73.86(54) 10 8 (17 ) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

41 Radiative muon decay µ eν νγ Radiative muon decay: µ eν νγ D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

42 Radiative muon decay Basic theory Michel Parameters of Muon Decay: µ eν ν d 2 Γ dx d(cos θ) = m µ 4π 3 W eµg 4 F 2 x 2 x0 2 [ F IS (x) + P µ + cos θ F AS (x) ] [ 1 + P e +(x, θ) ˆζ ] Isotropic part: Anisotropic part: F IS (x) = x(1 x) ρ(4x 2 3x x 2 0 ) + η x 0 (1 x) F AS (x) = 1 3 ξ x 2 x 2 0 (1 x + 23 [ )]) δ 4x 3 + ( 1 x 20 1 D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

43 Radiative muon decay Michel theory of RMD Michel Parameters of Radiative Muon Decay: µ eν νγ d 3 B(x, y, θ) dx dy 2π d(cos θ) = f 1(x, y, θ) + ηf 2 (x, y, θ) + (1 4 3 ρ)f 3(x, y, θ) ρ = [ g V LR 2 + g V RL g T LR g T RL 2 ] + R(gRL S g RL T + g LR S g LR T ) SM 3 4, η = ( grl V 2 + glr V 2) + 1 ( g LR S 8 + 2g LR T 2 + grl S + 2g RL T 2) ( + 2 glr T 2 + grl T 2) SM 0. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

44 Radiative muon decay Michel theory of RMD Experimental Limits (90 % C.L.) on g γ αβ g γ αβ S V T LL > LR RL RR max. values: g S αβ g V αβ g T αβ [For more details cf. reviews and publications by W. Fetscher et al.] D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

45 Radiative muon decay Michel theory of RMD Experimental Limits (90 % C.L.) on g γ αβ g γ αβ S V T LL > LR RL RR max. values: g S αβ g V αβ g T αβ [For more details cf. reviews and publications by W. Fetscher et al.] D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

46 Radiative muon decay Michel theory of RMD Experimental Limits (90 % C.L.) on g γ αβ g γ αβ S V T LL > LR RL RR max. values: g S αβ g V αβ g T αβ [For more details cf. reviews and publications by W. Fetscher et al.] D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

47 Radiative muon decay PIBETA Expt. Results RMD analysis (2004 data) [B. VanDevender s thesis] PEN Expt: (2008 data) P/B = 36; σ t 1 ns D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

48 Radiative muon decay PIBETA Expt. Results RMD analysis (2004 data) [B. VanDevender s thesis] PEN Expt: (2008 data) P/B = 36; σ t 1 ns D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

49 Radiative muon decay PIBETA Expt. Results Differential Branching Ratio [B. VanDevender] due to small-angle bremsstrahlung uncertainties in GEANT B exp = [4.40 ± 0.02 (stat.) ± 0.09 (syst.)] ! B theo = (E γ > 10 MeV, θ > 30 ) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

50 Radiative muon decay PIBETA Expt. Results Differential Branching Ratio [B. VanDevender] due to small-angle bremsstrahlung uncertainties in GEANT B exp = [4.40 ± 0.02 (stat.) ± 0.09 (syst.)] ! B theo = (E γ > 10 MeV, θ > 30 ) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

51 Radiative muon decay PIBETA Expt. Results Differential Branching Ratio [B. VanDevender] due to small-angle bremsstrahlung uncertainties in GEANT B exp = [4.40 ± 0.02 (stat.) ± 0.09 (syst.)] ! B theo = (E γ > 10 MeV, θ > 30 ) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

52 Radiative muon decay PIBETA Expt. Results RMD analysis: η and ρ [B. VanDevender s thesis] χ 2 contours for fits of Michel parameters η and ρ for relevant RMD kinematics. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

53 Radiative muon decay PIBETA Expt. Results RMD analysis: Final η and ρ [B. VanDevender s thesis] data set η ρ nine-piece target ± ± ± (fixed) one-piece target ± ± ± (fixed) Combined: η = ± 0.050(stat.) ± 0.034(syst.) η (68 % c.l.) or η (90 % c.l.) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

54 Radiative muon decay PIBETA Expt. Results Experimental History of η D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

55 Radiative muon decay PIBETA Expt. Results Summary of RMD results First precise measurement of B(µ eν νγ) over a large phase space 313 events (bubble chamber) events 30 % uncertainty 2 % uncertainty B exp = (4.40 ± 0.09) 10 3, (B theo = ) New measurement of Michel parameter η η η (68 % c.l.) new world average: η (68 % c.l.) reduced by a factor of 2.5. Above results based on our 2004 run data set; the PEN experiment will double this data set with lower backgrounds. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

56 The PEN Experiment π eν The PEN Experiment: π eν D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

57 The PEN Experiment π eν decay: status revisited Modern theoretical calculations: π eν B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 3629] (1) 10 4 Decker and Finkemeier, [NP B 438 (1995) 17] (1) 10 4 Cirigliano and Rosell, [PRL 99, (2007)] Experiment, world average [current PDG]: N.B.: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.230 ± 0.004) 10 4 PEN goal: δb B D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

58 The PEN Experiment π eν decay: status revisited Modern theoretical calculations: π eν B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 3629] (1) 10 4 Decker and Finkemeier, [NP B 438 (1995) 17] (1) 10 4 Cirigliano and Rosell, [PRL 99, (2007)] Experiment, world average [current PDG]: N.B.: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.230 ± 0.004) 10 4 PEN goal: δb B D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

59 The PEN Experiment SM calculations; mass limits π e2 Decay and the SM B(π eν) = Γ(π e2 )/Γ(π µ2 ) given in SM to 10 4 accuracy; dominated by helicity suppression (V A). Deviations from this rate can be caused by: (a) charged Higgs in theories with richer Higgs sector than SM, (b) PS leptoquarks in theories with dynamical symmetry breaking, (c) V leptoquarks in Pati-Salam type GUT s, (d) loop diagrams involving certain SUSY partner particles, (e) non-zero neutrino masses (and mixing). Proc s. (a) (d) PS currents. Most general 4-fermion π e2 amplitude: G F 2 [ ( dγµ γ 5 u ) ( ν e γ µ γ 5 (1 γ 5 )e ) f e AL In the SM: f l AL + f e PL ( dγ 5 u ) ( ν e γ 5 (1 γ 5 )e ) ] + r.h. ν term = 1, while f l xr = f Px l = 0, with l = e, µ. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

60 The f e PL The PEN Experiment and Mass Bounds SM calculations; mass limits Allowing for pseudoscalar coupling [Shanker, NP B204 (82) 375]: ( B πe2 = B SM 1 + 2m ) ( πa P fpl e / 1 + 2m ) πa P f µ m e a A m µ a PL, A where 2nd term in denominator is negligible because f e PL f µ PL, while a P a A m π m u + m d 14. Therefore ( ) Bπe2 obs Bπe2 SM /Bπe2 SM = B B SM 2m πa P fpl e m e a 7700f PL e! A Tgt accuracy of the PEN experiment is B/B , which gives a 1σ sensitivity of δf e PL We can use this sensitivity to get estimates of the mass reach of PEN. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

61 The PEN Experiment SM calculations; mass limits Mass Bounds from PEN Goal Accuracy (a) Charged Higgs, m H+ [Shanker, NP B204 (82) 375] Given a mixing angle suppression S 10 2, we get f e PL S m tm τ m 2 H+ yielding m H+ > 6.9 TeV. (b) Pseudoscalar leptoquarks, m P Given an estimated effective Yukawa coupling of y 1/250, we can find m P, mass of the color-triplet PS l-q: f e PL 2 G F y 2 2m 2 P yielding m P > 3.8 TeV. (c) Vector leptoquarks, M G Following Shanker who assumes gauge coupling g g SU(2), we get: f e PL 4M2 W M 2 G yielding M G > 630 TeV. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

62 The PEN Experiment Lepton universality Lepton universality (and neutrinos) From R e/µ = R τ/π = Γ(π e ν(γ)) Γ(π µ ν(γ)) = g e 2 me 2 (1 me/m 2 µ) 2 2 ( ) 1 + δre/µ gµ 2 mµ 2 (1 mµ/m 2 π) 2 2 Γ(τ e ν(γ)) Γ(π µ ν(γ)) = g τ 2 mτ 3 (1 mπ/m 2 τ 2 ) 2 ( ) 1 + δrτ/π gµ 2 2mµm 2 π (1 mµ/m 2 π) 2 2 one can evaluate ( ) ge = ± and g µ π For comparison ( ) ge = ± and g µ W ( gτ g µ ( gτ g e ) πτ ) W = ± = ± [Violation of LU at presently allowed level would account for NuTeV anomaly. ] D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

63 The PEN Experiment Lepton universality Departures from lepton universality Various models beyond the SM predict flavor non-universal suppressions of the lepton coupling constants in W lν: g l g l = g l(1 ɛ l ) where l = e, µ, τ 2 Linear combinations constrained by W, τ, π, K decays are: g µ = 1 + ɛ e ɛ µ, g e 2 g τ = 1 + ɛ µ ɛ τ, g µ 2 g τ = 1 + ɛ e ɛ τ, g e 2 Two of the three are independent; experimental constraints are on: eµ ɛ e ɛ µ, µτ ɛ µ ɛ τ, eτ ɛ e ɛ τ. Recent comprehensive reviews: A. Pich, Nucl. Phys. Proc. Suppl. 123 (2003) 1; (hep-ph/ ) W. Loinaz et al., PRD 70 (2004) ; (hep-ph/ ). D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

64 The PEN Experiment Lepton universality From Loinaz et al., PRD 70 (2004) ll = 2 g l g l D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

65 The PEN Experiment New detectors Central Detectors: 2007 Engineering Run 12,5 mm Active Collimator Active Degrader Target Counter Photomultiplier Module Hamamatsu H ,0 mm D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

66 The PEN Experiment New detectors Wedged Degrader: 2008 Run D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

67 The PEN Experiment Brief look at 2007 and 2008 results Timing in the central beam detectors Number of Events Number of Events HT Trigger 68 MeV/c π t = t target - t degrader (ns) DEG-CsI TDC (ns) Number of Events Number of Events HT Trigger 68 MeV/c π t = t target - t B0 (ns) DEG-CsI TDC (ns) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

68 The PEN Experiment Sample waveforms 2007: Brief look at 2007 and 2008 results π µ e (in TGT) TGT DSC Amplitude TGT DSC Amplitude Channel Number (ns*2) Channel Number (ns*2) π e (in TGT) TGT DSC Amplitude TGT DSC Amplitude Channel Number (ns*2) Channel Number (ns*2) Beam π + (in DEG) DEG DSC Amplitude Channel Number (ns*2) DEG DSC Amplitude Channel Number (ns*2) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

69 Waveforms 2008: Digitizer Amplitude B0 Waveform The PEN Experiment Brief look at 2007 and 2008 results B Channel Number (ns*2) DEG LR Waveform Digitizer Amplitude DEG horiz Channel Number (ns*2) DEG TB Waveform Digitizer Amplitude DEG vert Channel Number (ns*2) TGT Waveform Digitizer Amplitude TGT Channel Number (ns*2) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

70 The PEN Experiment Brief look at 2007 and 2008 results Target Digitizer Amplitude π µ e Target Digitizer Amplitude π µ e Digitizer channel (0.5 x ns/ch) Digitizer channel (0.5 ns/ch) Arbitrary Normalization Resolving the positron tail π µ e π e Efficiency Total Positron Energy (MeV) t = t µ - t π (ns) D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

71 Summary PEN: present status, plans PEN Experiment: Present Status and Plans Stopped beam at 15, 000 π + /sec. Pion decays detected in a 250 ns wide gate. Position sensitive two-piece wedged active degrader detector. Digitized signals of beam counters: forward (B0), active degrader (DEG), and active target (AT). Two development runs, in 2007 and 2008, ramping up beam stop and DAQ rates to design specifications. Total pions stopped in 2007 and 2008 runs: > To date > π eν decays recorded, corresponding to (δb/b) stat < Detailed data analysis under way in preparation for a 2009 run, planned to complete the required event statistics. Improved beam tracking with a minitpc under design. D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61

72 Summary PEN Collaboration Experiment R (PEN) collaboration members: L. P. Alonzi, a V. A. Baranov, c W. Bertl, b M. Bychkov, a Yu.M. Bystritsky, c E. Frlež, a N.V. Khomutov, c A.S. Korenchenko, c S.M. Korenchenko, c M. Korolija, f T. Kozlowski, d N.P. Kravchuk, c N.A. Kuchinsky, c D. Mekterović, f D. Mzhavia, c,e A. Palladino, a D. Počanić, a P. Robmann, g A.M. Rozhdestvensky, c V.V. Sidorkin, c U. Straumann, g I. Supek, f Z. Tsamalaidze, e A. van der Schaaf, g E.P. Velicheva, c and V.V. Volnykh c a Dept of Physics, Univ of Virginia, Charlottesville, VA , USA b Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland c Joint Institute for Nuclear Research, RU Dubna, Russia d Institute for Nuclear Studies, PL Swierk, Poland e IHEP, Tbilisi, State University, GUS Tbilisi, Georgia f Rudjer Bošković Institute, HR Zagreb, Croatia g Physik Institut der Universität Zürich, CH-8057 Zürich, Switzerland Web page: D. Počanić (UVa) Rare Pi and Mu Decays INT, 21 Nov / 61