Fundamental physics in rare pion and muon decays

Transcription

1 Fundamental physics in rare pion and muon decays Dinko Počanić University of Virginia IX LASNPA, Quito, Ecuador 18- July 011 D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

2 Overview Outline Overview and status of allowed π and µ decays Pion beta decay: π + π 0 e + ν Radiative pion decay: π + e + νγ Allowed muon decays: ordinary and radiative The π e decay: π + e + ν Summary D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul 011 / 40

3 Overview Summary of known decays Known and measured pion and muon decays Decay BR π + µ + ν (4) (π µ ) µ + νγ.00 (5) 10 4 (π µγ ) e + ν 1.30 (4) 10 4 (π e ) e + νγ 1.61 (3) 10 7 (π eγ ) π 0 e + ν 1.05 (34) 10 8 (π e3, π β ) e + νe + e 3. (5) 10 9 (π eee ) π 0 γγ (3) e + e γ (3) 10 (Dalitz) e + e e + e 3.14 (30) 10 5 e + e 6. (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 π, µ decays IX LASNPA, 1 Jul / 40

4 Overview Summary of known decays Pions, muons, fundamental interactions & symmetries Why isn t π e the dominant decay mode? Deep link to V A nature of the weak interaction PV; Pion triplet (π +, π 0, π ), are the Goldstone bosons in the spontaneous breaking of Chiral Symmetry; Explicit breaking of χs: m π m q (Gell-Mann Oakes Renner rel.); Conserved Vector Current: SU() V ; Why is the beta energy spectrum in µ e decay continuous (3-body decay, NO µ eγ)? Lepton Flavor Conservation. Today there are many excellent precise measurements exploring these topics: FAST, MEG, MULAN, Muon(g-), TWIST,... D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

5 Overview Recent measurements Recent π, µ allowed decay measurements π + π 0 e + ν e PIBETA ( 99 01) SM checks related to CKM unitarity π + e + ν e γ(or e + e ) PIBETA ( 99 04), PEN ( 06 10) F A /F V, π polarizability (χpt calibration) tensor coupling besides V A (?) µ + e + ν e ν µ TWIST (003 04) departures from V A in L weak µ + e + ν e ν µ γ(or e + e ) PIBETA ( 04), PEN ( 06 10) departures from V A in L weak { π + e + PEN ( 06 10) ν e PiENu ( 06 ) e-µ universality pseudoscalar coupling besides V A ν sector anomalies, Majoron searches, m h+, PS l-q s, V l-q s,... search for signs of SUSY (MSSM) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

6 Pion beta decay Pion beta decay: π + π 0 e + ν (PIBETA: runs) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

7 Pion beta decay Motivation Quark-Lepton (Cabibbo) Universality The basic weak-interaction V-A form (e.g., µ decay): M e l α ν e ū e γ α (1 γ 5 )u ν is replicated in hadronic weak decays 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 (CVC) comes from weak quark (Cabibbo) mixing: G V = G µ cos θ C (= G µ V ud ) cos θ C q generations lead to the V ud V us V ub Cabibbo-Kobayashi-Maskawa V cd V cs V cb (CKM) matrix (1973): V td V ts V tb CKM unitarity cond.: V = 1 ( V ud + V us + V ub )? = 0, stringently tests the SM. Prior to 004 there was a persistent.5σ shortfall in V, motivating many experiments to determine CKM m.e. s, esp. V ud and V us. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

8 Pion beta decay The apparatus and method The PIBETA/PEN apparatus stopped π + beam active target counter 40-det. CsI calorimeter central tracking digitized waveforms stable temp./humidity BC PEN Detector 009 π + beam vac. pure CsI mtpc AD AT PMT PH MWPC1 MWPC 10 cm D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

9 Pion beta decay The apparatus and method Number of events π + π 0 e + ν γ1 γ Simulation Data Number of Events Simulation Data π e ν Opening angle Θ γ1γ (degr) Positron Energy (MeV) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

10 Pion beta decay Results PIBETA result for π β decay [PRL 93, (004)] B exp-t πβ = [1.040 ± (stat) ± (syst)] 10 8, B exp-e πβ = [1.036 ± (stat) ± (syst) ± (π e )] 10 8, McFarlane et al. [PRD 1985]: B = (1.06 ± 0.039) 10 8 SM Prediction (PDG): B = (90% C.L.) ( excl. rad. corr.) PDG 010: V ud = () PIBETA: V ud = (5) or V ud = 0.978(30). D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

11 Pion beta decay Results Present Status of V ud.9800 V ud V = ud nuclear neutron nuclear mirrors pion Uncertainty Experiment Radiative correction Nuclear correction (Courtesy of John Hardy, May 009) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

12 Radiative pion decay π + e + νγ Radiative pion decay: π + e + νγ PIBETA: & 004 runs ( PEN: runs ) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

13 Radiative pion decay Motivation π + e + νγ: Standard IB and V A terms SM A tensor interaction, too? Exchange of S=0 leptoquarks P Herczeg, PRD 49 (1994) 47 D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

14 Radiative pion decay Motivation 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 ( kµ kq p µ pq + σ µνq ν ) (1 γ 5 ) ν. kq The structure-dependent amplitude: M SD = eg F V ud m π 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 = E γ /m π ; y = E e /m π ), dγ πeγ dx dy = α { ( π Γ FV m ) π πe IB (x, y) + f π m e [ (1 + γ) SD + (x, y) + (1 γ) SD (x, y) ] ( FV m π + f π ) [(1 + γ) S + int (x, y) + (1 γ) S int (x, y)] }. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

15 Radiative pion decay Previous data Available data on pion form factors F V CVC = 1 Γ(π 0 γγ) α πm π 0 = 0.059(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 004) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

16 Radiative pion decay Previous data Available data on pion form factors F V CVC = 1 Γ(π 0 γγ) α πm π 0 = 0.059(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 004) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

17 Radiative pion decay Previous data Available data on pion form factors F V CVC = 1 Γ(π 0 γγ) α πm π 0 = 0.059(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 004) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

18 Radiative pion decay Results F A Form Factor x σ σ 1σ F V CVC = 59(9) x 10-4 χ Contours Best values of pion form factor parameters: Combined analysis of and 004 data sets M. Bychkov, et al., PRL 103 (009) F V Form Factor x D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

19 Radiative pion decay Results Experimental history of pion F A and F V THIS WORK POCANIC (004) BOLOTOV (1990) DOMINGUEZ (1988) EGLI 1 (1986) PIILONEN (1986) BAY (1986) STETZ (1978) DEPOMMIER (1963) F V =0.059 F V = F V =0.055 CVC PREDICTION (006) THIS WORK BOLOTOV (1990) EGLI (1986) γ=f A /F V F V D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

20 Radiative pion decay Results Summary of pion form factor and B.R. results F V = ± (14 ) F A = ± exp (F CVC V ) (16 ) a = 0.10 ± 0.06 ( ) < F T < % C.L. Derived pion polarizability and π 0 lifetime (at L.O.): α E = β M = (.783 ± 0.03 exp ) 10 4 fm 3 τ π 0 = (8.5 ± 1.1) s { current PDG avg: 8.4 (4) PrimEx PRL 10: 7.8 () B πeγ (E γ > 10 MeV, θ eγ > 40 ) = 73.86(54) 10 8 (17 ) Above results will be improved with new PEN data and analysis. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

21 Muon decays µ + e + ν e ν µ(γ) Allowed muon decays: µ + e + ν e ν µ (TWIST ) µ + e + ν e ν µ γ (PIBETA 004, PEN ) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

22 Muon decays Basic theory Michel parameters of muon decay: µ eν µ ν e d Γ dx d(cos θ) = m µ 4π 3 W eµg 4 F x x0 [ 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) + 9 ρ(4x 3x x 0 ) + η x 0 (1 x) F AS (x) = 1 3 ξ x x 0 (1 x + 3 [ )]) δ 4x 3 + ( 1 x 0 1 D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

23 Muon decays Michel theory of RMD Michel parameters of radiative muon decay: µ eν µ ν e γ d 3 B(x, y, θ) dx dy π d(cos θ) = f 1(x, y, θ) + ηf (x, y, θ) + (1 4 3 ρ)f 3(x, y, θ) ρ = [ g V LR + g V RL + g T LR + g T RL ] + R(gRL S g RL T + g LR S g LR T ) SM 3 4, η = ( grl V + glr V ) + 1 ( g LR S 8 + g LR T + grl S + g RL T ) ( + glr T + grl T ) SM 0. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

24 Muon decays Michel theory of RMD OMD study: TWIST experiment (TRIUMF) Main results: ρ = (5) and δ = (7), MacDonald, et al., Phys. Rev. D 78 (008) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul 011 / 40

25 Muon decays Michel theory of RMD RMD differential branching ratio [B. VanDevender, PhD thesis] PRELIMINARY (new analysis+data) due to small-angle bremsstrahlung uncertainties in GEANT B exp = [4.40 ± 0.0 (stat.) ± 0.09 (syst.)] ! B theo = (E γ > 10 MeV, θ eγ > 30 ) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

26 Muon decays Michel theory of RMD Experimental History of η PIBETA preliminary (B. VanDevender, PhD thesis; 004 data set): η = ± 0.050(stat.) ± 0.034(syst.) η 0.033; new world average: η 0.08 (68 % c.l.) reduced by a factor of.5. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

27 The π e decay π + e + ν The π e decay: π + e + ν PEN and PiENu experiments (006 ) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

28 The π e decay π + e + ν π eν decay: SM calculations; measurements Modern theoretical calculations: B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = 1.35 (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 369] () 10 4 Finkemeier, [PL B 387 (1996) 391] 1.35 (1) 10 4 Cirigliano and Rosell, [PRL 99, (007)] Experiment, world average [current PDG]: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.30 ± 0.004) 10 4 N.B.: PEN, PiENu aim at: δb B D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

29 The π e decay π + e + ν π eν decay: SM calculations; measurements Modern theoretical calculations: B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = 1.35 (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 369] () 10 4 Finkemeier, [PL B 387 (1996) 391] 1.35 (1) 10 4 Cirigliano and Rosell, [PRL 99, (007)] Experiment, world average [current PDG]: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.30 ± 0.004) 10 4 N.B.: PEN, PiENu aim at: δb B D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

30 The π e decay π + e + ν π eν decay: SM calculations; measurements Modern theoretical calculations: B calc = Γ(π e ν(γ)) Γ(π µ ν(γ)) calc = 1.35 (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 369] () 10 4 Finkemeier, [PL B 387 (1996) 391] 1.35 (1) 10 4 Cirigliano and Rosell, [PRL 99, (007)] Experiment, world average [current PDG]: Γ(π e ν(γ)) Γ(π µ ν(γ)) exp = (1.30 ± 0.004) 10 4 N.B.: PEN, PiENu aim at: δb B D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

31 The π e decay SM calculations; mass limits π e Decay and the SM B(π e ) in SM dominated by (V A) helicity suppression. Deviations primarily due to PS int. terms. Most general 4-fermion π e amplitude: G F [ ( dγ µ 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. Strong helicity suppression amplifies sensitivity to f e PL : B obs πe BSM πe B SM πe = B B SM =... m π m e (m u + m d ) f e PL 7700f e PL! Tgt accuracy of the PEN experiment, B/B , translates into attractive mass limits: D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

32 The π e decay SM calculations; mass limits Example mass bounds from PEN goal accuracy (a) Charged Higgs, m H+ [Shanker, NP B04 (8) 375] Given a mixing angle suppression S 10, we get f e PL S m tm τ m H+ yielding m H+ > 6.9 TeV. (b) Pseudoscalar leptoquarks, m P Given an estimated effective Yukawa coupling of y 1/50, we can find m P, mass of the color-triplet PS l-q: f e PL G F y m P yielding m P > 3.8 TeV. (c) Vector leptoquarks, M G Following Shanker who assumes gauge coupling g g SU(), we get: f e PL 4M W M G yielding M G > 630 TeV. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

33 The π e decay SUSY tests MSSM calculations (RPC) [Ramsey-Musolf et al., PR D76 (007) ] minimal selectron, smuon masses: Re Μ SUSY R e Μ lowest mass chargino: Re µ SUSY R e µ Min mel,mµ L GeV m GeV mχ1 slepton mass degeneracy: Re µ SUSY R e µ 0.00 ReHiggsino mass param. µ and mũl : mel mµ L RPV scenario constraints also discussed. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

34 The π e decay 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 me (1 me/m µ) ( ) 1 + δre/µ gµ mµ (1 mµ/m π) Γ(τ e ν(γ)) Γ(π µ ν(γ)) = g τ mτ 3 (1 mπ/m τ ) ( ) 1 + δrτ/π gµ mµm π (1 mµ/m π) one can evaluate ( ) ge = ± and g µ π For comparison ( ) ge = ± and g µ W ( gτ g µ ( gτ g e ) πτ ) W = ± = 1.09 ± [Presently allowed level of LUV could account for NuTeV anomaly. ] D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

35 The π e decay Lepton universality Loinaz et al., PRD 70 (004) ll = ( gl g l ) 1 D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

36 The π e decay PEN experiment: status, plans 0.5*tgt_wf.mu3.mean-0.5*tgt_wf.pi3.mean {tgt_wf.fitattempt==1 && tgt_wf.subtintegral_left<10e3 && tgt_wf.subtintegral_middle<170e3 && tgt_wf.subtintegral_right<40e3 && 0.5*tgt_wf.e3.mean-0.5*tgt_wf.mu3.mean>10 && 0.5*tgt_wf.e3.mean-0.5*tgt_wf.mu3.mean<70 && trak.ecsi[0]<48} χ / ndf 976. / Constant ± 0. PEN experiment: status and plans Approved in 006; development runs: 007, 08; data runs 09, 10. Improved beam tracking (minitpc) implemented in 09, 10 runs. > 0 M π e s recorded (δb/b) stat Illustration: decays in the target detector (008 run): trigger-weighted events / ns top: bottom: muons positrons Events Measurement π decay curve pion decay time [ns] t µ - t π (ns) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

37 Mean RMS Underflow Overflow Integral Mean The π e decay PEN experiment: status, plans Waveform fitting in PEN [Anthony Palladino] t (0.5 ns) t (0.5 ns) t (0.5 ns) t (0.5 ns) D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul /

38 χ 3 The π e decay PEN experiment: status, plans χ 3 PEN: distinguishing π e and π µ e decays (measurement) 10 9 χ 3 vs χ for E e +<60MeV χ 3 vs χ for E e +>60MeV [A. Palladino & L.P. Alonzi] χ χ vs E e χ χ vs t e χ χ E e D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40 t e +

39 χ 3 The π e decay PEN experiment: status, plans χ 3 PEN: distinguishing π e and π µ e decays (simulation) 10 9 χ 3 vs χ for E e +<60MeV χ 3 vs χ for E e +>60MeV [A. Palladino & L.P. Alonzi] χ χ vs E e χ χ vs t e χ χ E e D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40 t e +

40 The π e decay PiENu experiment PiENu experiment (TRIUMF) π e ν π µ e π e ν Energy (MeV) Energy (MeV) π µ e π e ν Time (ns) Time (ns) Acceptance: Ω 0. 4π sr Excellent energy resolution. Project started in 006. Data taking currently under way. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

41 Summary Status of allowed π and µ decays A significant experimental effort is under way to make use of the unparalleled theoretical precision in the weak interactions of the lightest particles. Information obtained is complementary to expected collider results, and necessary for their proper interpretation. Orders of magnitude improvement in precision has been achieved; more lie in store. Modest scale of investment of resources required. Unique opportunity for scientific advancement. Great projects for graduate students and postdocs full range of professional training. D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

42 Summary PEN Collaboration Current and former PIBETA and PEN collaborators L. P. Alonzi a, K. Assamagan a, V. A. Baranov b, W. Bertl c, C. Broennimann c, S. Bruch a, M. Bychkov a, Yu.M. Bystritsky b, M. Daum c, T. Flügel c, E. Frlež a, R. Frosch c, K. Keeter a, V.A. Kalinnikov b, N.V. Khomutov b, J. Koglin a, A.S. Korenchenko b, S.M. Korenchenko b, M. Korolija d, T. Kozlowski e, N.P. Kravchuk b, N.A. Kuchinsky b, D. Lawrence h, W. Li a, J. S. McCarthy a, R. C. Minehart a, D. Mzhavia b,f, E. Munyangabe a, A. Palladino a,c, D. Počanić a, B. Ritchie h, S. Ritt a,c, P. Robmann g, O.A. Rondon-Aramayo a, A.M. Rozhdestvensky b, T. Sakhelashvili f, S.N. Shkarovskiy b, P. L. Slocum a, L. C. Smith a, N. Soić d, U. Straumann g, I. Supek d, P. Truöl g, Z. Tsamalaidze f, A. van der Schaaf g, E.P. Velicheva b, V.P. Volnykh b, Y. Wang a, C. Wigger c, H.-P. Wirtz c, K. Ziock a. a Univ. of Virginia, USA c PSI, Switzerland e Swierk, Poland g Univ. Zürich, Switzerland b JINR, Dubna, Russia d IRB, Zagreb, Croatia f IHEP, Tbilisi, Georgia h Arizona State Univ., USA Home pages: D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

43 Additional slides Current limits from RMD Additional slides D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40

44 Additional slides Current limits from 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 [Most recent global fit by C.A Gagliardi et al., PR D 7 (005) 07300; Add l TWIST constraints on L-R symmetric models: PRL 106 (011) ] D. Počanić (UVa) rare π, µ decays IX LASNPA, 1 Jul / 40